critical (temperature) thresholds and climate change ... · - macadamia 62 - capsicum 64 - avocado...

Project Number :- QP1005130 (1/5/2011) Project Title :-

Critical (temperature) thresholds and climate change impacts/adaptation in

horticulture. Author(s) Name :- Peter Deuter et al. Research Provider :- Department of Employment Economic Development and Innovation (DEEDI), Queensland

Project Number :- QP1005130 Project Leader :- Peter Deuter Senior Principal Horticulturist AgriScience Queensland Department of Employment Economic Development and

Innovation Gatton Research Station Warrego Highway, Gatton Queensland 4343 Phone – (07) 5466 2222 Mobile – (0407) 636 907 Email – [email protected]

Key Personnel :- Dr Neil White, Principal Research Scientist, Department of Employment Economic Development and Innovation, Toowoomba, Queensland. David Putland, Climate Change Officer, Growcom, Brisbane. Rachel Mackenzie, Chief Advocate, Growcom, Brisbane. Jane Muller, Senior Research and Policy Officer, Growcom, Brisbane.

Purpose of the report :- Final Report documenting critical temperature thresholds for major horticultural commodities in Australia Funding sources :- Woolworths, Landcare, Horticulture Australia Limited, Queensland Government Collaborating institutions :-

Date of the report :- 5th May 2011 Disclaimer: Any recommendations contained in this publication do not necessarily represent current HAL Limited policy. No person should act on the basis of the contents of this publication, whether as to matters of fact or opinion or other content, without first obtaining specific, independent professional advice in respect of the matters set out in this publication.

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Contents Page 1.0 Media Summary 2

2.0 Technical Summary 4

3.0 Introduction and Review of Literature 6

4.0 Overview of Critical Thresholds 13

5.0 Materials and Methods 14

6.0 Results 16

Case Studies - Lettuce 22

- Banana 39

- Apple 42

- Citrus 47

- Pineapple 52

- Tomato 54

- Macadamia 62

- Capsicum 64

- Avocado 68

7.0 Discussion 74

8.0 Technology Transfer 86

9.0 Recommendations - Scientific and Industry 87

10.0 Acknowledgments 90

11.0 Bibliography of Literature Cited 90

12.0 Appendix I - Literature Review 94

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1.0 Media Summary

Key Components of the Project A review of the literature and industry consultation was undertaken to document critical temperature thresholds for a number of major horticultural commodities.

The focus was on temperature thresholds, to the exclusion of rainfall effects, because the majority of horticulture in Australia is irrigated. While this approach does not discount the importance of rainfall and associated runoff into irrigation storages, it is temperature which determines to a great extent the location and performance of the majority of horticultural commodities in Australia.

Understanding the specific impact of temperature change on horticultural commodities is a necessary step in providing growers with the decision making tools to manage and adapt to climate change. Such information is critical to help preserve Australia’s profitable and productive horticulture industry.

Industry Significance Horticulture in Australia comprises a large number of commodities contributing ~ $7 billion annually to the economy. Horticultural crops are grown in a wide range of production regions due to the diversity of micro-climates.

Horticultural crops are particularly sensitive to temperature, most having specific temperature requirements for the development of optimum yield and quality.

Key Outcomes & Benefits for Industry The key outcome of this project has been a better understanding of the temperature thresholds affecting a small number of horticultural crops, and the impact of further temperature rises on these commodities, under a changing climate.

Conclusions In general, growers have managed past climate change quite well and are optimistic that they will continue to manage projected temperature increases into the medium term future.

In many horticultural regions where the temperature threshold is currently exceeded at some specific times of the year, growers in the main have avoided production during these periods, as in general yield and quality are reduced when the temperature exceeds the threshold for each commodity.

As temperatures continue to rise in all vegetable production regions through to 2030, growers are likely to respond by changing planting and harvest dates, and reducing the production season by a few weeks.

If more adaptable vegetable cultivars are available to growers, the impact of reducing the length of the production season will be reduced, until such time as the genetic capability of more adaptable cultivars is exceeded.

It is expected that it will not be until after 2030 that market access and the profitability of a reduced season in the majority of vegetable production districts will be a major factor in the increasing vulnerability of the vegetable industry.

In districts where the threshold is not exceeded currently, and will be exceeded only on occasions, or not at all by 2030, growers may be able to take advantage of earlier planting in the spring, and later planting in the autumn, as temperatures continue to rise.

For perennial fruit crops, the effects of exceeding thresholds is somewhat different to annual vegetable cropping. More adaptable varieties will be the long-term solution, where agronomic practices are not appropriate of not cost effective.

Recommendations for future R&D

Although the impacts of increasing temperatures on a range of horticultural crops are somewhat similar, there are sufficient differences between commodities, regions and seasons for additional assessment of critical temperature thresholds to be conducted for the very large number of horticultural commodities grown across a wide range of regions and seasons in Australia.

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The next step should be an assessment of the vulnerability of major horticultural commodities and/or production regions in Australia. Those commodities and/or regions which are most vulnerable will require particular attention from growers and industry bodies.

There is a need for additional assessment of other critical thresholds (e.g. rainfall) for the very large number of horticultural commodities grown across a wide range of regions and seasons in Australia.

Recommendations for industry application More adaptable cultivars are required by all vegetable industries in Australia to cope better with a

very variable as well as a changing climate.

Identify those commodities and regions which will be most impacted by further rises in temperature (and decreases in rainfall runoff), and potential new or alternative locations where temperatures will be more favourable, up to and after 2030.

Similarly, more adaptable fruit crop cultivars for some specific commodities such as apples will be required in the future as temperatures continue to rise.

Identify those countries/regions, which currently export product to Australia, which will be significantly impacted by rising temperatures, and those which will become more competitive on the Australian market because of favourable impacts as a result of further changes to the world’s climate.

Despite the lack of immediacy, growers and industry need to be vigilant in continuing to assess the changes in climate as they occur, and the impacts these changes will bring.

The specific outcomes for each of the individual horticultural commodities assessed in this project should be directed to the Industry Bodies representing those industries.

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2.0 Technical Summary

Nature of the Problem Horticulture in Australia comprises a large number of commodities contributing ~ $7 billion annually to the economy. Horticultural crops are grown in a wide range of production regions due to the diversity of micro-climates.

Horticultural crops are particularly sensitive to temperature, most having specific temperature requirements for the development of optimum yield and/or quality.

In agriculture, a critical threshold is the point at which the production of a commodity becomes unviable due to identifiable change in a production variable. In horticulture, yield and or quality are usually the first to suffer as the threshold is approached or exceeded. Critical temperature thresholds differ for each commodity and often between different varieties.

Science undertaken A review of literature and industry consultation was undertaken to document critical temperature thresholds for a number of major horticultural commodities.

The focus was on temperature thresholds, to the exclusion of rainfall effects, because the majority of horticulture in Australia is irrigated. While this approach does not discount the importance of rainfall and associated runoff into irrigation storages, it is temperature which determines to a great extent the location and performance of the majority of horticultural commodities in Australia.

The work program proceeded in the following stages:

The current understanding of critical temperature thresholds was identified and documented through a review of literature for a selection of the major horticultural crops.

Additional data on critical temperature thresholds was collected through consultation with informed growers, consultants and scientists.

The impact of projected temperature change in 2030 was determined for selected horticultural commodities in current production regions using the information gained from the literature review.

Potential adaption strategies documented.

Findings reported through commodity specific case studies.

Understanding the impact of temperature change on horticultural commodities is a necessary step in providing growers with the decision making tools to manage and adapt to climate change. Such information is critical to help preserve Australia’s profitable and productive horticulture industry through:

Establishing a practical understanding of critical temperature thresholds of significance to specific horticultural crops and production regions in Australia

Using this understanding to identify commodities and/or regions which, under climate change, are or will be significantly impacted by increasing temperatures

Assessing the impacts on production systems and/or regions, and identify adaptation strategies to address these impacts.

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Major Findings and Outcomes

Summary of Critical Temperature Thresholds for selected horticultural crops.

Crop Development Phase Critical Temperature Threshold

Lettuce Hearting 28oC – mean maximum Cauliflower Curd induction 22oC Banana Fruit maturity 38oC Apple Dormancy Chilling requirement – cultivar specific Citrus Early fruit development 30oC Pineapple Flower initiation and pre-harvest >35oC Tomato 2 week period Pre-anthesis 29oC – mean maximum Macadamia Retention of racemes and nuts Declines rapidly >30oC Capsicum Flowering 32°C Sweet Corn 3-4 weeks post flowering 32oC Avocado Flowering and fruit development 33oC Pumpkin Flowering >35oC

The key outcome of this project has been a better understanding of the temperature thresholds affecting a small number of horticultural crops, and the impact of further temperature rises on these commodities under a changing climate.

In general, growers have managed past climate change quite well and are optimistic that they will continue to manage projected temperature increases into the medium term future.

In many horticultural regions where the temperature threshold is currently exceeded at some time of the year, growers in the main have avoided production during these periods as in general yield and quality are reduced when the temperature exceeds the threshold for each commodity.






Recommendations.

Although the impacts of increasing temperatures on a range of horticultural crops are somewhat similar, there are sufficient differences between commodities, regions and seasons, for additional assessment of critical temperature thresholds to be conducted for the very large number of horticultural commodities grown across a wide range of regions and seasons in Australia.

The key outcome of this project has been a better understanding of the critical temperature thresholds affecting a small number of horticultural crops. The next step should be an assessment of the vulnerability of major horticultural commodities and/or production regions in Australia. Those commodities and/or regions which are most vulnerable will require particular attention from growers and industry bodies.

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Although the focus of this project has been on temperature thresholds, other meteorological

parameters are important to the performance of horticultural crops, there is a need for additional assessment of other critical thresholds for the very large number of horticultural commodities grown across a wide range of regions and seasons in Australia.


More adaptable cultivars are required by all vegetable industries in Australia, to cope better with a very variable as well as a changing climate.


Identify those countries/regions which currently export product to Australia, which will be significantly impacted by rising temperatures, and those which will become more competitive on the Australian market because of favourable impacts as a result of further changes to the world’s climate.

Despite the lack of immediacy, growers and industry need to be vigilant in continuing to assess the changes in climate as they occur, and the impacts these changes will bring.

The specific outcomes for each of the individual horticultural commodities assessed in

this project should be directed to the Industry Bodies representing those specific industries (see Table below).

Crop Industry Body

Lettuce AusVeg Cauliflower AusVeg

Banana Australian Banana Growers' Council (ABGC) Apple Apple and Pear Australia Limited (APAL) Citrus Citrus Australia Limited

Pineapple Growcom Tomato AusVeg

Macadamia Australian Macadamia Society Limited (AMS) Capsicum AusVeg

Sweet Corn AusVeg Avocado Avocados Australia Limited Pumpkin AusVeg

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3.0 Introduction

3.1 Nature of problem/issue:

Horticulture in Australia comprises a large number of commodities contributing ~ $7 billion annually to the economy. Horticultural crops are grown in a wide range of production regions due to the diversity of micro-climates. All horticultural crops are temperature sensitive and most have specific temperature requirements for optimum yield and quality. Climate indices and critical temperature thresholds of significance are poorly understood so the impact of climate change on businesses and cropping systems in specific regions has not been well documented, and the resilience of the system cannot be properly assessed. A review of the literature and industry consultation is required to document critical thresholds for major horticultural commodities, as well as understand the broader risks associated with climate change and the resilience of growers and industries.

3.2 The issue and its national/regional significance:

Climate change continues to grow as a global issue of highest importance. A recent study by the Climate Institute (2008) on attitudes of the Australian public found that 90% of Australians were concerned about climate change. Despite this concern, considerable uncertainty exists on the impact of climate change and the potential adaption responses. Rural communities are particularly susceptible to the uncertainty surrounding climate change due to their dependence on climate for their basic livelihood (Milne, Stenekes & Jacqui 2008). The need to “demystify” the potential impact of climate change on agricultural production systems in rural communities was highlighted in grower workshops on climate change and horticulture (Growcom 2008). This is in the context of a range of other issues which are influenced by climate change – viz. increasing costs of labour, fuel and fertilizers, food miles and carbon footprints, water availability and cost and marketing arrangements. It is projected that by 2030 climate change in Australia will result in considerable changes including annual warming of around one degree, increased risk of drought and severe weather events and increases in the number of days per year over 35oC (CSIRO & Australian Bureau of Meteorology 2007).

3.2.1 Temperature Sensitivity of Horticultural Commodities Horticultural crops are particularly sensitive to temperature, most having specific temperature requirements for the development of optimum yield and quality. A recent scoping study on climate change in horticulture (Deuter et al., 2006) found that horticultural industries are likely to be seriously affected by such change due to :-

The sensitivity of horticultural production to temperature variation and increases; The need for reliable irrigation supplies; An increasing incidence of pest and disease activity; and A lack of direct research into the effects of climate change on specific horticultural commodities.

A greater understanding of production risks is necessary to provide the high standard of crop management which will enable adaptation in intensive production systems, and to significantly increase industry and grower understanding of the regional and local impacts of climate change.

Temperature increases associated with climate change will impact horticultural commodities and regions through all of the following :-

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Changes in the suitability, availability and adaptability of cultivars; Changes in the optimum growing periods and locations for horticultural crops; Changes in the distribution of existing pests, diseases and weeds, including an increased

threat of new incursions; Increased incidence of disorders such as tip burn and blossom end rot; and Greater potential for downgrading product quality because of increased incidence of sunburn.

Temperature affects horticultural crops in many ways, including influencing the timing and reliability of plant growth, flowering, fruit growth and ripening and product quality. Due to the temperature sensitive nature of horticultural production, temperature related thresholds are frequently a critical production factor.

3.2.2 Thresholds In agriculture, a critical threshold is the crisis point at which the production of a commodity becomes unviable due to identifiable change in a production variable (Kenny et al. 2000). Arnell (2000) uses the term ‘dangerous levels of change’ to describe this crisis point. The point at which growing a commodity becomes unviable due to changes in a critical biological climate indicator (such as temperature) is known as a biophysical threshold (Kenny et al. 2000). Biophysical temperature thresholds differ for each commodity and often between different varieties. While projected temperature increases are becoming more regionally specific, these projections have yet to be connected to commodity and value chain impacts at an industry level. Climate indices and critical biophysical temperature thresholds of significance to the large range of horticultural crops are not well known, especially for the vegetable sector. Similarly little understanding exists on the capacity of management responses to extend the viability of different commodities beyond their temperature thresholds. The period where a particular management approach offers a feasible solution to temperature increases is referred to by Kenny et al. (2000) as an adjustment window. However, each management response has a limit of effectiveness after which more drastic adaptation responses are required. Thus, while certain management practices can be undertaken to reduce the impacts of climate change, these practices are only effective within a set range of change at which point a management threshold exists. Kenny et al. (2000) also describe a number of inter-related thresholds associated with ‘current climates’ and with climate change, whereas Arnell (2000) emphasises two types of threshold, the second being a ‘force threshold’, where a small change in one factor (e.g. - temperature increase due to climate change) produces a significant response (e.g. - in the way crop development is affected). This corresponds with the ‘critical thresholds’ terminology described in this project proposal. In this way, we do not properly understand where the critical biophysical temperature thresholds lie and if exceeding the threshold on its own will lead to a significant change in land use or production system, i.e. a tipping point, or the capacity of adaptive management strategies to create an adjustment window.

3.2.3 This raises a number of questions:

At which point will temperature increases become a critical factor in the production of a particular commodity (i.e. cause a critical reduction in the quality and/or yield in specific production systems, commodities and regions in Australian horticulture)?

Which horticultural production systems are exposed, sensitive, vulnerable and/or marginal? What management strategies are available to allow growers to adapt to such change and at

what temperature do these strategies become ineffective? How will projected temperature increases up to 2030 impact on the viability of key horticultural

commodities in Australia under a mid-range emission scenario?

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Can we avoid reaching the critical threshold(s) affecting profitability or sustainability? Answering these questions will provide critical insight into production and profitability opportunities and threats due to climate change to horticultural production in Australia and highlight risk management responses along the value chain. A review of literature and industry consultation has been undertaken to find answers to some of these questions including a documentation of critical temperature thresholds for a number of major horticultural commodities. This review and analysis has also documented some adaptation options for key commodities, to respond to increased temperature. The focus of this project has been on temperature thresholds, to the exclusion of rainfall effects, because the majority of horticulture in Australia is irrigated. While this approach does not discount the importance of rainfall and associated runoff into irrigation storages, it is temperature which determines to a great extent the location and performance of the majority of horticultural commodities in Australia. Understanding the specific impact of temperature change on horticultural commodities is a necessary step in providing growers with the decision making tools to manage and adapt to climate change. Such information is critical to help preserve Australia’s profitable and productive horticulture industry. 3.3 Prior Consultation:

Workshops conducted in projects funded by Horticulture Australia Ltd (HAL), Land and Water Australia (LWA) and Department of Agriculture Forestry and Fisheries (DAFF) (through the Queensland Department of Primary Industries and Fisheries (DPI&F) and Growcom respectively), have highlighted the importance of research into the impacts of temperature increases on horticultural production and the need for efficient communication of these climate change impacts. Engagement with leading growers and consultants during these workshops is summarised in the following :-

3.3.1 Leading growers, consultants and scientists

In the project “Australian horticulture's response to climate change and climate variability” (AH06019) funded by HAL and MCV, three regions in Australia were selected for their diversity of location and cropping, and the level of past and future climate change. Workshops were conducted with leading growers, consultants and scientists at the following locations - The Lockyer Valley, south-east Queensland; the Central Riverina, southern NSW; and the Burdekin, north Queensland.

The following questions were posed –

What are the impacts of climate change on selected horticulture regions and production systems?

What are some of the potential and acceptable strategies which growers and industries could consider, which will reduce the impacts of climate change on their business?

The outcome of these workshops was reported in Milestone # 4 submitted to HAL on 26/3/2008, and is summarised below :-

Because horticulture in Australia consists of a large number of diverse industries, which are grown in a wide range of production regions, climate change impacts and adaptation to these impacts will be equally diverse. Many horticultural regions have already experienced a rise in both maximum and minimum temperatures compared with the 1961 to 1990 base period. As a result of these changes, growers have already experienced the impacts of climate change of up to 1oC rise in temperatures, and in the main, have successfully adapted to these changes. Rises in temperature up to 4oC will be a real challenge to horticulture, as temperature thresholds of significance to the large range of horticultural crops are not well known.

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Growers have adapted to recent rises in temperature through implementing changes in production practices, timing of production and marketing.

Production timing - crops are developing more rapidly and mature earlier (taking less

time from planting or fruit set to harvest) Product Quality and Yield - increased heat stress is affecting fruit size, quality and

pollination The availability and costs of inputs are rising Cultural practices - most vegetable crops are developing more rapidly requiring

changes to crop schedules and marketing arrangements. More frequent consecutive plantings for crops such as lettuce and brassicas will be required to regain regular production patterns. This emphasizes the need for a better understanding of the indices (e.g. the number of days over a specific temperature threshold), and the effects these will have on yield and quality, as well as other factors such as time to harvest, pollination, etc

Pests, diseases and weeds - higher temperatures are increasing pest and disease activity, putting additional pressure on IPM systems

Marketing arrangements - Higher temperatures will change production and marketing arrangements between regions. Crops are developing more rapidly and maturing earlier (taking less time from planting or fruit set to harvest). Seasonality from region to region is changing, affecting marketing arrangements, and introducing ‘competition’ between regions

Production location - Production of some crops in some regions are currently benefiting from an extended production season, whilst in the future, it is expected that production in some regions will contract

It is expected that there will be a gradual induced relocation of production, especially in the absence of additional adaptation actions which include introduction of more adaptable cultivars in those areas where higher temperatures become a limitation to production.

To this end, a clear and defined understanding of how climate change will impact cropping systems and businesses in specific regions at temperatures up to 4oC is not readily available. Arriving at an understanding is made even more complex by the large number of commodities classified as horticultural crops (over 100 in Australia), and the wide range of regional climates which exist.

3.3.2 Industry Workshops (Growcom) In January 2008, a grower workshop was conducted by Growcom in Brisbane to gauge industry understanding of climate change, pinpoint production pressure points and identify existing strategies used to manage climate variability. The following is a summary of the key issues raised during the workshop :-

In the past, horticulture production in Queensland has prospered despite highly variable climatic conditions. On this basis, growers were quietly confident of their ability to adapt to the challenges posed by climate change providing the information required to make farm management decisions was available. Current approaches to managing climate variability include :-

Intensively irrigated crop systems supported by large water reserves; Diversification of crop production; Use of climatic information from the internet; Strategic planning on a 10 to 20 year planning cycle.

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Workshop participants highlighted the difficulties involved with identifying specific ‘tipping points’, due to the diversity of crop production in the horticulture industry. While some understanding existed amongst growers of the tipping points in tree crops (such as apples), it was more difficult to determine the tipping points in vegetable crops, due to continually changing vegetable cultivars. Such crop diversity combined with regional climatic variability, increases the challenges of comparing specific tipping points across regions.

A number of growers reported unusual climate events and the consequent loss of marketable produce. However, difficulty distinguishing between climate change and climate variability was a common occurrence. Particularly vulnerable regions were identified as Southern Queensland in general as well as the Lockyer Valley in Queensland.

3.3.4 Industry Workshops (AusVeg)

In November 2009, a series of grower workshops were conducted by AusVeg (the peak industry body for the Australian Vegetable Industry) at four vegetable growing regions in Australia (Granite Belt, Cowra, Ulverstone and Waneroo), to assist vegetable growers to gain an understanding of climate change impacts in the vegetable industry, as well as understand the opportunities and risks posed by ongoing climate change. The following is a summary of the key issues raised during the workshops :-

Climate change is considered in decision making by growers, as most have been aware of past changes, and future changes have been well publicised.

Growers have adapted to climate variability and market changes throughout their farming careers. The key issue for the viability of vegetable growing in some regions is water security – if water allocations are secure then vegetable growers felt they could adapt their operations to cope with other climatic changes.

With the expectation that the past changes will be repeated for the next 20 to 30 years, especially in those regions where changes have so far been quite small, growers were very confident that they will manage any negative impacts quite well. They were confident that they will be able to take advantage of increases in the length of the summer season, as a consequence of future warmer winters.

The general trend for more intensive rainfall in Eastern Australia is seen as an advantage to those growers who currently capture runoff in on-farm dams for irrigation.

Continuity of supply is the main driver of change, and many other factors such as urbanisation, and changing consumer preferences for food will remain important drivers of future change.

3.4 Project objectives:

Establish a practical understanding of critical temperature thresholds of significance to specific horticultural crops and production regions in Australia;

Use this understanding to identify commodities and/or regions which, under climate change, are or will be significantly impacted by increasing temperatures;

Assess the impacts on production systems and/or regions, and identify adaptation strategies to address these impacts.

3.5 Outputs:

Key project outputs include :-

“Critical Biophysical Thresholds affecting Australian horticultural crops” – Report for Milestone # 2 – Critical biophysical temperature thresholds identified and documented for major

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horticultural crops and growing regions in Australia – Appendix I is an updated version of this Milestone

“Ground truth critical biophysical thresholds by growers and supply chain participants” - Report

for Milestone # 3

Comparison of climate change scenarios for 2030 and data on temperature thresholds to establish where thresholds might be reached or exceeded

Analysis of the impact of exceeding these critical thresholds for major horticulture crops and regions against Climate Change scenarios at 2030

Identification of adaptation strategies which will reduce the impact of temperature increases and build resilience in horticulture systems

Commodity case studies – where sufficient data is available in the literature and through consultation to enable critical thresholds to be identified and impacts, vulnerability and adaptation strategies to be described

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4.0 Overview of Critical Thresholds

The peer reviewed literature provides a starting point in attempting to understand the critical temperature thresholds for a number of important horticultural crops.

A range of temperature thresholds exist for a specific crop, depending on the cultivar being grown, the location and the time of the year. These critical temperature thresholds will relate to a specific development phase, e.g. seed germination, floral initiation, dormancy, head filling etc.

Reviews have concentrated on one critical temperature threshold at a specific development phase for each of the horticultural crops selected.

Table 1 : Summary of Critical Temperature Thresholds for selected horticultural crops.


Lettuce Hearting 28oC – mean maximum Cauliflower Curd induction 22oC Banana Fruit maturity 38oC Apple Dormancy Chilling requirement – cultivar specific Citrus Early fruit development 30oC Pineapple Flower initiation and pre-harvest >35oC Tomato 2 week period Pre-anthesis 29oC – mean maximum Macadamia Retention of racemes and nuts Declines rapidly >30oC Capsicum Flowering 32°C Sweet Corn 3-4 weeks post flowering 32oC Avocado Flowering and fruit development 33oC Pumpkin Flowering >35oC

The Review of Literature, on which the thresholds in Table 1. are based, was reported in Milestones # 1 and 2. Appendix I - A Review of Literature, is an updated version of these Milestones.

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5.0 Materials & Methods

5.1 Overall approach to problem:

A review of the literature and industry consultation is required to document critical temperature thresholds for Australia’s major horticultural commodities, as well as understand the broader risks associated with temperature related climate change impacts and the adaptive capacity (resilience) of growers and industries to future climate change. Research by Kenny et al. (2000), provides valuable insight into the issue of understanding critical thresholds in New Zealand horticultural systems. The methodology of this project proceeded in the following stages:

For a selection of the major horticultural crops, identify and document current understanding of critical temperature thresholds through a review of literature – both peer reviewed and the ‘grey’ literature.

Collect additional data on critical temperature thresholds through consultation with informed growers, consultants and scientists.

Determine the impact of projected temperature change in 2030 on selected horticultural commodities in current production regions using the information gained from the literature review.

Document potential adaption strategies. Report findings through detailed commodity specific case studies.

5.2 Horticultural crops:

The horticultural crops of significance in Australia are Apples, Potatoes, Citrus, Bananas, Tomatoes (& capsicums), Stone Fruit, Brassicas, Mango, Avocado, Macadamia, Strawberries, Onion, Lettuce, Carrots, Pumpkin, Zucchini, Watermelon, Rockmelon, Green Beans and Sweet Corn (Australian Natural Resources Atlas). Although these commodities are grown in significant quantities in more than one production region in Australia, this project has targeted the most important regions, as well as those regions which appear to be more vulnerable to changing climates.

Table 2 : Regions in Australia where key horticultural crops are grown.

State Region Key Horticultural Commodities WA SW WA Carrots SA Riverland Onions

Werribee Brassicas vegetables, Leafy vegetables Yarra Ranges Strawberry

Vic

Goulburn Valley Pome fruit, Stone fruit Riverina Citrus, Cucurbits

NSW North Coast Macadamia Tas Northern Region Potato

Wet Tropics Bananas, Tropical fruit Dry Tropics Beans, Tomato, Capsicum, Melons, Sweet corn

Qld

Bundaberg Macadamia, Cucurbits

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5.3 Project objectives:

The project objectives and outputs have been met through the following :-

5.3.1 Literature Review - Critical temperature thresholds

The identification of critical temperature thresholds have taken place across a number of steps. Firstly, an extensive literature review was undertaken for each commodity identified. This review focused on literature that addressed the temperature thresholds and/or the adaptive management responses to increasing temperature in each of the identified commodities.

The following horticultural commodities were reviewed, and a critical temperature threshold identified from the peer reviewed literature, for each commodity :- Lettuce, Cauliflower, Banana, Apples, Citrus, Pineapple, Tomato, Macadamia, Capsicum, Sweet Corn, Avocado, Pumpkin. 5.3.2 Industry engagement and consultation.

The results of the literature review were informed and grounded by results from industry consultation from informed growers, key consultants, researchers and supply chain participants, and through this process understand the resilience of the socio-agronomic system to climate change and what factors would lead to a loss of resilience.

5.3.3 Comparison of climate change scenarios for 2030 and data on temperature thresholds to establish where thresholds might be reached/exceeded.

Analysis of the impact of exceeding these critical thresholds for major horticulture crops and regions against Climate Change scenarios at 2030.

5.3.4 Identification of adaptation strategies which will reduce the impact of temperature increases.

The resilience of specific horticultural commodities will be investigated by comparing the temperature thresholds with the projected temperature increases and available strategies for adaptive management. 5.3.5 Case Studies

The impact of temperature change on horticultural commodities are reported in commodity specific case studies.

These case studies summarise the findings of the literature review and industry consultation process, and identify the current level of knowledge on temperature thresholds.

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6.0 Results

6.1. Literature Review - Critical temperature thresholds: Appendix I provides the detail of the literature review conducted as part of this project. Table 3. provides a summary of the critical temperature thresholds identified by this literature review.



Lettuce Hearting 28oC – mean maximum Cauliflower Curd induction 22oC Banana Fruit maturity 38oC Apple Dormancy Chilling requirement – cultivar specific Citrus Early fruit development 30oC Pineapple Flower initiation and pre-harvest >35oC Tomato 2 week period Pre-anthesis 29oC – mean maximum Macadamia Retention of racemes and nuts Declines rapidly >30oC Capsicum Flowering 32°C Sweet Corn 3-4 weeks post flowering 32oC Avocado Flowering and fruit development 33oC Pumpkin Flowering >35oC 6.2. Industry engagement and consultation: For more details of industry engagement and consultation - see Milestone Report - #3. Summary of outcomes

In general, growers have managed past climate change very well and are optimistic that they will continue to manage projected temperature increases into the medium term future.

In many horticultural regions where the temperature threshold is currently exceeded at specific times of the year, growers in the main have avoided production during these periods, as in general yield and quality are reduced when the temperature exceeds the threshold for each commodity.

As temperatures continue to rise in all vegetable production regions through to 2030, growers are likely to respond by changing planting and harvest dates, and reducing the production season by one to four weeks. If more adaptable vegetable cultivars are available to growers, the impact of reducing the length of the production season will be reduced, until such time as the genetic capability of more adaptable cultivars is exceeded.

It is expected that it will not be until after 2030 that market access and the profitability of a reduced season in the majority of vegetable production districts will be a major factor in increasing the vulnerability of the vegetable industry to climate change.



Production Timing - crops will develop more rapidly and mature earlier. The winter lettuce and brassica season in south-east Queensland will be shortened by several weeks to a month unless more adaptable cultivars are made available to the industry. The availability of these more adaptable cultivars will be constrained by commercial realities (see following points).

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Availability of more Adaptable Cultivars - the majority of cultivars used in the vegetable industry are sourced from overseas. This will be exacerbated by the fact that Australian production is very small in relation to the major fruit and vegetable producing countries of USA and Europe, from where most cultivars are sourced. Climate changes in these countries may not necessarily result in the development of cultivars suitable for Australia’s future environments. Product Quality and Yield - increased heat stress will affect fruit size, quality and pollination of some crops. For avocados, increased heat stress will adversely affect fruit size and the capacity to ‘store’ a mature crop on the tree. Floral abortion will occur in capsicum when temperatures exceed 32ºC. Inputs (Availability and Costs) - more irrigation (water) will be required because of higher evaporative demand with increasing temperatures. This will increase the costs of irrigation pumping under hotter conditions. This, together with increasing fuel costs, will increase the cost of producing all irrigated crops. Pest and Disease effects - in general, higher temperatures will increase pest and disease activity, alter their development rate including that of host crops, and increase survivability of some organisms, especially in warmer winters. For example - an extra generation of insect pests such as heliothis will be possible in most locations; and higher temperatures will have negative effects on survivability and reproduction of scale parasites in citrus and trichogramma in vegetables. Production Location and Marketing Arrangements - production and marketing of some crops will benefit from an extended production season, whilst others will be negatively affected. For example - in tropical and sub-tropical regions, vegetable growers producing winter crops will be negatively impacted as the winter production season shortens. This will provide opportunities for other more southerly summer growing regions which are currently too cold to produce crops in late autumn and early spring, to expand production and market products in this time slot. It is expected that this will gradually induce relocation of production (in the absence of adaptation actions which include introduction of more adaptable cultivars) from those regions where higher temperatures become a limitation to production. Increased Productivity - increases in temperature and CO2 may increase yields of some crops in the absence of other limiting factors, providing positive productivity outcomes. For example - large variations in response to increased CO2 levels have been found across a range of horticultural commodities. Where positive responses have been found (e.g. potato, lettuce, avocado and citrus), increasing temperatures may offset this potential increased productivity. Financial Viability – for perennial horticulture which has a long-term investment horizon, there will be a need for more information and decision making tools to determine the long-term investments required for commodities (especially those where cultivars are not rapidly changing – avocados vs. low-chill stonefruit vs. vegetables). An increase in the intensity of cyclones will impact production systems, the community and consumers. For example – in the case of Cyclone Larry (March 2006) $A350 million crop, property and infrastructure losses were experienced by the banana industry and communities of North Queensland. Such extreme events could easily be experienced in the future in other industries and communities in northern Australia.

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6.3 Comparison of climate change scenarios for 2030 and data on temperature thresholds to establish where

thresholds might be reached/exceeded: Table 4 : Summary - Temperature Thresholds and Buffer Levels for selected horticultural crops.

Crop Development Phase Critical Temperature Threshold*

Regions #Buffer Level #Timeframe for Early Warning

Lockyer Valley, Qld 0.4oC in April 2030 Granite Belt, Qld 0.1oC in January At (Pre-) 2030

Hay, NSW 2.4oC in April 2030 Central West, NSW 0.4oC in November 2030 East Gippsland, Vic 0.7oC in January Post-2030

Lettuce Hearting. 28oC – mean monthly max.

Gingin, WA 0.5oC in April 2030 Innisfail, Qld 6.0oC in December 2030 Banana Fruit Maturity. 38oC

Carnarvon, WA 2.6oC in February 2030 Granite Belt, Qld 1.0-1.5oC 2030 Apple Dormancy. Chilling – cultivar specific.

Tatura, Vic 1.5-2.0oC 2030

Citrus Early Fruit Development. 30oC Griffith, NSW 0.0oC in March 2030

Pineapple Flower Initiation and Pre-harvest. >35oC Rockhampton, Qld 1.8oC in December 2030 Bowen, Qld 1.0oC in September 2030

Lockyer Valley, Qld 0.4oC in October 2030 Tomato 2 weeks Pre-anthesis. 29oC – mean monthly max. Granite Belt, Qld 1.1.oC in January Post- 2030

Macadamia Retention of Racemes and Nuts. Declines rapidly >30oC Southern Qld & Northern NSW 1.6-1.8oC in November 2030

Bowen, Qld 0.6oC in March 2030 Capsicum Pollination. 32°C Granite Belt, Qld 4.1oC in January Post-2030

Avocado Flowering and Fruit Development. 33oC Bundaberg 3.1oC in November 2030 #An estimate of the "buffer level" in oC between current temperatures and the temperature threshold as at 2030, for each commodity is provided in Table 4., including an estimate of the timeframes for early warning that would benefit each of the commodities/regions. This assumes that the relationship between the current climate (including its variability) and a changed climate in 2030 is roughly linear. As we approach 2030, this may not prove to be the case, but in the absence of a far more detailed understanding of climate change, which is not yet available, this assumption is a practical start to an understanding of the possible timing and the impacts of, temperature thresholds being met.

The temperature data presented for all case studies and locations, was sourced from OzClim (http://www.csiro.au/ozclim/home.do), using the Special Report on Emissions Scenarios (SRES) scenario of A1FI with moderate warming.

[The A1 family of scenarios assumes a world characterized by rapid economic growth, a global population reaching 9 billion by 2050 which then gradually declines. The A1FI scenario (Fossil Intensive) assumes a world which remains energy dependant on fossil-fuels]

* Mean Monthly Maximum Temperature

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6.4 Identification of adaptation strategies which will reduce the impact of temperature increases:

Lettuce In many production regions where the threshold is exceeded at some time of the year, growers in the main have avoided production during these periods, as quality is reduced when the mean monthly maximum temperature exceeds 28oC during the hearting development phase.

As temperatures continue to rise in all production regions through to 2030, growers are likely to respond by changing planting and harvest dates, and reducing the production season by a few weeks per year by 2030.

If more adaptable lettuce cultivars are available to growers, this impact of reducing the length of the production season will be reduced, until such time as the genetic capability of more adaptable lettuce cultivars are exceeded.

It is expected that it will not be until after 2030 that market access and the profitability of a reduced season in the majority of lettuce production districts will be a major determining factor in the vulnerability of the lettuce industry.

In districts where the threshold is not exceeded currently, and will be exceeded only on occasions by 2030, growers may be able to take advantage of earlier planting in the spring, and later planting in the autumn.

Banana The temperature threshold for banana growth of 38°C, is significantly higher than temperatures experienced in existing tropical growing regions such as Innisfail, North Queensland and Carnarvon, WA, and thus in the medium term it would seen unlikely that temperature increases associated with climate change will significantly impact production.

However, under a warming climate scenario, the growing conditions in more marginal sub-tropical regions such as in New South Wales, are likely to improve.

Apple The projected level of warming may decrease the suitability of some sites for apple production in Australia, however, the level of impact and the appropriate management responses will vary among regions.

The warmer production regions such as Applethorpe may struggle to achieve sufficient chilling units in some years for some varieties.

There are several potential adaptation strategies that growers will be able to use to minimise the adverse effects of increasing temperatures on reduced chill accumulation.

Dormancy breaking compounds (e.g. hydrogen cyanamide) can be applied to combat the effects of insufficient chilling hours by breaking dormancy and stimulating budbreak.

Manual defoliation is a simple treatment that may overcome problems with prolonged dormancy in warmer regions, although its effectiveness depends on the date of application.

New varieties with lower chill requirements and better adapted to warmer and drier climates are likely to be an important option. Because there is considerable genetic variation in chilling requirements within apple populations and cultivars, a selective breeding program would improve the genetic stock for warmer climate cultivars.

In the absence of new acceptable lower-chill cultivars, the more favourable regions for apple cultivation in Australia will gradually move southward.

Citrus Several adaptation strategies may be effective in reducing the impacts of higher temperatures on citrus yield and quality, at least in the short term.

Shading of young de-fruited citrus trees can enhance plant biomass and vegetative growth during the hot summer months in a subtropical climate. Shading can reduce the observed midday depression in net photosynthetic rate under higher temperatures.

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Micro sprinkler misting can be used to decrease temperature and increase humidity within a citrus orchard. At ambient air temperatures above 36°C, misting can reduce air temperature by up to 5°C within the canopy. Intermittent misting at times of high temperatures can increase fruit set and yield without apparent negative effects on fruit quality. Misting appears to be most effective at 30°C and less effective at higher temperatures, indicating that this strategy may be useful in a short-term transitional context.

The application of aminoethoxyvinylglycine (AVG), an ethylene synthesis inhibitor, can promote fruit set, elevate growth and improve quality of mandarins under higher temperatures. Application of AVG at the start of blooming reduced ethylene production from flowers and young fruit, and improved fruit set at 30°C.

Integrated pest management approaches show potential for the control of insect pests under a changing climate. For example, effective biocontrol of phytophagous mites (e.g. two-spotted mite and European red mite) can be obtained with predatory mites. Unfortunately, the possible responses of pests to climatic changes are largely unknown.

In contrast to short-season rotation crops, adaptive planting is not a viable option for perennial trees. For citrus, long-term adaptation strategies for altered climatic conditions will require the expansion or relocation of citrus orchards.

Pineapple

The “Buffer Level” between the current mean temperature and the threshold temperature in the hottest month in Rockhampton is 2.6oC (January). By 2030, this will be reduced to 1.9oC in January, significantly below the threshold for pineapples.

If a temperature threshold for pineapple at flower initiation is >35°C, then this is significantly higher than temperatures experienced in existing tropical growing regions such as Rockhampton, Queensland, and thus in the medium term it would seen unlikely that temperature increases associated with climate change will significantly impact production.

However, under a warming climate scenario, the growing conditions in southern sub-tropical regions are likely to improve.

Tomato As there is significant genetic variability between tomato cultivars in their capacity to set fruit under high temperature conditions, there is a capacity to utilise these differences in breeding programs to deliver high temperature tolerant commercial cultivars. In experiments conducted to determine critical temperature effects, sensitive cultivars are impacted when mean daily temperatures exceed 25oC, whereas more heat tolerant cultivars are not impacted until daytime (maximum) temperatures exceed 32oC, and the most sensitive period is 8-13 days prior to anthesis.

As maximum temperatures continue to rise through to 2030, due to further climate change, the temperature threshold of 29oC will impact on all other production districts in Queensland, except the Granite Belt. The impact will be in the form of reduced yields, in the absence of more adaptable cultivars.

As temperatures continue to rise, then the adverse effects of high temperature on tomato yields will demand more heat tolerant cultivars which will allow growers to maintain production. Without these more tolerant cultivars, the production season in all regions in Queensland will contract to the cooler months. Summer production will be very difficult in all regions in Queensland except the Granite Belt.

At the beginning and end of the season in those regions which are currently restricted to summer production, growers may be able to take advantage of earlier planting in the spring, and later planting in the autumn. These future early and late plantings are currently constrained by low minimum temperatures. The availability of a profitable market at these times of the year will also have a significant influence over the capacity of growers to take advantage of these earlier plantings, which will extend future planting and harvest times in these summer tomato growing districts.

Macadamia The impact of high temperatures on flowering and nut retention may be alleviated in situations where the orchard is irrigated or the utilisation of overhead misting. Other practices more generally aimed at

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reducing the overall flower load, such as pruning, might be useful as this allows more resources for the nuts that remain on the tree. It is not known if this would alleviate the effects of temperature stress.

Tree crops like macadamia are very long-lived and many of the trees planted in the next few years will experience the 2050 scenario without the benefit of 40 years of breeding and hence there will need to be a greater reliance on farm management practices.

Capsicum At beginning and end of the summer season in the Granite Belt and other summer production districts, growers may be able to take advantage of earlier planting in the spring, and later planting in the autumn. These future early and late plantings are currently constrained by low minimum temperatures. The availability of a profitable market at these times of the year will also have a significant influence over the capacity of growers to take advantage of these earlier plantings, which will extend future planting and harvest times in these summer capsicum growing districts.

As maximum temperatures continue to rise through to 2030, due to further climate change, the temperature threshold of 32oC will impact on all tropical and sub-tropical production districts, except the Granite Belt. The impact will be in the form of reduced yields, in the absence of more adaptable cultivars.

As temperatures continue to rise, then the adverse effects of high temperature on capsicum yields will demand more heat tolerant cultivars which will allow growers to maintain production. Without these more tolerant cultivars, the production season in all tropical and sub-tropical regions will contract to the cooler months. Summer production will be very difficult in all Queensland regions except the Granite Belt.

As there is significant genetic variability between cultivars in their capacity to set fruit under high temperature conditions, there is a capacity to utilise these differences in breeding programs to deliver high temperature tolerant commercial cultivars.

Avocado A number of adaptive management options may be appropriate for avocado producers in a climate change context. These include, information driven adaptive management and the use of record keeping and information management systems such as AVOMAN; using more long range weather and climate forecasting services to inform adaptive management; employing efficient irrigation systems and tighter irrigation management practices including monitoring, scheduling and maintenance; securing water supplies for irrigation and cooling; the use of varieties and rootstocks that are better suited to warmer conditions and diversification of orchard locations to spread climate risks, spread harvest seasons and optimize investment.

Many of these potential adaptation strategies will be dependent on considerable RD&E investment by industry and governments. For example, the use of new varieties and rootstocks, integrated pest management strategies, and reliable long-range forecasting all require ongoing research and development before being employed by growers.

The best opportunities for on-farm climate adaptation are likely to be:

Managing heat (particularly increased summer temperatures) through use of mulching, soil moisture monitoring and irrigation management, increasing water use efficiency and securing water supplies for irrigation and cooling and adaptive management relying on data collection, monitoring and information management systems.

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6.5 Case Studies: The following are the horticultural commodities chosen for case studies :-

Lettuce, Banana, Apple, Citrus, Pineapple, Tomato, Macadamia, Capsicum, and Avocado.

These case studies summarise the findings of the literature review and industry consultation process, and present the current level of knowledge on temperature thresholds and adaptation. They include :- Commodity production data - key varieties, optimum growing conditions, and seasonality;

The current level of knowledge on temperature thresholds;

Projected regional temperature changes;

Discussion on the impact of projected temperature increases on each commodity; and

The capacity for adaptation through management practices.

6.5.1 Lettuce

Lettuce, (Lactuca sativa L.), is an annual vegetable from the Asteraceae family. It is grown in all states of Australia and continents throughout the world, and is consumed mainly as a salad vegetable. The main lettuce production regions in Australia are the Lockyer Valley and Eastern Darling Downs (SE Qld); Hay and Central West (NSW); Lindenow and Robinvale (Vic); Manjimup and Gingin (WA); Virginia (SA) and Cambridge, Richmond, Devonport (Tas). a) Commodity production data

The value of lettuce production in Australia rose by 11.3% to $183 million in 2008/09; production totalled 161,646 tonnes from 7,358 hectares with an average yield of 22.2 tonnes/ha.

Lettuce was Australia’s 6th largest vegetable crop in 2008/09, accounting for 6.2% of total vegetable production by value.

Production is concentrated in the Eastern states – Queensland, NSW and Victoria produce over two-thirds of the national lettuce crop, with WA a significant producer in the west.

The total number of growers was 533 in 2009. The lettuce market consists of the fresh market segment and the processed segment (which is

mainly pre-packaged salads). There are a wide range of lettuce varieties available in Australia, with the most popular being in

the crisphead (iceberg), romaine (cos), butterhead and loose-leaf groups. Lettuce is in season all year round (Ausveg, 2011).

Iceberg lettuce is the main lettuce type grown commercially. It has a firm, compact, spherical heart, the leaves are crisp and firmly packed in the head. Cos (Romaine) lettuce is the second most commonly grown lettuce type and is distinguished by an elongated head (similar to Chinese cabbage) dark green, long, narrow, crisp leaves. All coral, babyleaf and salad mix lettuces belong to the loose leaf lettuce group. This group of lettuce has a great variety of sizes, shapes and colours.

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Table 5 : Lettuce Production – Australia 2005 to 2009

Lettuce (Iceberg & Cos) 2005-06 2006-07 2007-08 2008-09 Number of growers 322 343 293 329 Area planted (ha) 5,397 6,323 4,866 5,352 Production (t) 126,664 206,051 128,594 135,263 Yield (t/ha) 23.5 32.6 26.4 25.3 Gross value ($m) 118.7 213.4 117.7 151.1 Gross unit value ($/t) 937 1036 915 1117 Farm gate value ($m) 91.1 170.3 88.6 121.8

Lettuce (Looseleaf) 2005-06 2006-07 2007-08 2008-09 Number of growers 212 222 229 204 Area planted (ha) 2,490 3,435 2,316 2,006 Production (t) 305,16 57,686 34,223 26,383 Yield (t/ha) 12.3 16.8 14.8 13.2 Gross value ($m) 34.2 60.9 43.9 32.7 Gross unit value ($/t) 1,120 1,055 1,283 1,238 Farm gate value ($m) 27.9 48.2 35.4 26.5 Source : - AusVeg, 2011 - http://ausveg.businesscatalyst.com/resources/statistics/domestic-industry/detailed-data.htm

Table 6 : Proportion of Lettuce produced from each state

Fig. 1 – Lettuce – Value of Production – Australia 1999 to 2009

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Production Regions

Table 7 (i-iv) : Major Locations and Seasonal Production of Lettuce by State & Region

i) Queensland

Region Production Season Lockyer Valley Autumn/winter/spring Granite Belt Summer

Eastern Darling Downs Summer/autumn Winter production in the Lockyer Valley commences with the first plantings in mid-summer, followed by consecutive weekly plantings until mid winter. First harvest occurs in late April/early May with final harvest in October, harvest peaking from June to August. Lower yields and quality are often produced in October, especially in warmer years.

In the Granite Belt, production is summer only. Cold and frosty winters prevent all year round production. First transplantings occur in August, with harvests commencing in November; and final transplanting occurring in March, with harvest completed by May, after which frosts will affect head quality.

ii) Victoria

Region Production Season Werribee All year

East Gippsland All year

Lettuce can be grown all year around in southern Victoria, but the main growing season is from September to May, while in northern Victoria the season runs from May to October.

iii) NSW

Region Production Season Riverina Autumn/winter/spring

Sydney Basin All year

Central West Spring and Autumn

Lettuce production is centred in the three main growing areas of Sydney Basin, Riverina and Central West. In the Sydney Basin lettuce is sown and harvested all year round, but declines through summer due to the warm conditions. In the Riverina, lettuce is sown from early February through to late July for harvesting from April to the end of October. Production through summer is not possible due to high temperatures. In the Central West, lettuce is only scheduled for harvesting during spring and autumn. Production outside these times is difficult due to harsh climatic conditions. iv) Western Australia

Region Production Season Perth All year

Lettuce production is centred in the main growing areas north of Perth, where lettuce is sown and harvested all year round, but declines through summer due to the warm conditions.

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b) Current level of knowledge on temperature thresholds – Lettuce

Table 8 : Critical Temperature Threshold - Lettuce


Lettuce Hearting. 28oC – mean monthly maximum. For lettuce, the ‘hearting’ development phase is the most sensitive to temperatures above optimum.

The maximum temperature threshold for the ‘hearting’ development phase for lettuce, as identified from the literature, is 28oC mean monthly maximum. This has been confirmed through engaging with scientists and other supply chain participants, and by comparing mean monthly maximum temperature data with planting times and the commencement and the end of the lettuce harvesting season for a number of locations where lettuce is grown in Australia.

For iceberg lettuce, this ‘hearting’ development phase commences approximately 2 weeks prior to harvest. Therefore it is to be expected that if a ‘critical temperature threshold’ is reached, then this will negatively impact lettuce quality in the 2 week period prior to the commencement of peak harvest.

The engagement process with growers, consultants, resellers and supply chain participants was designed to confirm or otherwise the following assumption – “If maximum temperatures have a significant effect on harvest quality, then it is to be expected that first and final lettuce harvest will closely follow the maximum temperature threshold of 28oC, identified from the literature, for each of the production locations in Australia”.

The maximum temperature threshold of 28oC for lettuce at the ‘hearting’ development phase, identified from the literature, has been confirmed by comparing mean monthly maximum temperature data with the commencement and the end of the lettuce harvesting season for a number of the major locations where lettuce is grown in Australia :-

i) Queensland - Lockyer Valley (winter); Granite Belt (summer)

ii) NSW – Hay (winter); and Central West (summer)

iii) Vic – East Gippsland (all year round)

iv) WA - Gingin (all year round)

i) Queensland

Lockyer Valley (SE Queensland)

Lettuce harvest is substantially completed in the Lockyer Valley by the end of October each year, and the majority of the harvest is completed by the end of September, because rising temperatures in late spring and early summer negatively impact on head quality (the ‘hearting’ development phase in iceberg lettuce is the most sensitive to high temperatures).

The winter-based production season in the Lockyer Valley commences with the first plantings in February, followed by consecutive weekly plantings until the end of June. First harvest occurs in late April/early May, 2 weeks after the “critical threshold” period ends. Final harvests occur in October, with harvest peaking from June to August. Lower yields and poor head quality are often produced in October, especially in warmer years.

In determining the critical temperature thresholds for lettuce, the assumption, “If maximum temperatures have a significant effect on harvest quality, then it is to be expected that first and final lettuce harvest will closely follow the maximum temperature threshold of 28oC, identified from the literature, for each of the production locations in Australia”, has been tested for the production system in the Lockyer Valley, SE Queensland, and found to be true as demonstrated by Fig. 2. below.

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Fig. 2 – Gatton, Qld - Mean Monthly Maximum Temperatures

Granite Belt (SE Queensland)

Using 28oC as the mean maximum temperature threshold for lettuce in the ‘hearting’ development phase, and the temperature data from Applethorpe, Qld (Fig 3.), it would be expected that lettuce harvesting in the Granite Belt would be possible all summer (frosts and cold temperatures during winter, autumn and spring, restrict plantings during those seasons). This closely describes the production system in this district, where first plantings occur in August (and harvests commence in November); and final plantings occur in March (and are harvested in May). Due to a variable climate, the individual mean monthly maximum temperatures have exceeded 28oC on a few occasions since 1967 (Fig 3).

Fig. 3 – Applethorpe, Qld - Mean Monthly Maximum Temperatures

Applethorpe, Queensland - Mean Monthly Maximum Temperature - 1967 to 2008Threshold - 28 degrees Celcius

0

5

10

15

20

25

30

35

Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun

Deg

rees

Cel

cius

1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 19771978 1979 1980 1981 1982 1983 1984 1985 1986 1987 19881989 1990 1991 1992 1993 1994 1997 1998 1999 2000 20012002 2003 2004 2005 2006 2007 2008 Mean Threshold

Mean maximum temperature never exceeds 28 degrees C at Applethorpe,

Qld.In the Granite Belt, lettuce is

harvested from Nov to May because frosts and cold temperatures restrict production at other times of the year - otherwise all-year-round production

would be posssible.

Threshold - 28 degrees C.

Gatton - Mean Monthly Maximum Temperature (1965 to 2008)

0

5

10

15

20

25

30

35

40


Deg

rees

Cel

cius

1965 1966 1967 1968 1969 1970 1971 1972 1973 19741975 1976 1977 1978 1979 1980 1981 1982 1983 19841985 1986 1987 1988 1989 1990 1991 1992 1993 19941995 1996 1997 1998 1999 2000 2001 2002 2003 20042005 2006 2007 2008 Mean Threshold

Current mean maximum temperature exceeds 28 degrees C from mid-October

to early-April at Gatton, SE Qld.


In the Lockyer Valley, lettuce is harvested from April to October

because high temperatures restrict production at other times

of the year.

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ii) New South Wales

Hay (southern NSW)

For Gatton, the maximum temperature trend for September is more than 2oC above that of October for Hay, NSW for the past decade, with significant variability from year to year at both locations. That is, the maximum temperature threshold of 28oC, which occurs at Gatton in mid September (Fig. 2), does not occur at Hay until after the end of October (approximately 6 weeks later – Fig. 4), coinciding with the end of the harvest season at each location.

Fig. 4 – Hay, NSW - Mean Monthly Maximum Temperatures

Cowra (southern NSW)

Using 28oC as the mean maximum temperature threshold for lettuce in the ‘hearting’ development phase, and the temperature data from Cowra, NSW (Fig 5.), it would be expected that lettuce harvesting at Cowra would cease in mid-December and commence again in mid-March. This closely describes the production system in this district - “In the Cowra district, the early lettuce crops are planted from July to September and harvested from September to December. The late crops are planted from January to March and harvested from March to June” (Wade, 2005).

Fig. 5 – Cowra, NSW - Mean Monthly Maximum Temperatures

Hay, NSW - Mean Maximum Temperature (1958-2008)

0

5

10

15

20

25

30

35

40


Deg

rees

Cel

cius

1958 1959 1960 1961 1962 1963 1964 1965 19661967 1968 1969 1970 1971 1972 1973 1974 19751976 1977 1978 1979 1980 1981 1982 1983 19841985 1986 1987 1988 1989 1990 1991 1992 19931994 1995 1996 1997 1998 1999 2000 2001 20022003 2004 2005 2006 2007 2008 Mean Threshold

Current mean maximum temperature exceeds 28 degrees C from mid-

November to late-March at Hay, NSW.

At Hay, lettuce is harvested from April to October because high

temperatures restrict production at other times of the year.


Cowra (Central NSW) - Mean Monthly Maximum Temperature (1966 to 2008)

0

5

10

15

20

25

30

35

40


Deg

rees

Cel

cius

1966 1967 1968 1969 1970 1971 1972 1973 1974 19751976 1977 1978 1979 1980 1981 1982 1983 1984 19851986 1987 1988 1989 1990 1991 1992 1993 1994 19951996 1997 1998 1999 2000 2001 2002 2003 2004 20052006 2007 2008 Mean Threshold

Current mean maximum

temperature exceeds 28

degrees C from mid-December to early March at Cowra,

NSW.Late lettuce crops are planted from

January to March and harvested from March to June.

Early lettuce crops are planted from July to September and harvested from September

to December.


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iii) Victoria

East Gippsland

Using 28oC as the mean maximum temperature threshold for lettuce in the ‘hearting’ development phase, identified from the literature, and the temperature data from Bairnsdale, Vic (Fig 6.), it would be expected that lettuce harvests could occur in all months of the year – i.e. based on the long term mean monthly maximum temperatures, there would not be many years when the maximum temperature threshold for lettuce at the ‘hearting’ development phase, would be reached.

Lettuce harvesting occurs in all months in East Gippsland, but quality drops off significantly in the middle of winter (due to low temperature effects on quality). In East Gippsland heart size is smaller and quality is lower in winter than at locations such as Hay where the average winter temperatures are slightly higher.

Fig. 6 – Bairnsdale, Vic - Mean Monthly Maximum Temperatures

iv) Western Australia

Gingin

Using 28oC as the mean maximum temperature threshold for lettuce in the ‘hearting’ development phase, it would be expected that lettuce harvesting at Gingin, WA would cease by early December and commence again in April (Fig 7).

This does correspond with the production of high quality lettuce from this region. Production does however continue over the December to March period, with reduced quality and yields. This quality continues to be marketable in WA during this period. More southerly production districts (e.g. Manjimup), do produce higher quality lettuce over this period.

Fig. 7 – Gingin, WA - Mean Monthly Maximum Temperatures

Bairnsdale (East Gippsland), Vic - Mean Monthly Maximum Temperature (1984 to 2008)

0

5

10

15

20

25

30

35


Deg

rees

Cel

cius

1984 1985 1986 1987 1988 1989 1990 1991 19921993 1994 1995 1996 1997 1998 1999 2000 20012002 2003 2004 2005 2006 2007 2008 Mean Threshold

Mean maximum temperature has never exceeded 28 degrees C at

Bairnsdale, Vic.


In East Gippsland, lettuce is harvested all-year-round.

Gingin, WA - Mean Monthly Maximum Temperature - 1997 to 2008

0

5

10

15

20

25

30

35

40


Deg

rees

Cel

cius

1997 1998 1999 2000 2001 20022003 2004 2005 2006 2007 20082009 Mean Threshold

Current mean maximum temperature exceeds 28 degrees

C from mid-November to early April at Gingin, WA.


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c) Projected regional temperature changes - Lettuce

The projections of future maximum temperature change for the major lettuce production regions have been produced using the OZCLIM scenario generator developed by CSIRO Atmospheric Research and the International Global Change Institute (http://www.cmar.csiro.au/ozclim).

OZCLIM generates future climate change scenarios based on twelve different Global climate models (GCMs) and eighteen different greenhouse gas emission projections (IPCC, 2001). In this way it represents a comprehensive range of future climate uncertainties for use in climate change impact and adaptation research.

The CSIRO Mk3.5 Climate Model with the SRES Marker Scenario A1F1, chosen to represent a change in temperature, is a scenario based on the world community taking less action on climate change and remaining fossil fuel dependant.

Lockyer Valley, SE Queensland

Table 9 : Gatton, SE Queensland – Temperature oC

Month Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Current Mean

Max oC 20.8 22.5 25.7 28.0 29.7 31.0 31.5 30.8 29.8 27.4 23.9 21.4

Threshold 28 28 28 28 28 28 28 28 28 28 28 28 2030 Mean Max –

A1F1 Scenario 20.8 22.6 26.0 28.6 30.3 32.0 32.0 31.1 30.1 27.6 24.2 21.4

Using CSIRO Mk3.5 Climate Model with the SRES Marker Scenario A1F1, by 2030 the mean maximum temperature at Gatton (SE Queensland) exceeds 28oC from early-October through to mid-April - a potential reduction in season length of approximately 3 weeks (Fig. 8).

Fig. 8 – Gatton, Qld - Mean Monthly Maximum Temperatures & Projected Increases

Gatton - Mean Monthly Maximum Temperature (1965 to 2008)Threshold - 28 degrees Celcius & 2030 A1F1 Scenario

0

5

10

15

20

25

30

35


Deg

rees

Cel

cius

Mean Threshold 2030 A1F1 Scenario

Current mean maximum temperature exceeds 28 degrees C from mid-October

to early-April at Gatton, SE Qld.

By 2030, the mean maximum temperature exceeds 28 degrees C from early-October through to mid-

April at Gatton, SE Qld.


2030 A1F1 Scenario

By 2030, the lettuce season in the Lockyer Valley may be reduced by up

to 3 weeks.

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30

Granite Belt, SE Queensland

Table 10 : Applethorpe, SE Queensland – Temperature oC

Month Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Current Mean 13.9 15.5 18.8 21.8 23.5 25.8 26.4 25.2 23.9 21.1 17.4 14.6

Threshold 28 28 28 28 28 28 28 28 28 28 28 28 2030 Mean Max – A1F1 Scenario 15.4 17.1 20.6 23.5 25.5 27.6 27.9 26.9 25.6 22.7 19.1 15.9

Using CSIRO Mk3.5 Climate Model with the SRES Marker Scenario A1F1, by 2030 the mean monthly maximum temperature at Applethorpe (SE Queensland) does not yet exceed 28oC (although for practical purposes it does equal the threshold), enabling a continuation of planting and harvests over the summer as is currently occurring.

Due to a variable climate, the individual monthly mean maximum temperatures have exceeded 28oC on several occasions since 1967. It is expected that by 2030, this situation will occur more often, as the mean maximum temperature approaches and then exceeds the 2030 Scenario.

For January (the hottest month of the year in the Granite Belt), the mean maximum temperature is expected to almost reach the threshold by 2030 (Fig. 9), so actual temperatures for individual years at or about 2030 will exceed the threshold of 28oC, at times.

Fig. 9 – Applethorpe, Qld - Mean Monthly Maximum Temperatures & Projected Increases

Hay, NSW

Table 11 : Hay, NSW – Temperature oC



A1F1 Scenario 16.0 18.3 21.7 25.3 29.5 32.3 33.8 33.6 30.5 25.6 20.5 16.8

Applethorpe, Queensland - Mean Monthly Maximum Temperature (1967-2008) Threshold - 28 degrees Celcius & 2030 A1F1 Scenario

0

5

10

15

20

25

30


Deg

rees

Cel

cius


Current mean maximum temperature never exceeds 28 degrees C at

Applethorpe, Qld.

Nov to May Lettuce harvests can continue on the Granite Belt until at

least 2030.

By 2030, the mean maximum temperature does not exceed 28 degrees C at Applethorpe, Qld.


2030 A1F1 Scenario

22

31

Using CSIRO Mk3.5 Climate Model with the SRES Marker Scenario A1F1, by 2030 the mean maximum temperature at Hay (NSW) exceeds 28oC from early-November through to the end of March – a potential reduction in season length of approximately 3 weeks (Fig. 10).

Fig. 10 – Hay, NSW - Mean Monthly Maximum Temperatures & Projected Increases

Central West (Cowra), NSW

Table 12 : Cowra, NSW – Temperature oC



A1F1 Scenario 14.7 16.7 19.9 23.7 27.6 31.4 33.0 32.1 29.2 24.8 19.9 15.7

Using CSIRO Mk3.5 Climate Model with the SRES Marker Scenario A1F1, by 2030 the mean maximum temperature at Cowra (NSW) exceeds 28oC from mid-November to late-March – a potential reduction in season length of approximately 7 weeks (Fig. 11).

Fig. 11 – Cowra, NSW - Mean Monthly Maximum Temperatures & Projected Increases

Hay, NSW - Mean Maximum Temperature (1957-2008)Threshold - 28 degrees Celcius & 2030 A1F1 Scenario

0

5

10

15

20

25

30

35

40


Deg

rees

Cel

cius


By 2030, the mean maximum temperature exceeds 28 degrees C from early-November through to the

end of March at Hay, NSW.

Current mean maximum temperature exceeds 28 degrees

C from mid-November to mid-March at Hay, NSW.


2030 A1F1 Scenario

Cowra (Central NSW) - Mean Monthly Maximum Temperature (1966 to 2008)Threshold - 28 degrees Celcius & 2030 A1F1 Scenario

0

5

10

15

20

25

30

35


Deg

rees

Cel

cius


Current mean maximum

temperature exceeds 28

degrees C from mid-December to early March at Cowra,

NSW.


By 2030, the mean maximum temperature exceeds 28 degrees C from mid-November through to late-March at Cowra, Central NSW.

By 2030, the lettuce season in Central NSW may be reduced by up to 7 weeks.

2030 A1F1 Scenario

32

East Gippsland, Victoria

Table 13 : Bairnsdale, Vic – Temperature oC



A1F1 Scenario 15.6 17.0 19.0 21.4 23.4 25.5 27.3 27.6 25.3 22.2 18.9 16.0

Using CSIRO Mk3.5 Climate Model with the SRES Marker Scenario A1F1, by 2030 the mean maximum temperature at East Gippsland (Vic) does not yet exceed 28oC (although for practical purposes it does get close to the threshold), enabling a continuation of planting and harvests over the whole year as is currently occurring. Due to a variable climate, the individual monthly mean maximum temperatures have exceeded 28oC on a few occasions since 1984.

For January and February (the hottest months of the year in East Gippsland – Table 13), the mean maximum temperature is expected to almost reach the threshold by 2030, so actual temperatures for individual years at or about 2030 will exceed the threshold of 28oC, at times (Fig. 12).

Fig. 12 – East Gippsland, Vic - Mean Monthly Maximum Temperatures & Projected Increases

Gingin, WA

Table 14 : Gingin, WA – Temperature oC



A1F1 Scenario 18.2 18.9 20.8 24.0 27.7 30.8 33.7 33.8 31.8 27.5 22.9 19.3

Using CSIRO Mk3.5 Climate Model with the SRES Marker Scenario A1F1, by 2030 the mean maximum temperature at Gingin (WA) exceeds 28oC from mid-November through to mid-April – a potential reduction in season length of approximately 2 weeks (Fig. 13).

East Gippsland, Victoria - Mean Monthly Maximum Temperature (1984 to 2008)Threshold - 28 degrees Celcius & 2030 A1F1 Scenario

0

5

10

15

20

25

30


Degr

ees

Celc

ius


Current mean maximum temperature has never exceeded 28

degrees C at Bairnsdale, Vic.

By 2030, the mean maximum temperature does not exceed 28 degrees C at Bairnsdale, Victoria.

All year round Lettuce production will be able to continue in East Gippsland

until at least 2030.


2030 A1F1 Scenario

33

Fig. 13 – Gingin, WA - Mean Monthly Maximum Temperatures & Projected Increases

d) Impact of projected temperature increases - Lettuce


Climate is changing, and for the Lockyer Valley mean maximum temperatures have increased over the past five decades by 1.1oC. Climate is expected to continue to change, so that the effects of further increasing temperatures, especially during the spring in the Lockyer Valley, is expected to influence the timing of the first and final lettuce planting and subsequent harvest dates. Growers are likely to respond by delaying the first planting dates and bringing the last planting dates forward.

Currently, the winter-based production season in the Lockyer Valley commences with the first plantings in February, followed by consecutive weekly plantings until the end of June. First harvest occurs in late April/early May, 2 weeks after the “critical threshold” period ends. Final harvests occur in October, with harvest peaking from June to August.

Using CSIRO Mk3.5 Climate Model with the SRES Marker Scenario A1F1, by 2030 the mean maximum temperature at Gatton (SE Queensland) exceeds 28oC from early-October through to mid-April.

As a consequence, the first consecutive lettuce plantings in the Lockyer Valley will gradually be delayed as we approach 2030. Initially this will be by a few days, and eventually by up to 2 weeks. Similarly, at the end of the winter season, the last harvests will occur approximately one week earlier in the spring, because of increasing temperatures in September and October.

The impact of these changes is that the winter lettuce season in the Lockyer Valley will be shortened by approximately three (3) weeks. Initially this will have a small impact on lettuce growing businesses, but if over time the winter season continues to be reduced in length, market access and profitability will be negatively impacted.

The “Buffer Level” between the current mean maximum temperature and the threshold temperature in autumn and early summer (the two times when the mean temperatures cross the threshold) in the Lockyer Valley, is 0.6oC (April) and 2.3oC (September – Table 9). This will be reduced to 0.4oC and 2oC in 2030 respectively.

Consequently, a delay in the commencement of plantings is more likely under a future climate, than is the delay of final harvests, because the current and the 2030 mean maximum temperatures are closer to the threshold in the autumn, than they are at the close of the season in the early summer, in the Lockyer Valley.

If more adaptable lettuce cultivars are available to growers up to and after 2030, this impact will be ameliorated, until such time as the genetic capability of more adaptable lettuce cultivars are exceeded.

Gingin, WA - Mean Monthly Maximum Temperature - 1997 to 2008Threshold - 28 degrees Celcius & 2030 A1F1 Scenario

0

5

10

15

20

25

30

35

40


Deg

rees

Cel

cius


Current mean maximum temperature exceeds 28

degrees C from mid- November to early April at

Gingin, WA.


2030 A1F1 Scenario

By 2030, the mean maximum temperature exceeds 28 degrees C from mid-November through to mid-

April at Gingin, WA.

34

At this point, market access and the profitability of a reduced winter season in the Lockyer Valley will be a major determining factor in the vulnerability of the winter lettuce industry in south-east Queensland.

Granite Belt, SE Queensland

Mean Maximum Temperatures never exceed the 28oC threshold for lettuce at Applethorpe, so currently, lettuce harvesting in the Granite Belt is not constrained by summer temperatures. This closely describes the production system in this summer lettuce production district. The Granite Belt is a highland region of SE Queensland, and as such summer temperatures are influenced by altitude.

Because lettuce is a cold sensitive crop, production in the Granite Belt is constrained by low temperatures in the winter, rather than high temperatures in the summer.

Using CSIRO Mk3.5 Climate Model with the SRES Marker Scenario A1F1, by 2030 the mean monthly maximum temperature at Applethorpe (SE Queensland) does not yet exceed 28oC, enabling a continuation of planting and harvests over the summer, as is currently occurring.

Due to a variable climate, the mean monthly maximum temperatures have exceeded 28oC on a few occasions since 1967. It is expected that by 2030, this situation will occur more often as the mean maximum temperature approaches the 2030 Scenario.

As maximum temperatures continue to rise, due to further climate change, the temperature threshold of 28oC will eventually be reached in the Granite Belt. The impact will be in reduced quality, in the absence of more adaptable cultivars. This may be compensated for by higher returns, as other summer producing districts in Australia are more adversely affected. Eventually, this has the potential to induce a break in summer production, in the first instance in the hottest month which is January (Table 10).

At beginning and end of the summer season, growers may be able to take advantage of earlier planting in the spring, and later planting in the autumn. These future early and late plantings are currently constrained by low minimum temperatures. The availability of a profitable market at these times of the year will also have a significant influence over the capacity of growers to take advantage of these earlier plantings, which will extend future planting and harvest times in this lettuce growing district.

The “Buffer Level” between the current mean temperature and the threshold temperature in January, the hottest month in the Granite Belt, is 1.6oC. This will be reduced to 0.1oC in 2030 (Table 10).

Consequently, by 2030 individual January mean monthly maximum temperatures will exceed 28oC on more occasions than currently occurs.

Hay, NSW

Climate is expected to continue to change, so that the effects of further increasing temperatures will influence the timing of lettuce planting and harvest dates in this region. Growers are likely to respond by bringing these planting dates forward.

Currently, the winter-based production season in southern NSW commences with first harvests in late April, 2 weeks after the “critical threshold” period ends, and final harvests occur in October.

Using CSIRO Mk3.5 Climate Model with the SRES Marker Scenario A1F1, by 2030 the mean monthly maximum temperature at Hay (NSW) exceeds 28oC from early-November through to the end of March.

The “Buffer Level” between the current mean temperature and the threshold temperature in autumn and early summer (the two times when the mean temperatures cross the threshold) in southern NSW, is 3.7oC (Oct) and 3.8oC (April). This will be reduced to 2.7oC and 2.4oC in 2030 respectively (Table 11).

The consequence is that the winter lettuce season in southern NSW will be shortened by approximately three (3) weeks.

35

Initially this will have a small impact on lettuce growing businesses, but if over time the winter season continues to be reduced in length, then market access and profitability will be negatively impacted.

If more adaptable lettuce cultivars are available to growers up to and after 2030, this impact will be ameliorated, until such time as the genetic capability of more adaptable lettuce cultivars are exceeded.

At this point, market access and the profitability of a reduced winter season in southern NSW will be a major determining factor in the vulnerability of the winter lettuce industry in this region.


Currently, the lettuce production season in the Cowra district is based on early crops being planted from July to September and harvested from September to December, and late crops are planted from January to March and harvested from March to June.

Using CSIRO Mk3.5 Climate Model with the SRES Marker Scenario A1F1, by 2030 the mean monthly maximum temperature at Cowra (NSW) exceeds 28oC from late-November to mid-March.

The “Buffer Level” between the current mean temperature and the threshold temperature in early autumn and the summer (the two times when the mean temperatures cross the threshold) in the Central West, is 1.1oC (March) and 2.8oC (November). By 2030 this will be reduced to 0.4oC (November) and in March the threshold is exceeded by 1.2oC (Table 12).

Consequently, a delay in the commencement of plantings is more likely under a future climate, than is the delay of final harvests, because the current mean maximum temperatures are closer to the threshold in the early autumn, than they are at the close of the season in the early summer, and the threshold will be met in the early Autumn by 2030 .

The consequence is that the lettuce season in Central West NSW will be shortened by approximately three (3) weeks.

Initially this will have a small impact on lettuce growing businesses, but if over time the season continues to be reduced in length, then market access and profitability will be negatively impacted.

If more adaptable lettuce cultivars are available to growers up to and after 2030, this impact will be ameliorated, until such time as the genetic capability of more adaptable lettuce cultivars are exceeded. At this point, market access and the profitability of a reduced season in central west NSW will be a major determining factor in the vulnerability of the lettuce industry in this region.


Currently, mean monthly maximum temperatures never exceed the 28oC threshold for lettuce in East Gippsland, so lettuce harvesting in this region is not constrained by temperatures in excess of 28oC, so lettuce harvests can occur in all months of the year. Lettuce harvesting occurs in all months in East Gippsland, but quality drops off significantly (heart size is smaller and quality is lower) in the middle of winter, due to low temperature effects on quality.

East Gippsland’s weather is influenced by its proximity to the ocean, and as such summer and winter temperatures are ameliorated.

Using CSIRO Mk3.5 Climate Model with the SRES Marker Scenario A1F1, by 2030 the mean monthly maximum temperature at East Gippsland (Victoria) does not yet exceed 28oC, enabling a continuation of planting and harvests over the summer as is currently occurring.

As maximum temperatures continue to rise, due to further climate change, the temperature threshold of 28oC will eventually be reached in East Gippsland. The impact will be in reduced quality, in the absence of more adaptable cultivars. This may be compensated for by higher returns, as other summer producing districts are more adversely affected. Eventually, this has the potential to induce a break in summer production, in the first instance in the hottest month which is January.

The “Buffer Level” between the current mean temperature and the threshold temperature in January, the hottest month in East Gippsland, is 2.3oC. This will be reduced to 0.7oC in 2030 (Table 13).

36

Consequently, by 2030 individual January mean monthly maximum temperatures will exceed 28oC on occasions.

Because lettuce production is carried out all year round in East Gippsland, and quality drops off significantly (heart size is smaller and quality is lower) in the middle of winter due to low temperature effects on quality, in the future, growers may be able to take advantage of earlier plantings in the spring, and later plantings in the autumn. These planting times are currently constrained by low minimum temperatures.

The availability of a profitable market at these times of the year will also have a significant influence over the capacity of growers to take advantage of these earlier plantings, which will potentially extend future planting and harvest times in this lettuce growing district.

Gingin, WA

Using 28oC as the mean maximum temperature threshold for lettuce in the ‘hearting’ development phase, it would be expected that lettuce harvesting at Gingin, WA would cease by early December and commence again in April. This corresponds with the production of high quality lettuce from this region.

Currently, production does continue over the December to March period, with reduced quality and yields. This quality continues to be marketable in WA during this period.

Using CSIRO Mk3.5 Climate Model with the SRES Marker Scenario A1F1, by 2030 the mean maximum temperature at Gingin, WA exceeds 28oC from late-November through to mid-April.

Because lettuce production is carried out all year round in Gingin, and quality drops off significantly over the summer, in the future, quality will be more severely affected by increasing summer temperatures.

The “Buffer Level” between the current mean temperature and the threshold temperature in autumn and early summer (the two times when the mean temperatures cross the threshold) at Gingin, is 1.5oC (April) & 0.4oC (November). By 2030, this will be reduced to 0.5oC in April & 0.3oC in November - Table 14.

As a consequence, summer production at Gingin will eventually be discontinued, as the effects on quality are amplified by higher temperatures, especially in February, the hottest month.

If more adaptable lettuce cultivars are available to growers up to and after 2030, this impact will be ameliorated, until such time as the genetic capability of more adaptable lettuce cultivars are exceeded. At this point, market access and the profitability of a production season at Gingin will be a major determining factor in the vulnerability of the lettuce industry in this region of WA.

e) Adaptation through management practices - Lettuce


Climate is expected to continue to change, so that the effects of further increasing temperatures, especially during the spring in the Lockyer Valley, is expected to influence the timing of the final lettuce planting and harvest dates. Growers are likely to respond by bringing these planting dates forward.

The consequence is that the winter lettuce season in the Lockyer Valley will be shortened by approximately three weeks. Initially this will have a small impact on lettuce growing businesses, but if over time the winter season continues to be reduced in length, then market access and profitability will be negatively impacted.

It is expected that it will not be until after 2030 that market access and the profitability of a reduced winter season in the Lockyer Valley will be a major determining factor in the vulnerability of the winter lettuce industry in south-east Queensland.

If more adaptable lettuce cultivars are available to growers, this impact will be ameliorated, until such time as the genetic capability of more adaptable lettuce cultivars are exceeded.

37

Granite Belt, SE Queensland As maximum temperatures continue to rise, due to further climate change, the temperature threshold of 28oC will eventually be reached in the Granite Belt, although using the A1F1 Scenario, by 2030 the mean maximum temperature at Applethorpe (SE Queensland) does not yet exceed 28oC, enabling a continuation of planting and harvests over the summer until at least 2030. Due to a variable climate, the monthly mean maximum temperatures have exceeded 28oC on a few occasions since 1967. It is expected that by 2030, this situation will occur more often as the mean maximum temperature approaches the 2030 Scenario. At some period of time after 2030, when the threshold is reached, the impact will be in reduced quality, in the absence of more adaptable cultivars. This may be compensated for by higher returns, as other summer producing districts are more adversely affected. Eventually, this has the potential to induce a break in summer production, in the first instance in the hottest month which is February.

At beginning and end of the summer season, growers may be able to take advantage of earlier planting in the spring, and later planting in the autumn. These future early and late plantings are currently constrained by low minimum temperatures.

The availability of a profitable market at these times of the year will also have a significant influence over the capacity of growers to take advantage of these earlier plantings which will extend future planting and harvest times in this lettuce growing district.

Hay, NSW Climate is expected to continue to change, so that the effects of further increasing temperatures during the spring in southern NSW are expected to influence the timing of final lettuce planting and harvest dates in this region. Growers are likely to respond by bringing these planting dates forward.

The consequence is that the winter lettuce season in southern NSW will be shortened by approximately three weeks. Initially this will have a small impact on lettuce growing businesses, but if over time the winter season continues to be reduced in length, then market access and profitability will be negatively impacted.

If more adaptable lettuce cultivars are available to growers, this impact will be ameliorated, until such time as the genetic capability of more adaptable lettuce cultivars are exceeded. At this point, market access and the profitability of a reduced winter season in southern NSW will be a major determining factor in the vulnerability of the winter lettuce industry in this region.

It is expected that it will not be until after 2030 that market access and the profitability of a reduced winter season in Hay, will be a major determining factor in the vulnerability of the winter lettuce industry in southern NSW.


Climate is expected to continue to change, so that the effects of further increasing temperatures is expected to influence the timing of lettuce planting and harvest dates in this region. Growers are likely to respond by bringing these planting dates forward.

The consequence is that the winter lettuce season in southern NSW will be shortened by approximately three weeks. Initially this will have a small impact on lettuce growing businesses, but if over time the winter season continues to be reduced in length, then market access and profitability will be negatively impacted.

If more adaptable lettuce cultivars are available to growers, this impact will be ameliorated, until such time as the genetic capability of more adaptable lettuce cultivars are exceeded. At this point, market access and the profitability of a reduced winter season in central west NSW will be a major determining factor in the vulnerability of the winter lettuce industry in this region.

It is expected that it will not be until after 2030 that market access and the profitability of a reduced winter season in Cowra, will be a major determining factor in the vulnerability of the winter lettuce industry in central NSW.

38


As maximum temperatures continue to rise, due to further climate change, the temperature threshold of 28oC will eventually be reached in East Gippsland. The impact will be in reduced quality, in the absence of more adaptable cultivars. This may be compensated for by higher returns, as other summer producing districts are more adversely affected. Eventually, this has the potential to induce a break in summer production.

If more adaptable lettuce cultivars are available to growers, this impact will be ameliorated, until such time as the genetic capability of more adaptable lettuce cultivars are exceeded. At this point, market access and the profitability of a reduced winter season in south-eastern Victoria will be a major determining factor in the vulnerability of the lettuce industry in this region.

Gingin, WA

Because lettuce production is carried out all year round in Gingin, and quality drops off significantly over the summer, in the future, quality will be more severely affected by increasing summer temperatures.

As a consequence, summer production at Gingin will eventually be discontinued, as the effects on quality are amplified by higher temperatures, especially in February, the hottest month.

If more adaptable lettuce cultivars are available to growers up to and after 2030, this impact will be ameliorated, until such time as the genetic capability of more adaptable lettuce cultivars are exceeded. At this point, market access and the profitability of a production season at Gingin will be a major determining factor in the vulnerability of the lettuce industry in this region of WA.

39

6.5.2 Banana

a) Commodity production data

The banana is a tropical/subtropical plant best suited to warm, frost-free, coastal climates. Bananas are commercially grown from the equator to latitudes of 30 degrees or more (Turner and Lahav, 1983). While a few significant areas of banana cultivation do exist outside these limits (such as banana production in New South Wales), these areas are marginal during winter months. At a global level, the majority (20%) of world banana production is based in India. This is followed by Brazil, which produced 7.1 million tonnes of bananas annually.

In Australia, bananas are believed to have been imported from either Malaysia or the Pacific Islands in the 1870s. In 1891, plantations were established in Coffs Harbour and surrounding areas of New South Wales. Today over 90 percent of banana production is based in Queensland where bananas grow in high rainfall regions such as Innisfail and Tully.

The major production areas are Qld (Innisfail/Tully, Sunshine Coast, Bundaberg,) and NSW (mid north coast, far north coast) followed (distantly) by WA and NT (Table 15).

Table 15 : Australian banana production, year ended 30 June 2007

NSW Qld WA NT Total 2007 Production (t) 19,017 188,635 3,822 1,701 213,193

Area (ha) 1,668 9,793 137 65 11,662 (Source: ABS Catalogue 7121, 2006-07)

b) Current level of knowledge on temperature threshold

Table 16 : Critical Temperature Threshold - Banana


Banana Fruit Maturity. 38oC.

The banana is a tropical/subtropical plant best suited to warm, frost-free, climates, and is commercially grown from the equator to latitudes of 30 degrees or more.

The optimum temperature for banana growth is between 25°C and 30°C. Growth and development of bananas are impaired by temperatures outside this range. High air temperatures (usually greater than 38°C) and bright sunshine result in sunburn of exposed fruit, especially on the top hands of the bunch.

New leaves are continually emerging from the stem of the banana throughout the growth phase. The rate of appearance of new leaves is largely governed by temperature. In subtropical conditions during the winter, the rate of production is often significantly reduced, sometimes to a rate of one leaf in 20 days. In contrast, summer leaf emergence can be completed in around 4 days in tropical conditions.

In modelling undertaken on 17 banana cultivars at Alstonville, New South Wales, the optimum rate of leaf emergence occurred at 28.5°C.

Research by Turner and Lahav (1983) into the growth of banana cv. Williams (Giant Cavendish), concluded that plants showed heat injury at day/night temperatures of 37/30°C.

40

c) Projected regional temperature changes

Innisfail, North Queensland The projections of future maximum temperature change for Innisfail, the major banana production region in Australia, have been produced using the OZCLIM scenario generator developed by CSIRO Atmospheric Research and the International Global Change Institute (http://www.cmar.csiro.au/ozclim).



Table 17 : Innisfail, Queensland – Temperature oC


Max oC 24.1 24.9 26.9 28.3 29.6 30.7 30.9 30.7 29.9 28.3 26.4 24.7


A1F1 Scenario 24.8 25.8 27.7 29.7 31.1 32.0 31.8 31.6 30.9 29.0 27.2 25.3

Using CSIRO Mk3.5 Climate Model with the SRES Marker Scenario A1F1, by 2030 the mean maximum temperature at Innisfail (North Queensland) does not exceed the threshold.

Fig. 14 – Innisfail, Qld - Mean Monthly Maximum Temperatures & Projected Increases

Innisfail, Queensland - Mean Monthly Maximum Temperature (1990 to 2010)Threshold 38 Degrees Celcius & 2030 A1F1 Scenario

0

5

10

15

20

25

30

35

40


Deg

rees

Cel

cius

1990 1991 1992 1993 1994 19951996 1997 1998 1999 2000 20012002 2003 2004 2005 2006 20072008 2009 2010 Mean Threshold 2030 A1F1 Scenario


2030 A1F1 Scenario

Current mean maximum temperature never exceeds 38 degrees C at Innisfail, Qld.

By 2030, the mean maximum temperature does not exceed 38

degrees C at Innisfail, Qld.

41

Carnarvon, WA

Table 18 : Carnarvon, WA – Temperature oC


Max oC 22.7 23.4 24.4 26.2 28.1 29.8 31.1 32.3 31.8 29.4 26.8 23.6


A1F1 Scenario 23.9 24.6 26.2 28.0 29.7 32.1 33.9 35.4 34.4 31.3 28.4 25.0

Using CSIRO Mk3.5 Climate Model with the SRES Marker Scenario A1F1, by 2030 the mean maximum temperature at Carnarvon (Western Australia) does not exceed the threshold.

Fig. 15 – Carnarvon, WA - Mean Monthly Maximum Temperatures & Projected Increases

d) & e) Impact of projected temperature increases, and Adaptation through management practices

If a temperature threshold for banana growth is 37 or 38°C, then this is significantly higher than temperatures experienced in existing tropical growing regions such as Innisfail, North Queensland and Carnarvon, WA, and thus in the medium term it would seen unlikely that temperature increases associated with climate change will significantly impact production.


The “Buffer Level” between the current mean temperature and the threshold temperature in the hottest month in Innisfail is 7.3oC (January). By 2030, this will be reduced to 6oC in December, significantly below the threshold for bananas (Table 17).

The “Buffer Level” between the current mean temperature and the threshold temperature in the hottest month in Carnarvon is 5.7oC (February). By 2030, this will be reduced to 2.6oC, significantly below the threshold for bananas (Table 18).

Carnarvon, WA - Mean Monthly Maximum temperature (1990 to 2010) Threshold 38 Degrees Celcius & 2030 A1F1 Scenario.

0

5

10

15

20

25

30

35

40


Deg

rees

Cel

cius

1990 1991 1992 1993 1994 1995 1996 19971998 1999 2000 2001 2002 2003 2004 20052006 2007 2008 2009 2010 Mean Threshold 2030 A1F1 Scenario

Current mean maximum temperature never exceeds 38 degrees C at Carnarvon, WA.

By 2030, the mean maximum temperature does not exceed 38

degrees C at Carnarvon, WA.


2030 A1F1 Scenario

42

6.5.3 Apple


The Australian apple industry is the third largest horticultural industry in Australia. Apples are grown in all six Australian states, with Victoria being the largest in terms of both tonnage and number of producers (ABS 2010). Pome fruit is produced for both the domestic and export fresh markets and for value-adding via canning and juicing.

Table 19 : Australian Apple Production

State No. Growers Tonnes % National Production

VIC

NSW

W.A

QLD

TAS

S.A

TOTAL

349

188

270

61

116

117

1103

134241

41264

33089

25480

35085

25937

295134

45.5

14.0

11.2

8.6

11.9

8.8

Source : ABS 2010.

Australian apple production is considered to be vulnerable to a number of climate change impacts including reduced winter chilling, higher summer temperatures, more intense rainfall events and changes to rainfall patterns, as well as changes to the distribution of pests and diseases.

b) Current level of knowledge on temperature thresholds

The effects of temperature on the growth and productivity of apples are comprehensively reviewed by Putland et al. (2011). Temperature regulates many of the key growth parameters of apple trees, including vegetative growth, floral initiation, fruit set, fruit growth and fruit quality. The numerous commercial varieties of apples combined with their complex physiology leads to difficulties in identifying absolute climate thresholds.

The review identified two temperature thresholds that may be critical for apple production in Australia depending on the variety and growing region:

Insufficient chilling hours – Chilling refers to the low temperatures (e.g. below about 12˚C) that are required to trigger dormancy and the cessation of growth in apples (Heide and Prestrud 2005). The same low temperature conditions that induce dormancy are also required for dormancy release. For example, chilling at 6 or 9˚C for at least 6 weeks may be required for release from dormancy and resumption of growth (Tromp and Borsboom 1994). The period of chilling may be more important than the actual temperature (Jacobs et al. 2002). Increasing chilling hours improves the rate and magnitude of shoot growth, and also advances the onset of growth (Arnold and Young 1990). The chilling requirement varies greatly among varieties, and there is also significant genetic variation in chilling requirements within cultivars. Most commercially cultivated apple varieties in Australia have chill requirements between 500 and 1000 hours.

High temperatures during flowering and fruiting - Exposure to high temperatures during fruit development can affect post-harvest quality, including colour and texture (Sams 1999; Woolf and Ferguson 2000). Sunburn is the most common temperature-related disorder in apples. Direct sunlight can increase fruit surface temperatures by up to 15˚C above ambient air temperature (Ferguson et al. 1998). Sunburn browning results from damage to surface cells that occurs when the fruit surface

43

reaches 46 to 49˚C. Sunburn necrosis is a more serious disorder that occurs when fruit surface temperatures exceed about 52˚C (Piskolczi et al. 2004; Schrader et al. 2001; Schrader et al. 2003).

Table 20 : Critical Temperature Threshold - Apple


Dormancy Chilling requirement – cultivar specific Apple Fruit growth Number of days with high temperatures


Projections of temperature changes across 18 growing regions are presented in Putland et al. (2011).

Here, we summarise the climate data for two of these regions – Applethorpe in Queensland’s Granite Belt and Tatura in Victoria.

The historic climate in the two Australian sites, Applethorpe and Tatura, have been compared to demonstrate that Australian apple production is considered to be vulnerable to a number of climate change impacts.

The projected temperatures were estimated using three different global circulation models (GCMs; Miroc3.2, MRIcgcm2.3.2 and CSIRO Mk3.5).

Table 21 : Projected climate changes for Applethorpe (Qld). The historic mean is calculated using data from 1980-1999. Projected means for 2030 shows the range of values estimated using the 3 global circulation models.

The projected temperatures estimated using the CSIRO Mk3.5 global circulation model, A1FI scenario and moderate warming are in bold.

Climate variable Historic mean Projected 2030 mean

Mean annual temperature (˚C)

14.9 15.7 - 16.2 (1.3)

Maximum temperature in hottest month (˚C)

27.0 27.9 - 28.3

Minimum temperature in hottest month (˚C)

15.4 16.3 - 16.6

Number of days with temperatures above 35˚C

0.4 0.8 - 1.5

Chill units (Utah model) 1265 1036 - 1139

Annual rainfall (mm) 784 712 - 818 (724)

Annual evaporation (mm) 1412 1456 - 1479

() Change from historic mean.

The climate modelling suggests that the Applethorpe region is likely to experience: Significant increases in temperature (mean, minimum and maximum); Increased risk of days with temperatures in excess of 35˚C, although the absolute number of

days with extreme heat may still be low; Reduced chill accumulation (10 to 18%); Increased evaporation rates.

44

Table 22 : Projected climate changes for Tatura (Vic). The historic mean is calculated using data from 1980-1999. Projected means for 2030 shows the range of values estimated using the 3 global circulation models.

The projected temperatures estimated using the CSIRO Mk3.5 global circulation model, A1FI scenario and moderate warming are in bold.

Climate variable Historic mean Projected 2030 mean

Mean annual temperature (˚C)

14.8 15.6 – 15.9 (1.1)

Maximum temperature in hottest month (˚C)

30.3 31.1 – 31.5

Minimum temperature in hottest month (˚C)

14.7 15.5 – 15.8

Number of days with temperatures above 35˚C

11.8 15.2 – 17.3

Chill units (Utah model) 1565 1375 – 1449

Annual rainfall (mm) 468 416 – 460

Annual evaporation (mm) 1416 1440 – 1462

() Increase in oC from historic mean.

The results of the climate modelling suggest that the Tatura region is likely to experience: Significant increases in temperature (mean, minimum and maximum); Increased risk of days with temperatures in excess of 35˚C (with between 3 and 6 extra days

of extreme heat per year); Reduced chill accumulation (7 to 12%); Reduced rainfall (2 – 11%); Increased evaporation rates.

d) Impact of projected temperature increases

The main impacts of climate change on apple production are likely to result from: Increases in mean temperature; Increases in the risk or frequency of high temperature events; Decreases in accumulated chilling hours.

A potential problem facing apple producers is the risk of insufficient chilling hours required to break dormancy. Some growing regions are already too mild during winter to satisfy the requirements of some commercial apple varieties (Schmidt et al. 1999).

From the analyses of historical climate data presented in Putland et al. (2011), it is apparent that chill accumulation varies greatly between sites and years, and also depends on the method by which chill accumulation was calculated. There is a complex relationship between temperature and chill accumulation, but as a general rule, chill accumulation will decrease under warmer future climates for all sites.

Across all 18 sites analysed by Putland et al. (2011), there was a projected increase in the number of days with a maximum temperature greater than a particular threshold (such as 35°C), and a decrease in the number of days below a particular threshold (such as 0°C). Furthermore, average values for most temperature traits are likely to become as warm or warmer than that which is currently encountered in a 1 in 10 year warm year.

45

A potential consequence of elevated mean temperatures resulting from climate change may be a shortening of the chilling period and an increase in the occurrence of warmer non-chilling days within the chilling period.

Simulating the effect of climate change by making relatively small adjustments to the historical climate shows that the average values for most traits related to temperature are likely to became as warm or warmer than that which is currently experienced in a 1 in 10 year warm year.

Tatura and Applethorpe have dormant season temperatures around 10 to 11 degrees. Although this is reasonably cool, the more complex chill accumulation models indicate chill accumulation can easily be eroded – i.e. a small amount of warming will greatly decrease the chill accumulation.

Chill accumulation varies greatly between years, and depends on the method by which chill accumulation was calculated. This would be expected as the models used to calculate chill accumulation are non-linear functions related to temperature measured (or simulated) on an hourly basis.

Using the Utah Model, Tatura accumulates up to 1449 Utah Chill Units (UCU) in 2030, and Applethorpe up to 1139 UCU’s. Most commercially cultivated apple cultivars in Australia have chill requirements between 500 and 1000 UCU’s and the projected level of warming may decrease the suitability of some sites to apple production.

For example, warmer sites such as Applethorpe may struggle to achieve sufficient chilling units in some years for some varieties. If the projected temperature increases eventuate, we would expect equal to or less than the level of low chill accumulation that currently happens in a 1 in 10 year warmest year, to occur in 5 out of 10 years.

Applethorpe would require an increase of 1 to 1.5oC, whereas Tatura would require an increase of 1.5 to 2oC for this to be achieved – i.e. these are the “Buffer Levels” for these to sites.

Modelling of climate change impacts on apple production in Japan suggests that some current production areas will be unfavourable as early as the 2040’s and many areas will be unfavourable by the 2060’s. In contrast, new areas in the north will become suitable for apple production by the 2060's. These results from Japan provide an insight into the potential impacts of climate change on the Australian apple industry. In the absence of new acceptable lower-chill cultivars, the more favourable regions for apple cultivation in Australia will gradually move southward.

These results illustrate the variable impacts of projected climate changes across these two apple production regions. The greatest climate threat to apple production in the Applethorpe region is likely to be the reduction in chilling hours. In contrast, the major challenges to production in Tatura may be the increased number of days with extreme heat.

e) Adaptation through management practices

In general, the projected level of warming may decrease the suitability of some sites for apple production. However, the level of impact and the appropriate management responses will vary among regions. For example, warmer regions such as Applethorpe may struggle to achieve sufficient chilling units in some years for some varieties. For Tatura, the predicted increase in the frequency of extreme temperatures (e.g. above 35°C) may increase the frequency and severity of disorders such as sunburn browning. There are several potential adaptation strategies that growers will be able to use to minimise the adverse effects of the primary climate threats in a given region. Methods to address extreme temperatures.

Hail netting has been reported to reduce air and fruit temperatures, reducing the negative impacts of extreme temperatures. Nets are already employed to reduce damage from hail, but may have an added benefit of reducing temperature and sun damage to fruit. For example, white hail nets can reduce air temperature by about 1.6C (Solomakhin and Blanke 2007).

46

Evaporative cooling using microsprinkler irrigation has been shown to be an effective tool for reducing fruit temperatures. Spanish research has shown that microsprinkler irrigation reduced fruit and orchard temperatures, and that cooled fruit were larger, firmer with higher soluble solid concentrations (Iglesias et al. 2002; Iglesias et al. 2005).

Particle films can be effective in reducing heat stress and solar injury in extreme temperature conditions resulting in greater fruit weight (Glenn et al. 2003; Thomas et al. 2004).

All three of these methods have been shown to be effective to some degree. Shade netting appears to be the most effective method to lower fruit temperature and reduce the incidence of sunburn. However, these radiation-reducing methods may have negative effects on fruit development and colour (Gindaba and Wand 2005). Methods to address insufficient chilling hours.


Manual defoliation is a simple treatment that may overcome problems with prolonged dormancy in warmer regions, although its effectiveness depends on the date of application (Mohamed 2008).

New varieties with lower chill requirements and that are better adapted to warmer and drier climates are likely to be an important option. Because there is considerable genetic variation in chilling requirements within apple populations and cultivars, a selective breeding program could improve the genetic stock for warmer climate cultivars.

Methods to reduce water use.

Efficient irrigation systems such as micro sprinklers and drippers can reduce orchard water use. More sophisticated irrigation scheduling based on soil moisture monitoring and atmospheric demand can also be employed to reduce water use. In addition, irrigation strategies including deficit irrigation and partial rootzone drying may be effective methods to maintain production when water supply is limited (O'Connell and Goodwin 2007), although further research on effectiveness of these strategies under the broad range of Australian conditions is required.

Rootstock selection may provide reductions in orchard water use given the effect of rootstock on whole-tree water use. However, there is currently very little information on the relative water use efficiency of alternative rootstocks under the varied Australian growing environments.

Crop load manipulation is a strategy that may assist when irrigation water is scarce. Matching crop load with the level of plant water stress has been shown to allow production of a reduced volume of commercially sized fruit (Naor et al. 2008).

Hail netting can result in increased humidity in addition to reduced temperatures. The resulting reduction in vapour pressure deficit may decrease water use, although further work demonstrating the effectiveness of this method in field conditions is required.

Orchard design – densely planted dwarf orchards with lower wind speeds may have lower transpiration rates than taller and more widely spaced orchards.


47

6.5.4 Citrus


Australia’s citrus production amounts to 0.6% of total World production. 32,000 hectares were devoted to Citrus production in Australia in 2005-06. 75% of Australia’s production (24,000 ha) occurs in the Murray and Murrumbidgee Irrigation Areas (Riverland region – SA), Sunraysia and mid-Murray (northern Vic & southern NSW) and the Riverina (NSW).

Queensland has 4,800 ha (Central Burnett and Emerald) and the remaining 3,200 ha are in the Katherine region of Northern Territory, the south west coastal belt of Western Australia, and the Bourke/Narromine and central coast areas of NSW.

The industry’s gross value of production was $400 million, $446 million and $426 million in 2003/04, 2004/05 and 2005/06, respectively. The Australian citrus industry is the largest exporter of fresh fruit, worth approximately $200 million per year.

75% of the Australia’s total citrus production consists of ‘Navel’ and ‘Valencia’ orange varieties, with ‘Navel’ orange production increasing and ‘Valencia’ production decreasing. Mandarin production is also increasing.

Table 23: Australian orange production, 2008-09


VIC

NSW

W.A

QLD

N.T.

S.A

TOTAL

266

763

182

195

1

442

1849

64265

166562

7761

6789

102

102243

347724

18.5

47.9

2.2

2.0

0

29.4

Source : ABS (2010).


Several agrometeorological models have been developed to allow the forecasting of potential yields in citrus crops based on climatic data (reviewed in Ben Mechlia and Carroll 1989b; Paulino et al. 2007). One such model predicts the temporal progression of phenological stages, fruit growth, fruit maturation, and fruit coloration for two orange varieties (“Navel” and “Valencia”)(Ben Mechlia and Carroll 1989a). The required data were derived from an extensive body of published observations and selected to be variety specific and independent of local climatology or other site-specific effects. The factors considered included effects on both flowering (temperature and solar radiation) and fruit set (past stress, temperature, evaporation, wind, rain, planting density, and tree age). Table 24 provides a summary of some of the key data.

48

Table 24: The temperature sensitivity of citrus at different phenological stages (based on the summary of Ben Mechlia and Carroll 1989a presented in Rosenzweig et al. 1996). Phenological stage Optimum temp range

(C) Notes

Min. Max. Dormancy -4 14 Low physiological activity - Hardening -4 8 Reduced losses due to freezing - Pre-bloom 0 14 Required resting period for bloom Flowering 10 27 Requires daily mean > 20C to begin Fruit set 22 27 Range near end of bloom. A single day

max over 38C may causes losses Fruit growth 20 33 Requires heat, but expansion may be

reduced if temperatures are too high Maturation - Soluble solids 13 27 Sugars increase and acids decrease

with accumulated heat units - Colour 8 18 Heat may lead to re-greening A comprehensive analysis of the effects of temperature and precipitation on crop yields was presented in Lobell et al. (2007). The authors analysed the relationships between crop yield and three climatic variables (minimum temperature, maximum temperature, and precipitation) for oranges (and other crops) over a 24-year period (1980-2003) in California. Orange yield was most closely correlated with rainfall in May (reflecting a positive response in production of “Valencia” oranges) and minimum temperature in December (reflecting the negative impact of frost). Net photosynthetic rate of citrus trees is greatest between 25 and 30°C (Kriedemann 1968). Research on mandarins in China showed that citrus growing under full sun on hot days experienced a pronounced midday depression in net photosynthetic rate (Hu et al. 2007). This depression is less pronounced in shaded leaves. In young Navel oranges, the growth of fruit on young trees was significantly related to daily maximum temperatures (Storey and Treeby 1999). High temperatures and high atmospheric vapour deficits have been shown to lead to reduced photosynthesis and reduced growth in citrus (Medina et al. 2002). In addition, high temperatures (in excess of 30°C) can cause poor flower quality, lower fruit growth, reduced fruit quality and fruit drop in mandarins (Ogata et al. 2002). During fruit ripening, gradual changes occur in brix (total soluble solids), acid and juice content (Hutton and Landsberg 2000). The brix to acid ratio is an important indicator of fruit quality, particularly for juice production where fruit are often left on the tree for extended periods to ensure a lengthy supply of fresh fruit. The temperature sums (or effective heat units in day degrees) can be used to predict the internal quality of citrus fruit at harvest time during extended harvest periods (Hutton and Landsberg 2000). Brix is reduced with the accumulation of effective heat units, while acid content decreases at a faster rate, leading to a higher brix to acid ratio. Solar injury is a common disorder resulting in reduced fruit quality in tropical and temperate climates, and is caused by high fruit surface temperature, high visible light intensity, and ultraviolet radiation (Glenn et al. 2008). Elevated CO2 has beneficial effects on citrus including improved seedling growth, tree growth and yield (reviewed in Allen and Vu 2009; Soon et al. 1999) but this effect may be limited by increasing temperatures . Some early simulation work on citrus included combinations of three increased temperature regimes and three levels of CO2 enrichment, in addition to current ambient conditions (Rosenzweig et al. 1996). The authors conclude that the effects of increased temperature and enhanced CO2 will probably counteract each other.

49

Modelling of citrus production in the southern United States predicts that climate change will have significant benefits until the end of this century (Tubiello et al. 2002). These models predict significant increases in yield (20-50%), decreased use of irrigation water, and decreased losses to frost and freezing. However, these models also predict limited potential for expansion of citrus growing areas into higher latitudes. Similar modelling has not yet been done for Australian production regions.

Table 25 : Critical Temperature Threshold - Apple


Citrus Early fruit development 30oC.


This case study will focus on the major production region surrounding Griffith in the NSW Riverina. Fig. 16 - Mean maximum monthly temperatures for Griffith, NSW (all years, 1971-2010). The horizontal blue dotted line indicates the critical threshold of 30˚C. The end of the early fruit growth phase in early December (ACG 2003) corresponds with the mean maximum temperature reaching the 30˚C threshold.

Griffith - Mean Maximum Temperature (1971 to 2010)

0

5

10

15

20

25

30

35

40


Deg

rees

Cel

cius

1978 1980 1981 1982 1983 1984 19851986 1987 1988 1989 1990 1992 19941995 1996 1997 2010 Mean (1971-2010) Threshold

Fruit set and early fruit growth

50

Fig. 17 - Mean maximum monthly temperatures for Griffith, NSW, for historic (1971-2010) and projected 2030 climate. The projected temperatures were estimated using the CSIRO Mk3.5 global circulation model, A1FI scenario and moderate warming. The horizontal blue dotted line indicates the critical threshold of 30˚C. The solid lines indicate mean maximum temperatures (green for historic, red for the 2030 High Scenario). Dotted lines indicate the maximum monthly temperature in the historic data (green) and adjusted for the 2030 High Scenario (red).

Griffith - Mean Maximum Temperature (1971 to 2010) & 2030 High Scenario

0

5

10

15

20

25

30

35

40


Deg

rees

Cel

cius

Mean (1971-2010) Threshold Mean 2030 High Scenario Maximum (1971-2010) Max 2030 High Scenario d) Impact of projected temperature increases

Climate projections suggest that the critical temperature threshold will be reached earlier in the year in 2030 (by a week or two) in the Riverina region. This may have negative effects on fruit set and growth. However, elevated temperatures throughout the year may see advancement of the phenological stages and contraction of the fruiting period. This may have negative effects on fruit quality.

In addition, unusual or extreme high temperatures may be encountered earlier in the growth period (Fig. 17), with a potential increase in the risk of solar injury and premature fruit drop.

The “Buffer Level” between the current mean temperature and the threshold temperature in at Griffith, is 1.5oC (March) & 2.5oC (November). By 2030, this will be reduced to 0.0oC in March & 1.0oC in November.


Several adaptation strategies may be effective in reducing the impacts of higher temperatures on citrus yield and quality, at least in the short term.

Shading of young de-fruited citrus trees can enhance plant biomass and vegetative growth during the hot summer months in a subtropical climate (Raveh et al. 2003). Shading can reduce the observed midday depression in net photosynthetic rate under higher temperatures (Hu et al. 2007).

Micro sprinkler misting can be used to decrease temperature and increase humidity within a

citrus orchard (Garcia-Delgado et al. 2004). At ambient air temperatures above 36°C, misting can reduce air temperature by up to 5°C within the canopy. Intermittent misting at times of high temperatures can increase fruit set and yield without apparent negative effects on fruit quality. Misting appears to be most effective at 30°C and less effective at higher temperatures (Garcia-Delgado et al. 2004), indicating that this strategy may be useful in a short-term transitional context.

51

The application of aminoethoxyvinylglycine (AVG), an ethylene synthesis inhibitor, can promote fruit set, elevate growth and improve quality of mandarins under higher temperatures (Ogata et al. 2002). Application of AVG at the start of blooming reduced ethylene production from flowers and young fruit, and improved fruit set at 30°C.

Integrated pest management approaches show potential for the control of insect pests

under a changing climate. For example, effective biocontrol of phytophagous mites (e.g. two-spotted mite and European red mite) can be obtained with predatory mites (Grafton-Cardwell et al. 1997). Unfortunately, the possible responses of pests to climatic changes are largely unknown.

In contrast to short-season rotation crops, adaptive planting is not a viable option for perennial trees (Rosenzweig et.al.,1996). For citrus, long-term adaptation strategies for altered climatic conditions will require the expansion or relocation of citrus orchards.

52

6.5.5 Pineapple


The Pineapple industry in Australia supplies both the processing sector which is not expanding, and the fresh market sector which has been expanding since the mid 1990’s with the introduction of fresh market hybrids. Golden Circle Ltd is the only processor of pineapple in Australia.

Pineapple production occurs mainly in Queensland (with a very small area in NT). 70% of processed fruit, and 60% of the fresh market fruit are grown in southern Queensland. 30% of the processed fruit and 20% of fresh market fruit are grown in Central Queensland, and the remainder is grown in Far North Queensland (20% of fresh market fruit).

Table 26: Queensland pineapple production Districts.

District Number of farms

North Qld (North of Mackay) 14

Central Qld (Cawarral & Yeppoon) 18

Wide bay (Bundaberg, Hervey Bay & Maryborough) 29

Mary Valley & Nambour 8

Beerwah & Glasshouse Mountains 20

Wamuran & Elimbah 21

Total 110

The industry reached a peak of 6,660 ha in 1988. There are now less than 6,000 ha of pineapple grown in Queensland by about 110 growers.

Production for the processing market has declined in significant steps over recent years. Intake for the 2008/2009 year is estimated at 60,000 t. This will decrease to 40,000 t for the 2009/2010 season.


Table 27 : Critical Temperature Threshold - Pineapple


Pineapple Flower Initiation and Pre-harvest. >35oC.


Rockhampton, Queensland The projections of future maximum temperature change for Rockhampton have been produced using the OZCLIM scenario generator developed by CSIRO Atmospheric Research and the International Global Change Institute (http://www.cmar.csiro.au/ozclim).

OZCLIM generates future climate change scenarios based on twelve different Global climate models (GCMs) and eighteen different greenhouse gas emission projections (IPCC, 2001). In this way it

53

represents a comprehensive range of future climate uncertainties for use in climate change impact and adaptation research.


Table 28 : Rockhampton, Queensland – Temperature oC


Max oC 23.7 25.2 28.1 30.0 31.3 32.3 32.4 31.9 31.2 29.1 26.5 24.0


Using CSIRO Mk3.5 Climate Model with the SRES Marker Scenario A1F1, by 2030 the mean maximum temperature at Rockhampton (Queensland) does not exceed the threshold by 2030.

Fig. 18 – Rockhampton, Qld - Mean Monthly Maximum Temperatures & Projected Increases

d) & e) Impact of projected temperature increases, and Adaptation through management practices

If a temperature threshold for pineapple at flower initiation >35°C, then this is significantly higher than temperatures experienced in existing tropical growing regions such as Rockhampton, Queensland, and thus in the medium term it would seen unlikely that temperature increases associated with climate change will significantly impact production.

However, under a warming climate scenario, the growing conditions in southern sub-tropical regions, are likely to improve.

The “Buffer Level” between the current mean temperature and the threshold temperature in the hottest month in Rockhampton is 2.6oC (January). By 2030, this will be reduced to 1.8oC in December, significantly below the threshold for pineapples.

Rockhampton, Qld - Mean Monthly Maximum Temperature (1990 to 2010)Threshold 35 Degrees Celcius & 2030 A1F1 Scenario.

0

5

10

15

20

25

30

35

40


Deg

rees

Cel

cius

1990 1991 1992 1993 1994 1995 1996 19971998 1999 2000 2001 2002 2003 2004 20052006 2007 2008 2009 2010 Mean Threshold 2030 A1F1 Scenario

Current mean maximum temperature never exceeds 35 degrees C at Rockhampton,

Qld.By 2030, the mean maximum

temperature does not exceed 35 degrees C at Rockhampton, Qld.


2030 A1F1 Scenario

54

6.5.6 Tomato


In Australia, tomatoes are produced in Queensland (Bowen, Bundaberg, Lockyer Valley), NSW (Narromine, MIA, Sydney basin), Vic (Goulburn Valley – including processing), SA (Murray Bridge, Adelaide Plains) and WA.

Tomatoes are cold and frost sensitive, and production times in each region are regulated by both low and high temperatures.

In Queensland, production in Bowen is predominantly in autumn/winter/spring, whereas Bundaberg production is all year round with peaks in autumn and late spring to summer. The southeast Queensland crop is produced through summer and autumn because the winters are too cold for production.

Table 29 : Australian fresh tomato production. Year ended 30 June 2007

NSW Vic Qld SA WA Tas NT Total

Production (tonnes) 35,937 123,640 120,656 4,313 11,009 434 46 296,035

Area (ha) 798 2312 3,743 78 355 6 2 7,293

(Source: ABS Catalogue 7121, 2006-07)

Processing tomato production (147,544 tonnes in 2007-08) is largely confined to Victoria. Table 30 : Value of fresh tomato industry. Year ended 30 June 2006

NSW Vic Qld SA WA Tas Australia Value($m) 19.7 74.7 145.2 13.6 18.6 0.8 272.8


b) Current level of knowledge on temperature thresholds – tomato

Table 31 : Critical Temperature Threshold - Tomato


Tomato 2 week period Pre-anthesis. 29oC – mean maximum.

For tomato, the 8 to 13 day period prior to anthesis is the most critical developmental phase. The critical temperature, as identified from the literature for this phase, varies according to the cultivar tolerance to elevated temperatures. In tomato, elevated temperature impacts are complex, and it is difficult to determine one critical temperature effect during the reproductive development phase. In experiments conducted to determine critical temperature effects, sensitive cultivars are impacted when mean daily temperatures exceed 25oC, whereas more heat tolerant cultivars are not impacted until daytime (maximum) temperatures exceed 32oC.

For the purposes of this review, 29oC (mean monthly temperature) during the 2 week period up to anthesis has been selected as the critical temperature and critical development phase for tomato. In Queensland this critical period occurs ~ 9 weeks before harvest (Table 33).

55

Table 32 : Tomato Production Districts - Queensland

District Planting Harvest Critical Development Phase North Queensland

February – early September

June – early December April to early October

Lockyer Valley Late August – February November - May September to March Granite Belt September – December December - April November to Feb Source – Lovatt, et.al, 1998

Table 33 : Tomato Production Growth Stages - Queensland

Plant Stage Time Sowing to germination 4-10 days

Emergence to field planting 4-8 weeks Field planting to first flower 3-4 weeks

First Flower to harvest 6-8 weeks Duration of harvest 1-12 weeks

Critical Development Phase (2 weeks pre-anthesis)

8-10 (9) weeks prior to harvest

Source – Lovatt, et.al, 1998

The engagement process with growers, consultants, researchers and supply chain participants, was designed to confirm or otherwise the following assumption – “If maximum temperatures have a significant effect on the yield and/or quality of tomatoes, then it is to be expected that first and final harvests will closely follow the maximum temperature threshold of 29oC, identified from the literature, for each of the production locations in Queensland”.

The maximum temperature threshold of 29oC for tomato during the 2 week period up to anthesis, identified from the literature, has been confirmed by comparing mean monthly maximum temperature data with the commencement and the end of the tomato season for a number of the major locations where tomatoes are grown in Queensland :-

i) North Queensland (winter)

ii) Lockyer Valley (summer);

iii) Granite Belt (summer)

i) Bowen, North Queensland

Using 29oC as the mean maximum temperature threshold, and the temperature data from Bowen, Qld (Fig 19), it would be expected that tomato harvesting at Bowen would commence in June and cease by December. This closely describes the production system in this district.

Fig. 19 – Bowen, Qld - Mean Monthly Maximum Temperatures

Bowen - Mean Monthly Maximum Temperature (1988 to 2010)

0

5

10

15

20

25

30

35

40


Deg

rees

Cel

cius

1988 1989 1990 1991 1992 1993 1994 1995 1996 19971998 1999 2000 2001 2002 2003 2004 2005 2006 20072008 2009 2010 Mean Threshold

Current Mean maximum temperature is above 29 degrees C from mid-October to mid-April at

Bowen, Qld.

First harvest at Bowen occurs in Mid-June, ~ 9 weeks after 29 degrees temperature threshold

has been reached.

Final harvest at Bowen occurs in Mid-Dec., ~ 9 weeks after 29 degrees temperature threshold

has been reached.


56

As maximum temperatures continue to rise, due to further climate change, the temperature threshold of 29oC will gradually reduce the length of the Winter production season. The impact will be manifest in reduced yields, in the absence of more adaptable cultivars.

ii) Lockyer Valley (SE Queensland)

Using 29oC as the mean maximum temperature threshold, and the temperature data from Gatton, Qld (Fig 20), it would be expected that tomato harvesting at Gatton would not occur over the summer months from November to March. This does not describe the production system in this district – i.e. the first harvests of tomatoes at Gatton occur in November. This corresponds with the first planting made after the risk of frosts is reduced in August. The final harvests at Gatton occur in May, approximately 6 weeks after the 29oC threshold is reached, and the risk of frosts increases.

Therefore there is an expectation that growers in this region will suffer a yield and/or quality loss, and this is then expected to be compensated in some way to allow growers to continue to profitably produce tomatoes under such apparently adverse conditions.

Information provided by tomato growers in the Lockyer Valley (Gatton), shows that growers have historically been largely compensated for the temperature induced decrease in yields (and quality) which occur in the summer, through higher returns in most years in the past. Returns are subject to supply and demand, with quality playing a part as well. These higher returns are being continually eroded by competition from other summer producing districts, which are not impacted by temperatures over the threshold. If higher returns were available for producing at a time when high temperatures reduce yields, then growers will continue to plant for this market.

Fig. 20 – Gatton, Qld - Mean Monthly Maximum Temperature

As temperatures continue to rise, then the adverse effects of high temperature on tomato yields will demand more heat tolerant cultivars to allow growers to maintain supply especially in mid-summer. Without these more tolerant cultivars, mid-summer production will eventually decline and potentially cease in the Lockyer Valley.

iii) Granite Belt (SE Queensland)

Mean Maximum Temperatures never exceed 29oC at Applethorpe. Using 29oC as the mean maximum temperature threshold, and the temperature data from Applethorpe, Qld (Fig 21), it would be expected that tomato harvesting in the Granite Belt would not be constrained by temperatures in excess of 29oC. This closely describes the production system in this district, which is a summer tomato production district, due to the influence of altitude on maximum temperatures, especially during the summer.

Gatton - Mean Monthly Maximum Temperature (1965 to 2008)

0

5

10

15

20

25

30

35

40


Deg

rees

Cel

cius

1965 1966 1967 1968 1969 1970 1971 1972 1973 19741975 1976 1977 1978 1979 1980 1981 1982 1983 19841985 1986 1987 1988 1989 1990 1991 1992 1993 19941995 1996 1997 1998 1999 2000 2001 2002 2003 20042005 2006 2007 2008 Mean Threshold

Current mean maximum temperature exceeds 29 degrees C from early-October

to late-March at Gatton, SE Qld.


In the Lockyer Valley, tomatoes were harvested from November

to May even though high temperatures impact yield and

quality.

57

Because tomatoes are frost and cold sensitive, winter production in the Granite belt is constrained by low temperatures, rather than high temperatures.

As maximum temperatures continue to rise, due to further climate change, the temperature threshold of 29oC will eventually be reached in the Granite Belt. The impact will be in reduced yields, in the absence of more adaptable cultivars. This may be compensated for by higher returns, as other summer producing districts are more adversely affected. Eventually, this has the potential to induce a break in summer production, in the first instance in the hottest month which is January.

Fig. 21 – Granite Belt, Qld - Mean Monthly Maximum Temperatures At beginning and end of the summer season, growers may be able to take advantage of earlier planting in the spring, and later planting in the autumn, which are currently constrained by low minimum temperatures. The availability of a profitable market at these times of the year will also have a significant influence over the capacity of growers to extend their future planting and harvest times in this tomato growing district.

Applethorpe, Queensland - Mean Monthly Maximum Temperature - 1967 to 2008Threshold - 29 degrees Celcius

0

5

10

15

20

25

30

35


Deg

rees

Cel

cius

1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 19771978 1979 1980 1981 1982 1983 1984 1985 1986 1987 19881989 1990 1991 1992 1993 1994 1997 1998 1999 2000 20012002 2003 2004 2005 2006 2007 2008 Mean Threshold

Mean maximum temperature never exceeds 29 degrees C at Applethorpe,

Qld.In the Granite Belt, tomatoes are

harvested from Nov to May because frosts and cold temperatures restrict production at other times of the year - otherwise all-year-round production

would be posssible.


58

c) Projected regional temperature changes – Tomato

The projections of future maximum temperature change for the major tomato production regions have been produced using the OZCLIM scenario generator developed by CSIRO Atmospheric Research and the International Global Change Institute (http://www.cmar.csiro.au/ozclim).




Table 34 : Bowen, North Queensland – Temperature oC


Max oC 24.5 25.3 27.5 29.2 30.4 31.3 31.5 31.3 30.9 29.3 27.1 24.9


A1F1 Scenario 24.9 25.9 28.0 29.9 31.2 32.3 32.2 32.3 31.4 29.7 27.5 25.4

Using CSIRO Mk3.5 Climate Model with the SRES Marker Scenario A1F1, by 2030 the mean maximum temperature at Bowen (Queensland) exceeds 29oC from early-October through to the end of April - a potential reduction in season length of up to 4 weeks (Fig 22).

Fig. 22 – Bowen, North Qld - Mean Monthly Maximum Temperatures & Projected Increases


Table 35 : Gatton, SE Queensland – Temperature oC


Max oC 20.8 22.5 25.7 28.0 29.7 31.0 31.5 30.8 29.8 27.4 23.9 21.4


A1F1 Scenario 20.8 22.6 26.0 28.6 30.3 32.0 32.0 31.1 30.1 27.6 24.2 21.4

Bowen - Mean Monthly Maximum Temperature (1988 to 2010)Threshold 29 degrees Celcius & 2030 A1F1 Scenario

0

5

10

15

20

25

30

35


Deg

rees

Cel

cius


Current Mean maximum temperature is above 29 degrees C from mid-October to mid-April at

Bowen, Qld.


2030 A1F1 Scenario

By 2030, the mean maximum temperature exceeds 29 degrees C from early-October through to the end of April at Bowen, North Qld.

By 2030, the Tomato season in Bowen may be reduced by up to 4 weeks.

59

Using CSIRO Mk3.5 Climate Model with the SRES Marker Scenario A1F1, by 2030 the mean maximum temperature at Gatton (SE Queensland) exceeds 29oC from late-October through to early-April (Fig. 23).

Fig. 23 – Gatton, Qld - Mean Monthly Maximum Temperatures & Projected Increases





Using CSIRO Mk3.5 Climate Model with the SRES Marker Scenario A1F1, by 2030 the mean monthly maximum temperature at Applethorpe (SE Queensland) does not yet exceed 29oC, enabling a continuation of planting and harvests over the summer as is currently occurring.

For January (the hottest month of the year in the Granite Belt), the mean maximum temperature is expected to almost reach the threshold by 2030 (Fig 24), so actual temperatures for individual years at or about 2030 will most likely exceed the threshold of 29oC, at times.

Fig. 24 – Applethorpe, SE Qld - Mean Monthly Maximum Temperatures & Projected Increases

Gatton - Mean Monthly Maximum Temperature (1965 to 2008)Threshold - 29 degrees Celcius & 2030 A1F1 Scenario

0

5

10

15

20

25

30

35


Deg

rees

Cel

cius


By 2030, the mean maximum temperature exceeds 29 degrees C from late-October through to early-

April at Gatton, SE Qld.


2030 A1F1 Scenario

Current mean maximum temperature exceeds 29 degrees C from early-October

to late-March at Gatton, SE Qld.

Applethorpe, Queensland - Mean Monthly Maximum Temperature (1967-2008) Threshold - 29 degrees Celcius & 2030 A1F1 Scenario

0

5

10

15

20

25

30

35


Deg

rees

Cel

cius


Current mean maximum temperature never exceeds 29 degrees C at

Applethorpe, Qld.

Nov to May Tomato harvests can continue on the Granite Belt until at

least 2030.



2030 A1F1 Scenario

60

d) Impact of projected temperature increases - tomato

For tomato, the 8 to 13 day period prior to anthesis is the most critical developmental phase. The critical temperature, as identified by the literature, for this phase varies according to the cultivar tolerance to elevated temperatures.

Elevated temperature impacts are complex, but for the purposes of this review, 29oC (mean daily temperature) during the 2 week period up to anthesis has been selected as the critical temperature and critical development phase. This has been confirmed through engaging with growers, researchers and other supply chain participants and by comparing mean monthly maximum temperature data with the commencement and the end of the tomato harvesting season for a number of locations where tomato is grown in Queensland.

As temperatures continue to rise, then the adverse effects of high temperature on tomato yields will demand more heat tolerant cultivars which will allow growers to maintain production. Without these more tolerant cultivars, the production season in all regions in Queensland will contract to the cooler months. Summer production will be very difficult in all regions except the Granite Belt.


The “Buffer Level” between the current mean temperature and the threshold temperature in September at Bowen, is 1.5oC. This will be reduced to 1.0oC in 2030 (Table 34).

Consequently, by 2030, the tomato season in Bowen may be reduced by up to 4 weeks.


Using 29oC as the mean maximum temperature threshold, and the temperature data from Gatton, Qld, it would be expected that tomato harvesting at Gatton would not occur over the summer months from November to March. Therefore there is an expectation that growers in this region will suffer a yield and/or quality loss, and this is then compensated in some way to allow growers to continue to profitably produce tomatoes under such apparently adverse conditions.

Information provided by tomato growers in the Lockyer Valley (Gatton), shows that they have historically been largely compensated for the temperature induced decrease in yields (and quality) which occur in the summer, through higher returns in most years. Returns are subject to supply and demand, with quality playing a part as well.

These higher returns are being continually eroded by competition from other summer tomato producing districts, which are not as heavily impacted by temperatures over the threshold. If higher returns were available for producing at a time when high temperatures reduce yields, then growers will continue to plant for this market.

As temperatures continue to rise in the Lockyer Valley, then the adverse effects of high temperatures on tomato yields will demand more heat tolerant cultivars to allow growers to maintain supply especially in mid-summer. Without these more tolerant cultivars, mid-summer production will continue to decline and potentially cease in the Lockyer Valley.

The “Buffer Level” between the current mean temperature and the threshold temperature in October at Gatton, is 1.0oC. This will be reduced to 0.4oC in 2030 (Table 35).



As maximum temperatures continue to rise through to 2030, due to further climate change, the temperature threshold of 29oC will impact on all other production districts in Queensland, except the

61

Granite Belt. The impact will be in the form of reduced yields, in the absence of more adaptable cultivars.

Consequently, by 2030 individual January mean monthly maximum temperatures could exceed 29oC on rare occasions.

As maximum temperatures continue to rise, due to further climate change, the temperature threshold of 29oC will eventually be reached in the Granite Belt. In the absence of more adaptable cultivars, the impact will be in reduced yield and quality, initially for short periods in mid summer whilst the threshold is exceeded. This may be compensated for by higher returns, as other summer producing districts are more adversely affected. Eventually, this has the potential to induce a break in summer production, in the first instance in the hottest month which is February.

At beginning and end of the summer season, growers may be able to take advantage of earlier planting in the spring, and later planting in the autumn. These future early and late plantings are currently constrained by low minimum temperatures. The availability of a profitable market at these times of the year will also have a significant influence over the capacity of growers to take advantage of these earlier plantings, which will extend future planting and harvest times in this summer tomato growing district.


e) Adaptation through management practices - tomato

As there is significant genetic variability between cultivars in their capacity to set fruit under high temperature conditions (>35oC), there is a capacity to utilise these differences in breeding programs to deliver high temperature tolerant commercial cultivars.

In experiments conducted to determine critical temperature effects, sensitive cultivars are impacted when mean daily temperatures exceed 25oC, whereas more heat tolerant cultivars are not impacted until daytime (maximum) temperatures exceed 32oC, and the most sensitive period is 8-13 days prior to anthesis.

Climate change scenarios which include even moderate temperature increases in the order of 0.8oC, as published by the IPCC, are likely to affect the reproductive capacity of tomato plants, which will then have the potential to reduce yields of current cultivars.

As maximum temperatures continue to rise through to 2030, due to further climate change, the temperature threshold of 29oC will impact on all production districts in Queensland, except the Granite Belt. The impact will be in the form of reduced yields, in the absence of more adaptable cultivars.


At beginning and end of the summer season in the Granite Belt, growers may be able to take advantage of earlier planting in the spring, and later planting in the autumn. These future early and late plantings are currently constrained by low minimum temperatures. The availability of a profitable market at these times of the year will also have a significant influence over the capacity of growers to take advantage of these earlier plantings, which will extend future planting and harvest times in this summer tomato growing district.

62

6.5.7 Macadamia


The macadamia industry in Australia occurs along the east coast from northern New South Wales to Bundaberg with some limited production northern Queensland on the Atherton Tablelands and minor plantings in Western Australia. Approximately 17 000 ha are under production comprising some 6 million trees (45% > 15 years, 30 % in early stages of bearing and 25% yet to reach commercial production). Annual production over the period 2000-2009 averaged 36,260 t NIS1 with an average value of $91M. Prices have dropped from $3.45/kg NIS in 2004 to $1.65 in 2008 and $1.90 in 2009. The MPC notional price for NIS for the 2011 season is $3.232/kg2 with a forecast crop of 35,000t3.


Table 37 : Critical Temperature Threshold - Macadamia


Macadamia Retention of racemes and nuts Declines rapidly >30oC.

The main impact on macadamia production as temperatures increase above 30ºC (Table 38), is via the loss of racemes and effects on nut retention (Stephenson and Gallagher 1986, 1987). The period of raceme and nut development, corresponds to the period August through to early November for the various production regions in eastern Australia.

Table 38 : Effect of temperature on raceme and nut retention and nut production.

Day temperature 20ºC 25ºC 30ºC 35ºC Raceme retention (%) 70 70 40 10 Nut retention (%) 39 29 17 4 Number of nuts per tree 44.1 35.4 7.5 1.1

Productivity can also be reduced by extended periods of temperatures exceeding 26ºC, as photosynthesis declines rapidly (Allan and de Jager 1979, Huett 2004) above this threshold.


Projected changes in mean maximum temperature for Lismore, Beerwah and Bundaberg are presented in Table for the A1FI scenario and moderate rate of global warming4 using the CSIRO MK3.5 model. Up until 2030 there is very little difference between the various climate scenarios for these locations.

1 NIS: Nut in shell at 10% moisture content 2 Based on industry standard 33% premium kernel recovery, 2% commercial kernel recovery, 1% reject, and 50-60% whole kernel (source: http://www.intermac.com.au/2011-nis-pricing.html) 3 Forecast as of 23 March 2011- Australian Macadamia Society. 4 Rate of global warming (climate sensitivity) is the global average warming in response to a doubling of CO2

. Each model is tunes to a specific rate. CSIRO MK 3.5 is tuned to a moderate rate of warming.

63

Table 39 : Projected maximum temperatures (ºC) for three sites within the main macadamia production regions.

Projections are for 2030 using the A1FI scenario with moderate rate of global warming derived from the OzClim project using the CSIRO MK3.5 model (http://www.csiro.au/ozclim/).

Location Aug Sep Oct Nov Dec Jan

Bundaberg 24 26 28 30 31 31 Beerwah 22 24 26 28 29 29 Lismore 22 25 27 28 30 30


Reduced nut yield due to high temperatures, especially when accompanied by low humidity or windy conditions, has been reported in macadamia (Stephenson and Gallagher 1987). The number of days above 30ºC for current conditions and the A1FI and B1 scenarios (B1 is the most optimistic scenario) during the critical period for net retention at Bundaberg are shown in Table 40.

Table 40 : Number of days above 30ºC at Bundaberg for current conditions and two climate change scenarios used in Table 39.

Scenario August September October November

Current 0.6 2.8 5.3 15.3

B1 1.2 5.4 11.0 21.4

A1FI 1.4 6.7 12.6 22.8

Either scenario increases the number of days that are likely to exacerbate nut loss (which in macadamia is already high). By 2050 this increases to 14.4 and 19.8 days for the B1 and A1FI scenarios respectively in October (data not shown). It is by 2050 that the differences between moderate and high rates of global warming become noticeable.

The “Buffer Level” between the threshold temperature and the 2030 Scenario in southern Queensland and northern NSW is 1.6oC to 2.8oC (November).

Up to 2030 the macadamia industry does not exceed the threshold of 30ºC until December and January in Bundaberg when considering average monthly temperatures (Table 39). In the three main growing regions the number of days in which the threshold is exceeded per month is doubled for all months during the critical period for raceme retention and early nut drop (Table 38). Macadamia produce massive numbers of flowers but only a small percentage ever survive to produce nuts. This will tend to mask the effect of temperature thresholds as an additional factor. The impact on yield of a doubling of the number of days that exceed the threshold need to be assessed experimentally, although this will be difficult with commercially producing trees.


The impact of high temperatures on flowering and nut retention may be alleviated in situations where the orchard is irrigated or via overhead misting (Stephenson and Gallagher 1987). Other practices more generally aimed at reducing the overall flower load, such as pruning, might be useful as this allows more resources for the nuts that remain on the tree. It is not known if this would alleviate temperature stress.


64

6.5.8 Capsicum


The main production regions are Queensland (Bundaberg, Bowen, Granite Belt), the major producing state, then NSW (far north coast, MIA, Sydney basin), Vic (Goulburn Valley and Sunraysia), SA (Murray Bridge, Adelaide Plains) and WA (Perth metro). Table 41: Australian capsicum production. Year ended 30 June 2007

NSW Vic Qld SA WA Tas NT Total 2007

Total 2006

Production (tonnes)

910 2150 47,267 2,930 2,831 224 1 56,313 60,734

Area (ha) 62 69 1837 80 106 1 1 2,156 2,349 (Source: ABS Catalogue 7121, 2006-07)

b) Current level of knowledge on temperature thresholds – capsicum

Table 42 : Critical Temperature Threshold - Capsicum


Capsicum Flowering and Fruit Set 32oC.

For capsicum, flowering is the most critical developmental phase. The critical temperature, as identified from the literature for this phase, varies according to the cultivar tolerance to elevated temperatures. Temperatures above 32°C for prolonged periods reduce pollen viability and pollination. This leads to yield reductions and small and/or deformed fruit.


Using 32oC as the mean maximum temperature threshold, and the temperature data from Bowen, Qld (Fig 25), the current Mean maximum temperature does not exceed 32oC at Bowen, Qld.

Fig. 25 – Bowen, Qld - Mean Monthly Maximum Temperatures


0

5

10

15

20

25

30

35

40


Deg

rees

Cel

cius

1988 1989 1990 1991 1992 1993 19941995 1996 1997 1998 1999 2000 20012002 2003 2004 2005 2006 2007 20082009 2010 Mean Threshold 2030 A1F1 Scenario

Current Mean maximum

temperature does not

exceed 32 degrees C at Bowen, Qld.


2030 A1F1 ScenarioBy 2030, the mean maximum

temperature exceeds 32 degrees C from early-December through to the

end of February at Bowen, North Qld.

65

ii) Granite Belt (SE Queensland)

Mean Maximum Temperatures never exceed 32oC at Applethorpe. Using 32oC as the mean maximum temperature threshold, and the temperature data from Applethorpe, Qld (Fig 26), it would be expected that capsicum production in the Granite Belt would not be constrained by temperatures in excess of 32oC. This closely describes the production system in this district, which is a summer capsicum production district, due to the influence of altitude on maximum temperatures.

Because capsicums are frost and cold sensitive, production in the Granite Belt is currently constrained over the winter by low temperatures, rather than high temperatures over the summer.

Fig. 26 – Granite Belt, Qld - Mean Monthly Maximum Temperatures c) Projected regional temperature changes – capsicum


Table 43 : Bowen, North Queensland – Temperature oC


Max oC 24.5 25.3 27.5 29.2 30.4 31.3 31.5 31.3 30.9 29.3 27.1 24.9


A1F1 Scenario 24.9 25.9 28.0 29.9 31.2 32.3 32.2 32.3 31.4 29.7 27.5 25.4

Using CSIRO Mk3.5 Climate Model with the SRES Marker Scenario A1F1, by 2030 the mean maximum temperature at Bowen exceeds 32oC from early-December through to the end of February (Fig 27).

Applethorpe, Queensland - M ean M onthly M aximum Temperature - 1967 to 2008Threshold - 32 degrees Celcius & 2030 A1F1 Scenario

0

5

10

15

20

25

30

35


Deg

rees

Cel

cius

1967 1968 1969 1970 1971 1972 1973 19741975 1976 1977 1978 1979 1980 1981 19821983 1984 1985 1986 1987 1988 1989 19901991 1992 1993 1994 1997 1998 1999 20002001 2002 2003 2004 2005 2006 2007 2008Mean 2030 A1F1 Scenario Threshold

M ean maxim um temperature never

exceeds 32 degrees C a t

Applethorpe, Qld .

In the Granite Belt, caps icums are

harvested from Jan to April because frosts and cold temperatures

restrict production at other times of the year - o therwise all-

year-round production would


2030 A1F1 Scenario

By 2030, the mean maximum temperature does not exceed 32 degrees C a t Apple thorpe , Qld.

66

Fig. 27 – Bowen, North Qld - Mean Monthly Maximum Temperatures & Projected Increases





Using CSIRO Mk3.5 Climate Model with the SRES Marker Scenario A1F1, by 2030 the mean monthly maximum temperature at Applethorpe (SE Queensland) does not yet exceed 32oC, enabling a continuation of planting and harvests over the summer as is currently occurring (Fig 28). As maximum temperatures continue to rise, due to further climate change, the temperature threshold of 32oC will not be reached by 2030 in the Granite Belt.

Fig. 28 – Applethorpe, SE Qld - Mean Monthly Maximum Temperatures & Projected Increases


0

5

10

15

20

25

30

35

40


Deg

rees

Cel

cius

1988 1989 1990 1991 1992 1993 19941995 1996 1997 1998 1999 2000 20012002 2003 2004 2005 2006 2007 20082009 2010 Mean Threshold 2030 A1F1 Scenario

Current Mean maximum

temperature does not

exceed 32 degrees C at Bowen, Qld.


2030 A1F1 ScenarioBy 2030, the mean maximum

temperature exceeds 32 degrees C from early-December through to the

end of February at Bowen, North Qld.

Applethorpe, Queensland - Mean Monthly Maximum Temperature - 1967 to 2008Threshold - 32 degrees Celcius & 2030 A1F1 Scenario

0

5

10

15

20

25

30

35


Deg

rees

Cel

cius

1967 1968 1969 1970 1971 1972 1973 19741975 1976 1977 1978 1979 1980 1981 19821983 1984 1985 1986 1987 1988 1989 1990

Mean maximum temperature never

exceeds 32 degrees C at

Applethorpe, Qld.

In the Granite Belt, capsicums are

harvested from Jan to April because frosts and cold temperatures

restrict production at other times of the year - otherwise all-

year-round production would


2030 A1F1 Scenario


67

d) Impact of projected temperature increases - capsicum

For capsicum, Flowering and Fruit Set is the most critical developmental phase.


Using CSIRO Mk3.5 Climate Model with the SRES Marker Scenario A1F1, by 2030 the mean maximum temperature at Bowen exceeds 32oC from early-December through to the end of February.

As maximum temperatures continue to rise, due to further climate change, the temperature threshold will be exceeded earlier in the season. In the absence of more adaptable cultivars, the impact will be on the length of the production period over the winter.

The “Buffer Level” between the current mean temperature and the threshold temperature in March at Bowen, is 1.1oC. This will be reduced to 0.6oC in 2030 (Table 43).




e) Adaptation through management practices - capsicum

At beginning and end of the summer season in the Granite Belt, growers may be able to take advantage of earlier planting in the spring, and later planting in the autumn. These future early and late plantings are currently constrained by low minimum temperatures. The availability of a profitable market at these times of the year will also have a significant influence over the capacity of growers to take advantage of these earlier plantings, which will extend future planting and harvest times in this summer capsicum growing district.


As temperatures continue to rise, then the adverse effects of high temperatures on capsicum yields will demand more heat tolerant cultivars which will allow growers to maintain production. Without these more tolerant cultivars, the production season in all regions in Queensland will contract to the cooler months. Summer production will be very difficult in all regions except the Granite Belt.


68

6.5.9 Avocado

The avocado (Persea americana) is a tropical and sub-tropical evergreen tree producing a large oily fruit. Successful avocado production requires a warm climate and protection from frost. After grafting, avocado trees begin to crop after three years, peak at about around eight to nine years of age and continue for up to 20 years.

The avocado industry has identified climate change as a critical issue (Allen 2009). Given that avocados have been developed as a commercial crop relatively recently, there is comparatively limited scientific literature on the effects of climate on commercial production and virtually nil for some varieties. This hampers the assessment of the climatic factors critical to successful avocado production.


The Australian avocado industry produces up to 46,500 tonnes of avocados each year worth approximately $180 million at the farm gate and $430 million at retail level (Avocados Australia Ltd). Production is dominated by Queensland, which produces approximately 60% of the national crop (ABS 2010). Bundaberg is the major production region, with significant production also occurring on the Atherton Tableland in the Far North (ABS 2008). Other important growing areas include Northern and Central New South Wales, the Sunraysia or Tristate area (South Australia, Victoria and South Western New South Wales) and south west Western Australia. In total, about 5488 hectares are under production.

The Australian commercial industry was established as recently as the 1960s and is rapidly expanding (Allen 2009). A number of varieties are grown commercially; the majority (almost 80%) is ‘Hass’, about 15% is ‘Shepard’, and the remainder is a mix including ‘Sharwil’, ‘Wurtz’, ‘Reed’, ‘Bacon’ and ‘Fuerte’.

Table 45 : Australian avocado production 2008-09


NSW

VIC

QLD

S.A.

W.A.

N.T.

TOTAL

267

95

432

35

129

2

961

7033

1541

23357

1243

5302

0

38478

18.3

4.0

60.7

3.2

13.8

0

Source : ABS 2010.


The effects of temperature and other climatic factors on the growth and production of avocados are reviewed in Muller et al. (2010). Given the scarcity of literature on many minor varieties (e.g. ‘Shepard’), this case study focuses on the most common commercial variety, ‘Hass’.

Avocados are known to be highly sensitive to climatic conditions. Flowering, pollination and fruit set are the most critically temperature sensitive stages for avocado. While these growth stages can be affected by low temperatures, high temperatures are more detrimental, particularly when accompanied

69

by low relative humidity (Wolstenholme 2002). Different varieties are likely to have their own specific temperature optima and thresholds.

There is strong evidence for the negative impacts of high temperatures. High day or maximum temperatures have a negative effect on root growth, shorten the flowering period, cause abnormalities in flowers, cause pollination or fruit set failure or pollen tube burst, and fruit abscission (Sedgley et al. 1985).

Upper temperature thresholds appear to be 33°C for flowering and 35-37°C during fruit set. Photosynthesis has also been found to be irreversibly damaged by temperatures of 35-37°C (Schaffer and Whiley 2003). These high temperatures also have negative effects on yields (Bower and Cutting 1988; Buttrose and Alexander 1978; Lobell et al. 2007; Zamet 1990).

At 33°C, fruit abscission occurred in ‘Hass’ and ‘Fuerte’ varieties (Sedgley and Annells 1981) and daytime maximums of 35°C during flowering and fruit set caused all fruit to drop 10 days after pollination (Sedgley and Annells in Lomas 1988). ‘Hass’ could withstand short periods of temperatures above 30°C (Sedgley and Annells 1981).

This review suggests that key climate requirements and thresholds for avocado production include:

Average daily temperatures between 20-25°C are optimal conditions for avocado production;

A frost free climate is preferred, though mature trees can tolerate short-term exposure to -4˚ without damage;

Prolonged exposure to high temperatures will cause severe stress and loss of productivity, although temperatures of 40˚C can be tolerated for short periods;

A 6 to 8 week period of cool weather is required for floral initiation and growth of inflorescences (generally between May and July).

Night temperatures of 5-10˚C promote good flowering during the flower development phase. During this period, night temperature should not exceed 15˚C and day temperature should not exceed 25˚C;

During flowering and fruit set, the preferred day/night temperature range for ‘Hass’ is 21/14°C. Night minimum temperatures of 10°C or lower may be a threshold for negative effects on flowering and pollination for some varieties. A maximum daytime temperature threshold of 33°C or above during flowering and fruit set causes pollination failure and abscission of fruit.

Consultation with growers in the Bundaberg region confirmed a number of these thresholds based on extensive experience. A set of critical thresholds was developed, including:

July minimum temperatures below 15˚C (for flower induction) but above 4˚C (to avoid cold damage).

September minimum temperature above 12˚C for effective pollination.

Temperatures below 33˚C during flowering and fruiting (October or November depending on the region) to avoid the negative impact of high temperatures on fruit set.

Of these, growers indicated that temperatures below 33˚C during flowering and fruiting was the most critical threshold.

Table 46 : Critical Temperature Threshold - Avocado


Avocado (Hass) Fruit Set (October/November) 33˚C

70


This case study will focus on the most important production region; the Bundaberg / Childers region in Queensland.

Table 47 : Bundaberg, SE Queensland – Temperature oC


Max oC 22.0 23.2 25.3 26.9 28.3 29.4 30.1 29.8 29.1 27.3 24.7 22.7


A1F1 Scenario 23.1 24.5 26.7 28.6 29.9 31.6 31.7 31.4 30.6 28.6 26.0 23.6

The horizontal blue dotted line indicates the critical threshold of 33˚C. While the mean for all years does not reach the threshold, mean maximum temperatures approached the threshold during some years within this period (1998, 2002, 2005 and 2006).

Bundaberg - Mean Maximum Temperature (1960 to 2008)

0

5

10

15

20

25

30

35


Deg

rees

Cel

cius

1960 1961 1962 1963 1964 1965 19661967 1968 1969 1970 1971 1990 19911992 1993 1994 1995 1996 1997 19981999 2000 2001 2002 2003 2004 20052006 2007 2008 Mean (1960-2008) Threshold

Fig. 29 - Mean maximum monthly temperatures (all years, 1960-2008) for Bundaberg, Qld.

71

The projected temperatures were estimated using the CSIRO Mk3.5 global circulation model, A1FI scenario and moderate warming. The horizontal blue dotted line indicates the critical threshold of 33˚C. While the projected mean maximum temperatures for 2030 (solid green line) remain below the threshold, it is projected that the mean maximum temperatures in some years (solid red line) will approach or exceed the threshold between December and February (indicated by yellow arrows).

Bundaberg - Mean Maximum Temperature (1960 to 2008) & 2030 High Scenario

0

5

10

15

20

25

30

35


Deg

rees

Cel

cius

Mean (1960-2008) Threshold 2030 High Scenario Maximum (1960-2008) Max 2030 High Scenario Fig. 30 - Mean maximum monthly temperatures for Bundaberg, Qld, for historic (1960-2008) and projected 2030 climate.

72

Data on future climate conditions was extracted from CSIRO climate models featuring a medium emissions scenario (A2A model) at a spatial resolution of 2.5 arc-minutes (resulting in approximately 5km grid squares). Blue dots indicate current locations of avocado orchards. Green indicates the areas in which the mean maximum temperature in November remains below 33˚C, while orange indicates the areas in which this threshold is exceeded. This indicates a possible gradual contraction in areas suitable for avocado production without appropriate adaptation measures to minimise the effects of high temperatures during fruiting.

current 2020 2050 2080

Nor

th Q

uee

nsla

nd

Bu

nda

berg

& S

E Q

ld

Fig. 31 - Projected changes in the areas in which the critical temperature threshold is met across two major avocado production regions (North Queensland and Bundaberg/Southeast Queensland) for the current climate and projected climate at three future times (2020, 2050 and 2080).


As described in Muller et al. (2010), there are some consistent patterns in the level of projected climate risk using a number of different data sets and methods. Using CSIRO’s climate modelling based on a ‘medium’ emissions scenario, the climate projections for the avocado regions show that:

Climate changes are likely to vary considerably among avocado growing regions.

While temperatures are expected to rise over time across all regions, significant warming is not expected in most regions until 2050 to 2080.

Most east coast and southern production regions are likely to experience significantly less than a 5°C increase in summer maximum temperatures by 2020, but may face a 5-10°C increase by 2080.

Increases in maximum spring temperatures by 2020 may be small and variable across locations. There may be an average increase of up to 5°C by 2080.

Increases in winter minimum temperatures may be small.

The “Buffer Level” between the current mean temperature and the threshold temperature at Bundaberg is 4.7oC (Nov) and 6.1oC (October). This will be reduced to 3.1oC and 4.4oC in 2030 respectively.

73


A recent review of climate change impacts on the avocado industry (Muller et al. 2010) identified a number of adaptive management options that may be suitable for avocado producers in a climate change context. These include:

Information driven adaptive management and the use of record keeping and information management systems such as AVOMAN.

Employing long range weather and climate forecasting services to inform adaptive management.

Employing efficient irrigation systems and tighter irrigation management practices including monitoring, scheduling and maintenance.

Securing water supplies for irrigation and cooling, which may involve:

o Accessing additional water entitlements if required (surface, ground water, on-farm storage);

o Investing in water supply security/reliability;

o Maximising on-farm water use efficiency;

o Minimizing evaporation or seepage from on-farm storage.

Maintaining a strong focus on soil health and structure :

o Mulching for surface protection and to address the risks of heat or drought events and intense or prolonged rainfall events;

o Maintaining high organic matter content and high soil biodiversity.

Optimising free drainage in soils to reduce disease risk from heavy or prolonged rainfall events.

The use of varieties and rootstocks that are better suited to warmer conditions.

Integrated pest & disease management techniques to combat any climate related increase in risk.

Business planning and strategic thinking to manage potential climate risks, such as:

o Diversification of orchard locations to spread climate risks, spread harvest seasons and optimize investment;

o Employing business structures that increase adaptive capacity.

Many of these potential adaptation strategies will be dependent on considerable RD&E investment by governments and industry. For example, the use of new varieties and rootstocks, integrated pest management strategies, and reliable long-range forecasting all require ongoing research and development before being employed by growers.


Managing heat (particularly increased summer temperatures) through use of mulching, soil moisture monitoring and irrigation management.

Increasing water use efficiency and securing water supplies for irrigation and cooling.

Adaptive management relying on data collection, monitoring and information management systems.

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7.00 Discussion The results raise a number of questions:

7.1 At which point will temperature increase become a critical factor in the production of a particular commodity (i.e. cause a critical reduction in the quality and/or yield in specific production systems, commodities and regions in Australian horticulture)?

Table 48 : Summary - Temperature Thresholds and Buffer Levels for selected horticultural crops.

Crop Development

Phase Critical

Temperature Threshold

Regions #Buffer Level #Timeframe for Early Warning

Lockyer Valley, Qld 0.4oC in April 2030

Granite Belt, Qld 0.1oC in January At (Pre-) 2030 Hay, NSW 2.4oC in April 2030

Central West, NSW

0.4oC in November 2030

East Gippsland, Vic 0.7oC in January Post-2030

Lettuce Hearting. 28oC – mean monthly max.

Gingin, WA 0.5oC in April 2030 Innisfail, Qld 6.0oC in December 2030 Banana Fruit Maturity. 38oC.

Carnarvon, WA 2.6oC in February 2030 Granite Belt, Qld 1.0-1.5oC 2030 Apple Dormancy. Chilling – cultivar

specific. Tatura, Vic 1.5-2.0oC 2030

Citrus Fruit Set (near the end of bloom).

30oC. Griffith, NSW 0.0oC in March 2030

Pineapple Flower Initiation and Pre-harvest. >35oC. Rockhampton,

Qld 1.8oC in December 2030

Bowen, Qld 1.0oC in September 2030 Lockyer Valley,

Qld 0.4oC in October 2030 Tomato 2 weeks Pre-

anthesis. 29oC – mean monthly max.

Granite Belt, Qld 1.1.oC in January Post- 2030

Macadamia Retention of Racemes and Nuts

Declines rapidly >30oC.

Southern Qld & Northern NSW

1.6-1.8oC in November 2030

Bowen, Qld 0.6oC in March 2030 Capsicum Pollination 32°C Granite Belt, Qld 4.1oC in January Post-2030

Avocado Flowering and Fruit Development 33oC Bundaberg 3.1oC in November 2030

#An estimate of the "buffer level" in oC between current temperatures and the temperature threshold as at 2030, for each commodity is provided in Table 4., including an estimate of the timeframes for early warning that would benefit each of the commodities/regions. This assumes that the relationship between the current climate (including its variability) and a changed climate in 2030 is roughly linear. As we approach 2030, this may not prove to be the case, but in the absence of a far more detailed understanding of climate change, which is not yet available, this assumption is a practical start to an understanding of the possible timing and the impacts of, temperature thresholds being met.

The temperature data presented for all case studies and locations, was sourced from OzClim (http://www.csiro.au/ozclim/home.do), using the Special Report on Emissions Scenarios (SRES) scenario of A1FI with moderate warming.

[The A1 family of scenarios assumes a world characterized by rapid economic growth, a global population reaching 9 billion by 2050 which then gradually declines. The A1FI scenario (Fossil Intensive) assumes a world which remains energy dependant on fossil-fuels]

* Mean Monthly Maximum Temperature

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7.2 Which horticultural production systems are exposed, sensitive, vulnerable and marginal?

The key outcome of this project has been a better understanding of the temperature thresholds affecting a small number of horticultural crops, and the impact of further temperature rises, in a changing climate, on these commodities.

In general, growers have managed past climate change quite well and are optimistic that they will continue to manage projected temperature increases into the medium term future.

In many horticultural regions where the temperature threshold is currently exceeded at some time of the year, growers in the main have avoided production during these periods, as in general yield and quality are reduced when the temperature exceeds the threshold for each commodity.





For perennial fruit crops, the effects of exceeding thresholds is somewhat different to annual vegetable cropping. More adaptable varieties will be the long-term solution, where agro-economic practices are not appropriate of not cost effective.

Lettuce Winter lettuce production will be slightly impacted in all Australia production regions by 2030. This impact will be felt through a contraction in the length of the winter production season by one to four weeks. As a consequence, there will be a minor increase in vulnerability of the winter lettuce production regions.

Summer production will not be impacted until beyond 2030.

Banana If a temperature threshold for banana growth is 37 or 38°C, then this is significantly higher than temperatures experienced in existing tropical growing regions such as Innisfail, North Queensland and Carnarvon, WA, and thus in the medium term it would seen unlikely that temperature increases associated with climate change will significantly impact production.

Apple In general, the projected level of warming may decrease the suitability of some sites for apple production. However, the level of impact and the appropriate management responses will vary among regions. For example, warmer regions such as Applethorpe may struggle to achieve sufficient chilling units in some years for some varieties. For Tatura, the predicted increase in the frequency of extreme temperatures (e.g. above 35°C) may increase the frequency and severity of disorders such as sunburn browning.


Citrus Climate projections suggest that the critical temperature threshold will be exceeded earlier in the year (by a week or two) by 2030 (by a week or two) in the Riverina region. This may have negative effects

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on fruit set and growth. However, elevated temperatures throughout the year may see advancement of the phenological stages and contraction of the fruiting period. This may have negative effects on fruit quality.

In addition, unusual or extreme high temperatures may be encountered earlier in the growth period, with a potential increase in the risk of solar injury and premature fruit drop.

Pineapple If a temperature threshold for pineapple at flower initiation >35°C, then this is significantly higher than temperatures experienced in existing tropical growing regions such as Rockhampton, Queensland, and thus in the medium term it would seen unlikely that temperature increases associated with climate change will significantly impact pineapple production.


Tomato Winter tomato production in north Queensland will be slightly impacted by 2030, through a slight contraction of the length of the winter production season by up to four weeks. Summer production in the highland region of the Granite belt will be able to take advantage of the extended summer season afforded by increasing temperatures. Macadamia Macadamia are not considered to be at risk to the increased temperature likely to be experienced by 2030, however, they are vulnerable to temperature during flower development and early nut set (from August to early October). The impact of climate change needs to be considered from the perspective of acute rather than chronic exposure and thus a doubling of the number of days that exceed a critical threshold need to be understood rather than a change that occurs to average temperatures over a month or season.

Capsicum Winter capsicum production in north Queensland will be slightly impacted by 2030, through a slight contraction of the length of the winter production season by up to four weeks. Summer production in the highland region of the Granite belt will be able to take advantage of the extended summer season afforded by increasing temperatures. Avocado Climate changes are likely to vary considerably among avocado growing regions. While temperatures are expected to rise over time across all regions, significant warming is not expected in most regions until 2050 to 2080.

Most east coast and southern production regions are likely to experience significantly less than a 5°C increase in summer maximum temperatures by 2020, but may face a 5-10°C increase by 2080. Increases in maximum spring temperatures by 2020 may be small and variable across locations. There may be an average increase of up to 5°C by 2080.

Increases in winter minimum temperatures may be small.

7.3 What management strategies are available to allow growers to adapt to such change and at what temperature do these strategies become ineffective?

With increasing temperatures and changes to rainfall patterns which are currently uncertain, the simplest adaptation strategies (autonomous and assisted adaptation) will be employed and are currently being employed by growers. These will be the use of more adaptable cultivars and a range of cultural practices which enable growers to maintain current production in current locations – i.e. adapt to the ‘new’ climate in the current location. This will be driven in the first instance to maintain profitability through market timing, market access and market share.

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If climate change impacts exceed growers adaptation capacity at a specific location, more transformational adaptation responses will be required. A southward shift of production following the southward shift of agri-climatic zones is then more likely to occur if growers are to maintain profitability through appropriate market timing, market access and market share. Flexibility has been the key to adaptation in horticulture to date, and is likely to continue to be an important component of adaptation strategies as climates continue to change. Growers have been able to manage climate variability reasonably well, although major improvements could be made if tools to assist with the management of climate variability, both temperature and rainfall, were designed specifically with the needs of horticultural growers and industries in mind. Site Selection - Site selection to avoid unsuitable climate factors is practiced as a matter of course in horticulture. For all horticultural crops, temperature is the main climatic factor which determines where and when crops are grown, and also has a significant influence on crop performance (i.e. time to harvest, product quality, and to a less extent, yield). Crop Management - Cultural treatments including evaporative cooling through overhead irrigation, strategic applications of nitrogen and irrigation, and sunburn protection using kaolin based products are currently being used in subtropical and tropical cropping systems. Their use will increase, especially if alternative more adaptable cultivars are not available. Planting dates of some crops such as sweet corn are based on soil temperature conditions, which automatically allows the adaptation to climate variability to occur. The changes in production times which result from increasing temperatures, will need to be taken into account with changes to production and marketing plans, for most crops. Cultivar Selection - Selection of available cultivars which are more adaptable to a changing and variable climate will be the main tool for adaptation in the vegetable industry, and less so in the perennial fruit industry where long term investment in orchards reduces the application of this adaptation strategy. Water Management - Many horticultural growers have adopted more efficient irrigation technologies which are providing significant water-use efficiencies. This will continue, together with an increased understanding of crop water requirements and the use of new technologies to monitor and manage irrigation systems. Pests and Diseases - Integrated Pest and Disease Management (IPDM) practices are common in all horticultural regions and commodities, and continuous improvement in these systems, and their adoption, will be an important part of adapting to a changing climate. The following adaptation strategies have been identified for selected horticultural commodities : Lettuce In many production regions where the threshold is exceeded as some time of the year, growers in the main have avoided production during these periods, as quality is reduced when the mean monthly maximum temperature exceeds 28oC during the hearting development phase.




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Pineapple The “Buffer Level” between the current mean temperature and the threshold temperature in the hottest month in Rockhampton is 2.6oC (January). By 2030, this will be reduced to 1.9oC in January, significantly below the threshold for pineapples.

If a temperature threshold for pineapple at flower initiation is >35°C, then this is significantly higher than temperatures experienced in existing tropical growing regions such as Rockhampton, Queensland, and thus in the medium term it would seen unlikely that temperature increases associated with climate change will significantly impact production.


Tomato As there is significant genetic variability between cultivars in their capacity to set fruit under high temperature conditions (>35oC), there is a capacity to utilise these differences in breeding programs to deliver high temperature tolerant commercial cultivars.

In experiments conducted to determine critical temperature effects, sensitive cultivars are impacted when mean daily temperatures exceed 25oC, whereas more heat tolerant cultivars are not impacted until daytime (maximum) temperatures exceed 32oC, and the most sensitive period is 8-13 days prior to anthesis.

Climate change scenarios which include even moderate temperature increases in the order of 0.8oC, as published by the IPCC, are likely to affect the reproductive capacity of tomato plants, which will then have the potential to reduce yields of current cultivars.



At beginning and end of the summer season in the Granite Belt, growers may be able to take advantage of earlier planting in the spring, and later planting in the autumn. These future early and late plantings are currently constrained by low minimum temperatures. The availability of a profitable market at these times of the year will also have a significant influence over the capacity of growers to take advantage of these earlier plantings, which will extend future planting and harvest times in this summer tomato growing district.

Macadamia The impact of high temperatures on flowering and nut retention may be alleviated in situations where the orchard is irrigated or via overhead misting. Other practices more generally aimed at reducing the overall flower load, such as pruning, might be useful as this allows more resources for the nuts that remain on the tree. It is not known if this would alleviate temperature stress.


Capsicum At beginning and end of the summer season in the Granite Belt, growers may be able to take advantage of earlier planting in the spring, and later planting in the autumn. These future early and late plantings are currently constrained by low minimum temperatures. The availability of a profitable

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market at these times of the year will also have a significant influence over the capacity of growers to take advantage of these earlier plantings, which will extend future planting and harvest times in this summer capsicum growing district.


As temperatures continue to rise, then the adverse effects of high temperature on capsicum yields will demand more heat tolerant cultivars which will allow growers to maintain production. Without these more tolerant cultivars, the production season in all regions in Queensland will contract to the cooler months. Summer production will be very difficult in all regions except the Granite Belt.


Avocado A number of adaptive management options may be appropriate for avocado producers in a climate change context. These include, information driven adaptive management and the use of record keeping and information management systems such as AVOMAN, employing long range weather and climate forecasting services to inform adaptive management, employing efficient irrigation systems and tighter irrigation management practices including monitoring, scheduling and maintenance, securing water supplies for irrigation and cooling, the use of varieties and rootstocks that are better suited to warmer conditions and diversification of orchard locations to spread climate risks, spread harvest seasons and optimize investment




7.4 How will projected temperature increases for 2030 impact on

the viability of key horticultural commodities in Australia? Lettuce In districts where the threshold is not exceeded currently, and will be exceeded only on occasions by 2030, growers will be able to take advantage of earlier planting in the spring, and later planting in the autumn.

In many production regions where the temperature threshold is currently exceeded as some time of the year, growers in the main have avoided production during these periods, as quality is reduced when the mean monthly maximum temperature exceeds 28oC during the hearting development phase.



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Citrus Climate projections suggest that the critical temperature threshold will be exceeded earlier in the year (by a week or two) by 2030 (by a week or two) in the Riverina region. This may have negative effects on fruit set and growth. However, elevated temperatures throughout the year may see advancement of the phenological stages and contraction of the fruiting period. This may have negative effects on fruit quality.

In addition, unusual or extreme high temperatures may be encountered earlier in the growth period, with a potential increase in the risk of solar injury and premature fruit drop.

Pineapple The temperature threshold for pineapple at flower initiation is >35°C, and this is significantly higher than temperatures experienced in existing tropical growing regions such as Rockhampton, Queensland. Therefore, in the medium term, it would seen unlikely that temperature increases associated with climate change will significantly impact production.






Capsicum

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Avocado Many of the potential adaptation strategies will be dependent on considerable RD&E investment by governments and industry. For example, the use of new varieties and rootstocks, integrated pest management strategies, and reliable long-range forecasting all require ongoing research and development before being employed by growers.

7.5 Can we avoid the consequences (profitability or sustainability) of

reaching the critical threshold(s) affecting horticultural commodities and regions?

Lettuce In many production regions where the threshold is exceeded as some time of the year, growers in the main have avoided production during these periods, as quality is reduced when the mean monthly maximum temperature exceeds 28oC during the hearting development phase.











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Pineapple The temperature threshold for pineapple at flower initiation is >35°C, which is significantly higher than temperatures experienced in existing tropical growing regions such as Rockhampton, Queensland, and thus in the medium term it would seen unlikely that temperature increases associated with climate change will significantly impact production.





At beginning and end of the summer season in the Granite Belt, growers may be able to take advantage of earlier planting in the spring, and later planting in the autumn. These future early and late plantings are currently constrained by low minimum temperatures. The availability of a profitable

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market at these times of the year will also have a significant influence over the capacity of growers to take advantage of these earlier plantings, which will extend future planting and harvest times in this summer tomato growing district.



Capsicum As maximum temperatures continue to rise through to 2030, due to further climate change, the temperature threshold of 32oC will impact on all production districts in Queensland, except the Granite Belt. The impact will be in the form of reduced yields, in the absence of more adaptable cultivars.

At beginning and end of the summer season in the Granite Belt, growers may be able to take advantage of earlier planting in the spring, and later planting in the autumn. These future early and late plantings are currently constrained by low minimum temperatures. The availability of a profitable market at these times of the year will also have a significant influence over the capacity of growers to take advantage of these earlier plantings, which will extend future planting and harvest times in this summer capsicum growing district.



Avocado A number of adaptive management options may be appropriate for avocado producers in a climate change context. These include, information driven adaptive management and the use of record keeping and information management systems such as AVOMAN, employing long range weather and climate forecasting services to inform adaptive management, employing efficient irrigation systems and tighter irrigation management practices including monitoring, scheduling and maintenance, securing water supplies for irrigation and cooling, the use of varieties and rootstocks that are better suited to warmer conditions and diversification of orchard locations to spread climate risks, spread harvest seasons and optimize investment




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Table 49 : An assessment of Adaptive Capacity and Vulnerability in relation to selected climate change Impacts on horticultural crops in Australia.

Impacts Adaptive Capacity Vulnerability Production Timing and Location (crops mature earlier and take less time from planting or fruit set to harvest)

Growers are already making the following adaptations :- Changing marketing plans to account for these changes; Moving some of their production to more favourable locations; and Using more ‘adaptable’ crops/cultivars. Growers in some regions (summer season), may be able to take advantage of extending production into winter. Growers in other regions (winter season) will have their production season shortened.

Currently not vulnerable. This will change to being vulnerable if crops/cultivars are unable to cope with increasing temperatures (i.e. thresholds are reached). All vegetable growers and regions are vulnerable, if more adaptable cultivars are not available. Depending on the crop and location, those crops which are close to temperature thresholds, will be very vulnerable.

There is a need for more adaptable cultivars for the vegetable industry. The decision makers are the seed companies who currently source the majority of cultivars from overseas breeding programs.

Currently vulnerable, as the market for new vegetable cultivars which might be specifically adapted to the Australian environment is quite small in comparison to the overseas market. Likely to increase in vulnerability.

Product Quality (quality affected by increasing heat stress days)

Increasing number of heat stress days will result in a narrowing of production windows, and the potential for production to shift to more suitable (cooler) regions.

Growers are currently adapting well. All industries are increasing in vulnerability, especially as the critical temperature thresholds for available crops/cultivars are approached or exceeded.

Inputs (availability and costs of water and fuel)

Drought has been a driver of decisions involving access and use of irrigation water. Some vegetable growers have moved production to areas where water is available. Fuel costs will increase (as will all other inputs derived from fossil fuels – fertilizers and pesticides).

Some growers and some industries (especially permanent fruit crops) are very vulnerable (currently and into the future). All industries and growers are very vulnerable, as they have limited ability to reduce costs and/or pass on increased costs.

Pest and Disease Effects (increasing activity of pests & diseases)

Current (and future) Integrated Pest and Disease Management Systems (IPDM) will make a significant contribution to overcoming these impacts.

All industries are vulnerable to increased pest and disease activity (continually improving IPDM systems will be one mechanism to delay and reduce the impacts). All industries are vulnerable to the effects of new pests and diseases (new to Australia and/or new to current production regions).

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8.0 Technology Transfer This project was designed to :

Identify and document current understanding of critical temperature thresholds through a review of literature for a selection of horticultural crops.

Collect additional data on critical temperature thresholds through consultation with informed growers, consultants and scientists.

Determine the impact of projected temperature change in 2030 on selected horticultural commodities in current production regions using the information gained from the literature review.

Document potential adaption strategies. Report findings through detailed commodity specific case studies.

8.1 Communication of results: During the engagement process, the information gathered by the project team was exchanged with growers, consultants and scientists. The Case Studies (section 6.5) is the final product of this review and engagement process. The engagement process has also demonstrated that in general, growers have managed past climate change quite well and are optimistic that they will continue to manage projected temperature increases into the medium term future. For the majority of the commodities studied, this optimism has been confirmed. At least until 2030, climate change will have a minimal impact on the majority of commodities in the majority of regions, with some commodities not affected at all until much later than 2030.

Australian horticultural growers have for a number of years readily engaged in an understanding of the changing and variable climate in which they have been growing crops. In the main, this project has demonstrated that for the small number of commodities assessed, immediate impacts are quite small, and major impact for a few crops are not expected until or after 2030.

Despite this lack of immediacy, growers and industry need to be vigilant in continuing to assess the changes in climate as they occur, and the impacts these changes will bring.


8.2 Evaluation: The following are the objectives of this project : A practical understanding of climate indices and critical temperature thresholds of significance

to specific horticultural crops and production regions in Australia is established; Commodities and/or regions are identified which, under climate change, are or will be

significantly impacted by increasing temperatures; The impacts on production systems and/or regions are assessed, and adaptation strategies to

address these impacts are identified.

These objectives have been met through the following outputs :-

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Critical Temperature Thresholds for a number of major horticultural crops and regions in Australia have been identified.

Impacts of critical thresholds against climate change scenarios at 2030, and adaptation strategies which will address these impacts have been documented.

Case studies where critical thresholds have been identified and impacts, vulnerability and adaptation strategies described.

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9.0 Recommendations

The key outcome of this project has been a better understanding of the critical temperature thresholds affecting a small number of horticultural crops, and the impacts of further temperature rises, in a changing climate, on these commodities.

Although the impacts of increasing temperatures on a range of horticultural crops are somewhat similar, there are sufficient differences between commodities, regions and seasons, for additional assessment of critical temperature thresholds to be conducted for the very large number of horticultural commodities grown across a wide range of regions and seasons in Australia.

The key outcome of this project has been a better understanding of the critical

temperature thresholds affecting a small number of horticultural crops. The next step should be an assessment of the vulnerability of major horticultural commodities and/or production regions in Australia. Those commodities and/or regions which are most vulnerable will require particular attention from growers and industry bodies.

The focus of this project has been on temperature thresholds, to the exclusion of rainfall effects, because the majority of horticulture in Australia is irrigated. While this approach does not discount the importance of rainfall and associated runoff into irrigation storages, it is temperature which determines to a great extent the location and performance of the majority of horticultural commodities in Australia.

Although the focus of this project has been on temperature thresholds, other meteorological parameters are important to the performance of horticultural crops, and some of these have been identified through the Review of Literature, there is a need for additional assessment of other critical thresholds for the very large number of horticultural commodities grown across a wide range of regions and seasons in Australia.

For the Australian vegetable industry especially, the two most appropriate adaptation options available to growers of commodities in regions where temperature rises between now and 2030 will impact on yields and quality, are more adaptable cultivars, and/or producing or acquiring product from cooler regions. Many vegetable growers over the past 10 years have employed a similar option in response to the need for a more reliable source of irrigation water.


More adaptable cultivars are required by all vegetable industries in Australia, to

cope better with a very variable as well as a changing climate.


Although Australian horticultural commodities are not exported to the same level as other agricultural commodities such as wheat and beef, imports are making inroads into the Australian domestic market.

Identify those countries/regions which currently export product to Australia, which will be significantly impacted by rising temperatures, and those which will become more competitive on the Australian market because of favourable impacts as a result of further changes to the world’s climate.

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Australian horticultural growers have for a number of years readily engaged in an understanding of the changing and variable climate in which they have been growing crops. In the main, this project has demonstrated that for the small number of commodities assessed, immediate impacts are quite small, and major impact for a few crops are not expected until or after 2030.

Despite this lack of immediacy, growers and industry need to be vigilant in continuing to assess the changes in climate as they occur, and the impacts these changes will bring.


Table 50 : Commodities and relevant Industry Bodies

Crop Industry Body

Lettuce AusVeg Cauliflower AusVeg

Banana Australian Banana Growers' Council (ABGC) Apple Apple and Pear Australia Limited (APAL) Citrus Citrus Australia Limited

Pineapple Growcom Tomato AusVeg

Macadamia Australian Macadamia Society Limited (AMS) Capsicum AusVeg

Sweet Corn AusVeg Avocado Avocados Australia Limited Pumpkin AusVeg

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10.0 Acknowledgments

Engagement with growers, consultants and scientists throughout Australia has been critical to interpreting the information obtained from the peer reviewed and the grey literature.

The significant contribution by many growers, consultants and scientists is gratefully acknowledged.

11.0 Bibliography of literature cited

ABS Catalogue 7121 (2008) Agricultural Commodities, Australia, 2006-07. Australian Bureau of Statistics, Canberra. http://www.abs.gov.au/AUSSTATS/[email protected]/DetailsPage/7121.02006-07?OpenDocument

ABS. (2008) Agricultural Commodities: Small Area Data, Australia, 2006-07. Australian Bureau of Statistics, Canberra.

ABS. (2010) Agricultural Commodities, Australia, 2008-09. Australian Bureau of Statistics, Canberra.

ACG. (2003) Fruit Size Management Guide Part 1. Australian Citrus Growers Inc, Mildura.

Allan, P. and J. de Jager. 1979. Net photosynthesis in macadamia and papaw and the possible alleviation of heat stress. Acta Horticulturae 102:23-30.

Allen A. (2009) State of the industry: Australia. In: 4th Australian and New Zealand Avocado Growers Conference (ANZAGC09), Cairns, Australia.

Allen L. H. & Vu J. C. V. (2009) Carbon dioxide and high temperature effects on growth of young orange trees in a humid, subtropical environment. Agric. For. Meteorol. 149, 820-30.

Arnell, N.W. (2000). Thresholds and Response To Climate Change Forcing: The Water Sector. Climatic Change 46: 305–316. http://www.springerlink.com/content/qm6454945128l177/fulltext.pdf (accessed 2/6/2008)

Arnold M. A. & Young E. (1990) Growth and protein-content of apple in response to root and shoot temperature following chilling. Hortscience 25, 1583-8.

Australian Natural Resources Atlas (2007). Benchmarking Rural Industries' Practices and Productivity Performance and Review of Industries' Capacity to Change. http://www.anra.gov.au/topics/agriculture/horticulture/index.html (accessed 2/6/2008)

Ausveg (2011). Spotlight on Commodities. http://ausveg.com.au/resources/statistics/vegetable-spotlight/lettuce.htm (accessed 22/3/2011)

Ben Mechlia N. & Carroll J. J. (1989a) Agroclimatic modeling for the simulation of phenology, yield and quality of crop production: I. Citrus response formulation. Int. J. Biometeorol. 33, 36-51.

Ben Mechlia N. & Carroll J. J. (1989b) Agroclimatic modeling for the simulation of phenology, yield and quality of crop production: II. Citrus model implementation and verification Int. J. Biometeorol. 33, 52-65.

Bower J. P. & Cutting J. G. (1988) Avocado fruit development and ripening physiology. Horticultural reviews 10, 229-71.

Buttrose M. S. & Alexander D. M. (1978) Promotion of floral initiation in Fuerte avocado by low temperature and short daylength. Sci. Hortic. 8, 213-7.

Climate Institute (2008). “Climate of the nation: Australian attitudes to climate change and its solutions, Climate Institute”. http://www.climateinstitute.org.au//images/reports/climate%20of%20the%20nation%202008.pdf (accessed 27/5/2008)

91

CSIRO & Australian Bureau of Meteorology (2007). Climate change in Australia: summary brochure, Australian Government: Bureau of Meteorology, Department of the Environment and Water Resources Australia Greenhouse Office, 23 January 2008. http://www.climatechangeinaustralia.gov.au/resources.php (accessed 26/5/2008)

Deuter, P.L., Napier, A., Dimsey, R., McRae, D. and White, N. (2006). “Scoping Study - Climate Change and Climate Variability - Risks and Opportunities for Horticulture” – Horticulture Australia Ltd (HAL) Project VG05051 – Final Report.

Ferguson I. B., Snelgar W., Lay-Yee M., Watkins C. B. & Bowen J. H. (1998) Expression of heat shock protein genes in apple fruit in the field. Australian Journal of Plant Physiology 25, 155-63.

Garcia-Delgado M. A., Zermeno-Gonzalez A., Lee-Rodriguez V., Castro-Meza B. I., Briones-Encinia F. & Aguirre-Bortoni M. D. J. (2004) Effect of misting on air temperature and humidity and its relationship with fruit set and yield of navel orange. Agrociencia 38, 643-51.

Gindaba J. & Wand S. J. E. (2005) Comparative effects of evaporative cooling, kaolin particle film, and shade net on sunburn and fruit quality in apples. Hortscience 40, 592-6.

Glenn D. M., Erez A., Puterka G. J. & Gundrum P. (2003) Particle films affect carbon assimilation and yield in 'Empire' Apple. J. Am. Soc. Hortic. Sci. 128, 356-62.

Glenn D. M., Wunsche J., McIvor I., Nissen R. & George A. (2008) Ultraviolet radiation effects on fruit surface respiration and chlorophyll fluorescence. J. Horticult. Sci. Biotechnol. 83, 43-50.

Grafton-Cardwell E. E., Ouyang Y. L. & Striggow R. A. (1997) Predaceous mites (Acari: Phytoseiidae) for control of spider mites (Acari: Tetranychidae) in nursery citrus. Environ. Entomol. 26, 121-30.

Growcom (2008). Growcom horticulture and climate change workshop report Growcom, 15th of May 2008. http://www.growcom.com.au/home/inner.asp?pageID=64 (accessed 26/5/2008)

Heide O. M. & Prestrud A. K. (2005) Low temperature, but not photoperiod, controls growth cessation and dormancy induction and release in apple and pear. Tree Physiol. 25, 109-14.

Huett, D. O. 2004. Macadamia physiology review: a canopy light response study and literature review. Australian Journal of Agricultural Research 55:609-624.

Hu L. M., Xia R. X., Xiao Z. Y., Huang R. H., Tan M. L., Wang M. Y. & Wu Q. S. (2007) Reduced leaf photosynthesis at midday in citrus leaves growing under field or screenhouse conditions. J. Horticult. Sci. Biotechnol. 82, 387-92.

Hutton R. J. & Landsberg J. J. (2000) Temperature sums experienced before harvest partially determine the post-maturation juicing quality of oranges grown in the Murrumbidgee Irrigation Areas (MIA) of New South Wales. J. Sci. Food Agric. 80, 275-83.

Iglesias I., Salvia J., Torguet L. & Cabus C. (2002) Orchard cooling with overtree microsprinkler irrigation to improve fruit colour and quality of 'Topred Delicious' apples. Sci. Hortic. 93, 39-51.

Iglesias I., Salvia J., Torguet L. & Montserrat R. (2005) The evaporative cooling effects of overtree microsprinkler irrigation on 'Mondial Gala' apples. Sci. Hortic. 103, 267-87.

Jacobs J. N., Jacobs G. & Cook N. C. (2002) Chilling period influences the progression of bud dormancy more than does chilling temperature in apple and pear shoots. J. Horticult. Sci. Biotechnol. 77, 333-9.

Kenny, G.J., Warrick, R.A., Campbell, B.D., Sims, G.C., Camilleri, M., Jamieson, P.D., Mitchell, N.D., Mcpherson, H.G. & Salinger, M.J. (2000). 'Investigating climate change impacts and thresholds: an application of the CLIMPACTS integrated assessment model for New Zealand agriculture', Climatic Change, vol. 46, pp. 91-113. http://www.springerlink.com/content/t262145017509727/fulltext.pdf (accessed 2/6/2008)

Kriedemann P. E. (1968) Some photosynthetic characteristics of citrus leaves. Aust. J. Biol. Sci 21, 895-905.

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Lobell D. B., Cahill K. N. & Field C. B. (2007) Historical effects of temperature and precipitation on California crop yields. Clim. Change 81, 187-203.

Lomas J. (1988) An agrometeorological model for assessing the effect of heat stress during the flowering and early fruit set on Avocado yields. J. Amer. Soc. Hort. Sci. 113, 172-6.

Lovatt J, Heisswolf S, Carey D, Henderson C, O'Brien R, Deuter P, 1997. Lettuce information kit. Brisbane: Department of Primary Industries Queensland.

Medina C. L., Souza R. P., Machado E. C., Ribeiro R. V. & Silva J. A. B. (2002) Photosynthetic response of citrus grown under reflective aluminized polypropylene shading nets. Sci. Hortic. 96, 115-25.

Milne, M., Stenekes, N. & Jacqui, R. (2008). Climate risk and industry adaption, Australian Government: Bureau of Rural Sciences, 23 May 2008. http://www.affashop.gov.au/product.asp?prodid=13917 (accessed 26/5/2008)

Mohamed A. K. A. (2008) The effect of chilling, defoliation and hydrogen cyanamide on dormancy release, bud break and fruiting of Anna apple cultivar. Sci. Hortic. 118, 25-32.

Muller J., Putland D., Deuter P. & Newett S. (2010) Potential implications of climate change and climate policies for the Australian avocado industry. Report to Horticulture Australia Limited, Sydney.

Naor A., Naschitz S., Perez M. & Gal Y. (2008) Responses of apple fruit size to tree water status and crop load. Tree Physiol. 28, 1255-61.

O'Connell M. G. & Goodwin I. (2007) Responses of ‘Pink Lady’ apple to deficit irrigation and partial root zone drying: physiology, growth, yield, and fruit quality. Aust. J. Agric. Res. 58, 1068-76.

Ogata T., Hirota T., Shiozaki S., Horiuchi S., Kawase K. & Ohashi M. (2002) Effects of aminoethoxyvinylglycine and high temperatures on fruit set and fruit characteristics of heat-cultured satsuma mandarin. J. Jpn. Soc. Hortic. Sci. 71, 348-54.

Paulino S. E. P., Mourao F. D. A., Maia A. D. N., Aviles T. E. C. & Neto D. D. (2007) Agrometeorological models for 'Valencia' and 'Hamlin' sweet oranges to estimate the number of fruits per plant. Sci. Agric. 64, 1-11.

Piskolczi M., Varga C. & Racskó J. (2004) A review of the meteorological causes of sunburn injury on the surface of apple fruit (Malus domestica Borkh). Journal of Fruit and Ornamental Plant Research 12, 245-52.

Putland D., Deuter P., Hayman P., Hetherington S., Middleton S., Nidumolu U., Nimmo P., Thomas D., Wilkie J. & Williams D. (2011) The apple & pear industry's response to climate change and climate variability: A desktop study. Report to Horticulture Australia Limited, Sydney.

Raveh E., Cohen S., Raz T., Yakir D., Grava A. & Goldschmidt E. (2003) Increased growth of young citrus trees under reduced radiation load in a semi-arid climate. J. Exp. Bot. 54, 365-73.

Rosenzweig C., Phillips J., Goldberg R., Carroll J. & Hodges T. (1996) Potential impacts of climate change on citrus and potato production in the US. Agric. Syst. 52, 455-79.

Sams C. E. (1999) Pre-harvest factors affecting postharvest texture. Postharvest Biol. Technol. 15, 249-54.

Schaffer B. & Whiley A. W. (2003) Environmental regulation of photosynthesis in avocado trees - a mini review. In: World Avocado Congress V pp. 335-42, Mexico.

Schmidt K., Louw J. H., Sadie A. & Labuschagné I. F. (1999) Breeding low-chill requiring apple cultivars (Malus domestica Borkh.) in South Africa. pp. 281-8. ISHS.

Schrader L., Zhang J. G. & Sun J. S. (2003) Environmental stresses that cause sunburn of apple. Acta Horticulturae 618, 397-405.

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Sedgley M. & Annells C. M. (1981) Flowering and fruit-set response to temperature in the avocado cultivar Hass. Scientia Horticulturae 14, 27-33.

Sedgley M., Scholefield P. & Alexander D. M. (1985) Inhibition of flowering of Mexican- and Guatemalan- type avocados under tropical conditions. Scientia Horticulturae 25, 21-30.Schrader L., Zhang J. G. & Duplaga W. K. (2001) Two types of sunburn in apple caused by high fruit surface (peel) temperature. Plant Health Progress 10, 1-5.

Solomakhin A. A. & Blanke M. M. (2007) Overcoming adverse effects of hail nets on fruit quality and microclimate in an apple orchard. J. Sci. Food Agric. 87, 2625-37.

Soon W., Baliunas S. L., Robinson A. B. & Robinson Z. W. (1999) Environmental effects of increased atmospheric carbon dioxide. Clim. Res. 13, 149-64.

Storey R. & Treeby M. T. (1999) Short- and long-term growth of navel orange fruit. J. Horticult. Sci. Biotechnol. 74, 464-71.

Stephenson, R. A. and E. C. Gallagher. 1986. Effects of temperature on premature nut drop in macadamia. Queensland Journal of Agricultural and Animal Sciences 43:97-100.

Stephenson, R. A. and E. C. Gallagher. 1987. Effects of temperature, tree water status and relative humidity on premature nut drop from macadamia. Scientia Horticulturae 33:113--121.

Thomas A. L., Muller M. E., Dodson B. R., Ellersieck M. R. & Kaps M. (2004) A kaolin-based particle film suppresses certain insect and fungal pests while reducing heat stress in apples. J. Amer. Pomolog. Soc. 58, 42-51.

Tromp J. & Borsboom O. (1994) The effect of autumn and spring temperature on fruit-set and on the effective pollination period in apple and pear. Sci. Hortic. 60, 23-30.

Tubiello F. N., Rosenzweig C., Goldberg R. A., Jagtap S. & Jones J. W. (2002) Effects of climate change on US crop production: simulation results using two different GCM scenarios. Part I: Wheat, potato, maize, and citrus. Clim. Res. 20, 259-70.

Wade S, 2005. Vegetable Growing in the Central West. Prime Facts 56, Nov 2005. NSW Department of Primary Industries. - http://www.dpi.nsw.gov.au/data/assets/pdffile/0008/45926/Vegetable growing in the Central West – Primefact 56-final.pdf (accessed 16/3/2010)

Wolstenholme B. N. (2002) Ecology: climate and the edaphic environment. In: The Avocado: Botany, Production and Uses (eds A. W. Whiley, B. Schaffer and B. N. Wolstenholme) pp. 71-100. CABI Publishing, Oxon.

Woolf A. B. & Ferguson I. B. (2000) Postharvest responses to high fruit temperatures in the field. pp. 7-20. Elsevier Science Bv.

Zamet D. N. (1990) The Effect of Minimum Temperature on Avocado Yields. California Avocado Society 1990 Yearbook 74, 247-56.

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Appendix I

Critical thresholds (‘tipping points’) and climate change impacts/adaptation in horticulture (QP1005130).

“Critical Biophysical Thresholds affecting Australian Horticultural Crops” Contents Page

Introduction 94 Overview of Critical Thresholds 95 The influence of temperature on the growth and development of :-

Lettuce 96 Cauliflower 103 Banana 114 Apples 122 Citrus 133 Pineapple 141 Tomato 148 Macadamia 159 Capsicum 162 Sweet Corn 166 Avocado 171 Pumpkin 184

Introduction Temperature thresholds for the large range of horticultural crops are not well known, especially for the vegetable sector. We do not properly understand where the temperature thresholds lie and whether exceeding a threshold on its own will lead to a significant change in land use or production system. This is because cultivars have changed considerably over the last decade for many commodities, especially in the vegetable industry, leading to a change in temperature requirements for these crops.

Without such information, it is very difficult for growers to better understand and then manage the impact of climate change at an on-farm scale.

This project has focused on temperature, rather than rainfall effects, because the majority of horticulture in Australia is fully irrigated. While this approach does not discount the importance of rainfall and associated runoff into irrigation storages, it is temperature which determines to a great extent the location and performance of the majority of horticultural commodities.

This review focuses on literature that addresses the biophysical thresholds and the adaptive management responses to increasing temperature in each of the identified commodities, and provides information which will begin to answer the following questions:

When will temperature increases become a critical factor in the production of a particular commodity (i.e. cause a critical reduction in the quality and/or yield in specific production systems, commodities and regions in Australian horticulture)?

Which horticultural production systems are exposed, sensitive, vulnerable and marginal? What management strategies are available to allow growers to adapt to temperature increases

and at what temperature do these strategies become ineffective? How will projected temperature increases for 2030 impact on the viability of key horticultural

commodities in Australia under a mid-range emission scenario? Can we avoid reaching the critical threshold(s) affecting profitability or sustainability?

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Overview of Critical Thresholds The peer reviewed literature provides a starting point in attempting to understand the critical temperature thresholds for a number of important horticultural crops.

In agriculture, a critical threshold is the point at which the production of a commodity becomes unviable due to identifiable change in a production variable.

A range of temperature thresholds exist for a specific crop, depending on the cultivar being grown, the location and the time of the year. The addition of information from the ‘grey literature’ will assist in narrowing this range, and provide an opportunity to assess the vulnerability of a range of horticultural crops and regions to future climate change.

A number of critical temperature thresholds will exist for each crop. These critical temperature thresholds will relate to a specific development phase, e.g. seed germination, floral initiation, dormancy, head filling etc. This report concentrates on one critical temperature threshold at a specific development phase for each of the horticultural crops selected.



Lettuce Hearting. 28oC – mean maximum. Cauliflower Curd Induction. 22oC. Banana Fruit Maturity. 38oC. Apple Dormancy. Chilling requirement – cultivar specific. Citrus Fruit Set (near the end of bloom). 27oC. Pineapple Flower Initiation and Pre-harvest. >35oC. Tomato 2 week period Pre-anthesis. 29oC – mean maximum. Macadamia Retention of Racemes and Nuts Declines rapidly >30oC. Capsicum Flowering 32°C Sweet Corn 3-4 weeks post flowering 32oC Avocado Flowering and Fruit Development 33oC Pumpkin Flowering >35oC

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The influence of temperature on the growth and development of lettuce (Lactuca sativa).

Summary Temperature has a substantial influence on the formation of lettuce heads. Warm season lettuce cultivars in Queensland will not produce high quality heads once mean maximum temperatures exceed 28°C, and will not tolerate even light frosts. On the other hand, winter cultivars will tolerate mild frosts of around -3°C.

Hot weather during heading will produce uneven heads which do not form properly – i.e. less dense and smaller heads are produced. Denser Iceberg type lettuce heads are associated with optimum temperatures during the period just prior to and including the ‘hearting’ development phase.

Appropriate cultivar selection is used by growers to respond to regional temperature variations and decrease the risk of growth disorders such as tipburn.

For lettuce, the ‘hearting’ development phase is the most sensitive to temperatures above optimum.

The literature reviewed so far has not identified a narrow band of temperatures outside which a significant reduction in yield and/or quality will occur, except to say that for current warm season cultivars, temperatures above 28°C which occur over the hearting development phase, will have an adverse effect on quality.

Lettuce production does occur in regions where mean maximum temperatures occasionally exceed 28°C during the hearting phase. Assessment of the recent mean maximum temperature regimes which have historically occurred in these production regions and coinciding with the lettuce hearting development phase, provides additional information confirming the temperature threshold for this crop development phase.

Lettuce production throughout the world. Regions

Lettuce (Lactuca sativa) is a leafy temperate annual or biennial plant of the Asteraceae family that is grown throughout the world. Key growing regions including Belgium, France, Germany, Great Britain, Italy, the Netherlands, Spain, United States and China. Lettuce production also occurs to a lesser extent in Japan, Israel, Taiwan and Australia (Subbarao and Koike, 2007).

Since domestication as a vegetable crop, many different cultivars of lettuce have been developed. The choice to cultivate a specific type of lettuce is determined by a variety of factors such as geography, consumer preference, market forces and climate. According to Subbarao and Koike (2007) the most common types of lettuce grown throughout the world are Crisphead/Iceberg, Romaine, Green or Red Leaf, Butterhead, Batavia, Latin, Stem, and Oil-seed.

In Australia, lettuce is a salad vegetable which is grown in different regions throughout the year with Crisphead/Iceberg lettuce the major commercial type grown. Although other types of lettuce are grown, they are more commonly grown in hydroponic production systems for niche markets (Lovatt et al.,1997).

The main lettuce production regions in Australia are Lockyer Valley (SE Qld); Hay and Central West (NSW); Lindenow and Robinvale (Vic); Manjimup and Gingin (WA); and Cambridge, Richmond, Devonport (Tas).

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Table 2: Australian Lettuce Production.

Total Production (t) Number of Growers Value of production ($M)

Lettuce (Australian production – ABS

2006-07) 271,251 659 283

Source - http://www.ausveg.com.au/statistics.cfm?CID=6919

Temperature and Lettuce cultivars in Australia

Numerous cultivars exist for each type of lettuce grown in Australia. Lovatt et.al. (1997) lists 36 Iceberg cultivars, 12 Butterhead cultivars, 7 Cos cultivars, 11 Coral types cultivars, 8 Oakleaf cultivars, 5 for Loose-leaf cultivars.

In general, these cultivars can be divided into two groups - cool season and warm season (Lovatt et al.,1997). Lovatt et.al.(1997) comment that lettuce generally grows best under cool, sunny conditions with temperature below 24°C. Although some lettuce cultivars will tolerate warmer conditions, exposure to high temperatures reduces quality and yield. It is estimated that warm season cultivars will not produce quality heads once temperatures exceed 28°C (Department of Primary Industries and Fisheries, 2005). On the other hand, heavy winter frosts (-3 degrees) are likely to damage heads of established plants and kill young seedlings (Lovatt et.al.,1997). The strengths and weakness of warm and cold season cultivars are summarised in Table I.

Table 3: Production issues associated with Crisphead lettuce. Comments

Warm season cultivars o Less likely to bolt or split in hot weather.

o Some tolerance to tipburn.

o Heads usually smaller and tighter with frilly serrated margins.

o No frost tolerance.

Cold season cultivars o Some frost tolerance (frosts to -3 degrees).

o Need cool conditions to form solid heads.

o Warm conditions may induce tipburn, bolting, splitting and large soft heads.

Source: Lovatt et.al.,(1997).

Lettuce cultivars in Australia are constantly changing with new cultivars being developed to overcome production constraints and improve performance (Lovatt et.al.,1997). Lettuce cultivars are often specially bred to perform under a distinct temperature range.

The Influence of Temperature on Specific Growth and Development Phases. a) Influence of Temperature on Seed Dormancy and Germination.

Temperature has a considerable influence on lettuce seed germination. Lovatt et.al., (1997) states that it is difficult to establish a lettuce crop using direct-seeding techniques under hot conditions as elevated temperatures force seed into dormancy. Lovatt et.al., (1997) estimates that the ideal soil temperature for lettuce seed germination is 18 to 22°C. Temperatures below this range are associated with slower germination but have little impact on germination percentage (Lovatt et.al.,1997). Soil temperatures above 24°C result in reduced germination, while little germination occurs at 30°C. Lettuce seeds sown at 35°C in moist soil are unlikely to germinate due to seeds entering dormancy. Dormancy can be broken when temperatures decrease, but is likely to result in a non-uniform germination pattern (Lovatt et.al.,1997).

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The recommendations of Lovatt et.al.,(1997) are supported by the results from trials by Kretschmer (1978) into lettuce seed germination. Results show that at temperatures of 15°C and 20°C, 90 percent of the lettuce cultivars germinated. Kretschmer (1978) also found that for the majority of cultivars, the upper optimum germination temperature range was between 20°C and 25°C. However, it was suggested in this research that the upper limit of germination could be modified by altering ecological factors during seed development and maturation.

The potential to modify the upper limit of seed germination by increasing temperatures under which the seed development occurs is confirmed in the research of Sung et.al.,(1998). In these trials, various lettuce genotypes were screened for their ability to germinate at temperatures ranging from 20°C to 38°C. Seed which matured at day/night temperatures of 20/10°C or 25/15°C exhibited a lower percent germination at temperatures above 27°C than seed that matured at 30/20°C or 35/25°C. Similarly, seed of the cultivar 'Valmaine' produced at 20/10°C exhibited 40 percent germination at 30°C but seed that matured at higher temperatures exhibited over 95 percent germination at the same temperature.

In California, research by Steiner and Opoku-Boateng (1991) into the variation in ambient air temperature on seed production in the field during the reproductive development phase of 'Salinas' lettuce found that the advantage of increasing maximum temperature on percentage germination was overshadowed by the severe reduction in number of seeds produced, seed mass and seedling root length. Maximum temperatures greater than 35°C greatly reduced the number of seeds produced.

b) Influence of temperature on head formation.

Temperature has a substantial influence on the formation of lettuce heads. Lovatt et.al.,(1997) states that warm season lettuce cultivars in Queensland will not produce high quality heads once temperatures exceed 28°C, and will not tolerate even light frosts. On the other hand, winter cultivars will tolerate mild frosts of around -3°C. Furthermore, hot weather during heading will produce uneven heads which do not form properly. In general Lovatt et.al.,(1997) states that lettuce grows best under cool, sunny weather with temperature below 24°C.

Research by Wurr et.al.(1996) into the impacts of increasing temperatures on Iceberg lettuce in the United Kingdom found that the optimum mean temperatures for head weight in Iceberg lettuce was 12°C corresponding to temperature rises of 2°C above the average ambient temperature during the experiments. From these results, Wurr et.al.,(1996) conclude that increased temperatures in the United Kingdom would result in earlier lettuce maturity dates. The low optimum temperature of these results compared to the recommendations of Lovatt et.al.,(1997) can be explained by the large variation in temperature requirements of warm and cool season lettuce cultivars.

Wurr & Fellows (1991) found that Iceberg lettuce head weights at maturity were increased by high solar radiation in a specific period before hearting and by low temperature in a longer period up to and around hearting. They also showed that the final head weights were closely correlated with incident solar radiation in 7 day periods around the time of hearting. Similarly, research by Wurr, et.al.,(1992) found that denser Iceberg lettuce heads were associated with low temperatures during the period up to and around hearting while less dense and smaller heads were primarily associated with higher temperatures in the period up to hearting and high levels of solar radiation in periods well after hearting.

Research by Wheeler et.al.,(1993), into effects of temperature and radiation on Butterhead lettuce (Lactuca sativa L. cv. 'Rosana') in greenhouses, found that while maximum ground cover was attained earlier in warmer plots (around 30°C), final dry weights were greater in plants from cooler plots (around 19°C).

Crop Modelling. Analysis of the growth stages of lettuce have been undertaken in the past by Van Holsteijn (1980); Wurr, et.al.,(2002) and Alscher, et.al.,(2001). Research has also been undertaken into the projected impact of climate change on lettuce production in the United Kingdom (Wurr et.al.,1996). In this research, a thermo gradient tunnel 8.6 metres wide and 31.9 metres long was used to generate temperatures ranging from ambient at one end to approximately 4°C above ambient at the other.

Similarly, Pearson et.al.,(1997) use a mechanistic model to predict the effects of climate change (temperature and carbon dioxide) on the growth, yield and maturity of lettuce (“Rosana”). This model incorporated both instantaneous and long-term effects on growth and photosynthetic rate, and was validated using seven independent sources. The resulting model was then used to investigate the

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potential impacts of a range of temperature changes and CO2 concentrations based on meteorological data from Rothamsted, United Kingdom. It was found that changes to temperature of up to 3°C would reduce the production time from about 96 to 79 days for April plantings, and from 63 to 52 days for August plantings.

Pests and Diseases. Pests and diseases cause significant damage to lettuce production throughout the world. Lovatt et.al.,(1997) states that lettuce is susceptible to a range of pests including heliothis (budworm), cluster caterpillar, cutworms, aphids, thrips, slugs and snails damage. Lettuce is also affected by a range of bacterial, fungal and viral diseases and climatic related disorders such as tipburn and bolting. Key bacterial diseases include corky root, dry leaf spot and varnish spot. The main fungal diseases include downy mildew, sclerotinia rot, black root rot and septoria spot. Finally, viral diseases include big vein, necrotic yellows and mosaic. Although genetic advances in new cultivars have reduced the impact of some of these pests and diseases they remain a significant limiting factor on lettuce production (Lovatt et.al.,1997).

Bolting

Bolting is a term that is used to describe lettuce that has started to flower. Lettuce must be harvested prior to bolting to reduce head distortion and splitting. Although horticultural growers plan to harvest prior to flowing, increased temperatures can result in bolting occurring sooner then expected (Lovatt et.al.,1997).

Tip burn

Tipburn refers to the abiotic necrotic breakdown of marginal lettuce leaf tissue and is potentially a significant barrier to production in subtropical and tropical regions during the warm season. Typically, this production risk is overcome in commercial production by planting to avoid hot weather just prior to harvest (Saure, 1998). Similarly, Lovatt et.al.,(1997) recommends that the correct choice of cultivars will help prevent tip burn.

Research by Nagata and Stratton (1994) tested the susceptibility to tipburn in new lettuce cultivars under temperatures ranging from 28oC to 37oC. They showed that in detached lettuce heads tipburn symptoms are likely to occur if temperatures of 25oC to 28°C exist for a few days (Misaghi and Grogan 1978 cited in Saure, 1998).

Saure (1998) states that the risk of tipburn is greater if sudden periods of unseasonal warmer weather are experienced after an extended period at lower temperature or several days of high temperature together with low humidity. Despite the connection between temperature and tipburn, temperature is not the sole cause of this disorder. Tipburn is associated with several other factors including windy days, high nitrogen levels, water stress, and problems that prevent lettuce taking up enough water (for example root rot) (Lovatt et.al.,1997). While a direct relationship between high temperature and tipburn incidence has yet to be established (Imai,1987- cited in Saure, 1998), Wissemeier and Gudrun (2002) found that the high radiation levels also contributed significantly to the development of tipburn, particularly in the 3-4 weeks prior to harvest.

Lettuce Aphid

The lettuce aphid (Nasonovia ribisnigri) is a major pest that poses a significant threat to worldwide lettuce production and has found its way to Australia in recent years. Although not directly investigating the effects of temperature, research by Diaz et.al.,(2007) found that the low temperature threshold for both adult morphs (winged and non winged adults) was 3.1°C. On the other hand, the optimal and upper temperature thresholds for adult morphs was found to be between 26.1°C and 35.3°C. Vectors such as the lettuce aphid also spread viruses such as the lettuce mosaic virus which causes defects in heading, leaf distortions and leaf colour anomalies (Dinant and Lot, 2007).

Vegetable leafminer

The vegetable leafminer (Liriomyza sativae) is a fly-like pest, which is a serious threat to Australia’s plant industries. Although not yet recorded in Australia, this pest has been officially recorded in neighbouring countries such as East Timor (Department of Primary Industries and Fisheries, 2009).

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Research by Palumbo (1995) into the development rate of vegetable leafminer in glasshouses found that the developmental times for the immature stages varied from 14.1 days at 30°C to 50.8 days at 15°C, with pupae requiring more time for development than the combined egg and larval stages. Development from egg deposition to adult eclosion (the emergence of an adult insect from its pupal case) was 271.6 +/- 3.9 degree-days.

Fungi

Downy mildew is a fungus which thrives in cool moist conditions. High humidity immediately after the prolonged leaf wetness period increases the susceptibility of lettuce to this fungus (Wu et.al.,2005). Research in California by Wu et.al.,(2005) showed that increased midday temperatures are likely to reduce disease incidence.

Fungi of the genus Sclerotinia cause serious losses in many crops, including lettuce (“lettuce drop”). There has been some research on the germination of Sclerotinia under different soil temperature and moisture conditions (Wu and Subbarao, 2008). A 5-day period of exposure to high temperature (30°C) had little effect on germination. Germination also requires about 35 days of high soil moisture in the top soil. However, further research is required to understand the ecology of this fungus in commercial fields under fluctuating conditions of soil temperature and moisture (reviewed in Wu and Subbarao, 2008).

Viruses

Lettuce Big-Vein is a widespread problem for lettuce production in Australia (Latham et.al.,2004). It is associated with a complex of two viruses (Lettuce big-vein virus and Mirafiori lettuce virus), both spread by a soil-borne root-infecting fungus (Olpidium brassicae). The disease results in reduced yields and impaired quality, but published quantitative data are lacking (Latham et.al.,, 2004). There is some indication that symptoms may be reduced at higher temperatures of 27oC compared to 18oC (Maekawa et.al.,2004).

Management Strategies.

Few references exist in peer-reviewed journals to management strategies that will enable lettuce growers to adapt to increasing temperatures exist in peer-reviewed journals. Some research demonstrates that water can be used to reduce soil temperatures and increase germination percentages (Coons et.al.,1990; Steiner and Opoku-Boateng,1991). Similarly, Lovatt et.al.,(1997) shows that appropriate cultivar selection is used to respond to regional temperature variations and decrease the risk of growth disorders such as tipburn.

Research Gaps and Conclusions. Temperature significantly influences the development lettuce crops. From seed germination and head development to flowering, seeding and pest and disease management, understanding the effect of high temperature and temperature variation is a key component to successful lettuce production.

Although the information contained in journal articles on the topic of temperature and lettuce provides some highly detailed information on temperature and lettuce production for particular cultivars and regions, significant research gaps would appear to exist with regard to understanding the influence of temperature and exact temperature limitations for lettuce production in Australia. In general, the majority of research published in peer-reviewed journals has been undertaken by researchers in Europe and North America. Although not specifically targeted at the lettuce industry in Australia, these sources provide some useful insight into the influence of temperature on lettuce seed germination, head formation, crop maturity times, pest and disease, climate change and vegetable production. However, the capacity to generalise these findings to an Australian context is hampered by climatic and varietal differences between lettuce production systems in different countries. Furthermore, there appear to be significant knowledge gaps concerning management practices that may reduce the direct impacts of high temperatures on lettuce plants, and also concerning the potential for changes in the dynamics of pests and diseases.

Despite these limitations, this literature review provides a useful departure point from which to commence a more detailed exploration of the interaction of temperature change on lettuce production in Australia.

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Lettuce – Hearting Developmental Phase – Critical Temperature

Threshold For lettuce, the ‘hearting’ development phase is the most sensitive to temperatures above optimum.

Research by Wurr, et.al.,(1992) found that denser Iceberg lettuce heads were associated with low temperatures during the period up to and around hearting while less dense and smaller heads were primarily associated with higher temperatures in the period up to hearting and high levels of solar radiation in periods well after hearting.

Lovatt et.al.,(1997) state that warm season lettuce cultivars in Queensland will not produce high quality heads once temperatures exceed 28°C, and will not tolerate even light frosts. On the other hand, winter cultivars will tolerate mild frosts of around -3°C. Furthermore, hot weather during heading will produce uneven heads which do not form properly.

Appropriate cultivar selection is used by growers to respond to regional temperature variations and decrease the risk of high temperature induced growth disorders such as tipburn.

If maximum temperatures have a significant effect on harvest quality, then it is to be expected that first and final lettuce harvest will closely follow the maximum temperature threshold of 28oC, identified by the literature, for each of the production locations in Australia.

Lettuce is produced in Australia in various Regions and during different Seasons :-

v) Queensland - Lockyer Valley (winter); Granite Belt (summer)

vi) NSW – Hay (winter); and Central West (summer)

vii) Vic - Lindenow, Bairnsdale (all year round); and Robinvale (winter)

viii) WA - Manjimup (summer); and Gingin (all year round)

ix) Tas - Cambridge, Richmond (all year round) and Devonport (summer)

References Alscher G, Krug H, Liebig HP, 2001. Optimisation of CO2 and temperature control in greenhouse crops

by means of growth models at different abstraction levels III. Simulation and optimisation with the combined model. Gartenbauwissenschaft 66:213-218.

Coons JM, Kuehl RO, Simons NR, 1990. Tolerance of ten lettuce cultivars to high temperature combined with sodium chloride during germination. J Am Soc Hortic Sci 115:1004-1007.

Department of Primary Industries and Fisheries, 2005. Growing lettuce Common questions. Brisbane: Department of Primary Industries and Fisheries.

Department of Primary Industries and Fisheries, 2009. Vegetable leafminer. Department of Primary Industries and Fisheries.

Diaz BM, Muniz M, Barrios L, Fereres A, 2007. Temperature thresholds and thermal requirements for development of Nasonovia ribisnigri (Hemiptera : Aphididae). Environ Entomol 36:681-688.

Dinant S, Lot H, 2007. Lettuce mosaic virus. Plant Pathol 41:528 - 542.

Harper S, Deuter P, Galligan D, 1997. Vegetable Production in the Lockyer and Fassifern Valleys, eastern Darling Downs and Toowoomba range.

Kretschmer M, 1978. Temperature and lettuce seed germination. Acta Horticulturae 83:167-174.

Latham LJ, Jones RAC, McKirdy SJ, 2004. Lettuce big-vein disease: sources, patterns of spread, and losses. Aust J Agric Res 55:125-130.

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Lovatt J, Heisswolf S, Carey D, Henderson C, O'Brien R, Deuter P, 1997. Lettuce information kit. Brisbane: Department of Primary Industries Queensland.

Maekawa K, Sasaya T, Fujii H, Ishikawa K, Kanto T, Iwamoto Y, Aino M, 2004. The effect of growth temperature, on big-vein symptom and serological detection of Mirafiori lettuce virus and Lettuce big-vein virus in lettuce. Annals of the Phytopathological Society of Japan (Japan).

Napier T, 2004. Field Lettuce Production. NSW Agriculture AgFacts H8.1.40 First Edition May 2004.

Nagata RT, Stratton ML, 1994. Development of an objective test for tipburn evaluation. Proc Fla State Hortic Soc 107:99-101.

Pearson S, Wheeler TR, Hadley P, Wheldon AE, 1997. A validated model to predict the effects of environment on the growth of lettuce (Lactuca sativa L): Implications for climate change. J Horticult Sci 72:503-517.

Saure MC, 1998. Causes of the tipburn disorder in leaves of vegetables. Sci Hortic 76:131-147.

Steiner JJ, Opoku-Boateng K, 1991. Natural season-long and diurnal temperature effects on lettuce seed production and quality. J Am Soc Hortic Sci 116:396-400.

Subbarao KV, Koike ST, 2007. Lettuce diseases: ecology and control. In: Encyclopaedia of pest management (Pimentel D, ed): Pimentel, D.; 313-318.

Sung Y, Cantliffe DJ, Nagata RT, 1998. Seed developmental temperature regulation of thermotolerance in lettuce. J Am Soc Hortic Sci 123:700-705.

Van Holsteijn HMC, 1980. Growth of lettuce lactuca-sativa 2. quantitative analysis of growth. Mededelingen Landbouwhogeschool Wageningen 80:1-24.

Wade S, 2005. Vegetable Growing in the Central West. Prime Facts 56, Nov 2005. NSW Department of Primary Industries.

Wheeler TR, Hadley P, Morison JIL, Ellis RH, 1993. Effects of the temperature on the growth of lettuce (Lactuca sativa L.) and the implications for assessing the impacts of potential climate change. European Journal of Agronomy 2:305-311.

Wissemeier AH, Gudrun Z, 2002. Relation between climate variables, grown and the incidence of tipburn in field-grown lettuce as evaluated by simple, partial and multiple regression analysis. Sci Hortic 93:193-204.

Wu BM, Subbarao KV, 2008. Effects of soil temperature, moisture, and burial depths on carpogenic germination of Sclerotinia sclerotiorum and S-minor. Phytopathology 98:1144-1152.

Wu BM, Subbarao KV, van Bruggen AHC, 2005. Analyses of the relationships between lettuce downy mildew and weather variables using geographic information system techniques. Plant Dis 89:90-96.

Wurr DCE, Fellows JK, 1991. The influence of solar radiation and temperature on the head weight of crisp lettuce. J Horticult Sci 66:183-190.

Wurr DCE, Fellows JR, Hambridge AJ, 1992. Environmental-factors influencing head density and diameter of crisp lettuce cv saladin. J Horticult Sci 67:395-401.

Wurr DCE, Fellows JR, Phelps K, 1996. Investigating trends in vegetable crop response to increasing temperature associated with climate change. Sci Hortic 66:255-263.

Wurr DCE, Fellows JR, Phelps K, 2002. Crop scheduling and prediction - Principles and opportunities with field vegetables. In: Advances in Agronomy, Vol 76. San Diego: Academic Press Inc; 201-234.

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The influence of temperature of the growth and development of cauliflower (Brassica oleracea).

Cauliflower production. Cauliflower (Brassica oleracea) is primarily a cool season vegetable crop closely related to broccoli, brussels sprouts and cabbage. It is believed that the cauliflower originated from the Mediterranean region. Today, cauliflower is a short rotation crop that is grown throughout the world including the United Kingdom, America, China, Spain, France and Australia (Webb et.al.,2008).

Production of Brassica crops (mainly broccoli, cauliflower, cabbage and Brussels Sprouts) had a gross value of approximately $223 M in 2006/2007, or about 7.0 % of the total gross value of Australian horticultural production. Table 4: Total value and production statistics for the major Brassica crops.

Total Production (t) Gross value of

production ($M) 2006-7 2006-7 Broccoli 46,031 87.6 Cauliflower 69,793 58.8 Cabbage 81,563 58.3 Brussels Sprouts 5,849 18.2 TOTAL Brassicas 203,236 222.9 Source : (ABS 2006-07) In 2006/07, cauliflower was among Australia’s 10 top vegetable crops, accounting for 2.6% of total vegetable production with a gross value of $58.8M. Production is spread relatively evenly across Australia with Queensland and Victoria being the largest producers. Table 5: Australian cauliflower production. Year ended 30 June 2007

NSW Vic Qld SA WA Tas NT Total 2007

Total 2006

Production (t) 10,100 17,173 19,961 7,925 8,055 6,578 - 69,793 76,568 Area (ha) 415 1,379 902 253 290 341 - 3,580 3,039


Vegetable production 2007

0

5000

10000

15000

20000

25000

30000

35000

NSW Vic Qld SA WA Tas NT

Origin

Pro

duct

ion

(t)

BroccoliCabbageCauliflower

Fig 1 : Production of key Brassica vegetables by State

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Major production regions for Brassica crops in Australia

Werribee, Mornington Peninsula, East Gippsland (Vic)

North West Coast, Cole Valley (Tas)

Lockyer Valley, Granite Belt and Eastern Darling Downs (Qld)

Sydney Basin, Bathurst (NSW)

Adelaide Plains (SA)

Manjimup and Swan Coastal Plains (WA)

Temperature and Cauliflower Cultivars in Australia. In general, cauliflower grows best in cool to warm conditions with high humidity (Lancaster and Burt, 2001). Although sensitive to temperature change, cultivar selection has enabled cauliflower to be produced as both a summer/autumn and winter/spring crop. In Australia, Lancaster and Burt (2001) state that certain cultivars can be grown in relatively dry conditions with temperatures over 30°C. Despite the ability of certain cultivars to satisfactorily crop in elevated temperatures, most cultivars are suited to cool conditions. For this reason, cultivars grown out-of-season under elevated temperatures will often not develop adequately.

Signs of the adverse effects of elevated temperatures on cauliflower include curd browning and bracketing and conical-shaped heads (Lancaster and Burt, 2001). Although adapted to cooler temperatures and capable of sustaining mild frost, severe frosts can cause problems with curd quality and seedling development and may reduce curd weight (Lancaster and Burt, 2001).

The majority of research into cauliflower and temperature in peer-reviewed journal articles has been under taken in the United Kingdom. The limited information available in peer-reviewed journals states that Australia’s cauliflower industry is primarily based on hybrid cultivars (Lancaster and Burt, 2001). Research undertaken by Lancaster and Burt (2001) into the performance of 18 cauliflower cultivars planted in SW Western Australia at different dates during the summer season showed that the cultivar "Success" offered the best development times compared to quality, while "Boule de Neige" and "Abundantia" combined development times with a high yield.

The influence of Temperature on Specific Growth and Development Phases. Seed production in cauliflower is sensitive to temperature. In Aditya and Fordham (1995) techniques for advancing and synchronizing flowering in the tropical cauliflower cultivar “Early Patnai” and the temperate cultivar “Lawyna” were investigated. In tropical conditions, cauliflower cultivars may fail to flower due to insufficient exposure to low temperatures, whereas in more temperate conditions cultivars producing seed during the winter may require protection from low temperature effects.

Trials have shown that flowering in the topical cultivar “Early Patnai” was advanced by approximately 25 days following vernalisation of three week old plants by one week exposure to a temperature of 10°C. Application of the plant hormone gibberellin at 100 mg/l to “Early Patnai” prior to vernalisation advanced flowering by a further 3 to 5 days in plants grown at day/night temperature regimes of 20/10°C and 25/15°C. On the other hand, exposure of the temperate cultivar “Lawyna” to 2°C and 7°C for 18 days failed to advance flowering. Finally, gibberellin applications failed to affect either flowering or curd initiation in this cultivar.

Similarly, research by Guo et.al.,(2004) into flowing in cold-requiring cauliflower (Brassica oleracea cultivar “60 day”) found that the most effective temperature for inflorescence induction was 10°C. Application of gibberellin promoted inflorescence stalk elongation greatly in vernalised plants (10°C), but less so in partially vernalised plants (15°C or 20°C).

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a) Juvenile development phase

Cauliflower seedlings enter the juvenile phase following seedling emergence. During this phase, seedlings cannot be induced to initiate a curd by any temperature (Wurr et.al.,1995). Leaves are formed throughout the juvenile stage up until a set number have emerged. Sources differ considerably on the number of leaves required to develop before the end of the juvenile stage. Research by Wurr, et.al.,(1995) into the cauliflower cultivar “White Fox” in the United Kingdom based modelling around 17 leaves, while recognising that this number may vary with changed environmental conditions. On the other hand, research by Grevsen and Olesen (1994) found that the end of the juvenile phase was estimated to occur when plants had produced about 12 leaves. Furthermore, research by Wurr, et.al.,(1990a) found that the minimum number of leaves formed before curd initiation was in the range of 21 to 22 in cultivars “White Fox”, “Dok Elgon”, “White Rock” and “Revito”, while Booij and Struik (1990) using the cauliflower cultivar “Delira”, found that the juvenile phase ended when 16 to 18 leaves were initiated.

The time taken to complete the juvenile phase is highly variable and dependent on the season of planting and seasonal temperature. This can be seen in the data used in Wurr, et.al.,(1995) for the cultivar “White Fox” in the United Kingdom where the time taken to complete the juvenile phase varied from 33 days for plants that emerged in the middle of June compared to 100 days for plants that emerged at the end of February.

b) Curd induction/ vernalisation phase

During the curd induction phase of cauliflower, plants must receive sufficient vernalisation/chilling hours to initiate a curd. Fellows et.al.,(1999) suggest that under optimum conditions, curd induction takes around six days. Curd induction requires relatively low temperatures, while high temperatures are likely to cause delays in curd initiation. Booij and Struik (1990) suggest that weak curd-inducing temperatures exist at ~22°C, compared to strong curd-inducing conditions of ~14°C. Fujime and Hirose (1980) state that the stimulus of low temperatures is reduced but not nullified by subsequent high temperatures during days with large diurnal temperature variations.

A number of optimum summer/autumn temperatures for cauliflower vernalisation have been identified in the peer-reviewed journal articles. Wurr, et.al.,(1988) using the summer/autumn cauliflower cultivar “White Fox”, found that a vernalisation stimulus of between 5°C and 17°C was required. Other studies into optimum temperature conditions found that 12.8°C (Grevsen and Olesen, 1994) and 14°C (Pearson et.al.,1994) were optimum temperatures for curd induction in summer and autumn cauliflower. Similarly research undertaken by Wheeler et.al.,(1995) into the impact of increasing temperatures on the growth of the summer cauliflower cultivar “Plana F1” found that progress towards curd initiation increased to a maximum at 15.5°C and declined thereafter.

Research by Fellows et.al.,(1999) in summer cauliflowers in response to temperature found that the temperatures representing the lower limit, optimum and upper limit of curd induction, were estimated to be 2.2, 9.4 and 24°C for cultivar “Perfection” and 2.9, 13.0 and 23.1°C for cultivar “Gypsy”.

With regard to winter cultivars, modelling by Wurr, et.al.,(2004) found that the optimum temperature for curd induction was between 6°C and 9°C for the three hybrid types “Medaillon”, “Renoir” and “Tivoli” in the United Kingdom. In comparing summer and winter cauliflower cultivars, Wurr and Fellows (2000) found that in the United Kingdom early summer crops have the shortest period from planting to curd induction and initiate curds at the lowest numbers of leaves. On the other hand, it was found that winter cauliflower crops have the longest period from planting to curd induction and produce much higher numbers of leaves. In summary, Wurr and Fellows (2000) state that the optimum temperature for induction of summer and winter cauliflower ranges from 9°C to 14°C.

Further research into the development of a cropping model to describe curd induction in the winter cauliflower was conducted by Reeves et.al.,(2001). For two winter cauliflower plantings (“March” and “December/January”) the upper temperature limit was 17°C. However similar research into temperature requirements during curd induction based on Dutch data found that a common optimum temperature for curd induction was estimated to be 12.8°C with a maximum temperature of 25.6°C (Grevsen and Olesen, 1994).

Finally, the time taken to complete the curd induction phase is highly variable and dependent on the season of planting and temperature variation. Data used by Wurr, et.al.,(1995) for the cultivation of cultivar “White Fox” shows that the curd induction phase varied from 22 days for plants that emerged in the middle of June compared to 19 days for plants that emerged at the end of February.

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Cauliflower is less tolerant of temperature extremes than either cabbage or broccoli. It is best suited to cooler growing conditions preferring mild to warm days (18° to 30°C) and cool nights (10° to 15°C). Cauliflower can tolerate light frosts to –5°C but cold temperatures and lack of sunlight, for example, overcast days, in the seedling stage can lead to blindness (non-heading). Vegetative growth is promoted by temperatures above 27°C. Warm conditions can delay curd initiation and contribute to curd disorders such as riciness (elongated flower buds), misshapen and small curds, hollow stem, curd discolouration and small jacket (wrapper) leaves. Prolonged cool temperatures (below 14°C) can retard growth but promote curd initiation (Lovatt et.al, 2004).

c) Curd growth phase

Following curd induction, curd growth continues and is also affected by temperature. Frosts can cause damage to curds close to maturity (Pearson et.al.,1994).

In research by Wheeler et.al.,(1995), it was found that in controlled environments, the rate of increase in curd diameter was directly correlated to temperatures of between 5°C and 25°C. A similar upper range was found in research by Rahman, et.al.,(2007) who state that in the cauliflower cultivar “Nautilus F1”, grown at Reading in the United Kingdom, optimum temperatures for curd growth exist between 19°C and 23°C. Pearson, et.al.,(1994) also showed similar results in research into curd growth in cultivars “Jubro”, “Revito” and “White Fox”, with optimum temperatures for curd growth recorded as 16°C, 25°C and 21°C, respectively.

As with curd initiation, the time taken to complete the curd growth phase is also highly variable and dependent on the season of planting and temperature variation. Data used in Wurr, et.al.,(1995) for the cultivar “White Fox”, showed a variation in the curd growth phase ranged from 52 days for plants that emerged in the middle of June compared to 49 days for plants that emerged at the end of February.

d) Overall temperature requirements

Cauliflower growers often face difficultly in maintaining supply throughout the season due to variation in temperatures. Wurr, et.al.,(1995) comment that “short term fluctuations in temperature, typically found in any British summer, can result in ‘peaks’ and ‘troughs’ of supply. In this way, a change from warm to cool weather coinciding with the end of juvenility and the start of vernalisation will give rapid progression through both phases. However, a change from cool to warm weather at the same growth stage, will delay progression and consequently delay initiation. If these patterns (warm/cool, cool/warm) occur for consecutive transplantings then a gap in production is likely to occur”.

Overall the temperature requirements of cauliflower vary significantly in the existing literature. Research undertaken by Reeves et.al.,(2001) into the development of winter cauliflower indicated an upper temperature limit for crop planted in March and December of 17°C. Alternatively research by Grevsen and Olesen (1994) found that the temperature sum requirements (thermal time in Kelvin days) of six summer and autumn cauliflower cultivars was between 26 to 83 Kelvin days. Furthermore, later research by Olesen and Grevsen (1997) indicated an optimum temperature of 21°C.

Overall development times for cauliflower production varies depending on planting date and environmental conditions. In the United Kingdom, the time taken from the cauliflower cultivar “White Fox” to develop from beginning of the juvenility phase to completion of the curd growth phase ranged between 107 days for plants that emerged in the middle of June compared to 168 days for plants that emerged at the end of February (Wurr et.al.,1995).

Crop Modelling. A considerable body of literature exists on cauliflower harvest dates and crop modelling in the United Kingdom (Grevsen and Olesen, 1994; Pearson et.al.,1994; Wurr et.al.,1990a). Everaarts (1999) reports that in England a commercially available system exists to predict when curds reach a certain size. This modelling is based on research by Wurr and colleagues (Wurr et.al.,1988; Wurr et.al.,2004; Wurr et.al.,1990a; Wurr et.al.,1990b). This crop modelling system was also tested in the Netherlands and found to perform well (De Moel and Everaarts 1993 cited in Everaarts, 1999). A similar modelling system also exists in Germany (Everaarts, 1999).

In general, the duration of various phases of cauliflower development and growth in specified regions are well established using temperature driven models. In the literature on cauliflower modelling, a common approach is to divide cauliflower growth and development from transplanting to harvest into three distinct phases: juvenile phase, curd induction phase and curd growth phase (Olesen and Grevsen, 2000). In addition, research has been undertaken into the impact of temperature on the seed

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development phase. While each of these phases can be predicted with a degree of certainly in any given location, environmental variables, especially temperature, influence growth and development differently depending on the location (Olesen and Grevsen, 2000).

Climate Change Research. A significant amount of research has been undertaken in the United Kingdom into the effects of increasing temperatures associated with climate change on cauliflower production. Wurr, et.al.,(1995) used existing cauliflower crop models to simulate the impact of mean temperature increases of 0.3, 0.6, 0.9, 1.2, 1.5 and 3.0°C. Results showed that the juvenile and curd growth phases responded to increased temperatures differently to the curd induction phase for the cultivar “White Fox”. The curd induction phase increased in four of the six planting months due to temperatures being beyond the optimum vernalisation levels. In contrast, the development times for juvenile and curd growth phases decreased in all temperature scenarios and planting months. Therefore, despite the increase in development time associated with the curd initiation phase the overall crop development time reduced in all scenarios, except under a 3°C temperature increase for crops emerging in May and June. From these results, Wurr, et.al.,(1995) concluded that although the effects are largely positive, in a warming climate “the possibility of fluctuations in supply could occur as a consequence of shorter crop duration associated with temperature rises because individual crops will mature more rapidly and therefore be capable of being cut over a shorter period”.

These results are similar to more recent research undertaken by Wurr, et.al.,(2004) into simulated effects of climate change on the production pattern of winter cauliflower in the United Kingdom. This research draws on existing crop development models to predict the impact of temperature increases in 2020, 2050 and 2080 compared to the base line period of 1961 to 1990 for cauliflower cultivars “Medaillon”, “Renoir” and “Tivoli”. Results show that the phases of juvenility and curd growth are both shortened by temperature increases, while the curd induction phase was generally lengthened. Furthermore, increasing temperatures are likely to reduce the risk of frost damage to curds as they approach maturity.

Wurr, et.al.,(2004) also showed that under a low emissions scenario (low temperature increase), the duration of juvenility exceeded that of curd induction. However under the high emissions scenario, curd induction increased in length, particularly in the 2080 scenario, yet the effects of the increase in the duration of curd induction on the time to maturity were offset because of the reduction in the lengths of the juvenile and curd growth phases. Thus the overall effect was to advance maturity in all situations except for “Medaillon” grown in Cornwall. The trend of decreasing the length of the juvenile and curd growth phases and increasing the curd induction phase under high emissions scenarios can be seen in Figure 1.

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Fig 2 : An example of the effect of different climate change scenarios and time-slices on the duration (days) of the phases of juvenility, curd induction and curd growth for a Roscoff type cauliflower in Cornwall. Source: Wurr, Fellows & Fuller (2004) Additional research into the impact of climate change on cauliflower production in the United Kingdom has been undertaken by Rahman, et.al.,(2007). Experiments were conducted to assess the response of the cauliflower cultivar “Nautilus F1” grown at the University of Reading, to different constant temperatures after curd initiation. Rahman, et.al.,(2007) showed that growth parameters increased with increasing mean growing temperature up to an optimum temperature and then declined with further increases in temperature. It was found that the optimum temperature for the growth and development of cauliflower after curd initiation was between 19oC and 23°C. Rahman, et.al.,(2007) concluded that future warmer climates would likely be more beneficial for winter cauliflower production than for summer cauliflower production.

Additional research into the projected impact of climate change on cauliflower production in the United Kingdom has been undertaken by Wurr, et.al.,(1996). In this research, a thermogradient tunnel 8.6 metres wide and 31.9 metres long generated temperatures ranging from ambient at one end to ambient plus approximately 4°C at the other. The thermogradient tunnel was used to assess the potential impact of increased temperatures associated with global warming on the growth of Roscoff cauliflower cultivar “March”. Results showed that for this cultivar there was a maximum delay of 49 days in the time of initiation corresponding to a temperature lift of 2.9°C.

Pests, Diseases and Disorders. Cauliflower is susceptible to a range of pest, diseases and disorders. Weather and in particular temperature can have a significant impact on crop health and the risk of pest and disease outbreaks. The following section is a summary of literature relating to the connection between temperature and specific pest, diseases and disorders.

Diamondback moth

Diamondback moth (Plutella xylostella) is a common pest impacting cauliflower cultivation. The larvae of this moth tunnel into the heart of the plant and can be difficult to control with insecticides (Lancaster and Burt, 2001). Literature exists both on the association between temperature thresholds and the development of the diamondback moth and associated integrated pest management approaches.

Research by Golizadeh et.al.,(2007) into the development of diamond back moth larvae at different temperatures in Iran found that the time required for P. xylostella eggs to hatch ranged from 15.7 days at 10°C to 2.3 days at 32.5°C on the cauliflower cultivar “Niagara”. At 35°C, only 27.5% of eggs hatched. Furthermore the developmental time of individuals in the larval stage was found to range from 40.56 and 44.67 days at 10°C to 5.15 and 5.59 days at 30°C. The low temperature threshold for diamond back moth in cauliflower was 7.84°C with an optimal temperature of 30°C. On the other hand, the high temperature threshold for overall development was found to be 35°C. From these results, it was concluded that temperature has a significant effect on the development time of pupae with pupae developing more rapidly at higher temperatures.

Research has also been undertaken into the influence of temperature on certain integrated pest management techniques such as predatory wasps used to control diamond back moth. Work by Golizadeh et.al.,(2008) investigated the developmental periods of Ichneumon wasps and diamondback moths at five constant temperatures (15, 20, 25, 30, and 35°C) on cauliflowers (Ichneumon wasps are important parasitoids that use the larvae and pupae of other insects to host their eggs and are sometimes used in integrated pest management to control diamondback moth populations). Golizadeh et.al.,(2008) found that both the Ichneumon wasps and its host diamondback moth larvae failed to survive at 35°C. In addition, the low temperature threshold was estimated to be 6.9°C, with a thermal constant of 282.3 and 277.7 degree days in cauliflower.

Cabbage white butterfly

Cabbage white butterfly (Pieris rapae) is considered a significant pest in cauliflower cultivation with caterpillars often causing damage to seedlings, plants and curds. Growth rates of the cabbage white butterfly have been studied in Sood, et.al. (1994). This research showed that populations of cabbage white butterfly multiplied 56.53 times over a generation time of 43.2 days during the first generation (March-April) and 14.64 times over 34.2 days in the second generation (April-May). During these experiments, the daily mean temperature varied between 15-21°C in the first and 22-29°C in second

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generation while the relative humidity varied between 36-66 per cent and 30-35 per cent in the corresponding generations. The results demonstrate that the population growth of the cabbage white butterfly is greater in temperature conditions of between 22°C to 29°C compared to 15°C to 21°C. Sood and Bhalla (1996) comment that high temperature and more sunshine accompanied with low relative humidity and rainfall favoured population build-up.

Mosaic disease

Cauliflower mosaic virus results in the development of yellow bands on the leaf and leaf curling (Lancaster and Burt, 2001). The influence of temperature on the development of cauliflower mosaic virus has been research by Baruah and Chowfla (1991). They showed that the interaction between plants and virus was greatly influenced by mean air temperature as compared to relative humidity and cumulative rainfall. It was found that the virus appeared during October when the mean air temperature ranged between 13.7 to14.5°C with high build up of aphid populations.

Black rot

The bacterial disease black rot (Xanthomonas campestris) results in prominent brown to yellow V-shaped areas and black veins on the leaf margins, petioles and stems. Lancaster and Burt (2001) comment that this disease is most severe in warm moist conditions but give no indication of temperature limitations or optimum conditions.

Bacterial soft rot Bacterial soft rot (Erwinia carotovora) occurs mainly in mature cauliflower plants and is generally worse in wet conditions. Symptoms of this disease include a soft slime that develops in the curd or base of the curd. The influence of temperature on the development of this disease in cauliflower was studied in Shyam et.al., (2001). Results showed that mean air temperature (12°C -16°C) was the most important factor favouring disease development while relative humidity had non-significant and negative correlation.

Clubroot

The fungal disease clubroot (Plasmodiophora brassicae) is a soil-borne disease affecting cauliflower in Australia. The symptoms of this disease include stunting of root growth. Lancaster and Burt (2001) state that this disease is worst in warm, moist, acidic soil. In trials by Gabrielson and Robak (1998), the cauliflower cultivar “Bagder Shipper” was exposed to the disease at 12, 15, 20, 25 and 30°C. Results showed that the cauliflower was resistant at 15°C and 20°C and partially resistant at 25°C and 30°C

Sclerotinia

Symptoms of infection with Sclerotinia fungus include the development of a soft rot with a water-soaked appearance, fleecy white fungal growth on the rotted tissue followed by the formation of small, black, pebble-like fungal bodies (Lancaster and Burt, 2001). Lancaster and Burt (2001) comment that this disease is most severe in cool wet conditions but give no indication of temperature limitations or optimum conditions.

Premature heading, blindness, riciness and bracting

Premature heading occurs when curd are initiated before sufficient leaves have developed to support full curd formation. Lancaster and Burt (2001) state that this disorder may be do to the following factors:

o transplants which are too old;

o low temperatures;

o planting a cultivar at the wrong time;

o stress, caused by waterlogged soils, excess fertiliser, drought;

o low nitrogen.

Low temperatures especially after a preceding period of high temperature can also cause a disorder called riciness (Grevsen et.al.,2003). ‘Riciness’ is a term for extreme furriness in curds and is associated with small flower buds developing on the curd surface which often occurs when a cultivar is grown at the wrong time (Lancaster and Burt, 2001).

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On the other hand, high temperatures can cause a disorder known as “blindness” in cauliflower crops. Blindness refers to young plants losing their growing point and is often associated with extremes of temperature while seedlings are developing (Lancaster and Burt, 2001). High temperatures can also cause the appearance of small cauline leaves penetrating the curd surface known as bracting (Grevsen et.al.,2003).

Research into the association of bracting and riciness has been undertaken by Grevsen, et.al., (2003). While not identifying specific temperature ranges for these disorders, results showed that the curd diameter with the highest risk of induction of bracting was around 12 mm and that the apex diameter with the highest risk of riciness was around 0.35 mm.

Management Strategies. Existing literature touches briefly on potential management strategies to assist growers adapt to increased temperatures in cauliflower production. Lancaster & Burt (2001) suggest that in Australia where temperatures exceed 35°C, water cooling could be used to reduce crop stress. In the United Kingdom, Wurr, et.al.,(1995) state that to adapt to projected temperature increases growers may need to plant smaller areas of crop more frequently in an attempt to smooth out fluctuations in supply and use cultivars with a different vernalisation response more adapted to increased temperature.

In more recent research into this issue, Wurr, et.al.,(2004) suggest that to continue to meet market requirements, growers may need to change cultivar or consider later planting dates or move from traditional areas of production to cooler locations.

Similar findings emerged from Wurr, et.al.,(1996) who state that horticulture may respond to climate change by gradually altering crop production schedules and through using cultivars adapted to the changed environment. However, in some cases it was believed it may be necessary to shift production to new areas.

Discussion and Conclusions. In conclusion, the information contained in peer-reviewed literature firmly establishes cauliflower as a cool season vegetable crop highly sensitive to temperature variation. A considerable body of literature exists on cauliflower harvest dates and crop modelling in the United Kingdom. In the literature on cauliflower modelling, a common approach is to divide cauliflower growth and development from transplanting to harvest into three distinct phases: juvenile phase, curd induction phase and curd growth phase. While each of these phases can be predicted with a degree of certainly in any given location, environmental variables (especially temperature) influence growth and development differently at a given location.

Combined with complexities of differences in cultivars and growing seasons/regions means that the capacity to generalise these findings to an Australian context is hampered. However, it should be recognised that additional information on temperature and cauliflower production in Australia is likely to be contained in other information sources such as agricultural extension notes, web pages, books or general industry knowledge.

Despite the shortfall of this literature review to present detailed estimates of temperature thresholds for cauliflower cultivation in Australia, this report provides a useful framework from which to understand the influence of temperature on cauliflower growth phases.

During the curd induction phase of cauliflower, plants must receive sufficient vernalisation/chilling hours to initiate a curd. Curd induction requires relatively low temperatures, with high temperatures likely to cause delays in curd initiation. Weak curd-inducing conditions occur at about 22°C compared to strong curd-inducing conditions at about 14°C. Although optimum curd initiation conditions differ between cultivars and planting times, optimum curd initiation temperatures in the United Kingdom have been found to be around 9°C and 17°C for in summer/autumn cauliflower cultivation. On the other hand, winter cauliflowers have been found to be between 6°C and 9°C.

Like curd induction, the curd growth phase is also affected by temperature. However optimum temperatures in the curd growth phase are higher relative to temperature requirements for the curd induction phase. While optimum curd initiation conditions differ between cultivars and planting times, optimum temperatures of curd growth for different cultivars have been found to be between 16°C and 25°C.

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Beyond the direct impact of temperature on cauliflower development phases, temperature contributes significantly to the development of certain pests, diseases and disorders. Studies have been undertaken into the influence of key pests such as diamondback moth and cabbage white butterfly. A lesser amount of literature exits on diseases and disorders such as black rot, light leaf spot, bacterial soft rot, clubroot, sclerotinia, premature heading, blindness, riciness and bracting. The majority of this research has been undertaken in the United Kingdom. The literature imbalance on cauliflower modelling also carries through to research into the impact of climate change on cauliflower production. Results from authors working in the climate change field show that projected temperature increases are likely to extend the curd induction phase while decreasing the juvenile and curd growth phase. This trend is believed to be due to the temperature requirement needed to achieve adequate vernalisation in the curd induction phase. In this way, the effects of the increase in the duration of curd induction on the time to maturity under warming scenarios is offset because of the reduction in the lengths of the juvenile and curd growth phases. From these findings, it is concluded that projected temperature increases in the United Kingdom will be largely beneficial for cauliflower production particularly in winter production seasons.

Despite the largely beneficial nature of projected temperature increase in the United Kingdom, growers may need to employ various management strategies to adapt to future temperature change. In the literature these management strategies included planting smaller areas of crop more frequently, using cultivars with a different vernalisation response more adapted to increased temperature, changing planting dates and moving from traditional areas of production to cooler locations.

Cauliflower – “Curd Induction” Developmental Phase – Critical Temperature Threshold

For cauliflower, the ‘curd induction’ development phase is very sensitive to temperatures above optimum.

A very small range of cultivars are available which facilitate production under higher than optimum temperatures, but most cultivars are much more suited to cool conditions. For this reason, cultivars grown out-of-season under elevated temperatures will often not produce satisfactory yields of high quality heads.

During the ‘curd induction’ phase, plants must receive sufficient vernalisation (or chilling hours) to initiate a curd. Curd induction requires relatively low temperatures, and high temperatures occurring during this development phase are likely to cause delays in curd initiation. Weak curd-inducing temperatures exist at ~22°C, compared with strong curd-inducing conditions of ~14°C. The low temperature stimulus for curd induction is reduced, but not necessarily nullified, by subsequent high temperatures, especially during days with large diurnal temperature variations.

Vegetative growth is promoted by temperatures above 27°C. Warm conditions delay curd initiation and contribute to curd disorders such as riciness (elongated flower buds), misshapen and small curds, hollow stem, curd discolouration and small jacket (wrapper) leaves.

Future warmer climates will be more beneficial for winter cauliflower production than for summer cauliflower production, and to adapt to projected temperature increases, growers may need to plant smaller areas of crop more frequently in an attempt to smooth out fluctuations in supply.

Growers will also need to use cultivars with a different vernalisation response, more adapted to increased temperatures. Without adapted cultivars, it is likely that cauliflower production will need to shift to cooler regions.

Major production regions for Brassica crops in Australia

Werribee, Mornington Peninsula, East Gippsland (Vic)

North West Coast, Cole Valley (Tas)

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Lockyer Valley, Granite Belt and Eastern Darling Downs (Qld)

Sydney Basin, Bathurst (NSW)

Adelaide Plains (SA)

Manjimup and Swan Coastal Plains (WA)

References. Aditya DK, Fordham R, 1995. Effects of cold treatment and of gibberellic-acid on flowering of

cauliflower. J Horticult Sci 70:577-585.

Baruah BP, Chowfla SC, 1991. Epidemiology of mosaic disease of cauliflower. Indian Journal of Mycology and Plant Pathology 21:43-48.

Booij R, Struik PC, 1990. Effects of temperature on leaf and curd initiation in relation to juvenility of cauliflower. Scientia Horticulturae (Amsterdam) 44:201-214.

Everaarts AP, 1999. Harvest date prediction for field vegetables. A review. Gartenbauwissenschaft 64:20-25.

Fellows JR, Wurr DCE, Phelps K, Reader RJ, 1999. Initiation of early summer cauliflowers in response to temperature. J Horticult Sci Biotechnol 74:328-336.

Fujime Y, Hirose T, 1980. Studies on thermal conditions of curd formation and development in cauliflower cultivar nozaki-wase and broccoli cultivar wase-midori 2. effects of diurnal variation of temperature on curd formation. J Jpn Soc Hortic Sci 49:217-227.

Gabrielson RL, Robak J, 1998. Temperature sensitivity of resistance to two pathotypes of plasmodiophora-brassicae in brassica-oleracea. Acta Agrobotanica 41:237-243.

Golizadeh A, Kamali K, Fathipour Y, Abbasipour H, 2007. Temperature-dependent development of diamondback moth, Plutella xylostella (Lepidoptera : Plutellidae) on two brassicaceous host plants. Insect Science 14:309-316.

Golizadeh A, Kamali K, Fathipour Y, Abbasipour H, 2008. Life table and temperature-dependent development of Diadegma anurum (Hymenoptera : Ichneumonidae) on its host Plutella xylostella (Lepidoptera : Plutellidae). Environ Entomol 37:38-44.

Grevsen K, Olesen JE, 1994. Modelling cauliflower development from transplanting to curd initiation. J Horticult Sci 69:755-766.

Grevsen K, Olesen JE, Veierskov B, 2003. The effects of temperature and plant developmental stage on the occurrence of the curd quality defects "bracting" and "riciness" in cauliflower. J Horticult Sci Biotechnol 78:638-646.

Guo DP, Shah GA, Zeng GW, Zheng SJ, 2004. The interaction of plant growth regulators and vernalisation on the growth and flowering of cauliflower (Brassica oleracea var. botrytis). Plant Growth Regul 43:163-171.

Hartill WFT, Cheah LH, 1984. Some effects of climate and plant growth on the development of light leaf spot in cauliflowers brassica-oleracea-var-botrytis. New Zealand Journal of Agricultural Research 27:441-450.

Lancaster R, Burt J, 2001. Cauliflower Production in Western Australia. Bulletin 4521.

Lovatt J, Rigden, P, Heisswolf S, Carey D, Walsh B, Davis R, Henderson C, Bagshaw J. 2004. Brassica growers handbook. Brisbane: Department of Primary Industries Queensland.

Olesen JE, Grevsen K, 1997. Effects of temperature and irradiance on vegetative growth of cauliflower (Brassica oleracea L. botrytis) and broccoli (Brassica oleracea L. italica). J Exp Bot 48:1591-1598.

Olesen JE, Grevsen K, 2000. A simulation model of climate effects on plant productivity and variability in cauliflower (Brassica oleracea L-botrytis). Sci Hortic 83:83-107.

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Pearson S, Hadley P, Wheldon AE, 1994. A model of the effects of temperature on the growth and development of cauliflower (Brassica-oleracea l botrytis). Sci Hortic 59:91-106.

Rahman HU, Hadley P, Pearson S, 2007. Relationship between temperature and cauliflower (Brassica oleracea L. var. botrytis) growth and development after curd initiation. Plant Growth Regul 52:61-72.

Reeves J, Fellows JR, Phelps K, Wurr DCE, 2001. Development and validation of a model describing the curd induction of winter cauliflower. J Horticult Sci Biotechnol 76:714-720.

Shyam KR, Gupta SK, Mandradia RK, 2001. Role of abiotic stress on the development of bacterial curd rot of cauliflower seed crop in Himachal Pradesh. Journal of Mycology and Plant Pathology 31:199-201.

Sood AK, Bhalla OP, 1996. Ecological studies on the cabbage white butterfly in the mid- hills of Himachal Pradesh. J Insect Sci 9:122-125.

Sood AK, Bhalla OP, Verma AK, 1994. Studies on the growth rate of the cabbage white butterfly, Pieris brassicae (L.) (Lepidoptera: Pieridae) under laboratory conditions. Journal of Entomological Research (New Delhi) 18:69-74.

Webb L, Hennessy K, Whetton P, 2008. Horticulture. In: An overview of climate change adaptation in the Australian agricultural sector – impacts, options and priorities (Stokes CJ, Howden M, eds). n.p.: CSIRO.

Wheeler TR, Ellis RH, Hadley P, Morison JIL, 1995. Effects of carbon dioxide, temperature and their interaction on the growth, development and yield of cauliflower (brassica-oleracea l botrytis). Sci Hortic 60:181-197.

Wurr DCE, Elphinstone ED, Fellows JR, 1988. The effect of plant raising and cultural factors on the curd initiation and maturing characteristics of summer-autumn cauliflower crops. Journal of Agricultural Science 111:427-434.

Wurr DCE, Fellows JK, 2000. Temperature influences on the plant development of different maturity types of cauliflower. Acta Hort 539:69-74.

Wurr DCE, Fellows JR, Fuller MP, 2004. Simulated effects of climate change on the production pattern of winter cauliflower in the UK. Sci Hortic 101:359-372.

Wurr DCE, Fellows JR, Hambidge AJ, 1995. The potential impact of global warming on summer/autumn cauliflower growth in the UK. Agric For Meteorol 72:181-193.

Wurr DCE, Fellows JR, Hiron RWP, 1990a. The influence of field environmental conditions on the growth and development of four cauliflower cultivars. J Horticult Sci 65:565-572.

Wurr DCE, Fellows JR, Phelps K, 1996. Investigating trends in vegetable crop response to increasing temperature associated with climate change. Sci Hortic 66:255-263.

Wurr DCE, Fellows JR, Sutherland RA, Elphinstone ED, 1990b. A model of cauliflower curd growth to predict when curds reach a specified size. J Horticult Sci 65:556-564.

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The influence of temperature of the growth and development of banana (Musa acuminata).

Comment on existing literature. A large amount of literature has been published on the influence of temperature on banana growth and development both in Australia and around the world. Much of these early pioneering works are widely cited in publications such as Sastry (1988) and Turner and Lahav (1983) but are not easily accessible on current databases. Therefore, these sources have been identified via references to other works.

Banana cultivars. Bananas belong to a group of plants within the family Musaceae. Two genera make up this family, the most diverse being the genus Musa containing 35 species of bananas and plantains (Science Encyclopaedia, 2009). While some of these are purely ornamental plants, many are edible. Strictly speaking, the banana is not a woody tree but a herbaceous monocot and falls in to the same family as grasses along with corn, wheat and rice (Fortescue and Turner, 2005).

There are over 500 cultivars of banana plants in the world. The majority of the cultivated bananas derive from the species Musa acuminata and M. balbisina (Sastry, 1988). Key hybrids include “Dwarf Cavendish”, “Valery”, and “Williams” hybrid. Of hybrid cultivars, the “Cavendish” is the most popular due to its increased resistance to diseases, insects and mild storms (Australian Bananas, n.d.).

Key production regions in Australia and the world.

In general, the banana is a tropical/subtropical plant best suited to warm, frost-free, coastal climates. Bananas are commercially grown from the equator to latitudes of 30 degrees or more (Turner and Lahav, 1983). While a few significant areas of banana cultivation do exist outside these limits (such as banana production in New South Wales), these areas are marginal during winter months. At a global level, the majority (20%) of world banana production is based in India. This is followed by Brazil, which produced 7.1 million tonnes of bananas annually.

In Australia, bananas are believed to have been imported from either Malaysia or the Pacific Islands in the 1870s. In 1891, plantations were established in Coffs Harbour and surrounding areas of New South Wales. Today over 90 percent of banana production is based in Queensland where bananas grow in high rainfall regions such as Innisfail and Tully.

The major production areas are Qld (Innisfail/Tully, Sunshine Coast, Bundaberg,) and NSW (mid north coast, far north coast) followed (distantly) by WA and NT. Table 6: Australian banana production, year ended 30 June 2007

NSW Qld WA NT Total 2007 Production (t) 19,017 188,635 3,822 1,701 213,193

Area (ha) 1,668 9,793 137 65 11,662 (Source: ABS Catalogue 7121, 2006-07)

The Influence of Temperature on Specific Growth and Development Phases of Banana.

The main developmental stages of banana plants include sucker appearance, growth, flowering and harvest (Tixier et.al.,2004). Throughout growth and development, bananas are highly susceptible to temperature variation, in particular extremes of hot and cold temperatures.

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General temperature limitations on banana cultivation

Existing literature provides an indication of the temperature limitations of banana production. Simmonds (1966, cited in Sastry (1988)) identified the optimum temperature for banana growth at 27°C. Champion (1963 cited in Turner and Lahav, 1983) also found a similar result. As a tropical/subtropical crop, bananas require an temperature range of between 10°C to 40°C, with an optimum temperature of between 25°C to 30°C, and a mean temperature of 15.5°C (Sastry, 1988). The growth and development of bananas are impaired by temperatures outside this range.

With regard to specific temperature extremes, research by Turner and Lahav (1983) into the growth of banana cv. Williams (Giant Cavendish AAA) in relation to temperatures at latitudes of 29°, concluded that plants showed heat injury at day/night temperatures of 37/30°C. A low temperature threshold was identified by Fortescue and Turner (2005) of around 14°C. This limit is supported by results from research undertaken on banana cultivation in Jordan Valley in Israel (Smirin 1960 cited in Sastry, 1988). However, Sastry (1988) comments that in a subtropical region the frequent occurrence of temperatures below 18°C plays a large role in determining the suitability of a region for banana cultivation. These figures are further supported by the graphical representation of temperature limitations of Banana (Figure 2).

Fig 3 : Relation between temperature, growth and other processes in banana culture. Source: Samson (1980) cited in Sastry (1988)

Sucker appearance

As a tall perennial plant of up to 4 metres, the above ground biomass of the bananas is supported by an underground stem known as the “corm”. Roots spread from the corm in all directions. As well as supporting the main stem, the corm also supports aerial shoots known as “suckers” (Turner and Lahav, 1983). Corms continue to produce suckers, allowing the banana plant to continue to produce for up to 50 generations of suckers or more (Tixier et.al.,2004). Little literature exists specifically on the influence of temperature on the development of suckers from the corm. However, research by Ingram, et.al.,(1986) into the response of container-grown bananas to elevated root temperatures of 28, 34 and 40°C, found that banana shoot dry weight decreased linearly with increasing root zone temperature, but root dry weight was not affected. Furthermore, increasing temperatures were found to increase the ratio of sugars to starch in roots. In a different study by Turner and Lahav (1983) into the growth of the banana cultivar Williams (Giant Cavendish) in relation to temperature, root growth was favoured by day/night temperatures of 25/18°C and 21/14°C.

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Growth

New leaves are continually emerging from the stem of the banana throughout the growth phase. The rate of appearance of new leaves and is largely governed by temperature.

Although sometimes over 4 metres tall, the stem of a banana is not “woody” by rather made up of tightly wound petioles and leaf sheaths rolled around each other in a near circular shape (the pseudostem5).

Leaf production in bananas occurs around once a week in favourable tropical conditions for the cultivar “Dwarf Cavendish” in Queensland (Sastry, 1988). In winter subtropical conditions, the rate of production is often significantly reduced, sometimes to a rate of one leaf in 20 days (Summerville 1944 cited in Sastry, 1988). Similarly, in tropical conditions, summer leaf unfurling is completed in around 4 days, while in winter subtropical conditions it is known to take about 14 days or more (Sastry, 1988).

Studies into temperature and rate of banana leaf emergence in the tropics and in the subtropics indicate an optimum of about 28-30°C (mean day/night temperature) for the appearance of new leaves (Turner and Lahav, 1983). Other research by Champion (1963 cited in Turner and Lahav, 1983) found that the optimum temperature for crop growth to be about 25-27°C. In modelling undertaken by Allen et.al.,(1988) into 17 banana cultivars at Alstonville, New South Wales, the optimum rate for leaf emergence was found to be 28.5°C.

Research by Turner and Lahav (1983) into the growth of the banana cultivar “Williams” grown in New South Wales found a variety of optimum temperatures for different measures of plant development. A day/night temperature of 25/18°C was optimal for total plant dry weight. With regard to leaf area, day/night temperatures of 33/26°C were optimal. Finally, in terms of unit leaf rate (increase in whole plant dry weight per unit leaf area per unit time) a day/night temperature of 21/14°C was the most favourable.

High temperatures (>30°C) result in an increased rate of leaf emergence. Experiments by Turner and Lahav (1983) into the effect of temperature on Bananas (cv. Williams) found that plants grown at day/night temperatures of 33/26°C appeared to be the largest. Only three leaves were produced per plant in these trials under day/night temperatures of 17/10°C while nearly 12 leaves were produced at 33/26°C.

The folding of the lamina halves (leaf blades) was also identified as being influenced by higher temperatures. Folding of leave blade downwards helps reduce the temperature of the leaf and the amount water used by the leaf for cooling. Finally Turner and Lahav (1983) found that high temperatures produced more horizontal leaves at that unit leaf rate. On the other hand, low temperatures result in reduced rate of leaf appearance (Turner and Lahav, 1983). In the subtropics, where less favourable conditions exists in winter months, Summerville (1944 - cited in Sastry, 1988) reported a temporary decline in leaf area of “Dwarf Cavendish” during the Queensland winter in August and September.

Flowering

The floral initiation phase of banana development is particularly susceptible to damage resulting from low temperatures. As the flower bud matures and emerges from the stem of the banana plant, the hood-like bracts of the purple bell are slowly pealed back to reveal a cluster of slim, nectar-rich white flowers. Heenan (1973 cited in Sastry, 1988) states that cultivars may take six to seven months from planting to bunch emergence in Malaysia and nine and a half months in New Guinea.

Clusters of flowers occupying the first 5 to 15 rows are female followed by sterile flowers. The ovaries in the female flowers grow rapidly, developing without pollination (parthenocarpically) into clusters of fruits. Clusters of flowers go on to form “hands” of bananas (Turner and Lahav, 1983).

Flowering commences when the axis of the stem changes from vegetative to floral (Fortescue and Turner, 2005). This occurs around the time of the emergence of the 11th last leaf. Due to the relationship between temperature and leaf growth, the length of time from floral initiation to emergence

5 A false stem composed of concentric rolled or folded blades and sheaths that surround the growing point.

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is greatly influenced by temperature. The lower the temperature or the longer the duration of the lower temperatures, the longer the time from the floral initiation to emergence (Ke, 1981).

Damage to banana during inflorescence generally occurs in sub-tropical growing regions where temperatures move outside optimum growth conditions. Fortescue and Turner (2005) state that “bananas growing in subtropical environments suffer tissue malformation in fruit structures with mean daily temperatures of about 14°C during differentiation of the fruit tissues”. Summerville (1944 cited in Sastry, 1988) found that fruit number is influenced by climatic conditions during the period of development of the last three or four leaves which correspond to a month or so before flowering. Stoler (1962 cited in Turner and Lahav, 1983) found that the lower optimum temperature for bunch size was 22-24°C.

Fortescue and Turner (2005) comment that damage from low temperatures occur when the perianth, stamens and carpel are developing mid way up the pseudostem. Similarly, Sastry (1988) and Turner and Lahav (1983) comment that temperatures below 10°C lead to impedance of inflorescence and malformation of bunches.

Fruit growth and harvest

Time from planting to harvest for bananas takes approximately 10 to 14 months for the first crop and 8 to 11 for ratoon crops (Fortescue and Turner, 2005). Fruit growth rate increases has been positively correlated with temperatures above 14.4°C in the range 18°C to 29°C (Ganry and Mayer 1975 cited in Sastry, 1988). Furthermore, Hartman (1929 cited in Sastry, 1988) comment that average temperature of 25.5°C during the months when the bunch is due for harvesting is likely to increase banana weight. This effect remains up to temperatures of ~28-29°C, beyond which point maturity is accelerated but the fruit weights diminished.

Other sources not included in the peer-reviewed literature such as Treverrow, (2003), state that high air temperatures (usually greater than 38°C) and bright sunshine result in sunburn of exposed fruit, especially on the top hands of the bunch.

Temperature also effects banana ripening, however because the majority of bananas are harvested green and ripened in storage where temperature is artificially controlled, this issue will not be discussed.

Management response. In general little information exists in peer-reviewed literature on different management approaches to minimise the impact of temperature change on the banana industry. One example involves the use of polyethylene covers to protect developing banana bunches. Robinson and Nel (1984) investigated the influence of bunch covers on components of yield, fruit quality and microclimate with Dwarf Cavendish banana bunches in South Africa. Results showed that bunch mass was significantly increased by 11.7 and 16.7% under white and blue covers, respectively. Blue covers were found to result in slightly warmer conditions than white covers. While the use of banana covers can mitigate the impact of temperature extremes, they are likely to increase the pest and disease issues due to the more favourable microclimatic conditions (Robinson and Nel, 1984). While not discussed in this source, bunch covers can be used to reduce the impact of high temperatures although care is needed the place protective covering (such as paper) between the fruit and the cover, or covers with a reflective coating on the outer side (Treverrow, 2003).

Crop modelling.

In the past, various systems have been developed to predict harvesting periods over cropping cycles. Using these models, leaf emergence rates are calculated using mean monthly air temperature of between 13.3-27.9°C (Allen et.al.,1988). In contrast to other horticultural crops such as cauliflower (Wurr et.al.,, 2004), little research has been undertaken into the projected impact of temperature increases associated with climate change on banana production.

The temperature threshold for banana growth (37°C) is estimated to be significantly higher than temperatures experienced in existing tropical growing regions and thus in the medium term it would seen unlikely that any temperature increase associated with climate change would significantly impact production. However, under a warming climate scenario growing regions in more marginal sub-tropical conditions such as in New South Wales would be likely to increase production.

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Pests. Pests and disease affect the banana plant in a variety of ways, including impacts on roots, leaves and/or fruit. The following section outlines key publications relating to this topic.

Spiral nematode.

Nematodes are small, worm-like animals from 0.5-1.0 mm in length. Helicotylenchus multicinctus (spiral nematode) is a plant pathogenic nematode that results in mild stunting, and may cause reduced yields where populations are large. Research into the relationship between H. multicinctus, subtropical temperatures and banana cultivation showed that temperature was the major environmental factor limiting population size (Jones, 1980). Cold winter temperatures slow the development of H. multicinctus and the relationship between temperature and overall population size was offset by around 2 months.

Banana aphid.

Banana is the preferred host of the aphid Pentalonia nigronervosa and it is present in the majority of growing locations throughout the world, including Australia. Excessive aphid numbers can result in the malformation of banana leaves and, in some extreme cases, the death of young plants. Aphids may also transfer various plant diseases (see below), with the potential to cause substantially greater losses than just the injury incurred as a result of aphid feeding. In temperate regions, reproduction of aphids is favoured by mild winters, heavy spring rainfall followed by rapid temperature increases (Gallitelli, 2000). Research undertaken by Padmalatha & Singh (2003) investigated the influence of temperature on the body size of the banana aphid. Results showed that the aphid body size was adversely affected by high temperatures. At a mean temperature of 28.7°C the length of the antenna of alate forms was much longer than of alate forms collected from places where the mean temperature was 33.3°C. Similarly the wings of alate forms collected at 28.7°C had a longer wing span than the alates collected at 33.3°C.

Diseases. Bunchy top, Black Sigatoka and Panama disease are the three diseases that pose significant threats to the Australian banana industry.

Bunchy Top

Banana bunchy top virus (BBTV) is transmitted to the plant by the aphid Pentalonia nigronervosa (Anhalt and Almeida, 2008). The only effective control is for affected plants to be destroyed. Disease symptoms in recently planted suckers include the emergence of narrow, brittle leaves with interrupted dark green streaks along the secondary veins of the lamina. The relationship between BBTV and high temperatures was studied by Wu and Su (1991). Results showed that exposure of plants infected with BBTV to temperature of 40°C for 16 h daily and for periods of up to 5 weeks did not result in the eradication of the virus but did create more uneven distribution and low concentration of virus. In general, Wu and Su (1991) state that “high temperature is more favourable for aphid transmission of banana bunchy top virus (BBTV) to banana plantlets than low temperature”.

Similar results were found by Anhalt and Almeida (2008) into their study of the spread BBTV by vectors. Results of this research showed that adult aphids transmitted the virus more efficiently at 25 and 30°C than at 20°C. Furthermore, adult aphids transmitted BBTV more efficiently than third instar nymphs at all temperatures tested. However temperature had no impact on transmission efficiency by nymphs (Anhalt and Almeida, 2008).

Black Sigatoka

Sigatoka is a fungal growth that creates expanding blotches on leaves that start as small light yellowish spots and continue to enlarge into oval dark brown patches. Deleafing is an effective controlling the spread of this disease. The development of this fungus is directly related to temperature. Research by Jacome and Schuh (1993) into this disease found that germination temperatures were around 20 to 35°C, and that fungal growth increased as temperature increased up to 30°C, with an estimated optimum at 27.7°C. However, no growth was observed at 35°C.

Research by Romero and Sutton (1997) into sigatoka on bananas found that the incubation period was the shortest at 26°C, with disease severity the greatest at 26°C on non-resistant naturally-occurring hybrids Grand Naine and False Horn. However, there was no clear temperature effect on resistant

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hybrids (FHIA1 and FHIA2) at this temperature (Romero and Sutton, 1997). Similarly, work by Jacome & Schuh (1992) found that the optimal temperature range for development of sigatoka to be 25 to 28°C.

Panama Disease

Panama disease, or Fusarium wilt, is another major disease caused by the fungus Fusarium oxysporum. The history of the disease in Australia is well documented (reviewed in Pegg et.al.,1996). Soil properties play a large role in the occurrence of this disease (Dominguez et.al.,2001). Although the severity of the disease may vary with temperature, it appears that this may result from the effect of temperature on plant growth rather than on the aggressiveness of the pathogen (Brake et.al.,1995).

Other diseases

Crown rot is caused by a fungus blackening of the crown tissues, which spreads to the banana pulp resulting in rotting of the infected portion and separation of fingers from the banana hand. In research undertaken by Thangavelu, Sangeetha and Mustaffa (2007), crown rot infected banana samples collected from different regions of India revealed that the fungus Lasiodiplodia theobromae was the major pathogen responsible for crown rot and Colletotrichum musae and Fusarium spp. were the minor pathogens. This fungus can be controlled by immersing of bananas in hot water. Work by Reyes, Nishijima and Paull (1998) into crown rot into banana cultivars Santa Catarina Prata and Williams found that exposure of fruit to water of 45°C for 20 min given 15-20 min after dehanding reduced crown rot from 100% to less than 15%. Furthermore, when fruit was exposed to hot water at 50°C for 20 min, crown rot was reduced to less than 3% irrespective of the time after dehanding.

Banana streak is caused by the banana streak badnavirus (BSV). It appears that the symptoms of banana streak are reduced at higher temperatures, with plants grown at 22°C deg having higher virus loads and greater expression of symptoms than those grown at 28°C or 32°C (Dahal et.al.,1998).

The banana bract mosaic virus causes a red-brown mosaic pattern on bracts of banana flowers and/or green or red streaks on leaves and leave petioles (mosaic disease). The virus is transmitted by several aphid species and by using infected planting material. The ecology of the virus is very complex (Gallitelli, 2000) and further work is required to understand the temperature relationships.

Banana freckle is a disease of leaves and fruit caused by the fungus Phyllosticta musarum. The incubation period and severity of this disease is strongly affected by weather conditions (Chuang, 1984). Research in the Philippines revealed that the sporulation and severity of the disease is affected by temperature, rainfall and relative humidity (Corcolon, 2005).

Bananas – Critical Temperature Threshold The banana is a tropical/subtropical plant best suited to warm, frost-free, climates, and is commercially grown from the equator to latitudes of 30 degrees or more.

The optimum temperature for banana growth is between 25°C and 30°C. Growth and development of bananas are impaired by temperatures outside this range. High air temperatures (usually greater than 38°C) and bright sunshine result in sunburn of exposed fruit, especially on the top hands of the bunch.

New leaves are continually emerging from the stem of the banana throughout the growth phase. The rate of appearance of new leaves is largely governed by temperature. In winter subtropical conditions, the rate of production is often significantly reduced, sometimes to a rate of one leaf in 20 days. In contrast, summer leaf emergence can be completed in around 4 days in tropical conditions. In modelling undertaken on 17 banana cultivars at Alstonville, New South Wales, the optimum rate of leaf emergence occurred at 28.5°C.

Research by Turner and Lahav (1983) into the growth of banana cv. Williams (Giant Cavendish), concluded that plants showed heat injury at day/night temperatures of 37/30°C.

If a temperature threshold for banana growth is 37 or 38°C, then this is significantly higher than temperatures experienced in existing tropical growing regions and thus in the medium term it would seen unlikely that temperature increases associated with climate change will significantly impact production. However, under a warming climate scenario, the growing conditions in more marginal sub-tropical regions such as in New South Wales, are likely to improve.

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References. Allen RN, Dettmann EB, Johns GG, Turner DW, 1988. Estimation of leaf emergence rates of bananas.

Aust J Agric Res 39:53-62.

Anhalt MD, Almeida RPP, 2008. Effect of temperature, vector life stage, and plant access period on transmission of Banana bunchy top virus to Banana. Phytopathology 98:743-748.

Australian Bananas, n.d. Welcome to Australian Bananas Consumer Website. Australian Bananas

Brake VM, Pegg KG, Irwin JAG, Chaseling J, 1995. The influence of temperature, inoculum level and race of Fusarium oxysporum f. sp. cubense on the disease reaction of banana cv. Cavendish. Aust J Agric Res 46:673.

Chuang TY, 1984. Ecological study of banana freckle caused by phyllosticta-musarum. Plant Protection Bulletin (Taichung) 26:335-346.

Corcolon BM, 2005. Epidemiology of freckle disease of banana (Musa culminata C.) caused by Phyllosticta. Laguna: Phillipines University.

Dahal G, Hughes JD, Thottappilly G, Lockhart BEL, 1998. Effect of temperature on symptom expression and reliability of banana streak badnavirus detection in naturally infected plantain and banana (Musa spp.). Plant Dis 82:16-21.

Dominguez J, Negrin MA, Rodriguez CM, 2001. Aggregate water-stability, particle-size and soil solution properties in conducive and suppressive soils to Fusarium wilt of banana from Canary Islands (Spain). Soil Biology and Biochemistry 33:449-455.

Fortescue JA, Turner DW, 2005. The association between low temperatures and anatomical changes in preanthetic ovules of Musa (Musaceae). Sci Hortic 104:433-444.

Gallitelli D, 2000. The ecology of Cucumber mosaic virus and sustainable agriculture. Virus Research 71:9-21.

Ingram DL, Ramcharan C, Nell TA, 1986. Response of container-grown banana musa-spp cultivar grande-naine ixora ixora-coccinea citrus citrus-sinensis-x-poncirus-trifoliata cultivar carrizo and dracaena dracaena-marginata to elevated root temperatures. Hortscience 21:254-255.

Jacome LH, Schuh W, 1992. Effects of leaf wetness duration and temperature on development of black sigatoka disease on banana infected by mycosphaerella-fijiensis var difformis. Phytopathology 82:515-520.

Jacome LH, Schuh W, 1993. Effect of temperature on growth and conidial production in-vitro, and comparison of infection and aggressiveness in-vivo among isolates of mycosphaerella-fijiensis var difformis. Trop Agric 70:51-59.

Jones RK, 1980. Population dynamics of helicotylenchus-multicinctus and other nematodes on bananas from a subtropical environment. Nematologica 26:27-33.

Ke LS, 1981. Estimation of time of floral initiation of banana plants cultivar giant-cavendish in the kao-ping area taiwan and evaluation of present fertilization program. Journal of the Agricultural Association of China:51-58.

Padmalatha C, Singh AR, 2003. Influence of temperature on the body size of banana aphid Pentalonia nigronervosa (Homoptera : Insecta). Journal of Advanced Zoology 24:11-12.

Pegg KG, Moore NY, Bentley S, 1996. Fusarium wilt of banana in Australia: a review. Aust J Agric Res 47:637-650.

Reyes MEQ, Nishijima W, Paull RE, 1998. Control of crown rot in 'Santa Catarina Prata' and 'Williams' banana with hot water treatments. Postharvest Biol Technol 14:71-75.

Robinson JC, Nel DJ, 1984. Influence of polyethylene bunch covers on yield and fruit quality of winter-developing banana bunches. South Africa Department of Agriculture and Water Supply Technical Communication:26-28.

Romero RA, Sutton TB, 1997. Reaction of four Musa genotypes at three temperatures to isolates of Mycosphaerella fijiensis from different geographical regions. Plant Dis 81:1139-1142.

Sastry PSN, 1988. Agrometeorology of the banana crop. Geneva: World Meteorological Organization.

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Science Encyclopedia, 2009. Banana - biology of bananas, bananas and people. Science Encyclopedia.

Thangavelu R, Sangeetha G, Mustaffa MM, 2007. Cross-infection potential of crown rot pathogen (Lasiodiplodia theobromae) isolates and their management using potential native bioagents in banana. Austral Plant Pathol 36:595-605.

Tixier P, Malezieux E, Dorel M, 2004. SIMBA-POP: a cohort population model for long-term simulation of banana crop harvest. Ecol Model 180:407-417.

Treverrow N, 2003. Bananas - response to temperature. Alstonville: NSW Agriculture: Division of Plant Industries.

Turner DW, Lahav E, 1983. The growth of banana plants in relation to temperature. Australian Journal of Plant Physiology 10:43-54.

Wu RY, Su HJ, 1991. Regeneration of healthy banana plantlets from banana bunchy top virus-infected tissues cultured at high temperature. Plant Pathology (Oxford) 40:4-7.

Wurr DCE, Fellows JR, Fuller MP, 2004. Simulated effects of climate change on the production pattern of winter cauliflower in the UK. Sci Hortic 101:359-372.

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The influence of temperature on the growth and development of apples (Malus domestica).

The Australian apple industry is the third largest horticultural industry in Australia. Apples are grown in all six Australian states, with Victoria being the largest in terms of both tonnage and number of producers. Pome fruit is produced for the domestic and export fresh markets and for value-adding via canning and juicing.

Table 7: Australian Apple Production


VIC

NSW

W.A

QLD

TAS

S.A

TOTAL

327

166

220

65

94

115

987

115584

37387

31932

29521

28523

27529

270456

42.7

13.8

11.8

10.9

10.6

10.2

Source : ABS 2007

Australian apple production is vulnerable to climate change impacts including reduced winter chilling, higher summer temperatures, more intense rainfall events and changes to rainfall patterns, as well as changes to the distribution of pests and diseases.

The Australian Apple Industry has identified the following climate change related issues as requiring attention (Apple Industry Strategic Plan):-

Improving orchard productivity.

Developing tools to reduce production losses due to spatial variability of soil types, water distribution, pests, diseases, and environmental factors (wind, sunburn etc.) while containing costs and maintaining food safety and zero residues.

Determine the likely impact of exotic incursions and changes to distribution of endemic pests and diseases as a result of climate change and design IPM systems flexible enough to cope with such scenarios

Determine water requirements of high density production systems to improve nutrient and water use efficiency

Facilitating adoption of better farm management practices.

Improving Risk Management

Design systems and cost-effective infra-structure to mitigate adverse climatic events and the effects of climate change

Conduct risk assessment modelling to identify the major risks and appropriate controls that could be incorporated into a systems approach to biosecurity, climate change and variability, and market intelligence

Improving Environmental Performance.

Identifying and quantifying the major factors impacting on (greenhouse gas) emissions

Determining benchmark carbon footprints for the industry

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Developing an understanding of soil biology in Australian orchards and its implications for reducing the carbon footprint of the industry

Developing tools to monitor environmental performance and the impacts of any management changes in real time

The Influence of Temperature on Specific Growth and Development Phases of Apples. The effect of temperature on apple phenology. Temperature has a major influence on fruit growth rates, development and quality parameters (Woolf and Ferguson, 2000). Unfortunately, very little specific data exists on critical temperature thresholds for apples, particularly for upper limits and the effects of higher temperatures on growth and development.

In the apple, flowering is autonomous without direct environmental stimulus. Floral initiation is dependent on aspects of vegetative development in the growing season before anthesis (Wilkie et.al.,2008).

Basic temperature relationships. The temperature ranges assumed to be appropriate for the cultivation of apple are 6-14 C annual mean temperature, and 13-21C mean temperature from mid-spring to mid-autumn (Sugiura et.al.,2005; Sugiura and Yokozawa, 2004).

Repeated advances in the dates of flowering stages in apple and pear trees have been observed in cropping areas in France and Switzerland (Guedon and Legave, 2008). The coincidence between an abrupt change in phenological patterns and marked increases in temperature in the late 1980s led the researchers to consider the flowering advances to be impacts of global warming. In all areas studied, annual mean temperatures suddenly increased after 1988 (by about 1.1-1.3 C), although there were noticeable monthly differences. Warming was clearly more pronounced in winter/spring (by about 1.6 C) corresponding to the main period of heat requirements, than in autumn/winter (by about 0.8 C) corresponding to the main period of chilling requirements. Marked temperature increases during the heat phase would have suddenly resulted in more frequent years with relatively short duration for completion of the heat requirements and consequently more frequent early flowering years, despite the fact that some years still had relatively long chilling periods. Models of apple flowering time are consistent with these results and support the idea that global warming has exerted two opposing but simultaneous effects; a slower mean rate of completion for the chilling requirement and a higher mean rate of completion for the heat requirement (Legave et.al.,2008).

Similar results have been reported from the United States, where the date of flowering in apples has advanced by approximately one day every five years between 1965 and 2001 (Wolfe et.al.,2005). Other woody perennial species exhibit similar changes which are qualitatively consistent with the observed warming trend over the same period.

To investigate the relationship between temperature and flower-bud formation and growth, researchers exposed 3-year old apple trees (“SummerRed” cultivar) to a number of different temperature regimes for several months starting at full-bloom (Zhu et.al.,1997). A rise in temperature in the middle of the season from 13C to 20C enhanced flowering the following spring. However, increasing from 20C to 27C showed very little effect, and a reduction from 27C to 13C resulted in a severe reduction of flowering.

The effect of temperature on apple fruit yield and quality. Several studies investigating the effects of temperature and irrigation on apple fruit quality employed polytunnels (tunnels of transparent polyethylene sheeting) to elevate local temperature by between 0.8C and 1.6C (Atkinson et.al.,1995; Atkinson et.al.,1998). The early experiments showed little benefit to fruit size from higher temperatures but did show that irrigation enhanced the rate of fruit maturity (Atkinson et.al.,1995). The latter research showed that the largest fruits were obtained from the trees grown at higher temperatures in the complete polytunnels with irrigation, although fewer fruit were produced (Atkinson et.al.,1998). The differences in fruit size were most likely to result from

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changes in cell volume rather than in cell number. As a consequence, the larger fruit size was associated with a loss of fruit texture and quality during storage. Higher temperatures were associated with fewer fruit being retained and the individual fruit growing more than those at the lower temperature.

Other research has indicated that apple fruit growth is highly sensitive to temperature early in the season, but significantly less sensitive later in the season (Calderón-Zavala et.al.,2002). The fruit of potted “Royal Empire” apple trees were monitored in growth chambers for 4 consecutive weeks starting 15 days after full bloom. Four different day/night temperature regimes were used (12/7, 19/14, 26/21 and 33/28°C). In the first week, the rate of fruit growth was greatest for the highest temperature regimes, but cooler temperatures (19/14˚C) induced the highest fruit growth during the next 2 weeks. In the last week, fruit growth was relatively insensitive to temperature. The highest temperature (33/28°C) seems to be detrimental to fruit growth later than 3 weeks after full bloom (Calderón-Zavala et.al.,2002).

Results of glasshouse experiments using two temperatures (15 and 20C) showed that the fruit setting potential of apples (cultivars “Queen Cox'” and “Golden Delicious'”) was severely reduced by exposure to higher temperature for several weeks after anthesis (Atkinson et.al. 2001). A higher initial temperature produced the largest fruit but at the cost of fruit set. Measurements of cortical cell size showed that the higher temperatures produced larger fruit by inducing larger cells rather than more cells per apple. Fruit expansion rates are positively correlated with post-bloom temperature (between 6 and 20C) in several cultivars (“Braeburn”, “Delicious”, “Golden Delicious”, “Fuji” and “Royal Gala”). The greater rates of cell division occurring at higher temperatures early in the post-bloom period resulted in up to four times greater fruit weight at harvest (Warrington et.al.,1999). The total fruit cell number may be determined as early as about 50 days after pollination because of an early temperature-dependant cell division phase (Stanley et.al.,2000). After this period, it appears that temperature, crop load, shading and other factors influence cell size but not necessarily cell number.

The role of early-season temperatures in determining the growth potential of apple fruit were described in a “compartment model” of apple growth (Austin et.al.,1999). In this model, early-season temperatures have a strong effect on the potential size of fruit at harvest through increased fruit cell number resulting from increased resource allocation to young fruit. Temperature later in the season influences the ability of the fruit to achieve the potential growth. Subsequent tests of this model have shown it to be a good predictor of fruit size at harvest in another cultivar (“Royal Gala”) in New Zealand, and it has been included in software models of apple growth and fruiting (eg. The CLIMPACTS application; University of Waikato).

Various combinations of autumn and spring temperatures (between 9C and 24C) under controlled conditions were used to investigate variation in fruit set and pollination time (for “Golden Delicious”)(Tromp and Borsboom, 1994). Although higher autumn temperatures resulted in a slight delay of bloom, there was no effect of autumn temperature on fruit set. However, a decrease in temperature from 19C to 13C just after bloom results in a longer effective pollination treatment and better fruit set.

Increased differences in day and night temperatures late in the season show very little effect on ripening parameters (“Cox’s Orange Pippin” and “Elstar” cultivars) but flesh firmness is reduced through exposure to higher temperatures during this period (Tromp, 1999).

The intensity of the red blush on apple skin is an important indicator of fruit quality for consumers. The red blush appears on the fruit near ripening, arising from the synthesis of anthocyanin pigments in response to changes in the tree environment, particularly temperature and light (Lancaster, 1992). A combination of cool nights and warm clear days with high levels of visible and UVB light are the optimal conditions for the formation of red blush (Reay, 1999).

Root-zone temperatures.

The timing and proportion of flowering is affected by root-zone temperature in addition to air temperature. Rootzone temperatures were manipulated in a series of experiments on mature potted “Braeburn” apple trees (using temperatures of 7, 15 and 25 C), and the proportion and timing of bud break were enhanced as root-zone temperature increased (Greer et.al., 2006). The rate of floral cluster opening, soil respiration and leaf photosynthesis also tended to increase with increasing root-zone temperature.

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Effects of high temperatures.

The formation of flower buds was studied in two apple cultivars at several constant temperatures and several combinations of day and night temperatures. Flower formation was markedly reduced at the highest day temperature of 25°C. However, other day temperatures had no clear effect and a low night temperature appeared to have no effect (Jonkers, 1983).

The history of exposure to high temperatures during fruit development can affect post-harvest quality, including colour and texture (Sams, 1999; Woolf and Ferguson, 2000). Sunburn is the most common temperature-related disorder in apples, and its appearance increases with higher air temperatures and higher light intensities. Direct sunlight can increase fruit surface temperatures by up to 15C above air temperature (Ferguson et.al.,1998; Schroeder, 1965), resulting in fruit temperatures well above 40C in direct sunlight. Exposure to these temperatures leads to an increase in the expression of heat shock proteins (Ferguson et.al., 1998). Typical sun damage includes a light corky layer of flesh, golden or bronze discolouration, and other injuries to the surface tissues exposed to the sun. Sunburn browning results from damage to surface cells and happens when the fruit surface reaches 46º to 49º C, but direct sunlight also plays a role in its formation. A more serious disorder, sunburn necrosis, results from damaged permeability of cell membranes which occurs when fruit surface temperatures exceed about 52ºC (Piskolczi et.al.,2004; Schrader et.al.,2001; Schrader et.al.,2003).

Chilling and dormancy.

Low temperatures (e.g. below about 12C) trigger dormancy induction and the cessation of growth in apples, regardless of photoperiodic conditions (Heide and Prestrud, 2005). The same low temperature conditions that induce dormancy are also required for dormancy release. Chilling at 6 or 9C for at least 6 weeks (about 1000 h) was required for release from dormancy and resumption of growth (Tromp and Borsboom, 1994). The period of chilling is more important than the actual temperature (Jacobs et.al.,2002). Increasing chilling hours improves the rate and magnitude of shoot growth, and also advances the onset of growth (Arnold and Young, 1990).

A number of bioclimatic indices are available to assess the effect of the number of chilling units on the subsequent growth and development of fruit (reviewed in Valentini et.al., 2001). These indices vary with the base temperature chosen and the mathematical equation used to calculate the number of growing degree days. A review of the different methods on 15 different apple cultivars revealed that the Weinberger-Eggert model provides the most consistent index with the least statistical variability (Valentini et.al.,2001). Under this method, only temperatures between 0C and 7C contribute to the chilling unit value. A separate and later review of bioclimatic indices using available meteorological data and phenological data for “Golden Delicious” apples from northern Italy (Rea and Eccel, 2006) resulted in a revised “Progressive Utah” index which could successfully predict flowering date within two days accuracy.

A potential consequence of elevated mean temperatures resulting from climate change may be an increase in the occurrence of warmer non-chilling days within the chilling period. The effect of temporary exposure to higher non-chilling temperatures during the accumulation of chilling units depends on the temperature and timing of exposure (Young, 1992). Further research is required to assess these potential effects.

In warmer climates with insufficient chilling hours for good fruit production, there are other methods that can be employed to break dormancy and stimulate bud break. The application of dormancy-breaking agents (eg. cytokinins, growth regulators, and other chemicals) has been widely studied (Mohamed, 2008) and hydrogen cyanamide appears to be the most effective agent. Defoliation is another simple treatment but its effectiveness depends on the date of application. Manual defoliation in autumn and the onset of winter may overcome the problems of prolonged dormancy in sub-tropical regions by increasing fruit set and yield (Mohamed, 2008).

There is also significant genetic variation in chilling unit requirement (Gonzalez-Portillo et.al.,2008; Labuschagne et.al.,2002) within apple cultivars. The potential implications for this are discussed in the section on adaptation.

Modelling the potential impacts of climate change. Some recent work in Japan has attempted to model the impacts of global warming on apple production (Sugiura et.al.,2005; Sugiura and Yokozawa, 2004). These projects compared temperature ranges for production of apples (6-14C annual mean temperature) with projected temperature change scenarios

126

calculated from "Climate Change Mesh Data (Japan)" database. The results suggest that the favourable regions for apple cultivation in Japan will gradually move northward. Some current production areas will be unfavourable as early as the 2040’s and many parts will be unfavourable by the 2060’s. In contrast, new areas in Hokkaido will become suitable by the 2060's. These results hint at the potential impacts of climate change on the Australian apple industry.

These predictions are supported by other modelling work on the effects of climate change on fruit trees in Canada (Rochette et.al.,2004). Because of the general focus on fruit trees rather than single crops, the researchers have a more optimistic interpretation of the potential impacts. The risks of damage from early winter frosts are likely to decrease and milder winter temperatures will reduce cold stress. The authors conclude that the projected climate change should allow for the introduction of new cultivars and extension of production areas into higher latitudes.

CLIMPACTS is a software suite to assess the impacts of climate change on the environment and resource in New Zealand based on a range of climate and crop models (Kenny et.al.,1995). OzClim is a similar system that can be used to generate climate predictions for Australia based on different emissions scenarios and time frames (Page and Jones, 2001). Software of this type will be important tools for analysing the potential impacts of climate change on a range of horticultural crops.

Methods to reduce impact of increasing temperatures. Several techniques show potential for reducing the negative impacts of increased temperature on apple fruiting - e.g. hail nets, particle films and evaporative cooling.

Nets are already employed to reduce damage from hail and birds, but may have an added benefit of reducing temperature and sun damage to fruit. Early research suggested that nets reduce the quantity and quality of fruit (colour, mass, firmness and taste). For example, white hail nets can reduce air temperature by about 1.6C, but the reduction in light intensity (11-15%) also reduced fruit quality through less sugar (Solomakhin and Blanke, 2007) and may also reduce fruit set via less flower induction. Nets of different transmission spectra (colour) (Solomakhin and Blanke, 2008) and the addition of reflective mulches (Solomakhin and Blanke, 2007) may ameliorate these negative effects. Reflective plastic mulches (eg. Extenday or Daybright, Extenday Ltd, New Zealand) appear to be particularly effective in increasing fruit quality and can result in significant financial gains (Solomakhin and Blanke, 2007).

Evaporative cooling using micro sprinkler irrigation has been shown to be an effective tool for reducing fruit temperatures. Research on “Jonagold” apples showed that evaporative cooling reduced maximum fruit surface temperatures by about 8C and reduced visible sunburn injury by between 9 and 16% (Parchomchuk and Meheriuk, 1996). Cooling did not appear to affect fruit size, colour or firmness. More recent research using “Topred Delicious” and “Mondial Gala” cultivars in Spain also showed that micro sprinkler irrigation reduced fruit and orchard temperatures, and that cooled fruit were larger, firmer and with higher soluble solid concentrations (Iglesias et.al.,2002; Iglesias et.al.,2005).

Heat stress in apple fruit can also be reduced through the application of non-toxic particle films to the fruit surface. These films have the added benefit of suppressing some invertebrate pests. Experiments showed that processed kaolin particle films (e.g. Surround WP, Engelhard Corp., US) were effective in reducing heat stress and solar injury in extreme temperature conditions, resulting in greater fruit weight (Glenn et.al.,2003; Thomas et.al.,2004). The processed-kaolin film material was highly reflective to the ultraviolet wavelengths and the cooling effect was proportional to the amount of particle residue on the fruit surface (Glenn et.al.,2002).

Recent projects have attempted to assess the comparative performance of these three methods. Two apple cultivars (“Cripps’ Pink” and “Royal Gala”) grown under orchard conditions in South Africa were used to assess the effect of evaporative cooling, kaolin particle films, and shade net on sunburn, fruit temperature and quality (Gindaba and Wand, 2005). The results show that all three methods are effective to some degree, and the choice of method is likely to depend on the primary concern for particular growers. In terms of lowering fruit temperature, shade netting was the most effective treatment, followed by evaporative cooling and then particle films. Shade netting was also the most effective treatment for reducing sunburn, followed by particle films and then evaporative cooling. Evaporative cooling showed more consistent improvements in fruit size. The authors conclude that technologies that reduce irradiance as well as fruit temperature (shade net and particle films) are more effective in reducing sunburn than those which only reduce fruit temperature (evaporative cooling).

127

However, radiation-reducing technologies may have negative effects on fruit development and colour (Gindaba and Wand, 2005).

Another potential problem facing apple producers is the risk of insufficient chilling hours required to break dormancy. Some growing regions are already too mild during winter to satisfy the requirements of some commercial apple cultivars (Schmidt et.al.,1999). A South African research program has explored the potential for selective breeding to address problems with prolonged dormancy. The results of this research showed that there is considerable genetic variation in chilling requirements within populations and cultivars, and that a selective breeding program could improve the genetic stock for warmer climate cultivars (Schmidt et.al.,1999). Later research has confirmed the presence of utilisable genetic variance and identified budbreak number per 100cm of 1-year old shoots as a suitable pre-selection criteria for breeding programmes to avoid prolonged dormancy (Labuschagne et.al.,2003a,b).

The amount of water available for irrigation may become limited under climate change unless growers and governments make significant investments in water infrastructure. Deficit Irrigation (DI) involves supplying water at sub-optimal levels to control unwanted vegetative growth and has been successfully applied for some fruit trees where vegetative and reproductive growth occur in different periods. This technique is likely to reduce yields in apple trees where shoot and fruit growth occurs at the same time (Talluto et.al.,2008). Partial Rootzone Drying (PRD), an alternative technique in which only one half of the rootzone is irrigated, may help to improve the water use efficiency of apple plants. “Pink Lady” trees grown under PRD irrigation showed similar yields and fruit quality to those of conventionally irrigated trees (Talluto et.al.,2008). Further research on PRD is required to investigate potential cumulative effects, and to assess the relative benefits of this approach for other cultivars and regions.

Pests, Diseases and Disorders. Climate, topography, spatial arrangement and the mix of crops all influence the type and intensity of pest and disease pressure (Kaine and Bewsell, 2008). An integrated pest management approach is likely to be the best approach to tackle pest and disease issues. Spatio-temporal modelling can be employed to evaluate the impact of climate change of plant diseases, and disease forecasting systems based on non-linear relationships offer the most potential (Bourgeois et.al.,2004).

Apple scald has been shown to develop more in warmer growing areas than in cooler areas, and temperature has a greater effect on development than other factors such as harvest date (Bramlage and Watkins, 1994).

Fungal diseases, such as sooty blotch, black spot and powdery mildew, are dependent on both temperature and humidity. While disease growth can occur over a range of temperatures, optimum growth often occurs at intermediate temperatures (20 to 25C) and at very high humidity (typically over 95% RH) (Carisse and Bernier, 2002; Hernandez et.al.,2004; Johnson and Sutton, 2000; Xiao and Sitton, 2004; Xu and Butt, 1998). Growth of some diseases (eg. Potebniamyces pyri ) ceases at about 30C (but can resume if lower temperatures return) and can be stopped altogether after a period of exposure to 35C (Xiao and Sitton, 2004).

Efforts to develop commercially-viable biocontrol strategies are continuing. For example, potential biocontrol agents for apple scab have been identified (Carisse and Bernier, 2002; Raj and Sharma, 2009), but further work is required on the timing of application and optimal conditions for successful control. Soil solarisation (using transparent plastic mulch to capture solar energy to heat the soil) is another potential non-chemical control for soil-borne pathogens. It has been shown to be an effective control for white rot (Dematophora necatrix) and other pathogens in several crops, including apples, particularly when combined with other microbial biocontrol treatments (Raj and Sharma, 2009). Some fungal agents are also sensitive to air drying as it reduces conidial viability (Johnson and Sutton, 2000), and this may be an effective control in some situations.

The codling moth (Cydia pomonella) is one of the most damaging insect pests in apple orchards (Dorn et.al.,1999). Temperatures have a strong effect on the development rates of codling moths, and can be affected by plant architecture and shade netting. Simulations revealed that adult moths could appear up to six days earlier in dwarf trees compared to standard trees, and up to 5 days later in trees under hail nets (Kuhrt et.al.,2006a; Kuhrt et.al.,2006b). Other moth pests also show temperature dependent development. For example, the oblique banded leafroller (Choristoneura rosaceana), a serious pest of apple crops in other parts of the world, has a temperature range for successful development from egg to adult of about 10C to 30C (Jones et.al.,2005).

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Software tools have been developed to assist with investigating potential pest impacts under changing climates (Sutherst et.al.,2000). CLIMEX (http://www.csiro.au/solutions/ps1h3.html) can be used to predict the potential distribution and relative abundance of species in relation to climate, and DYMEX (http://www.csiro.au/solutions/DymexSoftware.html) allows the construction of detailed, multivariate life-cycle models. These tools have great promise for predicting potential changes in the distribution and abundance of pest species, and for developing effective preventative measures and management strategies. However, there are very few published examples of these tools being applied to pests of apples in Australia.

The effects of elevated CO2 The main response of plants to rising atmospheric CO2 is to increase resource use efficiency (Drake et.al.,1997). Exposure to elevated CO2 concentration may lead to increased growth and productivity if the increase in CO2 concentration also leads to elevated temperatures (Ro et.al.,2001). Dwarf apple saplings were acclimated to two atmospheric CO2 concentrations (360 and 650 mu mol mol-1) in combination with current ambient or elevated (ambient +5C) temperatures. Overall tree growth was reduced with exposure to elevated CO2 concentration alone, but tree growth was slightly enhanced when the elevated CO2 concentration was combined with an increase in temperature. The elevated CO2 concentration increased the optimum temperature for photosynthesis by about 4C. In “Golden Delicious”, an increase in CO2 resulted in accelerated leaf appearance, increased total leaf area, higher water consumption and greater water use efficiency. The authors conclude that enriched atmospheric CO2 will enable the plants to utilize available soil water more efficiency for dry mass production, improving apple productivity (Chen et.al.,2002).

Nutrient uptake. The rate of nitrogen uptake in “Fuji” apple trees increases with both soil temperature and advancing plant development. The application of nitrogen fertiliser early in the spring when soil temperatures are low or when the aboveground portion of the tree is not actively growing may be ineffective in promoting N uptake (Dong et.al.,2001), and may also lead to increased nitrous oxide emissions.

Apples - Developmental Phase – Critical Temperature Threshold A potential problem facing apple producers is the risk of insufficient chilling hours required to break dormancy. Some growing regions are already too mild during winter to satisfy the requirements of some commercial apple cultivars. Low temperatures trigger dormancy induction and the cessation of growth in apples. Chilling is required for release from dormancy and resumption of growth. Increasing chilling hours improves the rate and magnitude of shoot growth. A potential consequence of elevated mean temperatures resulting from climate change will be an increase in the occurrence of warmer non-chilling days within the chilling period.

In Japan some current production areas will be unfavourable as early as the 2040’s and many areas will be unfavourable by the 2060’s. In contrast, new areas in the north will become suitable for apple production by the 2060's. These results from Japan provide an insight into the potential impacts of climate change on the Australian apple industry. In the absence of new acceptable lower-chill cultivars, the more favourable regions for apple cultivation in Australia will gradually move southward.

Because there is considerable genetic variation in chilling requirements within apple populations and cultivars, a selective breeding program could improve the genetic stock for warmer climate cultivars.

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References. Arnold MA, Young E, 1990. Growth and protein-content of apple in response to root and shoot

temperature following chilling. Hortscience 25:1583-1588.

Atkinson CJ, Taylor L, Kingswell G, 2001. The importance of temperature differences, directly after anthesis, in determining growth and cellular development of Malus fruits. J Horticult Sci Biotechnol 76:721-731.

Atkinson CJ, Taylor L, Taylor JM, 1995. The influence of temperature and water-supply on apple fruit-growth and the development of orchard-grown trees. J Horticult Sci 70:691-703.

Atkinson CJ, Taylor L, Taylor JM, Lucas AS, 1998. Temperature and irrigation effects on the cropping, development and quality of 'Cox's Orange Pippin' and 'Queen Cox' apples. Sci Hortic 75:59-81.

Austin PT, Hall AJ, Gandar PW, Warrington IJ, Fulton TA, Halligan EA, 1999. A compartment model of the effect of early-season temperatures on potential size and growth of 'Delicious' apple fruits. Ann Bot 83:129-143.

Bourgeois G, Bourque A, Deaudelin G, 2004. Modelling the impact of climate change on disease incidence: a bioclimatic challenge. Natl Research Council Canada; 284-290.

Bramlage WJ, Watkins CB, 1994. Influences of preharvest temperature and harvest maturity on susceptibility of new-zealand and north-american apples to superficial scald. N Z J Crop Hortic Sci 22:69-79.

Calderón-Zavala G, Lakso AN, Piccioni RM, 2002. Temperature effects on fruit and shoot growth in the apple (Malus domestica) early in the season. ISHS; 447-453.

Carisse O, Bernier J, 2002. Effect of environmental factors on growth, pycnidial production and spore germination of Microsphaeropsis isolates with biocontrol potential against apple scab. Mycol Res 106:1455-1462.

Chen K, Hu GQ, Lenz F, 2002. Effects of doubled atmospheric CO2 concentration on apple trees IV. Water consumption. Gartenbauwissenschaft 67:99-106.

Dong SF, Scagel CF, Cheng LL, Fuchigami LH, Rygiewicz PT, 2001. Soil temperature and plant growth stage influence nitrogen uptake and amino acid concentration of apple during early spring growth. Tree Physiol 21:541-547.

Dorn S, Schumacher P, Abivardi C, Meyhofer R, 1999. Global and regional pest insects and their antagonists in orchards: spatial dynamics. Elsevier Science Bv; 111-118.

Drake BG, GonzalezMeler MA, Long SP, 1997. More efficient plants: A consequence of rising atmospheric CO2? Annu Rev Plant Physiol Plant Molec Biol 48:609-639.

Ferguson IB, Snelgar W, Lay-Yee M, Watkins CB, Bowen JH, 1998. Expression of heat shock protein genes in apple fruit in the field. Australian Journal of Plant Physiology 25:155-163.

Gindaba J, Wand SJE, 2005. Comparative effects of evaporative cooling, kaolin particle film, and shade net on sunburn and fruit quality in apples. Hortscience 40:592-596.

Glenn DM, Erez A, Puterka GJ, Gundrum P, 2003. Particle films affect carbon assimilation and yield in 'Empire' Apple. J Am Soc Hortic Sci 128:356-362.

Glenn DM, Prado E, Erez A, McFerson J, Puterka GJ, 2002. A reflective, processed-kaolin particle film affects fruit temperature, radiation reflection, and solar injury in apple. J Am Soc Hortic Sci 127:188-193.

Gonzalez-Portillo M, Rocha-Guzman NE, Simpson J, Rodriguez-Guerra R, Gallegos-Infante JA, Delgado E, Gil-Vega K, 2008. Determination of some apple (starking and golden delicious) quality attributes in comparison with their mutants and their relationship with chilling units. Cienc Tecnol Aliment 6:27-32.

Greer DH, Wunsche JN, Norling CL, Wiggins HN, 2006. Root-zone temperatures affect phenology of bud break, flower cluster development, shoot extension growth and gas exchange of 'Braeburn' (Malus domestica) apple trees. Tree Physiol 26:105-111.

130

Guedon Y, Legave JM, 2008. Analysing the time-course variation of apple and pear tree dates of flowering stages in the global warming context. Ecol Model 219:189-199.

Heide OM, Prestrud AK, 2005. Low temperature, but not photoperiod, controls growth cessation and dormancy induction and release in apple and pear. Tree Physiol 25:109-114.

Hernandez SM, Batzer JC, Gleason ML, Mueller DS, Dixon PM, Best V, McManus PS, 2004. Temperature optima for mycelial growth of newly discovered fungi in the sooty blotch and flyspeck complex on apples. Phytopathology 94:S41-S41.

Iglesias I, Salvia J, Torguet L, Cabus C, 2002. Orchard cooling with over tree micro sprinkler irrigation to improve fruit colour and quality of 'Topred Delicious' apples. Sci Hortic 93:39-51.

Iglesias I, Salvia J, Torguet L, Montserrat R, 2005. The evaporative cooling effects of over tree micro sprinkler irrigation on 'Mondial Gala' apples. Sci Hortic 103:267-287.

Jacobs JN, Jacobs G, Cook NC, 2002. Chilling period influences the progression of bud dormancy more than does chilling temperature in apple and pear shoots. J Horticult Sci Biotechnol 77:333-339.

Johnson EM, Sutton TB, 2000. Response of two fungi in the apple sooty blotch complex to temperature and relative humidity. Phytopathology 90:362-367.

Jones VP, Doerr MD, Brunner JF, Baker CC, Wilburn TD, Wiman NG, 2005. A synthesis of the temperature dependent development rate for the obliquebanded leafroller, Choristoneura rosaceana. J Insect Sci 5:8.

Jonkers H, 1983. Effect of temperature on formation of flower buds in two apple cultivars. Flowering and Fruit Set in Fruit Trees 149:49-52.

Kaine G, Bewsell D, 2008. Adoption of Integrated Pest Management by apple growers: the role of context. Int J Pest Manage 54:255-265.

Kenny GJ, Warrick RA, Mitchell ND, Mullan AB, Salinger MJ, 1995. CLIMPACTS: an integrated model for assessment of the effects of climate change on the New Zealand environment. Journal of Biogeography:883-895.

Kuhrt U, Samietz J, Dorn S, 2006a. Effect of plant architecture and hail nets on temperature of codling moth habitats in apple orchards. Entomol Exp Appl 118:245-259.

Kuhrt U, Samietz J, Hohn H, Dorn S, 2006b. Modelling the phenology of codling moth: Influence of habitat and thermoregulation. Agric Ecosyst Environ 117:29-38.

Labuschagne IF, Louw JH, Schmidt K, Sadie A, 2002. Genetic variation in chilling requirement in apple progeny. J Am Soc Hortic Sci 127:663-672.

Labuschagne IF, Louw JH, Schmidt K, Sadie A, 2003a. Budbreak number in apple seedlings as selection criterion for improved adaptability to mild winter climates. Hortscience 38:1186-1190.

Labuschagne IF, Louw JH, Schmidt K, Sadie A, 2003b. Selection for increased budbreak in apple. J Am Soc Hortic Sci 128:363-373.

Lancaster JE, 1992. Regulation of skin color in apples. Critical Reviews in Plant Science 10:487-502.

Legave JM, Farrera I, Almeras T, Calleja M, 2008. Selecting models of apple flowering time and understanding how global warming has had an impact on this trait. J Horticult Sci Biotechnol 83:76-84.

Mohamed AKA, 2008. The effect of chilling, defoliation and hydrogen cyanamide on dormancy release, bud break and fruiting of Anna apple cultivar. Sci Hortic 118:25-32.

Page CM, Jones RN, 2001. OzClim: the development of a climate scenario generator for Australia. 667-672.

Parchomchuk P, Meheriuk M, 1996. Orchard cooling with pulsed over tree irrigation to prevent solar injury and improve fruit quality of 'Jonagold' apples. Hortscience 31:802-804.

Piskolczi M, Varga C, Racskó J, 2004. A review of the meteorological causes of sunburn injury on the surface of apple fruit (Malus domestica Borkh). Journal of Fruit and Ornamental Plant Research 12:245-252.

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Raj H, Sharma SD, 2009. Integration of soil solarisation and chemical sterilization with beneficial microorganisms for the control of white root rot and growth of nursery apple. Sci Hortic 119:126-131.

Rea R, Eccel E, 2006. Phenological models for blooming of apple in a mountainous region. Int J Biometeorol 51:1-16.

Reay PF, 1999. The role of low temperatures in the development of the red blush on apple fruit ('Granny Smith'). Sci Hortic 79:113-119.

Ro HM, Kim PG, Lee IB, Yiem MS, Woo SY, 2001. Photosynthetic characteristics and growth responses of dwarf apple (Malus domestica Borkh. cv. Fuji) saplings after 3 years of exposure to elevated atmospheric carbon dioxide concentration and temperature. Trees-Struct Funct 15:195-203.

Rochette P, Belanger G, Castonguay Y, Bootsma A, Mongrain D, 2004. Climate change and winter damage to fruit trees in eastern Canada. Can J Plant Sci 84:1113-1125.

Sams CE, 1999. Preharvest factors affecting postharvest texture. Postharvest Biol Technol 15:249-254.

Schmidt K, Louw JH, Sadie A, Labuschagné IF, 1999. BREEDING LOW-CHILL REQUIRING APPLE CULTIVARS (Malus x domestica BORKH.) IN SOUTH AFRICA. ISHS; 281-288.

Schrader L, Zhang JG, Duplaga WK, 2001. Two types of sunburn in apple caused by high fruit surface (peel) temperature. Plant Health Progress 10:1-5.

Schrader L, Zhang JG, Sun JS, 2003. Environmental stresses that cause sunburn of apple. Acta Horticulturae 618:397-405.

Schroeder CA, 1965. Temperature relationships in fruit tissues under extreme conditions. 199-203.

Solomakhin A, Blanke MM, 2008. Coloured hail nets alter light transmission, spectra and phytochrome, as well as vegetative growth, leaf chlorophyll and photosynthesis and reduce flower induction of apple. Plant Growth Regul 56:211-218.

Solomakhin AA, Blanke MM, 2007. Overcoming adverse effects of hail nets on fruit quality and microclimate in an apple orchard. J Sci Food Agric 87:2625-2637.

Stanley CJ, Tustin DS, Lupton GB, McArtney S, Cashmore WM, De Silva HN, 2000. Towards understanding the role of temperature in apple fruit growth responses in three geographical regions within New Zealand. J Horticult Sci Biotechnol 75:413-422.

Sugiura T, Kuroda H, Sugiura H, Honjo H, 2005. Prediction of effects of global warming on apple production regions in Japan. Ferdinand Berger Soehne; 419-422.

Sugiura T, Yokozawa M, 2004. Impact of global warming on environments for apple and satsuma mandarin production estimated from changes of the annual mean temperature. J Jpn Soc Hortic Sci 73:72-78.

Sutherst R, Maywald G, Russell B, 2000. Estimating vulnerability under global change: modular modelling of pests. Agriculture, Ecosystems and Environment:303-319.

Talluto G, Farina V, Volpe G, Lo Bianco R, 2008. Effects of partial rootzone drying and rootstock vigour on growth and fruit quality of 'Pink Lady' apple trees in Mediterranean environments. Aust J Agric Res 59:785-794.

Thomas AL, Muller ME, Dodson BR, Ellersieck MR, Kaps M, 2004. A kaolin-based particle film suppresses certain insect and fungal pests while reducing heat stress in apples. J Amer Pomolog Soc 58:42-51.

Tromp J, 1999. Maturity of apple cvs 'Cox's Orange Pippin' and 'Elstar' as affected by mid-season and late-season temperature. Gartenbauwissenschaft 64:145-151.

Tromp J, Borsboom O, 1994. The effect of autumn and spring temperature on fruit-set and an the effective pollination period in apple and pear. Sci Hortic 60:23-30.

Valentini N, Me G, Ferrero R, Spanna F, 2001. Use of bioclimatic indexes to characterize phenological phases of apple cultivars in Northern Italy. Int J Biometeorol 45:191-195.

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Warrington IJ, Fulton TA, Halligan EA, de Silva HN, 1999. Apple fruit growth and maturity are affected by early season temperatures. J Am Soc Hortic Sci 124:468-477.

Wilkie JD, Sedgley M, Olesen T, 2008. Regulation of floral initiation in horticultural trees. J Exp Bot 59:3215-3228.

Wolfe DW, Schwartz MD, Lakso AN, Otsuki Y, Pool RM, Shaulis NJ, 2005. Climate change and shifts in spring phenology of three horticultural woody perennials in north-eastern USA. Int J Biometeorol 49:303-309.

Woolf AB, Ferguson IB, 2000. Postharvest responses to high fruit temperatures in the field. Elsevier Science Bv; 7-20.

Xiao CL, Sitton JW, 2004. Effects of culture media and environmental factors on mycelial growth and pycnidial production of Potebniamyces pyri. Mycol Res 108:926-932.

Xu XM, Butt DJ, 1998. Effects of temperature and atmospheric moisture on the early growth of apple powdery mildew (Podosphaera leucotricha) colonies. Eur J Plant Pathol 104:133-140.

Young E, 1992. Timing of high-temperature influences chilling negation in dormant apple-trees. J Am Soc Hortic Sci 117:271-273.

Zhu LH, Borsboom O, Tromp J, 1997. Effect of temperature on flower-bud formation in apple including some morphological aspects. Sci Hortic 70:1-8.

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The influence of temperature on the growth and development of citrus (Citrus spp).

32,000 hectares were devoted to Citrus production in Australia in 2005-06, which is 0.6% of total world citrus production. 75% of Australia’s production (24,000 ha) occurs in the Murray and Murrumbidgee Irrigation areas (Riverland region – SA), Sunraysia and mid-Murray (northern Vic & southern NSW) and the MIA (NSW).


The industry’s gross value of production was $400 million, $446 million and $426 million in 2003/04, 2004/05 and 2005/06, respectively.

75% of the Australia’s total citrus tonnage comes from navel and Valencia orange production, with navel orange production increasing and Valencia production decreasing. Mandarin production is also increasing.

The Influence of Temperature on Specific Growth and Development Phases of Citrus. Citrus reticulata (Mandarin)

Citrus sinensis (Orange)

Citrus limon (Lemon)

The effect of temperature on citrus phenology. Basic temperature relationships.

Several agrometeorological models have been developed to allow the forecasting of potential yields in citrus crops (reviewed in Ben Mechlia and Carroll, 1989b; Paulino et.al.,2007). The development of these models required the collection and review of extensive literature on the environmental requirements of citrus crops, and this greatly simplifies this review of relevant climatic factors.

One such project collated the data required to predict the temporal progression of phenological stages, fruit growth, fruit maturation, and fruit coloration for two orange cultivars (“Navel” and “Valencia”)(Ben Mechlia and Carroll, 1989a). These criteria were derived from an extensive body of published observations from many parts of the world, and were selected to be variety specific and independent of local climatology or other site-specific effects (as far as possible). The factors considered included effects on both flowering (temperature and solar radiation) and fruit set (past stress, temperature, evaporation, wind, rain, planting density, and tree age). These criteria, and the formulae derived from them, form the basis of a time-dependent model which uses daily air temperature and wind data for the prediction of these quantities (described in the modeling section). Table 2 provides a summary of some of the key data.

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Table 8: The temperature sensitivity of citrus at different phenological stages

Phenological stage Optimum temp range (C) Notes

Min. Max.

Dormancy -4 14 Low physiological activity

- Hardening -4 8 Reduced losses due to freezing

- Pre-bloom 0 14 Required resting period for bloom

Flowering 10 27 Requires daily mean > 20C to begin

Fruit set 22 27 Range near end of bloom. A single day max over 38C may causes losses

Fruit growth 20 33 Requires heat, but expansion may be reduced if temperatures are too high

Maturation

- Soluble solids 13 27 Sugars increase and acids decrease with accumulated heat units

- Colour 8 18 Heat may lead to re-greening Source : (based on the summary of Ben Mechlia and Carroll, 1989a presented in Rosenzweig et.al.,1996).

More recent research has evaluated the influence of meteorological variables in different phases of the growing cycle for two cultivars (“Valencia” and “Hamlin”) over 15 years in Brazil (Paulino et.al.,2007). The resulting model expresses the number of fruits per plant as a function of evapotranspiration rates, water deficit and water excess at different growth stages. While this model may be a useful predictor of fruit load in real cropping situations, these variables are of little value for broad scale predictions of climate impacts.

A comprehensive analysis of the effects of temperature and precipitation on crop yields was presented in Lobell et.al.,(2007). The authors analysed the relationships between crop yield and three climatic variables (minimum temperature, maximum temperature, and precipitation) for 12 major Californian crops (including oranges) over a 24-year period (1980-2003). In the case of oranges, yield was most closely correlated with rainfall in May (reflecting a positive response in production of “Valencia” oranges) and minimum temperature in December (reflecting the negative impact of frost). These two variables alone account for about 63% of the variation in orange yield. The highest average yields were obtained for December minimum temperatures of about 2°C. Average yields were reduced slightly at December minimum temperatures above about 3°C, and decreased rapidly with temperatures below about 1°C (Lobell et.al.,2007).

Net photosynthetic rate of citrus trees is greatest between 25°C and 30°C (Kriedemann, 1968). Research on mandarins (“Satsuma”) in China showed that crops growing under full sun on hot days experienced a pronounced midday depression in net photosynthetic rate (Hu et.al.,2007). This depression is less pronounced in shaded leaves. In young Navel oranges, the growth of fruit on young trees was significantly related to daily maximum temperatures (Storey and Treeby, 1999).

A review of citrus responses to temperature and CO2 showed that crop water use increased with temperature but declined under enhanced CO2 (Baker and Allen, 1993). CO2 assimilation and stomatal conductance are both negatively correlated with temperatures in the range of 25°C to 40°C (Ribeiro et.al.,2004).

Soil temperature can also influence the growth and function of roots (reviewed in Pregitzer et.al.,, 2000). In perennial plants such as oranges, root growth is highly seasonal with a flush of growth in spring. Rates of root growth increase with increasing temperature if soil moisture and nutrients are adequate. However, both water and nutrient availability often covary with changes in soil temperature and it is not yet fully understood how these factors interact. The authors conclude that global warming will result in earlier root growth in the spring, and if other factors do not limit carbon assimilation, warming of the soil will result in greater root production and greater flux of carbon to the soil (Pregitzer

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et.al.,2000). The rate of root respiration is positively correlated with root temperature, but is not affected by soil CO2 concentration or soil moisture content (Bouma et.al.,1997).

Early and mid-season temperatures have been identified as key factors influencing fruit development in “Satsuma” mandarins (Marsh et.al.,1999). Elevated temperatures advanced fruit development and shortened the phase of cell division. It appeared that early season temperatures may determine the ability of fruit to import carbohydrates at later stages of development. Experiments using “Satsuma” mandarins in plastic tunnel houses show that a 2-4°C rise in temperatures shortly after anthesis, increased the rate of fruit growth. Fruit grown in the tunnel houses were 48% larger than those grown in the outdoor control conditions (Richardson et.al.,1997).

The effect of temperature on citrus fruit yield and quality. Variation in day and night temperatures.

Many of the global and regional climate models indicate that temperature change may be asymmetric, where the increase in mean temperature occurs more through higher night time minima than higher day time maxima. Modelling results indicated that the potential effects of climate change on crop productivity may be less severe with asymmetric day-night warming than with equal day-night warming (Dhakhwa and Campbell, 1998).

Effects of high temperatures.

High temperatures and high atmospheric vapour deficits have been shown to lead to reduced photosynthesis and reduced growth in citrus (Medina et.al.,2002). In addition, high temperatures (in excess of 30°C) can cause poor flower quality, lower fruit growth, reduced fruit quality and fruit drop in “Satsuma” mandarins (Ogata et.al.,2002).

Not only were “Satsuma” mandarins, grown under higher temperatures in tunnel houses larger at the time of harvest, they also had higher soluble solid concentrations and lower acidity (Richardson et.al.,1997).

During fruit ripening, gradual changes occur in brix (total soluble solids), acid and juice content (Hutton and Landsberg, 2000). The brix to acid ratio is an important indicator of fruit quality, particularly for juice production where fruit are often left on the tree for extended periods to ensure a lengthy supply of fresh fruit. The temperature sums (or effective heat units in day degrees) can be used to predict the internal quality of citrus fruit at harvest time during extended harvest periods (Hutton and Landsberg, 2000). Brix is reduced with the accumulation of effective heat units, while acid content decreases at a faster rate, leading to a higher brix to acid ratio.

Methods to reduce impact of high temperatures on fruiting in citrus. In contrast to short-season rotation crops, adaptive planting is not a viable option for perennial trees (Rosenzweig et.al.,1996). For citrus, long-term adaptation strategies for altered climatic conditions will require the expansion or relocation of citrus orchards. However, several adaptation strategies may be effective in reducing the impacts of higher temperatures on citrus yield and quality, at least in the short term.

Shading of young de-fruited citrus trees in a subtropical climate during the hot summer months enhanced plant biomass and vegetative growth (Raveh et.al.,2003). In these experiments, shading was provided using aluminized woven plastic nets in either a tunnel or a flat overhead arrangement. The increased growth in the leaves led to increased shoot to root ratios, and was associated with large increases in leaf conductance and net CO2 assimilation rate. Shading can reduce the observed midday depression in net photosynthetic rate under higher temperatures (Hu et.al.,2007).

Micro sprinkler misting can be used to decrease temperature and increase humidity within a citrus orchard (Garcia-Delgado et.al.,2004). At ambient air temperatures above 36°C, misting can reduce air temperature by up to 5°C within the canopy. Intermittent misting at times of high temperatures increased fruit set and yield without apparent negative effects on fruit quality. Misting was most effective at 30°C, but the effectiveness of this treatment was reduced at higher temperatures (Garcia-Delgado et.al.,2004), indicating that this strategy may be useful in a short-term transitional context.

The application of aminoethoxyvinylglycine (AVG), an ethylene synthesis inhibitor, can promote fruit set, elevate growth and improve quality of mandarins under higher temperatures (Ogata et.al.,2002). Application of AVG at the start of blooming reduced ethylene production from flowers and young fruit, and improved fruit set at 30°C.

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Although higher temperatures reduced water use efficiency in citrus (“Ambersweet” oranges), this effect may be offset by the enhanced water use efficiency resulting from enriched atmospheric CO2 (Allen and Vu, 2009; Vu et.al.,2002).

Integrated pest management approaches show potential for the control of insect pests under a changing climate. For example, effective biocontrol of phytophagous mites (e.g. two-spotted mite and European red mite) can be obtained with predatory mites (GraftonCardwell et.al.,1997). Unfortunately, the possible responses of pests to climatic changes are largely unknown.

The effects of elevated CO2 Elevated CO2 has beneficial effects on citrus including improved seedling growth, tree growth and yield (reviewed in Allen and Vu, 2009; Soon et.al.,1999).

Orange trees were the subject of some of the earliest research into the effects of elevated CO2 on perennial fruit trees (Downton et.al.,1987). Over a 12-month period, CO2 enrichment enhanced the fruit load of “Valencia” oranges by about 35% through increased photosynthesis. These results were supported by a later review of citrus responses to enhanced CO2 and temperature (Baker and Allen,1993).

A 17-year study of CO2 enrichment of sour orange trees has provided valuable insights into these effects. Initial results showed dramatic increases in plant growth (over 2.5 times), but the level of enhancement declined slowly in subsequent years suggesting some effects of acclimation or self-shading (Idso and Kimball,1997). The enhancement of fruit biomass appeared to stabilise at about 1.8 times (elevated CO2 relative to ambient) after about nine years of growth (Idso and Kimball, 2001). The most recent results from this experiment revealed that the cumulative fruit biomass over the entire 17-year period was doubled under conditions of enriched CO2 (Kimball et.al.,2007). This increase in yield resulted from an increase in the number of fruit rather than in fruit size. Following the period of acclimation between about 3 and 9 years of growth, CO2 enrichment resulted in sustained enhancement of fruit production of about 70%. An additional result from this long-term experiment is that enhanced atmospheric CO2 can advance the onset of “biological spring” (Idso et.al.,2000).

The effects of elevated CO2 and temperature on “Ambersweet” oranges were tested in controlled conditions (Vu et.al.,2002). Two CO2 conditions (ambient and 2 x ambient) and two temperatures (1.5°C and 6°C above ambient) were used. Leaves grown under elevated CO2 had higher photosynthetic rates, lower transpiration and higher water use efficiency. The elevated CO2 compensated for the negative impact of temperature on water use efficiency (Vu et.al.,2002).

Later experiments also using “Ambersweet” oranges in temperature-gradient greenhouses revealed that elevated CO2 increased total plant growth by about 27% (Allen and Vu, 2009). Different growth parameters respond differently, but the only two measured parameters to not show an increase were leaf growth and fine root biomass. In these experiments, there were no significant interactions between CO2 concentration and temperature (Allen and Vu, 2009).

Temperature, pests and diseases. While there is published literature on the diseases and pests of citrus, very little targets the specific effects of temperature on the severity of disease or pest outbreaks.

It is expected that climate change will increase the risk of new diseases becoming established in agricultural areas (eg. Sutherst et.al.,2000; Vicent and Garcia-Jimenez, 2008). However, more information is required on the exact effects of microclimate on the epidemiology of specific diseases and ecology of potential pests to estimate accurately the risk of establishment.

Citrus canker Citrus canker is a major disease caused by the bacteria Xanthomonas smithii ssp. citri (formerly known as X. axonopodis pv. citri). The effects of temperature and leaf wetness on disease severity were investigated in Brazil, under controlled conditions with a range of temperatures between 12 and 42°C and leaf wetness durations between 0 and 24 hours (Dalla Pria et.al.,2006). Temperature had a greater effect than leaf wetness duration on the severity of citrus canker in the four cultivars tested (“Hamlin”, “Natal”, “Pera” and “Valencia”). The optimum temperature range for the development of the disease is 20 to 35°C. At these temperatures, all plants developed the disease with leaf wetness durations as short as 4 hours. The incidence of the disease is reduced outside of this temperature

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range (i.e. lower than 20°C or higher than 40°C), and severity drops rapidly at temperatures above 35°C (Dalla Pria et.al.,2006).

Phytophthora brown rot

Phytophthora brown rot affects citrus and ornamental trees and is caused by the Phytophthora palmivora and P. nicotianae fungi (Irwin et.al.,1995). This disease is favoured by conditions of high soil moisture and mild temperatures (Irwin et.al.,1995). In Florida, the optimum temperature range for infection is between 27 and 30°C with no development at temperatures below 22°C (Timmer et.al.,2000b).

Alternaria brown spot

The Alternaria brown spot fungus can cause reduced yield and compromised quality in many citrus cultivars. Laboratory experiments revealed that both temperature and leaf wetness affect the severity of infection (Canihos et.al.,1999). Infection was greatest at 27°C, decreased gradually with declining temperature and dropped sharply when temperature increased beyond 32°C. The level of infection also increased with the duration of leaf wetness. Field experiments in Florida revealed that brown spot disease severity was positively, but weakly, related to the amount of rainfall, duration of leaf wetness, and temperature (Timmer et.al.,2000a).

Citrus Leaf Miner

The citrus leafminer (Phyllocnistis citrella) is a serious moth pest in most citrus-growing regions of the world, including Australia. One study found little effect of air temperature on egg-laying, but only investigated a very narrow range of temperatures (18-27°C) (Vercher et.al.,2008).

Moths

The phenology of three moth pests (Helicoverpa armigera, Tortrix capensana and Cryptophlebia leucotreta) was investigated on Navel and Valencia oranges in South Africa (Begemann and Schoeman,1999). Although climatic factors had subtly different effects on the three species, there was a consistent effect of temperature on moth catches. For example, multiple regression analyses showed that moth numbers rose with increasing minimum temperatures for both H. armigera and C. leucotreta. For T. capensana, simple regressions showed that moth numbers increased with ambient temperature.

Aphids

Aphids cause significant damage to agricultural crops through both direct feeding and as a vector for viral diseases (reviewed in Ebert and Cartwright,1997). For the brown citrus aphid (Toxoptera citricida), the optimal range of temperature for population growth was 20 to 30°C (Tsai and Wang, 1999). While the mean generation time decreases with temperature, both survival and reproductive capacity are greatly reduced at temperatures of 32°C or higher. However, it appears that there may be significant inter-population variation in the response to temperature. For example, brown citrus aphid populations in Florida could tolerate higher temperatures than the populations in Japan, and higher temperatures (30°C) resulted in greater fecundity and faster reproduction (Tang et.al.,1999). The authors of this research concluded that different populations of brown citrus aphids may have greater genetic variation than was previously thought.

Mites

Infestations of two-spotted spider mites (Tetranychus urticae) and European red mites (Panonychus ulmi) cause reduced yield and fruit quality in citrus (reviewed in Readshaw, 1975). The duration of the mite life cycle is related to environmental temperature (reviewed in Boudreaux, 1963). The upper temperature limit for the Tetranychus genus appears to be about 38°C where most eggs fail to hatch. The optimum temperature range for development is between 24 and 29°C with the life cycle completed in about 7 to 12 days (Boudreaux, 1963).

Solar injury

Solar injury is a common disorder resulting in reduced fruit quality in tropical and temperate climates, and is caused by high fruit surface temperature, high visible light intensity, and ultraviolet radiation (Glenn et.al.,2008). Lab experiments on citrus peel revealed that UV exposure increases dark respiration, indicating the triggering of UV repair mechanisms (Glenn et.al.,2008).

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Modelling the potential effects of climate change. Simulation models have been used to predict the impacts of climate change on a number of different crops. Some early simulation work on citrus included combinations of three increased temperature regimes and three levels of CO2 enrichment, in addition to current ambient conditions (Rosenzweig et.al.,1996). The authors conclude that the effects of increased temperature and enhanced CO2 will probably counteract each other.

Modelling of citrus production in the southern United States predicts that climate change will have significant benefits until the end of this century (Tubiello et.al.,2002). These models predict significant increases in yield (20-50%), decreased use of irrigation water, and decreased losses to frost and freezing. However, these models also predict limited potential for expansion of citrus growing areas into higher latitudes.

Citrus – Fruit Set Developmental Phase – Critical Temperature Threshold

High temperatures and high atmospheric vapour deficits have been shown to lead to reduced photosynthesis and reduced growth in citrus. In addition, high temperatures (in excess of 30°C) can cause poor flower quality, lower fruit growth, reduced fruit quality and fruit drop in mandarins.

Net photosynthetic rate of citrus trees is greatest between 25°C and 30°C (Kriedemann, 1968).

Table 9: Temperature Effects on Citrus.

Fruit set (near the end of Bloom) – optimum temperature range.

22oC (min)

27oC (max)

A single day maximum over 38C may cause losses.

Source - Ben Mechlia and Carroll, 1989a presented in Rosenzweig et.al.,1996

75% of Australia’s production (24,000 ha) occurs in the Murray and Murrumbidgee Irrigation areas (Riverland region – SA), Sunraysia and mid-Murray (northern Vic & southern NSW) and the MIA (NSW).


References. Allen LH, Vu JCV, 2009. Carbon dioxide and high temperature effects on growth of young orange trees

in a humid, subtropical environment. Agric For Meteorol 149:820-830.

Baker JT, Allen LH, 1993. Contrasting crop species responses to CO 2 and temperature: rice, soybean and citrus. Plant Ecology 104:239-260.

Begemann GJ, Schoeman AS, 1999. The phenology of Helicoverpa armigera (Hubner) (Lepidoptera : Noctuidae), Tortrix capensana (Walker) and Cryptophlebia leucotreta (Meyrick) (Lepidoptera : Tortricidae) on citrus at Zebediela, South Africa. Afr Entomol 7:131-148.

Ben Mechlia N, Carroll JJ, 1989a. Agroclimatic modelling for the simulation of phenology, yield and quality of crop production: 1. Citrus response formulation. Int J Biometeorol 33:36-51.

Ben Mechlia N, Carroll JJ, 1989b. Agroclimatic modelling for the simulation of phenology, yield and quality of crop production: II. Citrus model implementation and verification Int J Biometeorol 33:52-65.

Boudreaux HB, 1963. Biological aspects of some phytophagous mites. Annual Review of Entomology 8:137-154.

139

Bouma TJ, Nielsen KL, Eissenstat DM, Lynch JP, 1997. Estimating respiration of roots in soil: Interactions with soil CO2, soil temperature and soil water content. Plant Soil 195:221-232.

Canihos Y, Peever TL, Timmer LW, 1999. Temperature, leaf wetness, and isolate effects on infection of Minneola tangelo leaves by Alternaria sp. Plant Dis 83:429-433.

Dalla Pria M, Christiano RCS, Furtado EL, Amorim L, Bergamin A, 2006. Effect of temperature and leaf wetness duration on infection of sweet oranges by Asiatic citrus canker. Plant Pathol 55:657-663.

Dhakhwa GB, Campbell CL, 1998. Potential effects of differential day-night warming in global climate change on crop production. Clim Change 40:647-667.

Downton WJS, Grant WJR, Loveys BR, 1987. Carbon dioxide enrichment increases yield of Valencia orange. Australian Journal of Plant Physiology 14:493-501.

Ebert TA, Cartwright B, 1997. Biology and ecology of Aphis gossypii Glover (Homoptera: Aphididae). Southw Entomol 22:116-153.

Garcia-Delgado MA, Zermeno-Gonzalez A, Lee-Rodriguez V, Castro-Meza BI, Briones-Encinia F, Aguirre-Bortoni MDJ, 2004. Effect of misting on air temperature and humidity and its relationship with fruit set and yield of navel orange. Agrociencia 38:643-651.

Glenn DM, Wunsche J, McIvor I, Nissen R, George A, 2008. Ultraviolet radiation effects on fruit surface respiration and chlorophyll fluorescence. J Horticult Sci Biotechnol 83:43-50.

GraftonCardwell EE, Ouyang YL, Striggow RA, 1997. Predaceous mites (Acari: Phytoseiidae) for control of spider mites (Acari: Tetranychidae) in nursery citrus. Environ Entomol 26:121-130.

Hu LM, Xia RX, Xiao ZY, Huang RH, Tan ML, Wang MY, Wu QS, 2007. Reduced leaf photosynthesis at midday in citrus leaves growing under field or screen house conditions. J Horticult Sci Biotechnol 82:387-392.

Hutton RJ, Landsberg JJ, 2000. Temperature sums experienced before harvest partially determine the post-maturation juicing quality of oranges grown in the Murrumbidgee Irrigation Areas (MIA) of New South Wales. J Sci Food Agric 80:275-283.

Idso CD, Idso SB, Kimball BA, Park HS, Hoober JK, Balling RC, 2000. Ultra-enhanced spring branch growth in CO2-enriched trees: can it alter the phase of the atmosphere's seasonal CO2 cycle? Environ Exp Bot 43:91-100.

Idso S, Kimball B, 1997. Effects of long-term atmospheric CO2 enrichment on the growth and fruit production of sour orange trees. Glob Change Biol 3:89-96.

Idso SB, Kimball BA, 2001. CO2 enrichment of sour orange trees: 13 years and counting. Environ Exp Bot 46:147-153.

Irwin JAG, Cahill DM, Drenth A, 1995. Phytophthora in Australia. Aust J Agric Res 46:1311-1338.

Kimball BA, Idso SB, Johnson S, Rillig MC, 2007. Seventeen years of carbon dioxide enrichment of sour orange trees: final results. Glob Change Biol 13:2171-2183.

Kriedemann PE, 1968. Some photosynthetic characteristics of citrus leaves. Aust J Biol Sci 21:895-905.

Lobell DB, Cahill KN, Field CB, 2007. Historical effects of temperature and precipitation on California crop yields. Clim Change 81:187-203.

Marsh KB, Richardson AC, MacRae EA, 1999. Early- and mid-season temperature effects on the growth and composition of satsuma mandarins. J Horticult Sci Biotechnol 74:443-451.

Medina CL, Souza RP, Machado EC, Ribeiro RV, Silva JAB, 2002. Photosynthetic response of citrus grown under reflective aluminized polypropylene shading nets. Sci Hortic 96:115-125.

O'Connell NV, Snyder RL, 1999. Cover Crops, Mulch Lower Night Temperatures in Citrus. California Agriculture 53:37-40.

Ogata T, Hirota T, Shiozaki S, Horiuchi S, Kawase K, Ohashi M, 2002. Effects of aminoethoxyvinylglycine and high temperatures on fruit set and fruit characteristics of heat-cultured satsuma mandarin. J Jpn Soc Hortic Sci 71:348-354.

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Paulino SEP, Mourao FDA, Maia ADN, Aviles TEC, Neto DD, 2007. Agrometeorological models for 'Valencia' and 'Hamlin' sweet oranges to estimate the number of fruits per plant. Sci Agric 64:1-11.

Pregitzer KS, King JA, Burton AJ, Brown SE, 2000. Responses of tree fine roots to temperature. New Phytol 147:105-115.

Raveh E, Cohen S, Raz T, Yakir D, Grava A, Goldschmidt E, 2003. Increased growth of young citrus trees under reduced radiation load in a semi-arid climate. J Exp Bot 54:365-373.

Readshaw JL, 1975. The ecology of tetranychid mites in Australian orchards. Journal of Applied Ecology:473-495.

Ribeiro RV, Machado EC, Oliveira RF, 2004. Growth- and leaf-temperature effects on photosynthesis of sweet orange seedlings infected with Xylella fastidiosa. Plant Pathol 53:334-340.

Richardson AC, Marsh KB, Macrae EA, 1997. Temperature effects on satsuma mandarin fruit development. J Horticult Sci 72:919-929.

Rosenzweig C, Phillips J, Goldberg R, Carroll J, Hodges T, 1996. Potential impacts of climate change on citrus and potato production in the US. Agric Syst 52:455-479.

Soon W, Baliunas SL, Robinson AB, Robinson ZW, 1999. Environmental effects of increased atmospheric carbon dioxide. Clim Res 13:149-164.

Storey R, Treeby MT, 1999. Short- and long-term growth of navel orange fruit. J Horticult Sci Biotechnol 74:464-471.

Sutherst R, Maywald G, Russell B, 2000. Estimating vulnerability under global change: modular modelling of pests. Agriculture, Ecosystems and Environment:303-319.

Tang YQ, Lapointe SL, Brown LG, Hunter WB, 1999. Effects of host plant and temperature on the biology of Toxoptera citricida(Homoptera: Aphididae). Environ Entomol 28:895-900.

Timmer LW, Darhower HM, Zitko SE, Peever TL, Ibanez AM, Bushong PM, 2000a. Environmental factors affecting the severity of Alternaria brown spot of citrus and their potential use in timing fungicide applications. Plant Dis 84:638-643.

Timmer LW, Zitko SE, Gottwald TR, Graham JH, 2000b. Phytophthora brown rot of citrus: Temperature and moisture effects on infection, sporangium production, and dispersal. Plant Dis 84:157-163.

Tsai JH, Wang K, 1999. Life table study of brown citrus aphid(Homoptera: Aphididae) at different temperatures. Environ Entomol 28:412-419.

Tubiello FN, Rosenzweig C, Goldberg RA, Jagtap S, Jones JW, 2002. Effects of climate change on US crop production: simulation results using two different GCM scenarios. Part I: Wheat, potato, maize, and citrus. Clim Res 20:259-270.

Vercher R, Farias A, Marzal C, Soto A, Tena A, Garcia-Mari F, 2008. Factors influencing adult female oviposition in the citrus leafminer Phyllocnistis citrella. Agric For Entomol 10:45-51.

Vicent A, Garcia-Jimenez J, 2008. Risk of establishment of non-indigenous diseases of citrus fruit and foliage in Spain: An approach using meteorological databases and tree canopy climate data. Phytoparasitica 36:7-19.

Vu JCV, Newman YC, Allen LH, Gallo-Meagher M, Zhang MQ, 2002. Photosynthetic acclimation of young sweet orange trees to elevated growth CO2 and temperature. J Plant Physiol 159:147-157.

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The influence of temperature of the growth and development of pineapples (Ananas comosus). The Pineapple industry supplies both the processing sector which is not expanding, and the fresh market sector which has been expanding since the mid 1990’s with the introduction of fresh market hybrids. Golden Circle Ltd is the only processor of pineapple in Australia.

Location Pineapple production occurs mainly in Queensland (with a very small area in NT). 70% of processed fruit, and 60% of the fresh market fruit are grown in southern Queensland. 30% of the processed fruit and 20% of fresh market fruit are grown in Central Queensland, and the remainder is grown in Far North Queensland (20% of fresh market fruit).

Table 10: Queensland pineapple production Districts.

District Number of farms

North Qld (North of Mackay) 14

Central Qld (Cawarral & Yeppoon) 18

Wide bay (Bundaberg, Hervey Bay & Maryborough) 29

Mary Valley & Nambour 8

Beerwah & Glasshouse Mountains 20

Wamuran & Elimbah 21

Total 110

Production and value The industry reached a peak of 6,660 ha in 1988. There are now less than 6,000 ha of pineapple grown in Queensland by about 110 growers.

Production for the processing market has declined in significant steps over recent years as Golden Circle Ltd strives to maintain profitability. Intake for the 2008/2009 year is estimated at 60,000 t. This will decrease to 40,000 t for the 2009/2010 season. Because there are two years between planting and harvest, growers have already planted many of the plants scheduled for the 2009/2010 season. It is likely this will be sold on the fresh market and is expected to cause a period of oversupply.

Table 11: Total Australian pineapple production. Year ended 30 June 2007

Qld NT Total 2007 Total 2006

Production (t) 164,691 42 164,732 153,015

Area (ha) 2731 5 2736 3034

Yield (t/ha) 60 60 50 (Source: ABS Catalogue 7121, 2006-07)

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Table 12: Market sector production (t) and value ($m)

Industry sector 2007/2008 2008/2009

Fresh market -’hybrids’

21,000 t 25,000 t

Fresh market – Cayenne

19,000 t 24,000 t

Processing market 60,000 t 60,000 t

Value processed $22.0m

Value fresh $44.3m

Total industry value $66.3m (Source: Golden Circle Ltd, Tropical Pines and Pinata Marketing)

Table 13: Processed pineapple detail for year ended Dec 2008

Grade (t) $/t Total value ($m)

Bulk 59,000 362 21.5

Juice 7,000 90 0.5

Total 22 (Source: Golden Circle Ltd)

There is a limited amount of peer-reviewed literature on the influence of temperature on pineapple growth and development both in Australia and around the world. This shortage of detailed research probably results from the view that crops such as pineapples, agaves and cacti that feature Crassulacean Acid Metabolism (CAM) are well-suited to hot and dry climates, and that the effects of raised temperature on these crops have been considered a low research priority. Much of the work that exists has been recently reviewed in Bartholomew et al. (2003b). However, the results of many of the existing studies performed in controlled environments may not necessarily extrapolate to field conditions, and there remains a need for detailed field research on the effect of various environmental factors on pineapple yield and fruit quality (Malezieux et al., 2003).

The Influence of Temperature on Specific Growth and Development Phases of Pineapple. Pineapple cultivation and physiology. The pineapple (Ananas comosus) is the third most important tropical fruit in world production (following banana and citrus)(Rohrbach et al., 2003) and the most important cultivated crop featuring CAM.

Thailand produces the most pineapples on a yearly basis, followed by the Philippines, Brazil, China and India. Australia is well down the list in terms of total productivity (16th in 2001, with about 140,000 t) but is among the highest in terms of yield (47 t/ha) and production efficiency (Rohrbach et al., 2003).

Pineapple is well suited to areas of low rainfall but does suffer reduced productivity in drought conditions (Malezieux et al., 2003). The crassulacean acid metabolism (CAM) photosynthetic pathway contributes to pineapples ability to grow productively under conditions of water stress (low rainfall and high temperatures). CAM is characterised by the nocturnal uptake of CO2 via open stomata and the daytime remobilisation of CO2 behind closed stomata (Luttge, 2004). The closure of stomata during the period of highest temperature and lowest humidity results in higher water use efficiency (WUE) in CAM plants compared to plants with other conventional photosynthetic pathways. Increased WUE in CAM plants is often considered to be the greatest benefit of the CAM pathway (Luttge, 2004), but CAM plants may also display more efficient light utilisation and carbon assimilation at higher temperatures (Osmond et al., 2008). Indeed, many CAM plants are typical inhabitants of arid environments (eg. cacti and agaves); however, CAM plants can be found in other habitats with problems with water supply (such as epiphytes in tropical rainforests).

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In addition to water availability, five other environmental factors have been identified as important for CAM plants – temperature, light, CO2, salinity and nutrients (reviewed in Luttge, 2004; Malezieux et al., 2003). The remainder of this review will concentrate on the effects of temperature and temperature-induced water stress.

Temperature and photosynthesis.

In a review of heat tolerance among a number of tropical fruit crops, pineapple was found to be one of the most tolerant of temperature and water stresses (Yamada et al., 1996). The intensity of the CAM pathway, and therefore the efficiency of photosynthesis, is highest at a day/night temperature of approx 30/20°C (Malezieux et al., 2003). At a given day temperature, an increase in the night temperature results in a drop in CO2 uptake (Malezieux et al., 2003; Neales et al., 1980; Zhu et al., 1999). For example, at a constant day temperature of 30°C, an increase in night temperature from 20 to 25°C resulted in a 50% decrease in CO2 uptake (Neales et al., 1980; Zhu et al., 1999). In contrast, at a fixed night temperature, a increase in day temperature results in an increase in the CO2 assimilated (Neales et al., 1980; Zhu et al., 1999).

Temperature transpiration and water use efficiency.

The effects of environmental factors on photosynthesis are closely linked to their effects on plant water relations. Leaf conductance is greater under cool conditions that favour stomatal opening (Neales et al., 1980) and water use efficiency (WUE) is greater under lower night temperature conditions. Pineapple plants maintained at a day/night temperature of 30/20°C have approx. 1.3 times greater night WUE than those maintained at 30/25°C (Zhu, 1996). Despite the lack of field data on WUE and stomatal conductance, Malezieux et al. (2003) predicted that water use would be higher in tropical environments with high night temperatures and a small day/night temperature differential than in subtropical environments with lower night temperatures and larger day/night temperature differentials.

The effect of temperature on pineapple productivity – flowering, yield and quality. Flowering

In commercial pineapple crops, flowering is artificially induced or forced using a chemical agent (Van de Poel et al., 2009). As a result, natural environmental variations have a relatively minor effect on flowering in commercial crops, although the factors that promote natural flower induction can increase sensitivity to chemical forcing (Bartholomew et al., 2003a). In particular, cool temperatures enhance the flowering response of pineapples (reviewed in Bartholomew et al., 2003a). The early work of Van Overbeek and Cruzado (1948, cited in Bartholomew et al., 2003a) revealed that a minimum night temperature of 16°C induced more flowering than 22°C in the variety ‘Red Spanish’. In a study of ‘Smooth Cayenne’ plants grown in greenhouses at night temperatures of 15, 20, 25 and 30°C, flowering was most rapid at 15°C and did not occur after 3 years at 30°C (Friend, 1981). The effectiveness of various chemical agents may also be temperature dependent. For example, high temperatures can lead to reduced uptake of ethephon, and the solubility of ethylene gas in water (the preferred delivery method) is reduced at higher temperatures (Van de Poel et al., 2009).

There may be an interaction between the effects of temperature and day length on fruiting. For example, for a short day length, a night temperature of 15°C was more successful in inducing flowering than temperatures of 23°C and 26°C (variety ‘Smooth Cayenne’). The same low temperature did not induce flowering at a normal day length (Gowing, 1961). The period of exposure may also be important. While a constant 20°C for 10 weeks induced flowering in 100% of specimens, a constant 10 or 15°C for up to 12 weeks did not induce flowering (Sanewski et al., 1998).

Natural induction of flowering can also be triggered by short periods of high temperatures. In this situation, it is thought that induction may be caused by wound-induced ethylene production (Sinclair, 1997).

In tropical countries, night temperatures above 25°C can reduce the number of plants forced and the size of the resulting fruit (Min and Bartholomew, 1997). Water stress may also reduce the response of plants to artificial forcing (Bartholomew et al., 2003a).

Fruit growth.

The optimum day/night temperature regime for maximum growth is approx. 30/20°C with an optimum mean temperature of approx. 23 to 24°C. The rate of plant growth decreases at temperatures below

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15°C or above 32°C (Neild and Boshell, 1976). Fruit growth has been shown to stop at temperatures below about 10°C and above about 35°C (Bartholomew et al., 2003a; Malezieux et al., 1994).

Despite the ability of pineapples to withstand high temperatures and drought conditions, these factors do have important consequences for growth. Under conditions of prolonged drought, growth and yield can be reduced significantly, and growth may actually stop under severe drought conditions (Malezieux et al., 2003; Swete Kelly and Bartholomew, 1993). Fortunately, the effects of drought are largely reversible and growth resumes when water becomes available. The symptoms associated with water stress in drought conditions may be exacerbated where soil moisture-holding capacity is low, where rooting depth is restricted or where the root system has been damaged by pests or disease (Broadley et al., 1993).

Similarly, extreme temperatures on leaves appears to cause little permanent harm, but the specific effects on physiological processes are not well understood (reviewed in Malezieux et al., 2003). The effect of temperature on growth can be complex; for example, it affects morphology in the variety ‘Smooth Cayenne’. While plant growth rate of pineapple is strongly influenced by temperature, there are few studies from controlled environmental conditions and the results of field studies have been difficult to interpret (reviewed in Malezieux et al., 2003). Pineapple plants attain greater weights when grown at night temperatures below 26°C compared to those grown at 30°C (Bartholomew, 1982). After a growth period of about 400 days, plants grown at the lower night temperatures attained two to three times the weight of those grown at the higher night temperature.

The effect of temperature on growth varies subtly with the developmental stage of the fruit. For ‘Smooth Cayenne’ pineapples in Hawaii, low night temperatures of about 15°C during a period 2 to 4 months before harvest produced higher fruit weight at harvest, while fruit weight is reduced if exposed to higher temperatures (30°C) during the same period (Friend, 1981). Subsequent work showed that, in the early stages of development (between induction and 1.3cm), growth is correlated with cumulative thermal time based on air maximum and minimum temperatures (Fleisch and Bartholomew, 1987). Following this stage, growth is more closely related to cumulative thermal time based on fruit temperature which can be influenced by irradiance (Malezieux et al., 1994). Exposure to direct sunlight can lead to elevated fruit temperatures relative to surrounding air temperature, and the temperature difference between exposed and shaded sides can be as much as 13°C (Teisson 1973, cited in Bartholomew et al., 2003a).

The total duration of fruit development can be variable in subtropical regions. In southern Queensland, the time of harvest can range from 180 to 280 days following forced induction (Sinclair, 1992).

Fruit quality.

High temperatures are not considered to be a major concern during vegetative growth of pineapples, while low temperature injury is of concern in areas where frosts may occur (Malezieux et al., 2003). However, both high and low temperatures can cause injury to fruits, and frost-damaged fruit are unmarketable as fresh fruit (Swete Kelly and Bartholomew, 1993).

High temperatures and high irradiance can lead to fruit sunburn, which can range from discolouration to severe injury including translucent or desiccated flesh. If sunburn injury occurs during the early stages of fruit development, the resulting fruit can be deformed. Cooking of the fruit can result from very high air temperatures (above 40°C) and result in fruit that are pale or translucent near the core (Swete Kelly and Bartholomew, 1993). Sunburned or cooked fruit are not only unmarketable as fresh fruit, but are also rejected for processing (Bartholomew et al., 2003a).

A period approx. 2 to 3 months prior to harvest appears to be critical in the development of translucency. In a study of Hawaiian field grown pineapples, the incidence of fruit translucency was most closely correlated with minimum and maximum air temperatures 2 to 3 months before harvest (Paull and Reyes, 1996). Translucency was most severe when both minimum and maximum temperatures were low (15°C and 23°C, respectively), but there was also a peak in translucency when minimum and maximum temperatures were both high (18°C and 28°C)(Paull and Reyes, 1996).

Shading materials or reflective coatings can protect against fruit sunburn (Swete Kelly and Bartholomew, 1993) but may not necessarily protect against translucency. Fruit temperature appeared to only have a significant effect on translucency when a heat-tolerance limit of flesh tissue was exceeded (Chen and Paull, 2001).

Very high temps (>35oC) will cause natural flower initiation, and a few weeks before harvest up to harvest can cause sunburn of fruit and upper leaves.

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There appear to be few published studies on the effects of drought on fruit development. Fruit weight is dependent on water availability, and decreased as irrigation interval was extended from twice weekly to bimonthly (Chapman et al., 1983 in Malezieux et al., 2003). Other work demonstrates reductions in the number of fruitlets or fruit weight with decreased water availability (reviewed in Bartholomew et al., 2003a).

Simulation models.

Simulation models have been developed that can predict harvest dates with “reasonable” accuracy based on the accumulation of heat units and a combination of air and fruit temperatures (Malezieux et al., 1994). This model was able to predict harvest date in a number of regions (Australia, Côte d’Ivoire, Hawaii and Thailand) with a mean error of less than 12 days. Further refinements of this model (“ALOHA-Pineapple” version 2.1) include the phasic development of plant leaf area, dry matter accumulation, and the partitioning of assimilates to stem, leaves, and fruit. The model performed well in a number of locations with different types of planting material and will be further refined as new data becomes available (Zhang et al., 1995).

The effects of elevated CO2. Elevated CO2 has been shown to increase the rate of CO2 fixation (Zhu et al., 1997). Water use efficiency over a 24 hour period can be 1.3 to 1.6 times greater at elevated CO2 levels (710 v 355 µmol mol-1), depending on the day/night temperature regime (Zhu et al., 1999). At approximately double ambient CO2 levels, WUE increases about 1.1-1.2 times during the night and 2.3-2.7 times during the day (Zhu et al., 1999).

There appears to be an interaction between the effects of CO2 and temperature on carbon assimilation and growth (Zhu et al., 1999). Experiments in controlled environment chambers demonstrated that elevated CO2 produced increases in both carbon assimilation and WUE, but that the elevated CO2 reduces the negative effect of higher temperatures on these two factors (Zhu et al., 1999). Based on these results, the authors concluded that the simultaneous increases in temperature and CO2 expected under climate change scenarios would be expected to increase growth rates in pineapples.

It should be noted that the level of elevated CO2 used in these experiments (700 µmol mol-1 or about double current ambient) is far in excess of the desired maximum level used to inform emissions policy decisions (approx 450 µmol mol-1) and there must be some questions about how these results will relate to a gradual increase in CO2 under field conditions. For all cultivated CAM plants (pineapples, cacti and agave), it is expected that daily net CO2 uptake and biomass production will increase by about 1% for every 10ppm increase it atmospheric CO2 (Nobel, 2000).

Future directions. The physiological characteristics of CAM plants suggest that they may have advantages over crops with conventional photosynthetic pathways in the changing climate of the future. For example, it is expected that the predicted rise in global mean temperatures will increase the latitudinal range of these species (Nobel, 1996). Furthermore, the increase in atmospheric CO2 will also be advantageous for productivity and water use efficiency in CAM crops (Nobel, 2000).

Of tropical fruit crops grown commercially, the pineapple is one of the most tolerant of both heat and water stresses (Yamada et al., 1996). It is expected that pineapple (and other CAM crops) will have predictable and probably favourable responses to predicted climatic changes over the coming decades (Nobel, 2000). The expansion of commercial cropping of CAM plants in those areas likely to suffer increased temperature and water stress may be an important adaptive strategy (Jose et al., 2007). Despite these potential advantages, further research is required to enhance yields under changing conditions (Nobel, 2000).

Pineapples - Developmental Phase – Critical Temperature Threshold The physiological characteristics of CAM plants suggest that they may have advantages over crops with conventional photosynthetic pathways in the changing climate of the future. For example, it is expected that the predicted rise in global mean temperatures will increase the latitudinal range of these

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species (Nobel, 1996). Furthermore, the increase in atmospheric CO2 will also be advantageous for productivity and water use efficiency in CAM crops (Nobel, 2000).

High temperatures are not considered to be a major concern during vegetative growth of pineapples (Malezieux et al., 2003). High temperatures and high irradiance can lead to fruit sunburn, which can range from discolouration to severe injury including translucent or desiccated flesh. If sunburn injury occurs during the early stages of fruit development, the resulting fruit can be deformed. Cooking of the fruit can result from very high air temperatures (above 40°C) and result in fruit that are pale or translucent near the core (Swete Kelly and Bartholomew, 1993). Sunburned or cooked fruit are not only unmarketable as fresh fruit, but are also rejected for processing (Bartholomew et al., 2003a).

Fruit growth has been shown to stop at temperatures below about 10°C and above about 35°C (Bartholomew et al., 2003a; Malezieux et al., 1994). Very high temps (>35oC) will cause natural flower initiation, and a few weeks before harvest up to harvest can cause sunburn of fruit and upper leaves.

Table 14: Pineapple Production Districts (Queensland).

District

North Qld (North of Mackay)

Central Qld (Cawarral & Yeppoon)

Wide bay (Bundaberg, Hervey Bay & Maryborough)

Mary Valley & Nambour

Beerwah & Glasshouse Mountains

Wamuran & Elimbah

References: Bartholomew DP, 1982. Environmental control of carbon assimilation and dry matter production by

pineapple. Crassulacean Acid Metabolism:278–294.

Bartholomew DP, Malezieux E, Sanewski GM, Sinclair E, 2003a. Inflorescence and fruit development and yield. In: The pineapple: botany, production, and uses (Bartholomew DP, Paull RE, Rohrbach KG, eds); 167.

Bartholomew DP, Paull RE, Rohrbach KG, 2003b. The pineapple: botany, production, and uses: CABI.

Broadley RH, Wassman RC, Sinclair ER. eds, 1993. Pineapple pests and disorders. Brisbane: Queensland Department of Primary Industries.

Chen C-C, Paull RE, 2001. Fruit temperature and crown removal on the occurrence of pineapple fruit translucency. Sci Hortic 88:85-95.

Fleisch H, Bartholomew DP, 1987. Development of a heat unit model of pineapple ('Smooth Cayenne') fruit growth from field data. Fruits 42:709-715.

Friend DJC, 1981. Effect of Night Temperature on Flowering and Fruit Size in Pineapple (Ananas comosus [L.] Merrill). Botanical Gazette 142:188-190.

Gowing DP, 1961. Experiments on the photoperiodic response in pineapple. American Journal of Botany 48:16-21.

Jose JS, Montes R, Nikonova N, 2007. Seasonal patterns of carbon dioxide, water vapour and energy fluxes in pineapple. Agric For Meteorol 147:16-34.

Luttge U, 2004. Ecophysiology of crassulacean acid metabolism (CAM). Ann Bot 93:629.

Malezieux E, Cote F, Bartholomew DP, 2003. 5 Crop Environment, Plant Growth and Physiology. In: The pineapple: botany, production, and uses (Bartholomew DP, Paull RE, Rohrbach KG, eds); 69.

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Malezieux E, Zhang JB, Sinclair ER, Bartholomew DP, 1994. Predicting pineapple harvest date in different environments, using a computer simulation model. Agron J 86:609-617.

Min XJ, Bartholomew DP, 1997. Temperature affects ethylene metabolism and fruit initiation and size of pineapple. Acta Horticulturae 425:329-338.

Neales TF, Sale PJM, Meyer CP, 1980. Carbon dioxide assimilation by pineapple plants, Ananas comosus (L.) Merr. II. Effects of variation of the day/night temperature regime. Australian Journal of Plant Physiology 7:375-385.

Neild RE, Boshell F, 1976. An agroclimatic procedure and survey of the pineapple production potential of Colombia. Agricultural Meteorology 17:81-92.

Nobel PS, 1996. Responses of some North American CAM plants to freezing temperatures and doubled CO2concentrations: implications of global climate change for extending cultivation. Journal of Arid Environments 34:187-196.

Nobel PS, 2000. Crop ecosystem responses of climatic change. Crassulacean acid metabolism crops. Climate Change and Global Crop Productivity:315-331.

Osmond B, Neales T, Stange G, 2008. Curiosity and context revisited: crassulacean acid metabolism in the Anthropocene. J Exp Bot 59:1489-1502.

Paull RE, Reyes MEQ, 1996. Preharvest weather conditions and pineapple fruit translucency. Sci Hortic 66:59-67.

Rohrbach KG, Leal F, Coppens DEG, 2003. I History, Distribution and World Production. In: The pineapple: botany, production, and uses (Bartholomew DP, Paull RE, Rohrbach KG, eds); 1-12.

Sanewski GM, Sinclair E, Jobin-Décor E, Dahler G, 1998. Preliminary studies into the effects of temperature on flower initiation of smooth cayenne in south east Queensland. In: Abstracts, Third International Pineapple Symposium. Pattaya, Thailand: Horticultural Research Institute; 57.

Sinclair ER, 1992. Seasonal growth rates in pineapple. In: Pineapple Field Day Book. Beerwah, Queensland: Pineapple Industry Farm Committee; 9-21.

Sinclair ER, 1997. Weather Summary for 1996/97. In: Pineapple Field Day Book. Beerwah, Queensland: Pineapple Industry Farm Committee; 29.

Swete Kelly D, Bartholomew DP, 1993. Other disorders. In: Pineapple Pests and Disorders (Broadley RH, Wassman RC, Sinclair E, eds). Brisbane

Queensland Department of Primary Industries; 43-52.

Van de Poel B, Ceusters J, De Proft MP, 2009. Determination of pineapple (Ananas comosus, MD-2 hybrid cultivar) plant maturity, the efficiency of flowering induction agents and the use of activated carbon. Sci Hortic 120:58-63.

Yamada M, Hidaka T, Fukamachi H, 1996. Heat tolerance in leaves of tropical fruit crops as measured by chlorophyll fluorescence. Sci Hortic 67:39-48.

Zhang J, Bartholomew DP, Malézieux E, 1995. ALOHA-Pineapple v. 2.1: a computer model to predict the growth, development and yield of pineapple. ISHS; 287-296.

Zhu J, 1996. Physiological responses of pineapple (Ananas comosus (L.) Merr.) to CO enrichment, temperatures and water deficit: University of Hawaii.

Zhu J, Bartholomew DP, Goldstein G, 1997. Effect of elevated carbon dioxide on the growth and physiological responses of pineapple, a species with Crassulacean acid metabolism. J Am Soc Hortic Sci 122:233-237.

Zhu J, Goldstein G, Bartholomew DP, 1999. Gas exchange and carbon isotope composition of Ananas comosus in response to elevated CO 2 and temperature. Plant, Cell and Environment 22:999-1007.

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The influence of temperature of the growth and development of tomato (Lycopersicon esculentum). Summary For tomato, the 8 to 13 day period prior to anthesis is the most critical developmental phase. The critical temperature for this phase varies according to the cultivar tolerance to elevated temperatures. In tomato, elevated temperature impacts are complex, and it is difficult to determine one critical temperature effect during the reproductive development phase. In experiments conducted to determine critical temperature effects, sensitive cultivars are impacted when mean daily temperatures exceed 25oC, whereas more heat tolerant cultivars are not impacted until temperatures exceed 32oC.

The literature reviewed so far has not identified a narrow band of temperatures at which a significant reduction in yield and/or quality will occur, except to say that for current cultivars, temperatures above 32°C which occur over the pre-anthesis development phase, will have an adverse effect on pollen viability, fruit set and yield.

Production of tomatoes does occur in regions where temperatures exceed 32°C during the pre-anthesis phase. Assessment of the recent maximum temperature regimes which have occurred in these production regions during the pre-anthesis development phase, will provide additional information to allow a narrowing down of the temperature threshold for this crop development phase.

Tomato production throughout the world. World production of tomatoes was 126 million tonnes in 2007 (FAOSTAT). Major producers are China (approx. 34 million tonnes), the US (12 million tonnes) and Turkey (10 million tonnes).

In Australia, tomatoes are produced in Queensland (Bowen, Bundaberg, Lockyer Valley), NSW (Narromine, MIA, Sydney basin), Vic (Goulburn Valley - including processing), SA (Murray Bridge, Adelaide Plains) and WA.

Table 15 : Australian fresh tomato production. Year ended 30 June 2007

NSW Vic Qld SA WA Tas NT Total

Production (tonnes) 35,937 123,640 120,656 4,313 11,009 434 46 296,035

Area (ha) 798 2312 3,743 78 355 6 2 7,293 (Source: ABS Catalogue 7121, 2006-07)

Processing tomato production (147,544 tonnes in 2007-08) is largely confined to Victoria. Table 16: Value of fresh tomato industry. Year ended 30 June 2006

NSW Vic Qld SA WA Tas Australia Value($m) 19.7 74.7 145.2 13.6 18.6 0.8 272.8


The Influence of Temperature on Specific Growth and Development Phases. Flowering, Pollination and Fruit Set

Significant flower drop occurs in tomato when daytime temperatures exceed 30oC and night time temperatures exceed 20oC (Rudich, et.al., 1977). This results in reduced fruit set (Went, 1944), because of the adverse effect of temperature on pollen germination and pollen viability (Sato, et.al., 2006).

Johnson and Hall (1953) report that pollen sterility occurs at temperatures between 35 oC and 38oC, but fruit set will be impacted prior to achieving these high temperatures, when working with both

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temperature sensitive and tolerant cultivars. They conclude that high daytime temperatures in excess of 35oC affects pollen viability and hence fertilization.

Higashide (2009) reports on a range of research papers (including Sato, et.al., 2002) which show that the time period of 8 - 15 days prior to anthesis in tomato to be the critical period where high temperatures adversely affect yield by influencing fruit set.

Peet et.al. (1997) report that mean daily temperatures of 27oC and 29oC which are only a few degrees above optimal, can have adverse effects on tomato fruit set and yield. They further demonstrate that the effects are independent of either day or night extremes, and daily mean temperature explained the most variation between temperature treatments. “The higher the daily mean temperatures in the range 25-29oC, the lower all the various indices of reproductive fitness. In most cases the decreases were linear.” They conclude that attempting to understand the effects of increasing temperatures under a changing climate can therefore be simplified by using daily mean temperatures, rather the more complex issues associated with assessing both day and night maximums. Varieties vary in their sensitivity to temperature and this will influence pollination and fruit set. Under marginal conditions fruit may set without adequate pollination but the internal fruit segments will contain few seeds and the tomato will be flat sided and puffy. Irregular pollination can also cause the fruit disorder known as catface. Fruit setting is reduced when temperatures fall below 10°C or rise above 27°C. Optimum temperature for fruit set is 18° to 24°C (Lovatt, et.al, 1998). The effect of temperature on fruit yield and quality. Basic temperature relationships. The tomato (Lycopersicon esculentum) has the ability to compensate for temperature variation within a certain range and period (De Koning, 1990). Mean temperature and the cumulative temperature sum (over a certain period) have greater effects on development than maximum or minimum temperatures. Only large temperature variations inhibited the development of the young plants slightly. This quality of tomatoes may provide a cushion for short-term, transient extreme temperatures likely to be encountered in the coming decades.

Other research into the effect of temperature on fruit growth and load of tomatoes (De Koning, 1989) involved applying different temperatures during an 8 week period from first flowering (17, 19, 21 and 23C). The temperature was held at a constant 18C before and after this period. Fruit growth was calculated from weekly measurements of fruit diameter and fresh weight of each fruit. High temperature enhanced early fruit growth at the expense of vegetative growth. Also, fruit growth continued at different rates even after the standard temperature had been restored to all treatments. These after effects of temperature on fruit growth can be explained by the influence of temperature on the assimilate partitioning within the plant.

Greenhouse experiments demonstrated that time to first flowering is negatively related to mean daily temperature at any given mean cumulative daily light intensity. Mean fruit weight increased with daily light intensity. Fruit production rate peaks at between 22 and 25C (depending on light intensity) and then decreased at higher temperatures (Uzun, 2007).

Other greenhouse experiments revealed that the total number and weight of fruit decreases as mean daily temperature increased above 25C (Peet et al., 1997). Importantly, mean daily temperature was the primary parameter driving fruiting, rather than day temperature, night temperature or the day-night range (confirming the earlier work of (De Koning, 1990)). This observation should simplify predicting the effects of projected climate change.

Field observations of tomato crops at four sites in the Mediterranean region over a three year period (1997-1999) showed that the proportional change of fruit types (i.e. percentage total fruit weight) was closely related to the accumulation of daily maximum temperature during crop maturation. The relationship was clearer for the percentage change in green fruit than for ripe fruit. Heat units were calculated based on the daily maximum and minimum temperatures by six different well-known methods. The reduction in percentage green fruit was significantly related to the sum of heat units calculated by all methods. However, the simplest method based on daily maximum temperature alone is as accurate as all the more complex methods (Machado et al., 2004)

Considerable effort has been invested in research on the effects of sub-optimal temperatures on growth, development and yield of tomato, reflecting the northern hemisphere, cool-climate focus (eg

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(Van Der Ploeg and Heuvelink, 2005). Temperature has a large effect on all aspects of development. Both leaf and fruit truss initiation rates decrease linearly with decreasing temperature. This response to temperature is the same across different varieties, although the rates of change may vary. Fruit set is reduced at cooler temperatures as a result of poorer pollen quality. (Van Der Ploeg and Heuvelink, 2005)

As series of greenhouse experiments demonstrated that truss flowering rate increased linearly with increasing daily temperature. Similarly, the number of flowering trusses had a positive linear relationship with temperature sum (Pek and Helyes, 2004).

(Adams et al., 2001) investigated the effect of temperature on the growth and development of tomato fruits. They developed a thermal time model of fruit maturation based on experimental treatments at four different but consistent temperature regimes. However, this thermal time model proved to be a poor fit to growth data when buds/fruits were heated at different stages in their development. Fruits were more sensitive to elevated temperature in their later stages of maturation. Temperature also affected the rates of fruit growth in volume, with low temperatures reducing the absolute volume growth rates. However, the response of fruit growth to temperature differed when only the temperature of the fruits themselves was modified. There was a tendency towards small parthenocarpic fruits at both high (26C) and low (14C) temperature regimes which, combined with low flower numbers and poor fruit set at 26C, resulted in low fruit yields. Temperature also affected the shoot dry matter content and partitioning (Adams et al., 2001).

The effects of minimum air temperatures during the seedling stage on single-truss tomatoes were studied by (Wada et al., 2001). Tomato seedlings were grown hydroponically in a greenhouse at 5 degrees, 10 degrees, 15 degrees and 20C. Plant growth increased as the minimum air temperature increased. Shoot fresh weight, plant height and leaf area were greatest at 20C. Leaf number increased in proportion to the integrated effective air temperature. As the minimum air temperature at the seedling stage was lowered, the number of flowers per plants significantly increased for most varieties. Fruit were heavier on seedlings exposed to 5 and 10C than at 15 and 20C, but the number of irregularly shaped fruits significantly increased, so that marketable fruit yield actually decreased.

Greenhouse experiments (Riga et al., 2008) demonstrate that tomato fruit quality is more dependent on temperature than on the level of photosynthetically active radiation. Over the range of temperatures used in these experiments (approx. 10 to 33C), the cumulative temperature of a 45 day period was strongly and positively correlated with fruit firmness, electrical conductivity, soluble solids content and total phenolic compounds. This research revealed that more and stronger relationships were found between various indicators of fruit quality and cumulative temperature compared to cumulative radiation.

Variation in day and night temperatures. The effects of different day and night air temperatures on tomato growth and yield were investigated by (Papadopoulos and Hao, 2001). Early season fruit yield increased with increasing average daily temperature but early fruit size decreased. The plants grown under high daily average air temperature regime early in the season had lower fruit yield later in the season. Plants grown under high night air temperature and low day air temperature during the early production period achieved high fruit yield in early season and also had high yield and large fruit size late in the season, and thus avoided the negative effects of high average daily temperature on early season fruit size.

(Peet and Bartholemew, 1996) investigated the potential effects of variation in night temperature independently of day temperature. They measured the pollen characteristics, growth, fruit set, and early fruit growth of tomato plants grown under 4 different night temperatures (18, 22, 24 and 26C) but a constant day temperature of 26C. The total and percentage normal pollen grains were higher in plants grown at the lower two temperatures, but germination was highest in pollen produced at the night temperature of 26C, Seed content was rated higher on the plants grown at the lowest night temperature than in any of the other treatments. The numbers of flowers and fruit on the first cluster were lower in the 26C night treatment than in the other treatments. Fruit fresh mass increased with night temperature, reflecting more rapid development. At night temperatures of 26C, slightly reduced fruit number and percentage fruit set were observed even though these temperatures were above optimal for pollen production and seed formation. This research revealed no consistent independent effects of night temperature treatment on pollen in fruit set, fruit mass, seed content, seedling germination or seedling dry mass.

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In another investigation of the effect of day and night temperatures on vegetative growth (Hussey, 1965), tomato seedlings were grown in a 12-hour day at constant and alternating day and night temperatures ranging from 10° to 30°C. The maximum rate of dry weight accumulation occurred at a constant temperature close to 25°C. The effects of day and night temperatures on total dry weight showed a considerable degree of independence and, on average, the effect of day temperature was roughly twice that of night temperature. The optimum day temperature was 25°C irrespective of the night temperature. In contrast, the optimum night temperature increased from 18° to 25°C over the whole range of day temperatures. The optimum day and night temperatures for leaf growth were both 25°C. High night temperature slightly accelerated nocturnal growth.

Effects of high temperatures. Even moderate increases in mean daily temperature (from 28/22C to 32/26C day/night) have been shown to result in a significant decrease in the number of fruit set (Sato et al., 2006). This occurs because temperatures slightly above the optimal range disrupt sugar metabolism and proline translocation during the narrow window of male reproductive development.

Heat-tolerant and heat-sensitive tomato varieties were compared under optimum- (27/23C, day/night) and high-temperature (35/23C) stress regimes in greenhouse experiments (Abdulbaki and Stommel, 1995). Under the optimum temperature treatment, fruit set ranged from 41% to 84% in the heat-sensitive variety and from 45% to 91% in the heat-tolerant variety. Under the high temperature regime, there was no fruit set in the most heat-sensitive variety, while fruit set in the heat-tolerant variety ranged from 45% to 65%. The response of pollen to heat treatments was dependent on the variety and was not a general predictor of fruit set under high-temperature stress.

Heat shock is a treatment ….. definition (Abdelmageed and Gruda, 2007) tested the effect of a previous heat shock on the subsequent growth and development of different tomato cultivars under defined heat stress conditions. Plants were grown under two day/night temperature regimes (26/20C and 37/27C). The number of pollen grains, number of fruits and fruit masses produced by the heat-tolerant cultivars were higher than those of the heat-sensitive cultivars. However, the heat shock pre-treatment’s had no positive effects on tomato growth and development.

Physiological factors can limit the fruit set of tomato under chronic but mild heat stress (Sato et al., 2000). Five different tomato cultivars were grown under three temperature regimes: (1) 28/22 or 26/22C (optimal temperature); (2) 32/26C (high temperature); and (3) 32/26 degrees C day/night temperatures relieved at 28/22C for 10 days before anthesis, then returned to 32/26C (relieving treatment). All five cultivars had fruit set under the relieving treatment, but only one cultivar had fruit set under the high temperature treatment. Longer periods of relief increased the percentage of fruit set and also increased the number of pollen grains released. Germination of pollen grains was also lowered in plants grown under the high temperature treatment. The number of pollen grains produced, photosynthesis and night respiration did not limit fruit set under chronic, mild heat stress, however. These results suggest that differences among the cultivars in pollen release and germination under heat stress are the most important factors determining their ability to set fruit.

Mildly elevated temperatures can also lead to the development of parthenocarpic fruit and undeveloped flowers (Sato et al., 2001). Similar optimal and high temperature regimes to those employed in the research described above were used to explore fruit development. No seeded fruit developed under the high temperature regime; flowers either developed into parthenocarpic fruit or failed to develop. Although the failure of flowers to develop may result from internal competition for carbohydrates (Bertin, 1995; Ho, 1996) several factors suggest that biochemical activities were not impaired in these plants. The authors recommend that further research should be conducted to clarify the factors affecting flower development in tomatoes.

Recent research has targeted the potential impacts of temperature fluctuations and high temperature pulses on fruit quality (Fleisher et al., 2006; Mulholland et al., 2003; Riga et al., 2008). Heat pulses of different magnitudes and duration were applied to greenhouse tomato crops (Mulholland et al., 2003). Yields were significantly increased in the week following heat pulse treatments, but fruit defects also increased. Longer pulse durations increased the incidence of uneven ripening, and the incidence of fruit defects was positively influenced by the pulse magnitude. Most significantly, a heat-pulse lasting three days and with a mean temperature of only 23.0C was sufficient to cause a 10% loss of Class I fruit.

Other experiments evaluated the effect of a 2-week long change in air temperature applied after the first fruit set (Fleisher et al., 2006). The results show that even short-term temperature perturbations

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following first fruit-set can influence both the external appearance of fruit and their internal characteristics. A high temperature treatment reduced the time to harvest and reduced fruit fresh weight later in the ripening process, and also reduced fruit firmness. Different temperature regimes alter the internal chemical characteristics of the fruit. For example, an increase in temperature from 21 to 26C reduced the total carotene content. Further temperature increases from 27 to 32C reduced ascorbate and lycopene but increases rutin, caffeic acid derivates, and glucoside contents (Gautier et al., 2008).

Some evidence for the impacts of high temperatures on tomato fruit production can be gleaned from research targeting the effects of row covers. In a study involving five different row cover designs and four different tomato varieties (Peterson and Taber, 1991), reduced yield was recorded for all row cover designs. All row cover designs resulted in periods of sustained high temperature (at least 40C for 3 consecutive hours) and correlated with early yield loss from increased flower abortion.

Methods to reduce impact of high temperatures on fruiting. Shading of tomato crops in summer is one method to sustain productivity under higher temperatures. Recent research shows that, as the level of shading is increased reducing the level of incident solar radiation, total fruit yield decreases through reduced fruit weight (Wada et al., 2006). However, shading reduces the proportion of cracked fruits under higher temperatures. The results show that a level of shading which decreased daily integrated solar radiation to 5-6 MJ.m(-2) effectively increased marketable fruit yields when the air temperature exceeded 25C. Other work has also shown that reduced solar radiation levels do not necessarily reduce the quality of tomato fruit (Riga et al., 2008), supporting the idea that shading may be an effective method to reduce the effects of overly high temperatures in tomato cultivation.

Cultivar variability

Temperatures above 34oC at pollen germination decreases germination percentage, and a number of field studies have demonstrated the range of cultivar responses to high temperatures, relating to the level of damage to pollen, and subsequent fruit set (Rudich, et.al, 1977). In the cultivar ‘Roma’, four hours exposure to 40oC on the 9th day before anthesis significantly reduced pollen viability and fruit set. Longer exposures produced no fruit at all.

‘Recovery’ from high temperatures.

Johnson and Hall (1953) show also that tomato cultivars vary in their ability to recommence fruit set after a period of excessively high temperatures. The most high temperature sensitive cultivars did not re-commence fruit set until 3 weeks after cool temperatures occurred, compared with the most high temperature tolerant cultivar which recommenced fruit set after 6 days at cooler temperatures.

Temperature, pests and diseases. Tomatoes are susceptible to a range of pests and diseases which may be influenced by changes in temperature. Climate change is expected to significantly affect the occurrence of plant diseases in agriculture over the coming decades (Boland et al., 2004). Changes in the epidemiology of plant diseases are expected, including the survival rate of the primary inoculum, the rate of disease progress and spread during a growing season, and the duration of epidemics. The spectra of diseases at particular locations are also expected to change. Higher temperatures may increase the activity of pest organisms, and changing rainfall patterns may result in an increase or decrease in the activity of fungi and other pathogens depending on location and timing (Webb et al., 2003).

Parasitic nematodes are a major agricultural pest for many Solonaceous crops, including tomatoes. Research on root-node nematode ecology revealed that they may be killed by extended exposure to high soil temperatures (eg. 36 to 40˚C), particularly in dry soils (Daulton and Nusbaum 1961). In tomatoes, resistance to nematodes (Meloidogyne arenaria) appeared to be independent of soil temperatures between 18 and 25˚C (Augustin et al. 2002).

Field surveys of the spatio-temporal distribution of budworm (Helicoverpa armigera) in Spain revealed no correlations between pest populations and either temperature or humidity (Garcia 2006).

Powdery mildew (Oidium neolycopersici, O. lycopersici) causes severe powdery mildew on all aerial parts of tomato, excluding the fruit (Jacob et al., 2008; Whipps et al., 1998). In a series of growth chamber experiments under controlled conditions (Jacob et al., 2008), the severity of the disease was negatively correlated with the duration of temperatures in the low and high ranges (5 to 15C and 35 to 40C) and with high relative humidity. These results suggest that a combination of high temperatures

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and low relative humidity may help reduce the severity of powdery mildew in greenhouse tomatoes and may also be a positive factor in large-scale cultivation.

Pythium aphanidermatum is a type of water mould that survives and grows best in wet soils and warm temperatures. High densities of this pathogen can result in reduced photosynthesis, transpiration, nutrient uptake and dry mass accumulation (Panova et al., 2004) . However, it does appear that the tomato can tolerate P. aphanidermatum infections at low root-zone temperatures (eg. At or below 20C).

Blossom-end rot is a common physiological disorder that can occur on the fruit of tomato, pepper, eggplant and some melon. The underlying cause of this disorder is an inadequate amount of Ca in the blossom-end of the fruit, but it is affected by many other factors including salinity, fluctuating moisture and high temperature (Taylor and Locascio, 2004). The main preventative measure is to understand the uptake of calcium from the soil and the factors that affect this process (Taylor and Locascio, 2004).

The effects of elevated CO2 Elevated CO2 levels may have important consequences for horticultural systems because of its effects on plant growth and reproduction. The potential effects of elevated atmospheric CO2 concentrations on a number of plant traits were investigated in a detailed meta-analysis of 79 crop and wild species (Jablonski et al., 2002). Across all species, CO2 enrichment above current ambient levels resulted in more flowers, more fruits, more seeds, greater individual seed mass, greater total seed mass, and lower seed nitrogen concentration. Crops were more responsive to elevated CO2 levels than were the wild species, and allocated relatively more mass to fruit and seeds. While this may at first seem like a positive result, interspecific differences in responses of seed number and other factors to elevated CO2 could also affect competitive interactions among co-occurring species (Jablonski et al., 2002). For example, elevated CO2 may increase seed production in invasive species more than in native species (Smith et al., 2000), potentially leading to reduced biodiversity in natural systems and increased weed activity in agricultural systems.

In tomatoes, CO2 enrichment can result in enhanced plant dry weight and can counteract any negative impact on yield from higher ozone concentrations (Reinert et al., 1997).

Climate Change Research. Sato, et.al. (2002), report that - “In tomatoes, 8-13 days before anthesis was the most sensitive period to moderately elevated temperature stress ....... These data suggest that, in evaluating individual flowers of (tomato) for tolerance to global warming, the 2 weeks before anthesis are the most critical”.

Results of experiments conducted by Sato, et.al (2006) on tomato, under moderately increased daily temperatures, suggest that the productivity of vegetable crops under elevated CO2 levels may not be significantly enhanced because reproductive development is significantly more sensitive to elevated temperatures, than to increasing CO2 levels.

Management Strategies. As there is significant genetic variability between cultivars in their capacity to set fruit under high temperature conditions (>35oC), there is a capacity to utilise these differences in breeding programs to deliver high temperature tolerant commercial cultivars (Rudich, et.al, 1977).

Discussion and Conclusions. In experiments conducted to determine critical temperature effects, sensitive cultivars are impacted when mean daily temperatures exceed 25oC, whereas more heat tolerant cultivars are not impacted until daytime (maximum) temperatures exceed 32oC, and the most sensitive period is 8-13 days prior to anthesis.

Climate change scenarios which include even moderate temperature increases in the order of 0.8oC, as published by the IPCC, are likely to affect the reproductive capacity of tomato plants, which will then have the potential to reduce yields of current cultivars (Sato, et.al., 2002).

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Tomato – Pre-anthesis Developmental Phase – Critical Temperature Threshold

For tomato, the 8 to 13 day period prior to anthesis is the most critical developmental phase. The critical temperature for this phase varies according to the cultivar tolerance to elevated temperatures. In tomato, elevated temperature impacts are complex, and it is difficult to determine one critical temperature effect during the reproductive development phase. In experiments conducted to determine critical temperature effects, sensitive cultivars are impacted when mean daily temperatures exceed 25oC, whereas more heat tolerant cultivars are not impacted until daytime (maximum) temperatures exceed 32oC.

For the purposes of this review, 29oC (mean daily temperature) during the 2 week period up to anthesis has been selected as the critical temperature and critical development phase for tomato (Peet et.al.,1997). In Queensland this critical period occurs ~ 9 weeks before harvest.

In Australia, tomatoes are produced in Queensland (Bowen, Bundaberg, Lockyer Valley and Granite Belt), NSW (Narromine, MIA, Sydney basin), Vic (Goulburn Valley - including processing), and SA (Murray Bridge, Adelaide Plains). Tomatoes are cold and frost sensitive, and production times in each region are regulated by both low and high temperatures.

In Queensland, Bowen production is predominantly an autumn/winter/spring crop, whereas Bundaberg production is all year round with peaks in autumn and late spring to summer. The southeast Queensland crop is produced through summer and autumn.

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Table 17: Tomato Production Districts - Queensland

District Planting Harvest Critical Development Phase

North Queensland

February – early September

June – early December April to early October

Bundaberg Mid January – mid April Mid July – mid September

Mid April – mid August October – early January

Feb to July Aug to late October

SE Queensland

Late August – February November - May September to March

Granite Belt October – December January - April November to Feb Source – Lovatt, et.al, 1998

Table 18: Tomato Production Growth Stages - Queensland Plant Stage Time

Sowing to germination 4-10 days Emergence to field planting 4-8 weeks Field planting to first flower 3-4 weeks

First Flower to harvest 6-8 weeks Duration of harvest 1-12 weeks

Critical Development Phase (2 weeks pre-anthesis)

8-10 (9) weeks prior to harvest

Source – Lovatt, et.al, 1998

References Abdelmageed AHA, Gruda N, 2007. Influence of heat shock pre-treatment on growth and development

of tomatoes under controlled heat stress conditions. J Appl Bot Food Qual-Angew Bot 81:26-28.

Abdulbaki AA, Stommel JR, 1995. POLLEN VIABILITY AND FRUIT-SET OF TOMATO GENOTYPES UNDER OPTIMUM-TEMPERATURE AND HIGH-TEMPERATURE REGIMES. Hortscience 30:115-117.

Abdullah NMM, 2008. Life history of the Potato Psyllid Bactericera cockerelli (Homoptera: Psyllidae) in Controlled Environment agriculture in Arizona. Afr J Agric Res 3:60-67.

Adams SR, Cockshull KE, Cave CRJ, 2001. Effect of temperature on the growth and development of tomato fruits. Ann Bot 88:869-877.

Adams SR, Valdes VM, 2002. The effect of periods of high temperature and manipulating fruit load on the pattern of tomato yields. J Horticult Sci Biotechnol 77:461-466.

Augustin B, Graf V, Laun N, 2002. Temperature influencing efficiency of grafted tomato cultivars against root-knot nematode (Meloidogyne arenaria) and corky root (Pyrenochaeta lycopersici). Z Pflanzenk Pflanzens-J Plant Dis Prot 109:371-383.

Bertin N, 1995. COMPETITION FOR ASSIMILATES AND FRUIT POSITION AFFECT FRUIT-SET IN INDETERMINATE GREENHOUSE TOMATO. Ann Bot 75:55-65.

Boland GJ, Melzer MS, Hopkin A, Higgins V, Nassuth A, 2004. Climate change and plant diseases in Ontario. Can J Plant Pathol-Rev Can Phytopathol 26:335-350.

Candido V, D'Addabbo T, Basile M, Castronuovo D, Miccolis V, 2008. Greenhouse soil solarisation: effect on weeds, nematodes and yield of tomato and melon. Agron Sustain Dev 28:221-230.

Criddle RS, Smith BN, Hansen LD, 1997. A respiration based description of plant growth rate responses to temperature. Planta 201:441-445.

De Koning ANM, 1989. THE EFFECT OF TEMPERATURE ON FRUIT GROWTH AND FRUIT LOAD OF TOMATO. Acta Horticulturae 248:329-336.

156

De Koning ANM, 1990. LONG-TERM TEMPERATURE INTEGRATION OF TOMATO - GROWTH AND DEVELOPMENT UNDER ALTERNATING TEMPERATURE REGIMES. Sci Hortic 45:117-127.

Fleisher DH, Logendra LS, Moraru C, Both AJ, Cavazzoni J, Gianfagna T, Lee TC, Janes HW, 2006. Effect of temperature perturbations on tomato (Lycopersicon esculentum Mill.) quality and production scheduling. J Horticult Sci Biotechnol 81:125-131.

Garcia FJM, 2006. Analysis of the spatio-temporal distribution of Helicoverpa armigera Hb. in a tomato field using a stochastic approach. Biosyst Eng 93:253-259.

Gautier H, Diakou-Verdin V, Benard C, Reich M, Buret M, Bourgaud F, Poessel JL, Caris-Veyrat C, Genard M, 2008. How does tomato quality (sugar, acid, and nutritional quality) vary with ripening stage, temperature, and irradiance? J Agric Food Chem 56:1241-1250.

Guichard S, Bertin N, Leonardi C, Gary C, 2001. Tomato fruit quality in relation to water and carbon fluxes. Agronomie 21:385-392.

Higashide T, 2009. Prediction of Tomato Yield on the Basis of Solar Radiation Before Anthesis under Warm Greenhouse Conditions. HORTSCIENCE 44(7):1874–1878. 2009.

Ho LC, 1996. The mechanism of assimilate partitioning and carbohydrate compartmentation in fruit in relation Ito the quality and yield of tomato. Oxford Univ Press United Kingdom; 1239-1243.

Hussey G, 1965. Growth and development in the young tomato. III The effect of night and day temperatures on vegetative growth. J Exp Bot 16:373-385.

Jablonski LM, Wang XZ, Curtis PS, 2002. Plant reproduction under elevated CO2 conditions: a meta-analysis of reports on 79 crop and wild species. New Phytol 156:9-26.

Jacob D, David DR, Sztjenberg A, Elad Y, 2008. Conditions for development of powdery mildew of tomato caused by Oidium neolycopersici. Phytopathology 98:270-281.

Johnson SP, Hall WC, 1953. Vegetative and Fruiting Responses of Tomatoes to High Temperature and Light Intensity Author(s): Source: Botanical Gazette, Vol. 114, No. 4 (Jun., 1953), pp. 449-460.

Jolliet O, Bailey BJ, 1992. THE EFFECT OF CLIMATE ON TOMATO TRANSPIRATION IN GREENHOUSES - MEASUREMENTS AND MODELS COMPARISON. Agric For Meteorol 58:43-62.

Lovatt J, Fullelove G, Wright R, Meurant N, Barnes J, O’Brien R, 1998. Tomato Information Kit. Brisbane: Department of Primary Industries Queensland.

Lurie S, Handros A, Fallik E, Shapira R, 1996. Reversible inhibition of tomato fruit gene expression at high temperature - Effects on tomato fruit ripening. Plant Physiol 110:1207-1214.

Machado RMA, Bussieres P, Koutsos TV, Prieto MH, Ho CL, 2004. Prediction of optimal harvest date for processing tomato based on the accumulation of daily heat units over the fruit ripening period. J Horticult Sci Biotechnol 79:452-457.

Mulholland BJ, Edmondson RN, Fussell M, Basham J, Ho LC, 2003. Effects of high temperature on tomato summer fruit quality. J Horticult Sci Biotechnol 78:365-374.

Newton P, Sahraoui R, Economakis C, 1999. The influence of air temperature on truss weight of tomatoes. In: Proceeding of the Third International Workshop on Models for Plant Growth and Control of the Shoot and Root Environments in Greenhouses. Louvain: International Society Horticultural Science; 43-49.

Nihoul P, 1993. CONTROLLING GLASSHOUSE CLIMATE INFLUENCES THE INTERACTION BETWEEN TOMATO GLANDULAR TRICHOME, SPIDER-MITE AND PREDATORY MITE. Crop Prot 12:443-447.

Panova GG, Grote D, Klaring HP, 2004. Population dynamics of Pythium aphanidermatum and response of tomato plants as affected by root-zone temperature. Z Pflanzenk Pflanzens-J Plant Dis Prot 111:52-63.

Papadopoulos AP, Hao XM, 2001. Effects of day and night air temperature in early season on growth, productivity and energy use of spring tomato. Can J Plant Sci 81:303-311.

157

Parmesan C, Yohe G, 2003. A globally coherent fingerprint of climate change impacts across natural systems. Nature 421:37-42.

Pearce BD, Grange RI, Hardwick K, 1993. THE GROWTH OF YOUNG TOMATO FRUIT .1. EFFECTS OF TEMPERATURE AND IRRADIANCE ON FRUIT GROWN IN CONTROLLED ENVIRONMENTS. J Horticult Sci 68:1-11.

Peet M, Willits D, Gardner R, 1997. Response of Ovule Development and Post-pollen Production Processes in Male-sterile Tomatoes to Chronic, Sub-acute High Temperature Stress. Journal of Experimental Botany, Vol. 48, No. 306, pp. 101-111, January 1997.

Peet MM, Bartholemew M, 1996. Effect of night temperature on pollen characteristics, growth, and fruit set in tomato. J Am Soc Hortic Sci 121:514-519.

Pek Z, Helyes L, 2004. The effect of daily temperature on truss flowering rate of tomato. J Sci Food Agric 84:1671-1674.

Peterson RH, Taber HG, 1991. TOMATO FLOWERING AND EARLY YIELD RESPONSE TO HEAT BUILDUP UNDER ROWCOVERS. J Am Soc Hortic Sci 116:206-209.

Reinert RA, Eason G, Barton J, 1997. Growth and fruiting of tomato as influenced by elevated carbon dioxide and ozone. New Phytol 137:411-420.

Riga P, Anza M, Garbisu C, 2008. Tomato quality is more dependent on temperature than on photosynthetically active radiation. J Sci Food Agric 88:158-166.

Rudich J, Zamski E, Yael Regev, 1997. Genotypic Variation for Sensitivity to High Temperature in the Tomato: Pollination and Fruit Set. Botanical Gazette, Vol. 138, No. 4 (Dec., 1977), pp. 448-452.

Sato S, Kamiyama M, Iwata T, Makita N, Furukawa H, Ikeda H, 2006. Moderate increase of mean daily temperature adversely affects fruit set of Lycopersicon esculentum by disrupting specific physiological processes in male reproductive development. Ann Bot 97:731-738.

Sato S, Peet MM, 2005. Effects of moderately elevated temperature stress on the timing of pollen release and its germination in tomato (Lycopersicon esculentum Mill.). J Horticult Sci Biotechnol 80:23-28.

Sato S, Peet MM, Gardner RG, 2001. Formation of parthenocarpic fruit, undeveloped flowers and aborted flowers in tomato under moderately elevated temperatures. Sci Hortic 90:243-254.

Sato S, Peet MM, Thomas JF, 2000. Physiological factors limit fruit set of tomato (Lycopersicon esculentum Mill.) under chronic, mild heat stress. Plant Cell Environ 23:719-726.

Sato S, Peet MM, Thomas JF, 2002. Determining critical pre- and post-anthesis periods and physiological processes in Lycopersicon esculentum Mill. exposed to moderately elevated temperatures. J Exp Bot 53:1187-1195.

Schmitz U, 2004. Frost resistance of tomato seeds and the degree of naturalisation of Lycopersicon escalentam Mill. in Central Europe. Flora 199:476-480.

Smith SD, Huxman TE, Zitzer SF, Charlet TN, Housman DC, Coleman JS, Fenstermaker LK, Seemann JR, Nowak RS, 2000. Elevated CO2 increases productivity and invasive species success in an arid ecosystem. Nature 408:79-82.

Stamp NE, Osier TL, 1997. Combined effects of night-time temperature and allelochemicals on performance of a Solanaceae specialist herbivore. Ecoscience 4:286-295.

Stamp NE, Osier TL, 1998. Response of five insect herbivores to multiple allelochemicals under fluctuating temperatures. Entomol Exp Appl 88:81-96.

Stirling GR, Ashley MG, 2003. Incidence of soilborne diseases in Australia's sub-tropical tomato industry. Austral Plant Pathol 32:219-222.

Taylor MD, Locascio SJ, 2004. Blossom-end rot: A calcium deficiency. J Plant Nutr 27:123-139.

Tchamitchian M, Martin-Clouaire R, Lagier J, Jeannequin B, Mercier S, 2006. SIERRISTE: A daily set point determination software for glasshouse tomato production. Comput Electron Agric 50:25-47.

158

Tubiello FN, Soussana JF, Howden SM, 2007. Crop and pasture response to climate change. Proc Natl Acad Sci U S A 104:19686-19690.

Uzun S, 2007. The effect of temperature and mean cumulative daily light intensity on fruiting behaviour of greenhouse-grown tomato. J Am Soc Hortic Sci 132:459-466.

Van Der Ploeg A, Heuvelink E, 2005. Influence of sub-optimal temperature on tomato growth and yield: a review. J Horticult Sci Biotechnol 80:652-659.

Wada T, Ikeda H, Matsushita K, Kambara A, Hirai H, Abe K, 2006. Effects of shading in summer on yield and quality of tomatoes grown on a single-truss system. J Jpn Soc Hortic Sci 75:51-58.

Wada T, Ikeda H, Morimoto K, Furukawa H, Abe K, 2001. Effects of minimum air temperatures at seedling stage on plant growth, yield, and fruit quality of tomatoes grown on a single-truss system. J Jpn Soc Hortic Sci 70:733-739.

Wahid OAA, Moustafa AF, Ibrahim ME, 2001. Integrated control of tomato Fusarium-wilt through implementation of soil solarisation and filamentous fungi. Z Pflanzenk Pflanzens-J Plant Dis Prot 108:345-355.

Webb L, Hennessy K, Cechet R, Whetton PH, 2003. Horticulture and vegetables. In: An overview of the adaptive capacity of the Australian agricultural sector to climate change: options, costs and benefits (Howden M, Ash A, Barlow S, Booth T, Charles S, Cechet R, Crimp S, Gifford R, Hennessy K, Jones R, Kirschbaum M, McKeon G, Meinke H, Park S, Sutherst R, Webb L, Whetton P, eds). Canberra: CSIRO Sustainable Ecosystems; 61-75.

Went, FW, 1944. Plant Growth Under Controlled Conditions. II. Thermo periodicity in Growth and Fruiting of the Tomato. American Journal of Botany, Vol. 31, No. 3 (Mar., 1944), pp. 135-150.

Whipps JM, Budge SP, Fenlon JS, 1998. Characteristics and host range of tomato powdery mildew. Plant Pathol 47:36-48.

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The influence of temperature on the growth and development of macadamia (Macadamia integrifolia)

Background to the report. This report is one of a series of literature reviews completed as part of the Critical Thresholds (‘Tipping Points’) and Climate Change Impacts/Adaptation in Horticulture project undertaken by the Queensland Primary Industries and Fisheries (QPIF) and Growcom. The purpose of this report is to synthesise information on the influence of temperature on the development of macadamia and, where possible, to identify specific temperature limitations associated with apple growth phases and key pest and diseases by assessing information contained in existing peer reviewed journal articles.

The effect of temperature on flowering, nut yield and quality. The formation of flowers, premature nut drop and of course yield are quality are the most important aspects of macadamia orchard management. Temperature has a key role in this. Floral buds become visible in May when minimum temperatures are between 11ºC to 15ºC (Moncur et al., 1985). After differentiation they remain dormant for 50 to 96 days depending on location. Mean minimum temperatures of around 12ºC in August and around 14ºC in September probably promote flowering, but temperatures below 12.5ºC in October and 15ºC in November adversely affect yield. This period is when there is rapid nut growth and oil accumulation. Yields are reduced if temperatures fall below 17ºC (Stephenson et al., 1986a). Warm nights , ~20ºC compared to 15ºC, just prior and after floral initiation followed by low night time temperatures, ~10.5ºC, prior to anthesis promoted floral bud production over an extended period. Warm nights promote greater raceme length, but overall nut production is not altered (Stephenson and Gallagher, 1986a). High temperatures (30-35ºC) were found to cause premature nut drop in 5-year old trees (Stephenson and Gallagher, 1986c, 1987). The effect of daytime temperature on raceme and nut retention is shown in Table 1 (Stephenson and Gallagher, 1986c). Table 1. Effect of temperature on race and nut retention and nut production#. Day temperature 20ºC 25ºC 30ºC 35ºC Raceme retention (%) 70 70 40 10 Nut retention (%) 39 29 17 4 Number of nuts per tree 44.1 35.4 7.5 1.1 # Plants were grown outside until nut set and then subjected to controlled temperatures for 19 days

after nut set. Night temperature was 15ºC with a day length of 12 hours. These experiments suggest that 30ºC represents a threshold for nut production during the period of raceme and nut development (approximately August to November in southeast Queensland). The duration of the exposure to high temperatures required to cause a premature nut drop is unknown, but nut drop occurs within the first 10 to 15 days (Stephenson and Gallagher, 1986c). Relative humidity was relatively unimportant (Stephenson et al., 1986b). Kernel growth is best at 25ºC and low at 15ºC and 35ºC (Stephenson and Gallagher, 1986b), although kernel weight at 30ºC was greater than at 25ºC and 15ºC.

The effect of temperature on flushing Vegetative flushing in macadamia occurs in February and September. Growth is restricted below 10ºC and abnormal above 30ºC. The optimal range is 16 to 25ºC (Stephenson et al., 1986c). Total leaf area was maximised at 25ºC and declined quickly on either side. New flushes were initiated more quickly at temperatures above 20ºC (Table 2).

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Table 2. Effect of temperature on the number of days to commence a new flush of growth (Trochoulias and Lahav, 1983)

Temperature (ºC) Means days S.E 10 No growth - 15 42.3 5.3 20 40.3 3.3 25 26.5 3.5 30 21.3 1.8 35 22.3 0.8

New leaves become chlorotic at 30ºC and most wither and die if kept at this temperature for long periods. Older leaves are not affected. Leaves thicken as the temperature changes from 25ºC, with leaves at 10ºC and 35ºC being twice as thick. Limits to growth Mature trees can survive high temperatures, Westree (1956) in (Trochoulias and Lahav, 1983) noted that trees survive a 20 day heat wave with daily maxima above 38ºC and a peak of 46ºC. Root growth can be restricted by high soil temperatures. In the experiments conducted by (Trochoulias and Lahav, 1983) in northern NSW, tree growth occurred across a wide range of temperatures from 15ºC to 30ºC, but showed no growth at either 10ºC or 35ºC. Increases in stem diameter were found over the same range of temperatures, however, there was a wide variability among the replicates. Photosynthesis occurs at a maximum rate at ambient temperatures 14ºC to 25ºC, decreases sharply at 26ºC and ceases above 38ºC (Allan and de Jager, 1979). Actual leaf temperatures can be much higher and although photosynthesis drops sharply once leaves exceed 38ºC (Huett, 2004).

The effects of elevated CO2 Macadamia (M. integrifolia) show positive photosynthetic response to elevated CO2. Increasing CO2 by 100 µmol.mol-1 (i.e. 440 ppm) produced a 50% increase in the rate of CO2 assimilation (de Kruiff, 1994).

References Allan P, de Jager J, 1979. Net photosynthesis in macadamia and papaw and the possible alleviation of

heat stress. Acta Horticulturae 102:23-30. de Kruiff H, 1994. Photosynthetic response of macadamia (Macadamia integrifolia Maiden & Betche) to

a range of light and CO2 levels: A comparison of field-grown and containerised trees. Nambour, Queensland, Australia: Maroochy Horticultural Research Station; 14.

Huett DO, 2004. Macadamia physiology review: a canopy light response study and literature review. Australian Journal of Agricultural Research 55:609-624.

Moncur MW, Stephenson RA, Trochoulias T, 1985. Floral development of Macadamia integrifolia Maiden & Betche under Australian conditions. Scientia Horticulturae 27:87--96.

Stephenson RA, Cull BW, Mayer DG, 1986a. Effects of site, climate, cultivar, flushing, and soil and leaf nutrient status on yields of macadamia in south east Queensland. Scientia Horticulturae 30:227--235.

Stephenson RA, Cull BW, Price G, Stock J, 1986b. Some observations on nutrient levels of three soils growing macadamias in south east Queensland. Scientia Horticulturae 30:83--95.

Stephenson RA, Cull BW, Stock J, 1986c. Vegetative flushing patterns of macadamia trees in south east Queensland. Scientia Horticulturae 30:53--62.

Stephenson RA, Gallagher EC, 1986a. Effects of night temperature on floral initiation and raceme development in macadamia. Scientia Horticulturae 30:213--218.

Stephenson RA, Gallagher EC, 1986b. Effects of temperature during latter stages of nut development on growth and quality of macadamia nuts. Scientia Horticulturae 30:219--225.

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Stephenson RA, Gallagher EC, 1986c. Effects of temperature on premature nut drop in macadamia. Queensland Journal of Agricultural and Animal Sciences 43:97-100.

Stephenson RA, Gallagher EC, 1987. Effects of temperature, tree water status and relative humidity on premature nut drop from macadamia. Scientia Horticulturae 33:113--121.

Trochoulias T, Lahav E, 1983. The effect of temperature on growth and dry-matter production of macadamia. Scientia Horticulturae 19:167-176.

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The influence of temperature on the growth and development of capsicum (Capsicum annum).

Introductory comments. Capsicum is a major crop in many parts of the World and there is a large body of existing literature on its cultivation. Unfortunately, the volume of literature devoted to the effects of temperature is relatively low compared to some other commodities. Additional complications are caused by the variety of names by which the capsicum is known (eg. ‘capsicum’ in Australia, NZ and south Asia, ‘bell pepper’ in the US and ‘sweet pepper’ in the UK and Europe) and because the Capsicum genus contains a large number of species including those normally referred to as ‘chillies’. This review concentrates on the large sweet variety marketed as ‘capsicum’ in Australia (Capsicum annuum varieties) but will refer to literature on other Capsicum species for additional information.

Influence of temperature on specific periods of capsicum growth and development.

Flowering and fruiting

Temperature-sensitive cultivars usually respond to high temperatures by the abortion of flowers prior to anthesis (Aloni et al. 1996). Greenhouse experiments on a more heat-tolerant variety (‘Mazurka’) investigated the effect on high temperatures on fruit set and carbohydrate levels (Aloni et al. 2001). Plants exposed to a high temperature regime (32/26˚C day/night) for the 8-day period leading up to anthesis has slightly higher rates of flower abortion than those raised under normal temperatures (28/22˚C). Plants raised at high temperatures produced a similar pollen count to those raised under normal temperatures, but with greatly reduced germination success. Elevated atmospheric CO2 (800µmol mol-1) restored the germination success to near normal levels for plants raised under high temperatures but had no effect on the germination success of normal temperature plants.

Erickson and Markhart (2001) investigated the role of temperature and water stress on flower production and fruit set. While elevated temperatures (33˚C) compromised fruit set, vapour pressure deficit had no effect on flower number, fruit set or other physiological measurements. These results suggest that reduced fruit set is a direct response to high temperatures rather than a response to temperature-induced water stress.

High temperatures after pollination result in decreased fruit set, suggesting that fertilisation is sensitive to high temperatures (Erickson and Markhart 2002). The effect of high temperature depends on the developmental stage of the flower. In a series of greenhouse experiments, flowers at four different developmental stages were maintained at day/night temperatures of 25/21˚C or exposed to an elevated temperature of 33˚C for between 6 and 120 hours (Erickson and Markhart 2002). Flowers exposed to the elevated temperature for 48 to 120 hours during stage 1 (buds less than 2.5mm long, 14-17 days before anthesis) and stage 4 (buds 7-8mm long with protruding petals, 3-5 days before anthesis) showed reduced fruit set (up to 79% reductions depending on the duration of exposure). Flowers exposed during stages 2 or 3 (buds 3-6.5mm, 6-13 days before anthesis) did not show reduced fruit set after any period of exposure to the higher temperature.

An examination of pollen germination rates at different temperatures for seven genotypes from five different capsicum species revealed variation in germination success (Reddy and Kakani 2007). The optimal temperature for maximum germination rates for these species varied between 29˚C to 32.8˚C, the minimum temperature for germination ranged between 14.8 to 16˚C, while the maximum temperature for successful germination ranged between 40 to 43.7˚C.

Temperatures below 15°C or above 32°C for prolonged periods reduce pollen viability and pollination. This leads to small and/or deformed fruit (Lovatt et.al, 1999).

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Fruit growth and harvest

Temperatures above 30˚C can cause reduced fruit growth in capsicum. When pollen from flowers exposed to 33˚C during early flower development were used to pollinate new flowers, the yield of fresh fruit produced is reduced and the fruit were deformed (Erickson and Markhart 2002).

Exposure to high temperatures (38/30˚C day/night) following anthesis may result in reduced fruit growth, as demonstrated in ‘Shishito’ peppers (Pagamas and Nawata 2008). The effect of heat stress varies with the timing of exposure relative to the developmental stage of the fruit. For example, exposure to heat stress in the period up to 10 days following anthesis can result in lower fruit weight. Heat stress between 10 and 30 days after anthesis resulted in reduced fruit weight and fruit width. Exposure to heat stress for the whole period after anthesis, or for the period between 30 days after anthesis and harvest, reduces the growth period by 10 to 15 days (Pagamas and Nawata 2008).

An evaluation of a number of heat-tolerant capsicum/chilli varieties in Nepal revealed great variation in yield potential among genotypes (Dahal et al. 2007). During the fruiting period, average weekly temperatures in excess of 32/15˚C max/min prevented fruit set in some genotypes. Temperatures above 40˚C had a negative effect on flower and fruit development in most varieties.

Pests. Nematodes

Parasitic nematodes are a major agricultural pest for many crops worldwide. Root-knot nematodes (Meloidogyne spp.) affect many Solanaceous crops, including Capsicum (Khan and Haider 1991). Despite the volume of research on nematode impacts and control, there appears to be very little existing work on the effect of temperature on nematode infestations in Capsicum. Work on the genetic resistance to nematodes of several capsicum varieties revealed that resistance was stable up to 42˚C (Djian-Caporalino et al. 1999). Early work on root-node nematode ecology revealed that they may be killed by extended exposure to high soil temperatures (eg. 36 to 40˚C), particularly in dry soils (Daulton and Nusbaum 1961).

Diseases. Sudden wilt

Sudden wilt is the main disease problem for the capsicum industry in Queensland (Stirling et al. 2004). In this disease, plants appear healthy until fruit set, at which point they suddenly wilt and drop leaves. The affected plants produce small, unmarketable fruit and may die. A number of soil-borne fungi have been linked to the disease, mainly Pythium spp. and Fusarium spp.. The Pythium genus contains a number of water moulds that survive and grow best in wet soils and warm temperatures. Two Pythium species (aphanidermatum and myriotylum) have been shown to be able to destroy root systems in capsicum within a few days of inoculation, and the extent of damage caused by these pathogens is more severe at higher temperatures (Stirling et al. 2004). The Pythium fungi caused little damage at a soil temperature of 30˚C but caused moderate to severe rotting of roots at 35 to 40˚C.

Tomato spotted wilt virus

Resistance to the tomato spotted wilt virus is provided by the Tsw gene that is less stable at continuous high temperatures. For example, continuous exposure to a temperature of 32˚C for nine days or more leads to systemic spread of the virus and necrotic symptoms in plants that show total resistance at lower temperatures (22˚C). The resistance to this virus is destabilised more in young plants than in older plants (Moury et al. 1998).

Tomato mosaic virus

The tomato mosaic virus can cause reduced plant height, root length and shoot dry weight in Capsicum (Schuerger and Hammer 1995). A review of the effects of temperature on symptom development shows that disease progress and the severity of symptoms decreases at temperatures below 20 to 24˚C (reviewed in Schuerger and Hammer 1995). Growth chamber experiments show that the reduction in plant growth in inoculated plants is greater (relative to control non-inocculated plants) at 24˚C than at either 18˚C or 32˚C. Root-inocculated plants incubated at 18˚C showed no negative symptoms (Schuerger and Hammer 1995).

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Management responses. In greenhouse production systems, evaporative cooling has been shown to increase yields by improving water status (Bar-Tal et al. 2006). This method may also reduce the incidence of fruit cracking and blossom end rot.

Shading may be an effective method to reduce temperatures at the surface of fruit, leaves and soil. For capsicum crops in Israel, shading reduced the level of sun damage (sun-scald) to fruits from 36% in full sunlight to 3-4% under shade (26% and 47% shade). The highest fruit yield was obtained with shade levels between 12 and 26% (Rylski and Spigelman 1986). Other Capsicum species grown under shade conditions may show higher total production and fruit weight. For example, results from field experiments in Venezuela (Jaimez and Rada 2006) indicate that Capsicum chinense can be successfully grown in partial shade (up to 40%) but that yield may be reduced at lower levels of incident sunlight (60% shade).

Developing new heat-tolerant cultivars through selective breeding may be an important strategy to adapt to higher temperatures (Reddy and Kakani 2007).

Capsicum – Flowering Developmental Phase – Critical Temperature Threshold

Temperatures above 32°C for prolonged periods reduce pollen viability and pollination. This leads to small and/or deformed fruit.

References.

Aloni B., Karni L., Zaidman Z. & Schaffer A. (1996) Changes of carbohydrate in pepper (Capsicum annuum L.) flowers in relation to their abcission under different shading regimes. Annals of Botany 78, 163-8.

Aloni B., Peet M., Pharr M. & Karni L. (2001) The effect of high temperature and high atmospheric CO2 on carbohydrate changes in bell pepper (Capsicum annuum) pollen in relation to its germination. Physiol. Plant. 112, 505-12.

Bar-Tal A., Aloni B., Arbel A., Barak M., Karni L., Oserovitz J., Hazan A., Gantz S., Avidan A., Posalski I. & Keinan M. (2006) Effects of an evaporative cooling system on greenhouse climate, fruit disorders and yield in bell pepper (Capsicum annuum L.). J. Horticult. Sci. Biotechnol. 81, 599-606.

Dahal K. C., Sharma M. D., Dhakal D. D. & Shakya S. M. (2007) Evaluation of Heat Tolerant Chilli (Capsicum annuum L.) Genotypes in Western Terai of Nepal. Journal of the Institute of Agriculture and Animal Science 27, 59.

Daulton R. A. C. & Nusbaum C. J. (1961) The Effect of Soil Temperature On the Survival of the Root-Knot Nematodes Meloidogyne Javanica and M. Hapla 1). Nematologica 6, 280-94.

Djian-Caporalino C., Pijarowski L., Januel A., Lefebvre V., Daubeze A., Palloix A., Dalmasso A. & Abad P. (1999) Spectrum of resistance to root-knot nematodes and inheritance of heat-stable resistance in pepper (Capsicum annuum L.). Theor. Appl. Genet. 99, 496-502.

Erickson A. N. & Markhart A. H. (2001) Flower production, fruit set, and physiology of bell pepper during elevated temperature and vapor pressure deficit. J. Am. Soc. Hortic. Sci. 126, 697-702.

Erickson A. N. & Markhart A. H. (2002) Flower developmental stage and organ sensitivity of bell pepper (<i>Capsicum annuum</i> L.) to elevated temperature. Plant, Cell & Environment 25, 123-30.

Jaimez R. E. & Rada F. (2006) Flowering and fruit production dynamics of sweet pepper (Capsicum chinense Jacq) under different shade conditions in a humid tropical region. J. Sustain. Agric. 27, 97-108.

Khan M. W. & Haider S. R. (1991) Comparative Damage Potential and Reproduction Efficiency of Meloidogyne Javanica and Races of Meloidogyne Incognita On Tomato and Eggplant. Nematologica 37, 293-303.

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Lovatt J, Meurant N, Wright R, Olsen J, Fullelove G. 1999. Capsicums and Chillies Information kit. Brisbane: Department of Primary Industries Queensland.

Moury B., Selassie K. G., Marchoux G., Daubèze A.-M. & Palloix A. (1998) High temperature effects on hypersensitive resistance to Tomato Spotted Wilt Tospovirus (TSWV) in pepper (Capsicum chinense Jacq.). European Journal of Plant Pathology 104, 489-98.

Pagamas P. & Nawata E. (2008) Sensitive stages of fruit and seed development of chilli pepper (Capsicum annuum L. var. Shishito) exposed to high-temperature stress. Scientia Horticulturae 117, 21-5.

Reddy K. R. & Kakani V. G. (2007) Screening Capsicum species of different origins for high temperature tolerance by in vitro pollen germination and pollen tube length. Scientia Horticulturae 112, 130-5.

Rylski I. & Spigelman M. (1986) Effect of shading on plant development, yield and fruit quality of sweet pepper grown under conditions of high temperature and radiation. Scientia Horticulturae 29, 31-5.

Schuerger A. C. & Hammer W. (1995) Effects of temperature on disease development of tomato mosaic virus in Capsicum annuum in hydroponic systems. Plant disease 79, 880-5.

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The influence of temperature on the growth and development of sweet corn (Zea mays L. var. rugosa).

1.0 Background to the report.

This report is one of a series of literature reviews completed as part of the Critical Thresholds (‘Tipping Points’) and Climate Change Impacts/Adaptation in Horticulture project undertaken by Queensland Primary Industries and Fisheries (QPIF) and Growcom. This purpose of this report is to synthesise information on the influence of temperature on the cultivation of sweet corn and where possible to identify specific temperature limitations associated with sweet corn growth, productivity and key pests and diseases by assessing information contained in existing peer-reviewed journal articles.

2. Introduction.

Sweet corn (Zea mays L. var. rugosa) is a variety of maize with a high sugar content. Maize is the most cultivated C4 species in the world, and the only C4 plant to be widely cultivated in temperate areas (Bird et al. 1977).

Plants that feature the C4 mechanism for carbon fixation during photosynthesis may have some advantages over plants with the more common C3 mechanism under conditions of drought, high temperatures, and nitrogen or CO2 limitation (Sage and Monson 1999). As a consequence, C4 plants are more concentrated in topical areas.

Past increases in corn yield appear to have been influenced primarily by both genetic improvement and increased use of fertiliser (Cardwell 1982). There is a healthy body of literature describing the effects of environmental conditions, including climate, on sweet corn production.

3.0 Effects of temperature.

On photosynthesis.

The optimum temperature ranges for warm season maize varieties is 15-20˚C at planting and 20-30˚C during the growing season (Bird et al. 1977). Controlled temperature experiments revealed that maize did not produce effective leaves at either 13˚C or 18˚C, and that the photosynthetic rate was greatest at temperatures of 23˚C or higher (Bird et al. 1977).

The net photosynthetic rate of maize increases up to a temperature of about 35˚C and then declines at higher temperatures (Lizaso et al. 2005). Further work by Ben Asher et al. (2008) using climate controlled growth chambers revealed that the optimal temperature for photosynthesis was about 32˚C (with a CO2 uptake of approx. 42µmol m-2 s-1) and declined at higher temperatures.

On growth and yield.

Field experiments in New Zealand revealed that the times from planting to silking for sweet corn varied from 82 to 109 days, and from silking to maturity from 37 to 67 days (Wilson and Salinger 1994). The thermal time requirements from planting to maturity ranged from 1215 to 1320 degree-days above a base temperature of 6˚C. The growing regions in New Zealand have experienced a warming trend since 1928 which has resulted in a decrease in climatic risk for sweet corn production, although the temperature variability results in the cooler regions remaining marginal for sweet corn production.

An analysis of climate/weather variability and corn production in the US corn belt between 1930 and 1983 failed to find a clear trend because of the strong weather variability (Thompson 1986). However, the greatest yields were generally associated with normal temperature in early summer, below normal temperatures in late summer, and normal or above rainfall. However, the author concludes that gains in corn yields will become more difficult if the climate warms.

Optimal temperatures during reproductive stages has been shown to be important for maximising yield (reviewed in Commuri and Jones 2001). During the period up to three to four weeks following pollination, temperatures greater than 32˚C can cause yield reductions greater than 4% per day (Shaw 1983). Further field experiments revealed that kernel growth is severely reduced when exposed to high temperature treatments (35˚C day and night for 4 or 6 days), although the degree of reduction is dependent on the genotype (Commuri and Jones 2001). These high temperature treatments could reduce final kernel dry weights by up to 95% under field conditions. The difference among genotypes was attributed to the different abilities to maintain ‘kernel sink capacity’ (the potential of kernels to

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achieve maximal mass by attracting assimilates) following exposure to high temperatures (Commuri and Jones 2001).

Greenhouse experiments on maize reveal that seed germination rates and vigour were greatest for seeds produced under medium temperature conditions (27/21˚C day/night) compared to those produced under low (22/16˚C) or high (33/27˚C) temperature conditions (Modi and Asanzi 2008).

Kim et al. (2007) investigated the effects of both temperature and CO2 concentration on a range of growth parameters for maize, including above ground dry matter (stalk, leaves and ear), leaf area, specific leaf area and days to silking. All of these growth parameters, except specific leaf area, differed among the experimental temperature treatments (19/13, 25/29, 31/25, 35/29 and 38.5/32.5˚C day/night). Final leaf area was negatively correlated with growth temperature, while the optimum temperature for leaf appearance rate was approximately 32˚C (regardless of CO2 concentration). The ceiling temperature for leaf appearance was 44˚C (Kim et al. 2007).

On quality.

Environmental factors can have a significant effect on sweet corn quality. For example, extreme drought and heat can result in low values for kernel water and sugar content (Ledencan et al. 2008).

On water use efficiency.

Water use efficiency (WUE) of maize was found to be about three times greater at day/night temperatures of 25/20˚C compared to 40/35˚C (Ben-Asher et al. 2008).

The biomass and yield of sweet corn can be reduced by water deficit, primarily as a result of reduced radiation use efficiency (Stone et al. 2001). This was demonstrated in an experiment that employed a mobile rain shelter to impose 6 irrigation treatments, including no deficit, full deficit, and a range of options at different growth stages (pre- and post-silking). For example, biomass declined at an average rate of 27kg/ha per mm maximum potential water deficit. In addition, yield (kernel fresh mass) declined by 16 kg/ha per mm maximum potential water deficit (Stone et al. 2001).

Garcia et al. (2009) demonstrated that water use and water use efficiency of sweet corn are not only affected by potential water deficit, but also by intra-seasonal weather variability. In addition, the results of these experiments confirmed that yield was positively and linearly related to water use, with water use explaining 94% of the variation in fresh ear yield (Garcia et al. 2009). The authors recommended that further work was required to determine the critical periods and developmental stages during which intra-seasonal weather variability and soil moisture conditions most affect crop yields.

4.0 Elevated CO2.

Under controlled conditions, elevated CO2 concentration can result in increased photosynthesis and improved water use efficiency in corn (Rosenberg 1981; Waggoner 1983).

An investigation into the effects of both temperature and CO2 concentration on a range of growth parameters for maize (Kim et al. 2007), revealed little evidence of increased growth under enhanced CO2 (double ambient) over a wide range of temperatures. Furthermore, there appeared to be no significant interaction between temperature and CO2 concentration, with the response to temperature consistent between the CO2 treatments.

5.0 Pests and diseases.

The most important pest in sweet corn is the larvae of the heliothis moth (Helicoverpa armigera). Besides lepidopteran larvae, other pests include root lesion nematodes (Pratylenchus zeae) and maize leafhoppers (Cicadulina bimaculata), a sap-sucking insect that can cause a condition called wallaby ear.

Development rates for heliothis are temperature dependent, with approximately 185 degree-days (above a floor of 12.5˚C required for larval development) (Coop et al. 1993). Analyses of population dynamics and environmental conditions in India reveal that the peak population density is dependent on temperature, humidity and rainfall during the wet season (Srivastava et al. 2010).

In Australia, the size of the Spring generation of heliothis in eastern cropping zones appears to be related to rainfall in inland source areas (Zalucki and Furlong 2005). The abundance of following generations may be related to the peak Spring population, the abundance of various crops and rainfall. Given the value of rainfall as a predictor variable for pest numbers, a CLIMEX model was developed to predict temporal variation in abundance. The resulting model appears to predict the known global

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distribution reliably (Zalucki and Furlong 2005), indicating that it may have value in predicting the effects of changing climates on distribution.

A changing climate is likely to lead to range shifts and changes in migration patterns. For example, there are indications that climate change may have lead to an increase in migratory moths and butterflies reaching the UK (Sparks et al. 2007). Results from a study in the southern UK conducted between 1982 and 2005 suggest that each 1˚C increase in temperature was accompanied by an additional 14 migratory species (14.4±2.4) (Sparks et al. 2007).

Northern leaf blight, or Turcicum leaf blight, is caused by the fungus Exserohilum turticum. In Ethiopia, disease incidence is positively correlated with morning humidity and low temperature, and cool nights with long dew periods can facilitate the infection of partially resistant cultivars (Tefferi et al. 1996). The minimal dew period for infection is temperature dependent; at 25˚C, one hour of dew is sufficient to facilitate infection (Levy and Pataky 1992). Some varieties possess partial resistance to northern leaf blight. While partial resistance appears to be a stable trait in these varieties, and is consistent over a wide temperature range, varietal differences are emphasised at higher temperatures (Carson and Vandyke 1994).

6.0 Modelling.

The relationships between agroecological factors and corn yields are sufficiently well-understood to inform reliable crop simulation models (CSM-CERES-Maize and CERES-Sweet corn; Jones et al. 2003; Lizaso et al. 2007). In these models, the marketable yield is dependent on the ear dry weight concentration which is a linear function of thermal time. The range of weather/climate variables in the model includes minimum daily temperature, maximum daily temperature, and CO2 concentration, among many others. In simulations to test the sensitivity of the sweet corn model, an environment 2.5˚C warmer would reduce marketable yield by 14% (Lizaso et al. 2007).

7.0 Adaptation.

Breeding to increase kernel sink capacity (the ability of seed endosperms to attract assimilates and increase kernel size) following exposure to high temperatures during endosperm cell division may increase tolerance to sustained high temperatures (Commuri and Jones 2001).

In temperate regions, plastic mulches can be used to advance maturity and increase sweet corn yields by increasing soil temperature and moisture (Kwabiah 2004). For example, field trials in Ontario demonstrated that both clear and wavelength selective mulch films increased soil temperature (by 1.1˚C to 4.8˚C at 5cm depth) and moisture relative to bare soil (by 2.0 to 8.1%) (Zhang et al. 2007). Wavelength selective mulches had a smaller effect on soil temperature but were better at retaining soil moisture and suppressing weed growth. As a result, wavelength selective mulches may be an effective method to reduce water loss in drought conditions provided the soil temperature is not elevated beyond the optimum range of 24-35˚C.

Field experiments in Israel suggest that high frequency microdrip irrigation may be used to increase water use efficiency and yield in sweet corn (Assouline et al. 2002), although the authors recommend that other effects of microdrip irrigation on plant-soil relationships should be investigated.

Altered planting dates used in response to environmental conditions can lead to morphological changes that can impact crop production (Williams 2008).

Improved integrated pest management approaches are likely to be the best adaptation to prevent and contain pest and disease outbreaks. Biological control programmes may be an important factor in controlling outbreaks of pests and weeds, although further work is required in assessing the effectiveness of potential control agents (Zalucki and van Klinken 2006). Selection for greater latent period may be an effective method to increase partial resistance to northern leaf blight infection (Carson 2006). Crop rotations are an effective method to control nematodes by breaking the population cycle.

Critical threshold.

Based on the literature reviewed above, it is suggested that the most significant temperature threshold for the successful production of corn is 32˚C during the period three to four weeks after pollination. Temperatures above this threshold during this period have been demonstrated to cause significant reductions in yield (Commuri and Jones 2001; Shaw 1983).

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Sweet Corn – Developmental Phase (3-4 weeks after pollination) – Critical Temperature Threshold

Temperatures above 32°C during the period three to four weeks after pollination cause significant reductions in yield.

References. Assouline S., Cohen S., Meerbach D., Harodi T. & Rosner M. (2002) Microdrip irrigation of field crops: Effect on yield, water uptake, and drainage in sweet corn. Soil Sci. Soc. Am. J. 66, 228-35.

Ben-Asher J., Garcia A. G. Y. & Hoogenboom G. (2008) Effect of high temperature on photosynthesis and transpiration of sweet corn (Zea mays L. var. rugosa). Photosynthetica 46, 595-603.

Bird I. F., Cornelius M. J. & Keys A. J. (1977) Effects of temperature on photosynthesis by maize and wheat. J. Exp. Bot. 28, 519.

Cardwell V. (1982) Fifty years of Minnesota corn production: sources of yield increase. Agronomy Journal 74, 984-90.

Carson M. L. (2006) Response of a maize synthetic to selection for components of partial resistance to Exserohilum turcicum. Plant Dis. 90, 910-4.

Carson M. L. & Vandyke C. G. (1994) Effect of light and temperature on expression of partial resistance of maize to Exserohilum turcicum. Plant Dis. 78, 519-22.

Commuri P. D. & Jones R. J. (2001) High temperatures during endosperm cell division in maize: A genotypic comparison under in vitro and field conditions. Crop Sci. 41, 1122-30.

Coop L. B., Croft B. A. & Drapek R. J. (1993) Model of corn-earworm (Lepidoptera, Noctuidae) development, damage and crop loss in sweet corn. Journal of Economic Entomology 86, 906-16.

Garcia A. G. Y., Guerra L. C. & Hoogenboom G. (2009) Water use and water use efficiency of sweet corn under different weather conditions and soil moisture regimes. Agric. Water Manage. 96, 1369-76.

Jones J. W., Hoogenboom G., Porter C. H., Boote K. J., Batchelor W. D., Hunt L. A., Wilkens P. W., Singh U., Gijsman A. J. & Ritchie J. T. (2003) The DSSAT cropping system model* 1. European Journal of Agronomy 18, 235-65.

Kim S. H., Gitz D. C., Sicherb R. C., Baker J. T., Timlin D. J. & Reddy V. R. (2007) Temperature dependence of growth, development, and photosynthesis in maize under elevated CO2. Environ. Exp. Bot. 61, 224-36.

Kwabiah A. B. (2004) Growth and yield of sweet corn (Zea mays L.) cultivars in response to planting date and plastic mulch in a short-season environment. Sci. Hortic. 102, 147-66.

Ledencan T., Sudar R., Simic D., Zdunic Z. & Brkic A. (2008) Effects of the agroecological factors on sweet corn quality. Cereal Res. Commun. 36, 1411-4.

Levy Y. & Pataky J. K. (1992) Epidemiology of northern leaf blight on sweet corn. Phytoparasitica 20, 53-66.

Lizaso J. I., Batchelor W. D., Boote K. J., Westgate M. E., Rochette P. & Moreno-Sotomayor A. (2005) Evaluating a leaf-level canopy assimilation model linked to CERES-maize. Agronomy Journal 97, 734.

Lizaso J. I., Boote K. J., Cherr C. M., Scholberg J. M. S., Casanova J. J., Judge J., Jones J. W. & Hoogenboom G. (2007) Developing a sweet corn simulation model to predict fresh market yield and quality of ears. Journal of the American Society for Horticultural Science (USA) 132, 415.

Modi A. T. & Asanzi N. M. (2008) Seed performance of maize in response to phosphorus application and growth temperature is related to phytate-phosphorus occurrence. Crop Sci. 48, 286-97.

Rosenberg N. J. (1981) The increasing CO 2 concentration in the atmosphere and its implication on agricultural productivity. Clim. Change 3, 265-79.

Sage R. F. & Monson R. K. (1999) C4 plant biology. Academic Pr.

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Shaw R. H. (1983) Estimates of yield reductions in corn caused by water and temperature stress'. Crop Reactions to Water and Temperature Stresses in Humid, Temperate Climates, Westview, Boulder, CO, 49-65.

Sparks T. H., Dennis R. L. H., Croxton P. J. & Cade M. (2007) Increased migration of Lepidoptera linked to climate change. European Journal of Entomology 104, 139-43.

Srivastava C. P., Joshi N. & Trivedi T. P. (2010) Forecasting of Helicoverpa armigera populations and impact of climate change. Indian J. Agric. Sci. 80, 3-10.

Stone P. J., Wilson D. R., Reid J. B. & Gillespie R. N. (2001) Water deficit effects on sweet corn. I. Water use, radiation use efficiency, growth, and yield. Aust. J. Agric. Res. 52, 103-13.

Tefferi A., Hulluka M. & Welz H. G. (1996) Assessment of damage and grain yield loss in maize caused by northern leaf blight in western Ethiopia. Z. Pflanzenk. Pflanzens.-J. Plant Dis. Prot. 103, 353-63.

Thompson L. M. (1986) Climatic change, weather variability, and corn production. Agron. J. 78, 649-53.

Waggoner P. E. (1983) Agriculture and a climate changed by more carbon dioxide'. Changing Climate: Report of the Carbon Dioxide Assessment Committee, 383-418.

Williams M. M. (2008) Sweet corn growth and yield responses to planting dates of the north central United States. Hortscience 43, 1775-9.

Wilson D. R. & Salinger M. J. (1994) Climatic risk for sweet corn production in Canterbury, New Zealand. N. Z. J. Crop Hortic. Sci. 22, 57-64.

Zalucki M. P. & Furlong M. J. (2005) Forecasting Helicoverpa populations in Australia: a comparison of regression based models and a bioclimatic based modelling approach. Insect Science 12, 45-56.

Zalucki M. P. & van Klinken R. D. (2006) Predicting population dynamics of weed biological control agents: science or gazing into crystal balls? Aust. J. Entomol. 45, 331-44.

Zhang T. Q., Tan C. S. & Warner J. (2007) Fresh market sweet corn production with clear and wavelength selective soil mulch films. Can. J. Plant Sci. 87, 559-64.

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The influence of temperature on the growth and development of avocado. Background to the report

This report is one of a series of literature reviews completed as part of the Critical Thresholds (‘Tipping Points’) and Climate Change Impacts/Adaptation in Horticulture project undertaken Agri-Science Queensland and Growcom. The purpose of this report is to synthesise information on the influence of temperature on the development of avocados and, where possible, to identify specific temperature limitations associated with avocado growth phases and key pest and diseases by assessing information contained in existing peer reviewed journal articles.

This contents of this report are adapted from a separate report on the impacts of climate change and climate policies on Australian avocado production (Muller et al. 2010).

Climate requirements for avocado production

Avocados have been commercialized relatively recently. While a significant body of research is developing for the crop, the scientific literatures is somewhat limited compared to more established crops. This has made assessment of the climatic factors critical to successful avocado production more of a challenge, and it should be noted that there is virtually no peer-reviewed scientific literature regarding one of Australia’s key varieties, ‘Shepard’.

The avocado, Persea americana Miller, is a tropical and sub-tropical evergreen tree producing a large oily fruit.

The varieties of avocado that are grown commercially around the world are from three distinct ecological races or botanical varieties:

P. americana var. drymifolia (Mexican),

P. americana var. americana (West Indian) and

P. americana var. guatemalensis (Guatemalan).

The Mexican and Guatemalan ecotypes originated in subtropical/tropical highland environments and the West Indian ecotypes originated in tropical lowland environments. Each geographical ecotype has distinctive adaptations and horticultural and botanical features (Perez-Jimenez 2008) which influences their adaptability to environmental conditions.

Successful avocado production requires a warm climate and protection from frost. After grafting, avocado trees begin to crop after three years, peaking around eight to nine years of age. A production span, however, can last up to 20 years.

Depending on the production region, avocado fruit takes between six and 15 months to grow to maturity. For a short period in cooler regions, trees carry last season’s mature fruit and next season’s recently set immature fruit. Avocado fruit does not ripen until it is mature and removed from the tree.

Avocado has a unique flowering behaviour known as complementary, synchronous, dichogamy (Schaffer and Whiley 2002). Group A varieties, such as ‘Hass’, ‘Pinkerton’, ‘Reed’, ‘Rincon’ and ‘Wurtz’, open as female in the morning of the first day and male in the afternoon of the second day. Group B varieties, such as ‘Fuerte’, ‘Bacon’, ‘Edranol’, ‘Ettinger’ and ‘Kona Sharwil’, open as female in the afternoon of the first day and male in the morning of the second day.

Avocados are known to be highly sensitive to both climatic and edaphic factors (Wolstenholme 2002). Climatic conditions affect avocado physiology, phenology, productivity and yields, fruit quality and the incidence of pests and diseases. To explore these effects and to identify optimal and threshold conditions, the scientific literature has been reviewed to identify the influence of temperature, rainfall, relative humidity, atmospheric carbon dioxide (CO2) levels and solar radiation.

Temperature

The preferred average annual temperature range for group A varieties is 6.5°C to 19°C and for group B varieties is 10°C to 20°C (Praloran in Whiley et al. 2002). A number of authors suggest that average daily temperatures between 20°C to 25°C provide optimal conditions for general growth, root growth, flowering and fruit set for most varieties (Lahav and Trochoulias 1982; Sedgley and Annells 1981). Lahav and Trochoulias (1982) found a day/night temperature range of 25/18°C resulted in optimal root

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growth and dry matter accumulation in ‘Fuerte’, while the range was 21/14°C for ‘Hass’. Optimum photosynthetic rate for the variety ‘Edranol’ has been found to occur at a temperature range of 19-24°C (Bower et al. in Bower and Cutting 1988), although this is not a commercial variety in Australia. Maximum net photosynthetic rates for ‘Fuerte’ occurred between 28-31°C (Scholefield et al. in Schaffer and Whiley 2003).

Temperature has a major influence on the avocado’s reproductive biology and is the key factor triggering the change from vegetative growth to the reproductive stage (Gazit and Degani 2002). During anthesis, temperature can severely disrupt the dichogamy, though Group A trees are generally more tolerant of both cooler and warmer temperatures (Schaffer and Whiley 2002). For example, Lahav and Trochoulias (1982) found that ‘Hass’ was less adversely effected by temperature extremes.

Flowering, pollination and fruit set have been found to be the most critically temperature sensitive stages for avocado. While avocado flowering and pollination can be affected by low temperatures, high temperatures are more detrimental. High temperatures accompanied by low relative humidity are particularly damaging (Wolstenholme 2002). Research suggests that each avocado variety probably has its own specific temperature optima and thresholds.

A six to eight week period of cool weather is required for the initiation, development and growth of inflorescences. During the flower development phase (from bud break to the point of flowering), night temperature of 5-10˚C stop vegetative and shoot growth and promote good flowering. Night temperature should not exceed 15˚C. Day temperature should not exceed 25˚C, though 20˚C preferred. (Vock et al. 2001)

Buttrose and Alexander (1978a) report that effective temperatures for flower initiation in ‘Fuerte’ were 20°C during the day and between 5 and 10°C at night. For ‘Hass’, 23/18°C day/night is likely to be the critical point for flowering (Gazit and Degani 2002). Loupassaki and Vasilakakis (1995) found that optimum in vitro germination of ‘Fuerte’ pollen occurred at 25°C. These authors also reported results suggesting the optimum temperature for avocado pollen germination was between 25°C and 29°C.

Gazit and Degani (2002) note that while the typical flowering season extends for approximately 2 months, it will be shorter in warmer weather and longer in cooler weather.

Effect of low temperatures

Flowering can be adversely affected by low night temperatures. Overnight temperatures around 10-12°C appear to be a threshold below which problems with pollination and fruit set start to emerge for many varieties (Lomas 1988; Zamet 1990); low temperatures have been found to reduce the number of flowers that open with a female stage (particularly in group B varieties), delay or retard the pollination process and slow pollen tube growth (Argaman 1983; Gafni 1984; Sedgley and Annells 1981; Sedgley and Grant 1982/1983). Group B varieties are less productive under cool conditions than group A. Low temperatures also reduce the activity of pollinating insects (Bergh 1967; Peterson 1955).

A temperature regime of 17/10°C day/night was found to restrict root growth and dry matter accumulation in both ‘Hass’ and ‘Fuerte’ (Lahav and Trochoulias 1982). A number of studies investigating the effect of temperature on avocado yields have also confirmed 10°C as a threshold for yield decline (Bower and Cutting 1988; Lobell et al. 2007; Zamet 1990).

Some studies, however, have shown that minimum temperatures may be less important than the diurnal temperature range, which influences the period of time both male and female flowers are open concurrently (Sedgley and Grant 1982/1983). Gafni (1984) found that low night temperatures of 5°C for 3-4 nights did not decrease fruit set in ‘Ettinger’ and ‘Fuerte’, and even cold minimums which commenced immediately after pollination and continued through the fertilisation process caused no damage. He concluded that regular low night minimums during most of the fruit-set season are not a limiting factor of avocado fertility. Others have suggested that low temperatures may be more detrimental when they are sustained over a prolonged period such as a week or more (Argaman 1983; Zamet 1990). Other experiments suggest that the absence of high temperature is more important than low temperatures (Buttrose and Alexander 1978b).

Effect of high temperatures

While there is some variation in the evidence presented in the literature regarding low temperature thresholds, there is strong agreement regarding the negative effects of high temperature – both high day or maximum temperatures and high night minimum temperatures.

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Researchers report that high day or maximum temperatures have a negative effect on root growth (Lahav and Trochoulias 1982), shorten the flowering period (Sedgley et al. 1985); cause abnormalities in flowers (Sedgley et al. 1985), cause pollination or fruit set failure or pollen tube burst (Argaman 1983; Gafni 1984; Sedgley and Annells 1981), and fruit abscission (Sedgley et al. 1985).

Upper temperature thresholds appear to be 33°C for flowering and 35-37°C during fruit set. Photosynthesis has also been found to be irreversibly damaged by 35-37°C temperatures (Schaffer and Whiley 2003). These high temperature thresholds are also reflected in research on yields (Bower and Cutting 1988; Buttrose and Alexander 1978b; Lobell et al. 2007; Zamet 1990). Growers who participated in the carbon footprinting component of this project also confirmed these temperature thresholds from their experience.

Lahav and Trochoulias (1982) found the 30-37°C range reduced root growth and dry matter accumulation by 60-70% compared with optimal temperature ranges for ‘Hass’ and ‘Fuerte’.

At 33°C, fruit abscission occurred in ‘Hass’ and ‘Fuerte’ varieties (Sedgley and Annells 1981) and daytime maximums of 35°C during flowering and fruit set caused all fruit to drop 10 days after pollination (Sedgley and Annells in Lomas 1988). ‘Hass’ could withstand short periods of temperatures above 30°C (Sedgley and Annells 1981).

Gafni (1984) found that a day/night range of 32/22°C for three weeks from the day of pollination caused significant decline in fruit set of ‘Fuerte’ and that for all varieties 2-4 days exposure to 20-22°C minimums and 38-39°C maximums damaged pollination and fruit set. Mature pollen was affected by several hours exposure to 34°C. Argaman (1983) also found that a temperature regime of 32-35°C day and 21-23°C night temperature lasting one week caused damage to ovules and especially to the pollen of ‘Fuerte’. Pollen tubes rarely penetrated the ovary or reached the embryo sac. On the other hand, pollen from the ‘Ettinger’ variety was unaffected by temperatures almost as high.

Sedgley et al. (1985) note that during flowering, a high night temperature and a high average diurnal temperature may be more significant than the daily maximum temperature. Studies of Californian crop yields also showed that night minimum temperatures in excess of 12°C during flowering and fruit set were detrimental to avocado yields (Lobell et al. 2007). High temperatures during fruit maturation, however, may assist post harvest fruit quality, as exposure to high temperatures on the tree can improve tolerance to low temperatures during storage (Ferguson et al. 1999).

High temperatures impact on the rate of photosynthesis: 32.2°C has been identified as the threshold for closure of the stomata in avocados (Liu in Hofshi 1998).

A two year trial on the impact of harvesting avocados in high temperatures (McCarthy 2009) tested the effect of high temperatures on softness, skin colour, body rots, vascular browning, diffuse discolouration and stem end rots. High temperatures at harvest (over 30°C) and delays in placing fruit into cool storage did impact on these quality parameters, but most impacts were minor. Body rot was found to be the most significant impact; the incidence increased by 0.17 with each 1˚C increase in temperature (based on a two hour delay in cooling).

Woolf and Ferguson (2000) discuss the effects of high flesh temperatures in fruit in the field on post harvest quality. High flesh temperatures (up to 15°C above the air temperature) can be recorded in the exposed side of fruits. In avocado, this can prolong ripening time by around 1.5 days but may improve fruit quality. ‘Hass’ and Fuerte fruits exposed to direct sunlight were found to be firmer than shaded fruits because sun exposure affected cell wall enzyme activity (Woolfe et al. 1999 in Moretti et al. 2009). McCarthy (2009) also found, in Western Australia, that the pulp of fruit exposed to direct sunlight was consistently 5-8˚C higher than the ambient air temperature.

‘Hass’ fruits have been found to be 17% smaller when grown in warm coastal environments compared to cool highland environments (Schaffer and Whiley 2002), so higher temperatures during fruit development may negatively affect fruit size. Research by Heath and Arpaia (2007) confirmed the effect of high temperatures on lowering carbon accumulation which led to smaller fruit and lower overall yields in California. Research by Cutting (1993) suggests that the tendency of the ‘Hass’ variety to produce smaller fruits in warmer environments may be related to concentrations of zeatin and dihydrozeatin type cytokinins in the seed and testa which were greater in fruit from cooler areas than warmer areas. While the relationship between cytokinin concentrations and testa health is still to be determined, it does appear to influence cell division throughout the life of the avocado fruit.

Moretti et al. (2009) review research showing how the postharvest quality of fresh fruit and vegetable crops can be directly and indirectly affected by high temperatures and exposure to elevated levels of

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carbon dioxide. The review notes that temperature increase can affect photosynthesis (through modulation of enzyme activity and electron transport chains), altering sugars, organic acids, flavanoids, firmness and antioxidant activity. Above certain temperature thresholds, many enzymes lose their function, potentially changing plant tissue tolerance to heat stresses.

Dry matter content (a harvest indicator used for avocado) directly correlates with oil content. ‘Hass’ avocados grown under higher temperatures (45˚C compared to 30˚C) had a higher moisture content and a reduced oil composition (Woolfe et al 1999 in Moretti et al. 2009).

The impact of temperature on avocado pests and diseases

Outbreaks of pests and diseases can occur when changes in climate result in more favourable conditions for their growth, survival and dissemination (reviewed in Aurambout et al. 2006).

Phytophthora root rot is undoubtedly the most destructive and important disease of avocado, limiting production in almost every country it is grown (Pegg et al. 2002; Perez-Jimenez 2008). Phytophthora is caused by the oomycete Phytophthora cinnamomi Rands, which destroys the fine feeder roots of avocado, limiting uptake of water and nutrients, in time killing the tree (Pegg et al. 2002). Its survival is strongly determined by clear temperature ranges, though soil moisture levels are also critical. Root rot is more severe and develops more rapidly in soils with poor drainage; disease development is optimal in wet soil at temperatures ranging between 21 to 30°C (Pegg et al. 2002). Zentmyer (1981) found in a Californian avocado orchard, maximum infections occurred during summer and autumn where maximum soil temperatures at 10cm depth were 24.5-25.5°C. Little or no infection occurs at or above 33°C or below 13°C (Pegg et al. 2002; Zentmyer 1981). Zentmyer (1981) also notes that the preferred temperature ranges for P. cinnamomi and its avocado host were very similar.

Under natural conditions, there are great seasonal variations in P. cinnamomi populations in soils which are correlated with soil temperature and, when temperatures are conducive, with soil-water potential (Perez-Jimenez 2008). Infections occur in the temperature range 15-27°C, though the optimum temperatures are between 22-26°C (Zentmyer 1981). Even when soil temperatures are optimal, however, the pathogen cannot survive outside the host if soil water potential is low (Zentmyer 1980 in Perez-Jimenez 2008), although some propagules such as chlamydospores can survive for many years under these conditions.

Research on Australian isolates of P. cinnamomi has found that growth did not occur outside a temperature range of 5-35°C (Shepherd and Pratt 1974). Phillips and Weste (1985) also found for Australian isolates that in vitro growth occurred at temperatures between 10-30°C, with a maximum growth rate at 25-30°C.

In international research, Zentmyer et al. (1976) tested 187 P. cinnamomi isolates from 24 countries and 59 hosts. They reported that the optimum temperature range for growth was 21-30°C, with most cultures growing best between 24-27°C. Their results confirmed findings from other authors of in vitro cardinal temperature ranges for growth of P. cinnamomi : minimums between 5-16°C; optimum growth between 20-32°C; and maximum temperatures 30-36°C.

Perez-Jiminez (2008) reports no growth at temperatures above 33-34°C and populations are limited when soil temperatures are less than 10°C. She also notes that P. cinnamomi does not survive 2-3 days at 36°C; 1-2 hours at 39°C and 10-30minutes at 45°C.

Nesbitt et al. (1979) investigated the effect of temperature and soil moisture on the formation of hyphal lysis and sporangi in P. cinnamomi. Hyphal lysis formed most rapidly in soils incubated at 25-27°C. Sporangia were not formed at temperatures below 15°C.

Studies of the effectiveness of soil disinfestation using solarisation provide another perspective on temperature thresholds for P. cinnamomi. Soil infested with P. cinnamomi was covered with clear plastic to raise the soil temperature: the research showed that P. cinnamomi was inactivated after 1-2 hours at soil temperatures of 38°C, and that 1-2 hours of 40°C was required to kill all propagules when chlamydospores were present (Gallo et al. 2007).

Other studies have investigated the effect of microbial antagonists of P. cinnamomi in organic mulches applied to avocado orchards (You and Sivasithamparam 1995). This research showed that the fungal and bacterial microbes in mulch decreased the infectivity of P. cinnamomi and that increasing temperatures and moisture content in the mulch had a significantly positive influence on their populations. The authors suggested that phytophthora root rot could possibly be limited by monitoring and manipulating the temperature and moisture of organic mulches.

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Denner et al. (1986) studied fungi that cause anthracnose and stem end rot: Colletotrichum gloeosporioides and Dothiorella achieved germination between the temperature range of 10-35°C, but optimal germination occurred at 25-30°C. For initiation of germination, temperatures needed to be between 20-35°C for at least 3 hours. No germination or growth occurred at 5°C or 40°C. Appressoria were produced at temperatures between 10 and 30°C. The optimal temperature for growth was 28°C, while temperatures exceeding 30°C and less than 10°C retarded growth. Denner et al. (1986) concluded that anthracnose infection will not take place at temperatures of 10°C or lower and temperatures lower than 15°C or exceeding 28°C will prevent extensive infection. He notes that further research would be required to assess the effects of soil moisture.

A major insect pest in avocado are coreid fruit spotting bugs, Amblypelta nitida and A. lutescens lutescens, which can cause severe damage to fruit, particularly in orchards close to the natural habitat of the insects such as rainforest, wet sclerophyll forests, dry Acacia/Eucalyptus forests and riparian vegetation (Drew 2007; Waite and Martinez-Barrera 2002). Fruit spotting bugs are common in Queensland and New South Wales but are not recognized as a problem in Western Australia or Sunraysia. Surveys of growers have identified that most fruit spotting bug damage occurs between November and February. Bugs have been found to be less active and move shorter distances in cool conditions. In temperatures in excess of 32°C bugs become highly active and fly longer distances, leading to sharp increases in damage in orchards. Growers have noted that damage to orchards is most common in south-east Queensland when there are hot northerly or north-westerly winds and high temperatures, particularly in orchards where there is a rich alternate habitat to the north of the orchard (Drew 2007).

Studies show that the avocado fruit borer (Stenoma catenifer) insect pest has a low temperature development threshold of 8°C, and the viability of these insects was greatest in the 18-28°C range (Nava et al. 2005).

Temperature can also influence the success of beneficial insects that assist in the biological control of winged insect pests such as fruit borers. Studies of Trichogramma species note a minimum temperature threshold of around 11°C (Maceda et al. 2003). More specific research showed T. pretiosum required a minimum temperature greater than 10.7°C and 151.83 degree days growing in the eggs of the host Mediterranean Flour Moth Anagasta kuehniella (Lepidoptera: Pyralidae) while T. acacioi required a minimum temperature greater than 10.46°C and 155.46 degree days in the same host (Pratissoli et al. 2005). Maceda et al. (2003) tested the effects of 15, 20, 25 and 30°C temperatures: maximum parasitisation of host Anagasta kuehniella (Lepidoptera: Pyralidae) occurred at 25°C; developmental rates for Trichogramma were similar at 20, 25 and 30°C and very slow at 15°C.

Ploetz (2009) encourages avocado producers to remain vigilant to the potential of new diseases and problems which may emerge as climate changes drive broader shifts in the behaviours and ranges of pathogens and host species. Laurel Wilt (a disease of tree species in the Laurel family (Lauraceae), caused by a fungus (Raffaelea lauricola) that is introduced into host trees by the Redbay Ambrosia Beetle (Xyleborus glabratus) is suggested as an example of an emerging global threat to avocado production due to climate change.

Rainfall

Effect of rainfall on phenology, yield and quality

Wolstenholme (2002) provides a summary of the optimal rainfall conditions for avocado. In subtropical growing areas with summer dominant rainfall, 1000mm per annum is considered the minimum required. Irrigation is necessary in many production regions, for example in the winter dominant rainfall regions, such as Western Australia and during the dry spring in summer dominant rainfall areas. Avocado water needs vary across the phenological growth stages: low water requirements during winter, moderate to high during flowering, high during the mid-summer fruit drop period and second aerial growth flush phase, and moderate during the general growing period (Whiley in Wolstenholme 2002).

Changes in rainfall could have negative effects on avocado production regions. The key risks are both around reduced rainfall impacting on the availability of irrigation water and the impacts of increased rainfall intensity. Significant reductions in rainfall in production regions could cause water deficit stress or inadequate irrigation supplies.

Water stress can occur suddenly, even at relatively low soil water tension, due to the avocado’s shallow root system, causing wilting or abscission of leaves or fruits (Bower and Cutting 1987; Bower et al. 1977). If fruit is not shed, size and quality may be affected (Bower and Cutting 1988). Maintaining

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optimal water status after fruit set is critical to sustain fruit growth; any setback in fruit growth has been found to be irreversible (Cutting 1984).

Vock et al. (2001) note that:

Severe water stress can occur during flowering, because the evaporative surface of the tree increases by up to 90% and flowers are unable to control water loss as they have no stomates. This can have significant impact on yield.

Water stress during early fruit growth can affect fruit size, quality and overall yield.

Water stress during summer can cause ring neck, particularly during hot dry conditions.

Experiments with partial and whole root zone drying irrigation treatments also showed that reduced water supply caused fruit abscission due to the dry soil around the roots rather than the water status of leaves or fruit (Neuhaus et al. 2009).

Water deficit stress has been found to significantly influence fruit ripening physiology. Avocados are unusual in that they only ripen after fruit have been removed from the tree. The chemical triggers for the ripening process are not well understood, however, long term water stress, particularly in the first three months of fruit development, has an irreversible effect on the ethylene evolution pattern, ripening rates, ripening evenness and fruit quality (Bower and Cutting 1988). Water stress also increased the activity of browning enzymes in ripe fruit after storage (Bower 1988).

Increased incidence of intense rainfall events could also pose significant management risks for orchards. Too much rain during flowering can cause flower shedding and reduce crop set (Wolstenholme 2002). Bower and Cutting (1987) report that excess water can reduce yield and fruit quality by reducing root oxygen availability and also creating conditions for root rot infection to occur. Low oxygen supply to the roots impacts on the uptake of essential nutrients (Labanauskas et al. 1978). High rainfall at critical stages has also been found to affect fruit set or cause fruit drop (Baxter in Bower and Cutting 1987). If soils are waterlogged for more than 2 days due to excessive rain or surface flooding, there is a high probability of tree death (Schaffer and Whiley 2002).

Harvesting can be disrupted by rain and dew. It is recommended that ‘Hass’ fruit should not be picked if it is wet as there is some evidence fruit harvested when wet has an increased incidence of lenticel damage and vascular browning (Duvenhage 1993).

The effect of rainfall on avocado pests and diseases

As the growth rates and survivability of many of the key avocado pests and diseases increase under conditions of high soil moisture content, changes in annual total precipitation or seasonal and short term rainfall patterns could have significant implications for avocado production.

Phytophthora root rot develops best where there is an excess of water in the soil. The moisture assists pathogen development and is a factor in the formation, dispersal and germination of spores (Perez-Jimenez 2008). Zentmyer (1980) notes that the disease can progress in well-drained soils under frequent rainy conditions or in especially rainy years. Wolstenholme (2002) notes that if rainfall exceeds 1800mm/yr and there are several consecutive months of greater than 300mm per month, the risk of soil water logging and, therefore, root rot is severe.

Low soil water suction pressure is the key issue, rather than absolute water content. Sporangia production will be higher in a sandy soil than a clay soil with equal water contents, because clay has a higher water suction pressure (Perez-Jimenez 2008). Rapid drying and rewetting of unmulched soils has also been found to cause large swings in soil salinity which makes the roots more susceptible to P. cinnamomi infection (Downer et al. 2002).

High rainfall and high relative humidity can also encourage diseases such as cercospora spot, anthracnose and scab, and insect pests such as thrips and scales (Wolstenholme 2002). For example, high humidity (>80%) and temperatures between 18 and 26°C promote anthracnose infections (Whiley et al. 2002; Wolstenholme 2002).

Anthracnose, caused by the fungus Glomerella cingulata (Colletotichum gloeosporioides) can occur in all production regions, especially in wet years but it is most common in eastern Australia where there is high summer rainfall. In south-west Western Australia the critical periods are autumn and spring. The ‘Fuerte’, ‘Rincon’ and ‘Wurtz’ varieties are the most susceptible, while ‘Hass’, ‘Pinkerton’, ‘Sharwil’ are the most tolerant due to higher levels of dienes (antifungal compounds) in the skin (Vock et al. 2001).

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There are two forms of anthracnose infection. The first follows insect damage and continues to develop causing rotting of the fruit. The second occurs in conditions where free surface water is present on fruit for 48 hours (for example, after rain, dew or irrigation). In this case, spores that land on the fruit surface germinate and penetrate the skin with an infection peg (or appressorium), which remains dormant until the fruit begins to ripen and its dienes (anti-fungal compounds) begin to break down, allowing the infection to develop (Vock et al. 2001).

Conidia of C. gloeosporioides can be produced in large numbers on dead leaves and twigs entangled in the canopy of the avocado orchard, which can be washed through the tree in rainy weather. For this reason, Anthracnose infection usually occurs during prolonged warm showery weather (Wolstenholme 2002).

Scab is noted as a problem in the humid tropics and subtropics where cool wet conditions are favourable for infection (Ploetz 2009).

Relative humidity

In general, a high relative humidity is beneficial for avocado production as it alleviates physiological stress and supports moderate to high stomatal conductivity and photosynthesis (Wolstenholme 2002). High humidity during and after fruit set is particularly important (Bower and Cutting 1988). The effect of high temperatures is exacerbated if it is accompanied by hot dry winds and low relative humidity (Wolstenholme 2002).

Bower et al. (1977) showed that decreasing relative humidity caused a decline in stomatal conductance and decreased photosynthetic responses. Relative humidity in excess of 32% has been reported as optimal during flowering and fruit set (Human in Bower and Cutting 1988). Avocado pollen viability is improved by higher relative humidity (Loupassaki and Vasilakakis 1995). Bower and Cutting (1988) also report that any sharp decreases in relative humidity after fruit set can cause fruit drop. Wolstenholme (2002) also notes that temperatures above 40°C accompanied by wind and very low relative humidity (less than 20%) cause significant abscission of newly set fruit.

Humid conditions associated with high rainfall, however, can encourage pest and disease problems including cercospora spot, anthracnose, scab, thrips and scale (Wolstenholme 2002) .

Atmospheric carbon dioxide

The potential effects of increased atmospheric carbon dioxide (CO2) concentration on agricultural productivity have now been the subject of a considerable volume of work (reviewed in Drake et al. 1997; Jablonski et al. 2002).

The main effect of increased atmospheric CO2 on plants is increased resource use efficiency (Drake et al. 1997). Exposure to elevated CO2 concentration may lead to increased growth and productivity if the increase in CO2 concentration also leads to elevated temperatures (Ro et al. 2001). For example, water use efficiency often increases as a result of reduced stomatal conductance and transpiration, while light-use efficiency also increases as a result of increased photosynthetic rates. There are potential negatives to increased atmospheric CO2. For example, there are some indications that weed species may respond to higher CO2 more readily than domesticated crops (eg. Ziska and Bunce 1993), while the greater carbon to nitrogen ratio may lead to reduced nutrient content.

Jablonski et al. (2002) conducted an analysis of plant responses to elevated CO2 across 79 species (both crop and wild). This analysis revealed a general pattern of more flowers, more fruits (an average of 28% in crops) and more seeds at higher CO2 concentrations, but lower seed nitrogen concentrations. Another meta-analysis of “free air CO2 enrichment” (FACE) experiments by Ainsworth & Long (2005) revealed a similar suite of effects, but with a lower stimulation of crop yield of 17%. The results of these more recent experiments showing lower than expected responses to increased CO2 cast doubt on earlier projections that rising CO2 will fully offset losses due to climate change (Long et al. 2006). In addition, many of the earlier chamber experiments use enriched conditions of twice the current ambient CO2 concentration which may enhance productivity gains. Current political responses to climate change have a general goal of stabilizing atmospheric concentrations at approx. 450ppm (about 1.2 times current ambient conditions).

Responses to enriched CO2 are crop-specific. For example, long-term experiments on citrus have revealed significant increases in growth and yield (Kimball et al. 2007) under conditions of elevated CO2, while the results have been equivocal for other crops. Possible sources of this variation among crops include different cropping systems, physiologies, research methodologies, water availability and

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nutrient availability (Cure and Acock 1986). Interactions between increased CO2 and higher temperatures further complicate the issue.

There appears to be very little research directly addressing the effect of CO2 enrichment on avocado growth and productivity. Under elevated CO2 (600 µmol mol-1), fruit loss occurs more rapidly for the first 25 days after anthesis but then the rate of loss levels off (Whiley 1999). In contrast, although the rate of fruit loss from trees grown at 350 µmol mol-1 CO2 is lower during the first few weeks after anthesis, fruit drop continues to occur for a longer period. As a result, trees grown at 600 µmol mol-1retained more fruit at 40 days after anthesis than did those grown at 350 µmol mol-1.

The higher rate of fruit loss during the first 25 days for trees grown at elevated CO2 may be a result of increased partitioning of photoassimilates into vegetative growth during the period of early fruit development. For example, trees grown under elevated CO2 display a greater allocation of dry matter to new leaves, new branches, trunk and roots.

While Whiley’s study demonstrated that increased atmospheric CO2 results in increased avocado fruit retention, he was unable to demonstrate an increase in yield under elevated CO2. Furthermore, this work assumes that mean temperatures in tropical and subtropical areas will not increase by more than 1-2˚C (which now seems unlikely; section 3.3), and that water and nutrients are not limiting.

Enrichment of atmospheric CO2 increased the accumulation of biomass in several tropical fruit trees, including avocado (reviewed in Schaffer et al. 1999). In avocado, an increase in fruit yield may be indirect and delayed, resulting from increased water and nutrient uptake via increased root mass (Schaffer et al. 1999). In vitro experiments using micro-propagated avocado plants show no change in maximum net photosynthetic rate between ambient and enriched (approx. 2.6 x ambient) CO2 conditions with constant sucrose concentration in the growth medium (de la Vina et al. 1999). However, the ratio of leaf to stem and root fresh weight was greater in plants grown under the enriched conditions. When radiation was not limiting, net photosynthetic rate was greater under enriched conditions (de la Vina et al. 1999). Better shoot growth and higher rates of biomass accumulation under enriched CO2 conditions have also been observed by Witjaksono et al. (1999).

This lack of information on avocado responses to enhanced atmospheric CO2 forces us to rely on the general observations of responses across multiple crop species to infer likely impacts on avocado production. Based on this information, the projected increase in atmospheric CO2 is likely to have a positive but relatively small influence on fruit yields. However, in those regions that are expected to experience fairly high temperature increases, the effect of CO2 enrichment is unlikely to counteract the negative impact of higher temperatures.

Solar radiation

There is little information on the critical amount of light required for productive avocado orchards (Wolstenholme 2002). Avocados appear to grow well in areas that receive at least 2000 hours of sunshine annually (Gaillard and Godefroy 1995, cited in Wolstenholme 2002). Production areas in California and Israel receive between 3000 and 3500 hours of sunshine per year, mostly during the summer.

Incident light has a major effect on the rate of photosynthesis. For avocados, maximum photosynthetic rate is achieved at an incident light level about 1/3 to 1/2 that of full sunlight (reviewed in Schaffer and Whiley 2002), reflecting the understorey rainforest origin of the species.

Direct sunlight can elevate the surface temperature of exposed fruit between 5 and 11°C above ambient temperature (Schroeder and Kay 1961), increasing the risk of fruit damage from elevated temperatures. In fact, some studies have shown surface temperatures as high as 18°C above ambient air temperature (Woolf et al. 1999). The amount of the temperature increase depends on the incident light level, degree of exposure, fruit colour and air temperature.

There is little precise information on the likely changes to cloud cover and therefore sunlight hours that may accompany future climate change. It is likely that the southern half of Australia will receive a slight increase in sunlight hours while the north will have little change.

Fortunately, the relatively low light requirement of avocados enables a range of management practices that can minimise the impacts of high air temperatures on fruit quality and yield.

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Key climate requirements for avocado production

This review suggests that key climate requirements and thresholds for avocado production include:

In general, optimal conditions for avocado production are an average daily temperature of between 20-25°C.

A frost free climate is preferred, though mature trees can tolerate -4˚ for short periods without damage.

Trees can tolerate temperatures of 40˚C for short periods. Prolonged exposure to high temperatures causes severe stress and loss of productivity

Following the summer growth stage, a 6 to 8 week period of cool weather is required for floral initiation and growth of inflorescences (generally between May and July).

During the flower development phase (from bud break to the point of flowering), night temperatures of 5-10˚C stop vegetative/shoot growth and promote good flowering. Night temperature should not exceed 15˚C. Day temperature should not exceed 25˚C, though 20˚C is preferred.

During flowering and fruit set, the preferred day/night temperature range for ‘Fuerte’ is 25/18°C and for ‘Hass’ is 21/14°C. Night minimum temperatures of 10°C or lower may be a threshold for negative effects on flowering and pollination for some varieties. A maximum daytime temperature threshold of 33°C or above during flowering and fruit set causes pollination failure and abscission of fruit. High night time minimums can also damage flowering, pollination and fruit set.

During the early fruit development period (August to November in eastern production regions), 35-37˚C is the maximum temperature threshold.

Relative humidity should generally exceed 32%, particularly during flowering and fruit set.

In subtropical growing areas with summer-dominant rainfall, successful avocado production requires at least 1000mm of rainfall per year. In most production regions, adequate water supplies are necessary to provide irrigation during the dry season and or at times of high water demand.

Water requirements are highest during flowering and the mid-summer fruit drop period.

Water stress and low relative humidity are particularly damaging to fruit development and post harvest fruit quality if they occur during the first three months of fruit development.

Heavy or prolonged rain during flowering and fruit set is detrimental to crop set, and intense rain over a number of consecutive days at any time of the year can waterlog soils, increasing the risk of root rot and anthracnose infections.

The preferred temperature ranges for key avocado pests and diseases are very similar to that of the avocado. Phytophthora cinnamomi root rot disease development is optimal in wet soils where soil temperatures are 21-30°C. Little or no infection occurs at or above 33°C, or below 13°C.

Optimal conditions for anthracnose infection occur within a temperature range of 18-26°C and relative humidity in excess of 80%.

Avocado – Flowering and Fruitset Developmental Phase – Critical Temperature Threshold

A maximum daytime temperature of 33°C or above during flowering and fruit set causes pollination failure and abscission of fruit.

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References Ainsworth E. & Long S. (2005) What have we learned from 15 years of free air CO2 enrichment (FACE)? A meta analytic review of the responses of photosynthesis, canopy properties and plant production to rising CO2. New Phytologist 165, 351-72.

Argaman E. (1983) Effect of temperature and pollen source on fertilization, fruit-set and abscission in avocado (Persea americana Mill.). The Hebrew University of Jerusalem, Israel.

Aurambout J.-P., Finlay K., Luck J. & Sposito V. (2006) The impacts of climate change on plant biosecurity. Victorian Government Department of Primary Industries, Werribee, Victoria.

Bergh B. O. (1967) Reasons for low yields of avocados. California Avocado Society 1967 Yearbook 51, 161-72.

Bower J. P. (1988) Pre- and Postharvest measures for long term storage of avocados. South African Avocado Growers’ Association Yearbook 1988 11, 68-72.

Bower J. P. & Cutting J. G. (1988) Avocado fruit development and ripening physiology. Horticultural reviews 10, 229-71.

Bower J. P. & Cutting J. G. M. (1987) Some factors affecting post-harvest quality in avocado fruit. In: Proceedings of the World Avocado Congress I pp. 143-6, South Africa.

Bower J. P., Wolstenholme B. N. & de Jager J. M. (1977) Incoming solar radiation and internal water status as stress factors in avocado, Persea Americana (mill.) cv Edranol. In: South African Avocado Growers’ Association Proceedings of the Technical Committee pp. 35-40, South Africa.

Buttrose M. S. & Alexander D. M. (1978a) PROMOTION OF FLORAL INITIATION IN FUERTE AVOCADO BY LOW-TEMPERATURE AND SHORT DAYLENGTH. Scientia Horticulturae 8, 213-7.

Buttrose M. S. & Alexander D. M. (1978b) Promotion of floral initiation in Fuerte avocado by low temperature and short daylength. Sci. Hortic. 8, 213-7.

Cure J. D. & Acock B. (1986) Crop responses to carbon dioxide doubling: a literature survey. Agric. For. Meteorol. 38, 127-45.

Cutting J. G. M. (1993) The cytokinin complex as related to small fruit in "Hass" avocado. South African Avocado Growers’ Association Yearbook 1993, 20-1.

de la Vina G., Pliego-Alfaro F., Driscoll S. P., Mitchell V. J., Parry M. A. & Lawlor D. W. (1999) Effects of CO2 and sugars on photosynthesis and composition of avocado leaves grown in vitro. Plant Physiol. Biochem. 37, 587-95.

Denner F. D. N., Kotze J. M. & Putterill J. F. (1986) The effect of temperature on spore germination, growth and appressorium formation of Colletotrichum gloeosporioides and Dothiorella aromatica. South African Avocado Growers' Association Research Report 9, 19-22.

Downer J., Faber B. & Menge J. (2002) Factors affecting root rot control in mulched avocado orchards. HortTechnology 12, 601-5.

Drake B. G., Gonzalez-Meler M. A. & Long S. P. (1997) More efficient plants: A consequence of rising atmospheric CO2? Annu. Rev. Plant Physiol. Plant Molec. Biol. 48, 609-39.

Drew H. (2007) Improving the management of spotting bugs in avocados. Horticulture Australia Ltd.

Duvenhage J. A. (1993) The influence of wet picking on post harvest diseases and disorders of avocado fruit. South African Avocado Growers’ Association Yearbook, 77-9.

181

Ferguson I., Volz R. & Woolf A. (1999) Preharvest factors affecting physiological disorders of fruit. Postharvest Biol. Technol. 15, 255-62.

Gafni E. (1984) Effect of extreme temperature regimes and different pollinizers on the fertilization and fruit set processes in avocado. The Hebrew University of Jerusalem, Israel.

Gallo L., Siverio F. & Rodriguez-Perez A. M. (2007) Thermal sensitivity of Phytophthora cinnamomi and long-term effectiveness of soil solarisation to control avocado root rot. Ann. Appl. Biol. 150, 65-73.

Gazit S. & Degani C. (2002) Reproductive biology. In: The Avocado: Botany, Production and Uses (eds A. W. Whiley, B. Schaffer and B. N. Wolstenholme) pp. 101-34. CABI Publishing, Oxon.

Heath R. L. & Arpaia M. (2007) Assimilation productivity from canopy to fruit as determined by avocado tree physiology. 2007 Production Research Report - California Avocado Commission, 17.

Hofshi R. (1998) Dreaming in reality. California Avocado Society 1998 Yearbook 82, 137-54.

Jablonski L. M., Wang X. Z. & Curtis P. S. (2002) Plant reproduction under elevated CO2 conditions: a meta-analysis of reports on 79 crop and wild species. New Phytol. 156, 9-26.

Kimball B. A., Idso S. B., Johnson S. & Rillig M. C. (2007) Seventeen years of carbon dioxide enrichment of sour orange trees: final results. Glob. Change Biol. 13, 2171-83.

Labanauskas C. K., Stolzy L. & Zentmyer G. A. (1978) Rootstock, soil oxygen, and soil moisture effects on growth and concentration of nutrients in avocado plants. California Avocado Society Yearbook 62, 118-25.

Lahav E. & Trochoulias T. (1982) The effect of temperature on growth and dry-matter production of avocado plants. Aust. J. Agric. Res. 33, 549-58.

Lobell D. B., Cahill K. N. & Field C. B. (2007) Historical effects of temperature and precipitation on California crop yields. Clim. Change 81, 187-203.

Lomas J. (1988) An agrometeorological model for assessing the effect of heat stress during the flowering and early fruit set on Avocado yields. J. Amer. Soc. Hort. Sci. 113, 172-6.

Long S. P., Ainsworth E. A., Leakey A. D. B., Nosberger J. & Ort D. R. (2006) Food for thought: lower-than-expected crop yield stimulation with rising CO2 concentrations. Science 312, 1918.

Loupassaki M. & Vasilakakis M. (1995) The effect of temperature and relative humidity on the in vitro germination of the pollen of avocado In: The World Avocado Congress III pp. 42-5, Israel.

Maceda A., Hohmann C. L. & dos Santos H. R. (2003) Temperature effects on Trichogramma pretiosum Riley and Trichogrammatoidea annulata de Santis. Braz. Arch. Biol. Technol. 46, 27-32.

McCarthy A. (2009) Harvesting Hass during high temperature. In: 4th Australian and New Zealand Avocado Growers Conference (ANZAGC09) Cairns, Australia.

Moretti C., Mattos L., Calbo A. & Sargent S. (2009) Climate changes and potential impacts on postharvest quality of fruit and vegetable crops: A review. Food Research International.

Muller J., Putland D., Deuter P. & Newett S. (2010) Potential implications of climate change and climate policies for the Australian avocado industry. Report to Horticulture Australia Limited, Sydney.

Nava D. E., Haddad M. D. & Parra J. R. P. (2005) Temperature requirements, estimate of the generations number of Stenoma catenifer and verification of the model in the field. Pesqui. Agropecu. Bras. 40, 961-7.

182

Nesbitt H. J., Malajczuk N. & Glenn A. R. (1979) Effect of soil moisture and temperature on the survival of phytophthora cinnamomi rands in soil. Soil Biology and Biochemistry 11, 137-40.

Neuhaus A., Turner D. W., Colmer T. D. & Blight A. (2009) Drying half of the root-zone from mid fruit growth to maturity in 'Hass' avocado (Persea americana Mill.) trees for one season reduced fruit production in two years. Scientia Horticulturae 120, 437-42.

Pegg K. G., Coates L., Korsten L. & Harding R. M. (2002) Foliar, Fruit and Soilborne Diseases. In: The Avocado: Botany, Production and Uses (eds A.W.Whiley, B. Schaffer and B. N. Wolstenholme) pp. 299-338. CABI Publishing, Oxon.

Perez-Jimenez R. M. (2008) Significant avocado diseases caused by fungi and oomycetes. The European Journal of Plant Science and Biotechnology 2 (1), 1-24.

Peterson P. A. (1955) Avocado flower pollination and fruit set. California Avocado Society 1955 Yearbook 39, 163-9.

Phillips D. & Weste G. (1985) Growth rates of four Australian isolates of Phytophthora cinnamomi in relation to temperature. Transactions of the British Mycological Society 84, 183-5.

Ploetz R. (2009) Status, impact and management of the major diseases of avocado. In: 4th Australian and New Zealand Avocado Growers Conference (ANZAGC09), Cairns, Australia.

Pratissoli D., Zanuncio J. C., Vianna U. R., Andrade J. S., Pinon T. B. M. & Andrade G. S. (2005) Thermal requirements of Trichogramma pretiosum and T. acacioi (Hym.: Trichogrammatidae), parasitoids of the avocado defoliator Nipteria panacea (Lep.: Geometridae), in eggs of two alternative hosts. Brazilian Archives of Biology and Technology 48, 523-9.

Ro H. M., Kim P. G., Lee I. B., Yiem M. S. & Woo S. Y. (2001) Photosynthetic characteristics and growth responses of dwarf apple (Malus domestica Borkh. cv. Fuji) saplings after 3 years of exposure to elevated atmospheric carbon dioxide concentration and temperature. Trees-Struct. Funct. 15, 195-203.

Schaffer B. & Whiley A. W. (2002) Environmental physiology. In: The Avocado: Botany, Production and Uses (eds A. W. Whiley, B. Schaffer and B. N. Wolstenholme) pp. 135-60. CABI Publishing, Oxon.

Schaffer B. & Whiley A. W. (2003) Environmental regulation of photosynthesis in avocado trees - a mini review. In: World Avocado Congress V pp. 335-42, Mexico.

Schaffer B., Whiley A. W. & Searle C. (1999) Atmospheric CO2 enrichment, root restriction, photosynthesis, and dry-matter partitioning in subtropical and tropical fruits. Hortscience 34, 1033-7.

Schroeder C. A. & Kay E. (1961) Temperature conditions and tolerance of avoado fruit tissue. California Avocado Society Yearbook 45, 87-92.

Sedgley M. & Annells C. M. (1981) Flowering and fruit-set response to temperature in the avocado cultivar Hass. Scientia Horticulturae 14, 27-33.

Sedgley M. & Grant W. J. R. (1982/1983) Effect of low temperatures during flowering on floral cycle and pollen tube growth in nine avocado cultivars. Scientia Horticulturae 18, 207-13.

Sedgley M., Scholefield P. & Alexander D. M. (1985) Inhibition of flowering of Mexican- and Guatemalan- type avocados under tropical conditions. Scientia Horticulturae 25, 21-30.

Shepherd C. J. & Pratt B. H. (1974) Temperature-growth relations and genetic diversity of A2 mating-type isolates of Phytophthora cinnamomi in Australia. Australian Journal of Botany 22, 231-49.

183

Vock N., Newett S., Whiley A. W., Dirou J., Hofman P., Ireland G., Kernot I., Ledger S., McCarthy A., Miller J., Pinese B., Pegg K. G., Searle C. & Waite G. (2001) Agrilink Horticulture Series. In: Avocado Information Kit (ed N. Vock). The State of Queensland Department of Primary Industries, Brisbane.

Waite G. K. & Martinez-Barrera R. (2002) Insect and mite pests. In: The Avocado: Botany, Production and Uses (eds A. W. Whiley, B. Schaffer and B. N. Wolstenholme). CABI Publishing, Oxon.

Whiley A. (1999) Investigation of potential productivity benefits to tropical and subtropical tree fruit and nut crops from elevated CO2 levels: report for RIRDC project DAQ-156A.

Whiley A. W., Schaffer B. & Wolstenholme B. N. (2002) The Avocado: Botany, Production and Uses. CABI Publishing, Oxon.

Witjaksono, Schaffer B. A., Colls A. M., Litz R. E. & Moon P. A. (1999) Avocado shoot culture, plantlet development and net CO2 assimilation in an ambient and CO2 enhanced environment. In Vitro Cell. Dev. Biol.-Plant 35, 238-44.

Wolstenholme B. N. (2002) Ecology: climate and the edaphic environment. In: The Avocado: Botany, Production and Uses (eds A. W. Whiley, B. Schaffer and B. N. Wolstenholme) pp. 71-100. CABI Publishing, Oxon.

Woolf A. B., Bowen J. H. & Ferguson I. B. (1999) Preharvest exposure to the sun influences postharvest responses of 'Hass' avocado fruit. Postharvest Biol. Technol. 15, 143-53.

Woolf A. B. & Ferguson I. B. (2000) Postharvest responses to high fruit temperatures in the field. pp. 7-20. Elsevier Science Bv.

You M. P. & Sivasithamparam K. (1995) Changes in microbial-populations of an avocado plantation mulch suppressive of Phytophthora cinnamomi. Applied Soil Ecology 2, 33-43.

Zamet D. N. (1990) The Effect of Minimum Temperature on Avocado Yields. California Avocado Society 1990 Yearbook 74, 247-56.

Zentmyer G. A. (1981) The effect of temperature on growth and pathogenesis of Phytophthora cinnamomi and on growth of its avocado host. Phytopathology 71, 925-8.

Zentmyer G. A., Leary J. V., Klure L. J. & Grantham G. L. (1976) Variability in growth of Phytophthora cinnamomi in relation to temperature Phytopathology 66, 982-6.

Ziska L. H. & Bunce J. A. (1993) The influence of elevated CO2 and temperature on seed germination and emergence from soil. Field Crop. Res. 34, 147-57.

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The influence of temperature on the growth and development of pumpkin (Cucurbita spp).

Background to the report.

This report is one of a series of literature reviews completed as part of the Critical Thresholds (‘Tipping Points’) and Climate Change Impacts/Adaptation in Horticulture project undertaken by the Department of Primary Industries and Fisheries (DPI&F) and Growcom. The purpose of this report is to synthesise information on the influence of temperature on the development of pumpkins (Cucurbita spp) and, where possible, to identify specific temperature limitations associated with pumpkin growth phases and key pest and diseases by assessing information contained in existing peer reviewed journal articles

Introduction.

Pumpkins are one of the most widely grown cucurbit crops. However, there appears to be relatively little research directly addressing the temperature requirements of pumpkins. As a result, this review will also refer to research conducted on related cucurbit crops such as zucchini and squash. The common name “pumpkin” may refer to the fruit of three different species from the Cucurbita genus:

Cucurbita pepo – some pumpkin, squash, gourd & zucchini.

Cucurbita moschata – eg. “Butternut”, “Jap” and “Kent” pumpkins. Varieties of C. moschata are generally more tolerant of hot, humid weather.

Cucurbita maxima – eg. “Queensland blue” and “Jarrahdale” pumpkins.

A further complication is caused by the inconsistent use of common names in different world markets. For example, the pumpkin varieties commonly grown for culinary purposes in Australia are referred to as “winter squash” in North America where the term pumpkin usually refers to ornamental varieties or those suitable for processing and canning.

This report will concentrate on the main varieties grown in Australia from the species C. maxima and C. moschata, but will also refer to literature on other members of the Cucurbita genus where necessary.

General temperature responses.

Despite the importance of pumpkins and other Cucurbita in global agriculture, there has been surprisingly little published research tackling physiological aspects of production, including responses to temperature (reviewed in Loy 2004). Cucurbits in general are warm climate crops that are sensitive to cold and frost (Nerson 2007). However, established C. maxima plants are sensitive to high rootzone temperatures and tolerant of relatively low soil temperatures (Zhang et al. 2007).

Germination.

Temperatures for successful germination in cucurbits have been reported in the range of 15 to 45˚C. Milani et al. (2007) reported that the minimum and maximum germination temperatures are 15˚C and 38˚C respectively. The optimum temperature range for germination of seeds in the Cucurbita genus has been reported as 20˚C to 30˚C (Ellis et al. 1985) or 20˚C to 32˚C (Kurtar 2010). Some cucurbits, such as some melons, do not germinate at soil temperatures below 17-19˚C (reviewed in Nerson 2007). Low temperatures at germination may be a limiting environmental factor for cucurbit crops (Nerson 2007).

Detailed modelling of germination temperatures in cucurbits (Kurtar 2010) suggested that pumpkins (both C. moschata and C. maxima) have an optimum temperature of 27˚C for both germination percentage and germination speed. For C. maxima, germination percentage and speed decline rapidly at temperatures higher than about 30˚C, and germination fails at 42˚C. Germination also fails for C. moschata at 42˚C; however germination percentage remains relatively high at 36˚C (approximately 70%). This study determined that the maximum thermal limit was 39˚C for both C. maxima and C. moschata.

Growth.

NeSmith (1997) developed a thermal time model of growth versus thermal time for C. pepo. Under this model, heat units were accumulated at temperatures between a base of 8˚C and a ceiling of 32˚C. These temperature limits were based on germination data on the same set of varieties (see above).

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The actual temperatures at the study sites frequently exceeded this range. The resulting model provided a good prediction of leaf number at a range of times following sowing (NeSmith 1997), suggesting that this temperature range may represent a suitable range for vegetative growth for these varieties of summer squash.

Flowering & Fruiting.

Pumpkins (and all other Cucurbita) are monoecious with male and female flowers occurring on the same plant. The pattern of flowering is generally similar across the domesticated species and plays a central role in productivity. Staminate (“male”) flowers tend to appear several days before the pistillate (“female”) flowers. In summer squash (C. pepo), the number of staminate flowers increases with increasing temperatures between 20˚C and 27.5˚C but declines at higher temperature (Woodson and Fargo 1991).

The effects of environmental variables on fruit set in pumpkins have received little attention (Loy 2004). The minimum temperature for pollen dehiscence (release) in cucurbits is about 9˚C - 10˚C and is not usually an important factor (Seaton and Kramer 1939, cited in Loy 2004). Pollen germination and pollen tube growth has been observed at temperatures of 20˚C and 30˚C. Pollen developed at 20˚C grew significantly longer pollen tubes and sired significantly more seeds than the pollen developed at 30˚C (Johannsson and Stephenson 1998), but the exact temperature limits have not be defined in detail (Loy 2004). In another species of subtropical cucurbit apparently adapted to similar environmental conditions to C. moschata, pollen viability is reduced following short periods of exposure to temperatures above 35˚C (Iapichino and Loy 1987).

There is some evidence that high temperatures may have a greater negative effect on the initiation and development of pistillate flowers than on pollen viability or flower function before or during anthesis (Loy 2004; NeSmith et al. 1994; Wien et al. 2002). For example, in research on several varieties in the US, fruit yields were much lower in regions with more frequent episodes of temperatures over 35˚C (Wien et al. 2002). Wien et al. (2002) suggested that the delay in fruit set from high temperatures may result in increased vegetative growth and suppression of female flower development. Episodes of low fruit yields in decorative pumpkins (C. pepo) appear to be associated with periods of high temperatures, and greenhouse experiments confirmed that high temperature delay formation and anthesis of female flowers (Wien et al. 2004). However, there appears to be significant genetic variation in susceptibility to high temperatures which might be exploited to improve performance under these conditions.

Elevated CO2.

Experiments using controlled-environment chambers reveal that elevated CO2 levels have no significant effect on the timing or success of germination in ornamental pumpkins (C. pepo)(Ziska and Bunce 1993). However, these experiments did reveal that a number of weed species do respond positively to enhanced CO2, which may be an indication of potential weed problems under future atmospheric conditions. Despite the amount of research on the effects of elevated CO2 on growth and productivity for a range of crops (eg. Jablonski et al. 2002), we were unable to find any quality information on pumpkin or cucurbits in general.

Fruit quality.

There appears to be very little published research on the effects of temperature on fruit quality. However, Nerson (1995) investigated the effect of harvesting at different developmental stages at high temperatures (30-35˚C) on fruit quality of butternut pumpkins (C. moschata). Fruit harvested at maturity initiation (~6 weeks after anthesis) have higher dry mass of flesh and longer shelf lives than those harvested when fully ripe (~8 weeks after anthesis). These results suggest that early harvesting may be a useful management adaptation to maintain product quality under high temperatures.

Pests & Diseases.

Although cucurbits are susceptible to a wide range of pests and diseases (Coleman 2004), very little research has been conducted on the influence of temperature. However, it would be reasonable to expect that some of the general patterns suggested for other crops may also apply to pumpkins; growers may face novel threats as insect pests expand in range and reproduce more quickly under higher temperatures, while the dryer conditions predicted for many regions may limit the damage caused by bacterial and fungal diseases.

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Aphids (Aphis gossypi) are a major pest of cucurbit crops and act as a vector for viral diseases. The nymphal stage developed more rapidly at temperature between 24˚C and 27˚C, but temperature of 30˚C or higher produced high rates of mortality (Leite et al. 2008).

Other insect pests such as bugs (hemiptera) that can cause stunted growth and deformities are also affected by temperature. For example, North American squash bugs (Anasa tistis) cause reduced vegetative growth rates and pistillate flower production in C. pepo. Squash bug fecundity increases with temperature, but mortality is higher at 25˚C than at 22.5˚C (Woodson and Fargo 1991).

Pumpkin – Flowering Developmental Phase – Critical Temperature Threshold

Pollen viability is reduced following short periods of exposure to temperatures above 35˚C.

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References.

Coleman E. (2004) Pumpkins and grammas: commercial production. Queensland Department of Employment, Economic Development and Innovation, Brisbane. Ellis R. H., Hong T. D. & Roberts E. H. (1985) Handbook of seed technology for genebanks. Roma. International Board for Plant Genetic Resources, IBPGR. Iapichino G. F. & Loy J. B. (1987) High temperature stress affects pollen viability in bottle gourd. Journal of the American Society for Horticultural Science (USA). Jablonski L. M., Wang X. Z. & Curtis P. S. (2002) Plant reproduction under elevated CO2 conditions: a meta-analysis of reports on 79 crop and wild species. New Phytol. 156, 9-26. Johannsson M. H. & Stephenson A. G. (1998) Effects of temperature during microsporogenesis on pollen performance in Cucurbita pepo L. (cucurbitaceae). Int. J. Plant Sci. 159, 616-26. Kurtar E. S. (2010) Modelling the effect of temperature on seed germination in some cucurbits. Afr. J. Biotechnol. 9, 1343-53. Leite M. V., dos Santos T. M., Souza B., Calixto A. M. & Carvalho C. F. (2008) Biology of Aphis gossypii Glover, 1877 (Hemiptera: Aphididae) on squash cultivar caserta (Cucurbita pepo L.) in different temperatures. Cienc. Agrotec. 32, 1394-401. Loy J. B. (2004) Morpho-physiological aspects of productivity and quality in squash and pumpkins (Culcurbita spp.). Crit. Rev. Plant Sci. 23, 337-63. Milani E., Seyed M., Razavi A., Koocheki A., Nikzadeh V., Vahedi N., MoeinFard M. & GholamhosseinPour A. (2007) Moisture dependent physical properties of cucurbit seeds. International Agrophysics 21, 157. Nerson H. (1995) Yield, quality and shelf-life of winter squash harvested at different fruit ages. Advances in horticultural science, 106-11. Nerson H. (2007) Seed Production and Germinability of Cucurbit Crops. Seed Science and Biotechnology 1, 1-10. NeSmith D. S. (1997) Summer squash (Cucurbita pepo L.) leaf number as influenced by thermal time. Sci. Hortic. 68, 219-25. NeSmith D. S., Hoogenboom G. & Groff D. W. (1994) Staminate and pistillate flower production of summer squash in response to planting date. HortScience: a publication of the American Society for Horticultural Science (USA). Seaton H. L. & Kramer J. C. (1939) The influence of climatological factors on anthesis and anther dehiscence in the cultivated cucurbits. Proc. Amer. Soc. Hort. Sci. 36, 627-31. Wien H. C., Stapleton S. C., Maynard D. N., McClurg C., Nyankanga R. & Riggs D. (2002) Regulation of female flower development in pumpkin (Cucurbita spp.) by temperature and light. In: Cucurbitaceae (ed D. N. Maynard) pp. 307-15. ASHS Press, Alexandria. Wien H. C., Stapleton S. C., Maynard D. N., McClurg C. & Riggs D. (2004) Flowering, sex expression, and fruiting of pumpkin (Cucurbita sp.) cultivars under various temperatures in greenhouse and distant field trials. Hortscience 39, 239-42. Woodson D. W. & Fargo S. W. (1991) Interactions of temperature and squash bug density (Hemiptera: Coreidae) on growth of seedling squash. Journal of Economic Entomology 84, 886-90. Zhang Y., Zhou Y. & Yu J. (2007) Adaptation of cucurbit species to changes in substrate temperature: Root growth, antioxidants, and peroxidation. J. Plant Biol. 50, 527-32.

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Ziska L. H. & Bunce J. A. (1993) The influence of elevated CO2 and temperature on seed germination and emergence from soil. Field Crop. Res. 34, 147-57.

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