production of seed potatoes solanum tuberosum l) for the ... · production of seed potatoes...

Production of seed potatoes (Solanum tuberosum L) for the tropics

Titik Kustiati

This thesis is presented for the degree of Master of Science in Horticultural ScienceSchool of Plant Biology, Faculty of Natural and Agricultural Sciences

The University of Western Australia2005

Abstract

Increasing Australia’s export of seed potatoes requires information about the

production of small seed which does not require cutting. Cutting increases the incidence

of disease in tropical countries and this substantially reduces yield. The response of five

potato cultivars suitable for tropical conditions to different period of cool storage, the

application of gibberellic acid and cutting was investigated. In the first experiment, seed

tubers of Atlantic were stored for 10-30 weeks and in the second experiment, Dawmor,

Eben, KT3 and PO3 were stored for 16 and 26 weeks. Sprouting was assessed (after 2

weeks at 20°C, 80-90% RH) and then tubers were grown in a glasshouse. Atlantic broke

dormancy at 16 weeks, PO3 and Eben before 16 weeks, Dawmor and KT4 after 16 weeks

but before 26 weeks.

Extending storage time accelerated emergence by 1-5 days in all cultivars and it

further hastened by application 20 mg L-1 GA3. Prolonged storage had little effect on

increasing above-ground stem number of Atlantic, KT3 or Eben, but it increased in

Dawmor and PO3. Gibberellic acid (GA3) increased stem number in Dawmor seed stored

for 16 weeks and PO3 seed stored for 16 or 26 weeks. However, increasing stem number

was not always followed by increasing stolon number per plant. Gibberellic acid

increased stolon branching in Atlantic, Eben and in Dawmor stored for 26 weeks.

The history of seed production influences the physiological age of seed, thus it

influences the effect of storage time and plant growth regulator in producing yield. Tuber

production in Atlantic peaked in plants grown from seed, which had been produced in

summer-autumn after 14-16 weeks storage, and after 26 weeks in seed grown in summer.

Gibberellic acid increased tuber number of Atlantic without affecting yield. In other

i

cultivars, older seed had lower yield but this may have been influenced by environmental

conditions during tuberisation. Tuber number was not influenced by GA3 except in young

Dawmor or old and young Eben, where it increased. Changes in stolon branching is

appeared to play a major role in tuber formation.

In a third experiment, carry over effect of GA application were examined on

Atlantic and Granola cultivars. Progeny tubers from plants using GA-treated seeds has

temporary effects on sprout behaviour, where they produced less sprout number and

sprout length than GA-untreated seeds, but sprouting capacity was not affected. However,

GA did not affect on the subsequent plant growth and yield at 7 weeks after planting.

In the fourth experiment, Atlantic, Eben, KT3 and PO3 were stored for 10 to 40

weeks and then sprouting was assessed (after 4 weeks at 20°C, 80-90% RH). Dormancy

broke after 12 weeks in Atlantic, 10 weeks in Eben and PO3, and after 22 weeks in KT3.

Maximum sprouting capacity occurred after 38 weeks in PO3 and was still rising after 40

weeks in Atlantic, Eben and KT3. Desprouting tubers benefits in increasing sprout

number in tubers with strong apical dominance including Eben, but not in tubers with

apical dominance has been broken by prolonging storage time, such as Atlantic. In PO3,

desprouting old tubers reduced sprouting capacity as older seeds loss their vigour.

In a fifth experiment, Eben, KT3 and PO3 were stored for 12 or 40 weeks, either

cut or left whole and grown in the field. Eben had similar yield and tuber number from 12

to 40 weeks and cutting had no effect. KT3 stored for 40 weeks performed better than 12

weeks and again cutting had no impact. In PO3, cutting was required in seed stored for 12

weeks but not in seed stored for 40 weeks.

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In conclusion, prolonged storage time can be used to improve sprout behaviour.

However, storing seeds for too long may have reduced subsequent plant growth. Further

study on storing seed under high temperature for shorter period is required, as higher

temperatures increase physiological age of tuber. Gibberellic acid can be used to increase

stem number and tuber number without reducing yield of Atlantic and Eben, and so was

effect in increasing the proportion of small tubers. Further research is needed to obtain

optimum conditions in Dawmor, KT3 and PO3. Cutting seeds can be used to increase

tuber number and yield of young KT3 and PO3 but in old seeds cutting has no effects.

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Acknowledgements

This Masters degree is the main dedication I have accepted when I received a

scholarship from the Australian Government. I am grateful to my supervisors Associate

Professor Julie A Plummer and Dr Ian McPharlin for giving me the opportunity to

improve my knowledge and broaden my vision through this project. My sincere thanks

for their continuous support, encouragement, supervision, advise at different stages

during my study. Their patience and friendship made me confident to do this research.

I would like to thank AusAid for providing this scholarship. Department of

Agriculture Western Australia and Horticultural Australia Limited (PT 2014) who was

financially supported my research. Directorate General of Horticultural Development,

Ministry of Agriculture, Indonesia for giving me this precious opportunity to undertake

the Masters degree at the University of Western Australia.

Mr. Kon Peos (from Southern Packers Pty. Ltd.) and Mr. Ben Taylor for

providing me the certified seed potatoes cv; Atlantic, Eben, KT3 and PO3. The School of

Plant Biology is also thankfully acknowledged for supporting me during my candidature.

There are also a number of people who I would like to acknowledge:

- Mrs. Rhonda Haskell and Mrs. Cathy Tang for their kind support, help and advice.

- Staff in Department of Agriculture, Western Australia in Perth and Medina Research

Centre: Tony Shimmin and Rob Deyl for their support on harvesting potatoes. Gavin

D’adhemar and staff of Medina Research Centre (Bob “uncle Roy”, Barry, Andrew,

Kent) who maintained my field trial. Andrew Taylor (Manjimup Horticultural

iv

Research Institute) and Stuart Vincent (Honors student from Curtin University) for

their help harvesting and grading potatoes of field experiment.

- Thank to Robert Creasy and Adrian Northover for providing me excellent facilities

and for their support and help during my research in the glasshouse.

- Gustavo Almada who always motivates me and encourages me to finish my study on

time. He is always near to me even though he lives miles away.

- My friends: Amer, Aslam, Harun, Jason, Nassar, Teguh, Bambang, Jenifer L who

were helping me in harvesting potatoes in the glasshouse experiment.

- I am deeply grateful to Asta, Pharma, Juni, Jos, Nukie and Umneea for their warmest

familiarity and support

- My colleagues: Caixia, Dan Mullan, Katherine Baker, Nassar Abbass, M. Aslam,

Nikki and all the postgraduate students, and research staff in the school of plant

biology for their lovely friendship.

- Thanks to Patrick Mitchell for proof reading my thesis

- Indonesian community in Perth, and Nedlands particularly, for being my second

family in Perth

- Suzie and Wanda for sharing their smiles and jokes while I’m finishing my thesis

- Mrs. Sri Kuntarsih for her continuous support and encouragement

- My dear family for their support and prayers so that I can complete my study on time

All this assistance, support, help, understanding, patience and love made this thesis a

reality.

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Publications Poster presentation Kustiati T, Plummer JA, McPharlin IR (2004). Effects of Storage Period and Gibberellic

Acid on Sprout Behaviour and Plant Growth of Potatoes Suitable for Tropical Conditions. In the proceeding of the Australian Society of Horticultural Science Conference entitled of “Harnessing the potential of horticulture in the Asia Pacific regions”. Sunshine Coast, 1 – 3 September 2004

Kustiati T, Plummer JA, McPharlin IR (2004). Effects of Storage Period and Gibberellic

Acid on Sprout Behaviour and Plant Growth of Potatoes Suitable for Tropical Conditions. In the proceeding of the Combine Biology (ComBio) 2004 Conference in Perth, Australia, 26-30 Sepember 2004

Journal Paper Kustiati T, Plummer JA, McPharlin IR (2004). Effects of Storage Period and Gibberellic

Acid on Sprout Behaviour and Plant Growth of Potatoes Suitable for Tropical Conditions. Acta Horticulturae (in press)

This thesis is presented as an Introduction, Literature Review, two research chapter which

have been prepared for submission to Australian Journal of Agricultural Research

(Chapter 3 and 4), and a General Discussion. Some aspects of the general discussion

included in chapter paper/paper ready for publication.

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Abbreviations ABA Abscisic acid

AGWEST Agriculture Department of Western Australia

ATP Adenosine triphosphate

° C degree Celsius

cm centimetre

CO2 Carbon dioxide

DAP days after planting

FAO Food and Agriculture Organization

Fig Figure

g gram

G0 generation 0

G1 generation 1

G2 generation 2

G3 generation 3

G4 generation 4

G5 generation 5

GA Gibberellic acid

GA3 Gibberellic A3

HACCP Hazard Analysis and Critical Control Point

ha Hectare

IAA Indole-acetic acid

kg kilo grams

m metre

m.a.s.l metre above sea level

mm millimetre

mt metric tones

O2 dioxide

pH A measure of acidity or alkalinity with the value of 0-14

RH Relative Humidity

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RIV Research Institute for Vegetable

SQF Safety and Quality Food

t tonne

T ha-1 tonne per hectare

t.p.a tonne per annum

Μmolm-2s-1 micro mole per metre square per second

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Table of Contents Page

Abstract iAcknowledgment ivPublications viAbbreviations viiTable of contents ixList of figures xiList of tables xiv Chapter 1 Introduction 1 1.1. Seed potato demand in Asia 21.2. Seed supply from Western Australia 3 Chapter 2 Literature Review 8 2.1. Potato 82.2. Review of Potato Production in Western Australia, Indonesia, Vietnam

and the Philippines 9

2.2.1. Potato production in Western Australia 92.2.2. Potato production in the Philippines 162.2.3. Potato production in Vietnam 202.2.4. Potato production in Indonesia 23

2.3. Maintenance the potato seed quality during storage 292.4. Physiological age 302.5. Potato seed behaviour during storage 33

2.5.1. Tuber dormancy 33 2.5.2. Sprout growth 37

2.5.2.1. The role of Auxin 382.5.2.2. The role of GA3 38

2.5.3. Sprouting capacity 402.6. The growth of potato 43

2.6.1. Plant growth 43 2.6.2. Tuber formation 45

2.6.2.1. Stolon initiation and elongation 452.6.2.2. Tuber formation and its growth 46

2.7. Manipulation of tuber size distribution 472.8. Effects of gibberellic acid on the growth of potato 49

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Chapter 3 Cultivar, storage time and gibberellic acid influence early growth of potatoes suitable for tropical conditions

53

Abstract 533.1. Introduction 543.2. Materials and Methods 563.3. Results 643.4. Discussion 83

3.4.1. Effects of storage time on sprout behaviour 83 3.4.2. Effects of storage time and GA3 on the subsequent growth and

yield 89 3.4.3. Carry over effects of GA3 98

3.5. Conclusion 99 Chapter 4 Effects of storage time and seed treatments on the growth and yield of potato (Solanum tuberosum L.) under field conditions

105

Abstract 1054.1. Introduction 1064.2. Materials and Methods 1084.3. Results 1114.4. Discussion 1254.5. Conclusion 134 Chapter 5 General Discussion 139Conclusion 153 References Appendix

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Lists of Figures Page

Figure 1.1 Healthy seed potato crops in Peter Ross’s field at Myalup, Western Australia (a), Ben Fox separates rejected tubers from healthy tubers before they are boxed, while seed exporter (Iwan) witnesses the seed selection (b), Certified Granola seeds that have been selected, packed, labelled at Lake Jesper seed company, Pemberton and are ready to be sent to Indonesia (c), Dedy Ruswandi, the seed inspector from West Java, Indonesia has a discussion with seed inspector from Western Australia (Dale Spencer) on seed quality (d), The label of Australian certified seed potatoes (e).

5

Figure 2.1 Potato production area in the Philippines 17Figure 2.2 Potato production areas in Vietnam 21Figure 2.3 Potato production areas in Indonesia 24Figure 2.4 Hypothetical scheme for the number of sprouts per seed tuber, the

sprouting capacity of seed tuber, and its growth vigour, as function of physiological age. The units along the x and y-axes are arbitrary. Sprouting capacity is expressed in sprout weight (g) per tuber, while growth vigour is expressed in grams or dry weight per plant

42

Figure 2.5 Potato plant: a) Main stem; b) stem branching on at the lower level of a main stem (near mother tuber); c) stem branching at the subsurface section of a main stem; d) stem branching stem above soil surface; e) daughter tubers at the stolon tips; f) daughter tubers from a branching stolon

44

Figure 2.6 The structure of biologically active gibberellic acid: GA1 and GA3 49Figure 3.1 Effects of storage time on number of sprouts/tuber, average sprout

length (mm) and sprouting capacity (mm g-1) of summer-autumn (-o-) and summer (-□-) grown Atlantic seeds. Vertical bars are l.s.d value at P = 0.05. Arrow is when 80% tubers have sprout length ≥3 mm. Equation for sprouting capacity of summer-autumn grown seeds was y = 0.1157x – 0.1384, r² = 0.99 and summer grown seeds was y = 0.0469x + 0.3987, r² = 0.87

65

Figure 3.2 Influence of GA3 on stem number of summer-autumn grown and summer grown Atlantic seeds. (-o-) is summer-autumn seeds without GA3, (-●-) is summer-autumn seeds plus GA3, (-□-) is summer seeds without GA3 and (-■-) is summer seeds plus GA3. Vertical bars are l.s.d value at P = 0.05

67

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Figure 3.3 Influence of GA3 on number of stolon/plant, length of the longest stolon (mm) and number of branching stolons of summer-autumn grown and summer grown Atlantic seeds. (-o-) is summer-autumn seeds without GA3, (-●-) is summer-autumn seeds plus GA3, (-□-) is summer seeds without GA3 and (-■-) is summer seeds plus GA3. Vertical bars are l.s.d value at P = 0.05

69

Figure 3.4 Influence of GA3 on tubers/plant and yield (g/plant) of branching stolons of summer-autumn grown and summer grown Atlantic seeds. (-o-) is summer-autumn seeds without GA3, (-●-) is summer-autumn seeds plus GA3, (-□-) is summer seeds without GA3 and (-■-) is summer seeds plus GA3. Vertical bars are l.s.d value at P = 0.05

70

Figure 3.5 Influence storage time on number of sprouts/tuber, average sprout length (mm) and sprouting capacity (mm g-1) of Dawmor, KT3, PO3 and Eben seeds stored for 16 weeks (□) or 26 weeks (■).Vertical bars are l.s.d value at P = 0.05

73

Figure 3.6 Effects of storage time (ST) and GA3 on tuber size distribution of five potato cultivars stored for 16 and 26 weeks

80

Figure 4.1 Proportion of sprouted eyes (sprouted eyes/total eyes in %) of 4 potato cultivars. Full symbols are undesprouted seeds and open symbols are desprouted seeds. Vertical bars are l.s.d value at P = 0.05

113

Figure 4.2 Number of sprout/tuber of 4 potato cultivars. Full symbols are undesprouted seeds and open symbols are desprouted seeds. Vertical bars are l.s.d value at P = 0.05

114

Figure 4.3 Average sprout length (mm) of 4 potato cultivars. Full symbols are undesprouted seeds and open symbols are desprouted seeds. Vertical bars are l.s.d value at P = 0.05

118

Figure 4.4 Sprouting capacity (% of sprouts fresh weight/tuber over initial tuber weight) of 4 potato cultivars. Full symbols are undesprouted seeds and open symbols are desprouted seeds. Vertical bars are l.s.d value at P = 0.05

119

Figure 4.5 Sprout characteristics of undesprouted Atlantic, Eben, KT3 and PO3 tubers stored for 10, 16, 26 and 40 weeks at 4°C, which were photographed after 4 weeks in the sprouting room at 20°C (I). Sprout characteristics of undesprouted and desprouted Atlantic and Eben tubers stored for 26 weeks at 4°C, which were photographed after 2 weeks in the sprouting room at 20°C (II)

120

Figure 4.6 Tuber weight loss (g) during 4 weeks of sprouting at 20°C following various periods of storage at 4°C for 4 cultivars. Full symbols are undesprouted seeds and open symbols are desprouted seeds. Vertical bars are l.s.d value at P = 0.05

121

Figure 5.1 Schematic diagram of the trends in sprouting capacity (% sprout weight over initial tuber weight) of 5 potato cultivars suitable for tropical conditions, with prolonged storage time

142

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Figure 5.2 Hypothetical scheme of the effects of GA3 on the development of sprouts into stems from tubers with different ages; (a) tuber with apical dominance; (b) tuber with normal multiple sprouting (more eyes produced sprouts); (c) tuber with multiple branching sprouts (more sprouts/eye)

154

Figure A.1 Influence of GA3 on tubers dry weight (g/plant) of summer-autumn grown and summer grown Atlantic seeds. (-o-) is summer-autumn seeds without GA3, (-●-) is summer-autumn seeds plus GA3, (-□-) is summer seeds without GA3 and (-■-) is summer seeds plus GA3. Vertical bars are l.s.d value at P = 0.05

165

Figure A.2 Influence of GA3 on plant emergence (DAP) of summer-autumn grown and summer grown Atlantic seeds. (-o-) is summer-autumn seeds without GA3, (-●-) is summer-autumn seeds plus GA3, (-□-) is summer seeds without GA3 and (-■-) is summer seeds plus GA3. Vertical bars are l.s.d value at P = 0.05

166

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Lists of Tables

Page

Table 1.1 Potato consumption in Southeast Asia 2Table 2.1 Comparison of yield (t/ha), number of tubers/plant, dry matter

content (%) and defect free potatoes (%) of Dawmor and Atlantic grown in Manjimup, Western Australia from October to November

13

Table 2.2 The availability of table potatoes, processing potatoes and seed potatoes in Western Australia

14

Table 2.3 Production, dry matter content, yield > 50 mm tubers, sugar content and index colour change after frying of six potato cultivars suitable for tropical conditions, grown in Viện CLT and Thuy Duöng

22

Table 2.4 Potato balance sheet for Indonesia (metric tons of fresh weight equivalents)

26

Table 2.5 Dormant period (weeks) after harvest of some cultivars tested in Britain (Burton, 1989) and in Israel (Susnoschi, 1981) potato varieties stored at different temperatures

35

Table 3.1. Average temperature (for 6 h blocks of time during the day e.g 00.00 to 5.45), average minimum daily temperature, average maximum daily temperature and average monthly temperature (°C) inside the glasshouse at the University of Western Australia

60

Table 3.2 Average light intensity per month (μmolm-2s-1), average total light per day (μmol-2s-1) inside the glasshouse and length of photoperiod (h)

60

Table 3.3 Seed growing conditions in Manjimup, South Western Australia and subsequent plant growth conditions in the glasshouse at the University of Western Australia, Perth

62

Table 3.4 Effect of gibberellic acid on tuber size distribution of physiologically young and old Atlantic seeds, at 8 weeks after planting

71

Table 3.5 Effects of storage time (ST) and GA3 on the stem number of four potato cultivars. Different letters indicate significant difference (p ≤ 0.5) within columns

75

Table 3.6 Effects of storage time (ST) and GA3 on length of number of stolons/stem, number of stolons per plant, length of the longest stolon, and number of branching stolons per plant of four potato cultivars. Different letters indicate significant difference (p≤0.5) within columns

77

Table 3.7 Effects of storage time (ST) and GA3 on tuber number and yield (g fresh weight/plant) of four potato cultivars. Different letters indicate significant difference (p ≤ 0.5) within columns

78

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Table 3.8 Effects of storage time (ST) and GA3 on tuber size distribution of four potato cultivars stored for 16 and 26 weeks. Different letters indicate significant difference (p ≤ 0.5) within columns

79

Table 3.9 Carry over effects of GA3 on sprout behavior after 2 weeks at sprouting room (20°C, 80-90% RH), including proportion of sprouted eyes (%), total sprout number/tuber, total sprout length (mm) and sprouting capacity (mm g-1) of two potato cultivars (Atlantic and Granola). Different letters indicate significant difference (p ≤ 0.5) within columns

81

Table 3.10 Carry over effects of GA3 on first emergence (days after planting) and stem number, plant height (mm) and leaf number 6 weeks after planting of two potato cultivars (Atlantic and Granola). Different letters indicate significant difference (p ≤ 0.5) within columns

82

Table 3.11 Carry over effects of GA3 on number of stolons per plant, tuber number, yield (g) and dry weight (g) of two potato cultivars (Atlantic and Granola) 7 weeks after planting. Different letters indicate significant difference (p ≤ 0.5) within columns

83

Table 4.1 Field conditions during potato growth in Medina Research Centre, Department of Agriculture, Western Australia from March to July 2004

111

Table 4.2 Effects of cutting and storage time (ST) of seed tubers on plant emergence, number of stems/plant, plant height (mm) and number of leaves/plant, 7 weeks after planting of Eben, KT3 and PO3 potato cultivars. Different letters indicate significant difference (p ≤ 0.05) within columns

123

Table 4.3 Effects of seeds treatments and storage time (ST) on tuber size distribution (g) and total tuber number per plant and total yield (t/ha) of Eben, KT3 and PO3 cultivars. Different letters indicate significant difference (p≤0.05) within columns

124

Table A.1 Effects of storage time (ST) and GA3 on the emergence (DAP)

of four potato cultivars stored for 16 and 26 weeks. Different letters indicate significant difference (p ≤ 0.5) within columns

167

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Chapter 1

INTRODUCTION

Potato is the fourth most important crop in the world, after rice, wheat and maize.

It was originally grown in the Andes Mountains in South America at an altitude of

2,800-4,000 m above sea level (Hawkes, 1990). After it was introduced to Europe in the

16th century potato growing spread all over the world and it was introduced to Asia in

the 17th century. Many varieties were selected for adaptation to particular climatic

conditions of temperate and humidity including the sub tropics and tropics.

Potato is not a staple food in Asia, but demand for potato is gradually increasing

due to population growth and the boom in western food and snack industries (Table 1.1).

Potato production in these areas is expanding due to increasing demand for fresh and

processed potato (Dowling 1995). This increase and future expansion requires a reliable

supply of good quality seed potatoes.

Potato production in South East Asia is using traditional methods with results in

low yields. Mostly, they are small scale farmers who have limited knowledge and

economic power to improve their production systems. The main problem in potato

production for these countries is lack of good quality seed, due to the limited number of

good seed producers and high cost of seed production due to disease problems.

Chapter1 Introduction

2

Therefore, seed is imported from other countries such as The Netherlands, USA,

Germany, Canada, China and Australia.

1.1. Seed potato demand in Asia

Increasing demand in South East Asian countries (Table 1.1) requires a matching

increase in supply of good quality seed of appropriate varieties, at a reasonable price.

Demand for seed potatoes in South East Asia is estimated at about 31,900 t p. a. (Batt,

1998). Seed for fresh table potatoes has been supplied locally or regionally but seed for

processed potatoes is mostly imported (Fuglie et al., 2003).

Table 1.1. Potato consumption in South East Asia (Fuglie et al., 2003)

1971 1981 1991 1998

Country Population

in 1998 (millions)* Kg of potato/capita/year*

Average annual growth in per capita potato consumption (1971-

1998) Indonesia 203.8 0.9 1.2 2.1 4.1 5.6% Malaysia 22.2 2.0 2.7 3.5 4.1 2.7% Philippines 75.2 0.5 0.6 1.1 1.8 4.7% Thailand 61.1 0.2 0.3 1.1 2.8 9.8% Vietnam 77.6 2.4 9.1 3.6 4.2 2.1% * Population and annual availability of fresh potatoes from Food and Agriculture Organization (2000)

Insufficient quantity and poor seed quality are the major problems facing potato

production in Asia (Dowling, 1995). Hot and humid conditions in tropical regions

increase the risk of seed born diseases. Moreover, lack of storage facilities causes seed

to degenerate more rapidly (Batt, 1999a). Low quality and inconsistent production make

it difficult to meet the market requirements especially for potato processing companies.

The demand from the factory is uncertain for each season. This is with regard to the


3

quantity and quality of potatoes, so potatoes from many farmers were rejected. This

resulted in many seed growers reducing or stopping seed production (Jayasinghe, 2003).

The demand for a particular potato variety varies with the country and their

customs. Granola is the most preferred variety in Indonesia for table potatoes whilst

Atlantic is preferred for processing. Processing companies require new cultivars to

substitute for Atlantic as its yield poorly in the tropics where late blight is prevalent. In

Vietnam, KT3 is one of the preferred cultivars because it has yellow flesh which is

associated with good luck as it is the color of gold. In the Philippines, Eben and PO3 are

promising cultivars for low lands as they can grow well in hot climates. Eben is good for

processing and this cultivar may grow well in other Asian countries and be able to

substitute for Atlantic in Indonesia.

In tropical countries small seed tubers (30-50 g) are required as economics

requires big tubers to be cut which increases the rate of infection and seed degeneration.

The size of imported seeds from European countries is bigger (> 60 g) and they are

physiologically old upon arrival due to the different in planting season and long shipping

time. This might influence subsequent plant growth and yield, as physiologically old

seed often produce plants with lower yield.

1.2. Seed supply from Western Australia

From a geographical perspective, Western Australia is in a good position to

supply seed and fresh potatoes to Asia and the Indian Ocean region. Already, Australia

exports seed potatoes to Thailand, Malaysia, Indonesia, Mauritius, Hong Kong and other

South East Asian countries (Pasqual et al., 1999). There has been an increasing focus in


4

shifting potatoes being produced for the local processing and seed market to export

markets.

Seed potatoes produced in Western Australia for domestic and export markets,

trade as registered and certified seeds under the National Seed Potato Certification

Standard. In Western Australia, potatoes are produced under favourable conditions

which enable the production of more mature seeds compared to Europe and North

America. When these seeds are planted under tropical conditions they have good

emergence, are more uniform and tuberise earlier. The other benefits of Western

Australian seed are reduced shipping costs and transit periods, so that seeds arrive in

better condition, at a cheaper price and give a greater out-turn (Batt, 1999a).

In order to supply seed potato to Asian countries, growers in Western Australia

multiplies seed potatoes that had been selected by national potato programs in Asia.

These varieties perform well in tropical countries as the Asian growers have experience

with the agro-ecological conditions in their country (Batt, 1999a). To support this

program, the Department of Agriculture Western Australia, Horticultural Australia Ltd

and Western Potatoes developed projects in Vietnam, Indonesia, Sri Lanka and

established collaborations with the Food Crops Research Institute of the Ministry of

Rural Development (Vietnam), PT. Indofood sukses makmur (Indonesia) and other local

Government institutions (Dawson et al., 2003). Some of these activities are illustrated in

Figure 1.1. Experiments in Indonesia and Vietnam showed that farmers have had good

results with Western Australian seed because yield is higher than local seed as these

potatoes are free from bacterial wilt, late blight, potato cyst nematode and potato virus Y

(Batt, 1999a).


5

Figure 1.1. Healthy seed potato crops in Peter Ross’s field at Myalup, Western

Australia (a), Ben Fox separates rejected tubers from healthy tubers before they are boxed, while seed exporter (Iwan) witnesses the seed selection (b), Certified Granola seeds that have been selected, packed, labeled at Lake Jesper seed company, Pemberton and are ready to be sent to Indonesia (c), Dedy Ruswandi, the seed inspector from West Java, Indonesia has a discussion with seed inspector from Western Australia (Dale Spencer) on seed quality (d), The label of Australian certified seed potatoes (e).

Potato cultivars suitable for tropical conditions including Eben, KT3 and PO3 are

not grown for Australian markets, due to lack of demand for these cultivars. All seed of

these cultivars produced in Western Australia needs to be exported, since they can not be

sold on domestic market, because of potato marketing regulations. For these reasons, it

is essential to increase the production of small tubers (30-50 g) so that it can meet the

demands of the Asian importers.

a b

c d

e


6

In many temperate varieties increasing the production of small tubers can be

achieved by manipulating of stem number (Kawakami, 1963; Struik and Wieserma,

1999). Increasing stem number increases tuber number per plant and with enhanced

competition for assimilates, tuber size is reduced. Many studies have been done on

increasing stem number and methods include using physiologically old seeds as planting

material, increasing plant density, application of growth promoter (GA3), and seed

treatments such as cut seed and desprouting tubers. However, most of these trials used

temperate cultivars and the response of tropical varieties is unknown.

Currently, there is limited research on increasing small tuber production in

tropical cultivars with growth promoters. In this present study, attempts will be made to

increase stem number by using physiologically old seeds, through the application of

growth promoter (GA3) and seed treatments. To study the response of sprout behaviour

of different physiologically aged, seeds will be observed in the laboratory and

subsequent plant growth will be monitored in the glass house and under field conditions

in Western Australia. In order to observe the response of different cultivars to these

treatments, three potato cultivars suitable for tropical conditions (Eben, KT3 and PO3)

were used. They were compared to potato cultivars selected for and commonly grown in

Australia (Atlantic and Dawmor). The hypotheses of this study are that:

1. Sprout behaviour influences subsequent plant growth. Sprout vigour is improved by

prolonging storage time as more eyes will sprout and sprout number and length

increase in more advanced seeds.


7

2. Increasing sprout number will result in more stems that will lead to an increase tuber

number. Greater tuber number will stimulate competition among tubers so that they

grow smaller.

3. Application of GA3 will increase tuber number by increasing stem number,

lengthening stolons and stimulating stolons to branch. GA3 will increase tuber

number without reducing yield.

4. Cutting will increase the number of stems emerging above the soil surface. More

stems will produce more small tubers as competition for assimilates is enhanced.

The main aim of this project is to provide information on how to increase the

proportion of small size potato tubers without reducing total yield. This will increase

profitability and market access for Western Australia into the Asian market.

Chapter 2

LITERATURE REVIEW

2.1. Potato

Potato is a vegetable crop. The plant is herbaceous and is classified as an annual

crop. The taxonomy of potato (Samadi, 1998) is:

Division : Spermatophyta

Sub division : Angiospermae

Class : Dicotyledonae

Order : Solanales

Family : Solanaceae

Genus : Solanum

Species : Solanum tuberosum L.

Potato is vegetatively propagated and is commonly planted using a piece of

tuber, termed a ‘seed’, or a whole tuber. A tuber is a swollen stem with nodes. The seed

tuber contains buds in the nodes, which are called eyes that form in a phyllotatic spiral

around the tuber. These eyes are dormant from tuber initiation until a few weeks or

months after harvesting. A range of conditions can break dormancy and generally a

certain period of cool conditions (3 to 4°C) or a shorter period of warm conditions (10 to

12°C) are required. When dormancy is broken, buds will grow into sprouts under

Chapter2 Literature Review

9

favourable conditions, such as darkness, warm temperature (18-20 °C) and high relative

humidity (RH 80-90%).

Potato plants have compound leaves, containing a terminal leaflet, secondary

leaflets and sometime tertiary leaflets. Stems grow from sprouts of a tuber. They are

usually branching at underground or aboveground level, which in turn influence tuber

production. A main stem is the stem that grows directly from the mother tuber or stem

branches close to mother tuber that will produce stolon (Beukema and Van der Zaag,

1990). The number of stems per unit area and number of stems per plant are important

factors for tuberisation (Struik et al., 1990).

Stolons are modified stems that mostly grow from basal nodes below the soil

surface (Cutter, 1992). Stolons grow diageotropically and their elongation is terminated

when tubers start to develop. This begins with stolon tips becoming hooked followed by

swelling of the sub-apical region of the stolon. This process continued with translocation

of photosynthate from shoots to the storage organs (Engels and Marschner, 1986).

Stolon elongation is regulated by gibberellic acid, while tuberisation is stimulated by

increasing ABA and jasmonic acid.

2.2. Review of Potato Production in Western Australia, Indonesia, Vietnam and

the Philippines

2.2.1. Potato production in Western Australia

Potato is a major Australian horticultural crop with increases in production of

about 500,000 t over the past 20 years (William et al., 1996). South-western Australia is

a major potato production area, as it has a good climate and is free of some important


10

pests and disease (Pasqual et al. 1999). About 100,000 t p.a. of potatoes are produced in

Western Australia for both the local and export markets (William 1996).

The potato industry in Western Australia mainly focuses on fresh potatoes for the

domestic market with additional markets for export and processing. In order to

continuously supply potatoes for the domestic market, at a reasonable price to

consumers, and to guarantee a minimum return for growers, the Commonwealth

Government set up the Marketing of Potatoes Act in 1946, which became the Potato

Marketing Corporation (trading as Western Potatoes) in 1995 (Learmonth and Dawson,

2004). The role of this organization is to manage the production, supply, marketing and

promotion to satisfy both growers and consumers (Anonymous, 2004c).

In Western Australia, potatoes are mostly produced from the South West of

Western Australia. The production areas are Albany (2%), Manjimup and Pemberton

(43%), Busselton (22%), Myalup (17%), Gingin and Perth Metropolitan (14%) and

Donnybrook (2%) (Anonymous, 2004c). Potato production for the domestic market is

regulated through a licensing system, which is monitored by field inspectors. In order to

control the supply, production of potato is divided into districts and seasons which serve

as pools for growers.

Potato varieties for the fresh market are mostly available throughout the year

including Carlingford, Delware, Désirée, Eureka, Kennebec, Kestrel, Leonardo,

Mondial, Nadine, Royal Blue, Russet Burbank, Ruby Lou and Spunta. Nadine, Delaware

and Désirée are the main table potato varieties in Western Australia. Atlantic, Cadima,

Dawmor, Nooksack, Shepody are mainly for processing. Granola, Désirée and Atlantic

are exported to Asian countries as seeds (Anonymous, 2005; Dawson et al., 2003).


11

Atlantic

Atlantic was bred and selected for cold temperate regions and was

first released in the USA in 1976 (Love et al., 1993). It was

selected from parents Wauseon and Lenape. Atlantic was released

in Australia in 1986.

Botanically, the Atlantic plant is medium to large, upright and open. Atlantic has

stems with purple pigmentation, nodes are slightly swollen and wings are conspicuous.

Leaves are closed, large and their colour is medium green. Terminal leaflets are ovate,

primary leaflets are in three pairs and secondary leaflets are numerous and small.

Flowers are numerous with medium size and they have light red-purple colour

(Anonymous, 2003a). Tubers are round to oval, with scally, buff coloured skin. The

flesh colour is creamy white. Atlantic has few, white coloured, well distributed eyes,

with medium depth. Sprouts are purple and pubescent (Anonymous, 2003a; Pavlista,

2003).

Atlantic has medium maturity and it is grown for 100–110 days. Yield is medium

to high with a high proportion of big tubers (> 112 g). However, large tubers tend to

have hollow hearts and brown centres.

Atlantic has a short dormancy of 3 to 4 months at 4°C (Pavlista, 2003). Atlantic

is a processing potato as it has high specific gravity (> 1.067) (Dawson et al., 2003) that

is good for crisping and chipping. Atlantic seeds stored at 3 – 5°C for 3 to 4 months

provide plants which produce tubers with the best chipping quality. Atlantic has high


12

specific gravity (1.085 – 1.100) and low sugar content at harvest, but when tubers are

stored below 10°C for a long time (> 6 months) sugar levels increase.

Atlantic is susceptible to most common potato viruses, such as verticillium wilt,

foliar early blight, common scab and storage rots. However, it is resistant to potato virus

X, leafroll-induced net necrosis and golden nematode (Anonymous, 2003a; Pavlista,

2003).

In Western Australia, farmers would expect most varieties, including Atlantic, to

emerge between 1-2 weeks after planting. Growers in Western Australia plant Atlantic at

150 mm apart in rows with 750-800 mm between rows and aim for approximately 3

stems per plant or per seed piece. Plants are harvested after 100-110 days. Closer

planting in rows (100-120 mm) is used for seed production. For seed production,

because small seed is desirable, growers may harvest earlier when tubers are small and

forego yield (Ian McPharlin, pers. comm). Ware potato growers have local market for

large tubers (e.g. Atlantic) and this is less important in seed production, as it means that

if a range of tuber size is produced there is a market for both small seed (for export) and

large (domestic) tubers. There is no market for large tubers of Granola, KT3, PO3 and

Eben. Therefore, increasing the production of small tubers is essential in these cultivars.

Atlantic is also a main processing potato in Indonesia. However, the biggest

processing potato company in Indonesia has sought new varieties to substitute for

Atlantic, because of reducing yield and tuber quality. Therefore new varieties with more

promising yield and good cooking quality are required.


13

Dawmor

Dawmor is a new processing variety that has high specific gravity

and is good for crisps. It was bred by Agriculture Victoria for the

National Potato Improvement and Evaluation Scheme (NaPIES). It

has been selected for mild temperate and Mediterranean climates.

Dawmor was produced from crossing Tarago and Linsay cultivars.

Dawmor was selected for late blight tolerance, but it is susceptible to potato cyst

nematode. In Western Australia, Dawmor is grown in Manjimup from October to

November (Dawson and Mortimore, 2002). In the field, Dawmor has wider spacing than

Atlantic, with a recommended planting distance of 20-25 cm within rows. Dawmor is

grown for 24 weeks or three weeks longer than Atlantic.

Dawmor performs better than Atlantic under Western Australian conditions. It

requires less seeds per hectare, produces more tubers, has a higher yield and has fewer

internal disorders than Atlantic (Table 2.1).

Table 2.1. Comparison of yield (t/ha), number of tubers/plant, dry matter content (%) and defect free potatoes (%) of Dawmor and Atlantic grown in Manjimup, Western Australia from October to November (Dawson and Mortimore, 2002, 2004)

Variety Yield

(t ha-1) Tubers/plant Dry matter

(%) Defect free

(%) Dawmor 61 11.2 20.2 90

Atlantic 45 6.8 19.4 82


14

Dawmor produces higher crisp grade tubers for export than Atlantic. In a trial in

Manjimup, Western Australia, the average yield of export grade tubers of Dawmor was

61 t ha-1 with the maximum of 100 t ha-1, while Atlantic only produced 45 t ha-1.

Dawmor produced 35% higher export grade than Atlantic (Dawson and Mortimore,

2002). Moreover, Dawmor also performed well in East Java, Indonesia (Iwan Gunawan,

Potato International Pty Ltd, pers. comm)

Seed potatoes are mostly grown in the Albany district, and some other south

costal areas, such as Margaret River, Scott River, Northclife, Bremer Bay and Esperance

(Learmonth and Dawson, 2004). Supply of seed potatoes for the domestic market is low

from October to February, followed by high supply from March to May. From June to

September seed potatoes are supplied from storage (Table 2.2).

Table 2.2. The availability of table potatoes, processing potatoes and seed potatoes in Western Australia (Dawson et al., 2003)

Month

J F M A M J J A S O N D Table potatoes h h h h h h h l l l h h Processing potatoes h h h h h h s s s l h h Seed potatoes l l h h h s s s s l l l h= High supply; l= Low supply; s = From storage

The market for export and processing potatoes is not regulated, and growers are

free to increase their production to supply these markets. However, in order to monitor

production of potatoes for export and processing purposes and to prevent those potatoes

from entering the domestic fresh market, growers need a licence from Western Potatoes

(Anonymous, 2004c). Potatoes from Western Australia are mainly exported as fresh


15

potatoes for crisps (Malaysia and Indonesia) or for table potatoes (Mauritius and

Singapore) and the total export in 2002/2003 was 13,000 t. Western Australia is also

exporting seed potatoes to other Asian countries including Thailand, Sri Lanka,

Philippines and Vietnam (Dawson, 2004) and this is expected to increase.

Potato is produced in Western Australia under a quality assurance program. The

implementation of food safety and quality assurance is assisted by Western Potatoes.

Growers committed to maintaining and improving potato quality and food safety will

achieve SQF 2000CM certification and they will earn an extra $5 per ton. The application

of SQF 2000CM also requires implementation of HACCP (Hazard Analysis and Critical

Control Point). In 1998-1999 there were 7 potato industry sectors which had achieved

the SQF 2000CM certificate and this sharply increased during 1999-2000 to 50 potato

industry sectors. In 2003-2004 80 potato industry sectors had achieved SQF 2000CM,

mostly ware potato growers (74%). This guarantees production of high quality potatoes

for domestic and export markets (Anonymous, 2004c).

Western Australia exports 2,000 t of fresh potatoes and 6,000 t of crisp potatoes

to South East Asian countries (Dawson, 2004). In the sales season of 2003/2004 Western

Australia exported about 1,500 t of seed potatoes of table and processing potato

varieties, of which 600 t were Delaware, 500 t Atlantic, 200 t Granola, 150 t Spunta and

50 t Royal Blue (Anonymous, 2004b). Recently, Western Australia has begun to export

other cultivars including KT3, Eben, and PO3 to Vietnam and the Philippines, which

could open the way to further expansion of the export sector. Trials in 2001/2002

(Anonymous, 2003c) showed that Eben, KT3 and PO3 seeds imported from Western

Australia to Vietnam have good quality and produce more than double the yield


16

compared to locally produced seeds. The average yield of potatoes in the Red River

Delta of Vietnam is about 12 t ha-1 (Tung, 2000), whereas yield KT3, Eben and PO3

using seeds from Western Australia is ≥ 30 t ha-1 (Anonymous, 2003c).

Seed potatoes produced in Western Australia for domestic and export markets,

trade as registered and certified seeds under the National Seed Potato Certification

Standard. Certified seeds are produced from the multiplication of generations 1 to 5. To

diminish pest and disease problems, the production of certified seed in Western

Australia is rotated for 3 (G4 and G5) to 5 years (G1 – G3) (Anonymous, 2001).

In order to guarantee seed quality, inspectors from the Department of Agriculture

Western Australia Plant Laboratories periodically undertake inspections of both growing

crops and harvested tubers (Fig. 1.1). In the field, crops are assessed for their generation,

rotation, crop isolation and virus, pest and disease controlling systems. Harvested tubers

are assessed for insect damage, malformed tubers, mechanical damage, stem end

discolouration, sunburn, foreign cultivars, oversize and undersize. Seeds are then packed

and labeled before shipping. The potato certified label includes grower name, variety,

generation, date of harvesting, date of packaging, fungicide treatment and content. This

quality assurance scheme is very valuable for the seed industry and its expansion into

Asia (Anonymous, 2001).

2.2.2. Potato Production in the Philippines

Potato was first introduced to the Philippines by Spanish missionaries to Cebu

and it was grown in the Luzon highlands. Today, potato is mostly grown (> 90%) in the

highlands of Northern Luzon (Benguet and Mountain Province), at 1600-2400 m above


17

sea level. It is also grown in Bukindon province of Mindanao at 800-1600 m above sea

level (Anonymous, 2004a).

In the Philippines, potato is mostly grown in hilly areas. In these areas,

expansion is limited due to inefficiencies in production, such as the use of steep slopes

where it is difficult to implement mechanisation. Potato production in the Philippines is

now expanding to the low land areas of Ilocos Norte and Cagayan Valley Provinces of

Northern Luzon which have 5000-6000 ha of suitable land for potato (Perez, 2001).

Figure 2.1. Potato growing areas in the Philippines (Source: http://geoweb.fao.org/GBR/GeoWEB.exe$ConsoleDefault?Ctry=PHI)


18

In high lands, there are two potato growing seasons. The first planting is from

February to March and it is harvested in June or July, and the second begins in

October/November with harvest in February/March. In low lands (Cagayan), farmers

plant potato from October to December when the air temperature is 17-31°C where there

is an annual rainfall of 99.75 mm (Anonymous, 2004b).

In 1986, several cultivars were tested in the low lands including Berolina, Baraka

and Cosima. There were problems with these highland cultivars, mainly due to their

poor physical and physiological state. Sprouting was delayed and tubers rotted. In 1991,

new potato cultivars, including Eben, were introduced and evaluated from highlands and

lowlands (Quitos, 2004). After 8 years of trials, in 1999, The Mariano Marcos State

University released Eben, which is also called Raniag which means ‘ray of light’. Eben

has consistently higher yield than Berolina, the main variety in lowlands, and it is good

as a processing potato. Another processing cultivar that is suitable for the low lands is

PO3 or Igorota even though it is a highland variety (Perez, 2001).

Eben

Eben was firstly introduced in 1991. It is well adapted to the hot

lowlands of Ilocos Norte and Abra, Cagayan during the dry

season. In the Philippine low lands, Eben has high yield, good

chipping quality, good storability and is profitable for farmers to

grow (Quitos, 2004). Eben is an early maturing plant that grows for 70 to 80 days.

Tubers are round with brown skin colour and shallow eyes. Eben has pale yellow flesh


19

colour, it has crisp, chrunchy texture and has good flavour. Eben is good for processing

because it has 18.8% dry matter content. Although Eben is grown for a short period in

hot climates, it can produce high yields. The maximum yield is 31 t/ha and minimum

yield is 14 t/ha, with the average yield of about 19 t ha-1.

Eben seeds are dormant for 87 days and they can be stored in diffuse light

storage for up to 8 months with minimal shrivelling and rotting. During storage, tuber

weight loss from respiration is 32% and death from rotting is 18%. During storage tubers

produce multiple sprouts (Quitos, 2004).

Eben grows well in light, well drained soils with pH of about 5.9 – 6.8. The soil

requires good irrigation for this potato. To avoid disease problems, it is recommended to

choose an area that has not been planted with another solanaceous plants beforehand.

Eben can be planted in single or double rows with a distance of 80 cm between double

rows and 40 cm between rows and a distance within rows of 30 cm. Tubers can be

planted 7 cm in light soil or 5 cm deep in heavy soil (Quitos, 2004).

PO3

PO3 was selected in the Philippines. It is used as a fresh and

processing potato. It has high dry matter content and strong flavour

(Perez, 2001). The tubers are round with yellow flesh colour,

yellow skin and very shallow pale pink eyes. PO3 is grown for 90

days (Anonymous, 2003b).

Similar to Eben, PO3 is usually stored in diffuse light storage with good ventilation for

6-8 months. Under these conditions, tubers produce short sturdy sprouts that are


20

damaged less during transport. They also produce a higher yield than tubers stored in

total darkness (Roettger, 1987). The most common problems are tuber moth, tuber rot

and aphids.

2.2.3. Potato Production in Vietnam

Potato was first introduced to Vietnam by French colonialis in 1890 (Batt,

1999b). In Vietnam potato is known as “khoai tâi” which means “Western root” or

“French tuber” and it was originally a minor vegetable crop cultivated in home gardens.

Potato became an important food crop in the late 1960’s after the introduction of short

duration rice varieties for spring and summer planting. Potato is suitable for growing in

the winter season between these two rice cropping seasons (Tung, 2000). Although it is

not a staple food, potato ranks fourth after rice, maize and sweet potato. In 1980, there

was a peak in potato production in Vietnam. About 100,000 hectares were cultivated

yielding about 20 t ha-1. However, due to lack of good seed quality, productivity

declined to about 10-12 t ha-1 followed by a decrease in the production area. Nowadays,

the potato production area has stabilized at about 30–35,000 ha.


21

Figure 2.2. Potato production areas in Vietnam (Rhoades et al., 2002b)

Potato is mainly grown in the Red River Delta (about 98%) where about 400,000

ha are suitable for potato, and also in the Dalat highland (Figure 2.2). In the Red River

Delta, potato is cultivated in winter from late October to early February, before spring

rice is planted in mid February. Therefore, potato in the Red River Delta is mostly

cultivated for no more than 90 days (Tung, 2000). Late planting is done in December in

upland areas (Dalat) where spring rice is not grown (Batt, 1998). In Dalat, potatoes are

grown all year round with the best planting season from October to March (dry season)


22

supported by irrigation systems. Planting potatoes during the wet season incurs a high

risk of late blight infection and typhoons that can cause substantial losses.

Five potato cultivars suitable for tropical conditions including Eben, Dawmor,

PO3, KT3 and Granola, were tested at Viện CLT and Thuy Duöng, Vietnam during

2002-2003 (Table 2.3). Eben performed best with the highest yield (19-30 t ha-1), high

dry matter content (20-21%), low reducing sugar content (0.21%) and a low changing

colour index after frying (1.75) (Tuyen et al., 2003).

Table 2.3. Production, dry matter content, yield > 50 mm tubers, sugar content and index colour change after frying of six potato cultivars suitable for tropical conditions, grown in Viện CLT and Thuy Duöng (Tuyen et al., 2003)

Production

(t ha-1) Dry matter content (%)

Yield >50 mm (%)

Cultivar Viện CLT

Thuy Duöng

Viện CLT

Thuy Duöng

Viện CLT

Thuy Duöng

Sugar content

(%)

Index colour change after

frying Eben 18.6 29.8 21.7 20.2 56.0 50.0 0.213 1.75 Dawmor 12.9 25.6 19.9 18.0 30.7 48.2 0.220 2.30 PO3 16.3 27.8 18.7 17.5 47.3 40.2 0.208 1.75 KT3 16.8 29.7 16.8 16.3 57.3 55.7 0.313 3.35* Granola 12.5 23.6 16.7 16.3 54.5 35.7 0.240 1.65 CV (%) 16.9 15.2 5.6 4.0 17.8 16.7 2.0 2.1 * Colour changed after frying

KT3

KT3 was selected in Vietnam, and it is consumed fresh as a table

potato. Tubers are round with golden yellow flesh and yellow skin

colour. The tuber contains many eyes and they are deep and dark

pink (Anonymous, 2003b). KT3 sprouts grow short and thick. KT3


23

has a long dormancy, so that it can be stored for a longer time.

In Vietnam, KT3 is grown for a short period of 2-3 months between rice crops,

and it is harvested 90 days after planting. Lack of storage facilities caused Vietnamese

farmers to select small whole tubers for use as seeds (about 20% of their production).

They store these KT3 seeds for 9-10 months under diffuse light storage in their kitchens.

Seed tubers are placed on bamboo racks near windows to provide ventilation. This kind

of storage has a high risk of contamination from various pathogens and viral diseases so

that it increases tuber weight loss and reduces seed quality. Without temperature control,

long storage increases tuber losses so that more than half of the seeds have lost their

vigour and the productivity is low from remaining seed (Tung, 2000).

2.2.4. Potato production in Indonesia

In Indonesia, potato was first introduced to West Java by the Dutch. It was then

cultivated in some regions of West Java Province including Pangalengan, Cipanas,

Lembang, Garut and Ciwidey. Potato is also planted in the highlands of Central Java

(Dieng, Wonosobo) and East Java (Pasuruan, Malang and Probolinggo). In addition to

Java Island, potato is grown in the high lands of North Sumatra (Karo, Brastagi,

Tapanuli), West Sumatra (Padang uplands), Bengkulu, Sulawesi and Nusa Tenggara

(Fig. 2.3). Java, Sumatra, Sulawesi and Nusa Tenggara are the major potato production

areas (Rhoades et al., 2002a).


24

Figure 2.3. Potato production areas in Indonesia (Rhoades et al., 2002a)

In Indonesia, potatoes are mostly consumed as table potatoes. Granola is a main

table variety and it is widely grown in Indonesia (about 80% of the total potato

production area), because it is tasty, has yellow flesh and is suitable for many uses.

Increasing urbanization, a booming fast food industry and a strong desire for

western snacks has increased the demand for processing potatoes. Atlantic is the main

processing variety along with Merbabu-17 (Basuki et al., 2003; Dimyati, 2003;

Jayasinghe, 2003). Other varieties have been released by the Indonesian Research


25

Institute for Vegetables including Thung, Rapan, Cipanas and Segunung (Dimyati,

2003).

Recently, the Indonesian Research Institute for Vegetables evaluated new clones

of table potatoes and processing potatoes (Dimyati, 2003). For processing potato,

farmers and potato industries prefer cultivars that yield ≥ 20 t ha-1, have early to medium

maturity (≤ 90 days), have a high proportion of marketable size (75%) and 25% seed

size, and are resistant or tolerant to leaf minner fly (liriomyza), late blight and bacterial

wilt. Seed also need to be able to be used up to the 4th generation and tubers must have

high specivic gravity (≥ 1.067 for chipping potato and ≥ 1.079 for French fries), low

sugar (< 0.5%) and high starch content (> 20%) (Basuki et al., 2003; Dimyati, 2003).

Eben appeared to be an alternative cultivar that might be introduced in Indonesia, since

it has average yield 19 t/ha with maximum yield 31 t ha-1, it has high proportion of big

tubers (50% tubers are > 5 cm) high dry matter content (18.8%), low sugar content

(0.2%) with high acceptability for processing potatoes (Perez, 2001; Quitos, 2004;

Tuyen et al., 2003).

In Indonesia, potato is planted at high elevation. The ideal altitude for cultivating

potato is 1,000 – 1,300 m above sea level (Samadi, 1998) but sometimes these areas

have steep slopes. Commonly, planting potatoes on these slopes has increased erosion

(Dimyati, 2003). In order to increase potato production, there has been expansion to the

medium altitude lands of 500-800 m above sea level (Samadi, 1998). Therefore,

cultivars adapted to warmer temperatures of these medium lands are required.

In Indonesia potato is mainly cultivated by small farmers using low technological

input. There are two growing seasons in Indonesia, one is during the wet season


26

(September to December) and the other is during the dry season (April to July). Due to

high rainfall and humidity in the highlands, potato is cultivated without irrigation, while

in medium altitude lands, irrigation is required. In Indonesia, potato is grown as a mono

crop or with multiple crops, and it is sometimes rotated with other crops such as rice,

cabbage or maize (Rhoades et al., 2002a).

Potato production area increased from 56,057 ha in 1994 to 73,068 ha in 2000,

and then it decreased to 62,839 ha in 2003. Total potato supply in Indonesia increased

from 1990 to 1996 and it has fluctuated since then. Potato production in Indonesia

increased from 628,727 Mt in 1993 to 877,146 Mt in 1994, and reached a peak in 1995-

1996, since then it has remained constant at about 900,000 Mt per year. Export has

declined since 1996, whilst importation of fresh and processed potatoes is increasing, so

that total supply for domestic consumption is increasing (Table 2.4).

Table 2.4. Potato balance sheet for Indonesia (metric tons of fresh weight equivalents) (Fuglie et al., 2003)

Imports Year Potato

production Seed and wastage

Export (fresh) Fresh Processed*

Total available supply

1990 628,727 125,745 98,254 69 12,196 416,9932000 966,608 193,322 30,676 5,824 53,127 801,562

Average 853,537 170,707 74,946 1,703 36,260 646,483* Consists of French fries, potato chips and potato starch. Numbers are shown as fresh weight equivalents

The most dangerous potato pest in Indonesia is the leaf miner (Liriomyza

huidobrenses). Lyriomyza sp. spreads in the elevation zone of 1,000 – 2,200 m above sea

level. It starts to swarm 21 days after planting and the worst plant damage occurs 42

days later. Lyriomyza can reduce yield by a third (Dimyati, 2003). Other pests are


27

Bemisia tabaci, nematodes (Meloidogyne sp.), aphids, thrips, Agrotis epsilon and

Spodoptera litura (Dimyati, 2003; Samadi, 1998). High humidity in Indonesia increases

disease problems. Late blight, bacterial wilt and Fusarium are the most serious diseases.

Planting good quality seed, free from these pests and diseases, is important to achieve

high yields.

Seed production in Indonesia is mostly through an informal seed system, due to

limited seed producers. Farmers usually make their own seeds by storing small size

tubers (30-50 g) in simple storage rooms. After harvest, small seeds are separated from

big tubers and heaped on the ground in a dark shade house without washing, which

results in damaged and rotten seeds with long sprouts at subsequent planting

(Jayasinghe, 2003).

The major problems in the production of good seed in Indonesia are poor seed

crop management and lack of good facilities. Seed producers usually practice the same

management for their seed crop and table potato crop as many farmers produce both

crops. Seed certification has not been implemented, and this, coupled with uncertain

demand from processing companies has left the seed industry without quality control

measures (Jayasinghe, 2003). Lack of good facilities, such as tissue culture laboratories

and net houses for G0 production, and cold storage rooms have limited seed production

and increased losses. Lack of seed available from seed producers has lead to an increase

in imports from other countries, including Germany, the Netherlands and Australia.


28

Granola

Granola is a Germany cultivar, which grows well under the 12 h

day regime commonly found in the tropics. Tubers are round to

oval with yellow, netted skin and yellow flesh colour.

The yellow eyes have shallow to medium depth with light pink sprouts (Carnegie,

2001b).

Granola is a fresh potato, which has medium to high dry matter and low starch

content allowing it to be used for various cooking purposes. Granola is a medium to late

maturing potato which can be stored for long periods due to its long dormancy under

temperate conditions (Carnegie, 2001b). However, in Western Australia, Granola does

not have long dormancy, possibly due to warmer growing conditions (Van Es and

Hartmans, 1987). Granola has medium to high yield potential. It can produce many

tubers per plant with medium size to large size and uniform shape (Carnegie, 2001b).

Under Western Australian conditions, Granola produces 82 t ha-1 from Manjimup

planting and 35 to 39 t ha-1 from Perth planting (Arpiwi, 2003).

Granola is preferred by Indonesian farmers since it has medium maturity, is high

yielding, produces a high proportion of marketable sized tubers and its seeds perform

well until the 4th generation (Basuki et al., 2003). Granola is more economical to grow in

Indonesia due to disease management. In Indonesia, Granola seed is mainly imported

from Germany and the Netherlands, and nowadays there are several types of Granola

that are officially released by the Indonesian Seed Board (e.g. Granola-L) or other types

that selected by farmers (e.g. Granola-J, Granola-PO) (Jayasinghe, 2003).


29

The potato production system differs between countries and within them, where

production occurs on both high and low lands. These factors influence which varieties

will be suitable for cultivated in each country and district.

2.3. Maintaining potato seed quality during storage

After harvesting, potatoes are stored to serve the needs of the fresh market, as

tuber seeds or for processing, into chips and crisps. Seed quality influences sprouting

behavior and influences the health and vigour of plants, which in turn, influences yield

(Struik and Wieserma, 1999). Usually after harvest, potato tuber respiration decreases

and remains low during storage (Burton, 1989). During storage, sucrose hydrolysis

supplies energy for respiration (Hertog et al., 1997).

Storage conditions and storage period influence the performance and quality of

potato seed tubers. Temperature, relative humidity and ventilation in the storage room

need to be controlled, because they influence potato metabolism during storage

(Rastovski and Van Es, 1987). Potato tubers contain carbohydrates, nitrogenous

compounds, lipids, vitamins and minerals (Salunkhe and Kadam, 1991). Starch is the

major component and making up about 95% of potato tubers. Starch consists of 21-25%

amylase and 75-79% amylopectine (Rastovski and Van Es, 1987). During storage, starch

and protein are broken down into sucrose (soluble sugar) and amino acids and the

sucrose will be used to maintain sprout growth and development (Hajirezaei et al.,

2003).

Placing potato tubers in low temperature reduces sugar loss, whereas high

temperatures accelerates respiration and stimulates sprout growth (Burton, 1989; Kumar


30

and Knowles, 1993a). High relative humidity (90-95%) promotes early suberization of

tubers damaged at harvest (Smith, 1968) and minimises weight loss (Iritani and Spark,

1985). Storage rooms should have a good ventilation system to remove heat and

maintain moisture level (Smith, 1968).

Weight losses in stored potato are largely due to water loss through transpiration

and respiration (Burton, 1989), as metabolic processes continue even during dormancy.

Respiration is an oxidative reaction in cellular metabolism involving starch and sucrose

degradation to produce energy, carbon dioxide and water. High respiration rates induced

losses in storage materials. Proper storage conditions, especially of relative humidity and

temperature, reduce these undesirable losses and maintain seed quality. Good conditions

for storing potatoes are high relative humidity (90-95%), low temperature (4-5°C) and

good ventilation (Rastovski and Van Es, 1987). Very low temperature (below 3°C) leads

to an accumulation of reducing sugars and is also undesirable.

2.4. Physiological age

Performance of potato is closely related to physiological age. Physiological age

of potato tubers influences their productive capacity and the potential of desprouted

tubers to produce new sprouts (Hartmans and Van Loon, 1987). In the field, it affects

plant growth, such as the rate of plant emergence, plant vigour, number of stems

produced per plant, time of tuber initiation and yield (Caldiz et al., 2001; Reust, 1986).

Physiological age of potato tubers is influenced by chronological age, growing

conditions, storage conditions and harvest time. Chronological age is the age of tuber

from appearance in the field, expressed in days, weeks or months, without regard to the


31

environment conditions (Reust, 1986). The harvest date is commonly uses as the start of

chronological age. A particular physiological age represents the stage of development

which is influenced by time and environmental conditions. This can be achieved by

prolonged storage of tubers at low temperature or shorter storage at high temperature

(Van der Zaag and Van Loon, 1987).

Different growing conditions also influence the physiological age of potato

tubers. Growing potatoes plants under high temperature will advance the physiological

age of tubers produced (Caldiz et al., 2001). The length of growing period also affects

the physiological age of potato tubers. Plants harvested earlier produce physiologically

younger tubers than late harvested tubers (Struik and Wieserma, 1999). After harvest,

storage temperature is the main factor that influences physiological age and increasing

temperature increases the rate of physiological aging of tubers (Hartmans and Van Loon,

1987).

Physiological age influences the sprouting behaviour of potato tubers. Starch is

the storage form of carbohydrate in tubers and it decreases through respiration during

storage. Therefore, physiologically old seed tubers contain less carbohydrate than

physiologically young seeds, and in time this can reduce sprout vigour (Kumar and

Knowles, 1996).

Potato sprout morphology changed with prolonged storage time. With time,

potato seeds lose their apical dominance leading to multiple sprouting (Krijthe, 1962;

Struik and Wieserma, 1999). Thus, more advanced seeds produce more sprouts and they

grow longer, thus increasing sprouting capacity. However, seeds stored for too long,

generally more than 12 months (in Alpha, Binjte and Libertas), decrease their sprouting


32

capacity (Krijthe, 1962). Seeds that are too old at planting have low yield due to

decreased sprouting capacity and loss of seed vigour (Fig. 2.4). Decreasing seed vigour

in physiologically old seeds is due to reduced stored carbohydrate and reduced ability to

synthesize enzymes involved in mobilisation of food reserves for developing sprouts

(Kumar and Knowles, 1993a).

Physiological age also influences subsequent plant growth including plant

emergence, stem and tuber production, tuber size distribution and yield. Physiologically

old seeds usually emerge earlier than physiologically young seeds (Struik and

Wieserma, 1999). Stem production is influenced by physiological age of the mother

tuber. The greater number of sprouts results in more stems developing from

physiologically older seeds (Struik and Wieserma, 1999). Stem number increases with

age and then begins to decrease. However, the response of stem production to

physiological aging varies with cultivar. Physiologically young Désirée seeds (stored at

4°C) produce more stems than physiologically old seeds (stored at 12°C), for the same

period of time. In contrast, physiologically old Jaerla (stored at 12°C) produce more

stems than physiologically young seeds (stored at 4°C) (Boadlaender and Marinus,

1987). Similarly, Russet Burbank stored at 4 then 16°C produce more stems than tubers

stored at 4°C continuously (Iritani and Weller, 1987).

Physiological age of seed potato affects haulm growth. Increasing stem number

by planting physiologically old seeds stimulates competition between emerging shoots

for light, water and nutrients so that foliage production and yield are lower than

physiologically young seeds (Struik and Wieserma, 1999). During early growth, shoot

development depends on the mother tuber for carbohydrate reserves and nitrogen. At


33

planting, old Russet Burbank seeds (17 months) produced more stems, which contain 2.8

times more total nitrogen than few stems produced from young seeds (5 months). Stems

from old seed had less nitrogen per shoot (Knowles, 1987). Moreover, old seeds contain

less sucrose than younger seeds and they can be less efficient in translocation

carbohydrates from mother tuber to developing shoots (Mikitzel and Knowles, 1989).

Planted old seeds (4400 day degree) results in poor emergence and low yield.

Small tubers are produced from plants with poor haulm or without haulm formation

(Reust et al., 2001). As a result, planting old seeds produces low yield as tuber number

per stem is reduced (Struik and Wieserma, 1999).

Studies of changes associated with physiological or chronological age on seed vigour

have been conducted on temperate potatoes, but none have been done on tropical

potatoes. Those studies indicate that the storage time required to change sprouting

behaviour and subsequent growth varies substantially. However it is not know what

responses may occur in potatoes from tropical conditions. In the present study, we

observed sprout behaviour of different physiologically aged potatoes suitable for tropical

conditions (Atlantic, Dawmor, Eben, KT3 and PO3). This information will be useful to

estimate the optimum storage period for seed to plant with a high yield.

2.5. Potato seed behaviour during storage

2.5.1. Tuber dormancy

Potato tubers remain dormant for several weeks after harvesting, (Turnbull and

Hanke, 1985), and no buds will grow even under favourable conditions (Burton, 1963).


34

This phenomenon is called innate dormancy (Sorce et al., 2000) or endodormancy.

When dormancy is broken, buds will emerge if conditions are suitable (Turnbull and

Hanke, 1985). During storage, the dormant period is influenced by storage temperature

and generally cooler conditions prolong dormancy and warm conditions hastened the

end of dormancy (Burton, 1963). Buds can be prevented from sprouting by maintaining

cool conditions and this is also called ecodormancy (Turnbull and Hanke, 1985); (Sorce

et al., 2000).

Dormancy of potato is considered over when 80% of tubers produce sprouts ≥ 3

mm when they are held at 20°C for 2 weeks (Krijthe, 1962; Reust, 1986). However,

different researchers have different definitions, especially in relation to sprout length,

which can be ≥ 1 mm (Susnoschi, 1981a) or ≥ 2 mm (Van Ittersum et al., 1992). In

India, potato seeds are stored in cool store (1-2°C) and then placed at the 15-16°C pre-

sprouting temperatures (Pushkarnath, 1976). Under these conditions, tuber dormancy

classified into three categories; varieties with a short dormancy period (sprouting in 4–5

weeks), varieties with a medium dormancy period (sprouting in 6–8 weeks) and varieties

with a long dormancy period (need > 8 weeks to sprouting). Varieties from different

growing conditions have different times to break dormancy (Burton, 1989; Susnoschi,

1981a). Time required is also influenced by storage temperature (Table 2.5).

The length of dormancy is influenced by endogenous factors (plant hormones)

and exogenous factors, such as growing and storage conditions (Sorce et al., 2000). The

balance of plant hormones is important in the control of tuber dormancy (Van Staden

and Dimalla, 1978), and this balance changes during storage (Sorce et al., 2000; Van der

Plas, 1987). Gibberellins and cytokinins are important hormones involved with


35

shortening tuber dormancy and stimulating sprout growth, whereas ABA and ethylene

may inhibit sprouting and play an important role during dormancy (Sonnewald, 2001;

Xu et al., 1998). Auxin also controls bud sprouting and dormancy (Cline, 1997; Sukhova

et al., 1993). The concentration of free IAA in eyes increases from harvest to the end of

dormancy, as auxin is translocated from the pith to the peripheral tissue (Sorce et al.,

2000). Applying gibberellins slightly decreases IAA concentration in the skin but

increases it in the buds (Smith, 1968). This hormonal control is complicated by changes

in concentration, interaction between hormones and the ability of tissues to respond.

Table 2.5. Dormant period (weeks) after harvest of some potato cultivars tested in

Britain (Burton, 1989) and in Israel (Susnoschi, 1981a) stored at different temperatures

Storage temperature Spring-grown Autumn-grown Variety 4.4 °C 10 °C 22.5 °C Variety 4 °C 22 °C 4 °C 22 °C

British varieties Israeli varieties Arran Consul > 28 12 8 Alpha 18 10 32 16 Arran Pilot 12 5 5 Avanti 10 6 24 8 Arran Victory 12 5 3 Desiree 14 6 28 10 Arran Vicking 16 5 8 Majestic 18 6 26 8 Craig’s Defiance 8 6 3 Rector 16 6 30 10 Golden Wonder 26 12 8 Renova 10 6 24 8 Home Guard 12 5 3 Rosita 8 4 22 8 King Edward 16 6 5 Senaeda 16 4 26 8 Majestic >28 12 8 Up-to-date 10 6 26 8 Ulster Chieftain 16 5 5 Ulster Prince 14 14 8

Factors that influence tuber dormancy are tuber characteristics, such as cultivar,

maturity and growing conditions including soil and weather (Van Es and Hartmans,

1987). Different cultivars have different cultivation methods and have different

physiological states and lengths of dormancy due to differences in their genetic make up,

planting conditions and harvesting times (Burton, 1963). Potato tubers that are harvested


36

at different times have different physiological states (Burton, 1963; Reust and Aerny,

1985). Potatoes grown in cold and wet weather have longer dormant periods than

potatoes grown in warm and dry weather (Van Es and Hartmans, 1987).

Dormancy is also influenced by storage conditions including temperature,

relative humidity, oxygen and carbon dioxide concentration (Van Es and Hartmans,

1987). Increasing temperature will enhance respiration and reduce the dormant period

(Burton, 1963). Low temperature prolongs tuber dormancy, perhaps by influencing

accumulation of reducing sugar (Sonnewald, 2001). Tubers stored at 3°C will start to

sprout after 50–80 days, whereas at 20°C they will sprout after 35–50 days (Suttle,

1995). Moreover, if they are stored in high humidity their dormant period will be

shortened (Burton, 1963). Besides temperature and humidity, concentration of oxygen

and carbon dioxide might influence tuber dormancy. Air with 20% CO2 and 40% O2 or

60% CO2 and 18-20% O2 enhances dormancy release (Coleman and McInerney, 1997).

As dormancy progresses, there are physiological and biological changes in the

potato tuber (Van der Plas, 1987) controlled by phytohormones such as abscisic acid

(ABA), gibberellic acids (GA) (Rappaport et al., 1957a) and cytokinin (Sonnewald,

2001; Van der Plas, 1987). As a dormancy regulator, ABA concentration in dormant

tubers is high and it decreases with extended storage period (Sonnewald, 2001; Suttle,

1995). The concentration of this inhibitor drops 10 to 100 times during the breaking of

dormancy (Van der Plas, 1987). In contrast, gibberellic acid concentrations are low

during tuber dormancy and rapidly increase to more than 30 times during sprouting

(Smith, 1968). This change in the ratio of inhibitor and promoter affects the termination

of tuber dormancy (Emilsson and Lindblom, 1963). If ABA concentration is high and


37

gibberellin is low, then tubers stay dormant and they will start to grow when gibberellin

content increases (Van der Plas, 1987).

Another hormone that influences the termination of tuber dormancy is cytokinin.

This hormone shifts the tuber out of the state of endodormancy (Turnbull and Hanke,

1985; Van der Plas, 1987). Concentrations of cytokinins are relatively low and constant

during dormancy then concentrations increase about 55% during sprouting (Sukhova et

al., 1993). During the dormant period, cytokinin is converted, from an inactive storage

form into the active free base form (Van Staden and Dimalla, 1978).

The range of duration of dormancy is only published for cool temperate to

Mediterranean climate potatoes with no literature from potatoes grown in tropical

conditions. Therefore the dormant period needs to be explored in tropical potato

varieties to see whether they differ from cool temperate potatoes.

2.5.2. Sprout Growth

Potato tubers have buds arranged spirally from the stem end to the bud end

region. Sprout growth is influenced by cultivar and physiological age of tubers (Burton,

1989). The characteristics of sprouts change during storage. Once dormancy is broken

the first sprouts are single and apically dominant. This is followed by normal multiple

sprouting, multiple-branching sprouts, hairy sprouts (senility) and little tuber formation

(Krijthe, 1962; Struik and Wieserma, 1999). The commencement of sprouting and

sprout development is promoted by auxin and gibberellic acid.


38

2.5.2.1. The role of auxin

The apical bud located at the apex, usually grows first. It exhibits apical

dominance as it inhibits lateral bud outgrowth (Pushkarnath, 1976). The phenomenon of

apical dominance is primarily controlled by auxin (Moore, 1989), although other

hormones are possibly involved (Turnbull and Hanke, 1985). Auxin is synthesised in the

apical region and is transported basally so its concentration is higher in the apical than

lateral buds (Marschner et al., 1984). Auxin concentration in the apical bud is ten times

higher than tissue below it, and about twenty times higher than in the tissue bellow

lateral buds (Michener, 1942). High concentration of Indole Acetic Acid (IAA) the main

endogenous auxin in the apical region, creates a metabolic sink in the apical bud that

directs nutrients and cytokinins away from lateral buds (Cline et al., 1997; Marschner et

al., 1984). Apical buds also contain more soluble sugar than lateral buds providing

greater support for sprout growth (Dimalla and Van Staden, 1977).

Release from apical dominance allows lateral buds to grow. This appears to

happen through physiologically aging of tubers. Aging appears to be influenced by

auxin. Apical eyes of older tubers contain less IAA during sprouting and this combined

with the reduced ability of older tubers to transport auxin to lateral buds, their increased

ability to conjugate IAA into biologically inactive forms and increased IAA catabolism

(Mikitzel and Knowles, 1990b), reduce the dominance of apical buds over lateral ones.

2.5.2.2. The role of GA3

Endogenous gibberellic acids have long been thought to stimulate breaking of

dormancy of potato tubers (Rappaport et al., 1957a). The concentration of gibberellic


39

acid is low during tuber dormancy and it increases prior sprouting (Bailey et al., 1978;

Suttle, 2000; Van der Plas, 1987). However, increasing gibberellins may not be the

reason for breaking dormancy but a result of it, as increasing GA occurs after sprouts are

visible (Bailey et al., 1978).

There are particular gibberellic acids that control sprouting, including GA3, GA4,

GA5 and GA7. Other gibberellins such as GA6, GA8 and GA9 have no effect on sprouting

or may even inhibit sprouting (Rappaport et al., 1965). The main commercial gibberellin

is GA3. When applied to potato tubers GA3 stimulates sprouting. It releases lateral buds

from apical dominance and increases the number of sprouted eyes (multiple sprouting)

so that more sprouts develop from treated tubers (Holmes et al., 1970; Rappaport et al.,

1957b; Suttle, 2000). Furthermore, GA3 is more effective when applied to the basal than

the apical region (Timm et al., 1962). Sprouts from GA3-treated tubers emerge earlier

than untreated tubers (Dyson, 1965; Marinus and Boadlaender, 1978). Increasing

sprouting with GA3 leads to an increase in the number of stems which emerge above the

soil (Holmes et al., 1970; Marinus and Boadlaender, 1978) and stem weight (Timm et

al., 1962).

Endogenous gibberellic acid regulates the mobilisation of food reserves for

developing sprouts (Bailey et al., 1978; Coleman, 1987). Applied GA3 penetrates cut

potato tubers (Timm et al., 1962), and further stimulates mobilisation of food reserves,

so that it accelerates and promotes sprout growth.

Many studies on the effects of gibberellic acid use cultivars grown in temperate

regions, (Bailey et al., 1978; Dyson, 1965; Holmes et al., 1970; Marinus and

Boadlaender, 1978); (Rappaport et al., 1957a; Rappaport et al., 1965). There is no


40

information on the influence of GA3 on potato cultivars grown for tropical conditions.

Dormancy, sprout number and subsequent growth are influenced by the genetic make up

of the cultivars and the environment. Potatoes grown for tropical regions may be

genetically distinct and have different physiologically characteristics which would

influenced their response to hormonal or environmental treatment. In the present study

we examined the responses to applied GA3 on the tropical potatoes Eben, KT3 and PO3,

and Atlantic and Dawmor were used as typical commercially grown, Australian control

varieties.

2.5.3. Sprouting capacity

Length of storage period influences the capacity of potato tubers to produce

sprouts. Sprouting capacity of a tuber is commonly expressed by the percentage of

sprout fresh weight divided by the initial tuber fresh weight (Krijthe, 1962; Reust, 1986).

Sprouting capacity is an important parameter in ascertaining seed quality and it is

influenced by physiological age of seed tubers (Hartmans and Van Loon, 1987; Struik

and Wieserma, 1999; Van der Zaag and Van Loon, 1987). During storage, sprouting

capacity increases gradually and after reaching a maximum it will then decline

(Hartmans and Van Loon, 1987).

When tubers are stored for longer than a certain time, apical dominance is

reduced and more sprouts grow from a tuber. The number of sprouts that tubers produce

and the proportion of these sprouts that develop into main stems are important factors in

predicting the number of main stems per plant (Struik and Wieserma, 1999). Once

dormancy is broken, the longer the period of storage the longer sprouts grow and sprout


41

development is usually measured by the total length of sprouts or length of the longest

sprout (Wurr, 1978) and this differs with variety. However, no work has been done on

the sprout behaviour of potato cultivars suitable for tropical conditions.

Storage of seeds at 4°C inhibits sprout growth. When seeds are stored at 4°C for

a certain period, the optimum physiological age will be reached, and they will produce

good growth vigour at planting. When seeds are stored for too long, sprout vigour

decreases and eventually they may have abnormal sprouts (hairy sprouts) and produce

small tubers directly on the sprouts (senility). At this stage, tubers are not suitable for

use as seed (Struik and Wieserma, 1999). Maximum sprouting capacity is reached

before maximum number of sprouts (Fig 2.4). So, although sprouting capacity start to

decrease, sprout number still increases for a short time and then starts to decrease (Struik

and Wieserma, 1999).

Different varieties have different trends in of sprouting capacity (Krijthe, 1962).

When stored at 5°C, Bintje, Alpha, and Libertas break dormancy at about 3-4 months

after harvesting. The maximum sprouting capacity of all these varieties occurs about 1

year after harvesting. Sprouting capacity of Bintje is constant during the first month in

storage then gradually increases and reaches maximum after another nine months before

starting to decrease one month later. Sprouting capacity of Alpha increases even after 1

year storage. Sprouting capacity of Libertas increases to a maximum after nine months

in storage plateaus for three months and then starts to decrease after 12 months storage.

Other varieties, such as Jaerla reach a maximum sprouting capacity at 9 to 10 months

and in Desiree 9 to 11 months storage at 4°C (Hartmans and Van Loon, 1987).


42

No cropNo

crop

In long cycle:

low yield (few stems)

Period of maximum vigour

In long cycle crop: high yield

In short cycle crop: high yield

In short cycle crop: Low yield

Growth vigour

Sprouting capacity

Sprout number

Physiological ageTime

Spro

utin

g ca

paci

ty (g

/tube

r)

Gro

wth

vig

our o

f see

d tu

bers

(g/p

lant

)

Num

ber o

f spr

outs

per

see

d tu

ber dormancy apical dominance normal sprouting senility + little tuber formation total decay

end of dormancy

end of apical dorminance

beginning of senility

start of little tuber formation

incubation period

No cropNo

crop

In long cycle:

low yield (few stems)

Period of maximum vigour

In long cycle crop: high yield

In short cycle crop: high yield

In short cycle crop: Low yield

Growth vigour

Sprouting capacity

Sprout number

Physiological ageTime

Spro

utin

g ca

paci

ty (g

/tube

r)

Gro

wth

vig

our o

f see

d tu

bers

(g/p

lant

)

Num

ber o

f spr

outs

per

see

d tu

ber dormancy apical dominance normal sprouting senility + little tuber formation total decay

end of dormancy

end of apical dorminance

beginning of senility

start of little tuber formation

incubation period

Figure 2.4. Hypothetical scheme for the number of sprouts per seed tuber, the sprouting capacity of seed tubers, and their growth vigour, as a function of physiological age. The units along the x and y-axes are arbitrary. Sprouting capacity is expressed in sprouts weight (g) per tuber, while growth vigour is expressed in grams of dry weight per plant. This figure is modified from (Struik and Wieserma, 1999).

Sprouting capacity is an important measure of seed tuber quality. This was

developed and applied to potatoes in temperate regions. However, no work has been

done on the response of tropical potatoes.


43

2.6. The growth of potato

2.6.1. Plant growth

Sprouts from a mother tuber will develop into stems. However, not all of them

will grow as there is competition among sprouts for food reserves from the mother tuber.

The relationship between number of stems per hill (S) and number of sprouts planted (P)

is:

S = aPb where a and b are constants (Moorby, 1967) (Equation 1)

The number of stems which emerge above the soil surface is important for

predicting tuber production and is closely related to number of sprouts per tuber at

planting (Bleasdale, 1965). When tubers with apical dominance are planted they will

produce less stems than tubers with multiple sprouting (Toosey, 1962). Sprouting is

generated from the number of eyes that sprout and number of sprouts per eye. Sprout

distribution can also be important for stem development. Not all eyes produce stems and

mostly stems grow from the apical complex (Allen and Wurr, 1992a).

There are four types of stem (Struik et al., 1990), and only certain types of stems

usually bear stolons and produce tubers (Fig. 2.5) which are main stems (a) and stems

branching at the lower level of main stem (stem b).


44

..

Figure 2.5. Potato plant: a) Main stem; b) Stem branching on at the lower level of a main stem (near mother tuber); c) Stem branching at the subsurface section of a main stem; d) Stem branching above soil surface; e) daughter tubers at the stolon tips; f) daughter tubers from a branching stolon. Modified from (Struik et al., 1990)

Increasing stem number can be achieved by planting physiologically old seeds

(Boadlaender and Marinus, 1987; Iritani and Weller, 1987; Struik and Wieserma, 1999),

or by applying GA3 (Holmes et al., 1970; Timm et al., 1962). Gibberellic acid can be

applied as a seed treatment during storage or before planting (Caldiz, 1996; Holmes et

al., 1970; Marinus and Bodlaendar, 1978) or as a spraying foliage (Caldiz, 1996;

Ittersum et al., 1993). Concentration of GA3 is important to increase stem number

without reducing growth vigour. Application of a high concentration of GA3 (40 mg L-1)

to Atlantic seeds decreases stem number, reduces tuber number and reduces yield

(Arpiwi, 2003). In this variety, the optimum concentration of GA3 to increase stem

number is 20 mg L-1.

Soil surface

a

c

b

d

mother tuber

e f


45

2.6.2. Tuber formation

2.6.2.1. Stolon initiation and elongation

Tuberisation is a change in cellular differentiation in the stolon tip (Rastovski

and Van Es, 1987). The process of tuberisation includes development and growth of the

stolon, inhibition of stolon elongation and swelling of the stolon tip. Stolons are

modified underground stems that grow diageotropically from stem nodes and bear tubers

(Booth, 1963; O'Brien et al., 1998). The number of nodes on stems that bear stolons

differs with variety and environment conditions (Lovell and Booth, 1969).

Stolon formation starts from the lowest node, near the mother tuber and

developes acropetally towards the upper nodes (Lovell and Booth, 1969; Plaisted, 1957).

Basal nodes produce the greatest number of stolons and they grow longer than stolons

from upper nodes. Moreover, stolons from the basal nodes tend to branch but this varies

with temperature, photoperiod, stem density and soil conditions (Struik et al., 1990). It is

suggested that stolon branching is also promoted by factors stimulating stolon elongation

such as long days, high temperature and high gibberellin levels (Vreugdenhil and Struik,

1989).

Stolon development influences tuber formation. Not all stolons will develop

tubers. Under favourable conditions, stolon tips stop growing, swell and then tubers start

to initiate (Vreugdenhil and Struik, 1989). However, stolon tips may fail to form tubers

because they remain very small or may be reabsorbed (Struik et al., 1990). Termination

of stolon growth starts tuber initiation and this is associated with increasing

concentrations of abscisic acid (ABA) and cytokinins in the stolon tip (Vreugdenhil and

Struik, 1989).


46

2.6.2.2. Tuber formation and its growth

Tuber initiation occurs through cell enlargement in the stolon tip, termination of

cell division in the longitudinal direction, increasing lateral cell division and

enlargement, followed by accumulation of growth substances such as protein, starch and

sucrose (Ewing, 1990; Plaisted, 1957). The first tuber grows from stolons at the lowest

node and its development is greater than tubers from upper stolons so that lower nodes

produced bigger tubers (Plaisted, 1957).

There are several factors that control tuber initiation. Tuber induction is

stimulated by short day length, low night temperature, high irradiance and low levels of

nitrogen (Chapman, 1958; Ewing, 1990). When tubers start to develop under short days,

shoot and root growth slow, buds become inactive and roots stop elongating (Chapman,

1958).

Tuber induction occurs before tuber initiation and it is characterized by swelling

of the stolon tip (O'Brien et al., 1998). Jasmonic acid stimulates radial cell expansion,

increasing meristem size, and terminating stolon elongation. This induces swelling of the

stolon tip which is the first sign of tuber induction (Abdala et al., 2002; Cenzano et al.,

2003; Takashi et al., 1994). Abscisic acid concentration is low during stolon elongation

and high during tuberisation (Ewing, 1990; Xu et al., 1998).

Concentration of gibberellic acid in stolons determines tuber formation. When

GA concentration is high, it promotes stolon elongation, and if the concentration is low,

and concentration of ABA is increasing starts tuberisation (Vreugdenhil and Struik,

1989). There are certain GA forms found during stolon growth, such as GA1, GA3,

GA4/7, GA20 and GA9 (Abdala et al., 2002; Xu et al., 1998). The pattern of tuber


47

formation is closely related to stolon formation, so that it depends on the stem

development (Struik et al., 1990). Tuber initiation is considered to commence when

tubers become visible (10 mm) (O'Brien et al., 1998). Tuber initiation occurs in 1-6

weeks, and it is completed more quickly under favourable conditions of rapid plant

growth (O'Brien et al., 1998). Tuber growth is influenced by variety, physiological age

of the seed and environmental conditions. Physiological status of seed also determines

the time to tuberise. Physiologically old seeds generally emerge earlier and they tuberise

earlier (Struik and Wieserma, 1999).

2.7. Manipulation of tuber size distribution

Tuber production is closely related to stem production and it depends on seed

factors as they influence plant development and tuber formation. Tuber size distribution

depends on plant density, number of stems per plant, number of tubers per stem, rate and

duration of crop growth (Struik et al., 1990). Number of plants or plant density can be

calculated by multiplying the seed tuber density (number of seed planted) by plant

emergence per seed (Struik et al., 1990) as described below:

ρp = ρs x ℮ in which ρs = Wp / Ws (Equation 2)

where ρp is plant density (plant/m²), ρs is seed tuber density (seed tubers/m²), ℮ is

the proportion of emergence (plants per seed), Wp is the weight of planted seed

(g/m²), Ws = the average seed size (g/seed)


48

ρp = ρr x dp (Equation 3)

where ρr is the row density (rows/m) and dp is plant distance within the row (plants

per m per row).

Tuber production per square metre (p) can be calculated from the number of seeds

sown per square metre, number of sprouts per tuber, number of sprouts which develop

into stems, number of stolons per stem and number of tubers per stolon (Haverkort et al.,

1990), with the formula as follows:

Tuber seed tuber sprout stem stolon tuber

production = population x x x x (Equation 4) seed tuber sprout stem stolon

However, stolon length and branching may also be important for tuber production, but

branching is rarely investigated, presumably due to difficulties in sampling in the field

or in pots.

Increasing the proportion of small tubers can be achieved by increasing stem

number per plant which increases tuber number so that tubers grow smaller which

competition for assimilates. Stem production is controlled by seed size, physiological

age of seed or by applying GA3. Cutting seed influences the physiological responses of

potato tuber, it results in earlier breaking dormancy and promotes multiple sprouting as

apical dominance is reduced (Struik and Wieserma, 1999).

These are the standard responses for temperate and Mediterranean potatoes, but

it is unknown how tropical potatoes will respond.


49

2.8. Effects of gibberellic acid on the growth of potato

Gibberellins are growth regulators. These are synthesized via the mevalonic acid

pathway to ent-kaurene (Fosket, 1994). GA12-aldehyde is the first formed gibberellin

from ent-7α-hydroxy-kaurenoic acid and it is further changed to produce other

gibberellic acids (Phinney, 1985). There are many types of gibberellins in plants, for

example GA1 is an active endogenous gibberellin that controls shoot elongation in many

higher plants. GA1 is chemically identical to GA3 (Fig. 2.6) except for the presence of a

double bond in GA3 in the C-1 to C-2 position (Phinney, 1985). GA1 and GA3 usually

have similar activity in plants. GA1 is synthesized from GA20, GA4 or GA3, where GA3

is synthesized from GA5 or GA7 (Davis et al., 1999). Furthermore, conversion of GA5 to

GA3 has been found in several plants such as in apricot, marah and apple seeds the

shoots of Zea mays (Hedden and Kamiya, 1997).

CO

OOH

H

H CO2HHOH

CO

OOH

H

H CO2HHOH

CO

OOH

H

H CO2HHOH

CO

OOH

H

H CO2HHOH

GA1 GA3

Figure 2.6. The structure of biologically active gibberellic acid: GA1 and GA3. Modified from (Davis et al., 1999)


50

In many higher plant species, the content of GA1 is high, while GA3 is low

(Hedden et al., 2002). However, GA1 and GA3 are found in all organs of potato plants,

and GA3 levels are always higher than GA1 (Abdala et al., 2002).

There are two possible sites of GA synthesis. Gibberellins may be synthesized in

roots then transported to the shoot through xylem, or they may be synthesized in young

leaves, and transported to the root through phloem (Crozier and Reid, 1971; Phinney,

1985). Transportation of GA from buds to stolons occurs along with transportation of

assimilates (Menzel, 1983).

In Phaseolus coccineus GA19 is synthesized in the shoots then transported to the

roots where it is converted to GA1. Then, GA1 is transported back to the shoots (Crozier

and Reid, 1971). Similar movement of gibberellins during synthesis and metabolism

probably occurs in potatoes.

The growth of sprouts requires nutrients and hormones supplied from the mother

tuber. Application of GA3 to tubers before planting increases the endogenous pool of

GA once it has penetrated the skin. Then, it stimulates sprout growth and accelerates

stem emergence (Dyson, 1965; Timm et al., 1962; Van Ittersum et al., 1993).

Application of GA3 to cut tubers is more effective than whole tubers, as GA can more

readily penetrate the cut surface (Holmes et al., 1970)

After sprouts develop into stems, the shoots gradually replace the role of the

mother tuber. The production of gibberellic acid in the growing plant depends on

environmental conditions (Vreugdenhil and Struik, 1989). High temperature stimulates

increased synthesis of GA in buds of shoots which promotes new shoot growth, rather

than basal transport to lower stems and stolons (Menzel, 1983).


51

When GA is applied to tubers before planting, stems emerge earlier and stem

elongation is accelerated (Marinus and Boadlaender, 1978). When GA is applied as a

spray to foliage, it increases leaf area, stimulates stem growth, and increases stolon

length, but delays tuberisation and at higher concentration can cause tuber malformation

(Dyson, 1965; Holmes et al., 1970). In GA treated plants, leaves may become paler as

there is less chlorophyll content per unit area (Timm et al., 1962; Wheeler and

Humphries, 1963). The number of stems emerging above the soil surface also increases

with application of GA3 as in addition to more sprouts, more stems branch (Holmes et

al., 1970; Timm et al., 1962). The synthesis and mobilisation of GA in the plant is

influenced by the environment. Endogenous concentration of GA is low under short

days and high under long day conditions (Kumar and Wareing, 1974). Transportation of

GA from buds to stolons is stimulated by low temperature (Menzel, 1983).

Gibberellic acid influences the early phase of tuberisation especially stolon

growth (Marinus and Boadlaender, 1978). Concentration of GA is high in young stolons

especially in the elongating stolon tip (Xu et al., 1998) where it stimulates cell division

in the sub apical meristem (Booth, 1963). Applied GA4/7 promotes stolon elongation,

inhibits tuber formation and reduces tuber size which supports the role of endogenous

GA1. The concentration of GA1 is high during stolon elongation and low during

tuberisation (Xu et al., 1998), implying its role in stimulating elongation of stolons and

inhibition of tuberisation. Moreover, GA3 was also found in stolons at the time of tuber

set (Abdala et al., 2002) but then declines.

Application of GA3 can increase tuber number without affecting yield, due to GA

shifting tuber size into smaller categories (Marinus and Boadlaender, 1978). White Rose


52

and Kennebec seeds dipped in GA solution have fewer big tubers (> 100 g), but yield is

unaffected (Bishop and Timm, 1968; Marinus and Boadlaender, 1978) as application of

GA increases the proportion of small tubers. In some cultivars GA does not affect tuber

number per stem, but increases tuber number per plant as stem number increases

(Marinus and Boadlaender, 1978). It has also been suggested that increases in tuber

number by application of GA3 is probably because of an increase in the number of

stolons or it may stimulate stolons to branch (Bodlaendar and Van de Waart, 1989) but

these factors have not been investigated. Different varieties have different responses to

applied GA. Gibberellic acid shifts tuber size distribution in Bintje, Alpha and Jarela,

but the effect was much greater in Alpha and Jaerla than Bintje (Marinus and

Boadlaender, 1978). The effects of GA3 on tuber growth and its impacts on tuber size

need to be explored in tropical cultivars as it is related to cultivars.

There has been little work on the effects of interaction between application of

GA3 and storage length of potato tubers. There has been no research on increasing tuber

number and reducing tuber size using GA3 in tropical cultivars. Experimentation is

required to elucidate the response of tropical cultivars to different storage regime and

application GA3, especially with regard to increasing the proportional of small tubers

without reducing yield as this very important for seed production for tropical countries.

This problem can be broken down into testable hypotheses 1) that GA will increase stem

number, 2) that an increase in stem number increase tuber number, 3) that this will

reduce tuber size and 4) that there will be no effect on yield.

* For submission to the Australian Journal of Experimental Agriculture

Chapter 3

Cultivar, Storage Time and Gibberellic Acid influence Early Growth of Potatoes Suitable for Tropical Conditions*

Abstract

Five potato cultivars suitable for tropical conditions were stored for 10-30 weeks

(Atlantic) and 16 or 26 weeks (Dawmor, KT3, PO3 and Eben). Tubers were cut then

dipped in 20 mg L-1 GA3 for 15 minutes. The carry over effect of applied GA3 was

assessed on Atlantic and Granola seeds from plants grown from GA-treated and

untreated seeds.

In general, extending storage time improved seed quality including number of

sprouts per tuber, average sprout length and sprouting capacity (mm/g tuber fresh

weight). Planting older seeds accelerated emergence but increases in stem number were

dependant on cultivar. Length of storage had little effect on stolon number, branching of

stolons and tuber number. Young seeds which had broken dormancy produced higher

yields than older seeds.

Application of gibberellic acid (GA3) usually accelerated emergence by 2 to 7

days, increased stem number by 1.3 to 1.9 times, stolon length by 1.5 to 3 times, and

stimulated stolon branching, but it did not always increase stolon number. GA3

increased number of tubers without reducing yield in 26 week old Dawmor and 16 or 26

week old Eben. Moreover, application 20 mg L-1 GA3 had no carry over effect on the

early growth and tuberization of the subsequent generation of Atlantic and Granola

seed.

Additional keywords: Solanum tuberosum, small seed tuber

Chapter3 Cultivar, storage time and GA3

54

3.1. Introduction

In the tropics, small round seed tubers are required for planting to avoid diseases

which can result after cutting. Western Australia has good seed growing areas, free of

late blight, bacterial wilt and potato cyst nematode which are ideally suited for seed

production for export to tropical countries (Ian McPharlin, pers. comm.). Most tropical

varieties have not been produced in Australia so that information about their growth and

development is required for commercial production, storage and handling.

In general, increasing stem number increases tuber number (Haverkort et al.,

1990; Iritani et al., 1983; Moorby, 1967; Struik et al., 1990). It is presumed that

increasing stem number increases stolon number, providing more sites for tuber

initiation. However, other factors may be involved such as stolon branching. Small

tubers are required for planting seed as whole seed and increasing tuber number can

reduce tuber size without reducing yield (Moorby, 1967).

Number of stems is closely related to the number of sprouts that are produced

from seed tubers. Sprout growth is influenced by several factors, such as genetic

background, growing conditions (temperature, soil conditions, sunlight and nutrition),

storage conditions (temperature, humidity, light and oxygen), physiological age and

application of growth regulators. Here, the effects of cultivar, storage duration and

gibberellic acid (GA3) on sprout growth and subsequent stem and early tuber growth

were examined.

Storage period leads to aging (the processes of increasing maturity with time)

and this influences the sprouting capacity of potatoes (Hartmans and Van Loon, 1987).

The period and conditions of potato storage influence physiological processes, such as


55

respiration, use of stored carbohydrate (Van der Plas, 1987), hormone concentration and

dormancy. Tubers are dormant at harvest and require time to break dormancy. Tubers

with different physiological age usually have different subsequent plant growth.

Physiologically old tubers tend to emerge earlier, produce more stems, less tubers per

stem and have lower yield (Kawakami, 1963; Struik and Wieserma, 1999; Van Es and

Hartmans, 1987b). Planting potato tubers of appropriate age is essential in obtaining

high plant performance, and this varies from 4 to 6 months from harvest depending on

variety and environment conditions (Kawakami, 1963).

Gibberellic acid is a growth regulator that influences dormancy. It plays an

important role in breaking dormancy of potato seed tubers and reducing apical

dominance (Holmes et al., 1970). The concentration of gibberellic acid is low during the

dormant period and it increasing when sprouts start to grow (Suttle, 2004; Timm et al.,

1962; Van der Plas, 1987). Applied gibberellic acid influences plant growth, as it

accelerates shoot emergence, and increases stem number and plant height, but it inhibits

tuber initiation. In some varieties applied GA increases tuber number and reduces tuber

size without decreasing yield (Arpiwi, 2003; Bishop and Timm, 1968; Holmes et al.,

1970).

Different potato varieties respond differently to application of gibberellic acid.

Tuber number in Atlantic seeds treated with 20 mg L-1 GA3 increased from 5 to 9 tubers

per plant, whereas in Granola tuber number increased from 8 to 9 tubers per plant

(Arpiwi, 2003). Although more seed tubers are shifted in the smaller size categories by

application of 20 mg L-1 GA3 it is expected that in the following growth, these seeds will

produce the usual large tubers required for processing purposes such as chips and crisps.


56

In order to evaluate the carry over effects of GA3, tubers produced from GA3-treated

seeds were replanted and their sprout behaviour and early growth were examined.

Most studies on physiological age have used varieties that have been developed

and grow in temperate regions, such as Russet Burbank in America and Canada

(Knowles and Bontar, 1991), and European cultivars such as Bintje, Alpha (Krijthe,

1962), Jaerla and Desiree (Hartmans and Van Loon, 1987). There have been no studies

of the influence of physiological age and plant growth regulators on growth of Atlantic

and Dawmor which are grown in Australia and exported to Indonesia, nor on cultivars

selected and grown in tropical regions such as Eben, KT3 and PO3. Cultivars adapted to

tropical regions may have very different responses to environmental and chemical

treatments.

The overall aim of this study was to increase the number of small tubers by using

seed with different physiological ages and an applied growth regulator. Five varieties

suitable for tropical regions were selected and grown under Western Australian

conditions. The effects of storage time and GA3 on early shoot growth and the

interaction between storage period and gibberellic acid were examined in the glasshouse.

3.2. Materials and Methods

Experiment 1: Effects of storage time and GA3 on Atlantic cultivar

Certified round seed tubers (second generation from mini tuber) of the variety

Atlantic grown in Manjimup, Western Australia were used in this experiment. Tubers

weighing 100-200 g were selected and cool stored at 4° C with 90-95% RH for 10, 14,

16, 18, 20, 22, 26 and 30 weeks. Two cohorts of seeds were used to cover this wide


57

range of storage period. The first group were grown from summer to autumn (planted in

January 2003 and harvested on 23 May 2003) and stored for 10, 14, 16, 18 and 20 weeks

and were regarded as young seeds. The second group were grown during summer

(planted on 20 November 2002 and harvested on 17 February 2003) and stored for 20,

22, 26 and 30 weeks and were regarded as old seeds. Seeds stored for 20 weeks were

used for both lots to assess the effect of growing conditions on sprout behaviour and

subsequent growth. Periodically, 40 seeds per treatment were removed from cold

storage, put in trays and sprouted at 20° ± 5°C for 2 weeks. On the first day in the

sprouting room, they were weighed for initial tuber weight.

Eyes were numbered from the apical region to the stem end and the length of

each sprout grown from each eye (> 2 mm) was measured. Number of sprouts and total

length of sprouts per tuber were measured. Length of the longest sprout was recorded

and average sprout length was calculated by dividing total sprout length by the number

of sprouted eyes. At the end of sprouting time, the proportion of sprouted eyes was

calculated (sprouted eyes/ number of eyes per tuber). Sprouting capacity (total length of

sprouts per tuber (mm)/initial tuber weight (g)) was calculated. Sprouting capacity was

calculated on a sprout length basis, not sprout weight basis, because tubers were planted

at the end of sprouting time and therefore sprouts could not be removed and weighed.

To remove tuber size effects, after 2 weeks of sprouting, potato seed tubers were

cut into 40 ± 0.1 g seed pieces, with 3 eyes. After cutting, they were dipped in 0 or 20

mg L-1 GA3 for 15 minutes, then air dried for 24 h. Before planting seed pieces were

dusted with fungicides Tatodust (2 g Mancozeb® kg-1 seed pieces) and Rhizolex (2 g

Rhizolex® kg-1 seed pieces).


58

The treatments of 9 storage times (physiologically young: 10, 14, 16, 18, and 20

weeks, physiologically old: 20, 22, 26 and 30 weeks) and 2 concentrations of GA3 (0, 20

mg L-1) were arranged in a randomized block design. Four replications were used with

five plants per sub sample.

One potato seed piece was planted in a 250 mm diameter pot filled with potting

mix (composted pine bark:cocco peat:river sand::2:1:1) and grown in a glass house for 8

weeks (Table 3.1) from winter to summer. In Experiment 1, Atlantic seeds from plants

grown from summer to autumn (physiologically young seeds) and grown during summer

(physiologically old seeds) in Manjimup, south-western Australia were planted in the

glasshouse at the University of Western Australia in Perth, from winter to summer

(Table 3.2, 3.2, 3.3). Environmental conditions were monitored (Table 3.2, 3.3).

Potato-E fertilizer containing N:P:K::4:7:7 NPK (produced by Baileys Fertilisers,

Kwinana, Western Australia) was applied (60 g/pot). Dipel® was used to control

budworm. First emergence, 100% emergence and number of stems per plant were

observed during early growth. Plant height and number of leaves per plant were assessed

three times (3, 5 and 7 weeks after planting).

At harvesting (8 weeks after planting), above ground performance was assessed.

Stems were cut 20 mm above the soil surface and numbered. Leaves were separated

from stems and their fresh weights and dry weights (after being oven dried at 70° C for 2

d) were measured.

To measure underground growth, roots were cut from stems, so that only stolons

were left. Plants were then evaluated by measuring number of stolons per stem, number


59

of stolons per plant and length of the longest stolon, number of tubers per plant, yield

(defined as tuber fresh weight per plant) and tuber dry weight.

To determine the tuber size distribution at early growth, the number of tubers per

plant was recorded. Tubers were weighed individually then graded into 6 categories (< 5

g, 5-19 g, 20-34 g, 35-49 g, 50-65 g, and > 65 g). Tubers were put in the oven (70° C)

for one week and their dry weights measured.

Experiment 2: Effects of storage time and GA3 on four potato cultivars

The effects of storage time and gibberellic acid were examined on four potato

cultivars (Dawmor, KT3, PO3 and Eben). Dawmor (G2), KT3 and PO3 (G5) were

planted in February 2003 and harvested in April 2003, whereas Eben (G5) was planted

in March 2003 and harvested in May 2003. Seed tubers were stored for 16 and 26 weeks

to examine the performance of physiologically young and old seeds. They were treated

same as Atlantic as previously mentioned, to evaluate their sprout behaviour,

emergence, plant growth and tuber size distribution.

Growing conditions: Experiment 1 and Experiment 2

Physiologically young Dawmor, KT3, PO3 and Eben seeds were grown during

spring to summer, while physiologically old seeds were grown in a glasshouse at the

University of Western Australia (Table 3.3) from spring to summer, and their seed

production environment and growing conditions in the glasshouse were monitored

(Table 3.1, 3.2).


60

Dawmor, KT3, PO3 and Eben seeds used in Experiment 2 were grown during

summer to autumn in Manjimup and were planted in the glasshouse from spring to

summer.

Table 3.1. Average temperature (for 6 h blocks of time during the day e.g 00.00 to 5.45), average minimum daily temperature, average maximum daily temperature and average monthly temperature (°C) inside the glasshouse at the University of Western Australia

Time (blocks of 6 h)

00.00 to

05.45

06.00 to

11.45

12.00 to

17.45

18.00 to

23.45Month

Average temperature °C Ave

rage

Min

D

aily

Te

mpe

ratu

re

(°C

)

Ave

rage

M

ax D

aily

Te

mpe

ratu

re

(°C

)

Ave

rage

D

aily

Te

mpe

ratu

re

(°C

)

June 12.99 18.00 22.07 14.90 12.18 13.19 12.69 July 13.27 17.44 22.13 15.16 14.08 14.64 14.36 August 12.76 17.27 22.24 15.22 11.72 23.95 17.84 September 14.81 20.56 24.38 17.25 13.79 27.22 20.21 October 16.40 22.66 26.13 18.81 15.10 28.11 21.61 November 19.03 24.55 27.56 21.13 17.94 29.84 23.89 December 19.42 24.11 26.60 21.53 18.32 28.64 23.48 January 20.10 26.55 31.24 23.28 20.14 32.85 26.50

Table 3.2. Average light intensity per month (μmolm-2s-1), average total light per day (μmolm-2s-1) inside the glasshouse and length of photoperiod (h)

Average light intensity/month (μmolm-2s-1)

Month 00.00 to

05.45

06.00 to

11.45

12.00 to

17.45

18.00 to

23.45

Average total light/day

(μmolm-2s-1)

Photoperiod (h)

June 0.00 246.00 299.13 0.00 545.13 10.46 July 0.11 249.75 346.13 1.21 597.20 10.64 August 0.00 318.88 440.35 0.27 759.50 11.29 September 0.02 408.36 569.00 1.06 978.44 12.18 October 0.85 600.07 777.87 3.17 1381.96 13.19 November 1.14 230.62 287.13 3.77 522.66* 14.08 December 1.36 228.65 321.59 9.28 560.88* 14.64 January 0.87 234.21 337.63 12.14 584.84* 14.69 * Under shade cloth


61

The average temperature during the day/night (6 h blocks), average minimum

daily temperature, average maximum daily temperature and average monthly

temperature varied with the month and hence period of assessment (Table 3.1), as did

average light intensity per month, average total light per day and length of photoperiod

(Table 3.2).

In Experiment 2, physiologically old Dawmor, KT3, PO3 and Eben cultivars

were grown under shade cloth (65% UV blocked) to obtain the similar light intensity to

a winter planting.


62

Table 3.3. Seed growing conditions in Manjimup, South Western Australia and subsequent plant growth conditions in the glasshouse at the University of Western Australia, Perth

Variety Seed growing conditions Plant growth conditions in glasshouse

Stor

age

time

Plan

ted

Har

vest

ed

Seas

on

Plan

ted

Har

vest

ed

Seas

on

Experiment 1: Young Atlantic 10 wks 18/8/03 10/10/03 winter to spring 14 wks 12/9/03 7/11/03 spring to summer 16 wks 26/9/03 21/11/03 spring to summer 18 wks 10/10/03 5/12/03 spring to summer 20 wks

Jan 2003

May 2003

Summer to

Autumn 24/10/03 19/12/03 spring to summer

Experiment 1: Old Atlantic 20 wks 23/7/03 17/9/03 winter to spring 22 wks 6/8/03 1/10/03 winter to spring 26 wks 5/9/03 31/10/03 spring 30 wks

Nov 2002

Feb 2003 Summer

29/9/03 24/11/03 spring to summer Experiment 2: Young Dawmor, KT3, PO3, Eben (16 weeks) Dawmor 5/9/03 31/10/03 spring KT3 5/9/03 31/10/03 spring PO3

Feb 2003

Apr 2003

Summer to

Autumn 5/9/03 31/10/03 spring

Eben Mar 2003

May 2003 Autumn 23/9/03 18/11/03 spring to summer

Experiment 2: Old Dawmor, KT3, PO3, Eben (26 weeks) Dawmor 12/11/03 5/1/04 summer KT3 12/11/03 5/1/04 summer PO3

Feb 2003

Apr 2003

Summer to

Autumn 12/11/03 5/1/04 summer

Eben Mar 2003

May 2003 Autumn 22/11/03 15/1/03 summer

Experiment 3: Carry over effects of GA3 on two potato cultivars

In a previous study (Arpiwi, 2003), two of potato varieties, Atlantic and Granola

(50 g seed pieces) were dipped in 0 or 20 mg L-1 GA3 for 15 minutes and then grown in


63

the field for 118 days. The proportion of seed used to tuber produced was 0.98 in

Atlantic and 0.97 in granola or approximately 1/10. If no synthesis and no metabolism of

GA occurred (this assumes all applied GA would go to tubers), the diluted concentration

of GA3 into plants would be about 1/10 times 20 or 2 mg L-1 GA3.

Small tubers (30–60 g) of two varieties, Granola and Atlantic produced from

plants using seeds pre-treated with 0 and 20 mg L-1 GA3 were used. Potato seeds were

removed from 4° C cold storage, put in trays and placed under ambient temperature (20

± 2° C) for two weeks, then their sprout behavior including proportion of sprouted eyes

(%), number of sprouts per tuber, total length of sprouts (mm) and sprouting capacity

(mm g-1) was observed.

Round seed tubers were planted 10 cm deep in 250 mm diameter plastic pots.

Before planting they were treated with fungicide (Rizolex®, 2 g kg-1). Four replicate

pots were placed in the glass house with a randomized block design. Potato E fertilizer

N:P:K:: 4:7:7 (Baileys Fertilisers, Perth) was applied at 60 g per pot.

During vegetative growth, first emergence, number of stems per plant emerging

above the soil surface, plant height and number of leaves per plant were recorded at 2, 4

and 6 weeks after planting. Potato plants were harvested at 7 weeks after planting. At

harvest, numbers of stolons per plant, tuber number, tuber fresh weight, tuber dry weight

were recorded.


64

3.3. Results

Experiment 1

Sprout behaviour

Pre-planting behaviour was influenced by storage time, where dormancy was

considered broken when 80% tubers had sprouts ≥3 mm. Atlantic seeds stored for 10

weeks at 4°C were still dormant. Prolonging storage time allowed Atlantic seeds to

break dormancy at 16 weeks. Sprout number significantly increased with prolonged

storage time from 10 to 20 weeks and reached a maximum of 17 sprouts per tuber at 20

weeks (Fig. 3.1). The number of sprouts per tuber in 20 weeks-old summer grown seed

was similar to 20 weeks-old summer-autumn grown seed and it decreased slightly when

storage time was extended from 20 to 30 weeks.

Sprouts grew larger when seeds were stored for longer time. The average sprout

length of summer-autumn grown Atlantic increased substantially from 0.38 mm at 10

weeks to 6.04 mm at 20 weeks, and they reached ≥3 mm long at 16 weeks (Fig. 3.1). In

summer grown seeds, average sprout length was less at 20 weeks and slightly increased

by prolonging storage time from 20 to 30 weeks.

A similar trend occurred in sprouting capacity where it increased sharply with

storage from 10 weeks and reached maximum of 0.7 mm/g at 20 weeks (Fig. 3.1).

Summer grown Atlantic seeds stored for 20 weeks had less sprouting capacity which

gradually increased to 0.6 with storage at 30 weeks. Sprouting capacity of summer-

grown seed at 20 weeks was less than summer-autumn grown seed at 20 weeks. Storage

from 20-30 weeks slightly improved sprouting capacity. Summer-autumn grown seed


65

0

5

10

15

20

25

30

Spr

outs

/tube

r

0

2

4

6

8

Ave

rage

spr

out l

engt

h(m

m)

0.0

0.2

0.4

0.6

0.8

10 14 16 18 20 22 26 30Storage time (weeks)

Spr

outin

g ca

paci

ty(m

m g

-1)

0

5

10

15

20

25

30

Spr

outs

/tube

r

0

2

4

6

8

Ave

rage

spr

out l

engt

h(m

m)

0.0

0.2

0.4

0.6

0.8


Spr

outin

g ca

paci

ty(m

m g

-1)

stored for 20 weeks had similar sprouting capacity to summer grown seed stored for 30

weeks.

Figure 3.1. Effects of storage time on number of sprouts/tuber, average sprout length

(mm) and sprouting capacity (mm g-1) of summer-autumn (-o-) and summer (-□-) grown Atlantic seeds. Vertical bars are l.s.d value at P = 0.05. Arrow is when 80% tubers have sprout length ≥3 mm. Equation for sprouting capacity of summer-autumn grown seeds was y = 0.0036e1.133x, r² = 0.89 and summer grown seeds was y = 0.0469x + 0.3987, r² = 0.87


66

Plant growth

Generally, plant growth of Atlantic was influenced by storage time and

gibberellic acid. For example, emergence was hastened with prolonged storage time and

it was further stimulated by applying GA3. Here, 10-week old summer-autumn grown

Atlantic had completely emerged by 20 days after planting and after 20 weeks storage

this had reduced to 7 days. However, 20-week old summer grown seeds took slightly

later (9 days) to full emerge and emergence remained the same when storage was

prolonged to 30 weeks.

Older seeds usually produced more stems than younger seeds (Fig. 3.2). Stem

number of Atlantic seeds increased when storage time was extended from 10 to 20 week

or 20 to 30 weeks. However stem number of 20 week-old, summer-autumn grown seeds

was the same as 30 week-old, summer grown seeds. Atlantic seeds dipped in GA3

increased stem number up to double that of untreated seeds. GA3-treated 20 week old-

summer-autumn grown seed had 6 stems which were similar to the number of stems of

GA3-treated 30 week-old seeds. The effects of GA3 were seen early in shoot emergence.

Stems grew taller, thinner and sometimes had chlorotic leaflets. Application of GA3

increased plant height and numbers of leaves in both physiologically young and old

seeds, but shoot fresh and dry weights were not affected.


67

0

3

6

9

12

15

10 14 16 18 20 22 26 30

Storage time (weeks)

Ste

m n

umbe

r

Figure 3.2. Influence of GA3 on stem number of summer-autumn grown and summer

grown Atlantic seeds. (-o-) is summer-autumn seeds without GA3, (-●-) is summer-autumn seeds plus GA3, (-□-) is summer seeds without GA3 and (-■-) is summer seeds plus GA3. Vertical bars are l.s.d value at P = 0.05

Underground performance

The number of stolons per plant, stolon length, stolon branching and tuber

numbers changed with storage period and application of GA3 (Fig. 3.3). In control

plants, 10 week stored seed produced 9 stolons per plant and it increased to 15 at 20

weeks. Stolons per plant decreased from 15 to 12 when storage was extended from 20 to

30 weeks. There was a marginal increase in the number of stolons per plant with the

application of GA3.

Stolon length peaked in summer-autumn grown seed and then declined (Fig.

3.3). In control plants, the longest stolon increased by approximately 50% when storage

was extended from 10 to 14 or 16 weeks, but longer storage periods gradually decreased

length. Application of GA3 to seeds increased length of the longest stolon by 20 to


68

nearly 30%. However, older seeds treated with GA3 still produced shorter stolons

compared to GA3-treated younger seeds.

The number of tubers per plant of physiologically young seeds was doubled by

prolonging storage time from 10 to 14 weeks (Fig. 3.4). Subsequently, tuber number was

relatively constant as storage was prolonged from 16 to 30 weeks. Treating seeds with

GA3 generally increased tuber number across all storage periods by about 25 to 50%.

Generally, longer storage time increased then decreased yield (Fig. 3.4). Yield

more than doubled from 200 g plant-1 at 10 weeks to 455 g plant-1 at 14 weeks then

declined 335 g plant-1 after storing seeds for 18 weeks. Similarly, in summer grown

seed, yield increased from 200 g plant-1 at 20 weeks to 530 g plant-1 at 26 weeks then

decreased to 412 g when seeds were stored for 30 weeks. Generally, application of GA3

did not affect yield or it resulted in a small increase in fresh (or dry) weight.

Application of GA3 generally increased the yield of small tubers, especially of

less than 5 g and 5-19 g. GA3 did not affect tubers of 50-64 g, but to some extent it

reduced tubers more than 64 g (Table 3.4). However, yield was generally not affected by

application of 20 mg L-1 GA3 (Fig. 3.4).


69

0

10

20

30

40

50

60

Sto

lons

/pla

nt

0

100

200

300

400

Long

est s

tolo

n (m

m)

0

2

4

6

8


Bra

nchi

ng s

tolo

ns

0

10

20

30

40

50

60

Sto

lons

/pla

nt

0

100

200

300

400

Long

est s

tolo

n (m

m)

0

2

4

6

8


Bra

nchi

ng s

tolo

ns

Figure 3.3. Influence of GA3 on number of stolon/plant, length of the longest stolon

(mm) and number of branching stolons of summer-autumn grown and summer grown Atlantic seeds. (-o-) is summer-autumn seeds without GA3, (-●-) is summer-autumn seeds plus GA3, (-□-) is summer seeds without GA3 and (-■-) is summer seeds plus GA3. Vertical bars are l.s.d value at P = 0.05


70

0

10

20

30

40

Tube

rs/p

lant

0

150

300

450

600

750


Yie

ld (g

/pla

nt)

Figure 3.4. Influence of GA3 on tubers/plant and yield (g/plant) of branching stolons of

summer-autumn grown and summer grown Atlantic seeds. (-o-) is summer-autumn seeds without GA3, (-●-) is summer-autumn seeds plus GA3, (-□-) is summer seeds without GA3 and (-■-) is summer seeds plus GA3. Vertical bars are l.s.d value at P = 0.05


71

Table 3.4. Effect of gibberellic acid on tuber size distribution of physiologically young and old Atlantic seeds, at 8 weeks after planting.

Tuber size (g)

Stor

age

time

(wee

ks)

GA

3 (m

g L-1

)

< 5 5 - 19 20 - 34 35 - 49 50 - 64 > 64

10 0 1.95 a 1.05 a 1.07 a 1.60 ab 0.50 a 0.70 ab 20 3.90 ab 2.60 bc 1.40 ab 1.00 a 0.55 ab 0.65 ab

14 0 4.45 b 2.25 b 1.30 ab 1.15 ab 1.35 bc 2.90 d 20 7.60 cd 3.60 c 3.15 c 3.00 c 1.05 ab 0.55 a

16 0 2.90 ab 1.05 a 1.15 ab 1.10 ab 1.65 bc 3.40 de 20 6.85 c 2.55 b 2.45 bc 2.15 b 1.85 c 1.90 c

18 0 2.90 ab 2.25 b 1.15 ab 1.85 b 1.45 bc 1.40 bc 20 5.70 bc 2.45 b 1.55 ab 1.45 ab 1.40 bc 1.25 b

20 0 6.10 bc 1.40 ab 1.65 b 1.15 ab 0.80 ab 0.50 a

You

ng se

eds

20 9.55 d 3.00 bc 2.00 bc 1.10 ab 0.55 ab 0.15 a 20 0 6.15 bc 1.35 ab 1.65 b 1.15 ab 0.80 ab 0.50 a 20 9.55 d 2.95 bc 2.00 bc 1.20 ab 0.55 ab 0.20 a

22 0 5.55 bc 1.75 ab 1.85 bc 2.05 b 1.15 b 0.25 a 20 8.00 cd 2.40 b 2.15 bc 1.65 ab 1.05 ab 0.35 a

26 0 2.65 ab 1.55 ab 2.25 bc 1.40 ab 1.45 bc 3.55 e 20 5.65 bc 3.00 bc 2.35 bc 2.05 b 1.10 ab 1.70 bc

30 0 3.95 ab 1.60 ab 1.50 ab 1.25 ab 1.65 bc 2.30 cd

Old

seed

s

20 7.55 cd 3.50 c 2.55 c 1.75 b 1.15 b 1.65 bc l.s.d ST 1.46 0.66 0.61 0.49 0.43 0.42 l.s.d GA3 0.69 0.31 0.29 0.23 0.20 0.60 l.s.d ST x GA3 2.07 0.93 0.87 0.66 0.61 0.60

Experiment 2

Sprout behaviour

Generally, sprout behaviour of potato seed tubers was influenced by storage

time, and tuber dormancy was gradually broken by extending storage time. Presumably,

Eben had broken dormancy less than 16 weeks followed by PO3, where Dawmor had


72

broken dormancy just after Atlantic. KT3 seemed to have long dormancy, where it had

broken more between 16 and 26 weeks. In the four potato cultivars physiologically old

seeds produced a higher proportion of sprouted eyes, more sprouts/tuber (except Eben),

longer sprouts and they had a higher sprouting capacity than physiologically young

seeds. Extending storage time substantially increased the number of sprouts/tuber of

Dawmor and KT3 seeds, with some increase in PO3 and no increase in Eben seeds (Fig.

3.5).

Average sprout length increased 2.6 times in Dawmor, 4 times in PO3 and 10

times in Eben when storage time extended from 16 to 26 weeks (Fig. 3.5). These trends

were similar to the changes in sprouting capacity (Fig. 3.5), where Dawmor, PO3, Eben

and KT3 substantially increased in sprouting capacity from 10 to 26 weeks. Compared

to 16 weeks, sprouting capacity at 26 weeks was increased about 8 times in Dawmor,

about 4 times in PO3 and 11 times in Eben. KT3 seeds were still dormant at 16 weeks

storage but sprouted at 26 weeks. Different cultivars also had different sprout growth

rate. KT3 sprouts grew slower (0.12 mm g-1 per week) than other cultivars while Eben

was the fastest (2.48 mm g-1 per week).


73

0

3

6

9

12

15

18

Spr

outs

/tube

r

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

Dawmor KT3 PO3 EbenCultivar

Spro

utin

g ca

paci

ty

(mm

g-1

)

0

10

20

30

40

50

Ave

rage

spr

out l

engt

h (m

m)

0

3

6

9

12

15

18

Spr

outs

/tube

r

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

Dawmor KT3 PO3 EbenCultivar

Spro

utin

g ca

paci

ty

(mm

g-1

)

0

10

20

30

40

50

Ave

rage

spr

out l

engt

h (m

m)

Figure 3.5. Influence storage time on number of sprouts/tuber, average sprout length

(mm) and sprouting capacity (mm g-1) of Dawmor, KT3, PO3 and Eben seeds stored for 16 weeks (□) or 26 weeks (■).Vertical bars are l.s.d value at P = 0.05


74

Plant growth

In general, the varieties grew differently in response to storage time and GA3

treatment. Generally, seeds treated with GA3 emerged earlier than control plants, except

Eben stored for 26 weeks. In both young and old seeds, application of GA3 accelerated

emergence and this was by 2 days in Dawmor, 1-5 days in KT3 and 1-2 days in PO3.

Young Eben seeds treated with GA3 emerged 2 days earlier than control plants, but old

seeds were not affected.

Effects of storage time and GA3 on stem number varied. In Dawmor and PO3,

26-week stored seeds produced more stems than those stored for 16 weeks, while in KT3

stem number declined with extended storage time and in Eben stem number did not

change. In Dawmor and PO3 seeds stored for 16 weeks, GA3 treatment doubled stem

number, where in PO3 seed stored for 26 weeks stem number increased by 1.3 times

(Table 3.5). Application of GA3 did not affect stem number of physiologically old

Dawmor seeds, nor in physiologically young or old KT3 and Eben seeds.

In general, old seeds produced taller plants with more leaves than young seeds

and this was further stimulated by application of GA3. Gibberellic acid increased number

of leaves in both physiologically young and old seeds except for young KT3 and old

Dawmor. Young Dawmor seeds treated with GA3 grew 24% taller and had 78% more

leaves than control plants, whereas in old seeds, plants treated with GA3 were 16% taller

than control plants but produced a similar number of leaves. In young KT3, there was no

difference between control and treated plants in plant height and number of leaves,

whereas in old seeds, GA3-treated plants were 27% taller than control plants and


75

produced 57% more leaves. GA3 did not affect plant height, but it increased number of

leaves of physiologically young and old PO3 (18%) and Eben (66%).

Table 3.5. Effects of storage time (ST) and GA3 on the stem number of four potato cultivars. Different letters indicate significant difference (p ≤ 0.5) within columns.

Potato variety Storage

time (weeks)

GA3 (mg L-1) Dawmor KT3 PO3 Eben

16 0 2.25 a 3.88 ab 3.20 a 2.90 ab 20 4.20 c 5.89 b 6.30 c 3.60 b

26 0 3.15 b 2.45 a 4.60 b 2.85 a 20 3.45 bc 3.25 a 6.15 c 3.55 ab l.s.d ST, GA3 ST x GA3

0.584 0.826

1.727 2.442

0.693 0.981

0.688 0.973

Underground performance

Prolonging storage time consistently decreased tuber number per plant (Table

3.7). In control plants, tuber number decreased by 34% in Dawmor, 84% in KT3, 39% in

PO3 and 34% in Eben when storage time was extended from 16 to 26 weeks. A similar

trend occurred with extension of storage in GA3-treated plants. Application of GA3 did

not influence tuber number of Dawmor, KT3 and PO3 stored for 16 or 26 weeks,

whereas in Eben, it increased tuber number by 37% in young seeds and by 39% in old

seeds.

Application of GA3 did not affect number of stolons per plant in either

physiologically young or old seeds of most varieties. The exception was Eben, where

GA3 increased number of stolons per plant by 61% (young seeds) and 28% (old seeds).


76

Generally, older seeds produced shorter stolons, except 26-week stored Eben. In

control plants, extending storage time from, 16 to 26 weeks reduced stolon length by

73% times in Dawmor, 84% in KT3 and 56% in PO3. Application of GA3 stimulated

stolon growth, so that seeds dipped in GA3 produced longer stolons than control plants

(except 16-week stored KT3). Gibberellic acid doubled stolon length in young Dawmor

and Eben seeds, and increased it by 1.6 times in PO3 (Table 3.6). In old seeds, GA3

increased stolon length about 2 to 4.5 times.

Application of GA3 to Eben increased the branching of stolons of both

physiologically young (3.6 times) and old seeds (5.5 times), whereas in Dawmor, GA3

only increased branching stolons of physiologically old seeds (from 0 to 5.5). GA3 did

not stimulate branching of stolons in KT3 or PO3 (Table 3.6).

Most plants had between 100-500 g of tubers/plant at harvest, which was 8

weeks from planting tuber at this time tubers had an average size of 6 to 29 g and were

still actively growing. Yield (fresh weight/plant) and tuber dry weight (data not

presented) from plants consistently decreased when seeds were stored longer (Table

3.7). In control plants, yield of seeds stored for 26 weeks was less than half of 16-week

stored in Dawmor, KT3 and PO3 and 63% of young Eben seeds. GA3 decreased yield in

young seeds of Dawmor, PO3 and KT3 but did not affect Eben. In contrast, in old seeds

GA3 did not influence yield of Dawmor, KT3 or PO3 but increased in Eben. These

trends were reflected in tuber dry weight (Appendix 1).


77

Table 3.6. Effects of storage time (ST) and GA3 on the number of stolons per plant, length of the longest stolon, and number of branching stolons per plant of four potato cultivars. Different letters indicate significant difference (p≤0.5) within columns.

Potato variety Storage time

(wks) GA3

(mg L-1) Dawmor KT3 PO3 Eben

Number of stolons/plant 16 0 16.40 a 21.20 a 17.50 a 15.87 ab 20 14.25 a 17.60 a 22.20 a 25.55 c

26 0 25.11 b 18.70 a 23.90 a 13.86 a 20 28.70 b 29.40 a 24.10 a 17.75 b l.s.d ST, GA3 ST x GA3

4.25 6.01

9.65 13.65

5.88 8.31

2.37 3.35

Length of the longest stolon (mm) 16 0 167.5 b 225.0 c 180.2 b 127.8 a 20 390.2 c 258.0 c 298.0 c 297.4 c

26 0 45.6 a 36.0 a 78.4 a 119.4 a 20 210.0 b 130.0 b 152.2 b 236.6 b l.s.d ST, GA3 ST x GA3

37.47 52.99

48.9 69.2

31.51 44.56

22.90 32.39

Number of branching stolons/plant 16 0 5.50 b 29.4 b 8.90 b 1.65 a 20 5.55 b 19.7 b 11.35 b 5.95 b

26 0 0.00 a 0.1 a 0.35 a 0.75 a 20 5.50 b 4.4 a 3.00 a 4.15 b l.s.d ST, GA3 ST x GA3

3.33 4.71

9.51 13.45

4.10 5.80

1.438 2.034


78

Table 3.7. Effects of storage time (ST) and GA3 on tuber number and yield (g fresh weight/plant) of four potato cultivars. Different letters indicate significant difference (p ≤ 0.5) within columns.

Potato variety Storage

time (weeks)

GA3 (mg L-1) Dawmor KT3 PO3 Eben

Tuber number

16 0 20.12 bc 58.5 b 22.96 b 13.87 b 20 22.40 c 55.8 b 22.75 b 18.95 c

26 0 13.22 a 9.5 a 14.10 a 9.19 a 20 17.96 b 17.5 a 14.45 a 12.75 b l.s.d ST, GA3 ST x GA3

2.64 3.74

11.91 16.84

4.36 6.17

1.67 2.37

Yield (g fresh weight/plant)

16 0 509.8 c 460.0 c 439.0 c 413.7 c 20 307.0 b 322.0 b 284.0 b 430.6 c

26 0 215.1 a 95.0 a 156.0 a 262.1 a 20 219.7 a 107.0 a 122.0 a 316.6 b l.s.d ST, GA3 ST x GA3

26.14 36.97

92.0 130.0

49.1 69.4

27.47 38.85

Generally, GA3 influenced tuber size distribution of Dawmor and Eben but not

KT3 and PO3 (Table 3.8). This effect varied with storage time. Plants grown from

young Dawmor seeds dipped in GA3 had about half the number of tubers > 35 g and

nearly double the number of small size tubers (< 20 g). In physiologically old Dawmor

the number of tubers > 35 g was not affected by GA3 but the number of small sized

tubers (< 20g) increased 1.6 times. Application of GA3 to young Eben halved the

number of big tubers (> 64 g) and tripled the number of 5 – 19 g tubers. Dipping old

Eben in GA3 increased the number of small size tubers (< 5 g) 1.4 times, but the number

of big tubers was not affected.


79

Table 3.8. Effects of storage time (ST) and GA3 on tuber size distribution of four potato cultivars stored for 16 and 26 weeks. Different letters indicate significant difference (p ≤ 0.5) within columns.

Tuber size distribution (g) Variety and

Storage Time (weeks)

GA3 (mg L-1) < 5 5 – 19 20 – 34 35 – 49 50 – 64 > 64

Dawmor 16 weeks 0 7.30 ab 2.55 a 3.00 a 2.45 b 1.65 b 1.50 b 16 weeks 20 9.70 b 6.90 c 3.35 a 1.45 a 0.55 a 0.45 a 26 weeks 0 6.50 a 2.30 a 2.45 a 1.20 a 0.60 a 0.30 a 26 weeks 20 9.45 b 4.80 b 2.75 a 0.95 a 0.35 a 0.25 a l.s.d ST, GA3 2.05 0.54 0.98 0.57 0.25 0.36 l.s.d ST X GA3 2.903 1.766 1.387 0.802 0.347 0.509 KT3 16 weeks 0 27.2 c 8.60 b 4.70 b 2.30 b 0.60 a 0.30 b 16 weeks 20 20.4 bc 9.00 b 3.00 b 0.70 a 0.00 a 0.05 a 26 weeks 0 6.1 a 1.40 a 0.55 a 0.55 a 0.30 a 0.25 ab 26 weeks 20 11.9 ab 2.20 ab 1.10 ab 0.35 a 0.25 a 0.05 a l.s.d ST, GA3 10.54 4.92 1.70 0.79 0.42 0.15 l.s.d ST X GA3 14.90 6.96 2.401 1.120 0.599 0.215 PO3 16 weeks 0 9.60 a 4.90 ab 2.85 a 2.60 c 1.15 c 1.50 b 16 weeks 20 11.05 a 6.80 b 2.50 a 1.65 b 0.60 b 0.45 a 26 weeks 0 9.65 a 4.60 a 2.80 a 0.50 a 0.05 a 0.00 a 26 weeks 20 7.70 a 4.30 a 1.65 a 0.50 a 0.10 ab 0.00 a l.s.d ST, GA3 2.82 1.54 1.15 0.63 0.37 0.41 l.s.d ST X GA3 3.986 2.183 1.624 0.893 0.525 0.585 Eben 16 weeks 0 4.40 a 2.15 a 2.00 ab 1.75 ab 1.40 a 2.20 b 16 weeks 20 5.05 ab 6.00 b 2.55 b 2.25 b 1.50 a 1.40 a 26 weeks 0 4.20 a 0.90 a 0.80 a 1.00 a 0.85 a 1.50 ab 26 weeks 20 6.00 b 1.35 a 1.60 ab 1.00 a 0.90 a 2.00 b l.s.d ST, GA3 1.04 0.90 0.93 0.56 0.64 0.37 l.s.d ST X GA3 1.464 1.273 1.311 0.791 0.902 0.525


80

Without GA3

Atlantic

Dawmor

KT3

PO3

Eben

16 week old 26 week old

PlusGA3 Without GA3 PlusGA3

20 mm

20 mm

20 mm

20 mm

20 mm

Without GA3

Atlantic

Dawmor

KT3

PO3

Eben

16 week old 26 week old

PlusGA3 Without GA3 PlusGA3

20 mm20 mm

20 mm20 mm

20 mm20 mm

20 mm20 mm

20 mm20 mm

Figure 3.6. Effects of storage time (ST) and GA3 on tuber size distribution of five potato

cultivars stored for 16 and 26 weeks.


81

Experiment 3

Tubers from plants grown with GA3 treated seeds had minor differences in

sprout behavior. Atlantic tubers produced from plants grown from seed tubers treated

with 20 mg L-1 GA3 had fewer sprouted eyes, fewer sprouts and shorter total sprout

length but they had the same sprouting capacity as control plants. In Granola, plants

grown from seed tubers treated with GA3 produced tubers with a lower proportion of

sprouted eyes, but sprout number, total length of sprouts and sprouting capacity were not

affected (Table 3.9).

Table 3.9. Carry over effects of GA3 on sprout behavior after 2 weeks at sprouting room

(20°C, 80-90% RH), including proportion of sprouted eyes (%), total sprout number/tuber, total sprout length (mm) and sprouting capacity (mm g-1) of two potato cultivars (Atlantic and Granola). Different letters indicate significant difference (p ≤ 0.5) within columns.

Variety GA3 (mg L-1)

Average tuber

weight (g)

Sprouted eyes (%)

Sprout number

Sprout length (mm)

Sprouting capacity (mm/g)

Atlantic 0 45.45 b 76.24 c 10.65 c 42.93 c 0.97 b Atlantic 20 38.23 a 48.65 ab 8.30 b 31.00 b 0.82 b Granola 0 39.94 a 51.75 b 6.00 a 24.88 ab 0.65 a Granola 20 37.48 a 42.4 a 5.3 a 20.93 a 0.56 a l.s.d Variety, GA3 3.34 6.14 1.14 4.52 0.11 Variety x GA3 4.76 8.68 1.61 6.397 0.15

In general, application of 20 mg L-1 GA3 had no carry over effects on the

subsequent growth of Atlantic and Granola plants. This was evident in timing of first

emergence and stem number, plant height and number of leaves 6 weeks after planting.


82

In Atlantic and Granola, tubers produced from plants grown from seeds treated with 20

mg L-1 GA3 emerged after a similar time and had the same number of stems per plant.

Atlantic plants were taller than Granola but they produced a similar number of leaves

(Table 3.10).

Generally, application of 20 mg L-1 GA3 to Atlantic and Granola seed tubers had

no carry over effects. Replanted Atlantic tubers from plants grown using seeds treated

with GA3 produced plants with a similar number of stolons per plant but initial tuber

number at 7 weeks was reduced by 20%. However, yield and tuber dry weight were not

affected. Across treatments, Atlantic and Granola plants yielded 100-140 g of tubers 7

weeks after planting. Replanted Atlantic and Granola tubers from plants grown using

seeds treated with 20 mg L-1 GA3 had no carry over effects on underground performance

at 7 weeks, including no difference in number of stolons per plant, tuber number, yield

and tuber dry weight (Table 3.11).

Table 3.10. Carry over effects of GA3 on first emergence (days after planting) and stem number, plant height (mm) and leaf number 6 weeks after planting of two potato cultivars (Atlantic and Granola). Different letters indicate significant difference (p ≤ 0.5) within columns.


First emergence (DAP) Stem number Plant height

(mm) Leaf number

Atlantic 0 12.81 a 3.25 a 523.80 b 46.20 a Atlantic 20 13.00 a 2.85 a 545.00 b 41.50 a Granola 0 12.45 a 2.55 a 432.00 a 35.80 a Granola 20 12.50 a 2.80 a 389.20 a 33.50 a l.s.d Variety, GA3 0.71 0.61 41.14 9.23 Variety x GA3 1.00 0.86 58.18 13.05


83

Table 3.11. Carry over effects of GA3 on number of stolons per plant, tuber number, yield (g) and dry weight (g) of two potato cultivars (Atlantic and Granola) 7 weeks after planting. Different letters indicate significant difference (p ≤ 0.5) within columns.


Stolons per plant

Tuber number

Yield (g)

Tuber dry weight (g)

Atlantic 0 20.70 b 13.85 b 140.30 a 27.50 a Atlantic 20 17.10 ab 11.00 a 118.70 a 22.30 a Granola 0 15.60 a 13.85 b 136.40 a 25.00 a Granola 20 16.00 a 13.80 b 138.50 a 24.00 a l.s.d Variety, GA3 3.32 1.60 34.74 7.39 Variety x GA3 4.70 2.27 49.13 10.45

3.4. Discussion

3.4.1. Effects of storage time on sprout behaviour

Dormancy gradually broke during seed storage. Atlantic seeds stored at 4°C

broke dormancy at 16 weeks. Most researchers define break of dormancy as when 80%

of tubers produce sprouts ≥ 3 mm after sprouting at 20°C for 2 weeks (Krijthe, 1962;

Reust, 1986) and this was the definition used here. Others have different definitions for

break of dormancy such as when any sprouts (≥ 1 mm) emerge (Susnoschi, 1981b) and

in Atlantic tubers sprouts were ≥ 1mm by 10 weeks and they were ≥ 2 mm long by 14

weeks which (Van Ittersum et al., 1992) defined as break of dormancy.

The time for breaking dormancy varied with variety. Dawmor, PO3, Eben and

KT3, had different dormancy behaviour to Atlantic. At 16 weeks only three quarters of

Dawmor tubers had produced sprouts ≥ 3 mm long and so it appeared to break dormancy

slightly later than Atlantic. In Western Australia, Dawmor is grown once a year, from


84

October-November to March-April (Dawson and Mortimore, 2002) so seeds need to be

stored for about 28-32 weeks before they are planted. At that time, Dawmor would have

broken dormancy with 4°C storage so they grow well and produce high yield.

Seeds of PO3 appeared to break dormancy in a similar time frame to Atlantic

with > 80% of tubers producing sprouts ≥ 3 mm by 16 weeks and Eben was earlier as all

tubers had sprouts ≥ 3 mm long by this time (Burton, 1989; Reust, 1986). Under the

4°C, dark storage, Eben and PO3 had broken dormancy at 16 weeks. In the Philippines,

Eben seeds stored under diffuse light storage and high temperature break dormancy by

about 12 weeks. Many studies confirm that dormancy is broken earlier at higher

temperature (Hartmans and Van Loon, 1987; Krijthe, 1962). Dark and cold storage of

Eben would delay breaking dormancy, and allow it to be stored for a longer time. Over

the same storage period, tubers stored at lower temperatures accumulate fewer day-

degrees than at higher temperatures, and are therefore physiologically younger. To

confirm seed vigour and sprouting patterns, further study is needed on breaking

dormancy of these cultivars under different temperature and light conditions.

Seeds of KT3 stored at 4°C were still dormant when stored for 16 weeks but they

had started to sprout by 26 weeks. Although there is no literature about breaking

dormancy in KT3, it was estimated that in Vietnam, where farmers store KT3 at higher

temperature (20 - 30°C), dormancy breaks in less than 26 weeks. Planting dormant

tubers can be a problem as they will grow slowly and sprouts produced are easily

attacked by microorganisms (Beukema and Van der Zaag, 1990).

Seed of other varieties, such as Avanti, Renova and Up-to-Date from Israel, also

start to produce sprouts of ≥ 1 mm at 10 weeks in 4°C, but most varieties emerge later


85

(Susnoschi, 1981b). Some early British varieties such as Craig’s Defiance, Arran Pilot,

Arran Victory, Home Guard and Ulster Prince break dormancy earlier than Atlantic

(Burton, 1989). Arran Viking, King Edward and Ulster Chieftain are similar to Atlantic

and these varieties are regarded as having medium dormancy whilst others such as Arran

Consul and Majestic have long dormancy of more than 28 weeks (Burton, 1989;

Carnegie, 2001a). Eben broke dormancy first, followed by PO3 and both were less than

16 weeks. Atlantic broke dormancy at 16 weeks followed closely by Dawmor and all

these varieties have medium dormancy (Burton, 1989; Pavlista, 2003). KT3 took longer

than 16 weeks but less than 26 weeks and may have a medium to long dormancy.

Sprout behaviour during cold storage was influenced by chronological age,

which is aging seeds at one temperature over a period of time. Sprout number per tuber

of Atlantic seed increased from 10 to 20 weeks, when there were a maximum of 17

sprouts per tuber. Not all buds in potato eyes developed into sprouts. Apical eyes

sprouted earlier followed by lateral eyes and the proportion of sprouted eyes similarly

increased from 10 weeks and reached a maximum of 78% at 20 weeks. In Atlantic,

further storage did not increase sprout number per tuber or proportion of sprouted eyes.

Each eye of a potato tuber consists of at least three buds (Artschwager, 1924). Generally

buds from the youngest eye in the apical region grew earlier, while other buds remained

dormant longer. Many of these progressively sprouted but some distal buds may never

grow (Burton, 1989). The increase in the number of eyes with sprouts had a greater

impact on the increase in number of sprouts per tuber than number of sprouts per eye.

Different varieties had different sprout growth in response to storage time. More sprouts

from more eyes would benefit the production of multiple stems. At 16 weeks KT3 was


86

still dormant and had no sprouts. At 16 weeks Dawmor had sprouted, it was still apically

dominant and produced only 3 sprouts per tuber, which might be insufficient for

commercial production. Planting seeds with apical dominance may produce plants with

too few stems (Hay and Hampson, 1991). In contrast there were 8 sprouts from PO3 and

Eben and most of the eyes had sprouted, which would benefit multiple shoot

development. Extending storage time until 26 weeks facilitated multiple sprouting in

Dawmor seeds and so they produced more stems. KT3 produced fewer sprouts than

other cultivars even after 26 weeks storage. Therefore, to accelerate sprout growth and

increase sprout number, KT3 might be stored for longer or at higher temperature

(Hartmans and Van Loon, 1987).

Changes in sprouting are due to physiological changes occurring inside the

potato during storage. Although tuber respiration is slow under low temperature (Burton,

1989), metabolism still continues including hormonal changes. During storage at low

temperature (2°C), the concentration of gibberellic acid increases (Suttle, 2004; Thomas

and Wurr, 1976; Timm et al., 1962) and reaches a maximum close to the onset of sprout

growth (Emilsson and Lindblom, 1963; Van der Plas, 1987). Gibberellic acid is

responsible for translocation food reserves from the tuber to growing sprouts (Coleman,

1987), and thus it facilitates the break of dormancy in tubers.

Sprouts grew longer with prolonged storage time. From 10 to 20 weeks storage

sprouts grew to an average of 6 mm in 2 weeks under sprouting conditions, but there

was no further increase in sprout length with longer storage. Prolonging storage time

from 10 to 20 weeks increased the total sprout length per tuber and length of the longest

sprout to a maximum of 12 mm. This increase in sprout length is also probably due to


87

the increase in endogenous GA concentration with prolonged storage time (Emilsson

and Lindblom, 1963; Suttle, 2004; Timm et al., 1962; Van der Plas, 1987).

Ideal sprout length for planting is 10 – 20 mm (Beukema and Van der Zaag,

1990). Dormant seed tubers without sprouts take a longer time to emerge and planting

seeds with sprouts that are too long incurs a high risk of sprout damage and infection

from diseases. Atlantic seeds can therefore be stored at 4°C for 20 weeks or longer or for

shorter periods at higher temperatures since high temperatures break dormancy faster

(Burton, 1989; Hartmans and Van Loon, 1987; Susnoschi, 1981b).

Sprout length varied with storage duration across cultivars. At 16 weeks,

Dawmor, PO3 and Eben had similar sprout length to Atlantic, while KT3 was still

dormant and had no sprouts. Dawmor stored for 26 weeks produced sprouts with an

average length of 9 mm, so storing Dawmor seeds for a few weeks longer may be

required to produce longer sprouts, as 10 – 20 mm is desirable (Beukema and Van der

Zaag, 1990). If sprouts grow more than 20 mm, tubers are not suitable for planting, since

sprouts may be damaged at planting. Therefore, Dawmor may be stored for longer in

cool store or placed in warmer storage. By 26 weeks, Dawmor and PO3 sprouts were

longer than Atlantic, but still within an acceptable range to plant.

The capacity of sprouts to grow from tubers changes with physiological age

(Krijthe, 1962). Sprouting capacity is usually measured after 4 weeks (Reust, 1986),

however potatoes were required for planting after 2 weeks and measurement at this time

gives a good indication of comparative sprouting capacity. In summer-autumn Atlantic

seed sprouting capacity increased from 0.01 mm g-1 at 10 weeks to 0.66 mm g-1 at 20

weeks. In summer grown Atlantic seed, sprouting capacity increased from 0.43 mm g-1


88

at 20 weeks and remained fairly constant and was 0.52 mm g-1 at 26 weeks. Generally

the increase in sprouting capacity is linear until it reaches a maximum (Van der Zaag

and Van Loon, 1987) and after the maximum is reached, sprouting capacity can plateau

before subsequently decreasing (Krijthe, 1962). Varieties differ in sprout growth and

sprouting capacity. For example, Désirée grows from 2 to 3 mm faster than Diamant

(Van Ittersum et al., 1992). At 26 weeks sprouting capacity of Dawmor was 1.7 times,

PO3 was 2.3 times and Eben was the greatest at 7.7 times higher than Atlantic at the

same time. KT3 was still coming out of dormancy at 26 weeks and so at this time, it had

the slowest sprout growth rate, least sprouts and a sprouting capacity of 0.12 mm g-1

which was about a quarter of the value for Atlantic.

In Atlantic cultivar, the most sprouts grew at 20 weeks but it may have continued

to increase. Varieties differ in their patterns of change in sprouting capacity and many

temperate varieties have a longer storage time before reaching maximum sprout growth;

Jaerla takes 35-46 weeks, Libertas takes 40 weeks while Désirée and Binjthe up to 52

weeks at 4-5 °C (Couilerot, 1993; Krijthe, 1962). The length of the plateau was also not

determined for Atlantic as slight increases occurred up to 30 weeks, which was the last

storage duration examined and this requires further study. In other varieties, the length

of the plateau varies, in Bintje it is 4 weeks and in Libertas it is up to 16 weeks (Krijthe,

1962). The correlation between seed age and sprout development was very high in

young Atlantic seeds indicating little variation between seeds and although more

variable it remained high in old seed (Hartmans and Van Loon, 1987).


89

3.4.2. Effects of storage time and GA3 on the subsequent growth and yield

Young seeds planted when they are still dormant will usually take longer to

emerge. Plant emergence is hastened by planting older, non dormanct seeds. In Western

Australia, Atlantic usually emerge about 1-2 weeks after planting and this time frame is

desired by farmers. In this study, prolonging storage time was useful to accelerate first

emergence from 21 days with 10 weeks storage to 7 days with 20 weeks storage. With

longer storage (20-30 weeks), emergence remained constant at about 10 days after

planting. Atlantic stored for 26 weeks had 50% emergence in 11 days and this was

similar to Russet Burbank seeds stored at 4°C for 26 weeks, which have 50% emergence

in 10 days (Knowles and Bontar, 1991).

Emergence was further hastened by application of GA3. During storage,

endogenous GA concentration increases (Suttle, 2004; Timm et al., 1962). Applied GA3

penetrates into buds and tubers thus increasing endogenous GA levels, which stimulate

sprouts to grow. The effect of GA3 on increasing emergence was high in dormant tubers,

where seeds stored for 10 weeks dipped in GA3 accelerated emergence from 20 to 13

days after planting.

Older Dawmor, KT3, PO3 and Eben seeds generally produced more and longer

sprouts than young seeds. Old Eben seeds, which had the longest sprout emerged earlier

than other cultivars, while young KT3 which was still dormant and had no sprouts at

planting, emerged last. Gibberellic acid accelerated emergence of most seed. However,

dormant eyes would have taken longer time to absorb GA than sprouted eyes (Holmes et

al., 1970). These were expressed in the time of emergence. In old Eben seeds, there were

no differences in shoot emergence, either because GA3 had less effect or they probably


90

had maximum endogenous GA concentration. GA3 promoted sprout initiation (Bailey et

al., 1978; Rappaport et al., 1965; Timm et al., 1960), but this effect is reduced when

tubers have already sprouted (Timm et al., 1962).

Increasing the number of above ground stems in Atlantic was achieved by

storing seeds for longer time or by applying GA3. Prolonged storage time from 10 to 30

weeks doubled the number of above ground stems. As the concentration of endogenous

GA increases with storage, the response of applied GA3 would probably diminish (Timm

et al., 1962). Thus, GA is not the only factor increasing stem number.

Production of stems is generally related to sprout number. Prolonged storage

time from 16 to 26 weeks increased stem number of Dawmor and PO3. Longer storage

time had little effect on increasing stem number of tubers that were apically dominant.

Stem numbers of Eben and KT3 were not affected by extending storage time. Eben and

KT3 seeds stored for 26 weeks produced 6-8 sprouts, but sprouts at the apical region

grew dominantly. Increasing stem number of Eben and KT3 probably can be achieved

by removing the apically dominant sprouts, such as desprouting tubers, prolonging

storage of seeds at low temperature or storing seeds at higher temperature (10-12° C).

Applied GA3 was involved in stem growth, but the process was not ascertained.

Gibberellic acid may have enhanced the number of sprouts which develop into stems or

stimulated underground stems to branch. Here, the same number of eyes per seed piece

was used and from one eye usually only one sprout grows but not all sprouts develop

into stems (Allen and Wurr, 1992b).

Similarly, application of GA3 doubled stem number of young Dawmor and PO3

but had no effect in any Eben or KT3 seed. Old Dawmor were unaffected but in old PO3


91

GA3 still increased stem number. In young Dawmor and PO3 apical dominance was

broken by GA (Suttle, 2004). Old Dawmor seed was no longer apically dominant and so

addition of GA3 had no effect. In PO3, although stem number increased from 16 to 26

weeks, sprouting of lateral buds was still stimulated by GA3 resulting in an increase in

stem number. PO3 had the potential to produce more stems, nearly twice that of

Dawmor, KT3 and Eben. During storage, concentration of cytokinins are increasing

(Suttle, 1998), especially isopenthenyl adenine-9-glucoside (IP-9-G) and it stimulates

the breaking of tuber dormancy (Turnbull and Hanke, 1985). Gibberellic acid increases

during storage and it stimulates sprouts to grow (Suttle, 2004; Turnbull and Hanke,

1985) so it would also assist in increasing stem number.

As endogenous GA increases with physiological age, mobilisation of reserves

increases. With further aging, older seeds contain less stored carbohydrate and they have

reduced ability to mobilise assimilates to developing sprouts and stems (Mikitzel and

Knowles, 1989).

Older, sprouted tubers had greater vigour than young dormant tubers. Plants from

Atlantic stored for 10 weeks, which were still dormant, grew shorter, had less leaves and

lower shoot fresh and dry weight than older sprouted tubers. Application of GA3

increased plant height and number of leaves in both young and old seeds, but shoot fresh

and dry weight was not affected. Gibberellic acid is known to stimulate cell expansion

(Xu et al., 1998) causing this response. Plants from GA3-treated seeds may have had

thinner stems and smaller leaves (Knowles and Bontar, 1991) to compensate for an

increase in stem number and this eliminated weight gain, but it was not examined in this

study.


92

Stolons are modified underground stems that bear tubers and tubers are initiated

when stolon growth is terminated (Booth, 1963). Stolons grow first from the basal nodes

of main stems then from the higher nodes (O'Brien et al., 1998; Plaisted, 1957). The

number of stolons per plant depends on the number of nodes below the soil surface,

which is in turn, depends on stem number (Allen and Wurr, 1992b; Haverkort et al.,

1990). There were only slight increases in stem number after 20-30 weeks storage

(summer grown seeds), so that Atlantic seeds stored for 14-30 weeks produced a similar

number of stolons per plant.

Prolonged storage time from 10-14 weeks increased stolon length in Atlantic, but

further storage reduced stolon length. The onset of tuber initiation is related to plant

emergence (O'Brien et al., 1998), where older seeds emerge earlier and probably tuberise

earlier (Struik and Wieserma, 1999), thus terminating stolon elongation. Stolon length of

young and old seeds was enhanced by GA3. Application of GA3 probably stimulated

stolon growth by promoting cell elongation in the apical meristem of stolons (Kumar

and Wareing, 1972) and temporarily delaying tuberisation (Timm et al., 1962).

Application of GA3 increased number of stems but only had a slight impact on

the number of stolons per plant. However, application of GA3 stimulated stolons to

branch (Fig. 3.3). This result has not been well documented due to difficulties in

removing intact stolons and observing their branches. In Atlantic, 16 week-old seeds

produced plants with the most branching stolons and seed tubers were the most

responsive to applied GA3 in terms of further increase in stolon branching.

Tuber production was related to stolon length. In control plants, tuber number

increased with stolon length and branching, but was constrained by stolon number. This


93

indicated that storage time greatly influenced the subsequent ability of stolons to branch.

Moreover, the timing of tuber formation is closely related to the pattern of stolon

formation (Struik et al., 1990), where stolons at the basal node, near the mother tuber

grow earlier and tend to branch. Tubers from those stolons developed earlier. Increasing

stolon length and increasing branching of stolons, perhaps increased tuber number.

Atlantic seeds stored for 14-16 weeks had vigorous plants and produced high

yield. Decreasing yield of older seeds (> 16 weeks) was presumably because of

decreased sink strength (from mother tuber to shoots), so that transportation of

assimilates from shoot to tuber was reduced (Mikitzel and Knowles, 1989). Application

of GA3 at the proper concentration generally increases tuber number without affecting

yield (Arpiwi, 2003; Bishop and Timm, 1968; Holmes et al., 1970), due to a shift of

tubers into smaller size categories. In the present study, young and old Atlantic tubers

dipped in GA3 had similar yield to control plants, as small tuber (< 20 g) numbers

increased. Furthermore, average tuber weight per plant decreased with application of

GA3 by an average of 35% in young seeds and 30% in old seeds.

Cultivars had different stem, stolon and tuber growth. In Atlantic, applied GA3

tended to increase stem number from seeds stored from 10 to 30 weeks. Occasionally

this led to more stolons per plant. However, the major impact of GA3 was on stolon

branching and stolon length. Presumably, stolon branching provides more sites for

tuberisation (Helder et al., 1993; Vreugdenhil and Struik, 1989), whereas increasing

stolon length simply delays tuberisation (Kumar and Wareing, 1974; Lovell and Booth,

1967; Vreugdenhil and Struik, 1989). There was a consistent positive relationship

between stolon branching and both tuber number and yield. This indicated the


94

importance of branching for increasing tuber number in Atlantic and possibly other

varieties. In total, Atlantic seeds stored for 16 weeks produced plants with a minimum of

14 sites for tuberisation and plants from seeds stored for 16 weeks had 17 sites for

tuberisation. Most of the sites from young seeds produced tubers whereas only two

thirds of sites in old seeds produced tubers. Addition of GA3 increased stolon number

and branching in young Atlantic seed resulting in 23 sites per plant for tuberisation and

all of these produced tubers. In old seeds GA3 did not increase stolons per plant but it

did increase stolon branching resulting in 19 sites for tuberisation. Most, but not all, of

these sites (84%) produced tubers. Atlantic seeds grew well under favourable growth

conditions, which are short day, with 20° day and 14°C night temperature (Slater, 1963)

or average daily temperature of 17-23° C (Menzel, 1980), and under these conditions,

tuber formation was promoted.

Dawmor seeds stored for 26 weeks produced more stems than seeds stored for 16

weeks. Stems from old seeds produced the same number of stolons per stem and so old

seeds produced more stolons per plant. However, young seed produced stolons, which

branched, but old seed did not produce branching stolons. In total, plants from young

seeds had 21 sites for tuberisation whereas plants from old seeds had 25 sites. Virtually

all of these sites in plants from young seeds produced tubers but only half of them

produced tubers in old seed. Application of GA3 increased stem number in young but not

old seeds. Gibberellic acid (GA3) reduced stolon number per stem in young but not old

seeds, and this resulted in plants from older seeds having more stolons per plant.

Gibberellic acid stimulated branching in stolons of both young and old seeds, resulting

in a minimum of 19 sites for tuberisation in plants from young seeds and 24 sites in old


95

seeds. In young seeds all sites produced tubers whereas only 75% of sites from old seeds

produced tubers. This was probably because older seeds had less vigour (Mikitzel and

Knowles, 1989; Mikitzel and Knowles, 1990b), stolons from old seeds are less likely to

tuberise, or environment conditions for tuberisation were not favourable. In young

Dawmor seed, GA3 had no effect on tuber number and although it shifted tubers to

smaller size categories there was a substantial reduction in yield. In old seed, a shift

towards smaller tubers increased tuber number without reducing yield and so GA3 may

have a role in small seed production from old seed. However, further research is

required to maximise yield.

In PO3, 26 week-old seeds also produced plants with more stem than 16 weeks

old seeds and they produced similar number of stolons per plant. Again, there was

substantial branching in plants from young seeds and virtually none in old seeds. This

resulted in a minimum of 26 sites in plants from young seeds and 24 sites in plants from

old seeds. Again, nearly all of the sites in young plants produced tubers, whereas closer

to half of the sites in plants from old seeds produced tubers. This supports the idea that

more photosynthate is translocated to stolons in plants from young seeds (Mikitzel and

Knowles, 1989). This is either due to a difference in the physiological state of the stolon

tips caused by internal factors or external factors such as the environment. Furthermore,

in both Dawmor and PO3 yield from plants grown from young seeds was nearly double

that from old seeds. This indicated that it was not just a re-directing of resources but a

greater availability of resources to direct to tubers. Application of GA3 increased stem

number of young and old PO3. However it did not affect number of stolons per plant or

branching of stolons, although it substantially increased stolon length. Consequently,


96

tuber number was not affected. There was a substantial reduction of tubers ≥35 g in

young PO3 seeds with applied GA3 that may have caused the reduction in yield. In old

seeds, tuber size distribution and yield were not affected.

In KT3 and Eben, increasing storage time did not influence stem number. In KT3

age had no effect but in Eben these were less stolons per stem from older seeds. The

number of stolons per plant for both varieties was the same when seeds were stored for

16 – 26 weeks. Young KT3 had many branching stolons, resulting in a minimum of 50

stolons for tuberisation, but old seeds produced few branching stolons resulting in only

19 sites for tuberisation. Eben had few branching stolons from either young or old seeds

resulting in 14-16 sites for tuberisation per plant. Plants grown from young KT3

produced over 50 tubers per plant, indicating all of these sites produced tubers.

Unfortunately nearly half of these tubers were in the smallest category (< 5 g) and these

may be too small to use as seed (Dawson et al., 2004; Samadi, 1998), even if plants were

grown in the field for longer rather than in pots for 8 weeks. In old seeds, about half of

the sites produced tubers. In Eben, most stolons (78%) from young seeds produced

tubers, but less than two thirds (60%) of the sites produced tubers in plants from old

seeds. In both cases this was reflected in yield differences.

Application of GA3 did not affect stem number of KT3 seeds stored for 16 or 26

weeks. Applied GA3 to young KT3 seeds reduced the number of stolons/stem but

stolons/plant was unaffected in both young and old seed. Branching was also not

affected by GA3, and nor was tuber number. There was a reduction in the number of

large tubers in plants from young seed with applied GA3 and this led to a reduction in

yield. Neither tuber number nor yield was affected by GA3 in old seed.


97

Gibberellic acid did not increase stem number of young nor old Eben. Applied

GA3 increases stolon numbers per plant and stimulated branching of stolons in young

and old Eben seed. Applied GA3 increased tuber sites by 80% in young seeds (32 sites)

and 50% in old seeds (22 sites). In both cases (young and old) only 60% of stolon tips

produced tubers, but this was enough for GA3 to increase tuber number in young and old

seeds. Gibberellic acid did not substantially affect tuber size distribution of young Eben

seeds and so yield was not affected. In old Eben seeds, application of GA3 increased the

number of small tubers, but did not reduce the number of old seed and this caused an

increase in yield.

Young and old seeds produced different numbers of sites for tuberisation.

Generally, all of these sites resulted tuberisation in young seeds but only half to two

thirds of these sites produced tubers in old seeds. This was probably due to physiological

aging of seeds; unfavourable environmental conditions or a combination of both internal

and external factors. Planting old seeds reduces sink strength so that tubers lost their

vigour and had reduced ability to transport assimilates (Iritani and Weller, 1987;

Mikitzel and Knowles, 1989). Thus, less assimilates were transported to shoots and

stolons, and caused the reduction in tuber production. Alternatively, high temperature

stimulates GA synthesis which stimulates shoot growth at the expense of tuber growth

(Menzel, 1980). At high temperature high respiration rates consume much of the

photosynthate that would otherwise be used for tuber production. Moreover, long

photoperiod also inhibits tuberisation (Escalante and Langille, 1998; Gregory, 1956). In

the present study, although young and old Dawmor, Eben, KT3 and PO3 seeds were

from the same seed production seasons, they were grown under different growing


98

conditions. This may have influenced plant performance and caused reduction in yield.

This is a common problem in field trials with potato.

3.4.3. Carry over effects of GA3

There did not appear to be any significant GA3 carry over effects on the growth

of Atlantic and Granola. Seed for the parent crop had been dipped in GA3 at 20 mg L-1

(i.e. GA3 pre-treatment) and grown in the field to produce a crop of potatoes (no GA3

pre-treatment) (Arpiwi, 2003). There were only insubstantial carry over effects from the

GA in the growth of plants from these potatoes.

Plants from both Atlantic and Granola progeny seed emerged at the same time

and there was no difference in stem and leaf number and plant height between the GA3

pre-treatment and controls (no GA3) at 6 weeks after emergence. With Atlantic there

were fewer and shorter sprouts in the GA3 pre-treatment compared to control tubers,

whereas with Granola there were no differences in sprout number and length between

the two pre-treatments.

In Atlantic, there was no difference in total tuber dry weight and yield between

the two GA3 pre-treatments although the GA3 pre-treatment produced fewer tubers. In

Granola, the GA3 pre-treatment had no effect on stolon number, tuber dry weight or

yield.

There is little information about carry over effects from applied GA3 on the

growth and subsequent of production potato. In previous studies, increasing

concentration of GA3 from 5 to 100 mg L-1 in a spray application on potato seeds

increased tuber numbers, and when those tubers were sprouted for subsequent planting,


99

they had similar sprout growth, and produced normal plants and yield compared with

untreated ones (Holmes et al., 1970). Our result confirms this observation that GA3

treatment of the parent seed has little effect on the crop grown from the progeny seeds.

3.5. Conclusion

Cultivars have different times to break dormancy. In Atlantic, dormancy was

broken in 16 weeks storage at 4°C, while Eben and PO3 were less than 16 weeks,

Dawmor broke dormancy just after Atlantic, while KT3 was between 16 and 26 weeks.

The optimum sprouting capacity for a maximum yield of Atlantic occurred at 16 weeks

(plants from summer-autumn grown seeds) or 26 weeks (plants from summer grown

seeds), even though sprouting capacity was still increasing. However, optimum

sprouting capacity of other cultivars was not confirmed in this experiment, and so

further study is required.

In Atlantic, prolonged storage time increased stem number and stimulated the

production of tuber sites but only two thirds these produced tubers, so that yield was

reduced. Application of GA3 increased stem number, stolon number, and stolon length

and branching so that treated seeds produced more tubers than control plants without

reducing yield, as tubers were shifted into smaller size categories. There was no

significant carry over effect of application of 20 mg L-1 GA3 on growth and yield of

progeny tubers of Atlantic and Granola.

In Dawmor, extending storage time increased stems and number of stolons per

plant, but due to branching, they had the same number of tuber sites. However, only half

of the tuber sites from old seed produced tubers, so yield was halved. Stem number of


100

both young and old seeds increased with applied GA3. In young seed this did not

increase tuber number but reduced yield. In old seed tuber number increased with GA3

and yield was constant. So GA3 may have a use in old but not young seed. Further

research is required to maximise yield.

Storing PO3 for longer produced more stems but a similar number of stolons per

plant. However, in old seeds only half of the tuber sites developed tubers so that plants

produced lower yield. Application of GA3 increased stem number of young and old PO3

and stimulated branching stolons in young seeds. However, GA3 did not increase tuber

number and reduced yield from young seeds. In old seeds neither tuber number nor yield

were changed by GA3, so that increases in stem number did not lead to increases in

tuber number in this cultivar.

In KT3, storage time did not affect stem number. Young KT3 seeds produced

more branching stolons and more tubers compared to old seeds, and yield was more than

three times greater. Applied GA3 did not increase stem number, stolon number, or

branching in young or old KT3. In young seeds, GA3 did not affect tuber number but

reduced yield, whereas, in old seeds tuber number and yield remained the same. So, 16

weeks of storage led to large numbers of tubers but many were very small.

Prolonged storage and applied GA did not affect stem number of young and old

Eben. Application of GA3 increased number of stolons and stolon branching, but not all

of them produced tubers. Tuber number increased without reducing yield of young

Eben, as GA3 shifted tubers to smaller sizes. However in old Eben, GA3 tended to

increase tuber number in most categories and increased yield.


101

Application GA3 increased stem number in Atlantic, Dawmor and PO3 but not in

KT3 and Eben. GA3 increased tuber number of young and old Eben, and old Dawmor.

In Atlantic, tuber size distribution was affected by GA, but not in tropical cultivars. So,

further study is needed to identify the optimum period for optimum sprouting capacity

for maximum yield, to explore a range of GA3 concentration to increase the production

of small tubers and to determine the interaction between these two factors in the field.

References

Allen, E. J., and Wurr, D. C. E. (1992). Plant Density. In "The potato crop:The scientific basic for improvement" (P. Harris, ed.). Chapman & Hall, London.

Arpiwi, N. L. (2003). The application of novel methods for increasing the yield of small round seed potatoes (Solanum tuberosum L.) cv. Atlantic and Granola, The University of Western Australia, Perth.

Artschwager, E. (1924). Studies on the potato tuber. Journal of Agricultural Research 27, 809-835.

Bailey, K. M., Phillips, I. D. J., and Pitt, D. (1978). The role of buds and gibberellin in dormancy and the mobilisation of reserve materials in potato tubers. Annals of Botany 42, 649-657.

Beukema, H. P., and Van der Zaag, D. E. (1990). "Introduction to potato production.," Pubdoc Wageningen, Wageningen.

Bishop, J. C., and Timm, H. (1968). Comparative influence of gibberellic acid and of plant population on distribution of potato tuber size. American Potato Journal 45, 182 - 187.

Booth, A. (1963). The role of growth substances in the development of stolons. In "The growth of the potato" (J. D. Ivins and F. L. Milthorpe, eds.), pp. 99-113. Butterworths, London.

Burton, W. G. (1989). "The potato," Third/Ed. Longman Scientific & Technical, New York.

Carnegie, S. (2001a). Cultivar: Atlantic. In "European cultivated potato database: Cultivars and breeding lines" (E. G. P. W. Group, ed.). Scottish Agricultural Science Agency, Edinburgh.

Coleman, W. K. (1987). Dormancy release in potato tuber: A review. American Potato Journal 64, 57-67.


102

Couilerot, J. P. (1993). Effects and distribution of 14C-gibberellic acid after application to stored potato microtuber. Phyton 54, 67-73.

Dawson, P., McPharlin, I., and Dharmadi, B. (2004). "A partnership to build Indonesian crisping potato capacity and Australian seed potato sales." Department of Agriculture Western Australia, Perth.

Dawson, P., and Mortimore, J. (2002). Dawmor - A new summer export crisp potato variety for Manjimup. In "Department of Agriculture: Farmnote No. 66". Department of Agriculture Western Australia, Perth.

Emilsson, B., and Lindblom, H. (1963). Physiological mechanisms concerned in sprout growth. In "The growth of potato" (J. D. Ivins and F. L. Milthorpe, eds.), pp. 45-61. Butterworths, London.

Escalante, B. Z., and Langille, A. R. (1998). Photoperiod, temperature, gibberellin and anti-gibberellib affect tuberisation of potato stem segments in vitro. HortScience 33, 701-703.

Gregory, L. E. (1956). Some factors for tuberisation in the potato plant. American Journal of Botany 43, 281-288.

Hartmans, K. J., and Van Loon, C. D. (1987). Effect of physiological age on growth vigour of seed potatoes of two cultivars. 1.Influence of storage period and temperature on sprouting characteristics. Potato Research 30, 397 - 409.

Haverkort, J. A., Van de Waart, M., and Bodlaendar, K. B. A. (1990). Interrelationships of the number of initial sprouts, stems, stolons and tubers per potato plant. Potato Research 33, 269-274.

Hay, R. K. M., and Hampson, J. (1991). Sprout and stem development from potato tubers of differing physiological age: the role of apical dominance. Frield Crops Research 27, 1-16.

Helder, H., Van der Maarl, A., Vreugdenhil, D., and Struik, P., C (1993). Stolon characteristics and tuber initiation in a wild potato species (Solanum demissum Lindl.). Potato Research 36, 317-326.

Holmes, J. C., Lang, R. W., and Singh, A. K. (1970). The effect of five growth regulators on apical dominance in potato seed tubers and on subsequent tuber production. Potato Research 13, 342 - 352.

Iritani, W. M., and Weller, D. L. (1987). The influence of physiological age, stem numbers and fertility on yield and grade of Russet Burbank potatoes. American Potato Journal 64, 291-299.

Iritani, W. M., Weller, L. D., and Knowles, N. R. (1983). Relationship between stem number, tuber set and yield of Russet Burbank Potatoes. American Potato Journal 60, 423-431.

Kawakami, K. (1963). Age of potato seed tubers affects growth and yield. American Potato Journal 40, 25-29.

Knowles, N. R., and Bontar, G. I. (1991). Modelling the effects of potato seed tuber age on plant establishment. Canadian Journal of Plant Science 71, 1219-1232.

Krijthe, N. (1962). Observation on the sprouting of seed potatoes. European Potato Journal 5, 316-333.

Kumar, D., and Wareing, P. F. (1972). Factor controling stolon development in the potato plant. New Phytol 71, 639-648.


103

Kumar, D., and Wareing, P. F. (1974). Studies on tuberisation of Solanum indigena. II. Growth hormones and tuberisation. New Phytol 73, 833-840.

Lovell, P. H., and Booth, A. (1967). Effect of gibberellic acid on growth, tuber formation and carbohydrate distribution in Solanum tuberosum. New Phytol 66, 525-537.

Menzel, C. M. (1980). Tuberisation in potato at high temperatures: responses to gibberellin and growth inhibitor. Annals of Botany 46, 259-265.

Mikitzel, L. J., and Knowles, N. R. (1989). Potato seed-tuber age affects mobilisation of carbohydrate reserves during plant establishment. Annals of Botany 63, 311-320.

Mikitzel, L. J., and Knowles, N. R. (1990). Effect of potato seed-tuber age on plant establishment and amelioration of aged-linked effects with auxin. Plant Physiology 93, 967-975.

Moorby, J. (1967). Inter-stem and inter-tuber competition in potatoes. European Potato Journal 10, 189-205.

O'Brien, P. J., Allen, E. J., and Firman, D. M. (1998). A review of some studies into tuber initiation in potato (Solanum tuberosum) crops. Journal of Agricultural Science, Cambridge 130, 251-270.

Pavlista, A. D. (2003). Atlantic: Characteristics. University of Nebraska, Nebraska. Plaisted, P. H. (1957). Growth of the potato tuber. Plant Physiology 32, 445-452. Rappaport, L., Goldschmidt, S. B., Clegg, M. D., and Smith, O. E. (1965). Regulation of

bud rest in tubers of potato Solanum tuberosum L. I. Effect of growth substances on excised potato buds. Plant and Cell Physiology 6, 587-599.

Reust, W. (1986). Working group "Physiological age of potato". Potato Research 29, 269-270.

Samadi, B. (1998). "Usaha tani kentang," Penerbit Kanisius, Yogyakarta. Slater, J. W. (1963). Mechanism of tuber initiation. In "The growth of the potato" (J. D.

Ivins and F. L. Milthorpe, eds.), pp. 114-120. Butterworths, London. Struik, P., C, Haverkort, J. A., Vreugdenhil, D., Bus, C. B., and Dankert, R. (1990).

Manipulation of tuber size distribution of a potato crop. Potato Research 33, 417-432.

Struik, P. C., and Wieserma, S. G. (1999). "Seed potato technology," Wageningen Pers, Wageningen.

Susnoschi, M. (1981). Seed potato quality as influenced by high temperatures during the growth period. 2. Sprouting pattern in several cultivars in response to storage temperature. Potato Research 24, 381-388.

Suttle, J. C. (1998). Postharvest changes in endogenous cytokinins and cytokinin efficacy in potato tubers in relation to bud endodormancy. Physiologia Plantarum 103, 59-69.

Suttle, J. C. (2004). Involvement of endogenous gibberellins in potato tuber dormancy and early sprout growth: a critical assessment. Journal of Plant Physiology 161, 157-164.

Thomas, T. H., and Wurr, D. C. E. (1976). Gibberellin and growth changes in potato tuber buds in response to cold treatment. Annals of Applied Biology 83, 317-320.

Timm, H., Rappaport, L., Bishop, J. C., and Hoyle, B. J. (1962). Sprouting, plant growth and tuber production as affected by chemical treatment of white potato seed


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pieces. IV. Responses of dormant and sprouted seed potatoes to gibberellic acid. American Potato Journal 39, 107-115.

Timm, H., Rappaport, L., Primer, P., and Smith, O. (1960). Sprouting, plant growth, and tuber production as affected by chemical treatment of white potato seed pieces. II. Effect of temperature and time of tratment with gibberellic acid. American Potato Journal 37, 357-365.

Turnbull, C. G. N., and Hanke, D. E. (1985). The control of bud dormancy in potato tuber: Evidence for primary role of cytokinins and a seasonal pattern of changing sensitivy to cytokinin. Planta 165, 359-365.

Van der Plas, L. H. W. (1987). Potato Tuber Storage: Biochemical and Physiological Changes. In "Biotechnology in Agriculture and Forestry 3: Potato" (Bajaj YPS, ed.), pp. 109 -135. Springer-Verlag, Berlin.

Van der Zaag, D. E., and Van Loon, C. D. (1987). Effect of physiological age on growth vigour of seed potatoes of two cultivars. 5. Review of literature and integration of some experimental result. Potato Research 30, 451-472.

Van Es, A., and Hartmans, K. J. (1987b). Effect of physiological age on growth vigour of seed potatoes of two cultivars. 2. Influence of storage period and storage temperature on dry matter content and peroxidase activity of sprout. Potato Research 30, 411-421.

Van Ittersum, M. K., Aben, F. C. B., and Keijzer, C. J. (1992). Morphological changes in tuber buds during dormancy and initial sprout growth of seed potatoes. Potato Research 35, 249-260.

Vreugdenhil, D., and Struik, P. C. (1989). An integrated view of the hormonal regulation of tuber formation in potato (Solanum tuberosum). Physiologia Plantarum 75, 525-531.

Xu, X., Van Lammeren, A. A. M., Vermeer, E., and Vreugdenhill, D. (1998). The role of gibberellin, abscisic acid and sucrose in the regulation of potato tuber formation in vitro. Plant Physiology 117, 575-584.

* For submission to the Australian Journal of Experimental Agriculture

Chapter 4

Effects of storage time and seed treatments on the growth and yield of tropical potato (Solanum tuberosum L.) varieties under Western

Australia field conditions*

Abstract

Small seed potatoes are required for export to tropical countries, as they do not

require cutting, which increases risk of diseases infection and reduces yield. Information

is needed on sprout behaviour following storage and the influence of sprout behaviour

on plant growth and tuber yield of the tropical potato cultivars. Intact or desprouted

tubers of four potato cultivars suitable for tropical conditions (Atlantic, Eben, KT3 and

PO3) were stored at 4°C for 10 to 40 weeks to observe their subsequent sprout

behaviour at 20°C. Prolonging storage from 10 to 40 weeks increased the proportion of

sprouted eyes, sprout number, average sprout length, sprouting capacity (g sprouts/g

tuber), sprout fresh weight and tuber weight loss (%) during sprouting. Sprouting

capacity of PO3 reached a maximum at 38 weeks storage, while in Atlantic, Eben and

KT3 it occurred at more than 40 weeks. Desprouting increased the proportion of

sprouted eyes and sprout number of Eben, but this decreased in PO3, while Atlantic was

not affected.

Three potato cultivars (Eben, KT3 and PO3) stored for 12 or 40 weeks at 4°C

(dark), were planted in the field as whole (50 g) or cut (2 pieces from 100 g) tuber seeds

to assess plant growth. Young seed (12 weeks) of KT3 and PO3 seeds which were still

dormant, had poor plant growth and tuber yield. Prolonged storage time and cutting

improved plant performance of KT3 and PO3, as more shoots emerge above the soil,

stem and tuber number increased, and yield of KT3 (22 t/ha) and PO3 (27-31 t/ha)

improved. Neither prolonging storage from 12-40 weeks nor cutting seed influenced

performance in Eben.

Additional keywords: cut tuber, whole tuber, sprout behaviour, sprouting capacity

Chapter 4 Storage time and seed treatments

106

4.1. Introduction

Little is known about storage responses, sprout behaviour, growth and

tuberization in tropical varieties of potato. Manipulation of these responses is important

to maximize yield, especially of small seed potatoes required for export to Asian

markets.

Storage of potato tubers at 2-4oC restrains growth, however physiological aging

continues (Burton, 1989). Potato tubers are usually dormant for 2–3 months after

harvest. During the dormant period, sprouts do not grow, even if tubers are transferred to

suitable conditions such as darkness, 20oC and 80-90% RH. Increasing storage time

beyond the dormant period, will lead to tuber aging. Once dormancy is broken sprouts

begin to grow but their growth changes over time. Sprouts will grow first from the apical

eyes and these sprouts will be dominant and inhibit lateral sprout growth. This stage is

called apically dominant. Prolonging storage time weakens the dominance of apical

sprouts and allows outgrowth of lateral sprouts, resulting in multiple sprouting. Over

time, sprout tips become less active, and sprouts will grow horizontally and branch

(Krijthe, 1962; Struik and Wieserma, 1999). Finally, small tubers may form directly

from sprouts of a tuber. Therefore, physiological age of potato tubers plays an important

role in sprout behaviour and this influences subsequent plant growth.

Studies on sprout behaviour of tubers stored under various regimes have been

conducted for many years using varieties selected from cold environments, including

Europe and North America. Yet, information about tropical varieties is very limited.

Physiological aging, which is controlled by temperature and storage duration, usually

increases the number of sprouts per tuber via release from dormancy and decline in


107

apical dominance (Struik and Wieserma, 1999). Physiological aging increases sprout

length (Allen et al., 1979; Krijthe, 1962; Susnoschi, 1981a), sprout fresh and dry weight

(Wurr, 1978), and sprouting capacity (Krijthe, 1962). Sprouting capacity is a common

measure of potential growth and it is usually expressed as sprout weight over the initial

of tuber weight (Krijthe, 1962; Wurr, 1984) or sprout length/tuber weight. The later can

be used as sprout weight is closely related to sprout length (Wurr, 1978).

Different countries have different methods of seed storage and production. In

temperate regions, potatoes were selected for storage over cold, dark winters and now

4°C storage in dark rooms. Whereas in tropical regions, potatoes were selected for long

storage of 8-9 months under warm (20-30° C) temperatures and diffuse lighting (Quitos,

2004; Tung, 2000). These potatoes will potentially have different responses to storage at

4°C. In temperate regions farmers plant potatoes using seed pieces, whereas in tropical

regions, farmers plant small round tubers (30-50 g) to avoid diseases which enter the

cutting wound. Cutting seeds can reduce apical dominance and stimulate lateral sprouts

to grow so that more stems will develop from a mother tuber. Increasing stem number

per hill increases overall tuber numbers, which affects yield and tuber size distribution.

So, common practice varies between temperate and tropical regions and this may also

influence plant growth and yield.

This experiment examined the influence of cutting of relatively young (stored at

4°C for 12 weeks) and old (40 weeks) seeds on their growth and seed tuber production

under field conditions in south-western Western Australia. In order to expand

Australia’s export seed potato industry, cultivars suitable for tropical conditions were

examined under Western Australian conditions.


108

4.2. Materials and methods

Experiment 1

Four potato cultivars, Atlantic, Eben, PO3 and KT3 were used to examine the

sprout behaviour of different physiologically aged tubers. Atlantic is commonly grown

in Western Australia and in Indonesia. Atlantic seeds collected were from plants grown

in Busselton, Western Australia (33°31’47.7”S, 115°45’47.7”E) from spring to summer

and harvested on 20th December 2003. Eben and PO3 are from the Philippines, whereas

KT3 is from Vietnam. These seeds were from plants grown in Medina Research Center,

Western Australia (32°13’00”S, 115°47’00”E), from spring to summer and harvested on

18th December 2003 (Eben) and 24th December 2003 (PO3 and KT3).

Tubers weighing 50 – 80 g were selected, placed on trays and held in 4° C dark,

cool store for 10, 12, 14, 16, 18, 20, 22, 24, 26, 30, 38 and 40 weeks. Periodically, at the

end of each storage period, 40 (Eben and PO3) or 20 (Atlantic and KT3) tubers were

removed. Samples of each cultivar were divided into 2 groups, undesprouted (intact

tuber) or desprouted (sprouts were removed by hand), except for KT3, since seeds stored

for 40 weeks at 4°C did not produce big enogh sprouts to be desprouted. Eyes, then were

numbered from heel to stem end. They were then placed in a darkened (10 lux)

sprouting room at 20° C with 80 to 90% RH. Initial tuber weight was measured after 3

hours at 20° C.

After 4 weeks in sprouting room, individual sprouts from each eye with length >

2 mm were measured. The proportion of sprouted eyes, number of sprouts per tuber,

sprout length, sprout dry weight per tuber and sprouting capacity were measured.

Dormancy was measured and it was considered broken when 80% of tubers had


109

produced sprouts ≥3 mm (Krijthe, 1962; Reust, 1986). The proportion of sprouted eyes

was calculated by dividing the number of eyes with sprouts by the number of eyes per

tuber. Average sprout length was calculated from total sprout length divided by number

of sprouts per tuber. Sprouting capacity was sprout fresh weight per tuber divided by the

initial tuber weight expressed as a percentage (Hartmans and Van Loon, 1987; Krijthe,

1962). Tuber loss was measured by calculating the difference between tuber weight at 4

weeks (without sprouts) and initial tuber weight.

Experiment 2

Three potato varieties, Eben, PO3 and KT3 were used. Tubers were stored at

4°C, in the dark for 12 or 40 weeks and these were considered as young and old seeds,

respectively. Young seeds were from plants grown in Medina Research Center

(32°13’00”S, 115°47’00”E) from spring to summer and harvested on 18th December

2003 (PO3 and KT3) and 24th December 2003 (Eben), as in Experiment 1. Old seeds

were from a commercial potato grower in Manjimup (34°07’43.7”S, 115°40’32.5”E)

and plants were grown from summer to autumn and harvested in May 2003.

For both young and old seeds, tubers weighing approximately 50 g were selected

and used as round seeds and tubers weighing approximately 100 g were cut into two

seed pieces. Healthy tubers were selected by visual inspection, and as an additional

precaution, Tacto® (Thiabendazol) was applied in storage. Before planting, seed tubers

were removed from cool store and placed under low light at 20°C for one week. Tubers

were dusted with fungicide (Mancozeb®) one day before planting and at planting with

Rizolex®. Tubers were planted in two rows per plot by machine on 12th March 2004 and


110

harvested on 29th July 2004. The size of each plot was 1.5 m wide by 6 m long

consisting of two beds containing 32 tubers planted per bed. At the end of each bed,

there were 0.5 m buffers. Before planting, K2SO4 (200 kg ha-1), trace element mix (147

kg ha-1) and double superphosphate (2,000 kg ha-1) were applied and 50 kg ha-1 N was

applied after sowing. Post planting fertilizers (450 kg ha-1 N; 520 kg ha-1 K, 1248 kg ha-1

P and 24 kg ha-1 Mg) were used at weekly intervals after emergence for 12 weeks. These

were applied in about 1 mm of water through the sprinkler system. Weather conditions

during potato production at the Medina Research Centre, Department of Agriculture

Western Australia were monitored (Table 4.1). At planting, all tubers appeared healthy.

However, some crops, from which the seed came, had stem rot.

Emergence was observed 2 weeks after planting. Seven weeks after planting

early plant growth was assessed. Assessment included number of plants emerged per

bed, stem number per plant emerged above soil surface, plant height (the tallest stem)

and number of leaves per plant.

At harvesting (20 weeks after planting), number of tubers per plant was counted.

Tuber size distribution was determined by weighing tubers individually and then grading

them into 5 marketable sizes: 0-35, 36-55, 56-110, 110-200, > 200 g. Total yield was

calculated as marketable plus rejected (damaged by harvester machine) tubers.


111

Table 4.1. Field conditions during potato growth in Medina Research Center, Department of Agriculture, Western Australia from March to July 2004*

Month Climates March April May June July

Mean daily max. temperature (°C) 29.0 25.8 21.9 19.3 18.1

Highest maximum temperature (°C) 43.0 35.5 32.9 26.2 25.8

Mean daily min. temperature (°C) 15.6 13.5 10.5 9.2 8.2

Lowest minimum temperature (°C) 4.5 2.4 2.0 -2.0 -1.0

Rainfall (mm) 21.6 38.3 101.8 156.1 156.6

Mean daily evaporation (mm) 6.2 4.0 2.3 1.8 1.8

Mean RH (%): 9 am 58 65 76 80 81 Mean RH (%): 3 pm 44 49 57 62 63 * Source: Australian Government, Bureau of meteorology (http://www.bom.gov.au/climate/averages/tables/cw_009194.shtml)

The design was a split plot with 3 varieties as main plots. Each main plot had 4

randomized blocks for the 2 seed treatments (cut and whole seed) and 2 physiological

ages (young = 12 weeks and old = 40 weeks).

4.3. Results

Experiment 1

Dormancy was considered broken when 80% of tubers had sprouts longer than 3

mm after 2 weeks in a sprouting room. The time to break dormancy in 4°C storage

varied with cultivar. In Atlantic seeds, dormancy was broken after 12 weeks in storage,

http://www.bom.gov.au/climate/averages/tables/cw_009194.shtml


112

whereas in Eben and PO3 dormancy had broken by 10 weeks. In contrast, KT3 had a

longer dormant period, which was broken by 22 weeks.

Sprouting capacity was determined after 4 weeks in the sprouting room and is

dependent on sprout characteristics which varied substantially between varieties. In this

study, KT3 seeds was not desprouted as seeds stored for 40 weeks at 4°C did not

produce big enogh sprouts to be desprouted. Prolonging storage time generally increased

the proportion of sprouted eyes in all cultivars of both undesprouted and desprouted

tubers (Fig. 4.1). Longer storage increased the proportion of sprouted eyes from 40% to

90% in Atlantic, from 27% to 49% in Eben, from 21% to 56% in KT3 and from 56% to

94% in PO3. PO3 generally had more sprouted eyes than other cultivars. KT3 seeds

stored from 10-22 weeks had the lowest proportion of sprouted eyes, but ≥ 24 weeks it

was similar to Eben with about 40% of eyes producing sprouts. Desprouted Atlantic

seeds produced a relatively constant proportion of sprouted eyes (55-65%) across the 10

to 40 weeks and generally it was not different to undesprouted tubers. In desprouted

Eben the proportion of sprouted eyes increased ≥ 18 weeks and reached a maximum of

81% at 40 weeks when it was about double the proportion in undesprouted tubers. The

proportion of sprouted eyes of desprouted PO3 seeds increased from 10 to 20 weeks,

then was relatively constant and similar to undesprouted tubers until it decreased when

they were stored for more than 24 weeks.


113

Atlantic

020

4060

80100

Eben

020

4060

80100

PO3

0

20

40

60

80

100

KT3

0

20

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100

10 12 14 16 18 20 22 24 26 30 38 40Storage time (weeks)

Figure 4.1. Proportion of sprouted eyes (sprouted eyes/total eyes in %) of 4 potato

cultivars. Full symbols are undesprouted seeds and open symbols are desprouted seeds. Vertical bars are l.s.d values at P = 0.05

Pro

porti

on o

f spr

oute

d ey

es (%

)


114

Atlantic

0

3

6

9

12

Eben

0

3

6

9

12

PO3

0

3

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9

12

KT3

0

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Atlantic

0

3

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9

12

Eben

0

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PO3

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KT3

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Figure 4.2. Number of sprouts/tuber of 4 potato cultivars. Full symbols are undesprouted

seeds and open symbols are desprouted seeds. Vertical bars are l.s.d values at P = 0.05

Num

ber o

f spr

outs

/tube

r


115

In all cultivars tested, the number of sprouts per tuber increased with prolonged

storage time (Fig. 4.2). Sprout number of undesprouted Atlantic seeds increased from

3.2 sprouts at 10 weeks to 7.6 sprouts at 40 weeks. Undesprouted Eben had the lowest

number of sprouts per tuber. It increased from 2.2 sprouts to a maximum of 5.8 sprouts

after 40 weeks. Prolonging storage time increased sprout number in undesprouted KT3

from 2.4 sprouts to 8.4 sprouts. Undesprouted PO3 generally had more sprouts per tuber

than other cultivars. Sprout number of undesprouted PO3 increased from 5 sprouts at 10

weeks to 9.3 sprouts at 38 weeks, then it slightly decreased to 8.5 sprouts at 40 weeks.

Undesprouted Atlantic had a similar number of sprouts per tuber (3.2 sprouts) to

desprouted seeds. Desprouted Eben seeds stored for 10 to 18 weeks had 2.7 to 3.6

sprouts. However following further storage, desprouted seeds had more sprouts than

undesprouted seeds. Sprout number increased in desprouted PO3 seeds from 4 sprouts at

10 weeks to 7.1 sprouts at 22 weeks and was similar to undesprouted tubers. However,

after 22 weeks, sprout number of desprouted PO3 tubers gradually decreased and by 40

weeks it was nearly half that of undesprouted tubers (4.8 sprouts).

Average sprout length per tuber of undesprouted Atlantic was relatively constant

at 20 mm until 20 weeks, then it increased with further storage up to 40 weeks (Fig. 4.3).

Sprout length of Eben and PO3 was similarly constant at about 10 mm until about 20

weeks and then gradually increased with extended storage time so that at 38 weeks Eben

was 72 mm and PO3 was 38 mm (Fig. 4.3). However, length decreased by 12% (Eben)

and 36% (PO3), at 40 weeks. KT3 produced much shorter sprouts but prolonging

storage time gradually increased sprout length from 2 mm at 10 weeks to 8 mm at 40

weeks. Sprout length of desprouted Atlantic seed remained relatively constant with


116

storage. The length of sprouts from desprouted Eben seeds was also relatively constant

until 30 weeks when it increased but remained shorter than undesprouted tubers. Sprout

length of desprouted PO3 was relatively constant (Fig. 4.3) and similar to undesprouted

seeds until week 38. Trends in total sprout length and length of the longest sprout were

very similar (data not presented).

Generally, sprouting capacity gradually increased with extended storage time

(Fig. 4.4). In undesprouted Atlantic sprouting capacity increased from 0.92% to 5.23%

when storage was extended from 10 to 40 weeks. In undesprouted Eben seeds sprouting

capacity steadily increased from 0.63% at 10 weeks to 4.93% at 30 weeks and then

doubled by 40 weeks (10.38%). Sprouting capacity of undesprouted PO3 gradually

increased to 2.80% at 30 weeks then doubled to 5.70% at 38 weeks, and then declined to

4.48% by 40 weeks. Sprouting capacity of KT3 was substantially lower than other

varieties and although it gradually increased, it only reached a maximum of 1.2% by 40

weeks. In very old seeds of 38 and 40 weeks storage, desprouted tubers produced lower

sprouting capacity than undesprouted tubers.

Sprout fresh weight usually increased gradually with prolonged storage time and

followed a very similar pattern to sprouting capacity. Sprout weight was influenced by

sprout morphology which differed with cultivars (Fig. 4.5). Atlantic sprouts were tall

and thin, Eben sprouts were shorter and thicker than Atlantic, thus sprout fresh weight

was greater than Atlantic. PO3 produced shorter sprouts than Atlantic and Eben, and

sprouts tended to branch when stored for longer time. KT3 sprouts were broad, and the

shortest compared with other cultivars. In Atlantic, there was a 9-fold increase in sprout

fresh weight from 0.43 g/tuber at 10 weeks to 3.92 g/tuber at 40 weeks. Undesprouted


117

Eben seeds stored for 40 weeks had the highest sprout fresh weight of 6.45 g/tuber, and

it was about 16-fold more than at 10 weeks storage. KT3 had the lowest sprout fresh

weight compared to the other cultivars and it only increased from 0.08 to 0.77 g/tuber

during the storage period. Sprout fresh weight of PO3 gradually increased with extended

storage time from 10 to 38 weeks, and thereafter declined. Desprouted tubers of ≤ 24

week-old Atlantic, Eben and PO3 produced similar sprout fresh weight to undesprouted

seeds. Sprout fresh weight of desprouted tubers ≥ 24 week-old was lower. These trends

were reflected in the sprout dry weight (data not presented).

Tubers lost more fresh weight in the sprouting room with extended storage time

(Fig 4.6). Atlantic seeds lost the least weight compared to other cultivars, with a

maximum of 4.86 g (8%) at 38 weeks. PO3 and Eben had similar tuber fresh weight loss

which increased from 2-4 g (4-5%) at 10 weeks to 5-6 g 10% at 40 weeks. Desprouted

seeds generally had similar tuber fresh weight loss to undesprouted seeds.


118

Atlantic

0

20

40

60

80

Eben

0

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40

60

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PO3

0

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Atlantic

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80

Eben

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PO3

0

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40

60

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KT3

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4

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Figure 4.3. Average sprout length (mm) of 4 potato cultivars. Full symbols are

undesprouted seeds and open symbols are desprouted seeds. Vertical bars are l.s.d values at P = 0.05

Ave

rage

spr

out l

engt

h (m

m)


119

Eben

0

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Atlantic

0

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Eben

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Atlantic

0

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12

PO3

0

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9

12

Figure 4.4. Sprouting capacity (% of sprout fresh weight/tuber over initial tuber weight)

of 4 potato cultivars. Full symbols are undesprouted seeds and open symbols are desprouted seeds. Vertical bars are l.s.d values at P = 0.05

Spro

utin

g ca

paci

ty (%

)


120

10 weeks 16 weeks 26 weeks 40 weeks

Atlantic

Eben

KT3

PO3

Storage time

10 weeks 16 weeks 26 weeks 40 weeks

Atlantic

Eben

KT3

PO3

Storage time EBEN

Desprouted tubers

ATLANTIC

Undesprouted tubers

Desprouted tubers

Undesprouted tubers

EBEN

Desprouted tubers

ATLANTIC

Undesprouted tubers

Desprouted tubers

Undesprouted tubers

I.

II.

Figure 4.5. Sprout characteristics of undesprouted Atlantic, Eben, KT3 and PO3 tubers stored for 10, 16, 26 and 40 weeks at 4°C, which were photographed after 4 weeks in the sprouting room at 20°C (I). Sprout characteristics of undesprouted and desprouted Atlantic and Eben tubers stored for 26 weeks at 4° C, which were photographed after 2 weeks in the sprouting room at 20°C (II).


121

Atlantic

0

2

4

6

8

Eben

0

2

4

6

8

PO3

0

2

4

6

8

KT3

0

2

4

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8


Atlantic

0

2

4

6

8

Eben

0

2

4

6

8

PO3

0

2

4

6

8

KT3

0

2

4

6

8


Figure 4.6. Tuber weight loss (g) during 4 weeks of sprouting at 20°C following various

periods of storage at 4°C for 4 potato cultivars. Full symbols are undesprouted seeds and open symbols are desprouted seeds. Vertical bars are l.s.d values at P = 0.05

Tube

r wei

ght l

oss

(g)


122

Experiment 2

In this experiment, potatoes were planted at Medina Research Center, Western

Australia in early autumn and harvested mid winter. Eben emerged first. After 2 weeks,

21 Eben plants had emerged but only three KT3 and a single PO3 plant. All were from

seeds stored for 40 weeks and these were both cut and whole seeds of Eben but only cut

seeds of KT3 and PO3.

There was a trend for old seeds to have better plant emergence (more plants

emerged and they emerge earlier) than young seeds and for cutting to assist in

emergence from young seeds but not old seeds. Most Eben seed tubers produced plants

but slightly more plants emerged from old seed than young seed. Cutting had no effect

on Eben. Very few plants grew from whole KT3 seed stored for 12 weeks. In three plots

no plants emerged from young KT3 seeds and across the experiment it had the lowest

plant emergence of less than 1%. Because of the low and delayed emergence, seeds were

dug up and examined at 7 weeks. Most tubers were rotten, but did not smell. Presumably

they did not have bacterial soft rot (Erwinia sp), and rot was probably due to Fusarium.

Cutting seeds of young KT3 increased plant emergence from 1% to 20%. Less than a

quarter of whole young PO3 seeds produced plants and this increased to more than a half

for old or cut seed.

In general, old seeds (40 weeks) produced more stems/plant than young seeds,

with both cut and whole seeds. Old seeds of Eben, KT3 and PO3 had twice as many

stems/plant as young seeds. In all PO3 and young KT3 seeds, cut tubers produced more

stems/plant than whole tubers. In physiologically old seeds of KT3 and all Eben, cutting

did not affect stem number/plant. Young whole seeds of Eben and PO3 had more than 1


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stem/plant, whilst the few plants from whole KT3 seeds had 1 stem/plant with an

average across beds of 0.25 stems, reflecting lack of emergence. All old whole seeds had

more than 2 stems/plant.

Table 4.2. Effects of cutting and storage time (ST) of seed tubers on plant emergence, number of stems/plant, plant height (mm) and number of leaves/plant, 7 weeks after planting of Eben, KT3 and PO3 potato cultivars. Different letters indicate significant difference (p ≤ 0.05) within columns

Variety (V)

Seed treatment

(T)

Storage time

(weeks)

Plant emergence

(%)

Number stems/plant

Plant height (mm)

No. of leaves

Eben Whole 12 61.7 cd 1.43 bc 123 bc 23.2 b 40 84.2 d 3.84 d 263 de 44.8 c Cut 12 76.7 d 1.93 c 128 bc 32.5 bc 40 77.5 d 3.77 d 215 cd 54.8 cd

KT3 Whole 12 0.8 a 0.25 a 20 a 0.7 a 40 58.3 c 2.09 c 165 c 40.4 bc Cut 12 20.0 b 1.10 b 113 b 25.2 bc 40 62.5 cd 2.44 c 170 cd 52.5 c

PO3 Whole 12 24.2 b 1.06 b 183 cd 23.9 bc 40 57.5 c 2.54 c 220 d 59.1 cd Cut 12 55.0 c 2.08 c 300 e 42.1 c 40 64.2 cd 4.11 d 263 de 71.6 d

l.s.d V x T x ST 18.16 0.61 51.19 18.31

Table 4.3. Effects of seeds treatments and storage time (ST) on tuber size distribution (g) and total tuber number per bed and total yield (t/ha) of Eben, KT3 and PO3 cultivars. Different letters indicate significant difference (p≤0.05) within columns

Tuber size distribution (g)

Var

iety

(V)

Seed

trea

tmen

t (T

)

Stor

age

time

(wee

ks)

0 –

35

36-5

5

56 –

110

111

- 200

> 20

0 Total tuber number per

bed

Total yield (t/ha)

Eben Whole 12 23.8 c 14.0 bc 44.0 c 16.0 bc 1.0 ab 98.8 c 23.09 c 40 14.3 bc 16.3 c 30.0 bc 10.5 b 1.75 ab 72.8 c 19.38 c Cut 12 16.8 bc 16.8 c 36.2 c 12.0 bc 1.00 ab 82.8 c 20.09 c 40 19.5 bc 10.0 c 31.2 bc 6.25 ab 0.0 a 76.0 c 14.80 bc

KT3 Whole 12 1.0 a 0.0 a 0.0 a 0.0 a 0.0 a 1.0 a 0.06 a 40 15.3 bc 15.3 bc 22.0 b 18.5 c 6.5 b 77.5 c 23.86 c Cut 12 4.0 ab 3.0 ab 6.5 ab 12.8 bc 4.0 b 30.3 b 11.94 b 40 19.5 bc 15.8 bc 23.0 bc 17.3 bc 4.0 b 79.5 c 22.04 c

PO3 Whole 12 1.5 ab 1.5 ab 4.5 a 10.0 b 7.5 b 25.0 ab 13.22 bc 40 10.5 b 16.8 c 28.5 bc 22.5 c 1.8 ab 80.0 c 23.24 c Cut 12 13.0 b 8.0 b 20.0 b 33.5 d 7.5 b 82.0 c 31.40 d 40 19.5 bc 17.0 c 36.0 c 24.5 c 1.3 ab 98.2 c 26.46 cd

l.s.d Vx T x ST 9.6 7.9 13.99 7.81 3.74 27.40 7.26 124


125

Across varieties yield was generally between 10-30 t/ha. PO3 had the highest

yield across treatments averaging 23 t/ha (Table 4.3). The influence of cutting and

physiological age on yield varied substantially with cultivar (Table 4.3). In Eben

treatments did not influence tuber number or yield. Physiologically old KT3 seeds

produced plants with higher numbers of tubers/bed and greater yield than

physiologically young seeds. Cutting physiologically young KT3 seeds considerably

increased numbers of tubers/bed (77 times) and yield (27 times). However, cutting old

KT3 seeds did not affect tuber number/bed or yield.

Old whole PO3 seeds had 3 times more tubers/bed than young seeds. Cutting

increased tuber number and yield three-fold in young PO3 seed. However, cutting had

no effect in old PO3.

The influence of treatments on total tuber number per bed and tuber size

distribution was very dependent on cultivar. Treatments did not change tuber number or

tuber size distribution in Eben. Prolonged storage increased overall tuber number and

yield in KT3, so also increased the number of tubers in each size category. Similarly,

cutting young seeds increased tuber number especially in large sizes. However cutting

did not influence tuber size distribution in plants from old KT3 seeds. In PO3, prolonged

storage substantially increased tuber number, especially in 36-200 g sized whole tubers.

4.4. Discussion

During storage, dormancy was gradually broken. Atlantic took 12 weeks to break

dormancy. Atlantic was selected in the USA under cold temperate growing conditions

and the period required in cool store may reflect selection for this type of dormancy. In


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Britain, commercial varieties that break dormancy by 12 weeks are relatively early, as

some varieties take longer than 28 weeks at 4°C (Burton, 1989). In Vietnam, potatoes

such as KT3, which took 22 weeks to break dormancy, are mostly grown in the Red

River Delta at sea level. Potatoes of Vietnamese origin, such as KT3, are grown for a

short period of less than 90 days between rice crops (Tung, 2000). So, seeds must

remain under hot temperatures and humid conditions in the diffuse light storage for up to

10 months between production season. Therefore, a long dormant period would have

been desirable, to assist in the maintenance of seed quality. In the Philippines, more than

90% of potatoes are produced in the cooler highlands, and there are two production

seasons per year, while in lowlands potatoes grow for one season so that seeds might be

stored for a few months (in highlands) or they can be stored for long period (in

lowlands) (Anonymous, 2004a).

Sprout behaviour varied with cultivar, where sprout number, average sprout

length, sprout fresh weight, sprouting capacity and tuber weight loss during sprouting

were closely related to the length of storage time in constant cold storage (4°C).

Sprouts in the apical region grew first and were usually dominant. This

dominance gradually decreased with prolonged storage times as has been observed in

many varieties (Krijthe, 1962). However, different cultivars had different degrees of

apical dominance and the range across the varieties was substantial. Cultivars also had

different responses to desprouting. Atlantic and PO3 seeds had weaker apical dominance

and it was released early. Eben and KT3 seeds had strong apical dominance and it was

released later. Atlantic and PO3 had reduced apical dominance by 10 weeks and by this

time had started to produce multiple sprouts. Desprouting Atlantic and PO3 seeds


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generally did not affect sprout number as tubers had already lost apical dominance and

therefore removing the apical sprouts had no impact. Desprouting is the removal of

sprouts and the first sprouts to emerge will be apical sprouts from apical eyes. Later,

with further storage, sprouts will emerge from other buds in the apical and lateral eyes.

When apical dominance is strong, removing the apically dominant sprout will result in

the emergence of another apically dominant sprout. As apical dominance is reduced,

removing the apical sprouts will result in multiple sprouts (Coleman, 1987). Decreasing

apical dominance is due to a reduction of auxin in the apical buds (Mikitzel and

Knowles, 1990b) and in addition to increasing cytokinins (Sukhova et al., 1993; Van

Staden and Dimalla, 1978), and supported by increasing concentration of gibberellic

acid (Suttle, 2004; Thomas and Wurr, 1976; Timm et al., 1962). With storage, changes

occur in endogenous hormone which lead to breaking of dormancy and a stimulation of

sprout grow. The concentration of free cytokinin increases especially in the apical bud

(Sukhova et al., 1993; Van Staden and Dimalla, 1978), while GA increases as sprout

grow and reaches maximum close to the onset of sprout growth (Emilsson and

Lindblom, 1963; Van der Plas, 1987).

Apical dominance is stronger in younger seeds, but prolonged storage time has

less effect on cultivars with strong apical dominance. Seeds of Eben and KT3 with

prolonged storage up to 40 weeks had a similar proportion of sprouted eyes to Atlantic

and PO3 at 10 weeks. Breaking the apical dominance of Eben seed was hastened by

desprouting, especially for tubers stored for more than 20 weeks. Increasing sprout

number in desprouted tubers was also found in Petland Javelin cultivar (Hay and

Hampson, 1991).


128

Desprouted tubers gradually produced fewer sprouts than undesprouted seeds,

because older tubers lost energy so that not all desprouted eyes grew new sprouts. Apical

dominance of PO3 had already broken by 10 weeks so tubers were producing multiple

sprouts. The production of multiple sprouting consumes reserves in the potato and so

there was less reserves and energy available for sprout growth, thus tubers eventually

produced fewer sprouts than undesprouted tubers.

Reducing apical dominance has a two-fold effect as it allows more eyes to sprout

and more sprouts to develop from each eye. Both contribute to sprout and then stem

number. In general, sprouts grew taller when tubers were stored for longer periods. It

reached a maximum and then started to decline, a common feature in potato tubers

(Struik and Wieserma, 1999). However the period required showed considerable

variation between the cultivars examined. Neither Eben nor KT3 appears to have

reached a maximum in sprout growth by 40 weeks, but PO3 appeared to have plateaued

for a short period at 38 weeks and then declined by 40 weeks. With prolonged storage,

desprouted tubers had shorter sprouts than undesprouted tubers. Increasing sprout

number by prolonging the storage period enhances competition between sprouts for food

reserves. While reserves are abundant sprouts grow well but eventually reserves limit

sprout growth. The ability to transport carbohydrate and nitrogen is also less in older

tubers (Kumar and Knowles, 1993b; Mikitzel and Knowles, 1989). This further limits

sprout growth with longer storage. Storing PO3 for 40 weeks may be the maximum

period as sprout growth was in decline at this stage. Cultivars have different patterns of

sprout growth when they are stored at 4°C (Hartmans and Van Loon, 1987). In some


129

temperate varieties it reaches maximum at 42-50 weeks (Jaerla) or 57-65 weeks

(Désirée) and this may be similar to Atlantic, KT3 and Eben but much longer than PO3.

More sprouts developed when tubers were stored for longer, and they grew taller.

As a result, tuber fresh weight loss increased. The ability to produce a certain weight of

sprouts is expressed as sprouting capacity. The trend of sprouting capacity was similar to

sprout length and sprout fresh weight, since there is a good linear relationship between

sprout weight and its length (Wurr, 1978). Sprouting capacity is commonly used as a

measure of seed quality, and it increases and then decreases with prolonged storage

(Krijthe, 1962). However, good seed quality is not neceserarily related to a maximum

sprouting capacity, since after it has reached an optimum, plant growth decreases

although sprouting capacity still increases for some time before it starts to decrease

(Struik and Wieserma, 1999). Therefore, it is important to store potato seeds until they

have an optimum sprouting capacity and produce high yield.

Tuber weight loss generally increased with prolonged storage, as more sprouts

grew taller and bigger. However, desprouting tubers did not affect tuber weight loss in

either young or old seeds. During sprouting, respiration rate of potato tubers remained at

a steady low rate (Mikitzel and Knowles, 1990a), and desprouting tubers does not

increase respiration. However, transpiration and respiration and consequently weight

losses varies between cultivars (Burton, 1989). Tuber weight loss during sprouting was

not always related to sprout length. Atlantic seeds had the lowest tuber weight loss (5 g)

though sprouts grew taller than other cultivars, whereas KT3 had the highest tuber

weight loss, but sprouts were shorter and lighter. High tuber weight loss also occurred

before sprouts started to grow (Figure 4.6). KT3 had long dormancy and sprouts started


130

to grow 22 weeks in storage. This long period of dormancy caused tuber weight loss in

KT3 that was higher than Atlantic, Eben and PO3 which sprouted earlier. Tuber weight

loss was probably also affected by disease during storage (Beukema and Van der Zaag,

1990; Rastovski and Van Es, 1987).

In tropical countries including Indonesia, Vietnam and the Philippines, potato

seeds are usually stored for a long time (16-38 weeks) under diffuse light storage, in

simple storage rooms (Batt, 1999b; Jayasinghe, 2003; Quitos, 2004; Tung, 2000). Very

few cool rooms are available to provide better storage conditions. Under inappropriate

conditions, seeds are generally of poor quality. They have pest and disease problems and

low seed vigour as sprouts grow long and there is a high tuber weight loss. This is a

problem, especially in KT3, which has substantial weight losses with sprouting. When

tubers are planted in the field, they produced low yield. Furthermore, tubers with long

sprouts are usually desprouted before planting (McPharlin, pers. comm.) and resprouted

tubers may be even less vigorous.

In the Philippines, Eben produces relatively high yield with a minimum of 19

t/ha and maximum yield of 31 t/ha (Quitos, 2004). Old Eben seed still had high

sprouting capacity and this was not reduced by desprouting until after 30 weeks of

storage. However this was at 4 °C, not under the warm conditions of diffuse light storage

in the Philippines. Furthermore, Eben had a low tuber weight loss of 9% (Fig. 4.6).

In Vietnam, KT3 were stored at 20-32 °C under diffuse light storage for 36-40

weeks after harvest. At planting, tubers have poor quality and yield is low. KT3 has an

average rate of tuber weight loss but sprouting capacity was relatively low land still

increasing, even after 40 weeks at 40 °C (Fig. 4.4). Perhaps, KT3 seed stored at higher


131

temperature would have higher tuber weight loss. Because of the single, short growing

season in Vietnam (Batt, 1999b; Tung, 2000), KT3 would be stored for a long period. Its

long dormancy period and delayed time for maximum sprouting capacity would be

advantageous under these conditions.

In the field experiment, plant emergence of Eben was higher than KT3 and PO3.

This was probably due to Eben having longer sprouts, sooner. It was selected for low

lands and it is adapted to hot temperatures (~ 30° C) (Quitos, 2004) and therefore grew

well with the warm field conditions experienced in this experiment. Young KT3 and

PO3 seeds were still dormant at planting, and therefore took longer to emerge and had

poor plant emergence with < 20% emerged. In Vietnam, KT3 seeds are usually stored

36-40 weeks in warmer temperatures, and then planted in the winter season with

temperatures around 20°C. In this experiment, very few plants survived. Perhaps, high

temperatures (≥ 30°C) are unsuitable for growing young KT3. In addition slow

emergence increased the risk of rots (Beukema and Van der Zaag, 1990) and these killed

many KT3 tubers. Prolonged storage time facilitated the breaking of dormancy, thus old

KT3 and PO3 tubers produced more sprouts and this improved emergence to a

maximum of 62% and 64% and increased production of stems per plant. Cutting seeds

further increased stem number. This was due to removal of the apex or otherwise

reducing apical dominance, and allowing more lateral buds to develop into stems. Old

Eben had broken apical dominance and more eyes produced sprouts. Therefore, old

seeds produced more stems per plant. Cutting seeds had no effect on increasing stem

number of old Eben seeds as tubers already had multiple sprouts.


132

The main aim of this study was to increase stem number as this increases tuber

number in many other cultivars (Allen, 1979; Iritani et al., 1983). There were very

different relationships between stem number and tuber number in these tropical

varieties. In KT3, older seeds produced more stems than younger, dormant seeds, and in

turn these produced substantially more tubers with greater yield. This supports the

relationship between stem number and tuber number (Allen, 1979), except yield usually

remains constant, whereas in KT3 it increased.

In PO3, older seed produced twice as many stems as young seed and plants from

older seed produced nearly 3 times the yield. Again, this follows the theory that more

stems produce more tubers. Cutting doubled stem number from both young and old PO3

seed. However, there was only an equivalent increase in tuber number from plants

grown from young seed. Cutting young seeds produced substantially bigger plants, that

were nearly twice the height of plants from uncut seed and had nearly twice the number

of leaves. This increase in plant growth was not observed in old seeds and so perhaps the

plants from older seed could not support an increase in tuber production. The range of

tuber yield across cultivars and treatments (excluding dormant seed) was 10-30 t/ha. Old

PO3 already had high yield and perhaps this could not be increased by seed treatments.

In young KT3 and PO3 seeds, cutting tubers increased yield, because cutting

tubers stimulated stem production that, in turn, increased tuber number. Cutting old

seeds did not affect yield, as stem number was similar to whole tubers. Tuber number of

old KT3 and PO3 seeds were greater than young seeds, where tubers were still dormant

at planting. Prolonged storage time caused multiple sprouting, thus more stems emerged

and produced more tubers. On the other hand, prolonged storage time did not affect


133

tuber number and yield of Eben, although stem number did increase. Eben appears to

have a long plateau during physiological aging and it was able to maintain sprouting

capacity, stem number, tuber number and yield, when stored from 12 to 40 weeks. KT3

was slow to break dormancy and may not have yet peaked in terms of sprouting

capacity, stem number, tuber number and yield by 40 weeks.

PO3 was slower to reduce apical dominance than Eben and Atlantic but seed still

performed well after 40 weeks of storage, in terms of tuber number and yield. In other

varieties, physiologically old seeds have decreased shoot sink strength and increased

competition among the multiple sprouts (Mikitzel and Knowles, 1989). So that

physiologically old seeds generally produce more stems but have fewer tubers and lower

yield (Struik and Wieserma, 1999). In the present study reduction of yield did not occur

even after seeds were stored for 40 weeks. Perhaps, these potato tubers still had good

sprouts (Figs. 4.1 to 4.5) and subsequent plant growth after 40 weeks of storage.

Therefore, the yield of old PO3 and KT3 seeds was substantially higher than young

seeds whereas, yield of old Eben seeds was similar to young seeds. In temperate

varieties, such as Désirée and Jaerla, relative plant growth vigour does not reduce until

seed are stored for more than 52 weeks (Van der Zaag and Van Loon, 1987). Plant

vigour of very old seed (76 weeks) is reduced as it has low sink strength and high

competition with increasing stem number (Mikitzel and Knowles, 1989).

Tuber size in Eben was not affected by planting young or old seed, nor by

cutting. However, none of these treatments influenced stem number, or tuber number so

it is not suprising that it did not influence tuber size distribution.


134

Young KT3 had poor plant growth as many seeds were killed by rots and the

remainder may have been infected and weakened by rots. Although older seed or cut

seed had larger plants, more tubers and greater yield, and hence more tubers in all

categories, the responses were compounded by disease. The young uncut tubers took

longer to emerge and this made them more susceptible to disease (Beukema and Van der

Zaag, 1990). Older plants had more stems but this was not the only reason for their

increased tuber number.

Old PO3 seed produced more tubers in all categories than young seed. Fewer

young seed emerged and those that did produced less stems. Both prolonged storage or

cutting reduced apical dominance and produced more tubers across all sizes. So,

increasing stem number increased the ability for plants to produce and fill tubers.

Competition between tubers was not great enough to reduce tuber size or increase the

overall proportion of small tubers.

4.5. Conclusion

The Australian and tropical potatoes performed very differently. Cultivars have

different sprout morphology and they behave differently during storage that results in

different subsequent plant growth in the field. This information will benefit seed growers

and potato industries in Western Australia to fulfil the Asian potato seed market.

Prolonged storage time can be used to increase physiological age of potato

tubers, which was reflected in an increase in the proportion of sprouted eyes, sprout

number, sprout length and sprouting capacity.


135

Dormant tubers grew slower and produced lower yield. Dormancy was broken

by 10 weeks in PO3 and Eben, by 12 weeks in Atlantic and by 22 weeks in KT3.

Potatoes should be planted after they have broken dormancy. Maximum sprouting

capacity was 38 weeks in PO3, and more than 40 weeks in Atlantic, Eben and KT3, but

this does not give higher yield. The optimum sprouting capacity for maximum yield

needs to be determined.

Desprouted tubers may further improve seed performance. However, this,

depends on cultivar, since different cultivars had different sprout characteristics. In

Atlantic, sprouting capacity was still increasing at 40 weeks of storage, and desprouting

did not improve sprout number.

Maximum sprouting capacity of Eben occurred at more than 40 weeks. Stem

number, tuber number and yield was the same in Eben stored for 12-40 weeks, with or

without cutting, making it a relatively easy cultivar to produce. However, the optimum

sprouting capacity needs to be explored, as it was not determined in this experiment.

Desprouting to produce more sprouts may be useful to increase stem and tuber number.

Maximum sprouting capacity of PO3 occurred at 38 weeks. PO3 stored for 40

weeks was better than 12 weeks with regard to yield. It is likely that the optimum

sprouting capacity for maximum yield occurred earlier than 40 weeks storage.

Desprouting is not recommended for old PO3 as in young seed it had no effect, but in

old seed it substantially reduced the sprout number. Cutting was useful in releasing

young seeds from apical dominance and increasing stem number. Further work is

required on this cultivar.


136

Sprouting capacity of KT3 was still increasing at 40 weeks. Storing KT3 for 40

weeks was better than 12 weeks, as young seed were still dormant. The optimum

sprouting capacity for maximum yield was not determined. Cutting 40 week-old seed

increased stem and tuber number, and yield. Desprouting was not possible due to the

small size of sprouts even at 40 weeks storage. Further work is needed on this cultivar.

References

Allen, E. J. (1979). Effects of cutting seed tubers on number of stems and tubers and tuber yields of several potato varieties. Journal of Agricultural Science, Cambridge 93, 121-128.

Allen, E. J., Bean, J. N., Griffith, R. L., and O'Brien, P. J. (1979). Effects of length of sprouting period on growth and yield of contrasting early potato varieties. Journal of Agricultural Science, Cambridge 92, 151-163.

Anonymous (2004). Information on potato production in Phillipines. In "The world geography of potatoes", Athens.

Batt, P. J. (1999). Potato production in the Red iver Delta (Vietnam). World Potato Congress, Canada.






Hay, R. K. M., and Hampson, J. (1991). Sprout and stem development from potato tubers of differing physiological age: the role of apical dominance. Field Crops Research 27, 1-16.


Jayasinghe, U. (2003). Potato seed system in Indonesia: A baseline survey. In "Progress in potato and sweet potato research in Indonesia. CIP-Indonesia research review


137

workshop, March 26-27 2002" (K. O. Fuglie, ed.), pp. 70-78. International Potato Center (CIP), Bogor, Indonesia.


Kumar, G. N. M., and Knowles, N. R. (1993). Involvement of auxin in the loss of apical dominance and plant growth potential accompanying aging of potato seed tubers. Canadian Journal of Botany 71, 541-550.

Mikitzel, L. J., and Knowles, N. R. (1989). Potato seed-tuber age affects mobilization of carbohydrate reserves during plant establishment. Annals of Botany 63, 311-320.

Mikitzel, L. J., and Knowles, N. R. (1990a). Changes in respiratory metabolism during sprouting of aged seed-potato tubers. Canadian Journal of Botany 68, 1619-1626.

Mikitzel, L. J., and Knowles, N. R. (1990b). Effect of potato seed-tuber age on plant establishment and amelioration of aged-linked effects with auxin. Plant Physiology 93, 967-975.

Quitos, R. D. L. N. (2004). Raniag: Potato variety for the lowlands. In "NEDA Knowledge Emporium". NEDA, Pasig City, Philippines.

Rastovski, A., and Van Es, A. (1987). "Storage of potato: Post harvest behaviour, store design, storage practice, handling," Pubdoc Wageningen, Wageningen.



Sukhova, L. S., Machackova, I., Eder, J., Bibik, N. D., and Korableva, N. P. (1993). Changes in the levels of free IAA and cytokinins in potato tubers during dormancy and sprouting. Biologia Plantarum 35, 387-391.

Susnoschi, M. (1981). Seed potato quality as influenced by high temperatures during the growth period. 1. Effect of storage temperature on sprout growth. Potato Research 24, 371-379.



Timm, H., Rappaport, L., Bishop, J. C., and Hoyle, B. J. (1962). Sprouting, plant growth and tuber production as affected by chemical treatment of white potato seed pieces. IV. Responses of dormant and sprouted seed potatoes to gibberellic acid. American Potato Journal 39, 107-115.

Tung, P. X. (2000). Potato production in Vietnam. International Potato Center (CIP) Bogor, Indonesia.



138

Van der Zaag, D. E., and Van Loon, C. D. (1987). Effect of physiological age on growth vigour of seed potatoes of two cultivars. 5. Review of literature and integration of some experimental results. Potato Research 30, 451-472.

Van Staden, J., and Dimalla, G. G. (1978). Endogenous cytokinin and the breaking of dormancy and apical dominance in potato tubers. Journal of Experimental Botany 29, 1077-1084.

Wurr, D. C. E. (1978). Studies of the measurement and interpretation of potato sprout growth. Journal of Agricultural Science, Cambridge 90, 335-340.

Wurr, D. C. E. (1984). Physiological age of the potato. Potato Research, 455-457.

139

Chapter 5

GENERAL DISCUSSION

Potato is usually planted using seed tubers, either as seed pieces or whole tubers.

Small tubers are required in the tropics since cutting tubers may incur disease problems,

which in turn, caused a reduction in yield. In this study, attempts were made to increase

the production of small tubers by manipulating stem number, which was done by storing

tubers for longer periods, application of GA3, cutting and desprouting treatments.

Potato production involves a complex process including sprout growth, stem

production, stolon and tuber development, and it is influenced by many factors. After

harvest, tubers are still dormant and sprouts will not grow even under favorable

conditions for sprouting, such as darkness, 20°C and 80-90% RH (Burton, 1963, 1989;

Rastovski and Van Es, 1987). Dormancy is gradually broken during storage and its

length differs with cultivar (Burton, 1989). Dormancy is considered broken when 80%

of tubers produce sprouts ≥ 3 mm after sprouting at 20°C for 2 weeks (Krijthe, 1962;

Reust, 1986). In this study, the Australian grown cultivars, Atlantic broke dormancy at

12-16 weeks, and Dawmor took longer than 16 weeks. Tropical potatoes including PO3

and Eben broke dormancy at 10 weeks, whereas KT3 was 22 weeks. It is necessary to

plant potatoes when tubers have broken dormancy, since dormant tubers take longer

from planting to emergence and they produce few stems with low yield (Struik and

Wieserma, 1999).

Chapter 5 General Discussion

140

Following breaking of dormancy, sprouts start to grow, and their behaviour is

related to storage period. Sprouting begins with a single sprout (apically dominant), then

normal multiple sprouting, multiple-branching sprouts, hairy sprouts (senility) and

finally little tuber formation (Krijthe, 1962; Struik and Wieserma, 1999). Once

dormancy is broken, sprouts also grow taller with longer storage.

The degree of apical dominance varies with cultivars and sprouting conditions.

Atlantic and PO3 seeds appeared to have weak apical dominance, while Eben and KT3

appeared to have strong apical dominance. Terminating apical dominance stimulates

lateral sprouts to grow and promotes multiple sprouting (Krijthe, 1962). Desprouting

tubers was used to reduce apical dominance in Eben seeds, while it was not effective in

Atlantic and PO3.

The length of sprouts at planting is important to minimise sprout damage for

subsequent plant growth. Planting dormant tubers without sprouts will delay sprout

emergence and result in poor plant performance and low yield. Ideal sprout length at

planting is 10 to 20 mm (Beukema and Van der Zaag, 1990). Planting tubers with

sprouts that are too long will increase damage during planting. Potato seeds stored for a

longer time produced longer sprouts. Longer sprouts emerged earlier. In practice, these

would usually be desprouted and then re-sprouted again to produce 10-20 mm sprouts.

However, cultivars had different responses to desprouting. Seed stored for a short time

needed a longer time to emerge, especially if the tuber was still dormant. Prolonged

storage stimulates sprouts to grow taller and faster so they emerge earlier. This was

probably due to increasing concentration of endogenous GA in the sprouts, as more GA


141

is transported with time in storage (Bailey et al., 1978; Suttle, 2000, 2004; Van der Plas,

1987).

The capacity of a tuber to produce sprouts changes with time. This was

expressed as percentage of sprout weight per tuber over initial tuber weight (Krijthe,

1962). The sprouting capacity was related to proportion of sprouted eyes, which is

reflected in number of sprouts per tuber, sprout length and sprout weight, and varied

across cultivars. During storage, sprouting capacity increased as more eyes sprouted,

tubers produced more sprouts and sprouts grew taller and bigger, which influenced

sprout weight. Atlantic seed produced thin and tall sprouts, while Eben sprouts grew

wider but with similar length to Atlantic. Therefore, Eben had a higher sprouting

capacity than Atlantic. On the other hand, PO3 and KT3 produced shorter sprouts than

Atlantic and Eben, and sprouting capacity of PO3 was about half of Eben and KT3 had

the lowest sprouting capacity.

The trends in sprouting capacity varied across cultivars but generally sprouting

capacity increased with prolonged storage time. PO3 seemed to reach maximum

sprouting capacity at 38 weeks, which was earlier than other cultivars, and it began to

decline at 40 weeks. However, the maximum sprouting capacity had not occurred in

other cultivars even at 40 weeks. The trends of sprouting capacity of 5 potato cultivars

suitable for tropical conditions can be estimated (Fig. 5.1). Further study is needed to

confirm when Atlantic, Dawmor, Eben and KT3 reach maximum sprouting capacity,

and when it starts to decline.


142

Atlantic, Dawmor

EbenPO3

KT3

Spro

utin

g ca

paci

ty

Time

Atlantic, Dawmor

EbenPO3

KT3

Spro

utin

g ca

paci

ty

Time

Figure 5.1. Schematic diagram of the trends in sprouting capacity (percentage sprout weight over initial tuber weight) of 5 potato cultivars suitable for tropical conditions, with prolonged storage time

Prolonged storage time increased sprout number and sprouting capacity. In

temperate potatoes increasing physiological age increases sprouting capacity and growth

vigour until it plateaus and then declines as tubers get too old (Struik and Wieserma,

1999). This is expressed by tubers are losing their capacity to develop sprouts. Sprouting

capacity is related to seed quality and influences subsequent plant growth (Struik and

Wieserma, 1999). It can be used to determine how long to store tubers to obtain

optimum or high sprouting capacity and to determine how much longer they can be

stored before sprouting capacity starts decreasing. This is critical for production, because

sprouting capacity influences subsequent plant growth and productivity (Struik and

Wieserma, 1999).


143

In the present study, sprouting capacity did not reflect the ability of seed to

produce high yield. In Atlantic, plant yield decreased when summer-autumn grown

seeds were stored for more than 16 weeks, even though sprouting capacity was still

increasing at 30 weeks of storage. Furthermore, in summer grown Atlantic seeds, 16

weeks was the optimum storage for maximum yield. This indicated that optimum

sprouting capacity of Atlantic is 16 weeks. In practice, farmers in Western Australia also

find a reduction in yield if they store Atlantic seeds for more than 16 weeks (McPharlin,

pers. comm.). However, cultivars, which had low sprouting capacity, did not necessarily

produce low yields. KT3 had the lowest sprouting capacity, but it produced similar yield

to Atlantic, Dawmor, Eben and PO3 at 16 weeks. Sprouting capacity was not useful to

compare between cultivars as has been observed before (Krijthe, 1962).

It is necessary to plant potatoes when they have optimum sprouting capacity. The

maximum sprouting capacity of Atlantic, KT3 and Eben was more than 40 weeks

storage, while PO3 was 38 weeks. However, the optimum sprouting capacities of

tropical potatoes were not defined in the present study. Therefore, further study is

required to explore the optimum sprouting capacity of tropical potatoes, since cultivars

have different trends in sprouting capacity (Krijthe, 1962). In Atlantic, optimum

sprouting capacity of summer-autumn grown seed occurred 10 weeks earlier than

summer grown seed. So the growing conditions of mother plant for seed also influenced

timing of the optimum sprouting capacity.

In addition to storage time, desprouting of tubers influenced sprout behaviour.

Desprouting tubers influenced the number of sprouts, but this varied across cultivars.

Desprouting tubers did not affect sprout number of Atlantic seeds stored for 10-40


144

weeks. However, sprouts from desprouted Atlantic, Eben and PO3 seeds stored for > 38-

40 weeks grew shorter than undesprouted seed. This was probably because older seeds

lose vigour as less carbohydrate and nitrogen are transported from mother tuber to

growing sprouts (Mikitzel and Knowles, 1989). Moreover, desprouting tubers was useful

to increase stem number of tubers with apical dominance as it reduced apical dominance

and stimulated multiple sprouting in Eben. Desprouting tubers did not further increase

sprout number of tubers where apical dominance had been broken by prolonging storage

time, such as in Atlantic and PO3.

Production of stems aboveground was determined by how many sprouts

developed into stems and how many stems branched (Haverkort et al., 1990; Moorby,

1967; Struik et al., 1990). Potato eyes consist of at least three sprouts (Artschwager,

1924), and not all sprouts from those eyes develop into stems (Haverkort et al., 1990).

There are several possibilities of how sprouts influence stem number. Firstly, sprout

number may not increase but aboveground stem number increases. This might happen in

apically dominant tubers. Single stems from tubers with apical dominance may branch

(Struik and Wieserma, 1999). Secondly, increasing sprout number may not increase

stem number. This might happen in tubers with normal multiple sprouts, when not all

sprouts emerge as stems. The third possibility is that increasing sprout number increases

stem number. This might occur in tubers with multiple branches sprouts, when most

sprouts grow into stems or additionally when stems branch (Struik and Wieserma,

1999).

Tuber production can be determined by controlling stem number, and this relates

to the number of sprouts that develop into stems (Struik and Wieserma, 1999).


145

Manipulation of stem number increases the production of small tubers in many

temperate varieties, such as Russet Burbank (Iritani et al., 1983), Désirée and Jaerla

(Boadlaender and Marinus, 1987). Four treatments were used in the present study to

increase stem number. Desprouting tubers might be used to increase number of sprouts

and increase stem number. Other treatments are storage time, application GA3 and

cutting seeds. These treatments could be used to increase above ground stem number of

tubers with no or reduced apical dominance including Atlantic, Dawmor and PO3. In

tubers with strong apical dominance, such as Eben and KT3, those treatments did not

affect stem number. Tubers with apical dominance generally produce fewer stems (Allen

and Wurr, 1992b; Hay and Hampson, 1991).

Increasing stem number of Atlantic, KT3 and PO3 by prolonging storage time

was not always followed by increasing number of stolons per plant. Stem type

determines stolon production, as stolons usually grow from the main stem or branching

stems near the mother tuber (Struik et al., 1990). In Dawmor, increasing stem number

was followed by increasing stolon number. While in Eben, length of storage time did not

affect stem or overall stolon production. This was because seeds stored for a longer time

produced a similar stem number and they produced the same number of stolons per

plant.

Stolon growth influences the potential number of tubers that could be developed.

Tubers can grow from the tips of primary stolons or branching stolons (Helder et al.,

1993). Therefore, increasing stolon number or stimulating branching in stolons may

increase tuber sites and tuber number. In the present study, prolonged storage time did

not affect stolon number per plant of Atlantic, Eben, KT3 and PO3. Length of storage


146

time increased stolon number per plant of Dawmor, but stolons from old seed did not

branch. Therefore, 16 week-old Dawmor seeds had a similar number of tuber initiation

sites as 26 week-old seeds.

Branching of stolons increased tuber sites so that it potentially increased tuber

number. Physiological age influences plant growth from seed that in turn, affects stolon

growth. Older seeds generally emerge earlier and they tuberise earlier (Struik and

Wieserma, 1999). This reduced the length of stolons. Furthermore, whilst stolons from

young seed branched, extending storage time did not stimulate stolons to branch.

Environmental conditions also affect stolon production. High temperature (32°C) and

long days increase stolon number whereas cool and short days reduce stolons (Menzel,

1980). Branching of stolons is more likely to occur from stolons at the lower nodes near

to the mother tuber (Struik and Ewing, 1995). They are promoted by high temperature

(until a certain point), long photoperiod and low stem density (Struik et al., 1990). Old

Dawmor, Eben, KT3 and PO3 were grown during summer in Western Australia with

high temperature (17-32°C) and long days (14 h). These conditions did not favour stolon

development or stolons branching in the cultivars tested.

Planting older Atlantic seeds did not increase tuber number, as stolon number

was not affected. However, there were big reductions in tuber number of Dawmor, Eben,

KT3 and PO3 with extended storage from 16 to 26 weeks. This was probably because

plants from older seeds were grown during summer when temperatures and light

intensity were high and they were exposed to long days. A combination of high

temperature and long photoperiod increases respiration rate, stimulates shoot growth and

reduces transport of assimilates from shoots to tubers (Bodlaender, 1963; Gregory, 1965;


147

Menzel, 1980) and so it inhibits tuber formation. These cultivars grow well under

tropical conditions, which usually includes high temperature and high light intensity, but

perhaps they are not suited to the longer day light length (13-14 h) experienced in Perth,

compared to the tropics (12-12.5 h).

Tuber production, including seed size distribution influences yield. Atlantic

seeds produced high yield when it was stored for 16 weeks when tubers had optimum

sprouting capacity, whereas planting older seeds reduced yield, as they produced more

small tubers. Atlantic seeds stored for more than 20 weeks doubled the proportion of

small tubers, especially tubers < 5 g and 5-19 g, leading to a reduction in yield.

Atlantic seeds stored for 16 weeks then treated with GA3 increased tuber

production by 60% compare to untreated seeds. The size of big tubers (> 64g) was

reduced to less than half and the proportion of small tubers size of < 5, 5-19, 20-34 and

35-49 g doubled. Therefore, increasing tuber number alone did not affect yield of 16

week-old Atlantic.

Yield of Dawmor, Eben, KT3 and PO3 stored for 26 weeks was lower than 16

week-old tubers. This reduction was possibly due to the physiological aging of these

seeds or environmental conditions (temperature and light). Older Atlantic produced

more stolons but tubers did not form in all of them, and these were grown under tropical

conditions for potato production. In the present study, old Dawmor, Ebe, KT3 and PO3

were grown under high night temperature (19-23 °C) which was not suitable for tuber

induction, so that not all stolons tuberised in these cultivars (Dawmor, Eben, KT3 and

PO3), but a greater proportion than Atlantic remained without tubers. This may have

been due to the age of the seed or due to the warmer temperature and long day length.


148

Optimum temperature for tuber induction is 10-17°C night temperature (O'Brien et al.,

1998). In addition, fewer stolons were produced so together these factors reduced tuber

number and yield.

Therefore, the effect of storage time on yield and tuber size distribution was not

confirmed. Furthermore, application of GA3 did not increase the proportion of smaller

tubers in tropical cultivars, although it increased tuber number of 16 week-old Eben.

Further study is needed on applying GA3 at different concentrations to different

physiologically aged seed.

Western Australia has advance seed production technologies as well as good

storage facilities, compared to tropical countries. This benefits maintenance of seed

quality during production, harvest and storage. Seed stored in cold temperatures also

lose less tuber weight during sprouting. In the present study, prolonging storage of

Atlantic, Eben, KT3 and PO3 at 4°C for 10-40 weeks increased tuber weight loss up to

9-10% after 4 weeks sprouting at 20°C. This was much lower than in tropical countries,

where farmers stored seed potatoes under diffuse light storage at 20-30°C for 36-40

weeks. Under these storage conditions in Vietnam, potato seeds degrade rapidly and

tuber weight loss is high. This causes a reduction in seed quality and when planted in the

field they produce low yield. In order to slow seed degradation, KT3 can be stored in

dark-cold storage for a longer period of time. KT3 seeds stored for ≥ 26 weeks at 4°C

had broken dormancy and produced multiple sprouting and tuber weight loss remained

low (less than 10%). In the Philippines, Eben and PO3 are stored at about 30°C, under

diffuse light for about 32 weeks. Eben and PO3 were selected for lowland areas and

withstand hot humid climates. Under these storage conditions, tuber weight loss is about


149

32% and tubers produce sturdy sprouts (Quitos, 2004). Eben and PO3 stored under dark-

cold (4°C) storage had little tuber weight loss (9%) and their sprouting capacity was still

increasing after 38-40 weeks in storage. Old seeds (40 weeks) produced the same or

higher yield than young seeds (12 weeks). This indicated that dark-cold room storage is

suitable for storing Eben and PO3 seeds for longer period, at least until 40 weeks and

seed quality can be maintained without reducing yield.

Gibberellic acid influenced sprout behaviour and plant growth, but responses to

applied GA3 depended on cultivar and physiological status of the tuber. Gibberellic acid

can be applied in different ways. GA3 sprayed on foliage increases plant height,

stimulates stolon length, delays tuberisation and sometimes causes tuber malformation

(Dyson, 1965; Holmes et al., 1970). Spraying tubers with GA3 during storage also

enhances breaking of dormancy and stimulates sprout growth (Couillerot, 1993; Marinus

and Boadlaender, 1978). Similarly, dipping potatoes in GA3 before planting usually

accelerates emergence, stimulates stem elongation, increases stem number, increases

tuber number without reducing yield (Arpiwi, 2003; Dyson, 1965; Holmes et al., 1970).

Here, application of GA3 accelerated emergence and increased stem number. However,

its effects on subsequent growth varied across cultivars. Dipping tubers in GA3 did not

consistently increase stem number, stolon number or tuber number. GA3 increased

number of above ground stems in Atlantic, Dawmor and PO3, but number of stolons per

plant was not affected. Stem and stolon number of KT3 were not affected by application

of GA3 while in Eben, GA3 increased production of stolons although stem number was

not affected. Moreover, GA3 applied on young and old Eben seeds increased tuber

number as stolons and stolon branching increased. In old Dawmor, GA3 stimulated


150

stolons to branch, so that tuber number increased, even though stolon number was not

affected. There were two possibilities of how GA3 influenced stem, stolon and tuber

production (Figure 5.2). Firstly, GA3 increased the number of stems or stems which

branched well below the soil surface and therefore increased the number of aboveground

stems. Mostly stolons grow from a main stem or branching stems near the mother tuber

(Struik et al., 1990). In this case, tuber number was increased because the number of

stolons was increased. Secondly, GA3 did not affect stem number or stimulated stems to

branch just below soil the soil surface, so that aboveground stem number increased. In

this case, tuber number may not be affected, because if stems branch just below the soil

surface or far from the mother tuber, they will not produce more stolons (Struik et al.,

1990).

Few works have been reported on the effects of GA3 on branching of stolons.

Gibberellic acid stimulated stolons to branch in Atlantic and Eben and it increased the

number of sites for tuberisation. As a result, tuber number increased even though stem

number was not affected. Gibberellic acid did not stimulate branching in stolons of

young Dawmor, KT3 and PO3. Their number of tuberisation sites was not affected and

so neither was tuber number. This suggests that increasing branching of stolons by

application of GA3 plays an important role in some cultivars, in addition to increasing

stolon number but it is not a universal response.

Usually, applied GA3 shifts tubers into smaller size categories so that it increases

the proportion and number of small tubers. It is expected that application of GA3 at the

appropriate concentration has no carry over effects in progeny tubers. Seeds for the

parent crop dipped in GA3 should produce normal seeds for a subsequent crop. Atlantic


151

and Granola seeds dipped in 20 mg L-1 GA3 had some carry over effects, which has not

been previously reported. Progeny tubers from plants using GA3-treated seeds had fewer

sprouts and shorter sprout length than untreated seeds, but sprouting capacity was not

affected. However, these effects were short lived and they did not influence subsequent

plant growth from 7 weeks after planting. Therefore, it is estimated that yield and tuber

size of progeny seeds would not be affected.

Cutting can also be used to manipulate growth. Big seed can be cut, in order to

increase propagule numbers, stimulate the breaking of dormancy, stimulate sprout

growth and increase stem number (Beukema and Van der Zaag, 1990; Struik and

Wieserma, 1999). A cutting treatment is useful for tubers with apical dominance, as it

can release buds from the influence of the apical bud and increase stem number (Struik

and Wieserma, 1999). Cutting seed pieces stimulates emergence and produces a higher

yield than whole tubers (Iritani, 1968). However, cutting seeds may facilitate the spread

of diseases and cause seed decay (Struik and Wieserma, 1999), and in the tropics it

substantially reduces yield. Cutting of young KT3 and PO3 which were still dormant,

increased stem number and yield compared with whole young tubers. In KT3 this was

due to a release from dormancy, which hastened emergence and plants outgrew the

potential infection from rots (Beukema and Van der Zaag, 1990). In PO3 it increased

emergence and stem number and hence tuber number. However, cutting treatment did

not affect stem number or yield of Eben. This was probably because Eben still had the

apical dominance effect.

Figure 5.2. Hypotetical scheme of the effects of GA3 on the development of sprouts into stems from tubers with different age. (a) Tuber with dominance; (b) Tuber with normal multiple sprouting (more eyes produced sprouts); (c) Tuber multiple branching sprouts (more sprouts/eye)

(a) (b) (c)

Figure 5.2. Hypotetical scheme of the effects of GA3 on the development of sprouts into stems from tubers with different age. (a) Tuber with dominance; (b) Tuber with normal multiple sprouting (more eyes produced sprouts); (c) Tuber multiple branching sprouts (more sprouts/eye)

(a) (b) (c)(a) (b) (c)

152


153

Conclusion

The Australian and tropical potatoes performed very differently. This project

provides some information on how to produce small size potato tubers without affecting

yield. This will benefit seed growers and potato industries in Western Australia to fulfil

the Asian potato seed market.

Improving plant performance of young tubers of KT3 and PO3 can be achieved

by a cutting treatment. However, cutting seeds needs to be done carefully since without

appropriate treatments, it may promote spread of diseases, which may decrease yield.

To produce high yield, potato seed can be stored at 4 °C until it breaks dormancy

and produces optimum sprouting capacity. In Atlantic optimum sprouting capacity was

at 16 weeks (summer-autumn grown seed) and 26 weeks (summer grown seed) storage.

Increasing small tuber number without reducing yield in Atlantic was achieved by

applying 20 mg L-1 GA3 and carry over effects were insignificant. In the other cultivars

the time required in storage to break dormancy was determined and this is critical for

emergence in the field. Dormancy was broken by 10 weeks in PO3 and Eben, and in 22

weeks in KT3. The time to maximum sprouting capacity was estimated and it was 38

weeks in PO3 and more than 40 weeks in Atlantic, Eben, and KT3. However, this was

not storage duration for optimum sprouting capacity for maximum yield. This might be

further complicated by environmental effects on the mother seed. This requires further

investigation with paired studies of sprouting capacity and field production.

Application of GA3 increased stem and tuber number in Atlantic. However,

further study needs to be done to investigate effects of GA3 in Dawmor, KT3 and PO3 at

the optimum sprouting capacity. The application of different concentrations of GA3 on


154

tropical potatoes needs to be explored, because these cultivars had very different

responses to many temperate varieties.

References

155

References

Abdala, G., Castro, G., Miersch, O., and Pearce, D. (2002). Changes in jasmonate and gibberellin levels during development of potato plants (Solanum tuberosum). Plant Growth Regulation 36, 121-126.

Allen, E. J. (1979). Effects of cutting seed tubers on number of stems and tubers and tuber yields of several potato varieties. Journal of Agricultural Science, Cambridge 93, 121-128.

Allen, E. J., Bean, J. N., Griffith, R. L., and O'Brien, P. J. (1979). Effects of length of sprouting period on growth and yield of contrasting early potato varieties. Journal of Agricultural Science, Cambridge 92, 151-163.

Allen, E. J., and Wurr, D. C. E. (1992a). Plant density. In "The Potato Crop" (P. Harris, ed.), pp. 292-333. Chapman & Hall, London.

Allen, E. J., and Wurr, D. C. E. (1992b). Plant Density. In "The potato crop:The scientific basic for improvement" (P. Harris, ed.). Chapman & Hall, London.

Anonymous (2001). "Western Australian certified seed potato scheme (incorporating National standards)," AGWEST Plant Laboratories, Perth.

Anonymous (2003a). Atlantic. University of Idaho, Idaho. http://wwwinfo.ag.uidaho.edu/Resources/PDFs/PNW0454.pdf. [257/5/2003]

Anonymous (2003b). "Increasing the capacity of the food crops research institute to enhance the production and management of potatoes in the Red River Delta 'Technical Report'." Department of Agriculture, Western Australia, Perth.

Anonymous (2003c). "Increasing the capacity of the food crops research institute to enhance the production and management of potatoes in the Red River Delta. 'Technical Report'." Department of Agriculture Western Australia, Perth.

Anonymous (2004a). Information on potato production in Phillipines. In "The world geography of potatoes", Athens.

Anonymous (2004b). Our Growing Business. In "The official Newsletter of the Potato Marketing Corporation of WA", Vol. 2004. Western Potatoes, South Fremantle.

Anonymous (2004c). "Potato Marketing Corporation of Western Australia. Annual Report 2004," Western Potatoes, Fremantle.

Anonymous (2005). Varieties: Which potato to use. Western Potatoes, Fremantle. Arpiwi, N. L. (2003). The application of novel methods for increasing the yield of small

round seed potatoes (Solanum tuberosum L.) cv. Atlantic and Granola. M.Sc. thesis at The University of Western Australia, Perth.

Artschwager, E. (1924). Studies on the potato tuber. Journal of Agricultural Research 27, 809-835.

Bailey, K. M., Phillips, I. D. J., and Pitt, D. (1978). The role of buds and gibberellin in dormancy and the mobilization of reserve materials in potato tubers. Annals of Botany 42, 649-657.

Basuki, R. S., Kusmana, Dimyati, A., Hartuti, N., Sofiari, E., and Jayasinghe, U. (2003). Evaluation of processing potato clones in Indonesia. In "Progress in potato and sweet potato research in Indonesia. CIP-Indonesia Research Review Workshop, March 26-27 2002" (K. O. Fuglie, ed.), pp. 44-60. International Potato Center


156

(CIP), Bogor, Indonesia. http://www.eseap.cipotato.org/AboutUs0204/Publications.htm [17/8/2004]

Batt, P. J. (1998). The demand for seed potatoes in South East Asia. In "Australian Agribusiness Review", Vol. 6.

Batt, P. J. (1999a). An alternative seed system for Asia: seed potato export from Western Australia. World Potato Congress, Canada. http://www.potatocongress.org/sub.cfm?source=135

Batt, P. J. (1999b). Potato production in the Red iver Delta (Vietnam). World Potato Congress, Canada. http://www.potatocongress.org/sub.cfm?source=137


Bishop, J. C., and Timm, H. (1968). Comparative influence of gibberellic acid and of plant population on distribution of potato tuber size. American Potato Journal 45, 182 - 187.

Bleasdale, J. K. A. (1965). Relationships between set characters and yield in maincrop potatoes. Journal of Agricultural Science 64, 361-366.

Boadlaender, K. B. A., and Marinus, J. (1987). Effect of physiological age on growth vigour of seed potatoes of two cultivars. 3. Effect on plant growth under controlled conditions. Potato Research 30, 423-440.

Bodlaendar, K. B. A., and Van de Waart, M. (1989). Influences of gibberellic acid (GA3) applied to the crop on growth, yield and tuber size distribution of seed potatoes. Netherlands Journal of Agricultural Science 37, 185-196.

Bodlaender, K. B. A. (1963). Influence of temperature, radiation and photoperiod on development and yield. In "The growth of potato" (J. D. Ivins and F. L. Milthorpe, eds.), pp. 199-210. Butterworths, London.

Booth, A. (1963). The role of growth substances in the development of stolons. In "The growth of the potato" (J. D. Ivins and F. L. Milthorpe, eds.), pp. 99-113. Butterworths, London.

Burton, W. G. (1963). Concept and mechanism of dormancy. In "The growth of potato" (M. F. Ivins JD, ed.), pp. 17-41. Butterworths, London.


Caldiz, D. O. (1996). Seed potato (Solanum tuberosum L.) yield and tuber number increase after foliar applications of cytokinins and gibberellic acid under field and glasshouse conditions. Plant Growth Regulation 20, 185-188.

Caldiz, D. O., Fernandez, L. V., and Struik, P., C (2001). Physiological age index: a new, simple and reliable index to assess the physiological age of seed potato tubers based on haulm killing date and length of the incubation period. Field Crop Research 69, 69-79.

Carnegie, S. (2001a). Cultivar: Atlantic. In "European cultivated potato database: Cultivars and breeding lines" (E. G. P. W. Group, ed.). Scottish Agricultural Science Agency, Edinburgh. http://www.ecpgr.cgiar.org/database/crops/potato_cutt.htm [18/4/2003]

Carnegie, S. (2001b). Cultivar: Granola. In "European cultivated potato database: Cultivars and breeding lines" (E. G. P. W. Group, ed.). Scottish Agricultural


157

Science Agency, Edinburgh. http://www.ecpgr.cgiar.org/database/crops/potato_cutt.htm [18/4/2003]

Cenzano, A., Vigliocco, A., Kraus, T., and Abdala, G. (2003). Exogenous applied jasmonic acid induces changes in apical meristem morphology of potato stolons. Annals of Botany 91, 915-919.

Chapman, H. W. (1958). Tuberization in the potato plant. Physiologia Plantarum 11, 215-224.

Cline, M. G. (1997). Concept and terminology of apical dominance. American Journal of Botany 84, 1064-1069.

Cline, M. G., Wessel, T., and Iwamura, H. (1997). Cytokinin/auxin control of apical dominance in Ipomoa nil. Plant Cell Physiology 38, 659-667.


Coleman, W. K., and McInerney, J. (1997). Enhanced dormancy release and emergence from potato tubers after exposure to a controlled atmosphere. American Potato Journal 74, 173-182.

Couilerot, J. P. (1993). Effects and distribution of 14C-gibberellic acid after application to stored potato microtuber. Phyton 54, 67-73.

Crozier, A., and Reid, D. M. (1971). Do roots synthesize gibberellins? Canadian Journal of Botany 49, 967-975.

Cutter, E. G. (1992). Structure and development of the potato plant. In "The Potato Crop. The scientific basis for improvement" (P. Harris, M, ed.). Chapman and Hall, London.

Davis, G., Kobayashi, M., Phinney, B. O., Lange, T., Crocker, S. J., Gaskin, P., and MacMilan, J. (1999). Gibberellin biosynthesis in Maize. Metabolic studies with GA15, GA24, GA25, GA7 and 2,3-Dehydro-GA9. Plant physiology 121, 1037-1045.

Dawson, P. (2004). "Western Australia agri-food and fiber industry outlook," Department of Agriculture Western Australia, South Perth.

Dawson, P., McPharlin, I., and Dharmadi, B. (2004). "A partnership to build Indonesian crisping potato capacity and Australian seed potato sales." Department of Agriculture Western Australia, Perth.

Dawson, P., McPharlin, I., and Howes, M. (2003). Potatoes: Table & seed potatoes from Western Australia at a glance.

Dawson, P., and Mortimore, J. (2002). Dawmor - A new summer export crisp potato variety for Manjimup. In "Department of Agriculture: Farmnote No. 66". Department of Agriculture Western Australia, Perth.

Dawson, P., and Mortimore, J. (2004). Quantum leaps through genetic revolution. SARDI, Adelaide. http://www.sardi.sa.gov.au/pages/horticulture/pathology/hort_pn_quantum.htm:sectI...

Dimalla, G. G., and Van Staden, J. (1977). Apical dominance and the utilization of carbohydrates during storage of potato tubers. Annals of Botany 41, 387-391.

Dimyati, A. (2003). Research priorities for potato in Indonesia. In "Progress in potato and sweet potato research in Indonesia. CIP-Indonesia Research Review


158

Workshop, March 26-27 2002" (K. O. Fuglie, ed.), pp. 15-19. International Potato Center (CIP), Bogor, Indonesia.

Dowling, B. (1995). Developing advanced seed potato technology: the case of Technico Pty Ltd. In "Australian Agribusiness Review", Vol. 3.

Dyson, P. W. (1965). Effect of gibberellic acid and chlorocholine chloride on potato growth and development. Journal of Science Food Agriculture 16, 542 - 549.


Engels, C. H., and Marschner, H. (1986). Allocation of photosynthate to individual tubers of Solanum tuberosum L. Journal of Experimental Botany 37, 1813-1822.

Escalante, B. Z., and Langille, A. R. (1998). Photoperiod, temperature, gibberellin and anti-gibberellib affect tuberization of potato stem segments in vitro. HortScience 33, 701-703.

Ewing, E. E. (1990). Induction of tuberization in potato. In "The molecular and cellular biology of the potato" (M. E. Vayda, ed.), pp. 25-41. C.A.B International, Texas.

Fosket (1994). "Plant growth and development: A molecular approach," Academic Press, California.

Fuglie, K. O., Suherman, R., and Adiyoga, W. (2003). The demand for fresh and processed potato in Southeast Asia. In "Progress in potato and sweet potato research in Indonesia. CIP-Indonesia Research Review Workshop, March 26-27 2002" (K. O. Fuglie, ed.), pp. 111-123. International Potato Center (CIP), Bogor, Indonesia.

Gregory, L. E. (1956). Some factors for tuberization in the potato plant. American Journal of Botany 43, 281-288.

Gregory, L. E. (1965). Physiology of tuberization in plants (tubers and tuberous roots). Handbuch der Pftanzen physiologie XV, 1328-1354.

Hajirezaei, M. R., Frederik, B., Martin, P., Yasuhiro, T., Jens, L., Ara, K., and S, U. (2003). Decrease sucrose content triggers starch breakdown and respiration in storage potato tubers (Solanum tuberosum). Journal of Experimental Botany 54, 477-488.


Haverkort, J. A., Van de Waart, M., and Bodlaendar, K. B. A. (1990). Interrelationships of the number of initial sprouts, stems, stolons and tubers per potato plant. Potato Research 33, 269-274.

Hawkes, J. G. (1990). "The Potato: Evolution, biodiversity and genetic resource," Belhaven Press, London.

Hay, R. K. M., and Hampson, J. (1991). Sprout and stem development from potato tubers of differing physiological age: the role of apical dominance. Field Crops Research 27, 1-16.

Hedden, P., and Kamiya, Y. (1997). Gibberellin biosynthesis: Enzymes, genes and their regulation. Annual Review of Plant Physiology and Plant Molecular Biology 48, 431-460.


159

Hedden, P., Phillips, A. L., Rojas, M. C., Carrera, E., and Tudzynski, B. (2002). Gibberellin biosynthesis in plants and fungi: A case of convergent evolution? Journal of Plant Growth Regulation 20, 319-331.

Helder, H., Van der Maarl, A., Vreugdenhil, D., and Struik, P., C (1993). Stolon characteristics and tuber initiation in a wild potato species (Solanum demissum Lindl.). Potato Research 36, 317-326.

Hertog, M. L. A. T. M., Tijskens, L. M. M., and Hak, P. S. (1997). The effects of temperature and senescence on the accumulation of reducing sugar during storage of potato (Solanum tuberosum L.) tubers: A mathematical model. Postharvest Biology and Technology 10, 67-79.

Holmes, J. C., Lang, R. W., and Singh, A. K. (1970). The effect of five growth regulators on apical dominance in potato seed tubers and on subsequent tuber production. Potato Research 13, 342 - 352.

Iritani, W. M. (1968). Factor affecting physiological aging (degeneration) of potato tubers used as seed. American Potato Journal 45, 111-116.

Iritani, W. M., and Spark, W. C. (1985). Potatoes: storage and quality maintenance in the Pacific Northwest. In "A Pacific Northwest Extension Publication", pp. 12 p, Washington.

Iritani, W. M., and Weller, D. L. (1987). The influence of physiological age, stem numbers and fertility on yield and grade of Russet Burbank potatoes. American Potato Journal 64, 291-299.


Ittersum, M. K., Scholte, K., and Warshavsky, S. (1993). Advancing growth vigor of seed potatoes by haulm application of gibberellic acid and storage temperature regimes. American Potato Journal 70, 21-34.

Jayasinghe, U. (2003). Potato seed system in Indonesia: A baseline survey. In "Progress in potato and sweet potato research in Indonesia. CIP-Indonesia research review workshop, March 26-27 2002" (K. O. Fuglie, ed.), pp. 70-78. International Potato Center (CIP), Bogor, Indonesia.

Kawakami, K. (1963). Age of potato seed tubers affects growth and yield. American Potato Journal 40, 25-29.

Knowles, N. R. (1987). Mobilization of seedpiece nitrogen during plant growth from aged potato (Solanum tuberosum L.) seed-tubers. Annals of Botany 59, 359-367.

Knowles, N. R., and Bontar, G. I. (1991). Modelling the effects of potato seed tuber age on plant establishment. Canadian Journal of Plant Science 71, 1219-1232.


Kumar, D., and Wareing, P. F. (1972). Factor controling stolon development in the potato plant. New Phytol 71, 639-648.

Kumar, D., and Wareing, P. F. (1974). Studies on tuberization of Solanum indigena. II. Growth hormones and tuberization. New Phytol 73, 833-840.

Kumar, G. N. M., and Knowles, N. R. (1993a). Age potato seed-tubers influences protein synthesis during sprouting. Physiologia Plantarum 89, 262-270.


160

Kumar, G. N. M., and Knowles, N. R. (1993b). Involvement of auxin in the loss of apical dominance and plant growth potential accompanying aging of potato seed tubers. Canadian Journal of Botany 71, 541-550.

Kumar, G. N. M., and Knowles, N. R. (1996). Nature of enhanced respiration during sprouting of aged potato seed-tubers. Physiologia Plantarum 97, 228-236.

Learmonth, S., and Dawson, P. (2004). Potato Growing in Western Australia. In "Western Potatoes", Vol. 2004. Western Potatoes, Fremantle.

Love, S. L., Baker, T. P., Ojala, J. C., Pavek, J. J., and Corsini, D. L. (1993). Atlantic. In "Characteristic of Potato Varieties in the Pacific Northwest". A Pacific Northwest Extension Publication, Idaho.

Lovell, P. H., and Booth, A. (1967). Effect of gibberellic acid on growth, tuber formation and carbohydrate distribution in Solanum tuberosum. New Phytol 66, 525-537.

Lovell, P. H., and Booth, A. (1969). Stolon initiation and development in Solanum tuberosum L. New Phytologist 68, 1175-1185.

Marinus, J., and Boadlaender, K. B. A. (1978). Growth and yield of seed potatoes after application of gibberellic acid to the tubers before planting. Netherland Journal of Agricultural Science 26, 354 - 365.

Marinus, J., and Bodlaendar, K. B. A. (1978). Growth and yield of seed potatoes after application of gibberellic acid to the tubers before planting. Netherlands Journal of Agricultural Science 26, 354-365.

Marschner, H., Sattelmacher, B., and Bangerth, F. (1984). Growth rate of potato tubers and endogenous contents of indole acetic acid and abscisic acid. Physiologia Plantarum 60, 16-20.

Menzel, C. M. (1980). Tuberization in potato at high temperatures: responses to gibberellin and growth inhibitor. Annals of Botany 46, 259-265.

Menzel, C. M. (1983). Tuberization in potato at high temperatures: Gibberellin content and transport from buds. Annals of Botany 52, 697-702.

Michener, H. D. (1942). Dormancy and apical dominance of potato tubers. American Journal of Botany 20, 558-568.

Mikitzel, L. J., and Knowles, N. R. (1989). Potato seed-tuber age affects mobilization of carbohydrate reserves during plant establishment. Annals of Botany 63, 311-320.

Mikitzel, L. J., and Knowles, N. R. (1990a). Changes in respiratory metabolism during sprouting of aged seed-potato tubers. Canadian Journal of Botany 68, 1619-1626.

Mikitzel, L. J., and Knowles, N. R. (1990b). Effect of potato seed-tuber age on plant establishment and amelioration of aged-linked effects with auxin. Plant Physiology 93, 967-975.

Moorby, J. (1967). Inter-stem and inter-tuber competition in potatoes. European Potato Journal 10, 189-205.

Moore (1989). "Biochemistry and physiology of plant hormones," second/Ed. Spinger-Verlag, New York.

O'Brien, P. J., Allen, E. J., and Firman, D. M. (1998). A review of some studies into tuber initiation in potato (Solanum tuberosum) crops. Journal of Agricultural Science, Cambridge 130, 251-270.


161

Pasqual, G., McPharlin, I., and Dawson, P. (1999). Potatoes in Western Australia at a glance. Vol. 2003. Department of Agriculture - Western Australia.

Pavlista, A. D. (2003). Atlantic: Characteristics. University of Nebraska, Nebraska. Perez, J. C. (2001). Revisiting lowland potato production. In "Upward Fieldnote", Vol.

10, pp. 27-29. Phinney, B. O. (1985). Gibberellin A1 dwarfism and shoot elongation in higher plant.

Biologia Plantarum 27, 172-179. Plaisted, P. H. (1957). Growth of the potato tuber. Plant Physiology 32, 445-452. Pushkarnath (1976). "Potato in Sub-tropics," Orient Longman, New Delhi. Quitos, R. D. L. N. (2004). Raniag: Potato variety for the lowlands. In "NEDA

Knowledge Emporium". NEDA, Pasig City, Philippines. Rappaport, L., Flippert, L. F., and Timm, H. (1957a). Sprouting, plant growth and tuber

production as affected by chemical treatment of white potato seed pieces: Breaking the rest period with gibberellic acid. American Potato Journal 34, 254-260.

Rappaport, L., Goldschmidt, S. B., Clegg, M. D., and Smith, O. E. (1965). Regulation of bud rest in tubers of potato Solanum tuberosum L. I. Effect of growth substances on excised potato buds. Plant and Cell Physiology 6, 587-599.

Rappaport, L., Lippert, L. F., and Timm, H. (1957b). Sprouting, plant growth and tuber production as affected by chemical treatment of white potato seed pieces. American Potato Journal 34, 254-260.

Rastovski, A., and Van Es, A. (1987). "Storage of potato: Post harvest behaviour, store design, storage practice, handling," Pubdoc Wageningen, Wageningen.


Reust, W., and Aerny, J. (1985). Determination of physiological age of potato tuber with using sucrose, citric acid and maleic acid as indicator. Potato Research 28, 251-261.

Reust, W., Winiger, F. A., Hebeisen, T., and Dutoit, J. P. (2001). Assessment of the physiological vigour of new potato cultivars in Switzerland. Potato Research 44, 11-17.

Rhoades, R. E., Hijmans, R. J., and Huaccho, L. (2002a). World Potato Atlas: Indonesia. Rhoades, R. E., Hijmans, R. J., and Huaccho, L. (2002b). World Potato Atlas: Vietnam.

International Potato Center (CIP), Peru, Lima. Roettger, D. J. (1987). "Seed potato production in the Philippines. In vitro culture and

rapid multiplication techniques," GTZ, Eschborn, Germany. Salunkhe, D. K., and Kadam, S. S. (1991). Introduction. In "Potato: Production,

Processing and Product" (K. S. Salunkhe DK, Jadhav SJ, ed.), pp. 1-7. CRC Press, Boca Raton.

Samadi, B. (1998). "Usaha tani kentang," Penerbit Kanisius, Yogyakarta. Slater, J. W. (1963). Mechanism of tuber initiation. In "The growth of the potato" (J. D.

Ivins and F. L. Milthorpe, eds.), pp. 114-120. Butterworths, London. Smith, O. (1968). "Potatoes: Producing, Storing, Processing," The AVI Publishing,

Westport.


162

Sonnewald, U. (2001). Control of potato tuber sprouting. Trends in Plant Science 6, 333-335.

Sorce, C., Lorenzi, R., Ceccarelli, N., and Renalli, P. (2000). Changes in free and conjugated IAA during dormancy and sprouting of potato tubers. Australian Journal of Plant Physiology 27, 371-377.

Struik, P., C, Haverkort, J. A., Vreugdenhil, D., Bus, C. B., and Dankert, R. (1990). Manipulation of tuber size distribution of a potato crop. Potato Research 33, 417-432.

Struik, P. C., and Ewing, E. E. (1995). Crop physiology of potato (Solanum tuberosum): responses to photoperiod and temperature relevant to crop modelling. In "Potato Ecology and modelling of crops under conditions limiting growth" (A. J. Haverkort and D. K. L. MacKerron, eds.), pp. 19-40. Kluwer Academic Publisher, Dordrecht, Netherlands.


Sukhova, L. S., Machackova, I., Eder, J., Bibik, N. D., and Korableva, N. P. (1993). Changes in the levels of free IAA and cytokinins in potato tubers during dormancy and sprouting. Biologia Plantarum 35, 387-391.

Susnoschi, M. (1981a). Seed potato quality as influenced by high temperatures during the growth period. 1. Effect of storage temperature on sprout growth. Potato Research 24, 371-379.

Susnoschi, M. (1981b). Seed potato quality as influenced by high temperatures during the growth period. 2. Sprouting pattern in several cultivars in response to storage temperature. Potato Research 24, 381-388.

Suttle, J. C. (1995). Postharvest changes in endogenous ABA levels and ABA metabolism in relation to dormancy in potato tubers. Physiologia Plantarum 95, 233-240.

Suttle, J. C. (1998). Postharvest changes in endogenous cytokinins and cytokinin efficacy in potato tubers in relation to bud endodormancy. Physiologia Plantarum 103, 59-69.

Suttle, J. C. (2000). The role of endogenous hormones in potato tuber dormancy. In "Dormancy in plants: from whole plant behaviour to cellular control" (J. D. Viemont and J. Crabbe, eds.). CABI Publishing, Cambridge.


Takashi, K., RFujino, K., Kikuta, Y., and Koda, Y. (1994). Expansion of potato cells in response to jasmonic acid. Plant Science 100, 3-8.


Timm, H., Rappaport, L., Bishop, J. C., and Hoyle, B. J. (1962). Sprouting, plant growth and tuber production as affected by chemical treatment of white potato seed pieces. IV. Responses of dormant and sprouted seed potatoes to gibberellic acid. American Potato Journal 39, 107-115.


163

Timm, H., Rappaport, L., Primer, P., and Smith, O. (1960). Sprouting, plant growth, and tuber production as affected by chemical treatment of white potato seed pieces. II. Effect of temperature and time of tratment with gibberellic acid. American Potato Journal 37, 357-365.

Toosey, R. D. (1962). Influence of pre-sprouting on tuber number, size and yield of King Edward potatoes. European Potato Journal 5, 23-27.

Tung, P. X. (2000). Potato production in Vietnam. International Potato Center (CIP) Bogor, Indonesia.

Turnbull, C. G. N., and Hanke, D. E. (1985). The control of bud dormancy in potato tuber: Evidence for primary role of cytokinins and a seasonal pattern of changing sensitivy to cytokinin. Planta 165, 359-365.

Tuyen, T. C., Tung, P. X., Hue, D. T., Thoai, N. D., McPharlin, I., and Dawson, P. (2003). Ket qua chon loc. Giong khoai tay Eben cho che bien. Science& Technology Journal of Agriculture & Rural Development 9, 1135-1137.


Van der Zaag, D. E., and Van Loon, C. D. (1987). Effect of physiological age on growth vigour of seed potatoes of two cultivars. 5. Review of literature and integration of some experimental results. Potato Research 30, 451-472.

Van Es, A., and Hartmans, K. J. (1987). Dormancy, sprouting and sprout inhibition. In "Storage of potato: Post-harvest behavior, storage design, storage practice, handling" (e. a. Rastovski A and A van Es, ed.), pp. 114-129. Pubdoc Wageningen, Wageningen.

Van Es, A., and Hartmans, K. J. (1987b). Effect of physiological age on growth vigour of seed potatoes of two cultivars. 2. Influence of storage period and storage temperature on dry matter content and peroxidase activity of sprout. Potato Research 30, 411-421.

Van Ittersum, M. K., Aben, F. C. B., and Keijzer, C. J. (1992). Morphological changes in tuber buds during dormancy and initial sprout growth of seed potatoes. Potato Research 35, 249-260.

Van Ittersum, M. K., Scholte, K., and Warshavsky, S. (1993). Advanching growth vigor of seed potatoes by haulm application of gibberellic acid and storage temperature regimes. American Potato Journal 70, 21-34.

Van Staden, J., and Dimalla, G. G. (1978). Endogenous cytokinin and the breaking of dormancy and apical dominance in potato tubers. Journal of Experimental Botany 29, 1077-1084.

Vreugdenhil, D., and Struik, P. C. (1989). An integrated view of the hormonal regulation of tuber formation in potato (Solanum tuberosum). Physiologia Plantarum 75, 525-531.

Wheeler, A. W., and Humphries, E. C. (1963). Effect of gibberellic acid on growth, gibberellin content and chlorophyl content of leaves of potato (Solanum tuberosum). Journal of Experimental Botany 14, 132-136.

William, C. M., Kirkham, R. P., Wilson, G., Jackson, K., Dawson, P., Fennel, J., and Hingston, L. (1996). The Australian national potato improvement and evaluation


164

scheme-revised program. In "3rd Australian Society of Horticultural Science", pp. 310-314, Gold Coast.

Wurr, D. C. E. (1978). Studies of the measurement and interpretation of potato sprout growth. Journal of Agricultural Science, Cambridge 90, 335-340.

Wurr, D. C. E. (1984). Physiological age of the potato. Potato Research, 455-457. Xu, X., Van Lammeren, A. A. M., Vermeer, E., and Vreugdenhill, D. (1998). The role

of gibberellin, abscisic acid and sucrose in the regulation of potato tuber formation in vitro. Plant Physiology 117, 575-584.

0

40

80

120

160

10 14 16 18 20 22 26 30

Storage time (weeks)

Tube

r dry

wei

ght (

g/pl

ant)

Figure A.1. Influence of GA3 on tuber dry weight (g/plant) of summer-autumn grown

and summer grown Atlantic seeds. (-o-) is summer-autumn seeds without GA3, (-●-) is summer-autumn seeds plus GA3, (-□-) is summer seeds without GA3 and (-■-) is summer seeds plus GA3. Vertical bars are l.s.d value at P = 0.05

165

0

7

14

21

28

35


Em

erge

nce

(DA

P)

Figure A.2. Influence of GA3 on plant emergence (DAP) of summer-autumn grown

and summer grown Atlantic seeds. (-o-) is summer-autumn seeds without GA3, (-●-) is summer-autumn seeds plus GA3, (-□-) is summer seeds without GA3 and (-■-) is summer seeds plus GA3. Vertical bars are l.s.d value at P = 0.05

166

Table A.1. Effects of storage time (ST) and GA3 on the emergence (DAP) of four potato cultivars stored for 16 and 26 weeks. Different letters indicate significant difference P ≤ 0.05 within columns

Potato variety Storage time

(weeks)

GA3 (mgL-1) Dawmor KT3 PO3 Eben

16 0 11.05 c 15.65 b 11.20 c 10.85 c 20 9.45 b 14.40 b 8.20 ab 8.30 b

20 0 10.95 c 14.15 b 8.85 b 4.65 a 20 8.05 a 9.15 a 7.35 a 5.10 a

l.s.d ST, GA3 0.77 1.22 0.67 0.58ST x GA3 1.04 1.72 0.95 0.81

167

Page Line Rewritten with a clear explanation in text Correction 2 Bottom “The uncertainly demand” is the demand of potato from

factory, base on the farmer’s point of view. Because farmers have produce potatoes, but the quality is not meet the requirement. Processing industry will not accept all of those productions (the percentage of accepted potatoes is vary each season). Therefore, farmers thought that the demand from the factory is uncertain. Actually this is because their product quality is low.

The demand from the factory is uncertain for each season. This is with regard to the quantity and quality of potatoes, so potatoes from many farmers were rejected. This resulted in many growers reducing or stopping seed production (Jayasinghe, 2003).

6 9 There is some research on increasing the proportion of small tubers of tropical potatoes using increasing plant density (Dedy Ruswandi, Pers.com) but none using GA (except Arpiwi, 2003)

Currently, there is limited research on increasing small tuber production in tropical cultivars with growth promoters.

12 Advanced seed = physiologically old seed Replace ‘advance seed’ with ‘physiological old seed’ 12-14 Remove “growth will be monitored (it was repeated) To study the response of sprout behaviour of different

physiologically age seeds and their subsequent growth, seed were observed in the laboratory then they were planted in the glass house and under field conditions in Western Australia.

12 3 Change “including” with “such as” …., such as verticillium wilt, foliar early blight, ….. 10 Change 21 weeks with 100-110 days Plants are harvested after 100-110 days. 14 2/4 The export grade tuber is the grade for consumed potato not

for seeds No changes

16 8 The definitions of G1 to G5 are in the abbreviation (page vii). This is the standard writing style for these terms

17 3 Information doesn’t match with figure 2.1 Remove: 10,960 ha

In the Philippines, potatoes are mostly grown in the hilly areas. In these areas, expansion is limited due to ….. mechanization.

20 3 Check with literature, details not provided in the original paper Change last sentence

The most common problems are tuber moth, tuber rot and aphids

23 9 In my opinion, the degenerated seed is seed reducing its vigour change last sentence

Without temperature control, long storage increases tuber loss so that more than half of the seeds have lost their vigour and productivity is low from remaining seed (Tung, 2000)

28 1/2 Change variety with cultivar Granola is a German cultivar which grows well under the 12 h day regime commonly found in the tropics.

29 4 from bottom

Check (error in original paper) change last sentence (line 3-6 from bottom)

During storage, starch and protein are broken down into sucrose (soluble sugar) and amino acids, and the sucrose will be used to maintain sprout growth and development (Hajirezaei et al., 2003).

33 1 / 2 Sentence change At planting, old Russet Burbank seeds (17 months) produced more stems, which contain 2.8 times more total nitrogen than few stems produced from young seeds (5 months). Stems from old seed had less nitrogen per shoot (Knowles, 1987). Moreover, old seeds contain less sucrose than younger seeds and they can be less efficient in translocation carbohydrates from mother tuber to developing shoots (Mikitzel and Knowles, 1989).

6 Calculation of day degree is a standard formula No change 16-18 Change the last paragraph of 2.4 (new sentences clarify

statements Studies of changes associated with physiological or chronological age on seed vigour have been conducted on temperate potatoes, but none have been done on tropical potatoes. Those studies indicate that the storage time required to change sprouting behaviour and subsequent growth varies substantially. However it is not know what responses may occur in potatoes from tropical conditions. In the present study, we observed sprout behaviour of different physiologically aged potatoes suitable for tropical conditions (Atlantic, Dawmor, Eben, KT3 and PO3). This information will be useful to estimate the optimum storage period for seed to plant with a high yield

35 Table 2.5

Change name of varieties. This is not important for this point. Caption is cganged.

Table 2.5. Dormant period (weeks) after harvest of some cultivars tested in Britain (Burton, 1989) and in Israel (Sunoschi, 1981a) stored at different temperatures.

Replace ‘Up-totdate’ with ‘Up-to-date’ Up-to-date 40 12 Change the line 3 …sprout fresh weight divided by the initial tuber fresh

weight (Kristje, 1962; Reust, 1986) 41 16 Change one as numeral …maximum after another 9 months before starting to

decrease 1 month later. 43 Equation 1 = No changes 47-48

Equation 2 is calculation of the number of plants or plant density. Equation 3 is calculation of tuber production per square meter Change the last sentence of 2.7.

Number of plants or plant density can be calculated by multiplying the seed tuber density (number of seed planted) by plant emergence per seed (Struik et al., 1990) as described below:

52 11/12 Change tropical cultivars with tropical varieties 63 3/4 Insert the suggestion after no metabolism of GA occurred …no metabolism of GA occurred (this assumes all applied

GA would go to tubers), the diluted concentration…… GA3.

64 12 Accepted Sprouts grew larger when seeds were stored for longer time.

65 Figure 3.1 Equation the summer-autumn seeds is not linear, it’s exponential, with the equation : 0.0036e1.133x, r² = 0.89

Changed

66 Data of plant emergence appendix Appendix added 67 6/7 Erase the “gradually” Stolons per plant decreased from 15 to 12 when storage

was extended from 20 to 30 weeks. 68 1 It was increased 20-30% No changes 12 Change increase with decrease …or it resulted in a small decreased in fresh (or dry)

weight 74 Data on plant emergence will be added Appendix added

77 Table 3.6

Remove number of stolons/stem use only number of stolons/plant, as in Atlantic (Figure 3.3)

Table amended

88 3 from bottom

Correlations were high (0.87-0.99), but they cannot be compared, because they came from different lots.

No changes

93 8 Explanation added to text (from mother tuber to shoot) 95 11/12 Change sentence, because data on the number of stolons/stem

was removed …than 16 weeks old seeds and they produced similar number of stolons per plant.

98 2 from bottom

Change affects with effects

99 10 It’s okay No changes 110 Yes, plants were irrigated (in methods) No changes 112 10 The number of eyes is varied with cultivars and tuber size.

Therefore in this experiment, we used sprouted eyes which was the percentage of sprouted yes over the number of eyes.

No changes

121 Figure 4.6. change Y axis Y axis = Tuber weight loss (g) 122 7 Old seeds emerge earlier than young seeds, and more seeds

emerged from old seeds lots than young seeds. Sentence changed

There was a trend for old seeds to have better plant emergence (more plants emerged and they emerge earlier) than young seeds and for cutting to assist in emergence from young seeds but not old seeds.

124 We used number of tubers per bed (not per m²), because some of those plants did not emerge (especially KT3). Then, yield is t/ha change the last column with Total Yield (t/ha) and change the title.

Table 4.3. Effects of seeds treatments and storage time (ST) on tuber size distribution (g) and total tuber number per bed and total yield (t/ha) of Eben, KT3 and PO3 cultivars. Different letters indicate significant difference (p≤0.05) within columns

128 1-4 No changes. The weight loss during cold storage was not calculated.

131 13 No changes. Temperature during summer season in Medina Research Station was above 30 °C (maximum 43 °C) Table 4.1

134 3 from bottom

The meaning of improve here is accelerate. Sentence changed to clarify

Prolonged storage time can be used to increase physiological age of potato tubers, …

143 4/6 Typing error: corrected 26 weeks should be 16 weeks. Furthermore, in summer grown Atlantic seeds, 16 weeks was the optimum storage for maximum yield.

144 I measured the initial sprout length after seeds were removed from cold store (or before seeds were placed in 20° C room). This experiment showed that after putting in the sprouting room for 4 weeks, desprouted seeds < 38 weeks produced similar sprout length than to undesprouted seeds. However, desprouted seeds > 38 weeks grew shorter than undesprouted seeds. This indicated that seeds lost their vigour.

No change

145 16-18 Changed sentence This was because seeds stored for a longer time produced a similar stem number and they produced the same number of stolons per plant.

146 Changed sentence Change Hot temperature with “high temperature” 147 14/15 Changed sentence Yield of Dawmor, Eben, KT3 and PO3 stored for 26 weeks

was lower than 16 weeks-old tubers. 16 Changed sentence. Add temperature and light after

environment conditions Yield of Dawmor, Eben, KT3 and PO3 stored for 26 weeks was lower than 16 week-old tubers. This reduction was possibly due to the physiological aging of these seeds or environmental conditions (temperature and light)

149 4-6 It’s clear enough. No changes 16 Changed sentence Replace ‘application’ with dipping’ 152 Insert (c) ; (c) tuber with multiple branching sprouts (more

sprouts/eye)

production of seed potatoes solanum tuberosum l) for the ... · production of seed potatoes...

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