session 10: myrtle rust epitomises a critical challenge for biodiversity conservation

biosecurity built on science

Myrtle Rust epitomises a critical challenge for biodiversity conservation

R.O. (Bob) Makinson 1, 2

1. Myrtle Rust Environmental Impacts Working Group.2. The Australian Network for Plant Conservation Inc.

[email protected]

Plant Biosecurity Cooperative Research Centre

mailto:[email protected]


Broad-impact pathogens and native biodiversity conservation

Few precedents, few response models; little preparatory work on environmental impacts.Already present in Australia

Phytophthora cinnamomi Water Mould Plants (wide range)Batrachochytrium dendrobatidis (Chytrid) Fungus FrogsPsittacine Beak and Feather Disease Virus (native?) Birds (Parrots)Puccinia psidii (Myrtle Rust) ‘pandemic strain’ Fungus Plants (Myrtaceae)

Yet to arrive in Australia Puccinia psidii other strains (some virulent on eucalypts)

Fungus Plants (Myrtaceae)

Ceratocystis fimbriata Fungus Plants (Eucalypts)Phytophthora ramorum ‘Sudden Oak Death’ Water Mould Plants (wide range)Xylella fastidiosa Bacterium Plants (wide range)

… and many more


c. 2253 native Myrtaceae species.

Up to 1,100 in zones of high probability of Myrtle rust establishment (based largely on overseas data).

Top left : : Risk map for Australia, overseas bioclimatic data, aggregated rust variants. (Magarey et al. 2007).

Top centre: Risk areas based on climatic conditions (by Booth & Jovanovic in Glen et al. 2007).

Top right: Distribution of potential Myrtaceae hosts within Rust climate suitability envelope.. (Kriticos et al. 2013)

Eventual no. of species affected will depend on WA:1568 native Myrtaceae species, of which 1043 are in just 5 south-west IBRA Bioregions (shown in dark red at right).

Right upper: IBRA v7 Bioregions (red = 1043 species of Myrtaceae). Data: WA Herbarium 2013.Right lower: Climate suitability for Myrtle Rust in SW WA (DPaW website, Feb. 2016, after Kriticos).

Myrtle Rust (Puccinia psidii) – bioclimatic estimates


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The Myrtle Rust east coast envelope, and spatial overlap with host species distributions – a preliminary assessment

165 native host taxa have natural distributions totally or near-totally within the zone of full Myrtle Rust naturalisation in eastern Australia.

32 of these are rated (fide Pegg et al., 2013) partly or wholly in the ‘Highly Susceptible’ or Extremely Susceptible’ categories. This number may rise.

A further 15 host species have natural distributions predominantly within the current Myrtle Rust east-Australian envelope.

More refined analysis is underway by K. Berthon at Macquarie University.


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Scrub TurpentineRhodamnia rubescens

Pre-2010: Widespread, ‘least risk’ status.

Carnegie et al. (2015): 43 sites, all found to be infected

Mean crown transparency 76% (cf. estimated ‘normal’ 30-35%).

Adult mortality variable, mean 12%.

Bottom: dead R. rubescens, Bongil Bongil NP, NSW. (M. Smith, NPWS, 2014).

Native Guava Rhodomyrtus psidioides

Pre-2010: Widespread, ‘least risk’ status

Carnegie et al. (2015):

• 18 sites, all found infected.• Mean crown transparency 95%, 82%

having > 90% transparency (estimated ‘normal’ is 25-35%).

• “All but three sites had exceptional levels of tree mortality … overall, 57% of trees surveyed were dead”.

Top: Rhodomyrtus psidioides adult tree deaths, NE NSW. (P. Entwistle).


Many species are relatively tolerant, at least on new seasonal growth – but cumulative effects over time?Severity ratings may not reflect susceptibility in wild or at critical life stages.Eucalypts: c. 85 taxa recorded as hosts (mixed field and lab).2 partial ‘High’, no ‘Extreme’ so far. Nevertheless …

Top: Euc. planchoniana cotyledonary seedling; G.Pegg.Bottom: Euc. tindaliae, coppice; P. Entwistle.

Pegg et al. (2014) rated the 165 ‘natural infection’ (non-lab) hosts in Queensland :• 67 “relatively tolerant”• 50 moderately susceptible• 48 highly or extremely susceptibleCaution:Proportions are of known hosts, not of all Myrtaceae in east Qld.The ratio may not hold for other regions.Susceptibility ratings are mainly for seasonal growth, and (28 spp.) flowers/fruits. Seedlings and re-sprouts mostly not studied yet.

Many, many unknowns


Known-host proportions alarmingly high in some genera,although susceptibility ratings vary at species level

Genus Known hosts Total Aust species

Austromyrtus 2 3Backhousia 12 13Gossia 12 20Lenwebbia 3 4Neofabricia 1 3Pilidiostigma 4 6Rhodamnia 14 19Rhodomyrtus 7 7 (one subsp. not yet known host)Ristantia 2 3Sphaerantia 1 2Syzygium sens. lat. 50 c. 75Xanthostemon 5 16


Environmental sector and agencies are not yet fully alert or adequately equipped for broad pathogen impacts

Assets Production sector & agencies

Environmental sector & agencies

Institutional infrastructure YES -- CRCs, PHA/AHA, etc None dedicated

Funding infrastructure YES – EPPRD etc None dedicated

Expertise (internal) YES – but declining Minimal to NO

Prediction and preparedness YES – predictive, aspirationally proactive

NO – reactive

Sector drivers (industry) YES NO

Worst case alternatives YES – switch crops, etc Usually NO - decline, extinction.(Translocation sometimes)

Political awareness YES Minimal

Cross-jurisdiction communication and coordination

GOOD (well, it looks that way!) POOR


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GETTING MYRTLE RUST ONTO THE ENVIRONMENTAL AGENDA• Strong statement of urgency and needs (review and draft action plan - PBCRC project pending);• Representation of issue (MREIWG).

PLANNING & INSTITUTIONAL• A clear ‘enabling mandate’ needed from governments.• New strain arrival – prevention, detection, and response war-gaming?

FIELD PRIORITIES• Rapid status-assessment (20-40 priority species).• Sustained resourcing of monitoring systems (incl. serious citizen science) for species and ECs.• Germplasm capture (large-scale; prior research needed for many); ex-situ resistance breeding.

RESEARCH AND KNOWLEDGE-ASSEMBLY ACTION NEEDS• Resistance studies (genetic, phylogenetic, metabolomic, phytochemical)• Mobilise / synthesise existing info (host demographics, biology, ecology, fauna)• Cultural significance appraisal• Scoping review for salvage and recovery – biocontrol; resistance breeding & reintroduction.

Directions for a Myrtle Rust environmental response


Resistance research and breeding (potentially cis- and transgenic, GE, other);

Germplasm research and seed production areas on an unprecedented scale;

Re-wilding strategies designed to avoid genetic bottle-necking;

– all of which pose technical, ecological, logistical and social challenges, with few Australian or international precedents, at least for plants.

The conservation sector needs to draw on the experience and technical knowledge of the biosecurity and plant health sector. Both sectors will need to help drive the cross-over.

The conservation response to Myrtle Rust will shape future capabilities for other pathogens …

… but will likely push the sector into difficult interventionist strategies


The conservation sector needs to draw on the experience and technical knowledge of the biosecurity and plant health sector. Both sectors will need to help drive the cross-over.

session 10: myrtle rust epitomises a critical challenge for biodiversity conservation

Science