Auckland, 25 November Veradina Dharjono Prof Paul Taylor, Dr Tonya Wiechel, and Dr Nigel Crump

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1 Auckland, 25 November 2013 Veradina Dharjono Prof Paul Taylor, Dr Tonya Wiechel, and Dr Nigel Crump

2 Verticillium wilt Soil borne fungi Verticillium dahliae, V. tricorpus V. albo-atrum recently has been found in Victoria and Tasmania (Prakash 2011) Secondary symptoms: interveinal chlorosis, necrosis, wilting that lead to premature death; vascular browning in tubers. Involved in potato early dying syndrome (PED) Hard to control (Prakash 2010)

3 Aims 1. Establish a glasshouse bioassay and optimise Verticillium dahliae inoculum concentration to differentiate host resistance 2. Study virulence of V. dahliae on plant growth using an eggplant model 3. Evaluate Australian commercial potato varieties for resistance to V. dahliae

4 1. Optimisation of glasshouse bioassay: Methodology Plant materials Potato tissue culture seedlings var. Russet Burbank Eggplant var. Black Beauty Inoculation Root dipped into different concentration of spore suspension: 10 2 to 10 6 spores/ml Assessment Disease severity & percentage of infection assessment 0-5 visual qualitative scale Eggplant only: biomass was measured

5 1. Optimisation of glasshouse bioassay: Summary of results Inoculum threshold for both potato and eggplant was at 10 4 spores/ml Therefore, inoculum concentration used for screening trials was between 10 4 to 5 x 10 4 spores/ml Increasing spore concentration of V.dahliae reduced growth and increased senescence in eggplant

6 2. Variety screening: Methodology Plant material 13 varieties of potato tissue culture seedlings Inoculation Root dipped into: 10 4 spores/ml (1 st trial) and 5x10 4 spores/ml (2 nd and 3 rd trials) Assessment Disease severity & percentage of infection assessment 0-5 visual qualitative scale Resistance/ susceptibility Resistance/ susceptibility was assigned based on the disease scale and infection at week 10 after inoculation

7 2. Varieties screening: Summary Varieties Use Spore concentration (spores/ml) x x 10 4 Atlantic Crisp/Fresh S MR Catani Crisp MR MR Coliban Fresh S R MR-S Denali Crisp R R R-MR Desiree Fresh R MR Kennebec Fry R S Nicola Fresh S S Pike Crisp R S S Ranger Russet Fry S MR Russet Burbank Fry S S Shepody Fry S S Simcoe Crisp S MR Trent Crisp S Resistance: Low disease scale (ie. 0-1) with/without infection Moderate resistance: Low to moderate disease scale (2) with infection Susceptible: Moderate to severe (or death) disease scale (3-5) with infection

8 Conclusion & industry implication Developed a method to screen varieties for Verticillium resistance Determined inoculum threshold for establishing infection in both potato and eggplant = 10 4 spores/ml Evaluated selected industry varieties Denali was moderate to highly resistant; Catani and Desiree were moderately resistant to V. dahliae

9 Future works Assessing microsclerotia inoculum to simulate field infection: Optimising glasshouse bioassay: Inoculating potato seedlings (var. Russet Burbank) with different concentration of microsclerotia Varieties screening: Validating resistance and susceptible varieties by inoculating these varieties with microsclerotia

10 Other experiments under this project Aim: to evaluate efficacy of soil amendments to reduce soil pathogen inoculum and prevent Verticillium wilt disease. Laboratory Soil microcosm assays Soil amendments: sulphur, brown coal & blood and bone Assessment: ph and viability of microsclerotia Glasshouse Optimisation Russet Burbank tissue culture seedlings Different inoculum (microsclerotia) concentration Assessment: 0-5 visual qualitative scale Glasshouse Russet Burbank tissue culture seedlings Soil amendment + inoculum Assessment: 0-5 visual qualitative scale

11 Microcosm assay: Preliminary Results & Discussion weeks after Amendment concentration incubation Control 1% % reduction Sulphur 0 84% 2 63% 14% 78% 4 24% 4% 85% 6 11% 2% 81% 8 8% 1% 89% % reduction 99% Brown coal 0 79% 2 72% 52% 27% 4 58% 8% 86% 6 38% 6% 85% 8 58% 15% 74% % reduction 81%

12 Acknowledgements This project has been funded by HAL using the processed potato industry levy and matched funds from the Australian Government. The University of Melbourne, Department of Environment and Primary Industry, and the Victorian Certified Seed Potato Authority have provided in-kind support.