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Development of glasshouse bioassay for assessing resistance to verticillium wilt disease in potato
V. N. DHARJONO (1), N. S. Crump (2), T. Wiechel (3), P. W. J. Taylor (1). (1) The University of Melbourne, Parkville, Australia; (2) ViCSPA, Toolangi, Australia; (3) Department of Environment and Primary Industries, Bundoora, Australia

<i>Verticillium dahliae</i> is a major and persistent soil pathogen known to cause verticillium wilt in potato (<i>Solanum tuberosum</i> L.). Resistance in commercial Australian potato cultivars is unknown. The threshold level of inoculum required to establish infection, symptom development and differentiate host reactions needs to be determined before a glasshouse screening trial can be undertaken. Different inoculum concentrations were assessed using root dip inoculation method of seedlings established from tissue culture for susceptible potato cv. Russet Burbank. The seedlings roots were dipped in water as a control and in six different inoculum concentrations 106, 105, 104, 5x103, 103, and 102 spores/mL for five minutes, followed by transferring plants to potting mixed. Similar experiments were conducted on eggplant seedlings (cv. Black Beauty). The eggplant bioassay was found to be less time consuming and more cost effective compared to tissue culture potato plant bioassay. Severity of foliar symptoms was determined using a 0–5 visual qualitative scale. An inoculum threshold level of 104 spores/mL was required to establish infection and wilt symptoms in both eggplant and potato plants, although <i>V. dahliae</i> was isolated from petiole tissue plants inoculated with as low as 102 spores/mL. In glasshouse potato cultivar screening trials using 5x104 spores/mL, cultivars Denali showed moderate to high resistance and Catani and Desiree moderate resistance to infection by <i>V. dahliae</i>.

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