Poster Board 33. Assessment of fungicide resistance in Botrytis cinerea from cherry fruit

Botrytis cinerea is the main cause of rot of sweet cherry fruit in Tasmanian orchards. Despite good crop hygiene practices, crop management and extensive fungicide programs, disease prevalence can be high in conducive conditions. A study was conducted to determine if, and to what extent, resistance of B. cinerea has developed to currently registered fungicides used in sweet cherry orchards. Over 100 isolates of B. cinerea were obtained from mature, symptomatic fruit following surveys at three commercial sweet cherry orchards in southern Tasmania in December 2018 and January 2019. Using a hyphal tipping method these isolates were prepared as single genotypes for fungicide sensitivity screening. In addition, 11 single genotype isolates of B. cinerea were used a reference, which were collected prior to exposure to the selected fungicides. Several fungicides with different categories are used to control grey mould disease in cherry production, including succinate dehydrogenase inhibitors (SDHI; FRAC group 7), quinone outside inhibitors (QoI; FRAC group 11) and dicarboximides (DC; FRAC group 2). We selected two SDHI fungicides (boscalid and fluopyram), one QoI fungicide (pyraclostrobin, a strobilurin) and one dicarboximide (iprodione). Measurement of fungicide sensitivity was conducted on potato dextrose agar amended with each fungicide at five concentrations (0, 0.05, 0.5, 5 and 50 μg a.i./ml) in triplicate. Radial fungal growth was measured after 4 days growth. Data analysis included determining the EC50 discriminatory dose, modelled EC50 and calculation of resistance factors (RF). Preliminary results have detected evidence of reduced fungicide sensitivity in the B. cinerea isolates from cherry orchards to boscalid and fluopyram, and full results are forthcoming.