Occurrence of Isolates of Botrytis cinerea in Mie Prefecture, Japan, with low susceptibility to fludioxonil

Abstract

We evaluated the susceptibility of Botrytis cinerea to fludioxonil by using 2,992 isolates from vegetables obtained from 2000 to 2016 in Mie Prefecture, Japan. Growth was not observed on potato dextrose agar that contained 0.2 ppm fludioxonil from 2000 to 2011. However, 27 of 971 isolates from 2012 grew under these conditions. Using these isolates, we performed a bioassay on cucumber cotyledons. Eight isolates showed less than 60% inhibition of lesion formation at 10% of the standard concentration. We defined these as low-susceptibility isolates.

In addition, when the susceptibility test was carried out using a microplate, the EC₅₀ value for the low-susceptibility isolates was between 0.188 and 0.271 ppm. This is an order of magnitude higher than the EC₅₀ values for susceptible isolates (0.012 to 0.063 ppm). Since the EC₅₀ value for the low-susceptibility isolates was 0.125 to 0.259 ppm higher than that of the susceptible isolates, the susceptibility of B. cinerea to fludioxonil can be evaluated using the microplate method.