Determining the baseline sensitivity for mycelial growth in Western Cape gray mould populations

Abstract: Botrytis cinerea is an important pre- and postharvest pathogen and is the causal agent of grey mould disease on pears. It infects the fruit via the calyx end, stem end or wounds. It quickly develops fungicide resistance due to its rapid life cycle and adaptability and resistance to multiple fungicides has been documented in the past. To determine the distribution of baseline sensitivities of 50 B. cinerea isolates recovered from stored ‘Packham’s Triumph’ pears, these isolates were tested in vitro for their sensitivity to technical grade benomyl and iprodione. EC50 values for individual isolates tested against benomyl ranged from 0.038 to 0.087 mg/l and between 0.146 and 0.304 mg/l for iprodione. The mean EC50 values for the population tested for iprodione was found to be 0.212 mg/l and the mean EC50 for benomyl was lower at 0.063 mg/l. Results from these tests showed that the benzimidazole and dicarboximide fungicides are still effective in controlling grey mould disease on pears. Data from this study contribute to monitoring future shifts in sensitivity of this population or future development of resistance.