Studies on some characteristics of dicarboximide‐resistant isolates of Botrytis cinerea from protected lettuce

Isolales of B. cinerea obtained directly from protected lettuce crops were either sensitive or moderately resistant to dicarboximides. Types with a high level of resistance to dicarboximides developed under laboratory conditions. Isolates with a high level of resistance grew poorly and sporulated feebly on cucumber cotyledons or lettuce leaves whereas growth and sporulation of moderately resistant isolates were only slightly poorer than of sensitive isolates. Moderately resistant isolates were stable in culture and there was no evidence that they produced mixtures of sensitive and resistant conidia. In polythene tunnel studies with mixed B. cineaea populations, in the absence of dicarboximides. no highly resistant isolates and only a small percentage of moderately resistant isolates were recovered.