Properties of dicarboximide-resistant strains of Botrytis cinerea

Dicarboximide-resistant strains of Botrytis cinerea were isolated from natural substrates and also produced in the laboratory. All these strains exhibited a similar degree of resistance to the dicarboximide fungicides iprodione and vinclozolin, and this resistance persisted in the absence of the fungicides. The natural frequency of resistance to both chemicals was approximately three in 10⁷ conidia but could be enhanced by up to 1000 times after a single exposure to sub-lethal concentrations of either chemical. Mycelium of the resistant strains was able to infect fruit and vegetables to a similar extent as that of sensitive strains, although infection of carrot roots was markedly less aggressive. The resistant strains were separable into two groups according to their growth habit on culture media. Both groups were relatively slow growing and showed a marked lack of sporulation compared with most sensitive strains. This lack of sporulation may account for the apparent failure of resistant strains to increase rapidly in strawberry plantations that had received dicarboximide sprays in successive seasons.