Resistance to sterol biosynthesis inhibitors and various other fungicides in Botrytis cinerea

Botrytis cinerea (anamorph of Botryotinia fuckeliana), the causal agent of grey mould, can infect a wide range of crops including grapevine. From isolates collected in French vineyards, the distribution of transposable elements and RFLP markers revealed the existence of at least two sympatric species: B. vacuma and B. transposa and of genetic recombinations within both groups. The possible consequence of this genetic diversity upon fungicide-resistance was checked towards sterol biosynthesis inhibitors, a group of compounds not used in French vineyards against grey mould. When tested on germ-tube elongation, the squalene epoxidase inhibitor tolnaftate allowed to distinguish sensitive and resistant strains. The tolnaftate-resistant strains, only found in B. transposa, were also less sensitive to anilinopyrimidines (e.g. cyprodinil, mepanipyrim, pyrimethanil). According to the in vitro toxicity of sterol 14 alpha-demethylation inhibitors and phenylpyrroles (e.g. fludioxonil), two phenotypes were recognized within tolnaftate-resistant strains. Since in both cases, cross-resistance occurred between fungicides having different modes of action, the putative mechanism could be a multidrug resistance based on an active excretion of toxicants. In vitro tests conducted with fenpropimorph, fenpropidin and spiroxamine, revealed the presence of strains highly susceptible to these sterol Delta(14)-reduction inhibitors. This property was correlated with a decreased sensitivity towards the hydroxyanilide botryticide fenhexamid and it was mainly recorded in B. vacuma.