Archivio Journal of Plant Pathology

Abstract:

Ten monoascosporic strains of Botryotinia fuckeliana were used in mycelium growth tests to evaluate baseline sensitivity to Fenhexamid; a fungicide recently introduced in the control of grey mould. Their response to the fungicide was EC50 = 0.1-0.3 µg ml-1 and MIC = 0.3-3 µg ml-1. Eight laboratory mutants resistant to the fungicide were obtained from UV-irradiated or unirradiated conidia plated on Fenhexamid-amended medium (3 µg ml-1). Mutation ratios were 1.7·10-6 of survivor conidia for UVinduced mutations and 0.6·10-8 for spontaneous mutations. Two levels of resistance to Fenhexamid were distinguished in mycelium growth tests: low (110 µg ml-1) and high resistance (EC50>100 µg ml-1). In conidial germination tests; Fenhexamid proved to be a powerful inhibitor of germ tube elongation (EC50 ~1 µg ml-1) even for mutants displaying high resistance in mycelium tests. Resistant mutants were crossed with Fenhexamid-sensitive reference strains to derive meiotic progeny and to assess the mode of inheritance of resistant phenotypes. Segregation of resistant/sensitive phenotypes in ascospore offspring indicated that resistant phenotypes were due to mutations in single major genes inherited in Mendelian fashion and unlinked with the Mbc1 and Daf1 genes; responsible for resistance to benzimidazole and dicarboximide fungicides; respectively.