Strong resistance to the fungicide fenhexamid entails a fitness cost in Botrytis cinerea, as shown by comparisons of isogenic strains

Abstract

Fenhexamid, a sterol biosynthesis inhibitor effective against Botrytis, inhibits the 3-ketoreductase (Erg27) involved in C-4 demethylation. Several fenhexamid-resistant phenotypes have been detected in Botrytis cinerea populations from French vineyards. The field isolates with the highest resistance levels display amino acid changes in Erg27 (F412S, F412I or F412V). Fenhexamid-resistant mutants were generated by site-directed mutagenesis of the erg27 gene in a sensitive recipient strain to overcome the impact of different genetic backgrounds. The wild-type erg27 allele was replaced by the three mutated alleles (erg27(F412S/I/V)) by homologous recombination. These isogenic strains were shown to be fenhexamid-resistant and were used to quantify the impact of F412 mutations on fungal fitness. Several parameters, including radial growth, the production of sclerotia and conidia, freezing resistance and aggressiveness, were quantified in laboratory conditions. Analysis of variance demonstrated significant differences between the mutant and parental strains for some characters. In particular, the mutants grew more slowly than the wild-type strain and displayed variations in the production of sclerotia and conidia with temperature and susceptibility to freezing. The results highlight a moderate but significant impact of F412 mutations on the survival capacity of B. cinerea strains displaying high levels of resistance to fenhexamid in laboratory conditions, potentially limiting their dispersal and persistence, particularly in terms of overwintering, in field conditions.