Botrytis cinerea is a common filamentous phytopathogen that causes serious pre- and postharvest losses worldwide. The phenylpyrrole fungicide fludioxonil has been reported to have high activity against B. cinerea and has been applied to control gray mold in tomato. A total of 206 B. cinerea isolates were collected from tomato greenhouses in Liaoning Province, China, in 2016 and 2017, and sensitivity to fludioxonil was demonstrated by discriminatory concentrations. One highly fludioxonil-resistant isolate, 5 medium-fludioxonil-resistance isolates, and 23 low-fludioxonil-resistance isolates were detected in the field. The fludioxonil-resistant isolates were less fit than the sensitive isolates and presented reduced sporulation, pathogenicity, and mycelial growth and hypersensitivity to osmotic stress, even though sclerotium production had no connection with resistance. Positive cross-resistance was observed between fludioxonil and the dicarboximide fungicides procymidone and iprodione but not between fludioxonil and the fungicides boscalid, fluopyram, fluazinam, and pyrimethanil. Sequence alignment of the BcOS1 gene indicated that the observed sensitivity was identical to that of B05.10 and the low-resistance mutant had two types of mutations, F127S+I365N and A1259T. The medium-resistance mutants had only one type of mutation linked with the 3-aa mutant Q369P+N373S+A1259T, and the highly resistant mutant had a 3-aa mutation with I365S+N373S+A1259T. Molecular docking illustrated that all the resistant isolates showed less affinity than the sensitive isolates with fludioxonil.
Keywords: Bos1; Botrytis cinerea; fludioxonil; point mutant; resistance.