Detection and fitness comparison of target-based highly fludioxonil-resistant isolates of Botrytis cinerea from strawberry and cucumber in China

Botrytis cinerea has a high risk of developing resistance to fungicides. Fludioxonil, belonging to phenylpyrroles, has been used for more than three decades, however, only few cases of field resistance against phenylpyrroles have been reported. In this study, the highly fludioxonil-resistant (HR) isolates of Botrytis cinerea were firstly detected in the commercial greenhouses of strawberry in China in 2015, and biochemical characterization differences in high fludioxonil-resistance from strawberry and cucumber were compared. All of the five HR isolates from greenhouses of strawberry and cucumber could grow on PDA amended with 100 mu g/mL fludioxonil, and exhibited a positive correlation between the resistance of dicarboximide fungicides and fludioxonil. Sporulation and sclerotium production of the strawberry-originated HR isolates were increased in comparison with the cucumber-originated HR isolates. No matter how the HR isolates were from strawberry and cucumber, all the HR isolates showed enhanced sensitivity to the osmotic agents, but with significant difference. Based on sequence alignment of the BcOS1 which codes protein bound by fludioxonil, two genotypes of the strawberryoriginated HR isolates were observed, i.e., (F127S + I365N + S426P) and (G538R + A1259T), which were totally different from those of the cucumber-originated HR isolates. Molecular docking of fludioxonil to the binding site of BcOS1 protein from the five HR isolates illustrated that all the HR isolates had less affinity than the sensitive isolates. Our data indicated that genotypes of the HR isolates match the corresponding fludioxonil-selection pressure on the field populations of B. cinerea in the commercial greenhouses of the two host plants.