-Associated Fludioxonil Resistance in Not Linked to Mutations in Transcription Factor .

Resistance to fludioxonil in and was previously found to be linked to either overexpression of the drug efflux pump activated by mutations in transcription factor or to mutations in the osmoregulation gene . In the present study, isolates of , group S, or collected from strawberry fields in the United States were resistant to fludioxonil with half-maximal effective concentration values ranging from 0.04 to 0.43 µg/ml for , 0.03 to 1.03 µg/ml for group S, and 0.28 to 3.48 µg/ml for . Analyses of sequences revealed various mutations linked to fludioxonil resistance in and group S isolates. However, no mutations in correlated with overexpression-mediated resistance in isolates. Neither nucleotide variations in the 1,370-bp upstream region of nor increased copy numbers could explain the overexpression in these isolates. Mutations in conferred resistance to iprodione in and group S isolates; none correlated with resistance to fludioxonil in . In contrast to European isolates, U.S. isolates contained a 3-bp insertion in the coding region of These isolates were more sensitive to osmotic stress but it is unclear whether the insertion is responsible for this phenotype. Our findings suggest that overexpression-associated fludioxonil resistance is an across-species mechanism of resistance to fludioxonil that can be induced by mutations in and other, still-unknown mechanisms.