Sensitivity to Fludioxonil of Botrytis cinerea Isolates from Tomato in Henan Province of China and Characterizations of Fludioxonil‐resistant Mutants

Grey mould, caused by Botrytis cinerea Pers ex Fr., is one of the most common diseases of tomato worldwide. Fludioxonil belongs to the phenylpyrrole fungicides, which have high activity against B. cinerea. The sensitivity of fludioxonil was evaluated on the basis of the level of inhibition of mycelium growth in 274 B. cinerea isolates collected from different locations (untreated with this fungicide) in Henan Province, China. The EC50 values for fludioxonil ranged from 0.0033 to 0.0415 mg/l, and the average EC50 values were 0.0156 ± 0.0078 mg/l. Three fludioxonil-resistant mutants were obtained by subculturing fludioxonil-sensitive wild-type isolates on continuously increasing fludioxonil concentrations. For the cross-resistance assay, fludioxonil revealed positive cross-resistance with procymidone but did not reveal cross-resistance with pyrimethanil, boscalid and trifloxystrobin. Mycelial growth, conidial production, hyphal dry weight and pathogenicity were diminished significantly between the fludioxonil-resistant mutants and their sensitive wild-type parental isolates. This study shows for the first time that fludioxonil-resistant isolates of B. cinerea are still not present in Henan Province because this fungicide is an attractive and effective fungicide for chemical control. Recommendations can be made to growers to use fludioxonil to control grey mould and to consider the potential moderate resistance risk of using this fungicide.