Characterization of high fludioxonil resistance in Botrytis cinerea isolates from calibrachoa flowers
The fungicide fludioxonil is one of the most effective single-site fungicides available for managing flower blight caused by Botrytis cinerea on fruit and ornamental crops. Though low and moderate levels of resistance to fludioxonil have been reported in the pathogen across the United States and Europe, high resistance has only been reported from greenhouses in China. In this study, two B. cinerea isolates with high resistance (EC50 >100 µg/mL) to fludioxonil were detected on ornamental calibrachoa flowers grown in a greenhouse. These isolates exhibited stable resistance for over 20 generations, produced symptoms on calibrachoa flowers sprayed with label rates of fludioxonil, and displayed in vitro fitness penalties with decreased mycelial growth (p<0.0001) and sporulation (p<0.0001) compared to sensitive isolates. Highly resistant isolates were identified as MDR1h, containing the ΔLV497 deletion in mrr1. However, resistance levels and in vitro fitness parameter characteristics were not consistent with this phenotype. One isolate contained the mutation L267V between HAMP domains 1 and 2 of the Bos-1 gene, and both isolates exhibited high osmotic sensitivity and reduced glycerol accumulation in the presence of fludioxonil, indicating that high resistance of these isolates may be associated with the HOG1 MAPK pathway.