Botrytis cinerea causes gray mold and is an economically important postharvest pathogen of fruits, vegetables and ornamentals. Fludioxonil sensitive B. cinerea isolates were collected in 2011 and 2013 from commercial storage in Pennsylvania. Eight isolates had EC50 values ranging from 0.0004 to 0.0038 µg/ml for fludioxonil and were dual resistant to pyrimethanil and thiabendazole. Resistance was generated in vitro, following exposure to a sub-lethal dose of fludioxonil, in seven of eight dual-resistant B. cinerea isolates. Three vigorously growing B. cinerea isolates with multi-resistance to postharvest fungicides were further characterized and found to be osmosensitive and retained resistance in the absence of selection pressure. A representative multi-resistant B. cinerea strain caused decay on apples treated with postharvest fungicides, which confirmed the in vitro results. The R632I mutation in the Mrr1 gene, associated with fludioxonil resistance in B. cinerea, was not detected in multi-postharvest fungicide resistant B. cinerea isolates, suggesting that the fungus may be using additional mechanism(s) to mediate resistance. Results from this study show for the first time that B. cinerea with dual resistance to pyrimethanil and thiabendazole can also rapidly develop resistance to fludioxonil which may pose control challenges in the packinghouse environment and during long-term storage.
|Scooped by Melvin Bolton|