Natamycin as a postharvest treatment to control gray mold on stored blueberry fruit caused by multi-fungicide resistant Botrytis cinerea

Botrytis cinerea is the cause of gray mold, a major postharvest disease of blueberries grown in California. Control of gray mold is largely dependent on the use of synthetic fungicides. However, multiple resistance to different classes of fungicides is commonly present in B. cinerea populations from blueberry in the region. Alternatives to conventional chemical fungicides are needed to control postharvest gray mold. Natamycin, a naturally occurring substance listed as biofungicide, is registered for postharvest use in certain fresh fruit and it was highly effective to control various postharvest fungal diseases. In this study, natamycin was evaluated for its effectiveness to control gray mold caused by B. cinerea with resistance to various commonly used fungicides as well as its effectiveness to reduce decays in general that resulted from natural infections. Our results showed that as low as a quarter rate of the label rate of natamycin reduced gray mold incidence and lesion size regardless of fungicide resistance phenotypes. Natamycin also reduced overall fruit decay caused by natural infections and it had no adverse effect on fruit quality. Natamycin can be a promising tool to control postharvest gray mold of blueberry fruit while maintaining fruit quality.