Bacillus and Pseudomonas spp. provide antifungal activity against gray mold and Alternaria rot on blueberry fruit

Gray mold and Alternaria rot are diseases of highbush blueberry (Vaccinium corymbosum L.) fruit that develop in storage, in particular with interruption in the retail cold chain. In this study, the effect of antagonistic bacteria from the Bacillus and Pseudomonas genera was assessed on mycelial growth of Botrytis cinerea and Alternaria alternata. The bacteria were also evaluated for their suppression of gray mold and Alternaria rot on stored blueberries. Isolation of antifungal extracts and identification of antifungal compounds from bacterial strains were also performed. The results showed that various bacterial antagonists reduced mycelial growth of B. cinerea and A. alternata by up to 42 and 27%, respectively. The bacteria also provided inhibition of blueberry fruit rot by both pathogens, reducing rot incidence and severity by as much as 50 and 64%, respectively. Extracts from the Bacillus and Pseudomonas spp. reduced mycelia growth and spore germination of B. cinerea. Antifungal compounds in these bacterial extracts, including arthrofactins in some Pseudomonas spp., indicated that antibiosis is a main mechanism of action. The results of this study suggest antagonistic bacteria may represent a potential method for controlling postharvest fruit rot of blueberries.