Postharvest control of blue mold and gray mold on apples using isolates ofPseudomonas syringae

Four isolates of Pseudomonas syringae, MA-4, MB-4, MD-3b, and NSA-6, from t he phyllospere of apple trees, were evaluated as biocontrol agents for cont rolling blue mold [Penicillium expansum] and gray mold [Botrytis cinerea] o f apples (Malus domestica) in storage. When separately co-inoculated with t he two pathogens, the four isolates at a concentration of 1 x 10(7) CFU/mL controlled blue mold by 78-94% after incubation at 20 degreesC for 5 days a nd by 64-70% at 4 degreesC for 28 days. The incidence of gray mold was also significantly reduced by P. syringae isolates MD-3b, NSA-6, and MA-4 under these conditions. However, a higher concentration of P. syringae MA-4 and NSA-6 was required to control gray mold compared to blue mold. Spray treatm ent with P. syringae MA-4 significantly controlled blue mold on 'Empire' an d 'Delicious' apples at 18 and 4 degreesC. Under conditions similar to thos e of controlled atmosphere in commercial storage, a dip treatment with P. s yringae MA-4 significantly controlled blue mold on 'Empire' and 'Delicious' apples and was more effective than the treatment with BioSave(TM), a comme rcially available biofungicide. Pseudomonas syringae MA-4 at a concentratio n of 1 x 10(8) CFU/mL controlled blue mold as efficiently as the chemical t reatment with a combination of thiabendazole and diphenylamine.