Biological Control of Blue Mold and Gray Mold on Apple and Pear withPseudomonas cepacia

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Abstract
Control of gray mold, caused by Botrytis cinerea, and reduction in blue mold, caused by Penicillium expansum, was obtained on Golden Delicious apples [Malus domestica] and Bosc pears [Pyrus communis] protected with Pseudomonas cepacia isolated from apple leaves. The bacterium strongly inhibited fungal growth during in vitro screening on nutrient yeast dextrose agar medium. An effective antifungal compound was isolated from the bacterial cells and culture medium. This compound, identified as a pyrrolnitrin, inhibited growth of both fungi at a concentration of 1 mg/L during an agar diffusion test in vitro. Complete control of gray mold was obtained on apples and pears protected with a pyrrolnitrin concentration of 10 mg/L at a pathogen inoculum level of 103-105 conidia/ml. Blue mold was controlled at the same concentration of pyrrolnitrin at inoculum concentrations of 103 conidia/ml for pears and 103 and 104 conidia/ml for apples. At concentrations of 50 mg/L or higher, complete control was obtained of both diseases on both fruits at all tested inoculum levels.