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Postharvest Pathology and Mycotoxins

Biological Control of Blue Mold and Gray Mold on Apple and Pear with Pseudomonas cepacia. W. J. Janisiewicz, U. S. Department of Agriculture, Agricultural Research Service, Appalachian Fruit Research Station, Kearneysville, WV 25430; J. Roitman, Western Regional Research Center, USDA, ARS, Albany, CA 94710 Phytopathology 78:1697-1700. Accepted for publication 1 August 1988. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1988. DOI: 10.1094/Phyto-78-1697.

Control of gray mold, caused by Botrytis cinerea, and reduction in blue mold, caused by Penicillium expansum, was obtained on Golden Delicious apples and Bosc pears 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.