Postharvest Control of Blue Mold and Gray Mold of Apples and Pears by Dip Treatment with Pyrrolnitrin, a Metabolite of Pseudomonas cepacia. W. Janisiewicz, Research Plant Pathologist, U.S. Department of Agriculture (USDA), Agricultural Research Service (ARS), Appalachian Fruit Research Station, Kearneysville, WV 25430-9802. L. Yourman, J. Roitman, and N. Mahoney. Biological Laboratory Technician, U.S. Department of Agriculture (USDA), Agricultural Research Service (ARS), Appalachian Fruit Research Station, Kearneysville, WV 25430-9802; and Research Chemists, USDA, ARS, Western Regional Research Center, Albany, CA 94710. Plant Dis. 75:490-494. Accepted for publication 29 October 1990. 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, 1991. DOI: 10.1094/PD-75-0490.

The antifungal compound pyrrolnitrin, isolated from Pseudomonas cepacia, an antagonist known to control gray mold (incited by Botrytis cinerea) and blue mold (incited by Penicillium expansum) of apples and pears, was assayed for its efficacy in controlling these diseases on wounded fruit at two temperatures (2 and 24 C). The compound was applied to wounded fruit after harvest at concentrations ranging from 6 to 200 µg/ml in dip solutions containing conidia of P. expansum or B. cinerea (1 × 10⁴ conidia per milliliter). Pyrrolnitrin provided effective control of both diseases on apples and pears. The type of wound had a profound effect on control; infections at cut wounds were the easiest and those at “bruise” wounds were the most difficult to control. Higher concentrations of pyrrolnitrin were required for control at 24 C than at 2 C. Pyrrolnitrin at 200 µg/ml, when applied up to 34 hr after inoculation, eradicated infections by both pathogens on Golden Delicious apples with cut wounds. The pH of the pyrrolnitrin solution, throughout a range corresponding to the pH of the fruit juice, did not change its fungicidal activity in in vitro tests.

Keyword(s): natural compound.