POSTHARVEST CONTROL OF BLUE MOLD AND GRAY MOLD OF APPLES AND PEARS BY DIP TREATMENT WITH PYRROLNITRIN, A METABOLITE OF PSEUDOMONAS-CEPACIA

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-mu-g/ml in dip solutions containing conidia of P. expansum or B. cinerea (1 x 10(4) 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-mu-g/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.