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Resistance

Biological Aspects of Citrus Molds Tolerant to Benzimidazole Fungicides. Y. Gutter, Division of Fruit and Vegetable Storage, Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel; A. Shachnai(2), M. Schiffmann-Nadel(3), and A. Dinoor(4). (2)Citrus Marketing Board, Tel Aviv, Israel; (3)Division of Fruit and Vegetable Storage, Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel; (4)Department of Plant Pathology and Microbiology, Faculty of Agriculture, The Hebrew University of Jerusalem, Rehovot, Israel. Phytopathology 71:482-487. Accepted for publication 22 September 1980. Copyright 1981 The American Phytopathological Society. DOI: 10.1094/Phyto-71-482.

A survey of the incidence and occurrence in Israel of strains of the green and blue molds of citrus (Penicillium digitatum and P. italicum, respectively) tolerant to benzimidazoles revealed that their incidence was low in the orchards, medium in the packinghouses, and high in the storage rooms. Strains were found that are tolerant to concentrations of benzimidazoles 500–1,000 times greater than those required to inhibit the sensitive “wild types.” The antifungal properties of benomyl were, in all cases, greater than those of thiabendazole at equal concentrations. All tolerant isolates under study were also tolerant to other compounds of the benzimidazole group—carbendazim, cypendazole, fuberidazole, and thiophanate-ethyl. A relatively constant degree of tolerance was maintained even after 16 weekly transfers to a fungicide-free medium or after inoculation to and recovery from untreated citrus fruits. Our results suggest that tolerant strains were capable of surviving extended periods along with the susceptible strains even in the absence of selection pressure.