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Postharvest Pathology and Mycotoxins

Synergy Between a Benzimidazole-Sensitive Isolate and Benzimidazole-Resistant Isolates of Penicillium digitatum. B. L. Wild, Graduate research assistant, Department of Plant Pathology, University of California, Riverside 92521, Present address of senior author: Gosford Horticultural Postharvest Laboratory, Gosford, NSW, 2250 Australia; J. W. Eckert, professor of plant pathology, University of California, Riverside 92521. Phytopathology 72:1329-1332. Accepted for publication 16 March 1982. Copyright 1982 The American Phytopathological Society. DOI: 10.1094/Phyto-72-1329.

A benzimidazole-sensitive isolate of Penicillium digitatum increased the infectivity of a benzimidazole-resistant isolate when mixtures of the two were inoculated into oranges subsequently treated with 500 mg of benomyl per liter. Benomyl and carbendazim reduced only slightly the percent germination of sensitive isolate spores, but the germ tubes were severely stunted and distorted. Spores of the sensitive isolate germinating in liquid culture containing carbendazim produced 5070% of the pectolytic enzyme activity that was measured in the cultures without fungicide. The infectivity of four benzimidazole-resistant isolates was increased by the addition of the dialyzed culture filtrate from the carbendazim-inhibited isolate. The synergy between resistant and sensitive isolates of P. digitatum during infection of oranges suggests that the effectiveness of the benomyl fruit treatment could be improved by strict sanitation of packinghouses to minimize spore populations of both resistant and sensitive isolates.

Additional keywords: citrus fruit, methyl benzimidazolecarbamate, postharvest decay control.