Effect of Ethylene on Activation of Lesion Development from Quiescent Infections of Colletotrichum gloeosporioides in Avocado Fruits. Dov Prusky. Department of Postharvest Science of Fresh Produce, Agricultural Research Organization, The Volcani Center, P.O. Box 6, Bet Dagan 50250, Israel. Castro Wattad, and liana Kobiler. Department of Postharvest Science of Fresh Produce, Agricultural Research Organization, The Volcani Center, P.O. Box 6, Bet Dagan 50250, Israel. MPMI 9:864-868. Accepted 16 August 1996. Copyright 1996 The American Phytopathological Society.

Exposure of Colletotrichum gloeosporioides conidia placed on avocado wax and on intact avocado to 45 µl of ethylene per liter stimulated spore germination, appressorium formation, and proliferation. Exposure of immature cultivar Fuerte avocado fruits inoculated with C. gloeosporioides to 45 µ1 of ethylene per liter enhanced appressorium proliferation and an early climacteric but did not affect lesion growth during 20 days following the treatment. During this period fungitoxic concentrations of the antifungal di-ene in the fruit peel remained at concentrations higher than 2,260 µg/g fresh weight. Overmature cv. Reed avocado fruits inoculated with C. gloeosporioides and exposed to 45 µl of ethylene per liter showed enhanced germination, single and multiple appressorium formation, and earlier fruit ripening. Lesion development by C. gloeosporioides occurred in ethylene-treated fruits in parallel to the development in untreated fruits. Levels of the antifungal diene from the second day after harvest decreased in parallel in ethylene treated and untreated fruits. We conclude that exposure of avocado fruits to exogenous ethylene treatment induces multiple appressorium formation and fruit ripening, but it does not activate lesion development by C. gloeosporioides.