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The Role of Ethylene in Anthracnose of Cucumber, Cucumis sativus, Caused by Colletotrichum lagenarium. C. L. Biles, Postdoctoral fellow, USDA, ARS, Appalachian Fruit Research Station, 45 Wiltshire Road, Kearneysville, West Virginia 25430; F. B. Abeles, and C. L. Wilson. Research plant physiologist, and Research plant pathologist, respectively, USDA, ARS, Appalachian Fruit Research Station, 45 Wiltshire Road, Kearneysville, West Virginia 25430. Phytopathology 80:732-736. Accepted for publication 2 February 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, 1990. DOI: 10.1094/Phyto-80-732.

Cucumber (Cucumis sativus) seedlings pretreated with ethylene gas had 21% more anthracnose lesions than did controls, following inoculation with Colletotrichum lagenarium. Ethylene fumigation 24 hr after inoculation increased lesion size by 36%. Silver thiosulfate (0.1 mM), an inhibitor of ethylene action, decreased lesion number and lesion size. Silver thiosulfate did not inhibit germination, growth, or the sporulation capacity of C. lagenarium. However, scanning electron microscopy showed an inhibition of C. lagenarium conidial germination when silver thiosulfate (1 mM) was applied to the leaf surface. Increased ethylene production was observed after 3 days, followed by increased peroxidase activity at 6 days. Isoelectric focusing gels indicated that pI 4 and 6.5 isozymes were enhanced by the invading pathogen. Since ethylene failed to induce disease resistance and silver thiosulfate failed to induce susceptibility, it was concluded that ethylene-induced proteins, such as peroxidase, do not play a role in limiting disease development in the cucumber-C. lagenarium system. However, ethylene action appears necessary for lesion development and senescence.

Additional keywords: silver thiosulfate, peroxidase isozymes, chlorophyll degradation.