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Anthracnose of Greenhouse-grown Watermelon Transplants Caused by Colletotrichum orbiculare in California. S. T. Koike, University of California Cooperative Extension, Salinas 93901. T. E. Tidwell, D. G. Fogle, and C. L. Patterson. California Department of Food and Agriculture, Sacramento 95814; and Oklahoma State University, Lane 74555. Plant Dis. 75:644. Accepted for publication 2 January 1991. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/PD-75-0644D.

Anthracnose, caused by Colletotrichum orbiculare (Berk. & Mont.) Arx. (= C. lagenarium (Pass.) Ellis & Halst.), was identified on seedlings of experimental lines of seedless watermelons (Citrullus lanatus (Thunb.) Matsum. & Nakai [= C. vulgaris Schrad.]) during greenhouse production of transplants. Symptoms included watersoaked lesions on epicotyls, cotyledons, and leaves. Infected plants collapsed and died. Acervuli morphologically similar to Colletotrichum spp. were produced in infected tissues, and C. orbiculare was isolated from the lesions. Pathogenicity tests were completed by inoculating watermelon seedlings (cv. Sugar Baby) in the three-leaf stage with spore suspensions. Symptoms identical to those observed in greenhouses developed about 7 days later, and the pathogen was reisolated from test plants. Watermelon anthracnose was previously reported in California (1), but diagnosis was not verified by host inoculation. For California, this is the first confirmation of the disease and the only account of cucurbit anthracnose in greenhouse production. Contaminated seed was likely the source of inoculum. Because of the high cost of seed, the use of greenhouse-produced hybrid and triploid (seedless) watermelon transplants is increasing. Thus, seed borne diseases will probably increase during greenhouse production and provide inoculum for disease development in the field.

Reference: (1) A. K. Sen and W. S. Barham. Plant Dis. Rep. 53:955, 1969.