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.