Disease Note.

Occurrence of Acremonium sp. and Monosporascus cannonballus in the Major Cantaloupe and Watermelon Growing Areas of California. B. D. Bruton, U.S. Department of Agriculture-ARS, Lane, Okla. 74555.. R. M. Davis, Department of Plant Pathology, University of California, Davis 95616; and T. R. Gordon, Department of Plant Pathology, University of California, Berkeley 94720. Plant Dis. 79:754. Accepted for publication 18 May 1995. Copyright 1995 The American Phytopathological Society. DOI: 10.1094/PD-79-0754B.

Since the early 1980s, a root rot caused by an unknown pathogen has resulted in serious yield losses in cantaloupe and honeydew melons in California. The term "vine collapse" has been ascribed to the disease because of the rapidity of symptom development from onset until plant death. Apparently-healthy plants wilted or declined within a period of 5 to 10 days as the melons approached maturity. A wide array of symptoms were encountered on the various cucurbits collected from affected fields. From the Sacramento Valley to the upper San Joaquin Valley (Colusa to Fresno counties), an Acremonium sp. was commonly isolated from roots of symptomatic plants of cantaloupe, honey dew, squash, and watermelon. Symptoms typically ranged from the presence of brown lesions at the juncture of the secondary and primary root to a general corking and distortion of the roots. The symptoms were similar to a newly described disease in Spain called "Acremonium collapse" (1). In the lower San Joaquin Valley and in the southern part of the state (Kern and Riverside counties), Monosporascus cannonballus Pollack & Uecker was isolated from roots of collapsed cantaloupe and watermelon plants. Diseased plants exhibited brownish lesions at the juncture of the secondary and primary root, a general decay of tertiary, secondary, and primary roots, and, occasionally, large, dark-colored perithecia superficially embedded in the roots. The symptoms were essentially identical to those described in south Texas for "Monosporascus root rot/vine decline" (2). Pathogenicity of ten selected isolates of each fungus was demonstrated on cantaloupe seedlings (cv. Magnum 45). After 28 days in the greenhouse, these two fungi produced symptoms that were identical to those produced by Spanish isolates of Acremonium sp. and Texas isolates of M. cannnn-ballns, respectively. This is the first report of Monosporascus root rot/ vine decline in California, and the first report of an Acremonium sp. associated with a mature vine collapse of cantaloupe and watermelon in the United Slates.