Zucchini Yellow Mosaic Virus Associated with Severe Diseases of Melon and Watermelon in Southern California Desert Valleys. S. T. Nameth, Graduate Research Assistant, Department of Plant Pathology, University of California, Riverside 92521. J. A. Dodds, Associate Professor, and A. O. Paulus, Extension Plant Pathologist, Department of Plant Pathology, University of California, Riverside 92521; and A. Kishaba, Research Entomologist, USDA, Boyden Laboratory, Riverside, CA 92521. Plant Dis. 69:785-788. Accepted for publication 4 February 1985. Copyright 1985 The American Phytopathological Society. DOI: 10.1094/PD-69-785.

A severe mosaic disease affected melon production in certain fields in Imperial County, CA, every spring during 1982–1984. Incidence of the disease has increased annually since 1982. The effects were especially severe in 1984, when diseased plants showed severe foliar mosaic and had small, deformed melon fruit with star-shaped cracking. Long, flexuous rod-shaped virus particles were associated with the disease. The virus was vectored by the green peach aphid (Myzus persicae). The host range was different from that of either watermelon mosaic virus-1 (WMV-1) or WMV-2 and was similar to that of zucchini yellow mosaic virus (ZYMV). Sap extracts from infected cantaloupes and purified virus reacted with a ZYMV antiserum from Italy. Antisera made against the California strain (ZYMV-Ca) did not react with WMV-1 or WMV-2. No resistance or tolerance to ZYMV-Ca was detected in seedlings of 30 cultivars of melon and watermelon grown in a greenhouse. Presently grown cultivars, selected in part for their tolerance to WMV-2, were included. Seed transmission of ZYMV-Ca was not detected in squash. Virus isolates from cucurbits grown in Oregon and Mexico also reacted with antiserum to ZYMV-Italy. ZYMV is a newly recognized threat to melon production in California.