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Disease Note.

Fusarium Wilt (F. oxysporum f. sp. niveum Race 2) of Watermelon in Oklahoma. B. D. Bruton, USDA-ARS, Lane, OK 74555. C. L. Patterson, and R. D. Martyn. Oklahoma State University, Lane 74555, and Texas A&M University, College Station 77843. Plant Dis. 72:734. Accepted for publication 15 April 1988. Copyright 1988 The American Phytopathological Society. DOI: 10.1094/PD-72-0734D.

Fusarium wilt of watermelon (Citrullus lanatus (Thunb.) Matsum. & Nakai) caused by Fusarium oxysporum Schlect. (emend. Snyd. & Hans.) f. sp. niveum E. F. Sm. has been observed throughout the watermelon-growing areas of Oklahoma. Wilted plants from commercial fields collected during the summer of 1987 consistently yielded F. oxysporum. Microconidia (106/ml) from monoconidial cultures of selected isolates were used to inoculate six race-differential watermelon cultivars: Florida Giant, Mirage, Jubilee, Madera, Charelston Gray, Crimson Sweet, and Calhoun Gray. Included ni the study were known isolates of race 0 and race 1 obtained from D.L Hopkins (University of Florida, Leesberg), a known race 2 isolate from Texas, and 23 isolates collected in Oklahoma. In independent tests conducted in Oklahoma and Texas, one Oklahoma isolate caused 70-93% wilt in all cultivars and is therefore designated as F. o. f. sp. niveum race2(2). Race 2 was confirmed in the United States (Texas) for the first time in 1985 (1). This is the first report of this race in the United States outside of Texas.

References: (1) R. D. Martyn. Plant Dis. 71:233, 1987. (2) D. Netzer. Phytoparasitica 4:131, 1976.