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Identity, Pathogenicity, and Comparative Virulence of Fusarium spp. Related to Stand Declines of Leafy Spurge (Euphorbia esula) in the Northern Plains. A. J. Caesar, U.S. Department of Agriculture, Agricultural Research Service, Range Weeds and Cereals Unit, Montana State University, Bozeman 59717. Plant Dis. 80:1395-1398. Accepted for publication 13 September 1996. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1996. DOI: 10.1094/PD-80-1395.

Strains of Fusarium spp. causing root disease and crown rot on leafy spurge in natural epidemics and in association with stand declines were identified as F. oxysporum, F. solani, and F. proliferatum. These species predominated among Fusarium spp. isolated from stunted and diseased feeder roots and crowns. There were significant differences in virulence for strains among and within each species. Two strains of F. oxysporum belonged to the same vegetative compatibility group. Ten of 11 strains of Fusarium originated from noncropped or wild areas. These results indicate that Fusarium spp. capable of causing disease on leafy spurge vary as to species, virulence, and compatibility group and arc found in a number of sites where this troublesome perennial weed occurs.

Keyword(s): rangeland, weeds