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Bean Common Mosaic Virus Strains Associated with Bean Mosaic Epidemics in the Northwestern United States. R. O. Hampton, Research Plant Pathologist, USDA-ARS, Department of Botany and Plant Pathology, Oregon State University, Corvallis 97331. M. J. Silbernagel and D. W. Burke, Research Plant Pathologists, USDA-ARS, Irrigated Agriculture Research and Extension Center, Prosser, WA 99350. Plant Dis. 67:658-661. Accepted for publication 24 November 1983. 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, 1983. DOI: 10.1094/PD-67-658.

Several bean (Phaseolus vulgaris) cultivars considered to be resistant to indigenous strains of bean common mosaic virus (BCMV) were attacked in varying degrees during a bean common mosaic epidemic throughout the northwestern United States in 1977. These cultivars included Black Turtle, Columbia Pinto, Great Northern UI 31, Great Northern UI 1140, Montcalm Red Kidney, Pinto UI 114, Red Mexican NW 59, Red Mexican NW 63, Rufus, and Viva. A milder epidemic, which was primarily restricted to Pinto UI 114, recurred in 1981. Using bean cultivars standard for differentiating BCMV strains, we identified the strains associated with these epidemics as members of strain groups II, III, and IV; one strain approximated strain group VII (~VII). Two of these strain groups, III and ~VII, were previously unknown in the United States. Strain group I (type strain) was isolated only from bean cultivars lacking any BCMV resistance. Only strain group V (NY-15 strain) was detected in Pinto UI 114 in the 1981 epidemic. Greenhouse isolates of each strain tended to be somewhat less virulent than the field cultures from which they originated. At least part of this difference appeared to result from a reduction in innate infective capacity of the virus during cultural subtransfers. Three BCMV isolates were readily seed-transmitted in the most susceptible cultivars, but cultivar susceptibility to infection did not predetermine susceptibility to seed transmission of BCMV.