Biological and Serological Characterization of Three Montana RMV-Like Isolates of Barley Yellow Dwarf Virus. S. K. Z. Brumfield, Laboratory Technician, Department of Plant Pathology, Montana State University, Bozeman 59717. T. W. Carroll, and S. M. Gray. Professor, Department of Plant Pathology, Montana State University, Bozeman 59717; and Agricultural Research Service, U.S. Department of Agriculture, Department of Plant Pathology, Cornell University, Ithaca, NY 14850. Plant Dis. 76:33-39. Accepted for publication 5 July 1991. Copyright 1992 The American Phytopathological Society. DOI: 10.1094/PD-76-0033.

Three Montana (MT) RMV-like isolates of barley yellow dwarf virus (BYDV) collected from Choteau (MT-RMV-C), Fort Ellis (MT-RMV-FE), and Valier (MT-RMV-V) were characterized on the basis of transmission, virulence, serology, and cross-protection studies. Aphid transmission characteristics of MT RMV-like isolates were determined and compared with those of New York (NY) RMV, SGV, RPV, PAV, and MAV isolates. Aphid vectors tested were Rhopalosiphum maidis, collected at four locations in Montana, and the NY biotypes of R. maidis, Schizaphis graminum, R. padi, and Sitobion avenae. Two different populations of each MT R. maidis karyotype, 2n=8, which is predominant on corn, and 2n=10, which colonizes barley, were used as vectors in this study. Although both karyotypes were efficient vectors of MT RMV-like isolates, there were differences in transmission efficiency between each of the four populations. Unlike NY-RMV, which is transmitted efficiently only by R. maidis, all MT RMV-like isolates were transmitted efficiently by R. maidis and S. graminum, two were occasionally transmitted by R. padi, and none were transmitted by S. avenae. MT RMV-like isolates were similar to NY-RMV isolates in that they reacted with NY-RMV immunoglobulin but not with NY-SGV, NY-RPV, NY-PAV, or NY-MAV immunoglobulins in enzyme-linked immunosorbent assay (ELISA). MT RMV-like isolates were more virulent in oats than either NY-RMV or NY-SGV. MT-RMV-C and MT-RMV-V isolates were each used individually in cross-protection experiments to determine if either could cross-protect against NY-SGV in oats. Little or no cross-protection was found.