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Purification and Partial Characterization of Beet Yellow Stunt Virus. R. R. Reed, Department of Plant Pathology, University of California, Davis 95616. B. W. Falk, Department of Plant Pathology, University of California, Davis 95616. Plant Dis. 73:358-362. Accepted for publication 23 November 1988. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/PD-73-0358.

Beet yellow stunt virus (BYSV), a suspected closterovirus, was compared with beet yellows virus (BYV), the type member of closterovirus subgroup I. Virions of BYSV and BYV were purified from herbaceous hosts. Purified virions of BYSV cosedimented in sucrose gradients with those of BYV, and the virions of each virus were indistinguishable by electron microscopy. The virions of BYSV and BYV are composed of a single major capsid protein subunit with molecular weight of approximately 24,500 (BYSV) or 24,000 (BYV) and a single species of single-stranded RNA with molecular weight of approximately 6.1 million (BYSV) or 5.5 million (BYV). Immunoblot analysis using antisera to both viruses showed that BYSV capsid protein is serologically unrelated to that of BYV. Double-stranded RNA (dsRNA) analysis confirmed results of virion single-stranded RNA analysis, in that BYSV-infected Chenopodium capitatum had a major dsRNA species with molecular weight of about 13 million, slightly larger than the dsRNA of BYV and slightly smaller than the dsRNA of citrus tristeza virus, another well-characterized closterovirus. Based on the properties described, BYSV is distinct from BYV yet sufficiently similar to it to warrant inclusion in closterovirus subgroup I.