VIEW ARTICLE

Etiology

Identification of a New Serotype and Antigenic Relationships Among Six Strains of Red Clover Necrotic Mosaic Virus. A. L. N. Rao, Department of Plant Science, University of Alberta, Edmonton, Canada T6G 2P5, Present address: Department of Biology, Texas A&M University, College Station, 77843-3258; D. K. Lakshman(2), S. T. Ohki(3), and C. Hiruki(4). (2)Department of Plant Science, University of Alberta, Edmonton, Canada T6G 2P5, Present address: Department of Botany and Plant Pathology, University of Maine, Orono, 04473; (3)Department of Plant Science, University of Alberta, Edmonton, Canada T6G 2P5, Present address: Laboratory of Plant Pathology, College of Agriculture, University of Osaka Prefecture, Sakai, Japan. Phytopathology 77:995-999. Accepted for publication 2 December 1986. Copyright 1987 The American Phytopathological Society. DOI: 10.1094/Phyto-77-995.

The antigenic relationships of three red clover necrotic mosaic virus (RCNMV) strains—Eng (England), Aus (Australia), and Can (Canada)—were compared with the three established serotypes of the virus—RCNMV-TpM 34 (serotype A), RCNMV-TpM 48 (serotype B), and RCNMV-Sw (serotype C)—by immunodiffusion tests. These tests differentiated RCNMV-Can from serotypes A and C but not from serotype B. It was demonstrated that both RCNMV-Eng and RCNMV-Aus constitute a new serotype, D, since they were serologically indistinguishable and differed from the three serotypes of the virus. By means of intragel cross-absorption experiments, antibodies specific for each serotype were demonstrated. These tests also showed that RCNMV-Aus antiserum contained heterospecific antibodies reacting specifically with serotypes B and C. Coat proteins from six RCNMV strains migrated as a single component in polyacrylamide gel corresponding to polypeptides with a molecular weight of about 40,000 daltons. Polyacrylamide gel electrophoretic analysis of coat proteins partially digested with V8 protease revealed significant differences between RCNMV-Sw (serotype C) and other strains of the virus. Similar analysis with chymotrypsin indicated that the coat proteins of RCNMV-Eng and RCNMV-Aus were identical and differed from the others. The antigenic and other properties of RCNMV serotypes are discussed in relation to taxonomic identity.