Present status of the sugarcane mosaic subgroup of potyviruses

Until recently, sugarcane mosaic virus (SCMV) was believed to be a single potyvirus consisting of a large number of strains, differing from each other in certain biological and antigenic properties. The use of affinity-purified polyclonal antibodies directed towards the surface-located, virus-specific amino termini of the coat proteins showed that 17 strains from Australia and the United States represented four distinct potyviruses, namely johnsongrass mosaic virus (JGMV), maize dwarf mosaic virus (MDMV), sorghum mosaic virus (SrMV) and SCMV. Comparisons of strains from each of these four viruses on the basis of reactions on differential sorghum and oat cultivars, cell-free translation of RNAs, morphology and serology of cytoplasmic cylindrical inclusions, amino acid sequence and peptide profiling of coat proteins, 3' non-coding nucleotide sequences, and molecular hybridization with probes corresponding to the 3' non-coding regions, resulted in exactly the same taxonomic assignments as obtained using amino-terminal serology. These results further confirm that the former sugarcane mosaic virus actually consists of four distinct viruses and show that MDMV, SrMV, and SCMV are more closely related to each other than they are to JGMV. Because these four viruses are closely related but distinct, formation of a sugarcane mosaic subgroup in the genus Potyvirus would be appropriate.