Towards a system for the identification and classification of potyviruses: I. Serology and amino acid composition of six distinct viruses

Abstract

Antigenic relationships of six distinct potyviruses were studied by immunodiffusion tests using highly purified sonicated virus preparations and anti-intact virus sera devoid of detectable antibodies to host-plant antigens. Three variants of bean yellow mosaic virus (BYMV) including BYMV sensu stricto and two variants of pea mosaic virus (PMV and SPMV) were shown to be antigenically very similar and also relatively closely related to lettuce mosaic virus (LMV). Distant antigenic relationships were detected between the BYMV variants and bean common mosaic virus (BCMV); between BCMV and passionfruit woodiness virus (PWV); and between PWV and potato virus Y (PVY). No antigenic relationships were detected between any of these viruses and sugarcane mosaic virus (SCMV). Antibodies in anti-viral sera were very poor in recognizing coat proteins dissociated with LiCl from homologous viruses and failed altogether to recognise those dissociated with pyrrolidine. Attempts to prepare antisera in mice against isolated viral coat proteins dissociated with either LiCl or pyrrolidine were unsuccessful due to poor immunogenicity of the preparations. Electrophoretic mobilities of the viral coat proteins relative to marker proteins in the presence of sodium dodecyl sulphate suggest that the protein subunits of all the viruses studied have molecular weights of about 33,000. However, the coat proteins were prone to partial degradation. The amino acid compositions of the antigenically closely related viruses were very similar, but similarities of those distantly related were no greater than those of the apparently unrelated viruses. The problems in the use of serological and amino acid composition data obtainable with currently available techniques for the classification of potyviruses are discussed.