Towards a system for the identification and classification of potyviruses. II. Virus particle length, symptomatology, and cytopathology of six distinct viruses.

The mean particle lengths of lettuce mosaic virus (LMV), bean common mosaic virus (BCMV), passionfruit woodiness virus (PWV), potato virus Y (PVY), sugarcane mosaic virus (SCMV), and one strain of bean yellow mosaic virus (BYMV) were all shown to be close to 750 nm. However, the length of two other serologically closely related strains of BYMV, variants of pea mosaic virus referred to as PMV and SPMV, had significantly longer particles, about 792 and 842 nm. Each of the distinct viruses had readily distinguishable host ranges. The strains of BYMV could also be distinguished from each other although they had many hosts in common with similar symptoms. Electron microscopy of plant cells infected by the viruses studied showed that the cell inclusions induced by infection were of two readily distinguishable types although some minor virus-specific differences were also observed. The BYMV strains and LMV induced long "relaxed" pinwheel inclusions whereas those induced by BCMV, PWV, PVY, and SCMV were shorter, "tighter," and curved. The significance of these observations to problems of potyvirus identification and classification is discussed.