III. Variation in plant viruses: Variation in ryegrass mosaic virus in relation to resistance

Prunus necrotic ringspot and apple mosaic viruses have been described separately but they are distantly related serologically and intermediate strains occur in hop and rose. They may therefore be regarded as type strains of two serotypic groups of a single virus (Prunus necrotic ringspot virus which was the first to be described). The host range of both serotypes is wide, mostly amongst woody plants and there have long been recurring difficulties of diagnosis based on symptoms produced in woody or herbaceous indicator plants. These problems have been overcome by the application of enzyme-linked immunosorbent assay which provides a rapid and convenient means of detecting and serotyping the various strains encountered.