Cytopathological evidence for the division of barley yellow dwarf virus isolates into two subgroups

The cytological survey of oat cells in tissue infected with different aphid-specific or aphid-nonspecific isolates of barley yellow dwarf virus (BYDV) was concluded in this study with the examination of the alterations induced by Schizaphis graminum-specific and S. graminum-nonspecific isolates. Cytological alterations were similar with all four isolates examined, except that proliferated membranous inclusions, common with three of the isolates, were absent with S. graminum-nonspecific isolate 6712. Isometric virus-like particles, slender filaments, and single-membraned vesicles containing densely staining fibrils occurred in the cytoplasm with all the isolates. Nuclear alterations consisted of distortion of the outline of the nucleus, followed by aggregation and accumulation of densely staining material within the nucleus. The cytopathological alterations observed in cells infected with isolate 6712 were similar to those found previously with aphid-nonspecific isolates transmitted most efficiently by Rhopalosiphum padi-, and Macrosiphum avenae-specific isolates of BYDV, while the other three isolates differed in the presence of the proliferated, membranous inclusions. Evidence from cytopathology indicates that the six known aphid-specific or nonspecific variants of BYDV may be categorized into two subsections. The general agreement of the cytopathological evidence, with that from serological and cross-protection studies is discussed.