Further characterization of Rhopalosiphum padi virus of aphids and comparison of isolates from South Africa and Illinois

A South African isolate of Rhopalosiphum padi virus (RhPV) was directly compared with an isolate from Illinois. Although these viruses were serologically closely related, differences were detected in their capsid protein molecular weights and particle buoyant densities. The South African isolate was further characterized; two additional putative capsid proteins were found, an RNA poly(A) tract was detected, and an RNA size of 10 kb was calculated. Virions were found to degrade quickly below pH 3.0, to be stable between pH 5.0 and 8.4, and to lose RNA when heated to 56°C. From this evidence, and from radioiodination and Western blot reactions of capsid proteins, it is proposed that RhPV be classified as an enterovirus. No serological relationship was detected between RhPV and several other picorna- and picorna-like viruses. Three RhPV-specific double-stranded RNA species were isolated from infected aphids. Although virions could be isolated after long periods from plants on which viruliferous aphids had fed, and clean aphids could become infected by feeding on such plants, no replicative form RNA was detected in these plants.