Abstract
The interaction in mesophyll protoplasts of two strains of raspberry ringspot virus, RRV-S and RRV-E, was studied using fluorescent antibody to detect strain-specific antigen. Staining with fluorescent antibody was weak and generalized unless the protoplasts were also infected with tobacco rattle virus (TRV), which induces RRV to form antigen aggregates and was therefore used routinely to make RRV antigen more easily detectable.