AbstractRaspberry veinbanding mosaic disease in Scotland was shown to be caused by dual infection with the aphid-borne viruses, rubus yellow net (RYNV) and raspberry leaf mottle and not by RYNV and black raspberry necrosis virus (BRNV) as is reported to occur in Canada. However, disease symptoms were intensified when plants were also co-infected with BRNV and raspberry leaf spot virus. Blackberry calico disease was induced in two blackberry cvs when infected with wineberry latent (WLV) and raspberry bushy dwarf (RBDV) viruses but not by RBDV alone, suggesting that WLV may be the causal agent of the disease. A mechanically transmissible virus with small bacilliform particles c. 130 x 30 nm was detected in gooseberry plants with veinbanding disease. In ultrastructural studies, strawberry plants affected by June Yellows (JY) showed severe disruption of chloroplasts and other cell organelles but no virus or virus-like particles were observed. Furthermore, JY was not eradicated from affected strawberry plants by combinations of heat treatment and meristem tip culture. However, several dsRNA species of mol. wt 1 x 106 to 4 x 106 were detected in JY-affected strawberry plants but not in healthy plants or healthy plants graft-inoculated with JY-affected sources.