In a pot experiment made to compare the effects in Lloyd George raspberry of infection with raspberry bushy dwarf (RBDV) and black raspberry necrosis (BRNV) viruses alone and in combination, the effects on growth were greatest in doubly infected plants. Such plants were less vigorous and had fewer and shorter canes than virus-free control plants. These effects, which closely resemble symptoms of bushy dwarf disease, suggest that this disease is caused by infection with RBDV + BRNV. Infection with either or both viruses delayed fruit ripening, decreased the mean berry weight significantly and adversely affected fruit form and structure, but total fruit yield was not significantly affected.
In a field experiment in which the effects of four aphid-borne viruses latent in red raspberry are being studied, observations over a two-year period indicate that virus infection adversely affected the quality of both cane and fruit in some cultivars. In addition, infection with raspberry leaf spot, raspberry leaf mottle or raspberry vein chlorosis viruses caused significantly earlier ripening in one cultivar.