Abstract

The incidence of infection with the pollen-borne raspberry bushy dwarf virus (RBDV) and some aphid-borne viruses was assessed in red raspberry cultivars Glen Clova, Glen Rosa, Leo, Glen Ample, Glen Prosen and Malling Landmark, in a field experiment at Invergowrie, Dundee, Scotland, UK, in 1996. The cultivars differed in their resistance to RBDV, and to strains of the main aphid virus vector, Amphorophora idaei. After 6 years, Glen Clova, containing the RBDV-resistance gene Bu, was not infected with RBDV, whereas all the remaining cultivars became infected, but the virus incidence varied greatly from 2 to 78%. Seemingly, factors other than the presence of Bu influenced the level of resistance to natural infection with RBDV under field conditions. All cultivars contained genes for resistance to strains of Amphorophora idaei present in the UK and, in PCR assays for Rubus yellow net virus (RYNV) transmitted by this aphid species, the incidence of infection varied greatly. The percent infection with RYNV in Glen Rosa and Leo, that contained the strongest resistance gene A₁₀, was 0 and 9 respectively, in Glen Ample, Glen Prosen and Malling Landmark, that contain gene A₁, it was 9, 53 and 19 respectively, and in Glen Clova, that had only minor gene resistance, it was 22. In the cultivars sensitive to the viruses inducing raspberry leaf spot mosaic disease, the lowest incidence of disease was 0.6% in the A₁₀-containing Glen Rosa and the highest was 80% in the A₁-containing Malling Landmark. Clearly, there are factors other than the major aphid resistance genes that influence resistance to virus inoculation by Amphorophora idaei under field conditions. None of the raspberry cultivars studied were resistant to raspberry vein chlorosis virus (RVCV) or to its aphid vector, Aphis idaei. Based on symptomatology, all cultivars became infected with RVCV but the incidence of infection varied from 1 to 100%.