Different rates of spread of Raspberry bushy dwarf virus and some aphid-borne viruses into red raspberry cultivars containing different resistance genes

The incidence of infection with the pollen-borne Raspberry bushy dwarf virus (RBDV) and some aphid-borne viruses was assessed in 6 red raspberry cultivars in a field experiment at Invergowrie, Dundee. The cultivars differed in their resistance to RBDV, and to strains of the main aphid virus vector, Amphorophora idaei. Six years after planting as healthy plants, cv. Glen Clova, that contains the RBDV-resistance gene Bu, was not infected with RBDV, whereas all 5 RBDV-infectible cultivars became infected with RBDV but the virus incidence varied greatly from 2 - 78%. Seemingly, factors other than the presence of gene Bu influence the level of resistance to natural infection with RBDV under field conditions. All cultivars contained genes for resistance to strains of Am. 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 cvs Glen Rosa and Leo, that contain the strongest resistance gene A10, was 0 and 9 respectively, in cvs Glen Ample, Glen Prosen and Malling Landmark, that contain gene A1, it was 9, 53 and 19 respectively, and in cv. Glen Clova, that has only minor gene resistance, it was 22. In the four cultivars sensitive to the viruses inducing Raspberry leaf spot mosaic disease, the lowest incidence of disease was 0.6% in the gene A10-containing cv. Glen Rosa and the highest was 80% in the gene A1-containing cv. Malling Landmark. Clearly, there are factors other than the major aphid resistance genes that influence resistance to virus inoculation by Am. 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 - 100%.