A survey in Scotland indicates that raspberry bushy dwarf virus (RBDV) is rare in or absent from commercial raspberry crops, presumably because the cvs predominantly grown contain gene Bu, which provides immunity from the common strain of RBDV (RBDV-S). Surveys in England, where resistance-breaking isolates of RBDV (RBDV-RB) occur, show that commercial loganberry crops are commonly infected with RBDV-RB but not RBDV-S and may have been so infected for several years. Studies on selfs of the RBDV-RB immune raspberry cv. Haida suggest that gene Bu may contribute to its immunity.
Red raspberry cvs of predominantly American origin, and black raspberry, have been identified as sources of immunity to raspberry vein chlorosis virus. Although the mechanism of this immunity and its inheritance is unclear, crosses between immune x infectible cvs produced a high proportion of immune segregants, offering the possibility of genetic control of this virus in future cvs.
Particles of the aphid-borne black raspberry necrosis virus (BRNV), which reach only very low concentrations in herbaceous test plants, attained much greater concentrations when BRNV was propagated in Nicotiana clevelandii plants also infected with an unrelated virus, solanum nodiflorum mottle virus (SNMV). SNMV is not indigenous in the UK and is not known to infect Rubus. Using an antiserum prepared to virus particles purified from the mixed culture, BRNV was detected by F(ab')2 ELISA in a range of Rubus plants. These consisted of naturally infected plants growing in the field and experimentally infected Rubus species and hybrids growing in the glasshouse, including red raspberry plants infected by means of the aphid vector Amphorophora idaei.
The severe virus-like symptoms on tayberry in Scotland, reported at the last Symposium, are now known to be caused by infestations of the leaf and bud mite (Phyllocoptes gracilis). The mites and tayberry symptoms were controlled by an application of vamidothion.