Abstract

Recent surveys of commercial Rubus crops in the UK have shown a large increase in the incidence of the pollen-borne raspberry bushy dwarf virus (RBDV). Much of this is attributable to the widespread displacement in commerce of RBDV-immune cultivars by those with improved agronomic qualities but that are infectible with common isolates of this virus. In England and Wales, there is also evidence for the spread of resistance-breaking isolates of RBDV. In addition, the widespread development of biotypes of the main virus vector aphid, Amphorophora idaei, able to overcome gene A₁ (that confers resistance to this aphid), has resulted in large increases in the incidence of the four viruses transmitted by this vector aphid. It is also of concern that biotypes of this aphid able to overcome gene A₁₀ (that confers strong resistance to the four known biotypes of this aphid) are also appearing in some crops. Raspberry vein chlorosis virus transmitted by the small raspberry aphid, Aphis idaei, is increasing in prevalence in crops. The response of several raspberry cultivars to infection with these viruses in a field experiment is reported, together with the possible strategies to minimize their levels of infection in crops. RBDV and aphid-borne viruses infect many cultivars symptomlessly but the results of trials have established that such symptomless infections by individual viruses can decrease the production of quality cane, fruit size and the time of fruit ripening. Such effects are likely to be greatly increased by multiple virus infections, the situation that normally prevails under commercial conditions. In addition to such losses, symptomless infection poses problems for the certification of healthy planting material.