Further studies on the effect of resistance to Amphorophora idaei in raspberry (Rubus idaeus) on the spread of aphid-borne viruses

The rate of spread of viruses transmitted by the aphid Amphorophora idaei into genotypes of raspberry differing in resistance to infestation by A. idaei was studied in a field experiment which exposed plants to large numbers of infective aphids. Under these conditions, genotypes that are readily colonised by A. idaei were totally infected with virus after two to three growing seasons, whereas genotypes with a high degree of resistance were substantially free of virus after four growing seasons but 56% of plants were infected after seven seasons. Genotypes with intermediate resistance were also substantially free of virus after three seasons but 76% of plants were virus infected after seven seasons. The effectiveness of resistance to A. idaei in raspberry in restricting spread of viruses transmitted by this aphid is discussed.