Genetics of resistance to Amphorophora idaei in red raspberry

Raspberry breeding aims to develop improved cultivars to satisfy market demands whilst allowing financially- and environmentally-sustainable production. The large raspberry aphid, Amphorophora idaei, transmits four viruses and thus its presence in raspberry plantings has a detrimental effect on fruit quality, yield and plantation longevity. Resistance to this vector has been central to the red raspberry breeding programme at East Malling for over 50 years and resistance genes (A1, A10, AK4a, AL518 and Acor) from different genetic backgrounds have been identified and introduced into our breeding lines. Selection pressure on the aphid, imposed by the widespread cultivation of resistant cultivars, has led to aphid populations overcoming A1, and more recently, A10 resistance. As part of efforts to produce a more durable resistance, breeders have made crosses to combine several of these genes. However, most of them produce identical responses from the predominant aphid biotype so it is currently impossible to determine which resistance genes, and how many, are carried by breeding lines. Further, the genetic basis of the resistance itself have yet to be unravelled. A series of crosses designed to identify molecular markers linked to the various aphid resistance genes have been carried out and thus far, A1 and A10 have been allocated to linkage groups 3 and 7 respectively. This paper briefly summarizes current knowledge of Amphorophora idaei, introduces our research strategy on aphid resistance genetics in red raspberry, presents progress to date and outlines future work.