Abstract

Breeding red raspberry for resistance to the large raspberry aphid (Amphorophora idaei) using single major genes or polygenic minor genes has proved successful in controlling this virus vector aphid for a period of more than thirty years. Currently, about 90% of raspberry UK plantations, valued at more than 28 million, contain varieties with these A. idaei resistance genes. However, surveys in 1990-93 found that more than 75% of the UK. A. idaei population consisted of biotypes with the ability to break the most widely used resistance gene, A₁. Since then growers in England (but not yet in Scotland) have reported intermittent breakdown of the formerly strongest resistance gene, A₁₀. Genetic analysis, based on rDNA IGS DNA patterns, has shown that A. idaei populations in the UK are genetically very variable within and between the 5 known A. idaei biotypes. Alate migrations of parthenogenetic females in summer and males in autumn means that resistance-breaking genes are readily exchanged between populations. It is therefore predicted that the A₁₀ gene will be overcome throughout the U.K. within the next few years. Virus incidence is increasing in parallel with breakdown of the aphid resistance genes in UK raspberry plantations. Other resistance genes are not readily available within the genus Rubus. Anti-aphid genes from other plants (lectins) have been genetically engineered into crops. Initial risk:benefit assessment of one candidate aphid resistance transgene was presented, together with future prospects for introducing other sources of aphid resistance.