Variation in resistance to the cabbage aphid ( Brevicoryne brassicae) between and within wild and cultivated Brassica species

Seven Brassica species were evaluated for their resistance to the cabbage aphid, Brevicoryne brassicae, in a series of field experiments. Four wild Brassica species, two 8 chromosome species with similarities to the B genome of Brassica nigra (Brassica fruticulosa and Brassica spinescens) and two 9 chromosome species containing the C genome (Brassica incana and Brassica villosa) were identified as possessing consistently high levels of antibiosis mediated resistance to B. brassicae. None of the species were shown to possess consistently high levels of antixenosis resistance. In more detailed glasshouse experiments one B-like genome species, B. fruticulosa, showed considerable variation between accessions collected from different sites for resistance to B. brassicae. In addition, individual accessions of one A genome species (Brassica rapa) and one C genome species (Brassica alboglabra) were shown to be highly variable in their resistance to B. brassicae, some plants of each accession being highly resistant and others very susceptible. The implications of the variability in resistance to B. brassicae within wild Brassica species for exploitation in Brassica breeding programmes are discussed.