Resistance to the cabbage root fly, Delia radicum, within Brassica fruticulosa

Fourteen accessions of the wild species Brassica fruticulosa were evaluated for resistance toward the cabbage root fly Delia radicum in comparison with a widely cultivated cauliflower cultivar and a rapid cycling Brassica oleracea line. The more resistant accession of B. fruticulosa had 60.6 percent plants escaping the attack, while only 2.6 percent of the cauliflower material survived. Larvae feeding on roots after inoculation with twenty D. radicum eggs per plant under glasshouse conditions effectively discriminated between both the two species and accessions within B. fruticulosa. Genetic determination of escape rate was high with 55.4 percent of total variation explained by genotypes, while average number of days without collapse and average number of days without symptoms showed genetic determination of 22.0 percent of total variation. All 11 diploid accessions of B. fruticulosa showed higher escape rates (14.7-60.6%) than the two B. oleracea cabbage lines (2.6 and 5.0%). The three tetraploid B. fruticulosa accessions formed an intermediate group with the B. fruticulosa ssp. glaberrima accession, having a higher escape rate (22.8%) than the accessions of B. fruticulosa ssp. mauritanica, and B. fruticulosa ssp. radicata (2.1 and 5.7%, respectively). Accessions among the diploid B. fruticulosa group on average survived 15.1 to 18.4 days without collapse in the test, while the tetraploid accessions had on average 11.7 to 14.2 days without collapse and the two B. oleracea accessions survived on average only 11.5 and 11.7 days without collapse. Results are discussed with respect to the possible transfer of such resistance from the wild species into breeding material of cultivated types of Brassica vegetables.