Identification and evaluation of root maggot (Delia spp.) (Diptera: Anthomyiidae) resistance within Brassicaceae

Current varieties of canola/oilseed rape, Brassica napus L. and Brassica rapa L., are susceptible to infestation by the root maggots Delia radicum (L.) and Delia floralis (Fallen) (Diptera: Anthomyiidae) in western Canada. Crop losses from root maggot infestations can be very significant, and infestation levels have increased substantially from 1983 to present. Although cultural and chemical strategies exist to reduce crop losses caused by root maggots, these methods are either not sufficiently effective or pose unacceptable environmental risk. This paper reports progress achieved to develop canola cultivars resistant to attack by root maggots as the most environmentally sustainable strategy for management of these pests. Twelve species of Brassicaceae, and many genotypes within species, were evaluated for levels of root maggot resistance, in addition to many intergeneric hybrids produced by crosses of Sinapis alba x B. napus. Sinapis alba had greatest resistance to infestation by root maggots among the Brassicaceae species evaluated, and five intergeneric hybrids had levels of resistance to root maggots that were similar to S. alba and were maintained from year to year. Low amounts of S. alba DNA were detected in the hybrids using genomic slot-blot analysis. These results indicate that a genetic basis for resistance to root maggot infestation exists in the Brassicaceae, and our research represents the first step toward introgression of genetic sources of root maggot resistance from related species into commercial canola varieties. (C) 2000 Elsevier Science Ltd. All rights reserved.