Identification, mapping, and economic evaluation of QTLs encoding root maggot resistance in Brassica

Commercial varieties of canola (Brassica napus L. and B. rapa L.) are susceptible to infestations by the root maggots Delia radicum (L.) and Delia floralis (Fallen) (Diptera: Anthomyiidae) in western Canada. Although cultural strategies can ameliorate crop damage from root maggot infestations, these methods are not sufficiently effective to prevent substantial economic losses. In this paper we report the development of germplasm for resistance to root maggot infestations and the introgression of genes from a resistant relative (Sinapis alba L.) to susceptible B. napus. The effectiveness of the conferred resistance to root maggot damage was validated by comparing different genotypes for pest damage and yield loss with and without insecticide applications. Yield of B. napus plants, susceptible to root maggot infestations, increased when insecticide was applied (by up to 24%), but no significant yield differences were observed among resistant intergeneric hybrids that were treated or not treated with insecticide. One hundred and thirty-five restriction fragment length polymorphisms (RFLPs) were used to construct a B. napus genetic linkage map and to identify quantitative trait loci (QTLs) associated with resistance to root maggot damage. Two QTLs, RM-G8 and RM-G4, were found to be associated with resistance to root maggot damage. Together, these two QTLs explain 54.6% of the total variation observed.