Breeding of rutabaga (Brassica napus var. napobrassica L. Reichenb.) based on biomarker selection for root maggot resistance (Delia radicum L.)

Cabbage root maggot (Delia radicum) is the most devastating and persistent pest for rutabaga (Brassica napus var. napobrassica) in all production areas in Canada. With the deregistration of terbufos (Counter^?) to combat maggot attack, only chlorpyrifos (Lorsban^?), an organophosphorous pesticide, remains and extensive use could lead to insecticide resistance. An unprotected crop would lead to serious domestic and export losses. Root maggot resistance from canola, that originated from the weedy crucifer, Sinapis alba, was transferred to rutabaga by standard hand crossing. A population of doubled haploids was developed from the F1s and screened in a high pressure root maggot rutabaga production field. Resistant and susceptible isolines were identified from different crossing groups and these isoline pairs were used to develop a biochemical selection protocol based on HPLC profiles where glucosinolates can be present as an aid to resistance breeding. Fourteen peaks in the HPLC profile were identified as markers and predictably varied between the more resistant and more susceptible lines. The 3–4 leaf stage was identified as the ideal stage for tissue extraction for profiling which is close to the stage when gravid female maggot flies seek host plants for oviposition utilizing olfactory signals from the host. Olfactory signals for Delia commonly are isothiocyanates which are volatile break down products of glucosinolates. The peaks in the HPLC profiles identified as markers for resistance contain glucosinolates and may be partially responsible for the plant-insect interaction. A predictive model is proposed as an aid to breeders for the development of root maggot resistant rutabaga lines.