The potential of resynthesized lines to provide resistance traits against rape stem weevil in oilseed rape

The rape stem weevil, Ceutorhynchus napi Gyll., is a serious pest of winter oilseed rape (Brassica napus L.) crops in Europe that causes stem distortion, severe disruption of stem growth, and significant yield loss. No resistance has been identified in current B. napus breeding material. Resynthesized lines of oilseed rape can be used to introduce genetic material from the parent species Brassica oleracea L. and B. rapa L. The susceptibility to C. napi of five resynthesized lines and three cultivars of oilseed rape was compared in a multi-choice field plot experiment. Morphological stem traits and stem levels of glucosinolates, carbon, and nitrogen were assessed as potential mediators of resistance. Eggs and larvae of C. napi in stems were counted weekly from the beginning of oviposition to larval maturation and stem pith degeneration in response to oviposition was assessed. Egg counts per stem were negatively dependent on stem length and positively dependent on the levels of five glucosinolates, glucobrassicanapin, glucoalyssin, glucobrassicin, neoglucobrassicin, and gluconasturtiin. The resynthesized line S30 was significantly more resistant to C. napi than the commercial cultivar Sollux, having fewer eggs and larvae. This resistance appeared to be largely antixenotic, due to the combination of a long stem and a paucity of the five key glucosinolates. We propose that resynthesized lines such as S30 should be used to introduce genes determining traits such as long stem length and glucosinolate profile into breeding programs to enhance resistance against C. napi in oilseed rape.