Assessment of Sinapis alba, Brassica napus and S-alba x B-napus hybrids for resistance to cabbage seedpod weevil, Ceutorhynchus assimilis (Coleoptera: Curculionidae)

Canola (Brassica napus L.), yellow mustard (Sinapis alba L.) and intergener ic crosses of S. alba x B. napus were assessed for resistance (antixenosis) to the cabbage seedpod weevil (Ceutorhynchus assimilis Paykull). Pod trich omes did not appear to be a major factor in the resistance of S. alba to we evils. The number of feeding punctures and eggs per pod in S. alba was not significantly different in pods with trichomes than in those where the tric homes had been removed. Choice and no-choice laboratory tests examining fee ding punctures and eggs laid per pod suggested that resistance in S. alba i s not conferred in the intergeneric cross, S. alba x B. napus. Similar data on feeding and weevil oviposition were found in field test plots. However, despite many eggs being laid in S. alba x B. napus hybrid plants, fewer ca bbage seedpod weevil larvae developed to exit the intergeneric hybrid pods. Glucosinolate analyses of leaves, pods and seeds showed that S. alba plant s have a high concentration of p-hydroxybenzyl glucosinolate in all three p lant parts, but B. napus has no p-hydroxybenzyl. Interestingly the intergen eric hybrid examined in this study had 62% and 60% of p-hydroxybenzyl conce ntration in the leaves and seeds, respectively, than was found in the S. al ba parent. However, pod tissues contained very little (3%) compared with th e S. alba parent. It is possible, therefore, that the adult cabbage seedpod weevil feeds on the pods of the intergeneric hybrid and lays eggs in the p od, because of the low concentration of p-hydroxybenzyl glucosinolate, but the larvae then fail to develop as they feed on the seeds containing high c oncentrations of p-hydroxybenzyl glucosinolate. It should be noted also tha t this hybrid produced pods that were more similar in physical shape to can ola pods and that this may also be a factor determining cabbage seedpod wee vil feeding and subsequent egg laying. In addition, both B. napus and the i ntergeneric hybrid produced 3-butenyl and 4-pentenyl glucosinolates in thei r pods, and degradation products (3-butenyl, and 4-pentenyl isothiocyanates ) from these glucosinolate types, are known to be stimulatory kairomones th at attract cabbage seedpod weevil. Further studies are being conducted to e xamine these factors in more detail.