Glucosinolate Content and Susceptibility for Insect Attack of Three Populations of Sinapis alba

Sinapis alba is less susceptible to damage by insect pests than Brassica napus. We investigated the composition and distribution of glucosinolates in different plant parts in three populations of S. alba; two populations selected for low-seed-glucosinolate content and one commercial cultivar. We have assessed the susceptibility of low-seed-glucosinolate content populations of S. alba to four insect pests, a flea beetle, a pollen beetle, and two species of aphids. Over 90% of the total glucosinolates in the cotyledons of the three populations of S. alba consisted of sinalbin. There was no difference in feeding damage by flea beetles on different S. alba populations at the cotyledon stage, nor was there a difference in sinalbin concentration of cotyledons. Total glucosinolate levels were highest in younger plant tissues. Sinalbin declined as a proportion of total glucosinolate content in later growth stages, especially in the low breeding lines. Reproduction by aphids was the same on all three populations despite differences in sinalbin content of the S. alba leaves at the growth stage tested. The specialist aphid, Brevicoryne brassicae, was found mainly on young tissues, while the generalist aphid, Myzus persicae, was found predominantly on older plant parts. There was no difference in oviposition by pollen beetles between the S. alba populations, despite the fact that on one population total glucosinolate concentration and the proportion of sinalbin found in the buds were much lower than on the other two populations.