GLUCOSINOLATE CONTENT AND SUSCEPTIBILITY FOR INSECT ATTACK OF 3 POPULATIONS OF SINAPIS-ALBA

Sinapis alba is less susceptible to damage by insect pests than Brassi ca napus. We investigated the composition and distribution of glucosin olates in different plant parts in three populations of S. alba; two p opulations selected for low-seed-glucosinolate content and one commerc ial cultivar. We have assessed the susceptibility of low-seed-glucosin olate content populations of S. alba to four insect pests, a flea beet le, a pollen beetle, and two species of aphids. Over 90% of the total glucosinolates in the cotyledons of the three populations of S. alba c onsisted of sinalbin. There was no difference in feeding damage by fle a 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 growt h stages, especially in the ''low'' breeding lines. Reproduction by ap hids was the same on all three populations despite differences in sina lbin content of the S. alba leaves at the growth stage tested. The spe cialist aphid, Brevicoryne brassicae, was found mainly on young tissue s, while the generalist aphid, Myzus persicae, was found predominantly on older plant parts. There was no difference in oviposition by polle n beetles between the S. alba populations, despite the fact that on on e population total glucosinolate concentration and the proportion of s inalbin found in the buds were much lower than on the other two popula tions.