Screening for potential bioactive varieties of Sesamum indicum Pedaliaceae, using diamondback moth as a test insect

摘要

Sesame, (Sesamum indicum) ( L) Pedaliaceae, has recently been found to be bioactive due to its constituent lignans: sesamin, sesamol and sesamolin. There exist thousands of races or cultivated varieties in addition to those growing as wild plants around especially the world's southern hemisphere. Sesame varieties (54) collected from Africa (the suggested origin) and Asia (the highest producing area) were tested for possible bioactivity on a susceptible strain of diamondback moth Plutella xylostella (L) ( Lepidoptera: Plutellidae) . Diamondback moth was chosen as an ideal test insect due to its record of resistance to most xenobiotics. This susceptible strain had been maintained on radish seedlings in the laboratory for at least 18 generations. Thesesame varieties, some of which had evaded insect incidence in a field trial, were individually incorporated into wheat germ-based artificial diets for diamondback moth. Differences in parameters such as developmental periods, survival, longevity, insectsize and fecundity were recorded. The results obtained indicate that the modified artificial diet with propionic acid as the only preservative, with 50% w/w composition of sesame leaves, showed differences among varieties and also when compared to leaves of radish seedlings in the diet. The bioactive mechanisms recorded could be attributed to either an antifeedant, a toxicant, a growth regulator or a combination. Comparisons between the radish-incorporated and the average of the sesame-incorporated artificial diets were as follows: 2nd instar larval survival up to 4 days, 84% and 59%; larval success to pupa, 64% and 28%; pupal success to adult, 53% and 9%, respectively. The average pupal weight was 7. 6mg for the control and 4. 8mg for the sesame varieties. Varieties with consistent bioactive indicators were further analyzed for other insect parameters.