Effect of Seed Texture Layer on Bruchid Infestation in Mungbean Vigna radiata (L.) Wilczek

Abstract

An experiment was carried out to evaluate the effect of texture layer of mungbean seed on infestation of bruchids (Callosobruchus maculatus and C. chinensis) (Coleoptera: Bruchidae). Seventeen BC9 near-isogenic mungbean lines (NILs) which are resistant to the insects, and their parents (KPS 1, CN 60 and the wild mungbean TC 1966), were compared. Each entry was prepared in two sets, one with intact texture layer and the other with texture layer removed by 15% NaOH. Each set was divided into 8 samples of 5 g each to test against the bruchids. The results revealed that both bruchid species laid more eggs on no texture layer seeds than on the intact ones. The difference in egg laying was especially high on seed of the wild mungbean TC 1966. The NILs, KPS 1 and CN 60 harbored several eggs on seed surfaces. However, the resistant lines had almost no damaged seed, regardless the removal of texture layer. The highest damage among the resistant NILs was only 5.5% while the susceptible recurrent parents were completely damaged. The texture layer seemed to affect only insect oviposition but not seed damage. Thus, to evaluate for chemical resistance to bruchids in a mixture of dull- and shiny-seeded mungbean, their texture layer should be removed to normalize the number of eggs laid on seeds.