Characterization of new sources of mungbean (Vigna radiata (L.) Wilczek) resistance to bruchids, Callosobruchus spp. (Coleoptera: Bruchidae)

The bruchid beetles Callosobruchus chinensis (L.) and C. maculatus (F.) are destructive pests of stored mungbean (Vigna radiata (L.) Wilczek). The development of resistant mungbean varieties to manage bruchids is a major breeding objective. In the present study, we investigated the characteristics of resistance to C. chinensis and C. maculatus in two new resistant mungbean accessions V1128 and V2817, and two previously reported resistant accessions V2709 and V2802, compared to the susceptible mungbean cultivar, KPS1. Evaluation for resistance to both bruchid species using whole and decorticated seeds revealed that V1128 and V2817 were free from damage, V2709 and V2802 showed partial damage with low or moderate number of bruchids emerging from seeds, and KPS1 showed complete damage with the highest number of bruchids emerged. Comparison of the seeds harvested at seed filling, early maturity and full maturity stages revealed that the percentage of damaged seeds from resistant accessions was lower at all stages compared with KPS1. V1128 and V2817 showed complete resistance against both bruchids regardless of when their seeds were harvested, while resistance in V2709 and V2802 were most pronounced at full maturity, and KPS1 was totally damaged at all times tested. These results suggest that the chemical factor(s) conferring resistance is synthesized as early as the seed filling stage. Evaluation of resistance using artificial seeds showed that increasing the percentage of resistant seed powder adversely affected bruchid growth and development. The number of adults emerging from seeds and number of damaged seeds decreased while adult developmental period increased as the proportion of resistant seed powder increased. The weight of emerging male and female adults of C. maculatus was lighter than those from the seeds containing susceptible seed powder alone. However, C. chinensis adults were not affected by the same test. The results suggest that biochemical(s) in cotyledon tissue are responsible for the resistance and the seed coat had no protective role against the bruchids. Although all four resistant accessions evaluated are useful for mungbean breeding, V1128 and V2817 show complete resistance to both C. chinensis and C. maculatus. Thus, these two new resistant sources may be the most effective for breeding purposes.