Resistance determination of a South Indian bruchid strain against rice bean landraces of Manipur (India)

Rice bean (Vigna umbellata) is one of the under-exploited tropical food legumes. It is regarded as a potentially valuable multipurpose (grain, fodder and green manure) crop among farmers in the marginal hill areas of North-Eastern India, Manipur in particular. Rice bean seeds are comparatively resistant to storage grain pests including bruchids (Callosobruchus spp.), which generally damages other pulses of the same genus Vigna and related legumes. However, there are reports of seed infestation by bruchids during storage. The present investigation involved subjecting seeds of rice bean landraces from Manipur to low and high bruchid infestation levels in order to determine their reaction. This is the first report on bruchid bioassay conducted on landraces of this remotely situated Indian state. The landraces were classified based on the seed damage per cent with 1-9 score. Although variations in oviposition response were observed among the landraces, regression and correlation studies between seed characteristics and bruchid life parameters suggested no significant role of antixenosis (non-preference) mechanism in imparting resistance to bruchids. To date, rice bean has not been subjected to systematic breeding, despite the species' many useful characteristics. The experiments revealed identification of new sources of bruchid resistance. Hence, these landraces can be effectively used as promising donors for hybridization in pulse improvement programmes.