Evaluation of screening methods for bruchid beetle (Callosobruchus chinensis) resistance in greengram (Vigna radiata) and blackgram (Vigna mungo) genotypes and influence of seed physical characteristics on its infestation.

Abstract

Bruchid beetle, Callosobruchus spp. (Coleoptera: Bruchidae) cause substantial reduction in quantity and quality of legumes during storage in tropical and sub-tropical regions of the world. C. chinensis is the most important bruchid in Asia and causes considerable damage to Vigna seeds. Four hundred seventy five accessions of two Vigna species, [335 of Vigna radiata (greengram) and 140 of Vigna mungo (blackgram)] were initially evaluated for resistance to bruchid beetle through ‘free choice’ test. Eight greengram and nine blackgram resistant accessions were further evaluated under lab conditions using ‘no choice’ test. Four greengram accessions (LM 131, V 1123, LM 371 and STY 2633) were found moderately resistant with less percentage survival (38.9 to 51.6%) and prolonged developmental period (30.5 to 31.5 days) as compared to susceptible check (90.8% survival and 26.1 days of developmental period). Similarly in blackgram, three accessions (UH 82-5, IC 8219 and SPS 143) were moderately resistant with less percentage survival (33.7 to 42.0%) and prolonged developmental period (26.8 to 28.1 days) as compared to susceptible check (83.2% survival and developmental period of 24.2 days). Physical characteristics of the seeds were related with the ovipositional preference of the bruchid. In greengram, lesser number of eggs were recorded in small and shiny seeds as compared to large and dull seeds while in blackgram, small and black seeds recorded lower number of eggs as compared to large and green seeds. In this study, ‘no choice’ test seemed to be most reliable and potentially useful for screening of bruchid resistance. Since, no cultivated germplasm exhibited complete resistance, the moderately resistant genotypes identified in the present study hold promise in breeding programme of greengram and blackgram.