Characterization of Callosobruchus chinensis (L.) resistance in Vigna umbellata (Thunb.) Ohwi & Ohashi

Resistance to azuki bean weevil, Callosobruchus chinensis, was studied in a series of field and laboratory experiments in two accessions of rice bean (Vigna umbellata (Thunb.) Ohwi & Ohashi), one accession of black gram (V. mungo (L.) Hepper), and one accession of mungbean, (V. radiata (L.) Wilczek). Weevil damage to immature pods of the rice bean accessions, ‘Menaga’ and ‘Miyazaki’, was significantly less than to the susceptible mungbean, VC1973A. In mature pods, the pest damage to the pod wall of Menaga was significantly higher than to VC1973A, whereas the damage to Miyazaki was similar to VC1973A. Seeds within the pods of both rice bean accessions were resistant no matter when the pods were harvested. When the insects were exposed directly on dry seeds, both rice bean accessions and a black gram accession VM2164 were resistant to them. In artificial seeds made by mixing flour of the individual resistant Vigna accessions with VC1973A and subsequently exposed to bruchid oviposition, the higher the quantity of resistant Vigna flour the lower the number of bruchids that emerged from such seeds. No bruchids emerged from artificial seeds containing crude starch fraction from the three resistant Vigna accessions when such seeds were exposed to bruchid infestation, whereas many insects emerged from the seeds containing starch of VC1973A or flour of VC1973A alone. In artificial seeds made by mixing crude protein fractions of the three resistant Vigna accessions with flour of VC1973A, as the concentration of protein increased the number of C. chinensis adults that emerged decreased. Fractionation of crude proteins into acetone-precipitable proteins and peptide and amino acid portions resulted in the loss of antibiosis effect. Artificial seeds made from purified starch-polysaccharides fraction, however, exhibited antibiosis effects if prepared from the rice bean seed of Menaga and Miyazaki but not if made from the black gram seed, VM2164.