alpha-Amylase inhibitors in resistance of common beans to the Mexican bean weevil and the bean weevil (Coleoptera: Bruchidae)

The arcelin-phytohemagglutinin-alpha-amylase inhibitor (Arc-Pha-alpha AI) locus of the common bean, Phaseolus vulgaris L., encodes plant defense proteins with different modes of action. Introgression of this locus from resistant wild bean accessions into cultivated varieties is, in some cases, able to confer resistance to the Mexican bean weevil, Zabrotes subfasciatus (Boheman), but not to the bean weevil, Acanthoscelides obtectus (Say). With respect to the Mexican bean weevil, resistance may be the result of one or a combination of the insect inhibitory proteins at this locus. However, for the bean weevil, resistance behaves as a quantitative bait encoded by different loci. We studied the relationship between the levels of alpha-amylase inhibitory activity, the polypeptide patterns, and weevil resistance. We evaluated the alpha AI activities in 64 wild and cultivated bean genotypes with different levels of resistance to both bruchids and also studied alpha AI peptide patterns in wild genotypes with 3 different arcelin isoforms and in the backcrosses of these 3 genotypes with 'Sanilac'. Our results show that alpha AIs do not confer detectable resistance to either of the bruchids in any of the genotypes tested and is probably only a minor contributor to this resistance.