Legume Seeds: the Defences of Wild and Cultivated Species of Phaseolus Against Attack by Bruchid Beetles

A range of accessions (182) of wild, semi-cultivated and cultivated Phaseolus were subjected to attack by two Old World bruchids, Callosobruchus maculatus and Caliosobruchus chinensis and two New World bruchids Zabrotes subfasciatus and Acanthoscelides obtectus. Six different stages in the progression of the brochid-legume interaction, at which resistance may occur, are described and assessed. Resistance is shown by: no oviposition; disrupted embryo development; failure of larvae to penetrate the testa; death of larvae within the cotyledon; failure of pupation or adult emergence; reduced fitness of adults. The occurrence of resistance at each of these stages is discussed in the context of possible causal mechanisms. The patterns of resistance to the two pairs of bruchids of different geographical origin is considered in relation to co-evolutionary processes