Abstract:

The bean bruchids, Acanthoscelides obtectus Say and Zabrotes subfasciatus Boheman (Coleoptera: Bruchidae),
are cosmopolitan pests of stored dry common beans (Phaseolus vulgaris L.), causing damage through reduction
of grain quality and seed germination. Biological resistance to these bruchids was definitively established in non
cultivated bean accessions and has been introgressed into a range of drybean market classes. However, existing
resistance to bruchids in Uganda’s common bean germplasm has not been systematically studied. In this study,
45 bean genotypes from the National Bean-Breeding Programme (25 genotypes) and agroecologically diverse
bean growing areas in Uganda (20 genotypes), were evaluated for postharvest bruchid resistance. None of the
evaluated bean genotypes expressed resistance to either bruchid species, with all the 45 bean genotypes supporting
bruchid development, reproduction and feeding. All genotypes were severely damaged by bruchids feeding,
resulting in significant (P<0.05) reduction of seed germination. Reduction in seed germination was related to the
number of emergence holes and seed size; small bean seeds damaged by up to 2 bruchid emergence holes had a
7.1% reduction in germination, while large bean seeds with a similar number of emergence holes showed a 25%
reduction in germination. Whereas this study further confirms bruchids as important storage pests of beans
causing direct loss through consumption of the seed and indirect loss through viability deterioration, the resistance
to bruchids in the evaluated range of Uganda’s dry bean germplasm is inadequate for direct exploitation in a
breeding programme.