Susceptibility to bruchids among common beans in Uganda

J.A Ebinu,A.J Agona,H.L Talwana,V Nsabiyera,M Otim,S.T Nkalubo,M Ugen

doi:10.4314/acsj.v24i3.6

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 noncultivated 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. Key Words : Acanthoscelides obtectus, Phaseolus vulgaris, Zabrotes subfasciatus

Highlights

The bean bruchids, Acanthoscelides obtectus Say and Zabrotes subfasciatus Boheman (Coleoptera: Bruchidae), are among the most important and widespread storage pests in all major dry common beans (Phaseolus vulgaris L.) growing regions world wide (Msolla and Misangu, 2002; Schmale et al, 2002; Nadir et al, 2005). These bruchid species have similar biology and coexist; with several adults of both A. obtectus and Z. subfasciatus infesting the same seed at the same time (Ware, 1988)
The objective of this study was to evaluate bean genotypes existing among farmers in agroecologically different bean growing areas in Uganda for resistance against post-harvest infestation and damage by bruchids (A. obtectus and Z. subfasciatus)
The data presented clearly shows that all the 45 dry bean genotypes evaluated supported reproduction, growth and development of A. obtectus and Z. subfasciatus (Tables 3 and 4), providing evidence of susceptibility of all materials to the two-bruchid species. This indicates that the discovery of bruchid resistance in Mexico has not yet been tapped into Uganda’s common bean germplasm

Summary

Introduction

The bean bruchids, Acanthoscelides obtectus Say and Zabrotes subfasciatus Boheman (Coleoptera: Bruchidae), are among the most important and widespread storage pests in all major dry common beans (Phaseolus vulgaris L.) growing regions world wide (Msolla and Misangu, 2002; Schmale et al, 2002; Nadir et al, 2005). These bruchid species have similar biology and coexist; with several adults of both A. obtectus and Z. subfasciatus infesting the same seed at the same time (Ware, 1988). The objective of this study was to evaluate bean genotypes existing among farmers in agroecologically different bean growing areas in Uganda for resistance against post-harvest infestation and damage by bruchids (A. obtectus and Z. subfasciatus)

Objectives

Methods

Results

Discussion

Conclusion