Inheritance of Bruchid resistance in selected common bean varieties in Uganda

Abstract

Common bean is an important food crop in Ugandan and the world at large, but its production is hindered by the major storage pests mainly the bruchids; Z. subfasciatus and Acanthoscelides obtectus. Control of this pest has been done by small scale farmers using traditional methods and pesticides but with little successes. Therefore knowledge of inheritance of resistance to bruchid would be important in devising strategies to breed for resistant varieties which are cost effective for the resource poor farmers and environmentally friendly. The objectives of the study therefore, were to determine: (1) the level of resistance to bruchids in exotic and selected genotypes grown in Uganda and (2) the inheritance of resistance to bruchids in selected commercial common bean varieties in grown in Uganda. Eleven common bean genotypes were evaluated in for resistance to Z.Z. subfasciatus and genotypes KK25/Nagaga/184-mw, KK25/Maluwa/19-mw and Nabe 4 were found to be moderately resistance while genotypes 19-mw, 9-mw, 112-mw, 184-mw, Nabe 4 and Nabe 15 were moderately resistant. Genotype Tapara showed high resistance to Acanthoscelides obtectus. Therefore there is potential for breeding for bruchid resistant varieties using these resistant varieties Nabe 4 and Tapara (land race) in breeding program for hybridization purpose together with the exotic KK25/Maluwa/184-mw, KK25/Maluwa/19-mw, Maluwa/KK25/443-mw, Maluwa/KK25/ 9-mw to develop resistant varieties to bruchid in common beans to prevent damage by the pest. The F2 seeds obtained from crosses made, exhibited significant variations for percentage weight loss, bruchid progeny emergence, median development period and Dobie susceptibility index. Baker’s ratio for Dobie susceptibility index as a parameter for determining resistance was high for Z. subfaciatus (0.80) but low for A. obtectus (0.4). Bruchid emergence was moderate for Z. subfaciatus (0.5) but low for A. obtectus (0.2). Narrow sense heritability was low for both species for the resistance parameters; 10-30% for Z. subfaciatus and 10-20% for Acanthoscelides obtectus. Both general combining ability (GCA) and specific combining ability (SCA) effects influenced the inheritance of the resistance suggesting that both additive and non-additive effects influence the inheritance of resistance to bruchid. Therefore, recurrent selection procedures and inter-crossing aimed at general combining ability would be more suitable for improvement of resistance to bruchid.