Breeding for resistance to colletotrichum lindemuthianum (sacc. and Magn. Scrib) in common bean (Phaseolus vulgaris L.)

THESIS MSC

Bean anthracnose caused by Colletotrichum lindemuthianum causes severe common bean (Phaseolus vulgaris L.) yield losses. Breeding for resistance is the best method to mitigate this problem. The objectives of this study were to; (1) screen and identify two common isolates of C. lindemuthianum from major bean growing areas in Zambia, (2) investigate the effectiveness of C. lindemuthianum multiple race inoculations on genotypic response in common bean and (3) determine the nature of inheritance to C. lindemuthianum in common bean genotypes. Seven parents were crossed in a 7 X 7 full diallel mating design. Forty-two progeny crosses together with their parents were raised in the green house, in a Completely Randomised Design (CRD) with four replications. The treatment used were (1) inoculation with race 54; (2) inoculation with race 311 and (3) a combination of inoculation of race 54 X race 311. The mean genotypic scoring were found to be 1.76, 2.62 and 3.06 for treatments 1, 2 and 3 respectively. There were significant differences (P < 0.01) among genotypic responses to C. lindemuthianum with respect to race 311 while race 54 and race 54 plus race 311(multiple inoculations) showed no significant differences among the genotypes. The t-test analysis revealed that multiple race inoculation (Treatment 3) had a higher disease severity expression than those of single race inoculations (Treatment 1 and Treatment 2). Multiple infection had a synergistic effect suggesting its suitability for the screening of resistant genotypes in the breeding program. With regards to treatment 2 (Inoculation with race 311), the analysis of variance revealed that general combining ability (GCA) and specific combining ability (SCA) were not significant for resistance to C. lindemuthianum. Only reciprocal effects were found to be significant implying that both cytoplasmic gene- and environmental effects were at play. Further on, the baker’s ratio of 0.15 obtained meant that inheritance was due to non-additive gene action. Breeders should therefore use hybridization as breeding strategy, in the production of resistant beans with regards C. lindemuthianum, race 311.