Gene Pyramiding Improved Resistance to Angular Leaf Spot in Common Bean

Aims: The study was conducted to determine the effectiveness of pyramided genes in improving angular leaf spot (ALS) resistance in susceptible common bean cultivars.

Study Design: The experiment was set in randomized block design with three replications.

Place and Duration of Study: The experiment was conducted at International Centre for Tropical Agriculture (CIAT) at Kawanda, Uganda in 2010-2014.

Methodology: Crosses among three Pseudocercospora griseola resistant lines of common bean (Phaseolus vulgaris) were developed. The crosses involved five inbred lines, AND277, Mexico 54, G5686 and two susceptible cultivars, K132 and Kanyebwa. The resistant lines were crossed in cascading pyramiding scheme to develop triple crosses (TC). The TC F1 and each of the resistant parents were crossed with each of the two susceptible cultivars to generate four parent crosses (FPC) and single crosses (SC), respectively. All the population developed was inoculated with 61:63 P. griseola isolate under screenhouse conditions and their reaction was elucidated.

Results: The SC exhibited resistance segregation ratios of 15:1 and 61:3 while TC best fitted for 249:7 and 247:9 ratios. This suggested that two or three genes were present in SC and four genes in the TC. The resistance present in the three sources to ALS race 61:63 is complex; with epistatic mode of inheritance. The four genes in FPC provided more effective resistance against isolate 61:63 than two or three genes in SC.

Conclusion: The FPC lines with combined resistance were more effective than the individual sources for transferring resistance to susceptible cultivars. Future studies needs to be conducted to determine how broad and effective combined resistances in these newly developed lines have against the variability of the ALS pathogen sampled in Uganda.