Pathogen variability and new sources of resistance to angular leaf spot among bean landraces in Uganda

Abstract

Angular leaf spot (ALS), a fungal disease caused by Pseudocercospora griseola, has a significant impact on bean productivity in Africa, causing up to 80% yield losses. Efforts to breed for ALS resistance are challenged by continuously evolving pathogen races that differ by location. Released bean varieties in Uganda are susceptible to ALS; the few exotic sources of resistance available are not well adapted to local environmental conditions. To overcome these challenges, a study was conducted to understand pathogen variability and identify new sources of ALS resistance for deployment in ALS resistance breeding. Variability in 45 P. griseola pathotypes was elucidated using a set of 12 ALS differential cultivars, random amplified microsatellite markers, and conserved sequences. The differentials and markers defined 12 pathotypes and 30 haplotypes, respectively, which belonged to the Middle American and Andean gene pool groups, each with high variability. Among the 74 bean landraces screened using the 1:6, 17:39, 21:39, and 61:63 P. griseola pathotypes, only U00279 showed consistent resistance to all the four pathotypes. U00297’s resistance to pathotype 17:39 was conferred by a single dominant gene, while digenic epistatic gene interactions were responsible for resistance to other pathotypes. The dominant gene in U00297 was independent of resistance genes harbored by documented resistance sources AND277 and G5686. The results revealed high variability in P. griseola and identified a new source of broad ALS resistance. The divergent inheritance patterns of resistance to the different pathotypes indicate the importance of race specificity of the target host plant in breeding for disease resistance.

Keywords: Pseudocercospora griseola, variability, resistance, inheritance, allelic