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.
