Genetic diversity of common bean (Phaseolus vulgaris L.) landraces from South Western Kenya for resistance to Pythium root rot disease

Common bean landraces represent an important source of genetic resources, which is under-exploited by Kenyan crop breeding programs. The objective of this study was to characterize 51 common bean landraces from South Western Kenya for resistance to Pythium root rot using 5 peroxidase gene (POX) markers. Following infection with Pythium spp., 11.77, 54.90 and 33.33% of the landraces were moderate-resistant, susceptible and highly susceptible, respectively. A total of 1119 alleles were amplified by the 5 primers, ranging from 3 to 8 alleles per locus. The polymorphism information content (PIC) of the POX markers varied from 0.10 to 0.47. The dendrogram generated using similarity coefficients and un-weighted pair group method with arithmetic averages (UPGMA) did not reveal any unique groupings according to their reaction to Pythium root rot disease. Population structure analysis separated the germplasm into 3 groups and all the groups contained landraces exhibiting both moderate resistance and susceptible to Pythium root rot. The lack of distinct grouping of landraces based on resistance suggests presence of significant genetic variability and different sources of resistance to Pythium root rot. These findings give valuable information for breeders and serve as a baseline for development of cultivars with Pythium root rot resistance.   Key words: genetic variability, population structure, peroxidase gene markers, Pythium root rot, resistance.