Characterization and selection Anthracnose and Pythium root rot resistance in common bean landraces grown in Kenya

Common bean (Phaseolus vulgaris L.) production in Kenya has not reached its potential yield due to various abiotic and biotic factors. Anthracnose, caused by Colletotrichum lindemunthianum and root rots caused by Pythium species are major production constraints. Landraces are preferred by farmers in Kenya due to yield stability and tolerance to some stresses. However, there is little information on the genetic diversity of the landraces and the level of resistance to anthracnose and Pythium root rot. The current study therefore focused on the following objectives (i) to characterize common bean landraces in Kenya based on morphological and simple sequence repeat (SSR) variations, (ii) screen for Pythium root rot and anthracnose resistance among Kenyan landraces and (iii) introgress anthracnose and Pythium resistance genes into farmer-preferred landraces. The study landraces were collected from farmers’ fields and local markets in western, central and eastern Kenya. The genetic diversity within the landraces was determined based on morphological data that was obtained from field experiments and simple sequence repeats (SSRs) markers. Commercial genotypes were included as checks in the study. The results showed significant differences (P≤0.05) among the genotypes for days to 50% flowering, days to plant maturity, leaf length, leaf width, number of pods per plant, number of seeds per pod, pod length, plant height, 100 seed weight and seed yield per plot, indicating high variability among the genotypes. In addition, 51 alleles were obtained from a set of 22 SSR markers, with a mean of 2.32 alleles. Through morphological cluster analysis, 4 distinct clusters were identified. The first cluster consisted of 20 large-seeded genotypes, the second cluster included 39 medium-seeded genotypes with a mixture of determinate and semi-determinate growth habits, the third cluster contained six medium-seeded indeterminate genotypes while the fourth cluster comprised of 34 small-seeded genotypes. Molecular analysis grouped the germplasm into three clusters. Cluster 1 was majorly composed of commercial genotypes of all seed sizes. Cluster 2 comprised of medium seeded genotypes while the third cluster comprised a mixture of genotypes with no unique observation within the clusters. Under greenhouse conditions, majority of the landraces were moderately resistant to anthracnose while most of the small seeded landraces were moderately resistant to Pythium root rot. None of the landraces possessed the molecular markers that are linked to anthracnose and Pythium root rot resistances. Three farmer-preferred landraces were selected for introgression of genes that confer resistance to anthracnose and Pythium root rot. The anthracnose differential cultivar, G2333, was used as the donor parent for anthracnose resistance in a marker assisted backcrossing scheme, while KK 8 was used as the donor parent for Pythium root rot resistance. Utilization of molecular markers enabled the development of 99 lines that carried Co 4 gene (anthracnose) and Pyult1 gene (Pythium). The introgression of disease resistance genes in landraces will ultimately enable bean growers achieve greater yields contributing to high income and improvement of their livelihoods. The information that was obtained from characterization of the landraces will inform breeders on suitable parents to use in breeding programs.