GENETIC VARIABILITY OF COMMON BEAN (Phaseolus vulgaris L.) GENOTYPES FOR MORPHO-AGRONOMIC TRAITS AND RESPONSE TO RHIZOBIUM INOCULATION AT HARAMAYA, EASTERN ETHIOPIA

Abstract

Common bean (Phaseolus vulgaris L.) is one of the most important legume crops in the tropics of Latin America, Asia, and Africa including Ethiopia as a cheap source of protein. Information on the genetic variability and the interrelationship between yield and yield related traits are important for developing high-yielding crop varieties with valuable yield attributes. The current study was carried out with two sets of experiments, i.e un-inoculated and inoculated with one rhizobial strain, namely 429, to assess the genetic variability and associations among yield-related traits, and their response to rhizobium inoculation in selected common bean genotypes. Ninety genotypes were evaluated in 2021/2022 at Rare, the research site of Haramaya University. A 9x10 alpha lattice design was used with two replications and nine blocks were nested within a replication. Data were collected on yield and other agronomic traits, and disease resistance. Analyses of variance, heritability, genetic advance, phenotypic and genotypic correlations, path coefficient analysis, principal component analysis, and genetic divergence were performed. Very highly significant (P ≤ 0.001) differences were observed among genotypes for grain yield and other agronomic traits, and disease reaction. Estimates of broad-sense heritability ranged from 39.92% for days to emergence to 98.9% for plant height for un-inoculated experiment, and from 39.83% to 98.92% for the same traits for inoculated experiment. GAM ranged from 6.32% for days to emergence to 95.0% for the number of nodules per plant for un-inoculated, and from 5.92% to 92.20% for inoculated plots for the same traits. Positive and significant (P ≤ 0.05) to highly significant (P ≤ 0.001) phenotypic and genotypic correlations were observed between grain yield and most of the agronomic traits in both experiments. However, of the nodule traits only nodule fresh and dry weights showed positive and significant (P ≤ 0.05) genotypic correlations with grain yield and with few agronomic traits in both experiments. Based on the result of path analysis, the highest (1.826) and (2.332) direct and positive effect on grain yield was exerted by the number of pods plant-1 at genotypic and phenotypic level, respectively, for un-inoculated, and the highest (7.522) and (1.286) direct and positive effect on grain yield was exerted by total number of seeds plant-1 at genotypic and phenotypic level, respectively, for inoculated plots. The first three principal components with Eigenvalues>1 accounted for 76.94% of the total variations. The genetic distance of 4005 pairs of common bean genotypes estimated using ED ranged from 0.94 to 9.72 with a mean of 4.64 ED and standard deviation of 1.58. Cluster analysis grouped the genotypes into six major clusters: I, II, III, IV, V, and VI each with 17, 20, 24, 15, 5, and 9 numbers of genotypes, respectively. In general, the present study showed the presence of considerable variability among common bean genotypes, and identified common bean genotypes that had responded well for rhizobium inoculation that should be further validated with more strains.