Abstract:
Common bean has a wide range of genetic diversity for various economical traits and possesses broad variation in terms of cultivation methods, range of adaptation to environments, and morphology. Knowledge of both morphological and molecular diversity of the crop is important in plant breeding for selecting superior genotypes for yield and other agronomic traits to utilize as parents in crossing programs. The present study was carried out to characterize the common bean cultivars in east Hararghe based on morphological and molecular (SSR) markers and to determine the genetic diversity and population structure of common bean cultivars using agro-morphological and SSR markers. Forty-nine common bean cultivars were evaluated in the cropping season of 2022 at Rare the research site of Haramaya University, in triple lattice design. Analysis of variance, phenotypic and genotypic correlations, heritability, genetic advance, path coefficient analysis, genetic divergence, and principal component analysis were performed. Analysis of variance revealed highly significant differences among the cultivars for all quantitative traits studied. Positive and highly significant (P< 0.01) genotypic and phenotypic correlations were observed for days to maturity, plant height, number of seeds per plant, and number of pods per plant. The number of seeds per plant exerted the highest positive direct effect on grain yield (0.988) followed by plant height (0.571) at genotypic level; indicating the existence of a true association between these traits and grain yield. At phenotypic level, the highest positive direct effects on grain yield were exerted by hundred seed weight (0.942) followed by plant height (0.469) and number of seeds per plant (0.459). The first four principal components accounted for 82.93% cumulative contribution to the total variation. Cluster analysis also categorized the 49 cultivars into four major clusters. The genetic distances among cultivars estimated by Euclidean Distance (ED) varied from 1.08 to 9.87 with a mean and standard deviation (SD) of 4.80 and 1.72, respectively. Molecular characterization using 10 simple sequence repeat (SSR) markers revealed a total of 27 polymorphic alleles with an average of 2.7 alleles per locus. The average polymorphic information content (PIC) was 3.67. The result from the analysis of molecular variance showed that genetic variation within individuals and variation among individuals accounted for 85% and 5% of the overall variance, respectively. Only 10% of the overall variance was linked to population divergence. The genetic variation was also estimated by the expected heterozygosity (He). The cultivars were grouped into two main and two sub-clusters based on genetic distances measured by SSRs markers. It is concluded that the observed wide genetic variation among cultivars could be utilized for improvement of the crop and the information generated could also be used for genetic conservation.
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