Abstract
The Ethiopian genetic center is considered to be one of the secondary centers of diversity for the common bean. This study was conducted to characterize the distribution of genetic diversity between and within ecological/geographical regions of Ethiopia. A germplasm sample of 116 landrace accessions was developed, which represented different common bean production ecologies and seed types common in the country. This sample was then analyzed with 24 simple sequence repeat (SSR) markers to assess the genetic diversity within and between common bean landraces, classifying them based on SSR clustering, and determining relationships between genetic and agroecological diversity. Representatives of both Andean and Mesoamerican gene pools were identified by STRUCTURE software analysis, as well as a high proportion of hybrid accessions as evidenced by a STRUCTURE K = 2 preset. At the optimum K = 5 preset value, mixed membership of Andean and Mesoamerican genotypes in some of the clusters was also seen, which supported previous findings. Cluster analyses, principal coordinate analysis, and analysis of molecular variance all indicated clustering of accessions from different collection sites, accompanied by high gene flow levels, highlighting the significant exchange of planting materials among farmers in different growing regions in the country. Values of allelic diversity were comparable to those reported in previous similar studies, showcasing the high genetic diversity in the landrace germplasm studied. Moreover, the distribution of genetic diversity across various bean-growing population groups in contrasting geographical/ecological population groups suggests elevated but underutilized potential of Ethiopian germplasm in common bean breeding. In summary, this study demonstrated the geographical, as well as gene pool diversity in common bean germplasm of Ethiopia. This substantial diversity, in turn, should be utilized in future common bean breeding and conservation endeavors in the nation. Key words: Hybridity, simple sequence repeat, microsatellite, structure, seed exchange, gene flow.
Highlights
Common bean is the most widely consumed legume species of the genus Phaseolus (Freytag and Debouck, 2002)
The analysis for K = 2 populations showed individual genotypes distributed between the two gene pools, which was congruent with the neighbor-joining and principal coordinate analysis (PCoA) analyses, which clearly separated the Mesoamerican and Andean gene pools
At K=3, looking jointly into the bar-graphs produced and membership coefficient values, the Mesoamerican gene pool genotypes further separated into two sub-groups but no meaningful interpretation of population structure could be made, while the Andean gene pool genotypes did not show any separation
Summary
Common bean is the most widely consumed legume species of the genus Phaseolus (Freytag and Debouck, 2002). It is a pulse crop used since pre-Columbian times in the Americas and, since the 16th century, in other regions of the world (Gepts et al, 2008). Recent efforts of the national beanbreeding program in Ethiopia have targeted improvement of on-farm common bean productivity and have benefited since the 1980‘s from continuous introduction of new germplasm from different parts of the world (Fisseha, 2015)
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