Assessment of genetic diversity and patterns of relationships among West African sorghum accessions using microsatellite markers
Kitavi, Mercy Nzilani
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An understanding of the extent, distribution, and patterns of genetic variation is useful for selection of genetic resources for conservation and establishment of core collections, estimation of any possible loss of genetic diversity prior to conservation programs, understanding the genetic variability available and its potential use in breeding programs. Sorghum is the major food crop& income source for 120 million people living in WCA. Production increase is mainly achieved by increasing the land area cultivated. There is risk of hunger in both rain fed and irrigated areas of WA due to lack of land because of the increasing population. There is also decrease of genetic diversity within primary gene pools. Sorghum has a great potential in providing food security in WA and knowledge of genetic diversity in germplasm will provide foundation for effective and sustained population breeding and hybrid development and also permit classification of germplasm into heterotic groups. The major objective was to assess the genetic diversity of sorghum accessions collected fromWest Africa using SSRs and the specific objectives were to (a)assess the level of variability of the selected sorghum accessions (b) determine the patterns of relationships among the study materials (c)evaluate the effect of geographical regions in genetic structure. 30 sorghum accessions were genotyped as bulks and individuals using 22 microsatellite markers, estimated genetic diversity and differentiation parameters were estimated. The 22 microsatellite markers showed a wide range of differences in quality index (0.07-0.48), polymorphic information content (0.020.81), and number of alleles (2-15). The 22 markers detected a total of 146 alleles among the 30 bulks and 108 alleles among the 10 accessions genotyped as individuals. Genetic similarities among the 30 accessions genotyped as bulks were lowest at 0.160 between and highest 0.833. A dendrogram of the genetic relationships among the bulks showed five clusters which grouped according to races while cluster and principal coordinate analysis distinct grouping according to their breeding origins irrespective of their geographical origins. Results from 10 accessions genotyped as individuals revealed (a) a wide range of polymorphism that varied from 22.7 to 86.4%; (b) relatively low level of heterozygosity (0.09-0.28) and gene diversity (0.12-0.37), and (c) Nei's genetic distance that varied from 0.036 to 1.0. Cluster and principal coordinate analysis produced two major groups. Analysis of molecular variance indicated that differences in country of origin explained 8.9% of the variation but it was not statistically significant while differences among the population explained 54.1% which was statistically significant at p<0.00. The FST value (0.63) indicated a very high genetic differentiation as expected for selfing species. The study provided a detailed analysis & quantification of genetic diversity in sorghum accessions of WA origin thus the data reaffirm the power of SSR markers to distinctly group closely related accessions. West African sorghum accessions contain a great deal of genetic diversity. Grouping of sorghum germplasm by genetic background and not by existing B- or R-line classification.