Analysis of genetic diversity and population structure in upland cotton ( L.) germplasm using simple sequence repeats.

Improvement of cotton fibre yield and quality is challenging due to the narrow genetic base of modern cotton cultivars, which emphasizes the great need to effectively explore the existing germplasm resources. With major objective to assess the genetic diversity and population structure at DNA level, 302 elite upland cotton germplasm accessions (253 Chinese and 49 different exotic origins), were genotyped using 198 simple sequence repeats (SSRs) markers. Each of the 198 markers differed greatly in its ability to detect variations in the panel of cotton germplasm. The SSRs amplified 897 alleles, of which 77.7% were polymorphic. The number of alleles varied from 2 to 12 (mean 4.53). Gene diversity ranged from 0.020 to 0.492 with a mean of 0.279. The polymorphic information content (PIC) values ranged from 0.371 to 0.019 (mean 0.225). Genetic distances in the whole cotton germplasm ranged from 0.451 to 0.052 (mean 0.270), demonstrating relatively wider genetic diversity range. Chinese-origin cotton germplasm showed the highest level of SSR polymorphisms (gene diversity=0.268, PIC=0.218), whereas American-origin revealed the highest mean genetic distance (0.274). Model-based Bayesian analysis clustered the whole cotton germplasm into three subpopulations, and the highest molecular variation ws revealed between subpopulations (4%, <0.001). The SSRs revealed moderate level of genetic diversity at DNA level, identified three structured subpopulations, suggesting a potential use of these markers for genomewide association mapping studies and for identifying and conserving useful alleles in upland cotton germplasm.