Abstract: To determine the level of microsatellite sequence differences and to use the information to construct a phylogenetic relationship for cultivated tetraploid cotton (Gossypium spp.) species and their putative diploid ancestors, 10 genome-derived microsatellite primer pairs were used to amplify eight species, including two tetraploid and six diploid species, in Gossypium. A total of 92 unique amplicons were resolved using polyacrylamide gel electrophoresis. Each amplicon was cloned, sequenced, and analyzed using standard phylogenetic software. Allelic diversities were caused mostly by changes in the number of simple sequence repeat (SSR) motif repeats and only a small proportion resulted from interruption of the SSR motif within the locus for the same genome. The frequency of base substitutions was 0.5%–1.0% in different genomes, with only few indels found. Based on the combined 10 SSR flanking sequence data, the homology of A-genome diploid species averaged 98.9%, even though most of the amplicons were of the same size, and the sequence homology between G. gossypioides (Ulbr.) Standl. and three other D-genome species (G. raimondii Ulbr., G. davidsonii Kell., and G. thurberi Tod.) was 98.5%, 98.6%, and 98.5%, respectively. Phylogenetic trees of the two allotetraploid species and their putative diploid progenitors showed that homoelogous sequences from the A- and D-subgenome were still present in the polyploid subgenomes and they evolved independently. Meanwhile, homoelogous sequence interaction that duplicated loci in the polyploid subgenomes became phylogenetic sisters was also found in the evolutionary history of tetraploid cotton species. The results of the present study suggest that evaluation of SSR variation at the sequence level can be effective in exploring the evolutionary relationships among Gossypuim species.

Key words: diploid, Gossypium, microsatellite, phylogenetic tree, simple sequence repeat (SSR), tetraploid.