Genetic Diversity and Phylogenetic Relationships in Cotton Based on Isozyme Markers

Summary Phylogenetic relationships among 16 diploid species, including at least one species for each of the A, C, D, E and G genomic groups, and for the natural AD tetraploid species and one synthetic AD tetraploid species were investigated using starch gel electrophoretic techniques for isozyme detection in conjunction with multivariate analysis. The species were polymorphic for phosphoglucomutase (PGM), malate dehydrogenase (MDH), shikimate dehydrogenase (SKDH), aconitase (ACO) and isozymes, but monomorphic for phosphoglucoisomerase (PGI). Similar isozyme arrays indicated close or perhaps conspecific relationships between natural tetraploids G. hirsutum and G. lanceolatum and between G. barbadense and G. darwinii. Natural tetraploid G. mustelinum was found to be relatively distinct from the other tetraploid species. The synthetic AD tetraploid was intermediate between the natural AD tetraploid and the A and D diploid clusters. The two A genome species, G. aboreum and G. herbaceum were closely related to each other. These results supported the hypothesis that the A and D genome species, or their closely related progenitors, were the ancestors of the tetraploid species. The C1 and E2 genome diploid species differed extensively from other diploid and tetraploid species, suggesting that they are very distantly related to the diploid and tetraploid species. These genome types would be very useful resources for germplasm introgression and improvement of the cultivated diploid and tetraploid species because of their significant genetic differences.

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