GENETIC DIVERSITY IN AND PHYLOGENETIC-RELATIONSHIPS OF THE BRAZILIAN ENDEMIC COTTON, GOSSYPIUM-MUSTELINUM (MALVACEAE)

Gossypium mustelinum, one of five tetraploid species in the cotton gen us, is geographically restricted to a few states in NE Brazil. Allozym e analysis was used to assess levels and patterns of genetic diversity in G. mustelinum and its relationship to the other tetraploid species . Genetic variation was low, with only 6 of 50 loci examined being pol ymorphic, a mean of 1.14 alleles per locus and a mean panmictic hetero zygosity of 0.08. These estimates are low relative to other tetraploid cotton species, but are typical of island endemics. Interpopulational genetic identities were uniformly high, lending support to the concep t of there being only one wild species of Brazilian cotton. The limite d allelic diversity observed was correlated with geographical distribu tion, although variability is so limited in the species that geographi cally marginal populations are electrophoretically ordinary. Phylogene tic and phenetic analyses demonstrate that G. mustelinum is isolated a mong polyploid cotton species, occupying one of the three basal clades resulting from an early radiation of polyploid taxa subsequent to pol yploid formation. We suggest that G. mustelinum represents a paleoende mic that presently exists as a series of widely scattered, relictual p opulations. Despite several centuries of sympatric cultivation of G. b arbadense and G. hirsutum, there was little evidence of interspecific introgression of alleles from cultivated cottons into G. mustelinum.