GENETIC DIVERSITY AND ORIGIN OF THE HAWAIIAN ISLANDS COTTON,GOSSYPIUM TOMENTOSUM

Gossypium tomentosum is the only member of the cotton genus endemic to the Hawaiian archipelago. It is morphologically distinct from other allopolyploid Gossypium species, and its phylogenetic relationships with them are uncertain. Chloroplast and ribosomal DNA restriction site variation were used to estimate the phylogeny of the allopolyploids. Gossypium mustelinum is resolved as sister to the remaining allopolyploid species, which include two species-pairs, G. barbadense-G. darwinii and G. hirsutum (including G. lanceolatum)-G. tomentosum. This indication that G. tomentosum is sister to G. hirsutum is supported by allozyme data. Gossypium tomentosum is proposed, based on biogeographic evidence and molecular data, to have originated by transoceanic dispersal from a Mesoamerican progenitor. Few restriction site variants were observed among the allopolyploids, suggesting that present lineages diverged relatively rapidly following polyploidization. Allozyme analysis of 30 G. tomentosum accessions collected from seven islands revealed relatively low levels of genetic diversity: 11 of 50 loci were polymorphic, mean number of alleles per locus was 1.24, and mean panmictic heterozygosity was 0.033. Little geographic patterning of allelic distributions was observed. Despite historical cultivation of G. barbadense and G. hirsutum in Hawaii and the existence of their naturalized derivatives, no allozyme evidence of interspecific introgression into G. tomentosum was detected.