Diversity and Determination of Natural Hybridization among G-genome Cotton.

Seventeen Gossypium species are endogenous to Australia, all diploid. These species are grouped under the subgenus Sturtia. On the basis of genome the subgenus is further divided into three sections, Grandicalyx (K-genome, 12 species), Hibiscoidea (G-genome, 3 species) and Sturtia (C-genome, 2 species). All three G-genome species and one species (G. sturtianum) from the C-genome have overlapping geographical distributions. The main objectives of this study were to identify the molecular similarity/diversity present in each species, and the extent of hybridization among Australian arid zone Gossypium species, G. australe, G. bickii, and G. nelsonii (section Hibiscoidea). Amplified Fragment Length Polymorphism (AFLP) markers were used to investigate the molecular diversity among the Australian arid zone Gossypium species. Accessions of G. sturtianum (C-genome) that were sympatric to G-genome species were also analyzed for possible hybridization. Six AFLP primer combinations generated 141 scorable DNA fragments, of which 133 were polymorphic. Molecular similarity/diversity was analyzed using neighbor-joining analysis. Analysis of molecular markers showed that the habitat of G. nelsonii may be invaded by G. australe. Also, G.  bickii shared higher genetic similarity with G. australe than G. sturtianum which strongly supported a monophyletic origin of the G-genome. These observations showed that trait introgression and natural hybridization is involved in the evolution of G. bickii, suggesting that speciation may be continuing among the the arid zone Gossypium species.