XVI International Botanical Congess

Phylogenetic analysis of molecular data sets has established an interpretative framework for the evolution of the 50 species of Gossypium. New World allotetraploid cottons (AD-genome) are inferred to have originated during the Pleistocene, when an A-genome diploid, now extinct in the New World, hybridized as female with a native D-genome diploid. The four cultivated species were derived independently from different wild progenitors, thereby providing a model of morphological convergence under domestication. Molecular markers clarify germplasm relationships and quantify the genetic bottlenecks that accompanied domestication. Allelic and nucleotide diversity for nuclear genes is low in allopolyploid cotton and is especially low in modern cultivars. Diversity may be greater in one genome of allopolyploid cotton than the other. Allopolyploidy has been associated with novel genic and genomic interactions, including inter-genomic sequence transfer and concerted evolution, and is suggested to have opened up new avenues for agronomic improvement.