REEVALUATING THE ORIGIN OF DOMESTICATED COTTON (GOSSYPIUM-HIRSUTUM MALVACEAE) USING NUCLEAR RESTRICTION-FRAGMENT-LENGTH-POLYMORPHISMS (RFLPS)

The origin of domestication in Mesoamerican G. hirsutum populations is obscured by several factors, including the absence of a clearly identified wild progenitor, a complex population genetic structure, and many centuries of human-mediated dispersal and gene flow. Phenetic and phylogenetic analyses of allelic variation at 205 restriction fragment length polymorphism (RFLP) loci were conducted in an effort to unravel this complicated history. The RFLP data, in conjunction with previously published molecular, morphorogical, and anthropological information, suggest that coastal Yucatan populations are truly wild rather than reestablished feral derivatives. The geographical proximity of these wild coastal populations to agronomically primitive forms of G. hirsutum implicates the Yucatan peninsula as the primary site for the earliest stages of domestication. Agronomically advanced cultigens developed in southern Mexico and Guatemala appear to have been derived from introduced Yucatan peninsular forms, thereby creating the secondary center of diversity that has traditionally been interpreted as the geographical point of origin of domesticated G. hirsutum. The gene pool of modern, improved (Upland) cultivars derives from Mexican highland populations that, in turn, trace their origins to southern Mexico and Guatemala. Gossypium hirsutum is the first tetraploid perennial surveyed for RFLP variation. Levels of RFLP variation in G. hirsutum (H-T= 0.048, A = 1.24, and P = 22%) are low relative to other plant taxa, and, in contrast to the few comparable studies, levels of allozyme variation are higher than levels of RFLP variation. Despite assaying 205 loci, only six of the 23 Upland cultivars were found to have unique multilocus genotypes.