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 ident ified wild progenitor, a complex population genetic structure, and man y centuries of human-mediated dispersal and gene flow. Phenetic and ph ylogenetic analyses of allelic variation at 205 restriction fragment l ength polymorphism (RFLP) loci were conducted in an effort to unravel this complicated history. The RFLP data, in conjunction with previousl y published molecular, morphorogical, and anthropological information, suggest that coastal Yucatan populations are truly wild rather than r eestablished feral derivatives. The geographical proximity of these wi ld 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 i n southern Mexico and Guatemala appear to have been derived from intro duced Yucatan peninsular forms, thereby creating the secondary center of diversity that has traditionally been interpreted as the geographic al point of origin of domesticated G. hirsutum. The gene pool of moder n, improved (Upland) cultivars derives from Mexican highland populatio ns that, in turn, trace their origins to southern Mexico and Guatemala . Gossypium hirsutum is the first tetraploid perennial surveyed for RF LP 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 cont rast to the few comparable studies, levels of allozyme variation are h igher than levels of RFLP variation. Despite assaying 205 loci, only s ix of the 23 Upland cultivars were found to have unique multilocus gen otypes.