Genetic Base of Upland Cotton Cultivars Released between 1970 and 1990

Most cotton (Gossypium spp.) breeders today, without recourse to critical data, assume that the genetic base in modern New World cotton cultivars is narrow. The objectives of this study were to: (i) determine the average coefficient of parentage for 260 upland cotton (G. hirsutum L.) cultivars released between 1970 and 1990; and (ii) determine the contributions of a number of public and private breeding programs and of various ancestral lines to the genetic diversity of those cultivars. Coefficients of parentage among 260 cultivars showed an average value of 0.07. This estimate suggests substantial remaining diversity. This conclusion must take into account possible bias from widespread reselection of cotton cultivars and the accompanying assumption of a genetic correlation of 0.75 between generations. The most influential breeding programs, in terms of genetic contributions to cultivar development, were Stoneville Pedigreed Seed Company, Coker's Pedigreed Seed Company, and New Mexico Agricultural Experiment Station. Historically, the most influential cultivar is Stoneville 2. The genetic contribution of 54 ancestral lines, including nine introductions, accounted for less than 25% of the total genetic variation among the 260 cultivars. This low value is thought to result from the loss of genetic information through the process of reselection. The genetic base in modern cotton cultivars is not particularly narrow and continue to offer opportunities for cultivar improvement.