GENETIC BASE OF UPLAND COTTON CULTIVARS RELEASED BETWEEN 1970 AND 1990

Most cotton (Gossypium spp.) breeders today, without recourse to criti cal data, assume that the genetic base in modern New World cotton cult ivars is narrow. The objectives of this study were to: (i) determine t he 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 valu e of 0.07. This estimate suggests substantial remaining diversity. Thi s conclusion must take into account possible bias from widespread rese lection of cotton cultivars and the accompanying assumption of a genet ic correlation of 0.75 between generations. The most influential breed ing programs, in terms of genetic contributions to cultivar developmen t, were Stoneville Pedigreed Seed Company, Coker's Pedigreed Seed Comp any, and New Mexico Agricultural Experiment Station. Historically, the most influential cultivar is Stoneville 2. The genetic contribution o f 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 t hrough the process of reselection. The genetic base in modern cotton c ultivars is not particularly narrow and continue to offer opportunitie s for cultivar improvement.