Genetic gain in fiber properties of upland cotton under varying plant densities

Competition from foreign grown cotton (Gossypium hirsutum L.) and artificial fibers have increased the demand for improved fiber quality. The genetic potential for effecting change in many traits can be judged by previous gains from selection. Nine upland cotton cultivars developed over the past century were grown during 2004 and 2005 in five plant densities to evaluate varying levels of interplant competition on genetic gain estimates for high volume instrument fiber properties. The rates of genetic gain since 1905 among this set of genotypes for fiber length and strength were significantly higher under the greatest planting densities, implying that genetic gains for these characteristics have been made for tolerance to interplant competition as well as for the fiber trait per se. Both fiber elongation and uniformity index appear to be largely unaffected by the stresses of increased interplant competition. Plant density impacted genetic gain in micronaire but cultivars were essentially unchanged over the century, reflecting that the market demands fiber micronaire to be within a range that neither maximizes nor minimizes this trait. Caution should be practiced in the interpretation of these data since the capability to objectively measure these traits has been widely available to breeders only since the 1980s and because selection pressure for these traits has been sporadic with little concentrated effort to maximize or minimize each characteristic.