|VAN ESBROECK, GEORGE|
|May Iii, Oscar|
Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/1/1997
Publication Date: N/A
Interpretive Summary: A narrow genetic base predisposes our crops to yield loss from pathogens and does not allow for new gene combinations. Objectives of this study were to investigate trends in cultivar diversity during the last 25 years. Mean coefficient of parentage and field uniformity were determined for cultivars occupying more than 1% of the hectarage. Coefficient of parentage is simply a statistic based on mathematical analysis of pedigrees that indicates the likelihood that two cultivars share a gene in common. Field uniformity is derived from coefficients of parentage among cultivars that growers produce in a region or year. This statistic indicates how genetically uniform the cotton hectarage has become. Our study found that genetic uniformity of the cotton crop has increased in the last 25 years. This increase in uniformity was due to the planting of genetically related cultivars on a large portion of the cotton hectarage. Private breeding firms that furnish the bulk of cultivars available to growers have released new cultivars, but they have generally been related to those already produced by growers. The few public cotton breeding programs remaining in the U.S. must, therefore, strive to provide private breeding firms with genetically diverse germplasm so that the cultivar genetic base will not further erode.
Technical Abstract: Little information exists regarding trends in cotton cultivar genetic diversity. Such data is necessary to prevent the genetic base of cultivars chosen by growers from becoming narrow. Objectives of this study were to investigate trends in cultivar diversity during the last 25 years and investigate possible causes. Mean coefficient of parentage (rp) and field uniformity (rf) were determined for cultivars occupying more than 1% of th hectarage. An average of 17 cultivars accounted for 97% of the cotton hectarage within a growing region. Regional rp ranged from 0.12 to 0.15 and then sharply increased to 0.20 in 1995. Higher rp among a small set of popular cultivars compared with rp among a larger group of available cultivars indicates that much of the cotton cultivar genetic diversity remains unused by growers. The increase in rp in 1995 was associated with the repeated use of a few cultivars as parents in breeding programs. Field dgenetic uniformity remained relatively stable at 0.30 for the last 25 years. This relatively high level of genetic uniformity results from the planting of a small number of genetically related cultivars. The recent introduction of genetically engineered cultivars that are backcrossed derived transformants of existing cultivars may further increase field genetic uniformity.