Degree of Whiteness and Maturity Among World Cotton Cultivars
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Increased US export of cotton and global competition necessitates that plant breeders continue to improve fiber properties of upland cotton, Gossypium hirsutum (L.). Cotton cultivars having whiter fibers and more mature fibers are desirable due to decreased processing costs. TAM B182-33 ELS (Extra Long Staple) germplasm line of upland cotton, and Tamcot CAMD-E, a short staple obsolete cultivar were crossed with 36 cultivars representing unique germplasm pools from China (12 cultivars), west and central Africa (7 cultivars), south Africa (10 cultivars), and the United States (7 cultivars) that represent distinct germplasm pools. Parents and F1s were grown in College Station, TX, in a Line x Tester design during the summers of 2010 and 2011. Seedcotton was harvested by hand (to avoid the presence of thrash particles in the lint that could bias the color measurements), deburred and allowed to dry in limited light. Cotton samples were ginned on a laboratory saw gin, separated into 2.00 gram subsamples, and color measurements were taken using a Konica-Minolta CR-310 reflectance colorimeter. Absolute color measurements were obtained in two color systems (tristimulus XYZ and CIE L*a*b*). At the Fiber and Biopolymer Research Institute (FBRI) in Lubbock, TX, 50.0 mg samples of the 38 parents and F1s were used to determine maturity ratio (MR), ribbon width (RbWth) and micronaire (Mic) on a Cottonscope. The fibers were cut into 2.0 mm snippets and immersed in an aqueous solution containing a surfactant and NaCl. Approximately, 20,000 snippets per entry were analyzed for MR, RbWth and Mic in the Cottonscope using polarized light. General and specific combining abilities for all the variables were calculated from the data collected. Despite the evident genetic variation from this study for the degree of fiber whiteness, the difficulties in the phenotypic screening of this trait and its importance relative to other fiber traits are problematic. At this time, it is not advisable to begin a cotton breeding program based upon degree of fiber whiteness. Genetic variation also existed for MR, RbWth and Mic among the distinct germplasm pools utilized in this study, but it is not advisable to begin a breeding program based on RbWth or Mic. However, a cotton breeding program to improve MR would be feasible, especially with fast and repeatable measurements from the Cottonscope.