Strength and Crystalline Structure of Developing Acala Cotton

Single fiber strengths (breaking force in grams and breaking tenacity in g/tex) are reported for greenhouse grown SJ-2 Acala cotton fibers during growth and development. The developmental stages, which are defined by the age of the boll in the number of days post-anthesis (dpa) include primary wall formation, primary-to-secondary wall transition, secondary wall thickening, and maturity. A total of 54 bolls from 12 plants were used. Fiber properties were measured on the middle sections of fibers sampled from the middle section of the most developed ovules or seeds at the specific development stages. The most significant increases in single fiber breaking forces and fiber linear densities occurred up to 35 dpa and were correlated to seed fibers weighing up to 150 mg. Maximum breaking strength or tenacity of the SJ-2 cotton fibers is reached at 21 dpa. The absolute forces required to break individual fibers continue to increase with fiber development beyond 21 dpa without further increases in fiber tenacity. Dried seed fiber weight, fiber thickness, lengths between adjacent twists, and linear density (tex) have shown close relationships with the developmental stages and can serve as indicators for fiber development. Positional effects on single fiber strength were not revealed for bolls above the fourth fruiting branch.