Reversal Frequencies in Developing Cotton Fibers

Directional reversals in the helical deposition of fibrils affect the performance of cotton fibers. A developmental study was therefore conducted to determine the in fluences of genetics and developmental pattern on the incidence of these reversals. One cultivar of cotton, Deltapine 61, was studied in both 1980 and 1981; four other cultivars, Acala SJ-5, Stoneville 825, Stoneville 213, and Pima S-5, were studied only in 1981. Of these, the first four are upland cotton (Gossypium hirsutum L.) while the latter is a long-staple cotton (G. barbadense L.). Reversal frequencies were measured by polarized light microscopic techniques. In each cultivar, reversals were first detected after the third week of fiber development, coincident with the initiation of secondary wall formation. Reversal frequency increased with fiber maturity. Because reversal frequencies increased with fiber age, it seems that not all layers of the secondary wall reverse together. Slippage between layers may result from reversals occurring during late stages of fiber development. A plausible explanation for the two types of reversals reported in the literature is offered.