Growth and Development of the Lint Fibers of Pima S‐4 Cotton1

Abstract

Lint fiber elongation, lint dry weight per seed, and lint dry weight per seed per unit length, was studied from anthesis to maturity in field‐grown ‘Pima S‐4’ cotton (Gossypium barbadense L.). These parameters of fiber growth and differentiation were plotted against boll age and fitted to best‐fit curves by curvilinear regression analysis. The curve fitting procedures yielded mathematical equations which were differentiated to give rate curves. Fiber growth stopped 39 days after anthesis. Splining analysis of fiber dry weight and fiber dry weight per unit length showed that the lint weight per unit length ratio was constant to 17.99 ± 2.35 days. This is the time that secondary wall thickening begins. This analysis also indicates that during the 48‐day boll development period, both fiber elongation and secondary wall thickening were occurring simultaneously for 21 days. During the 21‐day overlap period, 19.7% of the final fiber length was attained. At the end of fiber elongation, fiber dry weight and fiber dry weight per unit length had reached 90% of their final values. These data show that fiber elongation and secondary wall thickening are not separate phases and a substantial amount of secondary wall thickening occurred before fiber elongation stopped. This degree of overlap of fiber growth and differentiation phases is more striking than for upland cottons and may be related to the fact that the maximum rate of elongation continues for 12 days longer in ‘Pima S‐4’ compared to ‘Stoneville 213’ cotton (Gossypium hirsutum L.). The findings reported here show that deposition of almost pure cellulose in the secondary wall does not immediately stop all of fiber elongation.