Patterns of color formation in different fibers during development of colored cotton ('Gossypium hirsutum' l.) Cultivars

We analyzed color development in four cotton (Gossypium hirsutum L.) cultivars, brown cotton (ZX-1 and XC-1), green cotton (4560 and G-7), and compared color parameters to white cotton (LMY28). Color value, chroma (Cab*), and color difference (Delta Eab*) were studied by tristimulus colorimetry during fiber development. Results showed that lightness (L* values) dimmed gradually and differences were significant (F=25.86-1575.18, P<0.0001) at the same developmental stage, while chromaticity (a* values and b* values) increased and showed an obvious peak. In addition, there were significantly different between cultivars during fiber development (F= 40.12-13435.2, P< 0.0001). The Cab* of brown fiber increased slowly from 25 to 35 days post anthesis (DPA), deepened rapidly from 35 to 40 DPA, and from 55 DPA to maturation. The chroma of the XC-1 brown cotton cultivar was significantly higher than ZX-1 (F=130.36, P<0.0001) at maturation. The Cab* of green fiber gradually deepened from 25 to 45 DPA, reached a maxima at 45 DPA. The Cab* values of the G-7 green cotton cultivar were significantly higher than 4560 (F=46.28-4263.04, P<0.0001) during development. The Delta Eab* values of brown fiber were small before 35 DPA, rose rapidly from 35 to 40 DPA, and rose rapidly again sharply with maturation (F=182.95, P<0.0001). The Delta Eab* of green fiber increased rapidly, then slowly, but the rapidly increasing phases were different between cultivars, as the Delta Eab* of G-7 fiber rose rapidly from 35 to 40 DPA, while that of 4560 fiber rose most rapidly from 30 to 35 DPA. The final Delta Eab* of the 4560 cultivar reached a stable level of 12.84 at maturation, which was significantly lower than G-7 (F=4556.97, P<0.0001). Thus, the fiber color of brown cultivars gradually deepened before 35 DPA, rapidly deepened from 35 to 40 DPA, and from 55 DPA to maturation, while green cultivars gradually deepened from 25 to 45 DPA, reached a maxima at 45 DPA, and then faded from 55 DPA to maturation.