Abstract: 【Objective】To research the differences of colored cotton fiber quality and variation in physiological activities of boll development, an experiment was conducted to explore the main period and related influencing factors of fiber quality formation in the Yellow River Valley cotton-farming region of China. This study will provide a theoretical basis for quality improvement of colored cotton. 【Method】In field conditions, three colored cotton varieties, Zhongmian 51 (light brown, CCRI51, hybrid cotton), Zhongmian 81 (dark brown, CCRI81), Zhongmian 82 (dark green, CCRI82), and one ordinary white cotton variety Guoxin 3 (GX3) were used as experimental materials. The cotton flowers grown at 1-2 nodes of 5-6 fruit branches were marked in each district on the same day. Then, fiber quality of the marked bolls was tested at harvest time. In addition, the marked bolls were divided into boll shell, cotton seed and fiber in the 10 DPA (days post anthesis), 20 DPA, 30 DPA, 40 DPA, separately. For each organ of the marked bolls, indexes such as soluble protein content, POD activity, SOD activity, MDA content, and cellulose content of cotton fiber were measured. And fiber qualities, bolls’ development characteristics of different varieties, and the correlation between both were studied.【Result】CCRI 51, as a hybrid cotton variety, had the highest upper fiber length, uniformity, and strength. And the order of that of the other conventional cotton was GX 3＞CCRI 81 ＞CCRI 82. Micronaire value of GX 3 was significantly higher than that of the other cotton varieties. Soluble protein content in boll shell of GX 3 was higher than that in the other varieties in the boll development. Meanwhile, a significant difference was observed among varieties in each period. The largest decreased ratio of fiber soluble protein content of GX 3 appeared in the early time after flowering (10-20 DPA, 66.67%). However, for the other varieties, it appeared at the later stage after flowering (20-40 DPA, 23.08%-61.19%). POD activity of boll shell of all varieties rose in the 10-20 DPA. And that of the variety CCRI 82 was the highest. POD activity in boll shell of GX 3 and CCRI 51 was significantly higher than that of CCRI 81 and CCRI 82. In the 10 DPA, SOD activities in boll shell and cotton seed of GX 3 both were the highest in the 4 varieties. SOD activity in boll shell of CCRI 51 and CCRI 81 showed a gradual increasing trend during its development. SOD activity in cotton seed of CCRI 51 in the 40 DPA increased by 53.18% compared with that in the 30 DPA; also, the value was significantly higher than the other varieties. However, for CCRI 82 fiber, SOD activity declined time occurred 10 days earlier than that of the other varieties. MDA content of GX 3 cotton seed showed a decreasing trend in the 20-30 DPA. However, that of the other varieties showed an increasing trend in this period. The cellulose speedy accumulation time of CCRI 51 occurred earlier and longer than the other varieties. For GX 3, cellulose speedy accumulation time was 3 days earlier than that of CCRI 81 and CCRI 82, and its speedy accumulation duration was 1-5 days longer than that of CCRI 81 and CCRI 82. MDA content in cotton seed in the 10 DPA showed a significantly negative correlation with fiber length and fiber strength, and the coefficients were -0.964 and -0.968, respectively. POD activity in the boll shell in 10 DPA was significantly and positively correlated with fiber length. And cellulose speedy accumulation duration was significantly and positively correlated with fiber length and strength. Protein content in fiber in 20 DPA, MDA content in cotton seed in 30 DPA and cellulose speedy accumulation time were significantly and negatively correlated with fiber uniformity. MDA content in cotton seed in 20 DPA, protein content of boll shell in 30 DPA and MDA content in 40 DPA were all significantly and positively correlated with micronaire value. Both protein content in cotton seed in 40 DPA and POD activity in fiber in 20 DPA were significantly and positively correlated with tensile stretch. 【Conclusion】 Compared to white cotton, colored cotton bolls had a poor antioxidant enzyme system activity, which affected the formation and growth of the primary cell wall of fiber in 0-20 DPA, and promoted coloring substances deposited in the secondary cell wall of fiber, which affected the cellulose accumulation in secondary cell wall of fiber. Shorter cellulose accumulation duration and a late cellulose speedy accumulation time of colored cotton were both the direct cause of low fiber quality.

Key words: colored-cotton, antioxidant system, cellulose accumulation, fiber quality