Effect of Planting Date and Boll Position on Fiber Strength of Cotton (Gossypium hirsutum L.)

The effect of planting date and boll position on cell wall thickening of cotton fiber and development of fiber strength were studied by comparing the time course of the activity of key enzymes β-1,3-glucan synthase (callose) and sucrose synthase (SuSy) involved in cellulose biosynthesis, cellulose content and the indices of fiber structure X-ray diffraction of the fiber that developed at different planting dates or boll positions. The results showed that during the fiber cell wall thickening and fiber strength formation stage (25-50 days post-anthesis, DPA), there was an interactive effect between planting date and boll position. Different planting dates resulted in different mean daily temperatures during 25-50 DPA (TDPA 25-50), which was always an important factor that influenced fiber strength, while the impact of boll position in different temperature conditions was variable. When TDPA 25-50 was above 22.0°C, boll position might affect the cell wall thickening process and the fiber strength, while when TDPA25-50 was lower than 20.0°c, boll position affect little. The optimum conditions for the development of fiber cell wall thickening and the formation of fiber strength may be the eighth nodal position of the fruiting branch (PFB) and with the TDPA 25-50 of about 26.0°C.