Response of Cotton (Gossypium hirsutum L.) Fiber Quality to Carbohydrates and Nitrogen In the Subtending Leaf of Cotton Boll.

A two-year field experiment was carried out with cotton (Gossypium hirsutum L.) cultivars, Kemian 1 (average fiber strength is 35 cN tex^-1) and NuCOTN 33B (average fiber strength is 32 cN tex^-1) at five (2008) and four (2009) nitrogen (N) levels to clarify the relationships between plant nitrogen, plant carbohydrates and fiber quality. The results indicated that leaf (the subtending leaf of boll) N concentration can be more accurately to reflect the N status of the subtending leaves of boll than SPAD reading or free amino acid. Sucrose and non-structural carbohydrate had a quadratic relation with leaf N concentration (P<0.01). The optimal leaf N concentration is around 2.50%, and it follows a typical dilution curve. During 24-38 days post-anthesis (DPA), sucrose in fiber was positively related to sucrose or non-structural carbohydrate of the subtending leaves of boll (P<0.05), while was not correlated with starch or soluble sugar of the leaf (P>0.05). Fiber sucrose had a positive correlation with fiber strength before 38 days post-anthesis (DPA) (P<0.05), and it is more susceptible than fiber length, fineness and maturity to fiber sucrose. These suggested that (1) 24 - 38 DPA is a crucial period for fiber development which might be significant influenced by physiological and ecological factors, (2) sucrose or non-structural carbohydrate in the subtending leaf of boll could be taken as monitoring indices to evaluate sucrose level in the developing fiber, and then to estimate the final fiber quality.