Environmental effects on cotton fiber carbohydrate concentration and quality

Cotton (Gossypium hirsutum L.) grown in reduced light environments produces inferior fiber compared with that produced in abundant sunlight environmen ts. This response to low light suggests that insufficient photosynthetic as similates are the cause of the fiber quality reductions. The primary object ive of this research was to determine how fiber carbohydrates respond to va rying levels of sunlight during development. A field study was conducted fr om 1995 to 1997 in which cotton was exposed to two light regimes during rep roductive growth: (i) incident sunlight and (ii) 70% of incident sunlight a chieved with shade cloth. Samples of fiber, ovules, and leaves subtending t he boll were collected at 0, 14, 21, and 35 d post anthesis (DPA) and analy zed for starch, glucose, fructose, and sucrose. Fiber quality was determine d at the end of the season. With some exceptions, the shade treatment reduc ed carbohydrates levels in the leaf and ovule tissue. At 14 DPA, starch was reduced 29% in fiber grown under shade. Sucrose levels in shade fiber was reduced 31% at 21 DPA. The carbohydrate reductions at 14 and 21 DPA occurre d during a period of fiber development when strength is determined. These c arbohydrate reductions parallel the 3% fiber strength reductions seen with low light. The reduced sucrose levels at 21 DPA induced by the shade also o ccur during fiber secondary cell wall deposition and match the lower fiber micronaire produced under shade. These data present compelling evidence tha t adequate carbon assimilates are required to produce fiber quality approac hing genetic maximums.