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 environments. This response to low light suggests that insufficient photosynthetic assimilates are the cause of the fiber quality reductions. The primary objective of this research was to determine how fiber carbohydrates respond to varying levels of sunlight during development. A field study was conducted from 1995 to 1997 in which cotton was exposed to two light regimes during reproductive growth: (i) incident sunlight and (ii) 70% of incident sunlight achieved with shade cloth. Samples of fiber, ovules, and leaves subtending the boll were collected at 0, 14, 21, and 35 d post anthesis (DPA) and analyzed for starch, glucose, fructose, and sucrose. Fiber quality was determined at the end of the season. With some exceptions, the shade treatment reduced 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 occurred during a period of fiber development when strength is determined. These carbohydrate reductions parallel the 3% fiber strength reductions seen with low light. The reduced sucrose levels at 21 DPA induced by the shade also occur during fiber secondary cell wall deposition and match the lower fiber micronaire produced under shade. These data present compelling evidence that adequate carbon assimilates are required to produce fiber quality approaching genetic maximums.