Cotton (Gossypium hirsutum L.) yield and fiber quality can vary considerably among years and locations depending upon the prevailing environmental conditions, even if the genotypes used remain constant. How the environmental conditions during fiber development affect the quality of fiber is not completely understood. These environmental conditions can often alter the assimilate source:reproductive sink ratio of the developing crop. Thus, the objective of this study was to determine how source to sink ratio manipulations affected cotton lint yield and fiber quality.

Field studies were conducted in 1991 and 1992 with six source:sink ratio manipulations (partial defruited, partial leaf pruned, reflectors, open canopy, shaded plots, and an untreated control) imposed upon the 3 cotton genotypes 'DES 119', 'DPL 5690', and 'Prema'. White blooms were tagged on four dates each year and the fruit were harvested when the bolls had opened. These bolls were then ginned and fiber quality traits determined. Overall lint yields were determined for the reflectors, open canopy, shaded plots, and control treatments.

Lint yields from the open canopy and reflector treatments were 17% and 6% greater than the control, respectively, and the shaded plot yielded 20% less than the control. Boll number was the component of yield that accounted for these differences. The shaded plot treatment reduced fiber strength by 3% compared to the control. Fiber length from the shaded plot treatment was approximately 2% longer than the control when the shade was applied within the first 7 d of fiber development. Compared to the control, micronaire was decreased 7% when the shade was applied during the period of fiber development that the fiber secondary cell wall is being deposited. The partial defruited treatment consistently produced about 8% greater micronaire than the control treatment. This study demonstrates that alterations in the irradiance level available to a cotton canopy can affect both the amount and quality of the fiber produced, particularly fiber strength and micronaire. Cotton canopies bred for increased light penetration to lower leaves or for better utilization of the intercepted light may lead to lint yield increases.