Effects of a Hydrogel Polymer on the Physiology and Antioxidant Activity of Naturally Colored Cotton Cultivars Under Water Deficit

The objective of this study was to evaluate the effects of hydrogel polymer application on the antioxidant activity and physiological performance of colored-fiber cotton cultivars grown under different levels of water restriction. Two experiments were conducted under greenhouse conditions. In the first experiment, the effects of the hydrogel polymer, cultivars, and irrigation replacement levels were evaluated; in the second, the residual effect of the hydrogel polymer applied in the first experiment was assessed using the same cultivars and irrigation depths. Water restriction negatively affected relative water content, gas exchange, chlorophyll <i>a</i> fluorescence, and antioxidant activity, and increased electrolyte leakage in cotton cultivars. Water deficit reduced relative water content, gas exchange, chlorophyll <i>a</i> fluorescence, and antioxidant activity, while increasing electrolyte leakage in the cultivars. However, hydrogel polymer application up to 6.5 g dm^-3 of soil and its residual effect in subsequent cycles were beneficial. The polymer increased relative water content and antioxidant activity, in addition to improving gas exchange and chlorophyll fluorescence, suggesting maintenance of plant physiological health. Residual polymer doses also enhanced relative water content, antioxidant activity, gas exchange, and chlorophyll fluorescence in plants during Experiment II.