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Abstract
Two field experiments were carried out in the Agric. Exp. and Res. Station as well as in the Plant Analysis Lab. of the Plant Physiol. Section, Fac. Agric., Cairo Univ., Giza, Egypt, during the two successive seasons (2014 and 2015) to study the effects of putrescine (Put) and 24-epibrassinolide (EBL) foliar applications on the growth, yield and chemical composition of Egyptian cotton (Gossypium barbadense L. cv. Giza 90) plants grown under drought stress conditions. The soil of the experimental site was clay loam and plants were grown under three irrigation regimes, i.e., 100 % as control, 75 % and 50 % from well watering. Three different doses of Put (0, 1 and 2 ppm) or EBL (0, 10⁻⁹ and 10⁻⁷M) were sprayed on plants; plants were sprayed five times started at the day 40 after planting and repeated every 15 days. Drought caused a significantly and gradually decreases in the growth characters, yield and its components and chemical compositions e.g., chlorophyll a, b, total chl., total carotenoids, N, P and K concentrations, activities of IAA, CK and free GAs by increasing drought level and CAT activity. While drought stress increased lint percentage, No. of falling flowers/plant, flower abscission %, total sugars, total soluble phenols, total free amino acids, proline and Na concentrations, ABA activity and antioxidant enzyme POX, PPO and SOD activities. Moreover, the mean values for relative growth rate (RGR) and net assimilation rate (NAR) tended to be lower under drought stress compared to control non-stressed plant. Applications of Put or EBL positively affected cotton growth and yield under drought stress conditions.