Impact of putrescine and 24-epibrassinolide on growth, yield and chemical constituents of cotton (Gossypium barbadense L.) plant grown under drought stress conditions

Abstract

Background: Field experiment was carried 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. Materials and Methods: 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) and EBL (0, 10–9 and 10–7 M) were sprayed on plants 5 times started at the day 40 after planting (DAP) and repeated every 15 days. Results: Drought caused a significantly and gradually decreases in the growth characters, yield and its components and chemical compositions e.g., N, P and K concentrations and CAT activity by increasing drought level, while increased lint percentage, Na percentage, total sugars, total soluble phenols, total free amino acid and proline concentrations, antioxidant enzymes 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 especially 50% drought level compared to control non-stressed plant but its increased at 75% drought level between 60 and 90 DAP. Applications of Put and EBL positively affected cotton growth and yield under drought stress conditions. These treatments resulted an increase in morphological characters e.g., plant height, number of leaves/plant, leaf area/plant and total plant dry weight. Also, Put and EBL increase chemical constituents related to drought tolerance either inorganic (N, P, K and Na) or organic constituents e.g., total free amino acids, total sugars, total soluble phenols, antioxidant enzymes CAT, POX and SOD activities, while proline concentration, PPO activity as well as lint percentage were decreased. As a result of promoting growth induced by previous foliar applications, yield components e.g., number of open bolls, fiber length, fiber strength and micronaire value increased. Conclusion: Generally, Put at 2 ppm and EBL at 10–7 M applications recorded the highest values of growth and yield characters.