Effect of spraying of growth regulators on water use efficiency, some osmolites and physiological traits of potato in drought stress conditions

Drought is one of the most important environmental stresses that limits plant growth through effects on physiological processes. In order to evaluate of spraying growth regulators on some physiological traits and water use efficiency of potato under drip irrigation system, a study was conducted at the research farm in Malayer during 2015 growing seasons. The experiment was conducted as a split-plot scheme based on randomized complete block designs with three replications. Different drip irrigation intervals (once every day, once every 2days, once every 3days, once every 4days, once every 5days and once every 6days) and sprinkler irrigation (once every 6days) were considered as a main plots and substrate foliar application of growth regulators with four levels, including epibrassinolide, gibberellic acid, acetylsalicylic acid and control treatment (distilled water) were considered as a subplots. Results showed that with an increase in drip irrigation intervals the amount of water use efficiency and protein content and the amount of proline, sugar solution of leaf and tuber and potassium concentration increased significantly. The activity of antioxidant peroxidase and superoxide dismutase enzymes on potato seemed to increase as the irrigation frequency increased. The highest enzymatic activities were obtained from once every5 and 6days drip irrigation intervals. Foliar applications of growth regulators were effective in reducing hazard effects of drought stress via the increase in photosynthetic pigments and antioxidant enzymes. Foliar application of growth regulators increased the amount of peroxidase and superoxidase enzymes by 25% and 10%. Foliar application of growth regulators was effective in reducing the effects of stress caused by irrigation period prolongation and significantly increased water use efficiency, leaf protein content, proline, leaf and sugar solution of potassium, photosynthetic pigments, and antioxidants. Also, increasing the irrigation interval reduced the total chlorophyll content and carotenoid by 33% and 45% compared to control and increased the activity of peroxidase and superoxide dismutase enzymes by 50% and 41% in potato. Foliar application of growth regulators increased total chlorophyll content by 11%. The effect of epibrassinolide was higher than other growth regulators.