Foliar Application of Humic Acid and Some Exo-and Endophytic Growth Hormones on Yield, Yield Components and Fatty Acid Composition in Safflower (Carthamus tinctorius L.) under Drought Stress

A two-year field experiment was conducted in Varamin-Pishva Branch, Islamic Azad University, Iran to study the impact of drought stress and foliar application of some hormones on the safflower growth. The drought stress was induced at three levels and considered as main plots. Irrigating after 75% water depletion was considered to be normal irrigation (control), irrigating after 60 and 45% water depletion, defined as mild and severe drought stress, respectively. The foliar application of humic acid (HA), salicylic acid (SA), Gibberellic acid (GA(3)), ascorbic acid (AA), water, and the non-foliar application was considered as sub-plots. The main effect of irrigation regimes was significant on seed yield, oil yield, palmitic acid, and water use efficiency (WUE). Also, the main effect of foliar applications was significant for seed yield, oil yield, stearic acid, and WUE. Normal irrigation produced the maximum oil yield (2270 kg ha(-1)) that was decreased by 25.9% and 37.1% under mild and severe stress regimes, respectively. The maximum and minimum oil yields were produced by the application of SA and non-foliar treatment with average values 1970 and 1357 kg ha(-1), respectively. Although the palmitic acid content was enhanced under the drought stress conditions, oleic acid content was significantly decreased in such conditions. The current findings suggest that the foliar application of SA can be recommended when optimal water supply was applied to increase the quality and quantity of safflower oilseed.