Physiological and biochemical response of safflower (Carthamus tinctorius L.) cultivars to zinc application under drought stress

Drought is one of the major environmental stresses affecting the many crops performance by altering physiological and biochemical processes. Zinc application could mitigate the adverse effects of drought stress. To investigate the effects of foliar application of zinc on the morphophysiological and biochemical traits of safflower cultivars under drought stress, two field experiments were conducted as split plots based on randomized complete blocks design with three replicates during 2018-2019 and 2019-2020 growing seasons. Experimental factors included drought stress as the primary factor, safflower cultivars, and zinc foliar application as secondary factors. Drought stress included two levels (non-stress and drought stress); safflower cultivars were Isfahan, Linas, Padideh, Parnian, and Goldasht; foliar application of zinc was in three levels (0, 0.5, and 1 kg ha-1 Zn). Results showed drought stress decreased plant height, 1000-seed weight, seed yield, biological yield, soil plant analysis development (SPAD) chlorophyll index, relative water content (RWC), leaf area index (LAI), oil percentage, oil yield, palmitic acid, linoleic acid. Whereas, drought stress increased proline content, oleic acid, and antioxidant enzyme activity. Maximum plant height (145 cm) and oil percentage (29 %) were observed in Isfahan cultivar, maximum amounts of SPAD index (75.96 %), catalase enzyme (CAT) (0.69 mu mol min-1 mg protein-1), proline (5 mM g-1 FW), linoleic acid (76 %), and palmitic acid (7 %) were observed in Goldasht cultivar. Parnian cv. with the highest leaf area (2.98 cm2), RWC (78 %), 1000-seed weight (43 g), seed yield (3514 kg ha-1), biological yield (13,542 kg ha-1), peroxidase enzyme (POX) (2.84 mu mol min-1 mg protein-1), water-soluble carbohydrates (WSC) (107 mg g-1 DW), and oil yield (807 kg ha-1) had the highest economic yield among the experimented cultivars. Foliar application of 1 kg ha-1 Zn improved oil yield, RWC, SPAD index, proline content, carbohydrate content, LAI, and CAT and POX activities. Zinc application enhanced drought stress tolerance in different cultivars through improving effects on the antioxidant activity system, proline content, carbohydrate content, RWC, and SPAD index.