The Effect of Auxin Foliar Application in Two Irrigated Safflower Cultivars under Drought Stress

The current study tries to evaluate the effect of auxin foliar application in two safflower cultivars under drought stress condition, using a factorial split plot experiment with randomized complete block design in two years (2017-2018 and 2018-2019). It has been conducted at research field of Seed and Plant Improvement Research Institute in Karaj and evaluates irrigation at two levels including normal irrigation (control) and interruption of irrigation from the beginning of grain filling stage (drought) in the main plots and cultivars of Padideh and Goldasht and auxin foliar application in two levels of non-foliar application of distilled water (control) and foliar application of auxin (indole acetic acid) in one step (mid-flowering) at a concentration of 3000 mg.l-1 (30 ppm) in sub-plots as a factorial. In the auxin foliar application and non-foliar application (control) in both normal irrigation and drought stress treatments, the highest total number of heads per plant in Goldasht cultivar have been 26.3 and 24.3 respectively, and the highest grain number per plant observed in Goldasht cultivar have been at 708 and 592, respectively. Auxin foliar application and irrigation has had no significant effect on the grain oil percentage. Goldasht cultivar demonstrates a higher grain yield compared to Padideh cultivar due to lower head temperature, higher soluble carbohydrate concentration, number of heads, and 1000-grain weight. Generally, results show that the effect of the studied treatments is affected by the year and despite the positive effect of auxin foliar application on some yield components at both irrigation levels, foliar application of auxin at middle of flowering stage has no significant effect on grain yield.