The Effect of cytokinin application on photosynthesis, gas exchange and chlorophyll content of safflower under drought stress condition

In order to evaluate possibility of improvement photosynthesis, gas exchange and chlorophyll content of safflower by the application of cytokinin, a split factorial experiment was conducted based on randomized complete block design with four replications at the research farm of Agriculture Faculty, the University of Zanjan, during the 2019-2020 cropping season. In this experiment, irrigation levels included optimal irrigation and drought stress to main plots and safflower cultivars including Sina, Faraman, Parnyan, Gholdasht and Mahaly Esfahan, and three levels of cytokinin, including of no-application (control), 50 and 75 μM were allocated to subplots as factorial. At the flowering stage, simultaneously with drought stress safflower plants were sprayed with cytokinin. The results showed that drought stress had negative effects on the intercellular CO2 concentration, transpiration rate, stomatal conductance, photosynthesis rate, carboxylation efficiency, Photosynthetic water use efficiency, chlorophyll content and seed yield and the application of cytokinin minimized the negative effects of drought stress and increased in the above traits. The highest seed yield was obtained by application of 75 μM of cytokinin (3466.08 kg/ha) with an increase of 29 percent compared to the control. Therefore, the use of cytokinin can be suggested as a solution to decrease drought stress negative effects and enhance seed yield of safflower under optimal irrigation and drought stress conditions.