Univrsity of Tehran Press Iranian Journal of Field Crop Science 2008-4811 53 1 2022 03 21 . Effect of cytokinin application on photosynthesis, gas exchange and seed yield of safflower (Carthamus tinctorius) under drought stress condition . Effect of cytokinin application on photosynthesis, gas exchange and seed yield of safflower (Carthamus tinctorius) under drought stress condition 149 160 87169 10.22059/ijfcs.2021.314382.654777 FA Leyli Golchin Department of Production Engineering and Plant Genetics, University of Zanjan, Iran Afshin Tavakoli Department of Production Engineering and Plant Genetics, University of Zanjan, Iran 0000-0003-3585-6768 Ehsan Mohsenifard Department of Production Engineering and Plant Genetics, University of Zanjan, Iran Journal Article 2020 11 30 In order to evaluate the possibility of photosynthesis, gas exchange and chlorophyll content improvement of safflower by cytokinin application, a split factorial experiment was conducted based on a randomized complete block design with four replications at the research farm of Agriculture Faculty, University of Zanjan, during 2019-2020 growing season. In this experiment, irrigation levels included optimal irrigation and drought stress were the main plots (soil water potential: -0.4 and -2 MPa as control and drought stress treatments) and safflower cultivars (i.e Sina, Faraman, Parnyan, Gholdasht and Mahaly Esfahan), and three levels of cytokinin, (i. e no- application (control), 50 and 75 μM) were subplots. Drought stress was applied in the flowering stage and simultaneously, safflower plants were sprayed with cytokinin. The results showed that drought stress caused an increased in the intercellular CO₂ concentration (10%) and decreased transpiration rate (30.3%), stomatal conductance (46.4%), photosynthesis rate (41.1%), carboxylation efficiency (42.8%), Photosynthetic water use efficiency (14.4%), chlorophyll content and seed yield (40.17). Also, Parnian cultivar was more tolerant than other cultivars to drought stress condition. In contrast, cytokinin application minimized the negative effects of drought stress and increased the above traits. The highest seed yield was obtained by application of 75 μM of cytokinin (3494kg/ha) in drought stress condition (34/1% compared to the control). Therefore, cytokinin application can be suggested to decrease drought stress negative effects and enhance seed yield of safflower under optimal irrigation and drought stress conditions. In order to evaluate the possibility of photosynthesis, gas exchange and chlorophyll content improvement of safflower by cytokinin application, a split factorial experiment was conducted based on a randomized complete block design with four replications at the research farm of Agriculture Faculty, University of Zanjan, during 2019-2020 growing season. In this experiment, irrigation levels included optimal irrigation and drought stress were the main plots (soil water potential: -0.4 and -2 MPa as control and drought stress treatments) and safflower cultivars (i.e Sina, Faraman, Parnyan, Gholdasht and Mahaly Esfahan), and three levels of cytokinin, (i. e no- application (control), 50 and 75 μM) were subplots. Drought stress was applied in the flowering stage and simultaneously, safflower plants were sprayed with cytokinin. The results showed that drought stress caused an increased in the intercellular CO₂ concentration (10%) and decreased transpiration rate (30.3%), stomatal conductance (46.4%), photosynthesis rate (41.1%), carboxylation efficiency (42.8%), Photosynthetic water use efficiency (14.4%), chlorophyll content and seed yield (40.17). Also, Parnian cultivar was more tolerant than other cultivars to drought stress condition. In contrast, cytokinin application minimized the negative effects of drought stress and increased the above traits. The highest seed yield was obtained by application of 75 μM of cytokinin (3494kg/ha) in drought stress condition (34/1% compared to the control). Therefore, cytokinin application can be suggested to decrease drought stress negative effects and enhance seed yield of safflower under optimal irrigation and drought stress conditions. https://ijfcs.ut.ac.ir/article_87169_1461c17179e1cb31940baf947073b76e.pdf