Improving water productivity with the aim of more production and less water use is considered one effective strategic option for managing irrigation under water deficit conditions. In order to investigate the effect of irrigation regimes and application of different concentrations of tragacanth gum on the black cumin plant, a factorial experiment was conducted based on a completely randomized design with three replications in a greenhouse of the Agriculture Faculty of Kurdistan University in Kurdistan in 2018, 2020, and 2021 seasons. The experimental factors included irrigation at three levels of 100 % (full irrigation), 70 % (moderate drought stress), and 40 % (severe drought stress) of field capacity (FC) of soil and foliar application with tragacanth extract at six concentrations of 0, 1.25, 2.5, 5, 7.5, and 10 g/L. The results showed in three years that irrigation reduction led to more negative osmotic potential and leaf water potential, reduced pressure potential, leaf relative water content (RWC), cell membrane stability, chlorophyll content, the efficiency of photosystem II, grain weight, and water use efficiency (WUE), and increased the amount of hydrogen peroxide (H2O2). The results showed that the effect of various concentrations of application of tragacanth in different levels of irrigation was different. Considering the effect of proper concentration of this material on the improvement of measured traits and increasing the grain weight compared to non-application of tragacanth under moderate and severe drought stress conditions by 11.6 % and 28.2 % (2018), 8.1 %, and 33.9 % (2020), 15 % and 27.7 % (2021), respectively, tragacanth gum can be introduced as a new anti-transpirant agent of natural origin and its application can be useful in areas exposed to drought stress. Chlorophyll content, Osmoprotectants, Stomatal conductance, Transpiration rate, Water limitation
