Effect of Water Deficit Stress and Seed Biopriming on the Physiological Indices and Antioxidant Activity of Tansey (Tanacetum persicum (Boiss.) Mozaff)

Growing medicinal plants is important for utilizing their drug precursors, and preserving the genetic resources and diversity in the ecosystem. Tansyis one of the medicinal plants with its valuable therapeutic and antioxidant properties. To investigate the effect of plant growth promoting rhizobacteria on the physiological indices and antioxidant activity of tansyunder water deficit stress, a factorial pot experiment was conducted in a randomized complete block design at the Experimental Farm of Shahrekord University in 2016. The factors consisted at water deficit at three levels: full irrigation (control), 75% full irrigation and 50% full irrigation; and seed biopriming treatments at seven levels: non-bacterial inoculation (control), <em>Azotobacter chroococcum</em>, <em>Bacillus amyloliquefaciens</em>, <em>Bacillus</em> sp. strain A., <em>Bacillus</em> sp. strain B., <em>Pseudomonas fluorescens</em> and <em>Pseudomonas putida</em>. The results showed that bacterial inoculation treatments had a significant effect on all of the analyzed traits (p≤0.01).<em> Azotobacter chroococcum</em> inoculation had the most significant effect on chlorophyll <em>a</em> and carotenoids contents, biological yield, essential oil yield, and anthocyanin contents (0.020 µmol.ml^-1). <em>Bacillus</em> sp. strain A showed a 2.5-fold increase in proline content compared to that of control, and <em>Bacillus</em> sp. strain B had the greatest effect on antioxidant activity (IC₅₀5.32 μg.ml^-1). Moreover, <em>Pseudomonas</em> <em>fluorescence</em> increased the carotenoids content in 50% full irrigation treatment, and <em>Pseudomonas</em> <em>putida</em> had the highest effect on chlorophyll <em>b</em> and total chlorophyll contents, membrane stability, and leaf relative water content. The results revealed that the inoculation of Tansyseeds with <em>Azotobacter</em> and <em>Pseudomonas</em> bacteria, especially in deficit irrigation practices, is recommended to alleviate the adverse effects of water stress.