evaluation of the effect of osmotic stress and effective treatments on seed germination of stevia (stevia rebaudiana bertoni.)

Introduction: stevia, also known as stevia rebaudiana bertoni, is a perennial, short-statured, shrubby species of the composite family of herbaceous citrus trees. this plant is sensitive to cold and has small leaves that appear alternately on the stem (schiatti-sisó et al., 2023). poor germination of stevia is one of the important obstacles in the cultivation of this plant on a large scale. one of the methods to improve seed quality is the use of priming. priming is a technique that aligns seeds with the ecological conditions of the environment before sowing them in the environment, improving their germination readiness (afshari et al., 2020). micronutrients are required to a small extent for balanced plant growth and production, but deficiency of these elements can lead to disruption of physiological processes and changes in plant secondary metabolites (nasiri et al., 2020). under drought stress conditions, nutrient uptake is greatly reduced due to the increase in the concentration of soluble salts in the root medium and the increase in the osmotic potential of the soil (babajani et al., 2019). the plant s response to abiotic stresses depends on various factors, and phytohormones are investigated as the most important intrinsic substances for regulating physiological and molecular responses and an essential requirement for plant survival as a living organization (wani et al., 2016). in this regard, it seems necessary to investigate the effect of priming and growth regulators under drought stress conditions on the seeds and medicinal plant of stevia medicinal plant. materials and methods: the aim of this study was to determine the effect of seed priming on seed germination traits of stevia (indian cultivar) under drought stress in 2023. in this study, stevia seeds (indian) were investigated under priming treatments (no priming (control), hydropriming, selenite, selenate, and furchlorphenorone) and drought stress levels (0, -2.5, -5, and -10 bar using polyethylene glycol 6000) as a factorial experiment based on a completely randomized design with three replications. after being disinfected for priming, it was transferred into the desired solutions (hydro-priming, selenite, selenate and flavoring) for 24 h in a growth chamber with a temperature of 15±1°c. then, the seeds were washed with distilled water and dried at room temperature for 12 hours until their moisture content reached the original seed moisture content. data analysis was performed using sas 9.1 software. to compare the mean of the data, duncan s method was performed at 5% probability level. results and discussion: based on the results of germination percentage and rate, the mean time required for germination, and the average daily germination, germination uniformity, seedling length, and seedling vigor length index were significantly different under drought stress. applying drought stress and seed priming on germination of psyllium seeds showed that seeds had the highest germination percentage and, rate compared to other levels of priming and drought stress by applying selenate priming in non-drought stress followed by -2.5 bar stress. under the influence of drought stress levels, germination parameters including germination percentage, germination rate, and seedling length were reduced, and applying seed priming to some extent reduced the severity of drought stress on the studied characteristics of stevia under drought stress conditions (fig. 1, 2 and 3). drought stress is one of the important factors that can have negative effects on seed germination of medicinal plants. decrease in seed germination percentage and rate is clearly observed under drought stress conditions (ahmadpour et al., 2019). in various studies, it has been shown that with increasing drought stress intensity, germination percentage and rate decrease significantly. studies have shown that seed priming can significantly increase germination percentage and germination rate in medicinal plants under drought stress. for example, in a study conducted on the seeds of the medicinal plant cumin, it was found that seed priming using different methods has a positive effect on germination under drought stress conditions (piri et al., 2021). conclusion: all seed priming treatments showed no priming by increasing seed germination characteristics and seedling length and to some extent against drought stress induced by polyethylene glycol. selenate, furchlorphenorene, and hydropriming can act as effective methods to improve seed germination under drought stress.