Evaluating the role of nutri-priming in improving PEG-induced drought stress tolerance of stevia (Stevia rebuadiana Bertoni)

Poor germination and low seedling growth of stevia are common problems in the cultivation of the plant. Nutri-priming is a new, safe, easy, and effective method to increase germination characteristics and seedling tolerance against stress. The objective of this study was to assess the effect of nutri-priming with nano potassium (nano-K), paclobutrazol (PBZ), and salicylic acid (SA) on stevia seed germination indices and physiological traits under drought stress conditions (0, -3, -6, and -9 bar) induced by polyethylene glycol 8000. Results indicated that germination indices (germination percentage and rate, mean germination time, seedling length, and seedling vigor index) and photosynthetic pigment contents (chlorophyll a, b, and total) were negatively affected by drought stress. While drought stress increased activity of antioxidant enzymes (peroxidase, catalase, and superoxide dismutase) and proline content. Seed nutri-priming with nano-K + SA + PBZ was the best treatment in improving germination traits and physiological characteristics. The highest germination percentage was related to seeds that were treated with nano-K + SA + PBZ under control and - 3 bar drought treatments (62.4 and 64.0%, respectively). In all drought levels, the lowest amounts of germination percentage were found in unprimed seeds. The minimum germination percentage was obtained from unprimed seeds at -9 bar (29.05% reduction compared to unprimed seeds under the osmotic potential of 0 bar). As a result, this study indicated that the use of nano-K + SA + PBZ as a pre-sowing seed treatment can promote the poor germination performance of stevia and protect it from negative impacts of drought stress.