Evaluating the Morpho-physiological Responses of Stevia (Stevia rebaudiana) to Foliar Application of Various Plant Growth Promoters Under Drought Stress

The limited germination capacity of stevia is a serious problem in stevia cultivation. Drought stress is one of the most important environmental constraints that impact seed germination and the early growth of many crops. This study's objective was to assess the effects of foliar application of different plant growth promoters (PGPs), including salicylic acid (SA; 250 mu M), ascorbic acid (AsA; 250mM), moringa leaf extract (MLE; 10%), thiourea (TU; 10mM), and proline (PRO; 1mM), on a few germination indices and physiological characteristics of stevia (Stevia rebaudiana var. honey) seedlings under drought stress (half field capacity). Seeds were sown at 0.5-inch depth after 15 days of germination, seedlings were subjected to drought stress. Later after a week of drought stress, foliar supplementation of different PGPs were applied, and plants were harvested after 15 days of foliar supplementation. According to the findings, drought stress had a detrimental impact on various growth parameters such as shoot length, root length, fresh and dry shoot weight, fresh and dry root weight, and leaf number however PGPs helped to alleviate the detrimental impacts of drought stress improving root length (8.33-16.67%), shoot dry weight (9.09-55.68%), root dry weight (49.02-286.27%). Furthermore, drought stress significantly enhanced photosynthetic pigments, PRO accumulation, AsA content and peroxidase enzymatic activity several folds in all PGPs treatments as compared to the control. PRO and MLE were found to be most efficient than other PGP treatments in improving growth and physiological parameters under drought stress conditions. Nevertheless, the oxidative damage parameters, hydrogen peroxide, reduced dramatically (16.16-37.88%) after treatment with PGPs, maintaining membrane integrity under drought stress. Hence, foliar application of PGPs is suggested that may help to increase stevia seedling development under drought stress.