Morphological Properties of Stevia (Stevia Rebaudiana Bert.) Affected by Foliar Application of Iron, Zinc, and Salicylic Acid under Drought Stress

Background: Stevia (Stevia rebaudiana Bert.) is an important source of natural sugar, for the use of people, especially those with diabetes. However, there is no data on the growth of stevia under drought conditions affected by plant growth regulators (PGR).Methods: A two-year experiment using 5 kg pots was conducted under field conditions. The objective was to determine the morphological properties of stevia affected by the foliar use of iron (FeSO4, 4 mg/L), zinc (ZnSo4, 3 mg/L), and salicylic acid (1 mM) under different levels of drought stress including control (field capacity, 0.5 atm), 3.5, 6.5, and 10 Atm. Soil water potential was investigated during the experiment using an eco-tensiometer, set with a computer. Different plant morphological properties including plant height (PH), number of leaf per plant (NLP), number of stem per plant (NSP), aerial part fresh weight (AFW), aerial part dry weight or biological yield (ADW), leaf dry weight (LDW), stem dry weight (SDW), and the ratio of LDW/ SDW were determined.Results: Stress, PGR, and their interactions significantly affected the measured parameters. Accordingly, drought stress significantly decreased stevia growth, and there was not much of difference among different growth-related factors, under the stress, as they followed a similar trend of growth. The reduction of different growth parameters at the highest level of stress was in the range of 57-76%, related to the control. However, the use of PGR, especially the combined treatments, significantly increased the growth of the stressed plants related to the control treatment, with an increase range of 9.14-22.61% by the triple treatment.Conclusion: Among the single treatments, the iron treatment, and among the combined treatments, the combination of the three PGR, followed by Fe+Zn was the most effective ones. It is possible to increase stevia growth under drought stress using the PGR including Zn, Fe and salicylic acid tested in this research.