Morphological and Physiological Characteristics of Stevia rebaudiana Cultivated under Different Nitrogen Supplements and Growth Regulators

Steviol glycosides (SGs) are the important constituents of stevia. SGs biosynthesis is dependent on various nutrients. This study aimed to investigate the effects of nitrogen sources ( $${\text{NO}}_{3}^{-}$$ , $${\text{NH}}_{4}^{ + }$$ , and NH4NO3 each 150% in modified Hoagland solution) and the plant growth regulators including 200 µM cytokinin (i.e., BAP), 200 µM auxin (i.e., NAA), and their combination on leaf yield, branching, and SGs yield through a hydroponic experiment. The data revealed that the application of NH4NO3 + BAP increased the outgrowth of buds and branching due to a decrease in endogenous auxin and abscisic acid concentrations. Results also showed that there were significant negative correlations between developed axillary buds and branching with endogenous auxin and abscisic acid concentrations. Compared to the control, growth parameters including stem dry weight (567%) and total dry weight (358%) in the first year and leaf dry weight (160%) and height (483%) in the second year significantly increased when the combination of NH4NO3 and BAP was used. The highest stevioside concentration was observed at using NH4NO3 and BAP + NAA in both 2018 and 2019. Besides, the highest rebaudioside-A concentration was detected as NO3 and NAA were applied during the second year. However, the rebaudioside-B and steviolbioside concentrations were declined when plants were subjected to both nitrogen sources and plant growth regulators. Conclusively, the data acquired herein provided valuable clues as to how to successfully achieve the high productivity of stevia plant and biosynthesis of SGs under greenhouse conditions.