Effects of cytokinins, gibberellic acid 3, and gibberellic acid 4/7 on in vitro growth, morphological traits, and content of steviol glycosides in Stevia rebaudiana.

Steviol glycosides (SGs) and gibberellic acids share a part of their biosynthesis pathways. Despite the widespread studies on the effect of gibberellic acid 3 (GA), the effect of gibberellic acid 4 and 7 (GA) on Stevia rebaudiana has never been studied. This study aimed at a comparative evaluation of different hormone effects, i.e., 1 mg L GA, 1 mg L GA, or 0.5 mg L kinetin and 0.5 mg L 6-benzylaminopurine (BAP) (KB 0.5), on in vitro propagation, growth, morphological properties, and content of SGs in leaf samples of stevia. In comparison with the control group (hormone-free), the treatments of KB 0.5 or GA produced the highest biomasses and largest leaf areas. The three hormonal treatments produced a similar number of leaves, the ratio of fresh to dry weight, and leaf length. GA-treated explants produced the highest ratio of leaf area to leaf length. The effect of GA on shoot elongation was greater than that of the control or even GA. While the effect of GA on rebaudioside-A (Reb-A) production was similar to that of the control (16.2 and 18.04 mg g, respectively), GA resulted in a lower amount of it (13.31 mg g). Except for GA, which induced more stevioside accumulation, the treatments' effects were comparable to that of the control. The ratio of stevioside to Reb-A was the highest for GA (2.62), followed by GA (1.93), and then the two others. Sum of Reb-A and stevioside content was not changed by the use of any of the treatments.