Evaluation on Stevia rebaudiana Bertoni seed germination and seedling development under phytohormones treatment

Poor germination and the long period required for the development of seedlings suitable for planting in the field are among the major problems that affect the cultivation of Stevia rebaudiana. We investigated the abilities of different phytohormone concentrations to improve stevia seed germination and seedling growth. Seeds were germinated on agar gel (AG), supplemented with various concentrations (0, 1, 10 and 100 mu M) of gibberellic acid (GA(3)), thidiazuron (TDZ), kinetin (KN) and N6-benzyladenine (BA) under in vitro conditions. The resultant seedlings were transferred onto Murashige and Skoog (MS) medium for further growth. In most cases, a phytohormone concentration of 1 mu M was most favorable for germination. The highest germination was achieved in cases of AG enrichment at a concentration of 1 mu M GA(3). Regarding the seedlings, the optimal effect on fresh weight, stem, and root length, as well as leaf number was observed when KN was added at a concentration of 10 mu M during the germination stage. Generally, a high negative correlation was observed between the phytohormone concentration and the plantlets' appearance. Conversely, higher chlorophyll and carotenoid contents were observed when 100 mu M of GA(3), KN and BA was applied at the germination stage. In most cases, antioxidant enzyme activity was also higher under phytohormone treatments. We concluded that the addition of a certain phytohormone concentration at the germination stage enhanced stevia germination and improved seedling development.