Effect of mannitol on some morphological characteristics of in vitro stevia

Stevia rebaudiana Bertoni is a Paraguayan perennial antidiabetic herb belongs to Asteraceae family. The Leaves of stevia are about 300 times sweeter than sugar with no calories, that are the source of diterpene glycosides such as stevioside and rebaudioside A. Tissue culture is a rapid tool for propagation of stevia. In this research we studied the effect of different concentrations of mannitol on some morphological aspects of stevia under in vitro conditions. Axillary nodes were used as explants and they were cultured on Murashige and Skoog (MS) medium supplemented with different concentrations of mannitol (0, %1, %2, %3, %4 and %5) as an osmotic stress. The cultures were maintained for 4 weeks at a temperature of 25±2°C with a photoperiod of 16/8 hour low light/dark per day. Maximum shoot length (111.00±3.26 mm) was observed on a MS medium without mannitol and minimum shoot length (20.46±2.89 mm) was observed on a MS medium with %5 mannitol. It was observed that by increasing the concentration of mannitol in medium, shoot length, internode length, fresh weight of plants and growth rate were decreased. Maximum (54±1.45) and minimum (28.93±1.85) number of leaves was observed on a MS medium with %3 and %5 of mannitol respectively. Moreover, the results showed that osmotic stress significantly reduces the growth and yield components of S. rebaudiana Bertoni.