Response of quantitative and physiological parameters of stevia (Stevia rebaudiana Bertoni) medicinal plant to salinity stress under controlled conditions

The present study was aimed to investigate the response of the growth and physiological parameters of stevia (Stevia rebaudiana Bertoni) medicinal plant to salinity stress using a pot experiment in 2014. Ten levels of salt stress (0, 30, 60, 90, 120, 150, 180, 210, 240 and 270 mM of NaCl) were arranged in randomized complete block design with three replicates. Regression analysis of data indicated that some measured parameters such as stem diameter, plant height, green leaf number in plant, relative water content (RWC), chlorophyll a, b, leaf greening (SPAD value), leaf fresh weight, root and shoot dry weights linearly decreased when NaCl amount increased in the growing media. Green leaf number in plant and leaf greening (SPAD value) were more sensitive than other mentioned parameters. However, the response of some determined parameters such as electrolyte leakage, chlorophyll a/b ratio, stem, root, shoot and total fresh weights along with leaf, stem and shoot fresh weights were described by a segmented model. In conclusion, stevia plant could tolerate salt stress up to 80 mM and then its growth and physiological parameters significantly and adversely affected. Results, also, revealed that physiological parameters were more sensitive to salt stress than morphological parameters.