Effect of salicylic acid foliar application on the morphological and biochemical traits of Stevia (Stevia rebaudiana)

A greenhouse study was conducted to evaluate of salicylic acid foliar effect on morphological and biochemical characters of Stevia (Stevia rebaudiana) based on a Completely Randomized Design (CRD) experiment with three replications in Qazvin, Iran in 2016.  The treatments of this research were defined as salicylic acid foliar levels as 0 (control), 100, 300 and 600 µM which were applied three months after transplanting. Evaluated characters were as plant height, branch number, plant dry weight, leaves dry weight, branches dry weight, the ratio of leaf to total dry weight, the percentage and yield of stevioside, rebaudioside-A, rebaudioside-B and rebaudioside-c. The results of this study revealed that foliar levels of salicylic acid had a significant effect on all of the evaluated characters except for SPAD index. The treatment of foliar 100 µM salicylic acid led to a significant increase in plant height, stevioside percentage, rebaudioside C yield and its percentage compared with control treatment (18.2%, 91.7%, 160% and 186%, respectively). By increasing the concentration of salicylic acid foliar level to 300 µM, the branches dry weight, leaves dry weight, plant dry weight, stevioside yield, rebaudioside. A percentage and its yield were increased in comparison to control treatment (3.9%, 10.3%, 7.0%, 84.6, 78.3 and 100%, respectively). Finally the treatment of 600 µM salicylic acid foliar level was significantly led to an increase in lateral branches number, the ratio of leaves dry weight to branches dry weight, rebaudioside-B percentage and its yield compared to control treatment (365.8%, 43.0%, 383.3and 344.4%, respectively). Therefore, a concentration of 300 μM foliar application of salicylic acid can be effective for increasing the quantitative and qualitative performance of Stevia.