Effect of proline and salicylic acid on morphological and phytochemical characteristics of Stevia rebaudiana (Bert.)

To study the effect of foliar application of proline and salicylic acid on growth, morphological and phytochemical traits of Stevia, an experiment based on completely randomized block design in a factorial arrangement was conducted with three replications in the University of Zanjan. Foliar applications of proline in three levels (0, 1, 2 mM) as well as salicylic acid (0, 0.3, 0.6 mM) were applied after establishment of transplants in the field three times with 10 days intervals. Factors including leaf area, leaf fresh and dry weight, total fresh and dry weight, chlorophyll a, b and total chlorophyll, carotenoid, total phenol, total flavonoid and antioxidant activity were studied. Results showed that salicylic acid and proline applications significantly influenced above mentioned traits. The highest average leaf area/ plant (5949.39 cm2), leaf fresh (787.17 g/m2) and dry leaf weight (228.5 g/m2), total fresh (1339.23 g/m2) and total dry weight (327.52 g/m2) were recorded in 1 mM proline in combination with 0.3 mM salicylic acid. Solely applications of proline at 2 mM and salicylic acid at 0.6 mM enhanced chlorophyll a, b, carotenoid and total flavonoid contents. The highest average total chlorophyll (5.23 mg/g fw) observed in 2 mM proline in combination with 0.3 mM salicylic acid and highest phenol (19.94 mg/g dw) recorded in 1 mM proline in combination with 0.6 mM salicylic acid. Collectively, results showed that application of proline and salicylic acid significantly improved vegetative growth and production of active substances in Stevia rebaudiana.