Effect of Drought Stress on Growth and Steviol Glycosides Content of Stevia (Stevia rebaudiana)

To study the effect of soil moisture variation on growth and steviol glycosides contents in Stevia (Stevia rebaudiana B)، a potexperiment based on a randomized complete design with four treatments and three replications were conducted in a greenhouse of Agricultural Biotechnology Research Institute of Iran (central region، Isfahan)، in 2012. Experimental treatments applied as a combination of visual symptom appearance in plant (normal to severe wilting) and soil moisture. So، treatments irrigated in 19. 1، 15. 1، 11. 9 and 9. 1% of soil moisture content (w/w) that are created in greenhouse situation with irrigation of 3، 6، 9 and 12 days interval، respectively. Results showed that soil moisture reduction up to 9 days irrigation interval had no effect on plant height and leaf dry weight، but plant growth significantly reduced in 12 days irrigation period. Maximum of harvest index obtained in 6 days irrigation period (51. 36%). Soil moisture reduction caused significant increment in stevioside and dulcoside A، but not affected the rebaudioside types (A، F and C). Total steviol glycosides increased with the soil moisture reduction and plant grown with 3 days irrigation interval had minimum steviol glycosides. Stevioside was highest in steviol glycosides in all treatments. Plants grown under 6 days irrigation interval had the maximum of steviol sugar yield. Totally، the results of this experiment showed that leaf dry weight decreased with decline of soil moisture content (below 11. 9 w/w)، but steviol glycosides content had significant increment. The highest of harvest index and steviol sugar yield were obtained in the 6 days irrigation interval. Although، steviol glycosides content increased with the soil moisture reduction، it means that intensify of drought stress more than 6 days irrigation interval (reduction of soil moisture content below the 15. 1 w/w) caused downfall of Stevia yield due to significant reduction of leaf yield and steviol sugar yield in severity of drought stress.