The effect of soil moisture depletion on Stevia (Stevia rebaudiana Bertoni) grown in greenhouse conditions: Growth, steviol glycosides content, soluble sugars and total antioxidant capacity.

The purpose of the present study was to determine threshold values of soil moisture content for Ste-via (Stevia rebaudiana Bertoni) and to evaluate the effects of drought stress on the main metabolites ofthis species. For these purposes, a greenhouse experiment was carried out with four soil moisture lev-els and plant growth, steviol glycoside (SVglys) contents, soluble sugars and antioxidant capacity wereinvestigated at variable soil moisture content. Irrigation was scheduled at 3, 6, 9 and 12-day irrigationintervals, based on soil moisture content at 90, 75, 60 and 45% of field capacity (FC) respectively. Theresults showed that soil water depletion up to 60% FC (9-day irrigation interval) had no negative effecton plant growth and leaf dry weight, whereas a significant growth reduction occurred at 45% FC (12-dayirrigation interval). Similarly, the total SVglys content increased when soil moisture was depleted to 60ü (9-day irrigation interval), but these metabolites contents decreased by 45% FC treatment. AlthoughStevia growth and SVglys content significantly decreased under severe drought stress (45% FC), the totalantioxidant capacity and soluble sugars increased in the identical condition. The obtained results suggestthat Stevia plants can grow well with a soil water content near to 60% FC, showing a good SVglys content.The Stevia tolerance to mild water stress is noteworthy, especially in water limited regions. In addition,it was found that soil water depleted to 45% FC was detrimental to Stevia in greenhouse conditions. Theimprovement of antioxidant capacity and soluble sugar content by soil water stress conditions could beconsidered as physiological and biochemical responses to a progressive drought stress in Stevia and maybe an acclimation response to drought stress.