Effect of nutrient omission and pH on the biomass and concentration and content of steviol glycosides in stevia (Stevia rebaudiana (Bertoni) Bertoni) under hydroponic conditions

Steviol glycosides (SGs), have recently been approved in western countries as sources of intense natural sweeteners. SGs are found in Stevia rebaudiana, mainly in the leaves, and industry prefers rebaudioside A (Reb-A) over other steviol glycosides for its superior flavour profile. Hence leaf biomass and concentration of SGs (and their product, SG content) are of primary agronomic interest. Experiments were conducted under controlled conditions in nutrient solution to assess the effects of nutrient deficiencies and pH on biomass production, and concentration and plant content of SGs. Total SG content was low in plants deficient in the macronutrients N, P, S, Mg or Ca because of reduced photosynthesis and because of the decreased leaf yield, even though lack of N resulted in greater concentration of stevioside in the leaves. Lack of N or P reduced the proportion of Reb-A to total SGs. Plants deficient in K had less yield than in the nutrient-complete control, but not significantly so and SG concentration in the leaves was similar to that of the control. Deficiency of the micronutrients Cu and Fe led to low SG yield, because of reduced SG concentration in leaves, and because of reduced leaf yield, respectively. Lack of other micronutrients did not influence SG content. Neutral to alkali conditions reduced plant growth and leaf yield, most likely due to deficit of P, but pH had no effect on SG concentration. Our results are indicative, but preliminary, and require confirmation in open field trials over several years.