Effect of foliar salicylic acid application on growth, nutrient element uptake, antioxidative defense system and some secondary metabolite contents of stevia plant under potassium deficiency

Potassium (K) is one of the important macronutrients for plant growth and development. Salicylic acid (SA), an endogenous regulatory hormone, is a plant growth regulator that affects mineral nutrient uptake and metabolism in plants and plays an important role in the regulation of various physiological and biochemical processes. In this study, the effects of foliar SA applications (SA0=0 mM, SA1= 0.25 mM and SA2=0.50 mM) on growth nitrogen (N), phosphorus (P), K, calcium (Ca), magnesium (Mg) content, soluble protein concentration and antioxidative enzyme activities, total phenolic compounds and steviol glycoside contents of Stevia (Stevia rebaudiana Bertoni) plant grown at different potassium nutrition levels (K0=0 kg da-1, K1=8 kg da-1 and K2=16 kg da-1 KCl) were tested under field conditions. Fresh and dried herba, leaf and stem weights increased with K applications. As a result of potassium application, the K, P, Mg concentrations of the leaves were observed to increase. The highest K and P concentrations were found in K2 application, and the highest N and Mg concentrations were found in K1 application. Lipid peroxidation and concentrations of SH compounds decreased with increasing K and SA applications. The total phenolic substance concentration increased due to K2 and SA2 applications. SOD, CAT, APX, and GR activities decreased significantly as a result of increasing K applications. The total steviol glycoside concentrations were found to increase significantly, particularly with K2 and SA1 administrations. Current findings revealed that improving K nutrition and SA applications play a critical role on the antioxidative defense system and steviol glycoside components of Stevia.