Foliar application of KNO3 modulates the biomass yield, nutrient uptake and accumulation of secondary metabolites of Stevia rebaudiana under saline conditions

Stevia rebaudiana Bertoni is quickly becoming an important industrial crop throughout the world. However, the growth, biomass yield and secondary metabolites of stevia are negatively affected when the growing environment is adverse including salt affected soil. Though relatively little is understood of adaptation, physiological and metabolic changes of stevia under exposure to a salinity environment, it is hypothesized that foliar application of potassium (K+) could improved the salinity tolerance through ion homeostasis. Thus, an experiment was conducted in two years constitutively with twenty treatment combinations comprising four salinity levels (irrigation with normal water as control and three levels of NaCl at 40, 80 and 120 mM) and exogenous application of five different concentrations of KNO3 (water spray as control, KNO3 at 2.5, 5.0, 7.5, and 10.0 g L-1) to understand the sole and interaction effects of both the factors on stevia. The growth parameters and dry leaf yield were not negatively affected with salinity level up to 40 mM, irrespective of KNO 3 levels. However, the detrimental effects were observed at higher salinity (80 and 120 mM). The uptakes of K+, Ca2+, and N were significantly (P 50.05) reduced at higher salinity whereas accumulations of Na+ and Cl- ions in plant tissues were substantially increased. Application of KNO3 at 5.0 g L-1 registered significantly (P <= 0.05) higher dry leaf yield compared with water spray as control. The biochemical parameters such as total chlorophyll, praline and total phenols, were also significantly (P <= 0.05) influenced by the sole effects of salinity and KNO3. The negative effects of high salinity on leaf yield were reduced with foliar application of KNO3 by up to 26 %. Thus, it can be concluded that stevia can be grown in moderate saline (NaCl at 80 mM) conditions with exogenous follar application of KNO3.