Plant growth and steviol glycosides as affected by foliar application of selenium, boron, and iron under NaCl stress in Stevia rebaudiana Bertoni

Stevia (Stevia rebaudiana Bert.) is well known for its high content of sweet steviol glycosides (SVglys) in its leaves (about 4-20% of dry weight) depending on the environmental, climatic, and growth conditions. The present study aimed to investigate the effects of foliar iron, selenium, and boron on stevia, irrigated with different concentrations of saline water. The experiment was conducted during two consecutive years in Firuzabad and Anzali, Iran. Results indicated that plant height, number of branches, leaf and biological yield and leaf mass ratio decreased by increasing the NaCl concentration of irrigation water. In both places, total SVglys content, and SVglys yield increased when the plants were irrigated with a 30 mM of saline water while higher salinities (90 mM) resulted in decreasing the traits. In addition, the foliar application of selenium alone and in combination with boron, and iron played a significant role in growth, yield parameters and SVglys accumulation including rebaudioside-A,-B and -C, Stevioside, and Dulcoside-A. Firuzabad had the highest mean values of vegetative traits, leaf yield, and SVglys yield in the second year of the study. Regarding Firuzabad, leaf yield and SVglys percentages had a compensatory relationship, which can play a role in the observed increase in the SVglys percentage under a moderate level of NaCl (30 mM) stress. Finally, the foliar application of selenium either alone or in combination with iron could alleviate the adverse effects of NaCl stress on the studied traits. However, further studies are required to recognize the roles of selenium in SVglys accumulation and growth of stevia.