Selenium enrichment, fruit quality and yield of winter jujube as affected by addition of sodium selenite

Winter jujube (Zizyphus jujuba Mill.) is a kind of high quality, fresh jujube fruit originated from China. Selenium (Se) affects the chemical composition and antioxidative properties in plants. At appropriate concentrations, Se acts as an antioxidant or activates mechanisms that can alleviate oxidative stress in the chloroplast, and enhances plant growth. Although the addition of Se is known to increase Se uptake in crops, it is unclear whether exogenous Se affects nutritional and functional components in winter jujube. Winter jujube trees were sprayed with selenium (as sodium selenite) at five concentrations (0, 25, 50, 100, or 200 mg/L of Se) three times at the fruitlet stage between July and August. The Se content, ratio of organic Se to total Se in leaves and fruits, fruit quality, and yield were measured. At Se concentrations of 50 mg/L or higher, total Se content increased rapidly whereas the ratio increased initially and decreased later. Different Se concentrations affected the quality of fruits differently: at 50 mg/L, compared to their values in the unsprayed control trees, vitamin C content was greater by 20.94%; soluble sugars, 29.48%; total flavonoids, 43.48%; and the sugar: acid ratio, 41.81%. Along with the increase of Se addition, average fruit weight and yield of winter jujube presented a trend of increasing up to 50 mg L−1 and decreasing thereafter. Thus, the foliar spray of sodium selenite at Se concentration of 50 mg/L is recommended during the fruitlet stage of Zhanhua winter jujube.