Selenium biofortification strategies and their effect on plant nutrition and antioxidant metabolism in sorghum genotypes cultivated in tropical soils

Abstract

Sorghum bicolor L. is the fifth most important cereal in the world, being preceded by wheat, rice, maize, and barley. Selenium (Se) can have essential or toxic properties for animals and humans depending on the amount present in the ingested food. All over the world there are areas where soil Se can be considered deficient and other areas where it can be considered toxic, i.e., the range of soil-Se variation is very wide. As sorghum is the staple food for millions of people around the world, coinciding with areas where Se deficiency occurs, biofortification with Se can considerably improve Se nutrition in humans living in these areas. In this context, this study aimed to: i) evaluate the nutritional efficiency of Se provided to sorghum plants via soil and foliar application; ii) compare Se sources and doses to sorghum under field and greenhouse conditions, aiming its use in human and animal nutrition; and, iii) evaluate the effects of Se on antioxidant metabolism, proteins, carbohydrates, mineral elements and yields in sorghum plants. In the first study, an application of Se was made via soil, with cultivar BM737 being cultivated under greenhouse conditions. The supply of Se occurred through different doses of Se (0, 60, 240, and 480 μg dm-3) and different sources of Se (SeA - potassium hydroxy selenide, SeB - methyl hydroxy selenide, SeC - hydroxy selenide, and SeD – sodium selenate). In the second study, two foliar applications of equal Se concentrations were carried out under greenhouse and field cultivation (Lavras and Lambari) with eight cultivars (BM737, BRS310, Enforcer, K200, Nugrain320, Nugrain420, Nugrain430 and SHS410). In the second study Se was provided at different doses (0, 10, 20, and 40 g ha-1 of Se in the form of sodium selenate) and in the third study Se was provided with different sources (control – no selenium; SeA – sodium selenate, SeB – potassium hydroxy selenide, SeC – acetyl selenide (both at a dose of 10 g ha-1 of Se). Both forms of Se application (via soil or foliar) positively affected the antioxidant metabolism and mineral content of the tested sorghum cultivars. It also increased the Se content in grains and shoots of sorghum plants. With the application of Se via the soil, the highest efficiency of absorption by the roots and recovery of Se occurred with selenate. The application of Se increased the carbohydrate content. Biofortification of Se using methyl hydroxy selenide or hydroxy selenide with 240 μg Se dm-3 and sodium selenate with 60 μg Se dm-3 resulted in acceptable levels of this element in sorghum plants. Selenium via foliar was more efficient with selenate in low doses of Se. Sorghum responds positively to the application of Se.