Selenium supplementation of Portuguese wheat cultivars through foliar treatment in actual field conditions

Selenium (Se) is a trace element essential to the well-being and health quality of humankind. Plant-derived foodstuffs, namely cereals, are the major dietary sources of Se in most countries throughout the world, even if Se contents are strongly dependent upon the corresponding levels in cereal-growing soils. Therefore, wheat is one of the staple crops that appears as an obvious candidate for Se biofortification, considering its gross-tonnage production and nutritional relevance worldwide. The present paper focuses on the ability of bread and durum wheat—Triticum aestivum L. and Triticum durum Desf., respectively—to accumulate Se after supplementation via a foliar-addition procedure. Two of the most representative wheat cultivars in Portugal—Jordão (bread) and Marialva (durum)—have been selected for supplementation trials, following the same agronomic practices and field schedules as the regular (non-supplemented) crops of those varieties (sowing: November 2010; harvesting: July 2011). Foliar additions were performed at the booting and grain-filling stages, using sodium selenate and sodium selenite solutions at three different Se concentrations—equivalent to field supplementation rates of 4, 20 and 100 g of Se per ha—with and without potassium iodide. Selenium contents in wheat grains obtained under foliar application are compared to data from regular wheat samples (field blanks) grown at the same soil/season, yet devoid of any Se supplementation. Total Se in all field samples was determined by cyclic neutron activation analysis (CNAA), via the short-lived nuclide ^77mSe (half-life time: 17.5 s), in the Portuguese Research Reactor (RPI; CTN-IST, Sacavém). Quality control of the analytical procedure was asserted through concurrent analyses of NIST-SRM^® 1567a (Wheat Flour). Results show that foliar additions can increase Se contents in mature grains up to 15 and 40 times for Marialva and Jordão, respectively, when compared to non-supplemented crops. Jordão and Marialva varieties responded differently to the stage of application.