Strategies for agronomic biofortification of rice with selenium in tropical agroecosystems

Abstract

Selenium (Se) is an essential element for humans and animals. Its role in humans and animals is related to the activity of more than 25 selenoproteins, formed from the naturally occurring amino acids selenocysteine and selenomethionine (e.g. glutathione peroxidase). Selenium intake by humans depends fundamentally on the nutritional quality of the food with respect to this nutrient. In many regions of the world, especially in the tropics soils present a low content of Se. This is the main factor responsible for the low availability of Se for plants. In this sense, the agronomic biofortification of food with Se is a good strategy that can be used to enrich agricultural crops (as rice) decreasing the incidence of diseases in vulnerable populations. This study aimed to investigate the effects of the application of Se via soil (SeVI) and via leaf (SeIV and SeVI) on: i) grain yield; ii) contents of Se in different parts of the plant and of the grain; iii) physiological variables; and, iv) spatial distribution of Se and other elements in biofortified rice grains. Experiments were carried out in two agricultural production fields. Selenium rates ranging from 5 to 120 g ha-1 were evaluated in four replicates on Lambari-MG (Cropping seasons of 2015/2016 and 2016/2017) and Patos de Minas-MG (Cropping season of 2016/2017) municipalities. The application of SeVI via soil was carried out coating the fertilizer monoammonium phosphate (MAP) or as saline solutions. The application of SeIV and SeVI via leaf was carried out using saline solution at the flowering and grain-filling stages of rice. The physiological variables in all treatments were evaluated in the leaves. After harvest, grain yield, Se, macro, and micronutrient contents were determined in different parts of the rice plant. The results showed that the supplied Se rates positively affected some physiological variables and improved the nutritional quality of the polished rice grains in terms of their Se contents. Only a low percentage of the Se supplied to the plants was uptake by the grains. Adequate Se contents in the polished grain were achieved with the assessed Se rates, allowing safe consumption of Se for humans. The spatial distribution of the elements varied in the grain, with the highest concentration of Se being found in the endosperm. Other elements, as Fe, Ca, Zn, K, and Mn were located in the husk or in the embryo of the grain. We conclude that concluded that the agronomic biofortification of rice with Se is a promising strategy for tropical soils. However, peeling and polishing the rice grain can lead to significant losses of Se, macronutrients (as K and P), and micronutrients (as Zn and Fe).