Abstract
Widespread malnutrition of zinc (Zn), iodine (I), iron (Fe) and selenium (Se), known as hidden hunger, represents a predominant cause of several health complications in human populations where rice (Oryza sativa L.) is the major staple food. Therefore, increasing concentrations of these micronutrients in rice grain represents a sustainable solution to hidden hunger. This study aimed at enhancing concentration of Zn, I, Fe and Se in rice grains by agronomic biofortification. We evaluated effects of foliar application of Zn, I, Fe and Se on grain yield and grain concentration of these micronutrients in rice grown at 21 field sites during 2015 to 2017 in Brazil, China, India, Pakistan and Thailand. Experimental treatments were: (i) local control (LC); (ii) foliar Zn; (iii) foliar I; and (iv) foliar micronutrient cocktail (i.e., Zn + I + Fe + Se). Foliar-applied Zn, I, Fe or Se did not affect rice grain yield. However, brown rice Zn increased with foliar Zn and micronutrient cocktail treatments at all except three field sites. On average, brown rice Zn increased from 21.4 mg kg–1 to 28.1 mg kg–1 with the application of Zn alone and to 26.8 mg kg–1 with the micronutrient cocktail solution. Brown rice I showed particular enhancements and increased from 11 μg kg–1 to 204 μg kg–1 with the application of I alone and to 181 μg kg–1 with the cocktail. Grain Se also responded very positively to foliar spray of micronutrients and increased from 95 to 380 μg kg–1. By contrast, grain Fe was increased by the same cocktail spray at only two sites. There was no relationship between soil extractable concentrations of these micronutrients with their grain concentrations. The results demonstrate that irrespective of the rice cultivars used and the diverse soil conditions existing in five major rice-producing countries, the foliar application of the micronutrient cocktail solution was highly effective in increasing grain Zn, I and Se. Adoption of this agronomic practice in the target countries would contribute significantly to the daily micronutrient intake and alleviation of micronutrient malnutrition in human populations.
Highlights
An estimated 2 billion people suffer from micronutrient malnutrition, especially in the developing world
We aimed to investigate the foliar applications of Zn, I, Fe and Se alone or together in a cocktail solution on the grain concentrations of these micronutrients in rice grown under different soil and crop management conditions of five major rice growing countries over two years by using seven different rice cultivars
With the local control treatment, brown rice Zn concentration ranged from 15.0 mg kg−1 at the Ludhiana field site of India in 2017 to 26.9 mg kg−1 at CMU field site of Thailand in 2015 (Table 5)
Summary
An estimated 2 billion people suffer from micronutrient malnutrition ( known as hidden hunger), especially in the developing world. Particular micronutrient deficiencies include Fe, Zn, Se and I which result in severe health complications (Bailey et al, 2015; Harding et al, 2018) as well as significant economic losses (Gödecke et al, 2018). Due to their high requirements, infants, preschool children, and women of reproductive age are more vulnerable to micronutrient malnutrition. A large proportion of the world population is known to be at risk of Se malnutrition due to inadequate dietary Se intake (Jones et al, 2017)
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