Sewa Ram

Introduction: Micronutrient deficiencies, particularly iron (Fe) and zinc (Zn), are prevalent in a large part of the human population across the world, especially in children below 5 years of age and pregnant women in developing countries. Since wheat constitutes a significant proportion of the human diet, improving grain Fe and Zn content in wheat has become important in improving human health.Objective: This study aimed to quantify the effect of foliar application of iron sulfate heptahydrate (FeSO₄.7H₂O) and zinc sulfate heptahydrate (ZnSO₄.7H₂O) and their combination on grain Fe and Zn concentrations, as well as grain protein content (GPC). The study also aimed to assess the utility of these applications in large field conditions.Methods: To address this issue, field experiments were conducted using 10 wheat cultivars and applying a foliar spray of FeSO₄.7H₂O (0.25%) and ZnSO₄.7H₂O (0.50%) separately (@400 L of solution in water per hectare during each spray) and in combination at two different crop growth stages (flowering and milking) for three consecutive crop seasons (2017–2020). The study used a split-plot design with two replications to assess the impact of foliar application on GFeC, GZnC, and GPC. In addition, an experiment was also conducted to assess the effect of soil (basal) @ 25 kg/ha ZnSO₄, foliar @ 2 kg/ha, ZnSO₄.7H₂O (0.50%), and the combination of basal + foliar application of ZnSO₄ on the grain micronutrient content of wheat cultivar WB 02 under large field conditions.Results: GFeC increased by 5.1, 6.1, and 5.9% with foliar applications of FeSO₄, ZnSO₄, and their combination, respectively. GZnC increased by 5.2, 39.6, and 43.8% with foliar applications of FeSO₄, ZnSO₄, and their combination, respectively. DBW 173 recorded the highest increase in GZnC at 56.9% with the combined foliar application of FeSO₄ and ZnSO₄, followed closely by HPBW 01 at 53.0% with the ZnSO₄ foliar application, compared to the control. The GPC increased by 6.8, 4.9, and 3.3% with foliar applications of FeSO₄, ZnSO₄, and their combination, respectively. Large-plot experiments also exhibited a significant positive effect of ZnSO₄ not only on grain Zn (40.3%, p ≤ 0.001) and protein content (p ≤ 0.05) but also on grain yield (p ≤ 0.05) and hectoliter weight (p ≤ 0.01), indicating the suitability of the technology in large field conditions.Conclusion: Cultivars exhibited a slight increase in GFeC with solitary foliar applications of FeSO₄, ZnSO₄, and their combination. In contrast, a significant increase in GZnC was observed with the foliar application of ZnSO₄ and the combined application of FeSO₄ and ZnSO₄. In terms of GPC, the most significant enhancement occurred with the foliar application of FeSO₄, followed by ZnSO₄ and their combination. Data demonstrated the significant effect of foliar application of ZnSO₄ on enhancing GZnC by 39.6%. Large plot experiments also exhibited an increase of 40.3% in GZnC through the foliar application of ZnSO₄, indicating the effectiveness of the technology to be adopted in the farmer’s field.

In plants, iron (Fe) & zinc (Zn) uptake and transportation from the rhizosphere to the grain is a critical process regulated by complex transcriptional regulatory networks. However, understanding the combined effect of Fe & Zn starvation on their uptake and transportation and the molecular regulatory networks that control them lack in wheat. Here, we performed a comprehensive physiological, biochemical and transcriptome analysis in two bread wheat genotypes, i.e. Narmada 195 and PBW 502, differing in inherent Fe & Zn content to understand the mechanism of Fe & Zn homeostasis. Compared to PBW 502, Narmada 195 exhibited increased tolerance to Fe & Zn withdrawal by an increased level of antioxidant enzymes and DPPH radical scavenging activity along with less malondialdehyde (MDA), H ₂ O ₂ level, increased PS accumulation and lower reduction of root and shoot Fe & Zn content and length, leaf chlorosis, and leaf area. By integrating physiological and biochemical data along with co-expression & functional genome annotation and gene expression analysis, we identified 25 core genes associated with four key pathways, i.e. Met cycle (10), PS biosynthesis (4), antioxidant (3) and transport system (8) that were significantly modulated by Fe & Zn withdrawal in both the genotypes. Genes of these four pathways were more considerably up-regulated in Narmada 195, allowing better tolerance to Fe & Zn withdrawal and efficient uptake and transportation of Fe & Zn. Chromosomal distribution and sub-genome wise mapping of these genes showed a contribution from all the chromosomes except group 5 chromosomes with the highest number of genes mapped to chromosome 4 (24%) and sub-genome D (40%). Besides, we also identified 26 miRNAs targeting 14 core genes across the four pathways. Together, our work provides a crucial angle for an in-depth understanding of regulatory cross-talk among physiological, biochemical and transcriptional reprogramming underlying Fe & Zn withdrawal in wheat. Core genes identified can serve as valuable resources for further functional research for genetic improvement of Fe & Zn content in wheat grain. Highlight: Our work provides a crucial angle for a comprehensive understanding of the regulatory mechanism underlying Fe & Zn withdrawal associated with physiological, biochemical and transcriptional reprogramming in wheat.