Zinc Biofortified Rice Varieties: Challenges, Possibilities, and Progress in India

Biofortification as a solution for addressing nutrient deficiencies and malnutrition

Malnutrition, defined as both undernutrition and overnutrition, is a major global health concern affecting millions of people. One possible way to address nutrient deficiency and combat malnutrition is through biofortification. A comprehensive review of the literature was conducted to explore the current state of biofortification research, including techniques, applications, effectiveness and challenges. Biofortification is a promising strategy for enhancing the nutritional condition of at-risk populations. Biofortified varieties of basic crops, including rice, wheat, maize and beans, with elevated amounts of vital micronutrients, such as iron, zinc, vitamin A and vitamin C, have been successfully developed using conventional and advanced technologies. Additionally, the ability to specifically modify crop genomes to improve their nutritional profiles has been made possible by recent developments in genetic engineering, such as CRISPR-Cas9 technology. The health conditions of people have been shown to improve and nutrient deficiencies were reduced when biofortified crops were grown. Particularly in environments with limited resources, biofortification showed considerable promise as a long-term and economical solution to nutrient shortages and malnutrition. To fully exploit the potential of biofortified crops to enhance public health and global nutrition, issues such as consumer acceptance, regulatory permitting and production and distribution scaling up need to be resolved. Collaboration among governments, researchers, non-governmental organizations and the private sector is essential to overcome these challenges and promote the widespread adoption of biofortification as a key part of global food security and nutrition strategies.

Dynamics of starch formation and gene expression during grain filling and its possible influence on grain quality

In rice, grain filling is a crucial stage where asynchronous filling of the pollinated spikelet's of the panicle occurs. It can influence both grain quality and yield. In rice grain, starch is the dominant component and contains amylose and amylopectin. Amylose content is the chief cooking quality parameter, however, rice varieties having similar amylose content varied in other parameters. Hence, in this study, a set of varieties varying in yield (04) and another set (12) of varieties that are similar in amylose content with variation in gel consistency and alkali spreading value were used. Panicles were collected at various intervals and analysed for individual grain weight and quantities of amylose and amylopectin. Gas exchange parameters were measured in varieties varying in yield. Upper branches of the panicles were collected from rice varieties having similar amylose content and were subjected to gene expression analysis with fourteen gene specific primers of starch synthesis. Results indicate that grain filling was initiated simultaneously in multiple branches. Amylose and amylopectin quantities increased with the increase in individual grain weight. However, the pattern of regression lines of amylose and amylopectin percentages with increase in individual grain weight varied among the varieties. Gas exchange parameters like photosynthetic rate, stomatal conductance, intercellular CO2 and transpiration rate decreased with the increase in grain filling period in both good and poor yielding varieties. However, they decreased more in poor yielders. Expression of fourteen genes varied among the varieties and absence of SBE2b can be responsible for medium or soft gel consistency.

Stability of grain zinc concentrations across lowland rice environments favors zinc biofortification breeding

Introduction

One-third of the human population consumes insufficient zinc (Zn) to sustain a healthy life. Zn deficiency can be relieved by increasing the Zn concentration ([Zn]) in staple food crops through biofortification breeding. Rice is a poor source of Zn, and in countries predominantly relying on rice without sufficient dietary diversification, such as Madagascar, Zn biofortification is a priority.

Methods

Multi-environmental trials were performed in Madagascar over two years, 2019 and 2020, to screen a total of 28 genotypes including local and imported germplasm. The trials were conducted in the highlands of Ankazomiriotra, Anjiro, and Behenji and in Morovoay, a location representative of the coastal ecosystem. Contributions of genotype (G), environment (E), and G by E interactions (GEIs) were investigated.

Result

The grain [Zn] of local Malagasy rice varieties was similar to the internationally established grain [Zn] baseline of 18-20 μg/g for brown rice. While several imported breeding lines reached 50% of our breeding target set at +12 μg/g, only few met farmers' appreciation criteria. Levels of grain [Zn] were stable across E. The G effects accounted for a main fraction of the variation, 76% to 83% of the variation for year 1 and year 2 trials, respectively, while GEI effects were comparatively small, contributing 23% to 9%. This contrasted with dominant E and GEI effects for grain yield. Our results indicate that local varieties tested contained insufficient Zn to alleviate Zn malnutrition, and developing new Zn-biofortified varieties should therefore be a priority. GGE analysis did not distinguish mega-environments for grain [Zn], whereas at least three mega-environments existed for grain yield, differentiated by the presence of limiting environmental conditions and responsiveness to improved soil fertility.

Discussion

Our main conclusion reveals that grain [Zn] seems to be under strong genetic control in the agro-climatic conditions of Madagascar. We could identify several interesting genotypes as potential donors for the breeding program, among those BF156, with a relatively stable grain [Zn] (AMMI stability value (ASV) = 0.89) reaching our target (>26 μg/g). While selection for grain yield, general adaptation, and farmers' appreciation would have to rely on multi-environment testing, selection for grain [Zn] could be centralized in earlier generations.

Morpho-molecular and nutritional profiling for yield improvement and value addition of indigenous aromatic Joha rice of Assam

Short-grain aromatic Joha rice of Assam is a unique class of specialty rice having tremendous potential in domestic and international markets. The poor yielding ability of Assam's Joha rice demands its systematic characterization for an effective breeding program. This study investigates the morphological, molecular and biochemical profiles of twenty popular Joha (aromatic) rice cultivars indigenous to Assam. Distinctiveness, Uniformity and Stability (DUS) characterization of the cultivars revealed polymorphism in thirty-seven traits, establishing distinctiveness for their utilization in breeding programs. Unweighted Neighbor Joining (UNJ) clustering based on usual Euclidean distances for the polymorphic morphological markers grouped the cultivars into three clusters with eight, eleven, and one genotypes. The Joha rice cultivars showed significant differences for all the quantitative traits except for panicle length. The genotypic and phenotypic coefficients of variability (GCV & PCV) were high for grain yield ha-1 (24.62 & 24.85%) and filled grains panicle-1 (23.69 & 25.02%). Mahalanobis D2 analysis revealed three multi-genotypic and four mono-genotypic clusters of the cultivars. The first five principal components explain 85.87% of the variation among the cultivars for the traits under study; filled grain panicle-1 (0.91) and stem thickness (0.55) positively contributed to the first PC. The cultivars' average polyunsaturated fatty acids were 37.9% oleic acid, 39.22% linoleic acid, and 0.5% linolenic acid. Kon Joha 4 and Ronga Joha contained the highest iron (82.88 mg kg-1) and zinc (47.39 mg kg-1), respectively. Kalijeera, Kunkuni Joha, Kon Joha-5, Manimuni Joha and Kon Joha-2 accorded a strong aroma. PCR amplified 174 alleles with a mean value 2.64 across the 66 polymorphic SSR markers. PIC values ranged from 0.091 to 0.698, with an average of 0.326. The highly informative (PIC > 0.50) markers were RM316, RM283, RM585, RM1388, RM3562, RM171, R1M30, RM118, RM11and RM29 for identification of the twenty aromatic rice cultivars. PCR amplification of 27 SSR markers identified 28 unique alleles (97-362 bp) in 13 Joha rice cultivars, which can help their identification/DNA fingerprinting. The UNJ clustering based on Jaccard's coefficients classified the cultivars into three distinct clusters with eight, ten, and two genotypes. Our study revealed the nutritional richness of these specialty Joha rice cultivars and sufficient scope for yield enhancement through their interbreeding to keep quality intact.

Zinc portioning and allocation patterns among various tissues confers variations in Zn use efficiency and bioavailability in lentil genotypes

Zinc (Zn) is essential for plants and animals as it plays significant roles in several physiological and biological processes. Its deficiency in soil results in low Zn content food and is one of the major reasons for Zn malnutrition in humans. Biofortification of crops with zinc (Zn) is a viable approach to combat malnutrition, especially in developing countries. A hydroponic study was executed to study response and Zn partitioning in various lentil genotypes. Eight preselected lentil genotypes (Line-11504, Mansehra-89, Masoor-2006, Masoor-85, Line-10502, Markaz-09, Masoor-2004, and Shiraz-96) were grown in solution culture with two Zn levels (control and adequate Zn). Plants were sown in polythene lined iron trays with a two inch layer of prewashed riverbed sand. After 10 days of germination, seedlings were transplanted to a 25L capacity container with nutrient solution for 15 days, and afterward, these plants were divided into two groups, receiving either 2.0 mM Zn or no Zn levels. Three plants of each genotype were harvested at the vegetative growth stage (60 DAT) and the remaining three at physiological maturity (117 DAT). Plants were partitioned into roots, shoots, and grains at harvest. Significant variations in root and shoot dry matter production, grain output, partitioning of Zn in plant parts (root, shoot, and grain), grain phytate reduction, and Zn bioavailability were observed among genotypes. Lentil root accumulated more Zn (54 mg kg-1) with respect to shoot Zn (51 mg kg-1) under Zn supply. The Zn efficient genotypes (Line-11504 and Mansehra-89) produced more root and shoot dry weights at both harvests. There was a positive correlation between the relative growth rate of root and grain phytate concentration (r = 0.55) and [phytate]:[Zn] ratio (r = 0.67). Zn-efficient genotype Mansehra-89 had a maximum root shoot ratio (0.57) and higher grain Zn (60 mg kg-1) with a respectively reduced grain phytate (17 µg g-1) and thus, had more Zn bioavailability (3.01 mg d-1). The genotypic ability for Zn uptake and accumulation within different plant tissues may be incorporated into future crop breeding to improve the nutrition of undernourished consumers.

Dietary Zn deficiency, the current situation and potential solutions

Zinc (Zn) deficiency is a worldwide problem, and this review presents an overview of the magnitude of Zn deficiency with a particular emphasis on present global challenges, current recommendations for Zn intake, and factors that affect dietary requirements. The challenges of monitoring Zn status are clarified together with the discussion of relevant Zn bioaccessibility and bioavailability issues. Modern lifestyle factors that may exacerbate Zn deficiency and new strategies of reducing its effects are presented. Biofortification, as a potentially useful strategy for improving Zn status in sensitive populations, is discussed. The review proposes potential actions that could deliver promising results both in terms of monitoring dietary and physiological Zn status as well as in alleviating dietary Zn deficiency in affected populations.

Historical shifting in grain mineral density of landmark rice and wheat cultivars released over the past 50 years in India

The 'Green Revolution (GR)' has been successful in meeting food sufficiency in India, but compromising its nutritional security. In a first, we report altered grain nutrients profile of modern-bred rice and wheat cultivars diminishing their mineral dietary significance to the Indian population. To substantiate, we evaluated grain nutrients profile of historical landmark high-yielding cultivars of rice and wheat released in succeeding decades since the GR and its impacts on mineral diet quality and human health, with a prediction for decades ahead. Analysis of grain nutrients profile shows a downward trend in concentrations of essential and beneficial elements, but an upward in toxic elements in past 50 y in both rice and wheat. For example, zinc (Zn) and iron (Fe) concentration in grains of rice decreased by ~ 33.0 (P < 0.001) and 27.0% (P < 0.0001); while for wheat it decreased by ~ 30.0 (P < 0.0001) and 19.0% (P < 0.0001) in past more than 50 y, respectively. A proposed mineral-diet quality index (M-DQI) significantly (P < 0.0001) decreased ~ 57.0 and 36.0% in the reported time span (1960-2010) in rice and wheat, respectively. The impoverished M-DQI could impose hostile effects on non-communicable diseases (NCDs) like iron-deficiency anemia, respiratory, cardiovascular, and musculoskeletal among the Indian population by 2040. Our research calls for an urgency of grain nutrients profiling before releasing a cultivar of staples like rice and wheat in the future.

Extreme low-temperature events can alleviate micronutrient deficiencies while increasing potential health risks from heavy metals in rice

Despite global warming, extreme low-temperature stress (LTS) events pose a significant threat to rice production (especially in East Asia) that can significantly impact micronutrient and heavy metal elements in rice. With two billion people worldwide facing micronutrient deficiencies (MNDs) and widespread heavy metal pollution in rice, understanding these impacts is crucial. We conducted detailed extreme LTS experiments with two rice (Oryza sativa L.) cultivars (Huaidao 5 and Nanjing 46) grown under four temperature levels (from 21/27 °C to 6/12 °C) and three LTS durations (three, six, and nine days). We observed significant interaction effects for LTS at different growth stages, durations and temperature levels on the contents and accumulation of mineral elements. The contents of most mineral elements (such Fe, Zn, As, Cu, and Cd) increased significantly under severe LTS at flowering, but decreased under LTS at the grain-filling stage. The accumulations of all mineral elements decreased at the three growth stages under LTS due to decreased grain weight. The contents and accumulation of mineral elements were more sensitive to LTS at the peak flowering stage than at the other two stages. Furthermore, the contents of most mineral elements in Nanjing 46 show larger variation under LTS compared to Huaidao 5. Accumulated cold degree days (ACDD, °C·d) were found to be suitable for quantifying the effects of LTS on the relative contents and accumulations of mineral elements. LTS at the flowering stage will help alleviate MNDs, but may also increase potential health risks from heavy metals. These results provide valuable insights for evaluating future climate change impacts on rice grain quality and potential health risks from heavy metals.

Biofortification: an approach to eradicate micronutrient deficiency

Micronutrient deficiency also known as "hidden hunger" refers to a condition that occurs when the body lacks essential vitamins and minerals that are required in small amounts for proper growth, development and overall health. These deficiencies are particularly common in developing countries, where a lack of access to a varied and nutritious diet makes it difficult for people to get the micronutrients they need. Micronutrient supplementation has been a topic of interest, especially during the Covid-19 pandemic, due to its potential role in supporting immune function and overall health. Iron (Fe), zinc (Zn), iodine (I), and selenium (Se) deficiency in humans are significant food-related issues worldwide. Biofortification is a sustainable strategy that has been developed to address micronutrient deficiencies by increasing the levels of essential vitamins and minerals in staple crops that are widely consumed by people in affected communities. There are a number of agricultural techniques for biofortification, including selective breeding of crops to have higher levels of specific nutrients, agronomic approach using fertilizers and other inputs to increase nutrient uptake by crops and transgenic approach. The agronomic approach offers a temporary but speedy solution while the genetic approach (breeding and transgenic) is the long-term solution but requires time to develop a nutrient-rich variety.

Rice biofortification: breeding and genomic approaches for genetic enhancement of grain zinc and iron contents

Rice is a highly consumed staple cereal cultivated predominantly in Asian countries, which share 90% of global rice production. Rice is a primary calorie provider for more than 3.5 billion people across the world. Preference and consumption of polished rice have increased manifold, which resulted in the loss of inherent nutrition. The prevalence of micronutrient deficiencies (Zn and Fe) are major human health challenges in the 21^st century. Biofortification of staples is a sustainable approach to alleviating malnutrition. Globally, significant progress has been made in rice for enhancing grain Zn, Fe, and protein. To date, 37 biofortified Fe, Zn, Protein and Provitamin A rich rice varieties are available for commercial cultivation (16 from India and 21 from the rest of the world; Fe > 10 mg/kg, Zn > 24 mg/kg, protein > 10% in polished rice as India target while Zn > 28 mg/kg in polished rice as international target). However, understanding the micronutrient genetics, mechanisms of uptake, translocation, and bioavailability are the prime areas that need to be strengthened. The successful development of these lines through integrated-genomic technologies can accelerate deployment and scaling in future breeding programs to address the key challenges of malnutrition and hidden hunger.

Improving nutrition through biofortification-A systematic review

Nutritious foods are essential for human health and development. However, malnutrition and hidden hunger continue to be a challenge globally. In most developing countries, access to adequate and nutritious food continues to be a challenge. Although hidden hunger is less prevalent in developed countries compared to developing countries where iron (Fe) and zinc (Zn) deficiencies are common. The United Nations (UN) 2nd Sustainable Development Goal was set to eradicate malnutrition and hidden hunger. Hidden hunger has led to numerous cases of infant and maternal mortalities, and has greatly impacted growth, development, cognitive ability, and physical working capacity. This has influenced several countries to develop interventions that could help combat malnutrition and hidden hunger. Interventions such as dietary diversification and food supplementation are being adopted. However, fortification but mainly biofortification has been projected to be the most sustainable solution to malnutrition and hidden hunger. Plant-based foods (PBFs) form a greater proportion of diets in certain populations; hence, fortification of PBFs is relevant in combating malnutrition and hidden hunger. Agronomic biofortification, plant breeding, and transgenic approaches are some currently used strategies in food crops. Crops such as cereals, legumes, oilseeds, vegetables, and fruits have been biofortified through all these three strategies. The transgenic approach is sustainable, efficient, and rapid, making it suitable for biofortification programs. Omics technology has also been introduced to improve the efficiency of the transgenic approach.

A tale of two metals: Biofortification of rice grains with iron and zinc

Iron (Fe) and zinc (Zn) are essential micronutrients needed by virtually all living organisms, including plants and humans, for proper growth and development. Due to its capacity to easily exchange electrons, Fe is important for electron transport in mitochondria and chloroplasts. Fe is also necessary for chlorophyll synthesis. Zn is a cofactor for several proteins, including Zn-finger transcription factors and redox metabolism enzymes such as copper/Zn superoxide dismutases. In humans, Fe participates in oxygen transport, electron transport, and cell division whereas Zn is involved in nucleic acid metabolism, apoptosis, immunity, and reproduction. Rice (Oryza sativa L.) is one of the major staple food crops, feeding over half of the world's population. However, Fe and Zn concentrations are low in rice grains, especially in the endosperm, which is consumed as white rice. Populations relying heavily on rice and other cereals are prone to Fe and Zn deficiency. One of the most cost-effective solutions to this problem is biofortification, which increases the nutritional value of crops, mainly in their edible organs, without yield reductions. In recent years, several approaches were applied to enhance the accumulation of Fe and Zn in rice seeds, especially in the endosperm. Here, we summarize these attempts involving transgenics and mutant lines, which resulted in Fe and/or Zn biofortification in rice grains. We review rice plant manipulations using ferritin genes, metal transporters, changes in the nicotianamine/phytosiderophore pathway (including biosynthetic genes and transporters), regulators of Fe deficiency responses, and other mutants/overexpressing lines used in gene characterization that resulted in Fe/Zn concentration changes in seeds. This review also discusses research gaps and proposes possible future directions that could be important to increase the concentration and bioavailability of Fe and Zn in rice seeds without the accumulation of deleterious elements. We also emphasize the need for a better understanding of metal homeostasis in rice, the importance of evaluating yield components of plants containing transgenes/mutations under field conditions, and the potential of identifying genes that can be manipulated by gene editing and other nontransgenic approaches.

Genomic prediction of zinc-biofortification potential in rice gene bank accessions

A genomic prediction model successfully predicted grain Zn concentrations in 3000 gene bank accessions and this was verified experimentally with selected potential donors having high on-farm grain-Zn in Madagascar. Increasing zinc (Zn) concentrations in edible parts of food crops, an approach termed Zn-biofortification, is a global breeding objective to alleviate micro-nutrient malnutrition. In particular, infants in countries like Madagascar are at risk of Zn deficiency because their dominant food source, rice, contains insufficient Zn. Biofortified rice varieties with increased grain Zn concentrations would offer a solution and our objective is to explore the genotypic variation present among rice gene bank accessions and to possibly identify underlying genetic factors through genomic prediction and genome-wide association studies (GWAS). A training set of 253 rice accessions was grown at two field sites in Madagascar to determine grain Zn concentrations and grain yield. A multi-locus GWAS analysis identified eight loci. Among these, QTN_11.3 had the largest effect and a rare allele increased grain Zn concentrations by 15%. A genomic prediction model was developed from the above training set to predict Zn concentrations of 3000 sequenced rice accessions. Predicted concentrations ranged from 17.1 to 40.2 ppm with a prediction accuracy of 0.51. An independent confirmation with 61 gene bank seed samples provided high correlations (r = 0.74) between measured and predicted values. Accessions from the aus sub-species had the highest predicted grain Zn concentrations and these were confirmed in additional field experiments, with one potential donor having more than twice the grain Zn compared to a local check variety. We conclude utilizing donors from the aus sub-species and employing genomic selection during the breeding process is the most promising approach to raise grain Zn concentrations in rice.

Agronomic Biofortification of Zinc in Rice for Diminishing Malnutrition in South Asia

Zinc (Zn) is increasingly recognized as an essential trace element in the human diet that mediates a plethora of health conditions, including immune responses to infectious diseases. Interestingly, the geographical distribution of human dietary Zn deficiency overlaps with soil Zn deficiency. In South Asia, Zn malnutrition is high due to excessive consumption of rice with low Zn content. Interventions such as dietary diversification, food fortification, supplementation, and biofortification are followed to address Zn malnutrition. Among these, Zn biofortification of rice is the most encouraging, cost-effective, and sustainable for South Asia. Biofortification through conventional breeding and transgenic approaches has been achieved in cereals; however, if the soil is deficient in Zn, then these approaches are not advantageous. Therefore, in this article, we review strategies for enhancing the Zn concentration of rice through agronomic biofortification such as timing, dose, and method of Zn fertilizer application, and how nitrogen and phosphorus application as well as crop establishment methods influence Zn concentration in rice. We also propose data-driven Zn recommendations to anticipate crop responses to Zn fertilization and targeted policies that support agronomic biofortification in regions where crop responses to Zn fertilizer are high.

FE-SEM/EDX Based Zinc Mobilization Analysis of Burkholderia cepacia and Pantoea rodasii and Their Functional Annotation in Crop Productivity, Soil Quality, and Zinc Biofortification of Paddy

The experimental study was contrived to characterize two zinc-solubilizing bacteria (ZSB), namely BMRR126 and BMAR64, and their role in zinc (Zn) biofortification of rice. These bacteria solubilized Zn profoundly, determined qualitatively by halo-zone formation on a solid medium and quantitatively in a liquid broth by AAS and SEM-EDX. The lowering of pH and contact angle assessment of the liquid broth unveiled the establishment of the acidic conditions in a medium suitable for Zn solubilization. The characterization of both isolates on the basis of 16S rRNA gene analysis was identified as Burkholderia cepacia and Pantoea rodasii, respectively. These strains were also found to have some plant probiotic traits namely phosphate solubilization, production of siderophore, indole acetic acid (IAA), exopolysaccharide (EPS), and ammonia. The field experiments were performed at two diverse locations and under all treatments; the simultaneous use of BMRR126 and BMAR64 with zinc oxide (ZnO) resulted in the highest growth and productivity of the paddy crop. The utmost Zn achievement in the grain was estimated in a treatment (T9) (25.07 mg/kg) containing a consortium of BMRR126 and BMAR64 along with ZnO for the Terai region. The treatment containing single ZSB bioinoculant BMRR126 (T7) showed an elevated Zn amount in the rice grain (33.25 mg/kg) for the Katchar region. The soil parameters (pH, EC, organic carbon, NPK, available Zn, and dehydrogenase activity) were also positively influenced under all bacterial treatments compared to the uninoculated control. Our study clearly accentuates the need for Zn solubilizing bacteria (ZSB) to provide the benefits of Zn-biofortification in different regions.

Zinc deficiency responses: bridging the gap between Arabidopsis and dicotyledonous crops

Zinc (Zn) deficiency is a widespread phenomenon in agricultural soils worldwide and has a major impact on crop yield and quality, and hence on human nutrition and health. Although dicotyledonous crops represent >30% of human plant-based nutrition, relatively few efforts have been dedicated to the investigation of Zn deficiency response mechanisms in dicotyledonous, in contrast to monocotyledonous crops, such as rice or barley. Here, we describe the Zn requirement and impact of Zn deficiency in several economically important dicotyledonous crops, Phaseolus vulgaris, Glycine max, Brassica oleracea, and Solanum lycopersicum. We briefly review our current knowledge of the Zn deficiency response in Arabidopsis and outline how this knowledge is translated in dicotyledonous crops. We highlight commonalities and differences between dicotyledonous species (and with monocotyledonous species) regarding the function and regulation of Zn transporters and chelators, as well as the Zn-sensing mechanisms and the role of hormones in the Zn deficiency response. Moreover, we show how the Zn homeostatic network intimately interacts with other nutrients, such as iron or phosphate. Finally, we outline how variation in Zn deficiency tolerance and Zn use efficiency among cultivars of dicotyledonous species can be leveraged for the design of Zn biofortification strategies.

Effect of parboiling conditions on zinc and iron retention in biofortified and non-biofortified milled rice

BACKGROUND

Zinc-biofortified rice could contribute to zinc intake in deficient populations, but processing it into parboiled rice could affect this potential benefit. Zinc and iron true retention (TR) in milled rice produced under conditions resembling household and commercial parboiled methods was evaluated. Zinc and iron TR in milled rice obtained from biofortified and non-biofortified rice subjected to different soaking temperatures during parboiling was also evaluated.

RESULTS

Conditions resembling commercial parboiling methods resulted in 52.2-59.7% zinc TR and 55.4-79.1% iron TR, whereas those used for household parboiling resulted in 70.7-79.6% zinc TR and 78.2-119.8% iron TR. Zinc TR in milled (8-16% bran removal) biofortified and non-biofortified parboiled rice was 50.6-66.8% when soaking rough rice at 20 °C and 29.9-56.0% when soaking rough rice at 65 °C; both had lower zinc TR than non-parboiled rice (58.0-80.6%). Iron TR was generally similar between milled non-parboiled and parboiled rice (26.2-67.6%) and between parboiled biofortified and non-biofortified milled rice.

CONCLUSION

Parboiling conditions used to obtain milled rice targeted for own household consumption resulted in higher zinc and iron TR compared to parboiling conditions used for milled rice targeted for markets. More zinc from the inner endosperm moved towards the outer layers at high soaking temperature, resulting in lower zinc TR for milled parboiled rice soaked in hotter water. Parboiled rice soaked at temperatures used in households could provide more zinc to diets compared to rice soaked in hotter water commonly used in large rice mills, especially when rice is extensively milled. © 2021 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Biofortified Wheat Increases Dietary Zinc Intake: A Randomised Controlled Efficacy Study of Zincol-2016 in Rural Pakistan

A new variety of zinc biofortified wheat (Zincol-2016) was released in Pakistan in 2016. The primary aim of this study was to examine the effects of consuming Zincol-2016 wheat flour on biochemical and functional markers of zinc status in a population with widespread zinc deficiency. An individually-randomised, double-blind, placebo-controlled cross over design was used. Fifty households were recruited to participate in the study, with each household included at least one woman of reproductive age (16–49 years) who was neither pregnant nor breast feeding or currently taking nutritional supplements. All households were provided with control flour for an initial 2-week baseline period, followed by the intervention period where households were randomly allocated in a 1:1 ratio to receive biofortified flour (group A; n = 25) and control flour (group B; n = 25) for 8-weeks, then switched to the alternate flour for 8-weeks. The trial has been registered with the ISRCTN (https://www.isrctn.com), ID ISRCTN83678069. The primary outcome measure was plasma zinc concentration, and the secondary outcome measures were plasma selenium and copper concentrations, plasma copper:zinc ratio and fatty acid desaturase and elongase activity indices. Nutrient intake was assessed using 24-h dietary recall interviews. Mineral concentrations in plasma were measured using inductively coupled plasma mass spectrometry and free fatty acids and sphingolipids by mass spectrometry. Linear Mixed Model regression and General Linear Model with repeated measures were used to analyse the outcomes. Based on an average flour consumption of 224 g/day, Zincol-2016 flour provided an additional daily zinc intake of between 3.0 and 6.0 mg for white and whole grain flour, respectively. No serious adverse events were reported. This resulted in significant, increase in plasma zinc concentration after 4 weeks [mean difference 41.5 μg/L, 95% CI (6.9–76.1), p = 0.02]. This was not present after 8 weeks (p = 0.6). There were no consistent significant effects of the intervention on fatty acid desaturase and elongase activity indices. Regular consumption of Zincol-2016 flour increased the daily zinc intake of women of reproductive age by 30–60%, however this was not associated with a sustained improvement in indices of zinc status.

Zinc in plants: Integrating homeostasis and biofortification

Zinc plays many essential roles in life. As a strong Lewis acid that lacks redox activity under environmental and cellular conditions, the Zn²⁺ cation is central in determining protein structure and catalytic function of nearly 10% of most eukaryotic proteomes. While specific functions of zinc have been elucidated at a molecular level in a number of plant proteins, wider issues abound with respect to the acquisition and distribution of zinc by plants. An important challenge is to understand how plants balance between Zn supply in soil and their own nutritional requirement for zinc, particularly where edaphic factors lead to a lack of bioavailable zinc or, conversely, an excess of zinc that bears a major risk of phytotoxicity. Plants are the ultimate source of zinc in the human diet, and human Zn deficiency accounts for over 400 000 deaths annually. Here, we review the current understanding of zinc homeostasis in plants from the molecular and physiological perspectives. We provide an overview of approaches pursued so far in Zn biofortification of crops. Finally, we outline a "push-pull" model of zinc nutrition in plants as a simplifying concept. In summary, this review discusses avenues that can potentially deliver wider benefits for both plant and human Zn nutrition.

Nutrient Adequacy of Global Food Production

A major challenge for countries around the world is to provide a nutritionally adequate diet to their population with limited available resources. A comprehensive analysis that reflects the adequacy of domestic food production for meeting national nutritional needs in different countries is lacking. Here we combined national crop, livestock, aquaculture, and fishery production statistics for 191 countries obtained from UN FAO with food composition databases from USDA and accounted for food loss and waste occurring at various stages to calculate the amounts of calories and 24 essential nutrients destined for human consumption. We then compared the domestic production quantities of all nutrients with their population-level requirements estimated from age- and sex-specific intake recommendations of WHO to assess the nutrient adequacy of the national food production. Our results show inadequate production of seven out of 24 nutrients (choline, calcium, polyunsaturated fatty acids, vitamin A, vitamin E, folate, and iron) in most countries, despite the overall adequacy of the total global production. High-income countries produce adequate amounts of dietary nutrients in general, while the foods produced in low-income countries mainly comprising roots and cereal products often lack in important micronutrients such as choline, calcium, and vitamin B12. South Asian food production barely fulfills half of the required vitamin A. Our study identifies target nutrients for each country whose domestic production should be encouraged for improving nutritional adequacy through interventions such as increasing the production of foods or fortified foods that are rich in these inadequate nutrients while not undermining the local environment. This assessment can serve as an evidence base for nutrition-sensitive policies facilitating the achievement of the Sustainable Development Goals of zero hunger and good health and well-being.

Biofortification of Cereals and Pulses Using New Breeding Techniques: Current and Future Perspectives

Cereals and pulses are consumed as a staple food in low-income countries for the fulfillment of daily dietary requirements and as a source of micronutrients. However, they are failing to offer balanced nutrition due to deficiencies of some essential compounds, macronutrients, and micronutrients, i.e., cereals are deficient in iron, zinc, some essential amino acids, and quality proteins. Meanwhile, the pulses are rich in anti-nutrient compounds that restrict the bioavailability of micronutrients. As a result, the population is suffering from malnutrition and resultantly different diseases, i.e., anemia, beriberi, pellagra, night blindness, rickets, and scurvy are common in the society. These facts highlight the need for the biofortification of cereals and pulses for the provision of balanced diets to masses and reduction of malnutrition. Biofortification of crops may be achieved through conventional approaches or new breeding techniques (NBTs). Conventional approaches for biofortification cover mineral fertilization through foliar or soil application, microbe-mediated enhanced uptake of nutrients, and conventional crossing of plants to obtain the desired combination of genes for balanced nutrient uptake and bioavailability. Whereas, NBTs rely on gene silencing, gene editing, overexpression, and gene transfer from other species for the acquisition of balanced nutritional profiles in mutant plants. Thus, we have highlighted the significance of conventional and NBTs for the biofortification of cereals and pulses. Current and future perspectives and opportunities are also discussed. Further, the regulatory aspects of newly developed biofortified transgenic and/or non-transgenic crop varieties via NBTs are also presented.

The Potential Impact of Climate Change on the Micronutrient-Rich Food Supply

Micronutrient deficiencies are a major cause of morbidity and mortality in low- and middle-income countries worldwide. Climate change, characterized by increasing global surface temperatures and alterations in rainfall, has the capacity to affect the quality and accessibility of micronutrient-rich foods. The goals of this review are to summarize the potential effects of climate change and its consequences on agricultural yield and micronutrient quality, primarily zinc, iron, and vitamin A, of plant foods and upon the availability of animal foods, to discuss the implications for micronutrient deficiencies in the future, and to present possible mitigation and adaptive strategies. In general, the combination of increasing atmospheric carbon dioxide and rising temperature is predicted to reduce the overall yield of major staple crops, fruits, vegetables, and nuts, more than altering their micronutrient content. Crop yield is also reduced by elevated ground-level ozone and increased extreme weather events. Pollinator loss is expected to reduce the yield of many pollinator-dependent crops such as fruits, vegetables, and nuts. Sea-level rise resulting from melting of ice sheets and glaciers is predicted to result in coastal inundation, salt intrusion, and loss of coral reefs and mangrove forests, with an adverse impact upon coastal rice production and coastal fisheries. Global ocean fisheries catch is predicted to decline because of ocean warming and declining oxygen. Freshwater warming is also expected to alter ecosystems and reduce inland fisheries catch. In addition to limiting greenhouse gas production, adaptive strategies include postharvest fortification of foods; micronutrient supplementation; biofortification of staple crops with zinc and iron; plant breeding or genetic approaches to increase zinc, iron, and provitamin A carotenoid content of plant foods; and developing staple crops that are tolerant of abiotic stressors such as elevated carbon dioxide, elevated temperature, and increased soil salinity.

Enhancing health benefits of milled rice: current status and future perspectives

Milled rice is an essential part of the regular diet for approximately half of the world's population. Its remarkable commercial value and consumer acceptance are mostly due to its promising cooking qualities, appealing sensory properties, and longer shelf life. However, the significant loss of the nutrient-rich bran layer during milling makes it less nutritious than the whole grain. Thus, enhancing the nutritive value of milled rice is vital in improving the health and wellbeing of rice consumers, particularly for those residing in the low-economic zones where rice is the primary source of calories and nutrition. This article provides a critical review on multiple frontiers of recent interventions, such as (1) infusing the genetic diversity to enrich amylose and resistant starch to reduce glycaemic index, (2) enhancing the minerals and vitamins through complementary fortification and biofortification as short and long-term interventions, and (3) developing transgenic solutions to improve the nutrient levels of milled rice. Additionally, the review highlights the benefits of functional ingredients of milled rice to human health and the potential of enhancing them in rice to address the triple burden of malnutrition. The potential merit of milled rice concerning food safety is also reviewed in this article.

Grain Fe and Zn content, heterosis, combining ability and its association with grain yield in irrigated and aerobic rice

Genetic improvement of rice for grain micronutrients, viz., iron (Fe) and zinc (Zn) content is one of the important breeding objectives, in addition to yield improvement under the irrigated and aerobic ecosystems. In view of developing genetic resources for aerobic conditions, line (L) × tester (T) analysis was conducted with four restorers, four CMS lines and 16 hybrids. Both hybrids and parental lines were evaluated in irrigated and aerobic field conditions for grain yield, grain Fe and Zn content. General Combining Ability (GCA) effects of parents and Specific Combining Ability (SCA) effects of hybrids were observed to be contrasting for the micronutrient content in both the growing environments. The grain Fe and Zn content for parental lines were negatively correlated with grain yield in both the contrasting growing conditions. However, hybrids exhibited positive correlation for grain Fe and Zn with grain yield under limited water conditions. The magnitude of SCA mean squares was much higher than GCA mean squares implying preponderance of dominance gene action and also role of complementary non-allelic gene(s) interaction of parents and suitability of hybrids to the aerobic system. The testers HHZ12-SAL8-Y1-SAL1 (T1) and HHZ17-Y16-Y3-Y2 (T2) were identified as good combiners for grain Zn content under irrigated and aerobic conditions respectively.

The global challenge of hidden hunger: perspectives from the field

The aim of this review paper is to explore the strategies employed to tackle micronutrient deficiencies with illustrations from field-based experience. Hidden hunger is the presence of multiple micronutrient deficiencies (particularly iron, zinc, iodine and vitamin A), which can occur without a deficit in energy intake as a result of consuming an energy-dense, but nutrient-poor diet. It is estimated that it affects more than two billion people worldwide, particularly in low- and middle-income countries where there is a reliance on low-cost food staples and where the diversity of the diet is limited. Finding a way to improve the nutritional quality of diets for the poorest people is central to meeting the UN sustainable development goals particularly sustainable development goal 2: end hunger, achieve food security and improved nutrition and promote sustainable agriculture. As we pass the midpoint of the UN's Decade for Action on Nutrition, it is timely to reflect on progress towards achieving sustainable development goal 2 and the strategies to reduce hidden hunger. Many low- and middle-income countries are falling behind national nutrition targets, and this has been exacerbated by the COVID-19 pandemic as well as other recent shocks to the global food system which have disproportionately impacted the world's most vulnerable communities. Addressing inequalities within the food system must be central to developing a sustainable, cost-effective strategy for improving food quality that delivers benefit to the seldom heard and marginalised communities.

Identification of Promising RILs for High Grain Zinc Through Genotype × Environment Analysis and Stable Grain Zinc QTL Using SSRs and SNPs in Rice (Oryza sativa L.)

Polished rice is one of the commonly consumed staple foods across the world. However, it contains limited nutrients especially iron (Fe) and zinc (Zn). To identify promising recombinant inbred lines (RILs) for grain Zn and single plant yield, 190 RILs developed from PR116 and Ranbir Basmati were evaluated in two environments (E1 and E2). A subset of 44 contrasting RILs for grain Zn was screened in another two environments (E3 and E4). Phenotypic data was collected for 10 traits, viz., days to 50% flowering, plant height, panicle length, number of tillers, single plant yield (SPY), test weight, Fe and Zn in brown (IBR, ZBR), and polished rice (IPR, ZPR). Stepwise regression analysis of trait data in 190 RILs and a subset of 44 RILs revealed the interdependence of ZPR, ZBR, IPR, and IBR and the negative association of grain Zn with single plant yield. Based on the additive main effect and multiplicative interaction (AMMI) and genotype and genotype × environment interaction (GGE) analyses of the subset of 44 RILs across four environments (E1-E4), six promising RILs were identified for ZPR with >28 ppm. Mapping of 190 RILs with 102 simple sequence repeats (SSRs) resulted in 13 QTLs for best linear unbiased estimates (BLUEs) of traits including advantage over check (AOC). Using genotype-based sequencing (GBS), the subset of 44 RILs was mapped with 1035 single-nucleotide polymorphisms (SNPs) and 21 QTLs were identified. More than 100 epistatic interactions were observed. A major QTL qZPR.1.1 (PV 37.84%) and another QTL qZPR.11.1 (PV 15.47%) were identified for grain Zn in polished rice. A common major QTL (qZBR.2.1 and qZPR.2.1) was also identified on chromosome 2 for grain Zn content across SSR and SNP maps. Two potential candidate genes related to transporters were identified based on network analyses in the genomic regions of QTL < 3 Mb. The RILs identified for grain Zn and SPY were nominated for national evaluation as under rice biofortification, and two QTLs identified based on BLUEs could be used in the rice biofortification breeding programs.

Genome-wide association mapping revealed numerous novel genomic loci for grain nutritional and yield-related traits in rice (Oryza sativa L.) landraces

A core set of 190 rice landraces were used to decipher the genetic structure and to discover the chromosomal regions containing QTLs, affecting the grain micro-nutrients, fatty acids, and yield-related traits by using 148 molecular markers in this study. Landraces were categorized into three sub-groups based on population stratification study and followed by neighbor-joining tree and principal component analysis. Analysis of variance revealed abundant variations among the landraces for studied traits with less influence of environmental factors. Genome Wide Association Studies (GWAS) revealed 22 significant and consistent QTLs through marker trait association (MTAs) for 12 traits based on 2 years and pooled analysis. Out of 22 QTLs, three have been reported earlier while 19 QTLs are novel. Interestingly, 13 QTLs out of 22 were explained more than 10% phenotypic variance. Association of RM1148 and RM205 with Days to 50% flowering was comparable with flowering control genes Ghd8/qDTH8 and qDTH9, respectively. Similarly, Zn content was associated with RM44, which is situated within the QTL qZn8-1. Moreover, significant association of RM25 with oleic acid content was closely positioned with QTL qOle8. Association of RM7434 with grain yield/plant; RM184 with spikelet fertility %; R3M10, R9M42 with hundred seed weight; RM536, RM17467, RM484, RM26063 with Fe content; RM44, RM6839 with Zn content are the major outcomes of this study. In addition, association of R11M23 with days to 50% flowering, panicle length and total spikelets per panicle are explained the possible occurrence of pleiotropism among these traits. Prominent rice landraces viz., Anjani (early maturity); Sihar (extra dwarf); Gangabaru (highest grain yield/plant); Karhani (highest iron content); Byalo-2 (highest zinc content) and Kadamphool (highest oleic acid) were identified through this study. The present study will open many avenues towards utilization of these QTLs and superior landraces in rice breeding for developing nutrition-rich high yielding varieties.

Stable SNP Allele Associations With High Grain Zinc Content in Polished Rice (Oryza sativa L.) Identified Based on ddRAD Sequencing

Polished rice is widely consumed staple food across the globe, however, it contains limited nutrients especially iron (Fe) and zinc (Zn). To identify promising genotypes for grain Zn, a total of 40 genotypes consisting 20 rice landraces, and 20 released high yielding rice varieties were evaluated in three environments (wet seasons 2014, 2015 and 2016) for nine traits including days to 50% flowering (DFF), plant height (PH), panicle length (PL), total number of tillers (TNT), single plant yield (SPY), Fe and Zn in brown (IBR, ZBR) and polished rice (IPR, ZPR). Additive Main Effect and Multiplicative Interaction (AMMI), Genotype and Genotype × Environment Interaction (GGE) analyses identified genotypes G22 (Edavankudi Pokkali), G17 (Taraori Basmati), G27 (Chittimuthyalu) and G26 (Kalanamak) stable for ZPR and G8 (Savitri) stable for SPY across three environments. Significant negative correlation between yield and grain Zn was reaffirmed. Regression analysis indicated the contribution of traits toward ZPR and SPY and also desirable level of grain Zn in brown rice. A total of 39,137 polymorphic single nucleotide polymorphisms (SNPs) were obtained through double digest restriction site associated DNA (dd-RAD) sequencing of 40 genotypes. Association analyses with nine phenotypic traits revealed 188 stable SNPs with six traits across three environments. ZPR was associated with SNPs located in three putative candidate genes (LOC_Os03g47980, LOC_Os07g47950 and LOC_Os07g48050) on chromosomes 3 and 7. The genomic region of chromosome 7 co localized with reported genomic regions (rMQTL₇.₁) and OsNAS3 candidate gene. SPY was found to be associated with 12 stable SNPs located in 11 putative candidate genes on chromosome 1, 6, and 12. Characterization of rice landraces and varieties in terms of stability for their grain Zn and yield identified promising donors and recipients along with genomic regions in the present study to be deployed rice Zn biofortification breeding program.

Genetic Manipulation for Improved Nutritional Quality in Rice

Food with higher nutritional value is always desired for human health. Rice is the prime staple food in more than thirty developing countries, providing at least 20% of dietary protein, 3% of dietary fat and other essential nutrients. Several factors influence the nutrient content of rice which includes agricultural practices, post-harvest processing, cultivar type as well as manipulations followed by selection through breeding and genetic means. In addition to mutation breeding, genetic engineering approach also contributed significantly for the generation of nutrition added varieties of rice in the last decade or so. In the present review, we summarize the research update on improving the nutritional characteristics of rice by using genetic engineering and mutation breeding approach. We also compare the conventional breeding techniques of rice with modern molecular breeding techniques toward the generation of nutritionally improved rice variety as compared to other cereals in areas of micronutrients and availability of essential nutrients such as folate and iron. In addition to biofortification, our focus will be on the efforts to generate low phytate in seeds, increase in essential fatty acids or addition of vitamins (as in golden rice) all leading to the achievements in rice nutrition science. The superiority of biotechnology over conventional breeding being already established, it is essential to ascertain that there are no serious negative agronomic consequences for consumers with any difference in grain size or color or texture, when a nutritionally improved variety of rice is generated through genetic engineering technology.

Simultaneous Biofortification of Rice With Zinc, Iodine, Iron and Selenium Through Foliar Treatment of a Micronutrient Cocktail in Five Countries

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.