Integrating foliar zinc (Zn) application into common practices, e.g. application of pesticides, phosphorus (P) or biostimulants, is a feasible agronomic strategy of wheat biofortification. However, it remains unclear how this integrated approach affects the efficacy of foliar Zn sprays, especially under unfavourable environmental conditions. Here, two field experiments considering Zn forms (ZnSO₄ and zinc-glycine) and applications (alone or combined with pesticides, KH₂PO₄, and biostimulants amino acids or fulvic acids) were conducted in two seasons (2017 and 2018), and their effects on the magnitude of grain Zn increment and bioavailability were evaluated. The results showed that less precipitation in 2018 caused 11.7–52.2% yield losses than in 2017, which increased grain Zn concentration by 13.4–58.4%. Foliar application of Zn-glycine did not surpass ZnSO₄ spray in regarding to grain Zn concentration and bioavailability. Grain Zn concentration substantially decreased in plants sprayed with KH₂PO₄ irrespective of Zn forms applied, indicating strong antagonistic effects of P supply on grain Zn enrichment. There were no differences in grain Zn density between the applications of amino acids and fulvic acids. However, grain Zn bioavailability significantly increased by 22.3 and 23.4% in the Zn plus pesticides treatment when sprayed with fulvic acids in 2017 and with amino acids in 2018, respectively. Overall, environmental conditions and foliar Zn management considering Zn forms and applications accounted for 35–45% and 20–37% of explained variation in the magnitude of grain Zn increment, respectively. The results demonstrated that management and environment are crucial factors to consider in agronomic biofortification of wheat.

Wheat (Triticum aestivum L.) is one of most widely consumed cereal crops globally. More than two billion people are affected by nutritional deficiencies caused by zinc (Zn) and iron (Fe) deficiency. Therefore, biofortification is a strategy supposed to be economical, sustainable and easily implemented to increase the micronutrient content in the crops. However, micronutrient distribution, especially Zn and Fe, within the spike has been rarely reported. For this, different concentrations of Zn (0, 30, 60, 90 and 120 μmol L^–1) and sucrose (2%, 4%, 6%) were supplied at Zn concentrations of 30 and 90 μmol L^–1 under detached-ear culture. The results showed that grain weight and grain Zn, Fe and protein contents were higher in superior grains than in inferior grains, and higher in central spikelets than in basal and apical spikelets. Zn supply significantly improved grain Zn, Fe and protein content. Increasing sucrose concentration at low and high Zn supply levels significantly increased grain weight, and grain Zn, Fe and protein contents. The percentage increase in dry weight and nutrient contents of superior and inferior grains was higher in central spikelets than in apical and basal spikelets. It is concluded that grain position significantly affected the grain weight and nutrient content, and these effects could be improved by application of Zn and sucrose. These findings suggest Zn and sucrose application for increasing mineral nutrients contents in wheat grain, and mechanisms of nutrient accumulation in relation to external sucrose and Zn supply should be elucidated in the future.

Plant growth relies on the bioavailability of essential nutrients in the growth environment. Access to mineral nutrients is particularly challenging for crops cultivated in alkaline soil, and in these environments, postharvest application may be effective. Advancements in nanotechnology have provided approaches to improve the essential nutrient content of plants and shelf life of produce. Mineralisation by nanoparticles is a promising postharvest technique that can fortify the essential minerals of plants. This study investigated the role of zinc oxide nanoparticles (ZnO-NPs) as a potential nano-agent to enhance Zn content in tomato (Solanum lycopersicum L.), with ZnO-NPs at 100 mg L^–1 applied externally to tomatoes postharvest for 4 weeks. The assimilation of Zn into the tomato tissues was quantified by inductively coupled plasma-mass spectrometry. The main shelf life factors affecting tomato quality, including microbial spoilage, water loss and colour change, were studied. All experimental data were incorporated through the neural networks model to simulate microbial involvement in fruit spoilage. The biological spoilage factor in the shelf life of tomatoes was projected with high accuracy and a relative error of 3%. Application of ZnO-NPs was associated with 47% inhibition of microbial growth on tomatoes, which may enhance the total lycopene content by up to 6%. In addition, the Zn content of tomatoes was significantly enhanced by 17%. The results also shed light on the thermal conductivity of Zn metal, which increased the dehydration of tomatoes and improved colour maturation. This study provides vital information about the beneficial application of ZnO-NPs and their role in mineralisation to enhance the shelf life of tomatoes.

Suboptimal or inadequate diet of iron (Fe) represents a latent health problem affecting over two billion people worldwide. To tackle micronutrient deficiency in crops, a short-term approach is agronomic biofortification in which nutrients can be enhanced by their accumulation in food plant tissue either by fertilisation or by other eliciting aspects. The present study evaluated the comparative influence of various Fe application methods, including (i) Fe seed coating (300 mg Fe kg^–1 seed), (ii) Fe osmopriming (0.5% Fe solution), (iii) surface broadcasting (8 kg ha^–1), (iv) Fe foliar application (0.3% Fe solution), on paddy yield, net benefits, grain Fe accumulation, bioavailability, and Fe-use efficiencies in conventional (puddled transplanted rice, PTR) and conservational (direct-seeded aerobic rice, DSAR) production systems. Hydro-priming and foliar water spray were also included in treatments as a positive control for osmopriming and foliar spray of Fe respectively. Iron application by either method enhanced productivity, profitability, and biofortification in both rice systems. Grain yield improved in both years by the application of Fe in the following order: osmopriming > foliar application > surface broadcasting > seed coating, with the respective increase of 18%, 14%, 10%, 8% relative to no Fe application. Grain Fe concentration was the highest by Fe applied as foliar (37% over control) in both production systems. Similarly, minimum phytate concentration and phytate:Fe molar ratio were recorded with foliar-applied Fe. In crux, Fe application by osmopriming increased the productivity and profitability under PTR and DSAR systems, whereas foliar-applied Fe improved the grain Fe accumulation.

Agronomic biofortification with selenium (Se) maybe employed to improve the nutritional value of food crops while increasing the plant’s tolerance to water deficit conditions. Although not essential for plants, Se may increase plant tolerance to water stress by boosting plants’ defence system activity. This study aimed to enrich common bean grains with Se and alleviate water deficit effects on common bean by applying Se to plants growing under greenhouse. Selenium was applied to soil at 0, 0.25, 0.5, 1.0, and 2.0 mg kg^–1, under irrigated and water-deficit conditions. Antioxidant enzyme activities (SOD, CAT, and APX), H₂O₂ content, gas exchange, and SPAD index were assessed in plant leaves, and Se and nutrient concentrations were determined in grains. Results showed that water deficit decreased photosynthetic rate, stomatal conductance, transpiration rate, and increased water use efficiency. Selenium did not influence SPAD index in leaves from pod formation to maturity stage but improved the plant defence system by decreasing H₂O₂ content. Increasing Se rates increased Se concentration in grains and leaves. At lower Se rates, mainly at 0.25 mg Se kg^–1, under water deficit, the activities of SOD, CAT, and APX reached their maximum values, and H₂O₂ content was minimum without reducing biomass production and nutrients accumulation. The highest Se rate (2 mg kg^–1) was detrimental, since it decreased biomass production and the plant defence system under water deficit. Conclusively, soil Se addition enriched common bean plants with Se and showed positive responses against water deficit when applied at lower rates.

Selenium (Se) is essential for animals and humans, and studies assessing the influence of sulfur (S) and phosphorus (P) on Se availability and biofortification in tropical soils are required. This study evaluated the adsorption of selenate (SeVI) and selenite (SeIV) in two oxidic soils with contrasting soil texture and assessed effects of phosphate and sulfate as competitive anions on Se desorption. The study also examined Se biofortification of Panicum maximum cv. Mombaça grown in Se-treated clayey soil under increasing rates of P fertilisation. In the laboratory, different Se concentrations were added to soils for adsorption studies (0, 1, 2, 4 mg L^–1 for SeVI and 0, 4, 8, 16 mg L^–1 for SeIV), with Se desorption performed by adding different concentrations of P (0, 2.18, 4.36, 10.90, 21.90 mg L^–1) or S (0, 3.75, 7.5, 15, 30 mg L^–1). Mombaça grass was grown in pots for 43 days in the clayey soil fertilised with SeVI and increasing P rates. Selenium adsorption varied depending on Se speciation, Se rate and soil texture, with SeIV showing greater adsorption than SeVI. In general, amounts of SeVI desorbed increased with increasing addition of P and (mainly) S. However, only P had a positive effect for releasing SeIV from soils. At all SeVI rates added in the clayey soil, Se contents in the shoot dry matter of Mombaça grass increased with increasing P fertilisation rate, agreeing with the desorption results. Further studies combining desorption with biofortification data are recommended for assessing the influence of P in sandy clay loam tropical soils.

This study was designed to investigate the growth characteristics, chlorophyll content and nutritional properties of Tetragonia decumbens, an indigenous plant species of the South African Western Cape. One hundred and eight cuttings generated from a mother plant obtained from a garden were cultivated in hydroponic systems over 7 weeks. The hydroponic experiment comprised three nutrient solutions of graded concentrations (0.2, 0.1, and 0.05% w/v) of Nutrifeed fertiliser prepared in the water whereas the control had no nutrients. Soilless treatments were made of 100% silica sand medium heaped in plastic pots near the brim. Each hydroponic system was run for 2 h/week at the pH and electrical conductivities (EC) of 4.5, 5.5, 6.5, and 3.38, 2.34, 1.10 dS/m respectively, whereas frequencies of irrigation were set at 2 L/h for 15 min at an intermittent break of 2 h between 0900 and 1700 hours. For the first time, this study reported macronutrients and micronutrients present in dune spinach. At P < 0.05, post-harvest results showed that fertigation did not affect the macronutrients, however, micronutrients were significantly affected. Therefore, a well-drained soilless media (100% silica) with a high nutrient application (0.2% w/v), low electrical conductivities, and moderate pH levels had better results in vegetative growth and nutritional composition compared with other treatments.

Iron (Fe) and zinc (Zn) are recognised as micronutrients of clinical significance to public health globally. Major staple crops (wheat, rice and maize) contain insufficient levels of these micronutrients. Baseline concentrations in wheat and maize grains are 30 µg/g for Fe and 25 µg/g for Zn, and in rice grains, 2 µg/g for Fe and 16 µg/g for Zn. However, wheat grains should contain 59 μg Fe/g and 38 μg Zn/g if they are to meet 30–40% of the average requirement of an adult diet. Scientists are addressing malnutrition problems by trying to enhance Fe and Zn accumulation in grains through conventional and next-generation techniques. This article explores the applicability and efficiency of novel genome editing tools compared with conventional breeding for Fe and Zn biofortification and for improving the bioavailability of cereal grains. Some wheat varieties with large increases in Zn concentration have been developed through conventional breeding (e.g. BHU1, BHU-6 and Zincol-2016, with 35–42 µg Zn/g); however, there has been little such success with Fe concentration. Similarly, no rice variety has been developed through conventional breeding with the required grain Fe concentration of 14.5 µg/g. Transgenic approaches have played a significant role for Fe and Zn improvement in cereal crops but have the limitations of low acceptance and strict regulatory processes. Precise editing by CRISPR-Cas9 will help to enhance the Fe and Zn content in cereals without any linkage drag and biosafety issues. We conclude that there is an urgent need to biofortify cereal crops with Fe and Zn by using efficient next-generation approaches such as CRISPR/Cas9 so that the malnutrition problem, especially in developing countries, can be addressed.

Micronutrient deficiency is a widespread food-related health problem around the world. The present study was conducted to evaluate a set of 63 advanced breeding lines of bread wheat (Triticum aestivum L.) for grain iron (GFe) and grain zinc (GZn) concentrations, and to characterise the germplasm set via simple sequence repeat (SSR) markers (both genic and random). Substantial variation was found for both micronutrients. GFe concentration ranged from 28.9 to 67.4 mg kg^–1 and GZn from 26.3 to 56.6 mg kg^–1. Molecular characterisation with six genic and 20 random SSR markers detected 168 alleles with an average of 3.170 alleles per locus. Analysis of genotypic data based on division into two subpopulations revealed 165 alleles with an average of 3.113 alleles per locus in the low GFe–GZn subpopulation, whereas in the high GFe–GZn subpopulation, 149 alleles with an average of 2.811 alleles per locus were detected. Genic SSRs detected a higher average number of alleles (3.273 alleles per locus) than random SSRs (3.143 alleles per locus). Hierarchical clustering using genic markers alone clustered the whole germplasm set into two distinct groups: one possessing low GFe–GZn genotypes, the other with high GFe–GZn genotypes. Study of marker–trait associations (MTAs) identified seven new MTAs (six for GZn and one for GFe) and validated one MTA for GZn concentration. The promising genotypes and MTAs identified during the study will prove useful in wheat bio-fortification programs in the future.

Phytic acid (PA) is a major anti-nutritional factor in maize grains and significantly reduces the bioavailability of minerals such as iron and zinc in humans. Reduction of PA in maize (Zea mays L.) thus assumes great significance. Despite the availability of low phytic-acid (lpa) mutants in maize, their utilisation in breeding has been limited because of non-availability of well adapted lpa-based inbreds. A set of 24 subtropically adapted lpa1-1-based maize inbreds derived through molecular breeding was evaluated along with seven wild-type inbreds at multilocation. The lpa1-1 inbreds possessed 35.8% lower PA (1.68 mg/g) than the wild-type inbreds (2.61 mg/g). Mean proportion of PA was lower in the lpa1-1-based inbreds (62.8%) than in the wild-type inbreds (91.6%). The lpa1-1 inbreds showed similar performance for plant- and ear-height besides flowering behaviour as did wild types. Average grain yield among lpa1-1 inbreds (2735.9 kg/ha) was at par with the original versions (2907.3 kg/ha). Molecular profiling of these lpa1-1 inbreds using 60 genome-wide single-sequence repeats generated 172 alleles, with a mean of 2.87 alleles per locus. Mean polymorphism information content and mean gene diversity were 0.41 and 0.48 respectively. Genetic dissimilarity ranged from 0.23 to 0.81, with an average of 0.64. Cluster analyses grouped 24 lpa1-1 genotypes into three major clusters, and principal-coordinate analysis depicted the diverse nature of genotypes. The study also identified a set of potential hybrid combinations with low PA for their direct utilisation in biofortification program. This is the first study on comprehensive characterisation of lpa1-1-based inbreds adapted to subtropical conditions.

Bread wheat (Triticum aestivum L.) is an important cereal crop that provides >20% of the global calorie intake. Bread wheat contains micronutrients, and thus plays a significant role in nutritional and food securities especially in developing countries. However, its grains are inherently deficient in some micronutrients, particularly iron and zinc, which makes them important biofortification targets. Our objective was to investigate variations in micronutrients and their relationship with grain yield components in wheat under four environments in South Africa. A population of 139 doubled haploid lines derived from a cross between cvv. Tugela-DN and Elands was phenotyped for grain iron and grain zinc concentrations and grain yield components. Heat and drought conditions at Arlington resulted in higher grain zinc concentrations and lower yield component traits; the opposite trend was observed at Bethlehem and Harrismith for both micronutrients and yield components. All traits showed transgressive segregation. Grain iron and zinc concentrations were significantly positively correlated in all four environments. The correlations between these minerals and yield components were inconsistent and ranged from significant to insignificant depending on the environment, indicating that this relationship is non-genetic. The results demonstrate that biofortification of both grain iron and grain zinc can be included as part of the breeding objectives and will not necessarily have adverse relationships with grain yield components.

Iron (Fe) is essential for plant growth and human health. Fe deficiency reduces yield and quality traits of wheat (Triticum aestivum L.). Grains of modern bread wheat varieties contain low levels of Fe, and Fe uptake and translocation in wheat grown in Fe conditions have not been studied in detail. This study investigates Fe homeostasis and biofortification in genetically stable spring wheat Almaken and Zhenis M₅ mutant lines, developed with 200 Gy for higher grain Fe content. Mutant lines and parents were analysed for the expression of genes involved in Fe homeostasis under normal and deficient Fe. Wheat homologues of genes that participated in phytosiderophore (PS) synthesis and transport were significantly upregulated in the Fe-limited roots of Almaken M/1 and both Zhenis M/2 mutant lines, emphasising the role of deoxymugineic acid (DMA) in iron acquisition. The combined overexpression of SAMS, NAS1, TaNAAT, DMAS and TOM was also revealed in the roots of Almaken M/1 and both Zhenis M5 mutant lines, suggesting their involvement in PS synthesis, Fe chelation and transport. Under Fe deficiency, levels of TaYS1A encoding the wheat homologues of the metal-NA transporter YSL, also showed 2.6-, 5.1- and 5.9-fold increases in the roots of Almaken M/1 and both Zhenis M5 mutant lines, respectively. Vacuolar iron transporters (VIT2), natural resistance associated-macrophage protein (NRAMP) genes and the transcription factor basic-loop-helix (bHLH) were significantly upregulated under Fe starvation in shoots. Fe-deficiency-related genotype-dependent and tissue-specific gene expression differences provide new insights into genes involved in iron homeostasis and biofortification genes in wheat.

Iron (Fe) deficiency leads to an overproduction of reactive oxygen species (ROS) in plants that activate their antioxidant systems to control oxidative burst. In this study, contrasting Medicago truncatula genotypes, A17 and TN8.20 (tolerant) and TN1.11 (sensitive), were grown under Fe deficiency. The superoxide dismutase (SOD: EC1.15.1.1) activity, their isoforms’ coding genes, the copper chaperone expression patterns, and leaf phenolic contents were analysed. Our results showed that Fe deficiency decreases the photosynthetic capacity and plant biomass production with a prominent effect on TN1.11 genotype. The tolerance of A17 and TN8.20 was correlated with a maintenance of Fe content and the photosynthetic apparatus and an increase of Cu concentration compared with the sensitive genotype. We revealed a significant increase of H₂O₂ in Fe-deficient plants, mainly in TN1.11 sensitive genotype. TN8.20 and A17 tolerance were concomitant with a significant increase of SOD activities (SOD, Cu/Zn-SOD, and Mn-SOD) under Fe deficiency. This increment was correlated to an induction of the copper chaperone gene expression level, as well as an accumulation of isoquercitin phenolic compound. Our study provides new insights into the orchestration of SOD’s isoforms activities, the expression of the copper chaperone, FeSOD, Cu/ZnSOD genes, and the leaf phenolic compounds accumulation that allows Medicago truncatula to overcome Fe deficiency.

Widespread distribution, toxicity and exposure through rice and rice-based food products make arsenic (As) contamination of environment a serious issue. This review discusses various strategies that can be utilised to tackle the As problem in rice, and the socioeconomic impacts of the As problem. The countries of south and south-east Asia are renowned as hotspots of As contamination owing to occurrence and enrichment of As in soil and groundwater via natural biogeochemical weathering of rocks and As-enriched sediment. The irrigation of rice is mostly applied through the use of contaminated groundwater leading to high As accumulation in rice grains. The intensification of research to address the problem of As in rice has been seen in the past two decades. It has been realised that appropriate irrigation water management, which acts as a major driver of As chemistry in soil and As uptake and transport in plants, can be an easy and affordable solution. Further, balanced supplement of various nutrient elements like selenium (Se), silicon (Si), sulfur (S), nitrogen (N), iron (Fe) and zinc (Zn) has been found to impart dual benefits in terms of reduced As toxicity as well as enhance the nutritional quality of rice grains. Several other agronomic and biotechnological approaches, processing, and cooking methods of rice were found to have profound impacts on rice As and its speciation from farms to table.

Among the toxic heavy metal(loid)s, cadmium (Cd) and arsenic (As) have devastating effects on crop productivity and human health. In plants, mechanisms of detoxification of Cd and As proceed via a glutathione (GSH) dependent common pathway, despite their different modes of toxicity. In this context, the present study aimed to investigate how the common detoxification mechanisms for Cd and As influence the physiological and biochemical responses of seedlings of an important plant used for phytoremediation purposes, Brassica juncea, under Cd and As stress. We demonstrated that Cd and As trigger mostly distinct, but partly overlapping, responses in B. juncea. Exposure of B. juncea seedlings to 100 μM Cd stress for 12 days in a hydroponic system led to a significant reduction in the growth of roots and shoots, and in total chlorophyll content. However, As stress caused a decline in root length only. High-performance liquid chromatography analyses revealed a significant increase in cysteine levels in roots and shoots in response to As stress compared with control and Cd-treated plants. Concomitant elevated sulfur content in response to As stress was observed in roots and shoots. In terms of GSH content, Cd and As triggered similar responses, with a significant decrease in GSH in roots, and non-significant changes in shoots, compared with untreated plants. Inductively coupled plasma-atomic emission spectroscopy revealed that under Cd stress, plants preferentially accumulated zinc (Zn) in the roots compared with iron (Fe) and manganese (Mn). Responses in roots under As and Cd stress were similar with respect to Fe accumulation but opposite in terms of Zn and Mn accumulation. Our data provide valuable insights for design of future strategies for sustainable plant growth on As and Cd polluted soils.

Contamination of arsenic (As) presents a health hazard that affects home gardeners neighbouring contaminated environments. The use of chitosan-modified biochar was investigated to immobilise As(V) from aqueous solution and zucchini seedlings (cv. Courgette d’Italie) were grown as a test crop. The results of characterisation revealed that the presence of chitosan on biochar (BR) surface improved its efficiency of As(V) immobilisation from the contaminated environment. A sorption study further showed that compared with the BR, (BR-C) chitosan-modified biochar (0.1 g) depicted the increased immobilisation of As(V) (10 ppm) from solution. Both Langmuir and Freundlich models fitted well, showing monolayer as well as multilayer sorption. BR-C showed a high Langmuir arsenic sorption capacity of 57.83 mg/g, which effectively decreased the level of As(V) toxicity. As demonstrated in results, As-stress reduced plant growth, seedling length, photosynthetic pigments, soluble sugar, increased hydrogen peroxide contents, and electrolyte leakage percentage. Simultaneously, BR and BR-C were effective against As(V) stress-induced changes in the zucchini plant. Collectively, the results of this study indicate that the modification of BR with chitosan can efficiently immobilised arsenic in the root medium and enhance growth of zucchini under controlled conditions by reducing the uptake of As(V).

Considerable amounts of heavy metals have contaminated the soil from potential manmade point and non-point sources such as industry, urbanisation and agriculture. In both managed and natural ecosystems, beneficial plant–microbe interactions play a significant role improving the growth and health of plants, and could be applied for improving soil fertility as well as crop productivity. Additionally, plant–microbe interactions could be utilised in bioremediation of heavy metal-contaminated soils. The efficiency of phytoremediation can be improved with the aid of plant-growth-promoting bacteria (PGPB), which can change metals to bioavailable and soluble forms. PGPB perform remediation through processes such as production of siderophores, organic acids and biosurfactants, biomethylation, redox processes, phosphorus solubilisation, nitrogen fixation and iron sequestration. These processes improve plant growth and increase plant biomass along with phytoremediation. A crucial solution to the problem of heavy metal contamination might be an appropriate understanding of hyperaccumulator plants and their interaction with microbes. Emerging strategies for either enhancing or reducing the bioavailability of heavy metals in the rhizosphere, such as improving plant establishment, growth and health can significantly accelerate the heavy metal bioremediation process. In this review, we feature the function of PGPB to assist phytoremediation of heavy metals as an eco-friendly and economical approach.