Mineral biofortification and metal/metalloid accumulation in food crops: recent research and trends (Part II)

This is the second part of the special issue on Mineral Biofortification and Metal/Metalloid Accumulation in Food Crops (Hussain 2022). The agricultural sector is under major challenge to produce high yields and nutritious foods from soils that are suffering fertility decline and metal(loid) contamination (Qin et al. 2021; Silver et al. 2021). A short description of the research articles included in this part of the special issue is given below.

A key solution to mineral deficiencies in animals and humans is the use of mineral fertilisers for the biofortification of food/fodder crops. In a field study, ZnSO₄ application increased yield, quality and profitability of grass forages (oat, barley, annual ryegrass and triticale) cultivated in calcareous soil (Sher et al. 2022). Other methods of nutrient application, such as seed priming and foliar application, have also been recommended by researchers for the biofortification of food crops. Su et al. (2022) suggested foliar Zn application for increasing grain Zn and decreasing grain phytic acid concentrations in 19 rice cultivars. In another study on rice, seed priming with Zn and K increased seedling growth, whereas foliar Zn application increased grain yield and grain Zn concentration (Yamuangmorn et al. 2022). Ram et al. (2022) reported that integrating foliar Zn with thiamethoxam and propiconazole did not reduce their efficacy for enriching Zn in grains and controlling insect and disease attacks on field-grown wheat. In another study on wheat grown on low-Zn calcareous soils, seed priming with 0.5 M ZnSO₄ improved grain yield (by 63%) and grain Zn concentration (by 43%) compared with non-primed seeds (Rehman et al. 2022).

Microorganisms govern nutrient dynamics in soils and their uptake by plant roots. Therefore, microorganisms can contribute to agronomic mineral biofortification. In field-grown maize, seed inoculation with Zn-solubilising Bacillus biofertilisers (Bacillus sp. ZM20, B. aryabhattai ZM31, B. aryabhattai S10 and B. subtilis ZM63) was effective in increasing grain Zn and Fe concentrations (Mumtaz et al. 2022). Inoculation of B-primed chickpea seeds with Bacillus sp. MN54 increased grain yield and grain B concentration over control seeds (Mehboob et al. 2022). In glasshouse and field experiments, seed inoculation with Streptomyces albus (CAI-24 and KAI-27) significantly increased the concentration of Fe, Zn and Ca in grains of pearl millet hybrids (Srinivas et al. 2022).

Genotypic variations in grain mineral densities are important for biofortification programs. Field experiments were conducted at six locations in Kazakhstan and Russia to study genotype × environment interactions for grain mineral densities in 18 spring wheat cultivars of the region (Morgounov et al. 2022). Prominent cultivars were identified for high grain yield, and high grain concentrations of P, S, Mn, Cu, Zn and proteins. From a 3-year field experiment on low-Zn calcareous soils of southern Loess Plateau, China, 19 high-yielding cultivars were identified that had similar yield potentials but had grain Zn concentrations ranging from 9 to 27 mg kg⁻¹ (Wang et al. 2022).

Genotypic variation in soil salinity tolerance may also be linked with the accumulation of minerals in grains. Significant genotypic differences in grain accumulation of Zn (26–54 mg kg⁻¹), Fe (32–62 mg kg⁻¹) and Se (2–62 μg kg⁻¹) were detected in 20 wheat genotypes grown in saline soil (Zhao et al. 2022). In another study, resistance to NaCl salinity correlated positively with the accumulation of Fe and Zn in wheat genotypes (Abbas et al. 2022b). Considering plant growth and mineral uptake, wheat cultivar SARC-1 was recommended for the environments low in Zn and Fe and affected by salts. Taqdees et al. (2022) reported negative effects of NaCl stress on plant growth and mineral uptake that were mitigated by the use of Si/Zn-nanoparticle-enriched miscanthus biochar.

Toxic levels of metals, such as Cd, damage the antioxidative defence system and nutrient accumulation in plants (Abbas et al. 2022a). Suitable nutrient management can alleviate such negative effects by limiting the uptake and translocation of metal(loid)s in food crops. Rather et al. (2022) reviewed the beneficial role of S and its assimilatory products in tolerance, detoxification and partitioning of heavy metal(loid)s in plants. Shi et al. (2022) recommended applying CaCl₂ to immobilise As, Sb and Cd in soils and to decrease their accumulation in grains of rice grown in flooded soil co-contaminated by Sb and Cd. By contrast, under these conditions, the application of P (as NaH₂PO₄) increased the soil mobility and grain accumulation of Sb and As.

The author declares no conflicts of interest.