Ontario Corn and Soybean Micronutrients Knowledge Hub

Throughout a growing season, plants experience a multitude of short periods of various abiotic stresses. These stress events have long-term impacts on plant performance and yield. It is imperative to improve our understanding of the genes and networks underlying plant stress tolerance to mitigate end of season yield loss. The majority of studies examining transcriptional changes induced by stress focus on single stress events. Few studies have been performed to examine the transcriptional response of plants exposed to sequential stress exposure, which better reflects field conditions. In this study, we examine the transcriptional profile of soybean plants exposed to iron deficiency stress followed by phosphate deficiency stress (-Fe-Pi). Comparing this response to previous studies, we identified a suite of genes unique to the novel sequential stress exposure (-Fe-Pi)

Iron deficiency chlorosis (IDC) is a yield limiting problem in soybean (Glycine max (L.) Merr) production regions with calcareous soils. Genome-wide association study (GWAS) was performed using a high density SNP map to discover significant markers, QTL and candidate genes associated with IDC trait variation. A stepwise regression model included eight markers after considering LD between markers, and identified seven major effect QTL on seven chromosomes. Twelve candidate genes known to be associated with iron metabolism mapped near these QTL supporting the polygenic nature of IDC. A non-synonymous substitution with the highest significance in a major QTL region suggests soybean orthologs of FRE1 on Gm03 is a major gene responsible for trait variation. NAS3, a gene that encodes the enzyme nicotianamine synthase which synthesizes the iron chelator nicotianamine also maps to the same QTL region. Disease resistant genes also map to the major QTL, supporting the hypothesis that pathogens compete with the plant for Fe and increase iron deficiency. The markers and the allelic combinations identified here can be further used for marker assisted selection.

Iron deficiency chlorosis (IDC) is a significant yield-limiting problem in several major soybean [Glycine max (L.) Merr.] production regions in the United States. Soybean plants display a variety of symptoms that range from a slight yellowing of the leaf to interveinal chlorosis, to stunted growth that reduces yield. The objective of this analysis was to employ single nucleotide polymorphism (SNP)-based genome-wide association mapping to uncover genomic regions associated with IDC tolerance. Two populations [2005 (n=143) and 2006 (n=141)] were evaluated in replicated, multilocation IDC trials. After controlling for population structure and individual relatedness, and selecting statistical models that minimized false positives, 42 and 88 loci, with minor allele frequency 10%, were significant in 2005 and 2006, respectively. The loci accounted for 74.5% of the phenotypic variation in IDC in2005 and 93.8% of the variation in 2006. Nine loci from seven genomic locations were significant in both years. These loci accounted for 43.7% of the variation in 2005 and 47.6% in 2006. A number of the loci discovered here mapped at or near previously discovered IDC quantitative trait loci (QTL). A total of 15 genes known to be involved in iron metabolism mapped in the vicinity (500 kb) of significant markers in one or both populations.

Improving the nutritional quality of crops is crucial for human health, livestock, and agricultural productivity, especially on nutrient-limited soils. To address this, we investigated the variation and the genetic basis of mineral content, including, among others, calcium, iron, phosphorus, and zinc, in a diverse panel of maize (Zea mays L.) grown across environments. Our results show that genetic variation significantly contributes to differences in mineral content. Genotype-by-environment interaction and environmental factors, such as reduced phosphorus fertilisation, substantially impact the ionome composition, particularly decreasing zinc content and altering grain quality. Correlations between the 12 minerals were mostly positive, with variation observed in mineral composition between tissues and in translocation from vegetative to generative tissue. In addition, elite lines exhibited distinct mineral profiles compared to landraces. Genome-wide association mapping revealed a quantitative inheritance of the minerals and few common quantitative trait loci. Significantly associated markers were found in proximity to candidate genes involved in processes like mineral transport, detoxification and storage, which represent potential targets for marker-assisted selection to improve nutritional quality in maize. In conclusion, our results highlight the temporal and spatial dynamics of the maize ionome as a basis toward its targeted design for future agriculture. Summary statement: In maize (Zea mays L.), significant genetic variation exists for mineral content, with genotype-by-environment interactions influencing the ionome.Phosphorus fertilisation alters mineral profiles, and genome-wide association mapping revealed a quantitative inheritance and common QTL between minerals.

Glyphosate has been demonstrated to reduce the macronutrient and micronutrient content of glyphosate-susceptible (GS) and first generation glyphosate-resistant (GR) or Roundup Ready (RR) soybean, possibly by complexation of the herbicide molecule with the nutrient. The recent release of newer GR soybean cultivars, second generation Roundup Ready 2 Yield (RR2Y), provides growers with newer technology for weed management programs, but it is unclear how the nutrient content of these cultivars is affected by glyphosate in a field setting. The objective of this experiment was to identify the effect of glyphosate on the concentration of macronutrient and micronutrients in RR and RR2Y soybean when grown using standard agronomic practices in Indiana. The macronutrients analyzed were nitrogen, phosphorus, potassium, sulphur, magnesium, and calcium. The micronutrients analyzed were boron, zinc, manganese, iron, copper, and aluminum. Our results indicate that while differences in accumulation of macro and micronutrients exist between the two cultivars tested, there was no consistent effect due to glyphosate treatment. Glyphosate-induced deficiency symptoms observed in previous reports were not observed in this study. Growers should continue to monitor soil nutrient levels to identify and correct nutrient deficiencies.

Iron deficiency chlorosis (IDC) is a form of abiotic stress that negatively impacts soybean yield. In a previous study, we demonstrated that the historical IDC quantitative trait locus (QTL) on soybean chromosome Gm03 was composed of four distinct linkage blocks, each containing candidate genes for IDC tolerance. Here, we take advantage of virus-induced gene silencing (VIGS) to validate the function of three high-priority candidate genes, each corresponding to a different linkage block in the Gm03 IDC QTL. We built three single-gene constructs to target GmGLU1 (GLUTAMATE SYNTHASE 1, Glyma.03G128300), GmRR4 (RESPONSE REGULATOR 4, Glyma.03G130000), and GmbHLH38 (beta Helix Loop Helix 38, Glyma.03G130400 and Glyma.03G130600). Given the polygenic nature of the iron stress tolerance trait, we also silenced the genes in combination. We built two constructs targeting GmRR4+GmGLU1 and GmbHLH38+GmGLU1. All constructs were tested on the iron-efficient soybean genotype Clark grown in iron-sufficient conditions. We observed significant decreases in soil plant analysis development (SPAD) measurements using the GmGLU1 construct and both double constructs, with potential additive effects in the GmRR4+GmGLU1 construct. Whole genome expression analyses (RNA-seq) revealed a wide range of affected processes including known iron stress responses, defense and hormone signaling, photosynthesis, and cell wall structure. These findings highlight the importance of GmGLU1 in soybean iron stress responses and provide evidence that IDC is truly a polygenic trait, with multiple genes within the QTL contributing to IDC tolerance. Finally, we conducted BLAST analyses to demonstrate that the Gm03 IDC QTL is syntenic across a broad range of plant species.

Abstract: Salt stress is a major yield-limiting factor in crops by reducing nutrient uptake and plant growth. Under salt stress, decreased water and nutrient uptake results in nutrient imbalance in plants. In addition, at high pH in saline conditions, solubility of minerals is also reduced leading to low availability of certain nutrients. Perspectives to overcome these limitations by Zn seed priming were studied with maize plants exposed to NaCl as salt stress. Maize seeds were primed for 24 hr in deionized water and 4 m m ZnSO4·7Hsub2O solution (ZnP) and subsequently air-dried at room temperature before further use. The DTZ (diphenylthiocarbazone) staining method was used for showing Zns2+ localization in the seeds. Zn2+ and other nutrient concentrations in unprimed, water and ZnP seeds and maize plants were analysed by inductively coupled plasma mass spectroscopy (ICP-MS). Maize plants (cv. Sun star L.) were grown for 3 weeks in complete nutrient solution with or without salt stress (100 m m NaCl) under glasshouse conditions. Seed Zn2+ contents were increased after ZnP treatment by 600%. In maize seeds, most of the primed Zn2+ accumulated in the outer tissues (particularly, aleurone layer) of maize seed. Zn priming decreased the injurious effects of salt stress on plant growth. Under salt stress conditions, biomass production of plants from ZnP treatments was 25% higher compared to water priming treatment. Zn seed priming also improved mineral nutrient status of plants grown in both control and salt stress conditions. Plants from ZnP treatments also showed higher accumulation of Na+ in the shoots. This offers perspectives for using Zn seed priming for improving early seedling development and plant nutrient status of maize under salt stress conditions.

This University of Minnesota Extension guide explains how to diagnose and manage zinc nutrition in crops. Zinc is an essential micronutrient required for enzyme activity, carbohydrate, protein, and chlorophyll formation, so deficiency can reduce growth and yield. Zinc availability is influenced by soil conditions, especially cool temperatures, sandy or highly leached soils, low organic matter, erosion, high calcium carbonate, and certain crop rotations. Excessive phosphorus can also induce deficiency in very low-zinc, calcareous soils, although this generally requires unusually high fertilizer rates. Soil testing, particularly the DTPA zinc test, should guide applications. A response is possible below 0.75 ppm and likely below 0.5 ppm. Recommended rates are 5 to 10 pounds per acre broadcast or 1 to 2 pounds banded when tests are low. Corn is among the crops most likely to respond to zinc, particularly when the soil DTPA zinc test is below 0.75 ppm, and especially below 0.5 ppm. Recommended rates for low-testing soils are 5 to 10 lb zinc per acre broadcast or 1 to 2 lb per acre banded. Starter fertilizer or banding is generally preferred, while broadcast zinc should be incorporated if starter application is not possible. Research does not support widespread use of chelated zinc applied in-furrow, because yield increases have been inconsistent. Corn deficiency commonly causes broad white stripes along the leaf midrib and plant stunting; tissue analysis can help confirm suspected deficiency. Zinc sufficiency range for corn whole tops less than 12? tall and base of ear at initial silk is 20-70 ppm. There was no documented soybean yield increase from zinc applications across 31 Minnesota locations, including soils testing from 0.4 to 3.9 ppm DTPA zinc. Soybean zinc deficiency is uncommon, and its symptoms can resemble iron deficiency chlorosis, so visual diagnosis should be confirmed with tissue analysis. Sinc sufficiency range for soybean (trifoliate leaves) at early flowering is 21-80 ppm.

Zinc (Zn) priming is a technique used to increase seed Zn reserves for improving seed quality, crop growth, and enhancing stress tolerance in crop plants. The present study demonstrated the effect of water and Zn priming on the distribution and accumulation of endogenous and primed Zn in maize seeds ( Zea mays L.). Zn concentration in unprimed, water and Zn primed seeds and germinated seedlings were analyzed by ICP-MS (Inductivity Coupled Plasma Mass Spectroscopy). DTZ (Diphenyle Thio-Carbazone) staining method and LA-ICP-MS (Laser Ablation Inductivity Coupled Plasma Mass Spectroscopy) scanning was used for showing Zn distribution and localization in the seeds. Zn priming significantly increased Zn concentration and content in seeds. Results of ICP-MS analysis showed a substantial increase in the testa and endosperm tissues after Zn priming. DTZ staining and LA-ICP-MS scanning of maize seeds revealed an uneven distribution of Zn in water and Zn primed seeds. Laser ablation data of water primed maize seeds demonstrated a significant (p 0.05) relocation of endogenous Zn from the aleurone layers towards the inner endosperm. Zn priming increased endosperm Zn content 3-fold compared with water primed seeds, while in the testa this increase was 50-fold. Furthermore, Zn priming significantly (p 0.05) increased the biomass of 10-d old maize seedlings grown in rolls of filter paper. Translocation of primed Zn towards shoots and roots was double than that of endogenous Zn in unprimed and water primed maize seeds. This is the first report of the distribution and accumulation of primed Zn in maize seeds. Further investigations are needed to understand the binding capacity of the different tissues within maize seeds and the retranslocation of primed Zn during early seedling development and plant growth.

This Michigan State University Extension article addresses zinc (Zn) and manganese (Mn) deficiencies in sensitive field crops, explicitly including corn (for Zn) and soybean (for Mn). Soils with pH ?7.0 are more vulnerable to both Zn and Mn deficiency. Zinc deficiency in corn appears as yellow striping of leaves; in dry beans, light green to yellow interveinal areas near leaf tips/edges in severe cases. Manganese deficiency causes yellow or olive-green foliage and reduced leaf size, and looks generally similar to zinc deficiency. Corn is listed among crops with a high response to zinc fertilizer (along with dry edible beans, onions, snap beans, sorghum, spinach, and sweet corn); soybean is listed among crops with a high response to manganese fertilizer (along with cucumbers, dry beans, lettuce, oats, onions, peas, potatoes, radishes, snap beans, sorghum, spinach, sudangrass, sugarbeets, sweet corn, table beets, and wheat). Management: both deficiencies can be corrected by applying an appropriate starter fertilizer near the seed at planting, or by foliar application once deficiency symptoms appear. Diagnosis: soil testing (specific Zn or Mn tests, $4 each or $7 for a combined sticker at MSU's lab) can determine whether Zn or Mn is needed; plant tissue analysis ($24 for field/vegetable crops) covering N, P, K, Ca, Mg, Zn, Mn, Cu, Fe, B, S, Na, and Al can also confirm sufficiency. The article does not provide specific application rates or soil-test critical thresholds, instead directing readers to MSU's "Secondary and Micronutrients for Vegetables and Field Crops" bulletin and a related "Micronutrient decisions for field crops" article for further detail.