Soybean Tolerance Research Articles

Compositional Analysis of Herbicide Tolerant and Conventionally Improved Soybeans in Nigeria

Aim/Background:Comparative compositional analysis was carried out between two herbicide tolerant soybean varieties and two conventionally improved non-GM soybeans (Glycine max) varieties for base line data and safety analysis for subsequent breeding purposes. Method:The experiment was laid in completely randomized design with three replications. The moisture content, ash content, nitrogen content, crude protein content, Percentage crude fibre content, crude lipid, metabolizable energy and calories values were determined for each of the samples using AOAC, 2000 method. Collected data was subjected to analysis of variance and pertinent means were separated using Fisher’s least significant difference (LSD) at 5% level of probability. Results:The moisture content values observed for the four varieties ranged from 5.0 – 5.9 % which were not significantly different from the standard reference of 6.12%. Ash content was lowest for TGX-1448-2E at 1.2%, followed by E 14017 at 4.2 %; while it was 4.7 % for TGX 1904-6F;.and the highest observed value was 6.42 % in E 14086. The least nitrogen content value was observed in E14017 at 6.12%, followed by TGX 1448-2E at 8.17 %; TGX 1904-6F at 8.9 % and the highest observed in E14086 at 11.6%. All values were within range of standard reference value of 496.37 Kcal/g except for TGX 1904-6F(363.09Kcal/g) which was relatively low. Conclusion:It could be concluded that contents of the key components of the HT soybean had no significant difference with those of the non-GM soybean ascertaining the safety and this data is necessary for onward varietal development.

Enhancement of soybean tolerance to water stress through regulation of nitrogen and antioxidant defence mechanisms mediated by the synergistic role of salicylic acid and thiourea

Water stress (WS) poses a significant threat to global food and energy security by adversely affecting soybean growth and nitrogen metabolism. This study explores the synergistic effects of exogenous salicylic acid (SA, 0.5 mM) and thiourea (TU, 400 mg L−1), potent plant growth regulators, on soybean responses under WS conditions. The treatments involved foliar spraying for 3 days before inducing WS by reducing soil moisture to 50% of field capacity, followed by 2 weeks of cultivation under normal or WS conditions. WS significantly reduced plant biomass, chlorophyll content, photosynthetic efficiency, water status, protein content, and total nitrogen content in roots and leaves. Concurrently, it elevated levels of leaf malondialdehyde, H2O2, proline, nitrate, and ammonium. WS also triggered an increase in antioxidant enzyme activity and osmolyte accumulation in soybean plants. Application of SA and TU enhanced the activities of key enzymes crucial for nitrogen assimilation and amino acid synthesis. Moreover, SA and TU improved plant growth, water status, chlorophyll content, photosynthetic efficiency, protein content, and total nitrogen content, while reducing oxidative stress and leaf proline levels. Indeed, the simultaneous application of SA and TU demonstrated a heightened impact compared to their separate use, suggesting a synergistic interaction. This study underscores the potential of SA and TU to enhance WS tolerance in soybean plants by modulating nitrogen metabolism and mitigating oxidative damage. These findings hold significant promise for improving crop productivity and quality in the face of escalating water limitations due to climate change.

Biochemical Analysis to Understand the Flooding Tolerance of Mutant Soybean Irradiated with Gamma Rays.

Flooding stress, which reduces plant growth and seed yield, is a serious problem for soybean. To improve the productivity of flooded soybean, flooding-tolerant soybean was produced by gamma-ray irradiation. Three-day-old wild-type and mutant-line plants were flooded for 2 days. Protein, RNA, and genomic DNA were then analyzed based on oppositely changed proteins between the wild type and the mutant line under flooding stress. They were associated with cell organization, RNA metabolism, and protein degradation according to proteomic analysis. Immunoblot analysis confirmed that the accumulation of beta-tubulin/beta-actin increased in the wild type under flooding stress and recovered to the control level in the mutant line; however, alpha-tubulin increased in both the wild type and the mutant line under stress. Ubiquitin was accumulated and genomic DNA was degraded by flooding stress in the wild type; however, they were almost the same as control levels in the mutant line. On the other hand, the gene expression level of RNase H and 60S ribosomal protein did not change in either the wild type or the mutant line under flooding stress. Furthermore, chlorophyll a/b decreased and increased in the wild type and the mutant line, respectively, under flooding stress. These results suggest that the regulation of cell organization and protein degradation might be an important factor in the acquisition of flooding tolerance in soybean.

GWAS and transcriptome analysis reveal key loci associated with drought tolerance in soybean

Genome-wide association and gene expression studies were conducted to identify key genes and markers associated with drought tolerance. GWAS panel consisting around 300 diverse soybean accessions were phenotyped for morpho-physiological traits under control and drought stress condition for three years during 2019-2021. Genotyping by Sequencing (GBS) of GWAS panel identified 66300 SNPs distributed over all the 20 chromosomes and were used for association analysis. GWAS analysis revealed closely located significant SNPs on chromosome 4 (50500762, 52098616 and 53008801) and chromosome 16 (32371663, 33082976 and 33283177). Key candidate genes related to MYB family, cell signaling gene (GPCR), salicylic acid synthesis, oxidative stress, auxin and ABA synthesis pathway were identified. Further few tolerant and susceptible haplotypes were also identified for real-time based expression analysis under drought stress condition.

Genome wide association studies reveals genetic loci associated with water logging tolerance in Soybean [Glycine max (L.) Merr.

In this investigation, a GWAS analysis was performed for four water logging tolerance traits in a panel of 265 soybean germplasm accessions with 66719 SNPs. A total of 29 SNPs and some candidate genes associated with different water logging tolerance traits were identified. This study also identified some soybean accessions, having superior water logging tolerance ability at vegetative and reproductive stages, which may be used as potential donors in soybean improvement programs.

Exploring microbial symbionts for improving soybean production andsoil carbon sequestration

To meet UN 2030’s agenda for Sustainable Development Goals (SDGs), the use of non-renewable bioresources is being campaigned globally to ensure food security and resource sustainability while minimizing environmental impact. Among oilseeds, soybean is the most important leading oilseed crop worldwide and being a high rich seed protein (40%) crop requires high N for its growth. Its requirement is largely met through biological nitrogen fixation (BNF) and to certain extent from native pool. BNF in soybean takes place via specific N fixing symbiotic bacteria (e.g., bradyrhizobia) inside the root nodules of the plant-soil rhizosphere (rhizobiome) wherein other microbes such as arbuscular mycorrhizal (AM) fungi are also actively involved in performing various soil functions. However, during crop growth, BNF activity is limited by number of environmental and ecological factors. Amongst all, drought and nutritional stress are the most limiting factors affecting the productivity of soybean. Hence to mitigate the adverse conditions, improve soil biological health and overall productivity there is need to have well adapted microbial symbionts such as super nodulating and moisture tolerant soybean rhizobia and AM fungi for sustaining the productivity of soybean.

Elevated CO2 concentration enhances drought resistance of soybean by regulating cell structure, cuticular wax synthesis, photosynthesis, and oxidative stress response

The atmospheric [CO2] and the frequency and intensity of extreme weather events such as drought are increased, leading to uncertainty to soybean production. Elevated [CO2] (eCO2) partially mitigates the adverse effects of drought stress on crop growth and photosynthetic performance, but the mitigative mechanism is not well understood. In this study, soybean seedlings under drought stress simulated by PEG-6000 were grown in climate chambers with different [CO2] (400 μmol mol−1 and 700 μmol mol−1). The changes in anatomical structure, wax content, photosynthesis, and antioxidant enzyme were investigated by the analysis of physiology and transcriptome sequencing (RNA-seq). The results showed that eCO2 increased the thickness of mesophyll cells and decreased the thickness of epidermal cells accompanied by reduced stomatal conductance, thus reducing water loss in soybean grown under drought stress. Meanwhile, eCO2 up-regulated genes related to wax anabolism, thus producing more epidermal wax. Under drought stress, eCO2 increased net photosynthetic rate (PN), ribulose-1,5-bisphosphate carboxylase/oxygenase activity, and alerted the gene expressions in photosynthesis. The increased sucrose synthesis and decreased sucrose decomposition contributed to the progressive increase in the soluble saccharide contents under drought stress with or without eCO2. In addition, eCO2 increased the expressions of genes associated with peroxidase (POD) and proline (Pro), thus enhancing POD activity and Pro content and improving the drought resistance in soybean. Taken together, these findings deepen our understanding of the effects of eCO2 on alleviating drought stress in soybean and provide potential target genes for the genetic improvement of drought tolerance in soybean.

Drought Tolerance in Soybean (Glycine max L. Merr.) Genotypes during the Flowering Stage of Development

Aims: To access the responses of 22 soybean genotypes under drought stress during the flowering stage of development.
 Study Design: A completely randomized experimental design (CRD) was adopted in this study. Five seeds of each of the 22 soybean genotypes were planted in 12-liter (L) plastic buckets (with holes at the bottom) containing sandy loam soil. There was one genotype per pot with three replications. The setup was repeated to represent experimental (drought-stressed (DS) and control (well-watered (WW) groups.
 Place and Duration of Study: Teaching and Research Farm of the School of Agriculture, College of Agriculture and Natural Sciences, University of Cape Coast, Cape Coast, Ghana in 2019.
 Methodology: Twenty-one exotic soybean genotypes and a local variety were assessed for their responses to drought stress at the flowering stage of development using pot experiment in the greenhouse. One group (experimental) was exposed to drought stress by withholding water for 15 days whilst the other group (control) was watered regularly at three-day intervals. Data collected were the number of leaves, plant height, stem girth, leaf area, and number of flowers, at 5, 10, and 15 days after treatment (DAT) and relative leaf water content at 15 DAT. The number of days to permanent wilting of the genotypes was also recorded.
 Results: Drought stress reduced the number of leaves and plant height significantly (P-values = 0.033, 0.000) and (P-values = 0.004, 0.000) at 10 and 15 days after drought treatment respectively. Also, stem girth, leaf area, and number of flowers were significantly reduced at all sampling dates (P-value = 0.002, 0.000, 0.000), (P-values = 0.004, 0.000, 0.000) and (P-values = 0.009, 0.000, 0.000) respectively. At 15 DAT, drought significantly (P < 0.001) reduced relative leaf water content. Genotypes TGX-1989-11F and TGX-1987-62F were the first and last to wilt at 7 days and 16 days after rewatering respectively.
 Conclusion: The pot screening method revealed that the number of leaves, plant height, stem girth, leaf area, number of flowers, relative leaf water content, and days to permanent wilting differed significantly (P = 0.05) at 15 days of drought exposure.

In-silico identification and characterization of sucrose transporter genes and their differential expression pattern under salinity stress in Glycine max

Plant sucrose transporters, involved in sugar transport, are key in facilitating sugar flux across the plant cell membranes. However, external stress stimuli significantly impact these sucrose transporters (SWEET/MST/SUT) and, ultimately, the distribution of photosynthates. This has importance as sucrose is a prime energy source, a signaling molecule, and an osmolyte playing a key role in growth and development processes. This study aims to identify and comprehensive in silico characterization and involvement of soybean sucrose transporters GlymaSWEET, GlymaMST, and GlymaSUT in plant development and salt stress responses in an important oilseed crop soybean (Glycine max L.). A genome-wide screening of soybean revealed 13 GlymaSWEET, 6 GlymaMST, and 5 GlymaSUT orthologues as confirmed from the eggNOG database. Probable sites of these proteins were found to be the membranes of cells and organelles, as suggested by their sub-cellular localization. The cis-regulatory elements of these transporters’ promoters indicated their involvement in environmental stress responses. MicroRNA interactions with these transporters were also studied, besides 3-D protein structure prediction using in silico approaches. To gain an insight into the functional divergence of GlymaSWEET, GlymaMST, and GlymaSUT transporters, qRT-PCR-based gene expression analysis was done both in control and salt-treated root and leaf tissues of two contrasting Indian soybean varieties MAUS-47 (salt-tolerant) and Gujosoya-2 (salt-sensitive). Differential gene expression was observed with varying degrees amongst the varieties and the treatments. Overall, we can conclude that the identified GlymaSWEET, GlymaMST, and GlymaSUT have the potential to be explored as candidate genes for engineering salinity stress tolerance in soybean and other plants.

Genome-wide identification of QTLs associated with iron deficiency tolerance in soybean reveals GATA12 as the integrator of iron signaling in roots

Genome-wide identification of QTLs associated with iron deficiency tolerance in soybean reveals GATA12 as the integrator of iron signaling in roots

Promising salt tolerant soybean mutants developed through gamma ray irradiation

An experiment was conducted to evaluate the performance of three promising lines along with two check varieties of soybean in respect of plant height, branches per plant, pods per plant, seeds per pod, days to maturity and seed yield, at five different locations during January to April 2022. Significant variations were observed both in individual location and combined over locations for all traits. Among the mutants, average days to maturity ranged from 109-114 days. It indicated that, all the mutant lines as well as check varieties had prolonged days to maturity, which eventually reflected significantly higher grain yield at all locations. Plant height ranged from 34-62 cm and number of branches plant-1 from 2.9 to 3.6. Mutant SBM-22 produced highest pods plant-1 (76); whereas, the check varieties Binasoybean-2 and Binasoybean-6 produced 43 Hundred seed weight was higher in Binasoybean-2 (13.4g) and lower hundred seed weight was obtained from SBM-26 (11.1g). Seed yield obtain from the mutants and checks significantly differs from each other. Mutant SBM-25 produced the highest seed yield of 2836 kg ha-1. Among the locations, all mutants as well as check varieties gave the highest seed yield at Satkhira. Comparing with imposed salinity level and time, plant height as well as leaf was decreased. All the germinated genotypes were survived at initial salinity 4 dS m-1 (though 4 dS m-1 is not at all a problem for salinity) up to 21 days. All the mutants showed moderately tolerant at same treatment up to 7 days after sowing. Binasoybean-2, Binasoybean-6 and Lokon performed well with the advancement of time. Among the mutants SBM-22 and SBM-26 will be selected on the basis of yield contributed characters for further trials. Bangladesh J. Nuclear Agric, 37(1): 101-109, 2023

Jasmonic acid priming augments antioxidant defense and photosynthesis in soybean to alleviate combined heat and drought stress effects

In the aftermaths of global warming, plants are more frequently exposed to the combination of heat stress and drought in natural conditions. Jasmonic acid (JA) has been known to modulate numerous plant adaptive responses to diverse environmental stresses. However, the function of JA in regulating plant responses to the combined effects of heat and drought remains underexplored. In this study, we elucidated the functions of JA in enhancing the combined heat and drought tolerance of soybean (Glycine max). Our results showed that priming with JA improved plant biomass, photosynthetic efficiency and leaf relative water content, which all together contributed to the improved performance of soybean plants under single and combined heat and drought conditions. Exposure to single and combined heat and drought conditions caused oxidative damage in soybean leaves. Priming soybean plants, which were exposed to single and combined heat and drought conditions, with JA, on the other hand, substantially quenched the reactive oxygen species-induced oxidative burden possibly by bolstering their antioxidant defense system. Together, our findings provide direct evidence of the JA-mediated protective mechanisms in maintaining the optimal photosynthetic rate and plant performance under combined heat and drought conditions.

Ensifer sp. GMS14 enhances soybean salt tolerance for potential application in saline soil reclamation

Rhizosphere microbiomes play an important role in enhancing plant salt tolerance and are also commonly employed as bio-inoculants in soil remediation processes. Cultivated soybean (Glycine max) is one of the major oilseed crops with moderate salt tolerance. However, the response of rhizosphere microbes me to salt stress in soybean, as well as their potential application in saline soil reclamation, has been rarely reported. In this study, we first investigated the microbial communities of salt-treated and non-salt-treated soybean by 16S rRNA gene amplicon sequencing. Then, the potential mechanism of rhizosphere microbes in enhancing the salt tolerance of soybean was explored based on physiological analyses and transcriptomic sequencing. Our results suggested that Ensifer and Novosphingobium were biomarkers in salt-stressed soybean. One corresponding strain, Ensifer sp. GMS14, showed remarkable growth promoting characteristics. Pot experiments showed that GMS14 significantly improved the growth performance of soybean in saline soils. Strain GMS14 alleviated sodium ions (Na+) toxicity by maintaining low a Na+/K+ ratio and promoted nitrogen (N) and phosphorus (P) uptake by soybean in nutrient-deficient saline soils. Transcriptome analyses indicated that GMS14 improved plant salt tolerance mainly by ameliorating salt stress-mediated oxidative stress. Interestingly, GMS14 was evidenced to specifically suppress hydrogen peroxide (H2O2) production to maintain reactive oxygen species (ROS) homeostasis in plants under salt stress. Field experiments with GMS14 applications showed its great potential in saline soil reclamation, as evidenced by the increased biomass and nodulation capacity of GMS14-inoculated soybean. Overall, our findings provided valuable insights into the mechanisms underlying plant-microbes interactions, and highlighted the importance of microorganisms recruited by salt-stressed plant in the saline soil reclamation.

GmWRKY17-mediated transcriptional regulation of GmDREB1D and GmABA2 controls drought tolerance in soybean.

Drought affects soybean growth and ultimately led to yield reduction. WRKY transcription factors involve in the regulation of abiotic stress. Few functions of WRKY transcription factors underlying drought tolerance in soybean are clear. Here, we reported a WRKY transcription factor named GmWRKY17 that positively regulates soybean drought tolerance by regulating drought-induced genes and ABA-related genes. Transcriptome sequencing (RNA-Seq) and yeast one hybrid analysis identified downstream genes regulated by GmWRKY17. ChIP-qPCR, EMSA and dual-luciferase reporter assay showed that GmWRKY17 directly bound to the promoters of the GmDREB1D and GmABA2, and activated their expression under drought stress. Overexpression of GmDREB1D gene enhanced drought tolerance of soybean. Taken together, our study revealed a regulatory mechanism that GmWRKY17 transcription factor may improve soybean drought tolerance by mediating ABA synthesis and DREB signaling pathway.

Improving drought tolerance in soybean by classical breeding leads to physiological adjustments of photosynthesis and stomata functioning

Soybean (Glycine max) is one of the main crops cultivated worldwide and drought is the main abiotic stress affecting its production. However, breeding towards drought tolerance is often set aside due to the difficulties in phenotyping. The aim of this study was to design an effective and simple screening technique that allows to discriminate genotypes according to their drought response and to identify physiological traits responsible for a superior tolerance. This rapid screening evaluated morphological (shoot and root length and weight) and developmental traits (days to germination and plant establishment) of 604 genotypes under control and drought conditions. Two genotypes with contrasting responses (Sensitive Genotype and Tolerant Genotype, SG and TG, respectively) were selected according to their performance in the screening, and were subjected to further testing in order to physiologically characterize the drought response of the chosen cultivars. Wilting, normalized transpiration ratio, leaf gas exchange parameters, water use efficiency (WUE) and stomatal characterizations were performed. TG plants exhibited slow wilting and higher WUE when subjected to drought treatments, product of a reduced water loss due to an anticipated stomatal closure which allowed to preserve soil moisture. Besides, under control conditions, the TG genotype presented a higher stomatal aperture index and a bigger density of epidermal cells and stomata than the drought-sensitive genotypes analyzed. In summary, the analysis of easily quantifiable traits, as the growth of the plant aerial organs and root development, together with the plant development timing, allowed us to select two soybean cultivars with contrasting drought responses. In our opinion, this selection method might be efficiently applied for the selection of drought tolerant cultivars in plant species of agronomic interest.

РЕГУЛЯТОРЫ РОСТА ПОВЫШАЮЩИЕ ПРОДУКТИВНОСТЬ СОИ

Plant growth regulators have a wide spectrum of physiological activity. Thanks to their action, resistance of soybean plants to adverse environmental factors, diseases, growth, development and quality is observed. Soy is the most widely used oilseed in the world. The world annual production of soybeans exceeds 260 million tons. It is the main edible plant and the main source of vegetable protein worldwide.The global demand for soybeans is constantly growing as its seeds provide essential proteins, oils and nutraceuticals. In an effort to meet the increased demand for this crop, it has become necessary to introduce cultural practices that promote adaptation to difficult environmental conditions, can improve soybean tolerance to abiotic stress and increase yields. Plant growth regulators are mainly used for this purpose due to their critical role in plant growth and development. One of the main growth regulators are such phytohormones as: auxins, gibberellins, cytokinins, brassinolides, ethylene, abscisic and jasmonic acid. Each of the groups of phytohormones produces its own characteristic action, which is similar in plants of different species. Cell division and elongation, which underlie all processes of growth and morphogenesis, are under the control of auxins and cytokines in plants, so their complete absence can lead to death. These compounds generally have a positive effect on the morphology, physiology and quality of the soybean crop. They are also able to regulate and control to a large extent the processes of growth and differentiation of plant cells. It should be noted that these phytohormones are required in small amounts for the activation and regulation of morphogenetic processes in soybean and other agricultural plants.

A novel natural variation in the promoter of GmCHX1 regulates conditional gene expression to improve salt tolerance in soybean.

Identification and characterization of soybean germplasm and gene(s)/allele(s) for salt tolerance is an effective way to develop improved varieties for saline soils. Previous studies identified GmCHX1 (Glyma03g32900) as a major salt tolerance gene in soybean, and two main functional variations were found in the promoter region (148/150 bp insertion) and the third exon with a retrotransposon insertion (3.78 kb). In the current study, we identified four salt-tolerant soybean lines, including PI 483460B (Glycine soja), carrying the previously identified salt-sensitive variations at GmCHX1, suggesting new gene(s) or new functional allele(s) of GmCHX1 in these soybean lines. Subsequently, we conducted quantitative trait locus (QTL) mapping in a recombinant-inbred line population (Williams 82 (salt-sensitive) × PI 483460B) to identify the new salt tolerance loci/alleles. A new locus, qSalt_Gm18, was mapped on chromosome 18 associated with leaf scorch score. Another major QTL, qSalt_Gm03, was identified to be associated with chlorophyll content ratio and leaf scorch score in the same chromosomal region of GmCHX1 on chromosome 3. Novel variations in a STRE (stress response element) cis-element in the promoter region of GmCHX1 were found to regulate the salt-inducible expression of the gene in these four newly identified salt-tolerant lines including PI 483460B. This new allele of GmCHX1 with salt-inducible expression pattern provides an energy cost efficient (conditional gene expression) strategy to protect soybean yield in saline soils without yield penalty under non-stress conditions. Our results suggest that there might be no other major salt tolerance locus similar to GmCHX1 in soybean germplasm, and further improvement of salt tolerance in soybean may rely on gene-editing techniques instead of looking for natural variations.

Phytohormonal modulation of the drought stress in soybean: outlook, research progress, and cross-talk.

Phytohormones play vital roles in stress modulation and enhancing the growth of plants. They interact with one another to produce programmed signaling responses by regulating gene expression. Environmental stress, including drought stress, hampers food and energy security. Drought is abiotic stress that negatively affects the productivity of the crops. Abscisic acid (ABA) acts as a prime controller during an acute transient response that leads to stomatal closure. Under long-term stress conditions, ABA interacts with other hormones, such as jasmonic acid (JA), gibberellins (GAs), salicylic acid (SA), and brassinosteroids (BRs), to promote stomatal closure by regulating genetic expression. Regarding antagonistic approaches, cytokinins (CK) and auxins (IAA) regulate stomatal opening. Exogenous application of phytohormone enhances drought stress tolerance in soybean. Thus, phytohormone-producing microbes have received considerable attention from researchers owing to their ability to enhance drought-stress tolerance and regulate biological processes in plants. The present study was conducted to summarize the role of phytohormones (exogenous and endogenous) and their corresponding microbes in drought stress tolerance in model plant soybean. A total of n=137 relevant studies were collected and reviewed using different research databases.

Enhancement of osmotic stress tolerance in soybean seed germination by bacterial bioactive extracts.

Soybean (Glycine max (L.) Merr.) is important to the global food industry; however, its productivity is affected by abiotic stresses such as osmosis, flooding, heat, and cold. Here, we evaluated the bioactive extracts of two biostimulant bacterial strains, Bacillus butanolivorans KJ40 and B. siamensis H30-3, for their ability to convey tolerance to osmotic stress in soybean seeds during germination. Soybean seeds were dip-treated in extracts of KJ40 (KJ40E) or H30-3 (H30-3E) and incubated with either 0% or 20% polyethylene glycol 6000 (PEG), simulating drought-induced osmotic stress. We measured malondialdehyde content as a marker for lipid peroxidation, as well as the activity of antioxidant enzymes, including catalase, glutathione peroxidase, and glutathione reductase, together with changes in sugars content. We also monitored the expression of genes involved in the gibberellic acid (GA)-biosynthesis pathway, and abscisic acid (ABA) signaling. Following osmotic stress in the extract-treated seeds, malondialdehyde content decreased, while antioxidant enzyme activity increased. Similarly, the expression of GA-synthesis genes, including GmGA2ox1 and GmGA3 were upregulated in KJ40E-dipped seeds at 12 or 6 h after treatment, respectively. The ABA signaling genes GmABI4 and GmDREB1 were upregulated in H30-3E- and KJ40E-treated seeds at 0 and 12 h after treatment under osmotic stress; however, GmABI5, GmABI4, and GmDREB1 levels were also elevated in the dip-treated seeds in baseline conditions. The GA/ABA ratio increased only in KJ40E-treated seeds undergoing osmotic stress, while glucose content significantly decreased in H30-3E-treated seeds at 24 h after treatment. Collectively, our findings indicated that dip-treatment of soybean seeds in KJ40E and H30-3E can enhance the seeds' resistance to osmotic stress during germination, and ameliorate cellular damage caused by secondary oxidative stress. This seed treatment can be used agriculturally to promote germination under drought stress and lead to increase crop yield and quality.

Synergistic N2-fixation and salt stress mitigation in soybean through dual inoculation of ACC deaminase-producing Pseudomonas and Bradyrhizobium

We investigated the potential dual application of two Bradyrhizobium strains (B. diazoefficiens USDA110 and B. ottawaense SG09) and plant growth-promoting bacteria, PGPB (Pseudomonas spp.: OFT2 and OFT5), to improve nodulation and N2-fixation in soybean plants. The growth-promoting effects of dual inoculation were observed on plant growth, physiology, and nodulation of soybean under normal conditions compared with plants individually inoculated with either USDA110 or SG09. Both OFT2 and OFT5 promoted N2-fixation by 11% and 56%, respectively, when dual inoculation with USDA110 and by 76% and 81%, respectively, when dual inoculation with SG09. Salinity stress significantly reduces soybean growth, physiology, nutrient uptake, nodulation, and N2-fixation. However, these adverse effects were attenuated by the dual inoculation of PGPB and rhizobia depending on the combination of inoculants. In particular, dual inoculation of PGPB with SG09 was more effective in enhancing the salt tolerance of soybean by reducing salt-induced ethylene production and improving nutrient uptake. However, no such effect was observed with the combined inoculation of USDA110 and OFT5. An effective symbiotic association between SG09 and two Pseudomonas bacteria can be considered a beneficial approach to improving the symbiotic efficiency of nodulation and mitigating salinity stress in soybeans.