Search Results (416)

The intensive use of chemical fertilizers in soybean (Glycine max) cultivation has caused significant environmental degradation, underscoring the urgent need for sustainable alternatives. In Argentina, Bradyrhizobium japonicum E109 is widely employed as a liquid bioinoculant, yet its efficiency is limited by loss of viability during storage. This study investigated the physiological and biophysical mechanisms underlying membrane adaptation of B. japonicum E109 under storage stress and evaluated lipid supplementation as a stabilization strategy. During six months of liquid storage at 28 °C, bacterial viability (Log CFU mL⁻¹) declined from 10.0 to 7.7, accompanied by morphological collapse and a 29% reduction in membrane fluorescence polarization, indicating increased fluidity. Fatty acid analysis revealed a drastic decrease of unsaturated 18:1 (from 80% to 40%) and a 300–400% increase in saturated 18:0, reducing the U/S ratio from 4 to 1. Spectral phasor analysis confirmed a shift in the lipid microenvironment from an ordered to a disordered state. Supplementation with 400 µM of stearic acid (18:0) restored membrane rigidity, lowered the U/S ratio to 1.5, and improved thermal tolerance. After one month of storage, 18:0-treated cultures maintained 8.0 Log CFU mL⁻¹ and preserved viability after exposure to 37 °C, whereas controls dropped to 3.8 Log CFU mL⁻¹. These results identify lipid remodeling as a key determinant of B. japonicum stability and demonstrate that exogenous 18:0 supplementation mimics natural adaptation, preventing membrane fluidization and enhancing inoculant shelf-life. This lipid-biophysical approach provides a rational framework for developing next generation, more resilient rhizobia formulations for sustainable agriculture. Full article

Microbial toxicity tests in the rhizosphere play an important role in the risk assessment and phytoremediation of chemical compounds in the environment. Tests for the inhibition of nodule number (NN), Rhizobia in the rhizosphere (RhR), Rhizobium in nodules (RhN) and arbuscular mycorrhizal fungi (AMFs) are important to evaluate the toxicity as well as the removal of total petroleum hydrocarbons (TPHs), 15 linear alkanes (LAs), and total linear alkanes (TLAs). The inhibition and removal was evaluated at 60 (vegetative stage, VS) and 154 days (reproductive stage, RS) of the life cycle of Crotalaria incana and Crotalaria pallida in soil with four doses of CRO (3, 15, 30, and 45 g/kg) plus a control (16 treatments). Results indicated that RhN and five structures of the AMFs present an index of toxicity (IT < 1), and the microbiological variable is inhibited by the CRO. RhR exhibits a hormesis index (IT > 1) that is stimulated by the CRO in the VS and RS for C. incana and C. pallida. The highest removal of TPHs (77%) was in the rhizosphere of C. incana in the RS with 45 g/kg of CRO. C. pallida removed the greatest amount of TLA (91%). There was a positive correlation between the RhR and the removal of TPHs, TLA, and LAs (higher molecular weight). It could be argued that symbiotic microorganisms are significant for use in toxicity testing, and the rhizosphere of C. incana and C. pallida can be used for the phytoremediation of HTPs and ALs in loamy-clay soil contaminated with CRO. Full article

Aims: The plant and soil microbiome serve as a reservoir of beneficial endophytic bacteria, including plant-growth-promoting (PGP) Bacillus subtilis, which enhances nutrient acquisition and protects plants against environmental stresses. We isolated novel bacteria from cultivated peanut plants selected from agricultural fields that survived a season of water scarcity and high temperatures. Experiments were conducted to determine whether plant survival was partially attributable to the presence of beneficial microbes that could be harnessed for future biotechnology applications. Methods and Results: Seven bacterial isolates of Bacillus spp. were identified through 16S rRNA sequencing, revealing close affiliations to B. subtilis, B. safensis, and B. velezensis. Growth curve analysis and colony morphology characterization revealed distinct growth patterns across different media types, while phytohormone production assays demonstrated variable indole-3-acetic acid (IAA) synthesis among isolates. When applied as seed biopriming agents to two hybrid peanut varieties, bacterial inoculation significantly enhanced root surface area and root tip development, with B. subtilis-TAM84A showing the most pronounced effects on ‘Schubert’ roots. In addition, vegetative growth assessments indicated increased branch numbers and plant height, particularly with treatments with B. velezensis strains TAM6B and TAM61A, and a consortium of all isolates. Under drought conditions, inoculated plants exhibited delayed wilting and improved recovery after rehydration, indicating enhanced drought resilience. Conclusions: Several local Bacillus strains recovered from drought-tolerant peanut plants showed improved growth and drought tolerance in greenhouse-grown peanut plants. Ongoing field studies aim to evaluate the potential of regionally adapted microbial populations as soil amendments during planting. Impact Statement: This study demonstrates that local strains of Bacillus isolated from drought-resistant peanut plants possess significant potential as bioinoculants to improve growth and drought tolerance in potted peanut plants. This work provides a foundation for utilizing regionally adapted microbial populations to address agricultural challenges related to water scarcity. Full article

N is the most crucial nutrient for plant growth and yield. Soybeans require a large amount of N for growth and seed production because of their high protein content. Soybean plants fix N₂ by root nodules in association with soil bacteria, rhizobia, but both the fixed N and the N absorbed from roots are essential to obtain a maximum seed yield. However, excess or inappropriate N fertilizer application represses N₂ fixation and reduces seed yield. A basal deep placement of lime nitrogen promoted soybean seed yield without inhibiting N₂ fixation activity in Japan. This study aimed to evaluate whether this technology can be applied in the Far East of Russia. The effects of deep placement of lime N with a wide row (75 cm) on the growth and seed yield of four Russian varieties were investigated. Without N fertilization, the average seed yield in wide rows was 2.77 t/ha, which was not significantly different from that in narrow rows (2.39 t/ha). Deep placement of lime nitrogen with wide rows increased total mechanical seed yield by 38%, 53%, 17%, and 6% in Primorskaya 4, 13, 81, and 86, respectively. The effect of basal urea application in narrow rows varied among cultivars. Soil analysis and the N composition in xylem sap indicated that the Russian field is richer in soil N than that in Niigata, and the contribution of N derived from N₂ fixation was lower than that in Niigata. The effects of row spacing and N fertilization on seed yield varied by variety; therefore, it is necessary to evaluate each variety to determine the optimal row spacing and N fertilization. The field experiment indicated that the deep placement of lime N promoted seed yield of Russian cultivars. This technique may be applied in soybean cultivation in a large field if the appropriate machine is available. Full article

Soil fertility constraints, particularly N and P deficiencies, limit the productivity of common bean (Phaseolus vulgaris L.) in Ethiopia. This study is the first to systematically evaluate the combined effects of phosphorus (P) fertilization and Rhizobium inoculation on biological nitrogen fixation (BNF) and yield across soils with varying levels of indigenous rhizobia populations in southern Ethiopia. The aim of the study was to evaluate the effects of P fertilization and Rhizobium inoculation on nodulation, growth, yield, nutrient concentration, and BNF in soils characterized by high, moderate, and low indigenous rhizobia populations. Field experiments were conducted over two years using four P rates (0, 10, 20, and 30 kg P ha⁻¹) and five Rhizobium strains (uninoculated, 102CB, 106CB, 44CB, and HB-429). P application significantly improved nodulation, growth, yield, nutrient concentration, and N₂ fixation, with 20 kg P ha⁻¹ consistently resulting in superior performance. At this rate, grain yields reached 2.51, 2.25, and 2.31 t ha⁻¹ in soils with high, moderate, and low indigenous rhizobia populations, respectively. Inoculation responses depended strongly on indigenous rhizobia abundance: in soils with high indigenous populations, inoculation did not significantly improve growth and yield, whereas in low-population soils, inoculation with strain 102CB produced the highest yield (2.06 t ha⁻¹). For BNF, 20 kg P ha⁻¹ resulted in the highest fixation (44.61 and 36.82 kg N ha⁻¹) in soils with high and moderate indigenous rhizobia populations. Inoculation with 102CB further enhanced N fixation to 44.77 and 36.13 kg N ha⁻¹ in these soils. In low-population soils, the combined application of 102CB and 20 kg P ha⁻¹ significantly increased BNF to 55.34 kg N ha⁻¹. Overall, these findings demonstrate that P fertilization provides universal benefits, while inoculation effectiveness is site-specific. Integrating P fertilization with effective Rhizobium strains offers a practical and sustainable strategy to improve common bean productivity and sustainability of common bean–based farming systems in Ethiopia. Full article

Canavalia ensiformis (L.) DC. (Fabaceae) is used in Cuba in soils dedicated to coffee cultivation, contributing to soil nutrition and crop productivity. However, no rhizobial isolates are currently available for inoculating this legume in Chromic Eutric Cambisol soils. The aim of this study was to select rhizobial strains that promote the growth of C. ensiformis in Chromic Eutric Cambisol soils. Nodules were collected from C. ensiformis plants, surface-sterilized, and macerated to isolate potential rhizobia. The isolates were characterized based on cultural, morphological, and biochemical traits, and their symbiotic effectiveness was evaluated through in vitro inoculation assays in Macroptilium atropurpureum (siratro) plants. Inoculation trials were conducted under semi-controlled conditions and in the field between coffee rows. The number and dry weight of effective nodules, number of trifoliate leaves, and shoot dry biomass were measured. Nine bacterial isolates were obtained, grouped into four morphotypes, and assigned as possible members of the families Phyllobacteriaceae, Methylobacteriaceae, or Nitrobacteraceae. Under semi-controlled conditions, inoculation with three isolates increased the number of nodules (by 56–80%), the number of trifoliate leaves (by 20–45%), and shoot biomass (by 10–40%) compared to the non-inoculated treatment. Additionally, one of the isolates increased nodule dry weight by 27%. In the field between coffee row, increases were also observed in the number of trifoliate leaves (by 18–26%) and shoot biomass (by 15–24%). This study supports the selection of efficient rhizobia adapted to the edaphoclimatic conditions of Cuban coffee agroecosystems. Full article

The study of wild relatives of crop legumes offers an inexhaustible source of useful properties and microorganisms for agriculture. In this study, we morphologically examined vavilovia (Vavilovia formosa (Steven) Fed.) nodules induced by strains of Rhizobium ruizarguesonis RCAM1026, Rhizobium leguminosarum sv. viciae TOM, as well as R. leguminosarum sv. viciae strains Vaf-12 and Vaf-108, isolated from nodules of wild-type plants of V. formosa. The nodules induced by R. leguminosarum sv. viciae strain Vaf-12 maintained histological and ultrastructural organization typical for indeterminate nodules. Different ultrastructural abnormalities were revealed in nodules induced by the other strains. When using the R. leguminosarum sv. viciae strain Vaf-108, pinkish nodules formed, in which a senescence zone developed in four weeks after inoculation. Furthermore, small brownish pseudonodules were also formed. In the nodules induced by the R. leguminosarum sv. viciae strain TOM bacteroids rapidly degraded and were excluded from the cytoplasm into the vacuole. Nodules induced by the R. ruizarguesonis strain 1026 were characterized with excessive accumulation of starch grains in mature infected cells. Full article

Endophytic rhizobia have the functions of dissolving organic phosphorus, secreting auxin, fixing nitrogen, and promoting growth. The proliferation of endophytic rhizobia in alfalfa and their symbiotic nodulation with alfalfa seedlings are regulated by various plant hormones. In this study, the alfalfa seeds (Medicago sativa L.) containing CFP-labeled rhizobium R.gn5f (isolated from the seeds of Gannong No.5 alfalfa) were used as materials, and the concentrations of 3-indoleacetic acid (3-IAA), 6-benzylaminopurine (6-BA) and homobrassinolide (HBR) suitable for the growth of R.gn5f were used for seed soaking treatment, and distilled water was used as the control. The proliferation of endophytic rhizobium, plant nodulation, nitrogen fixation performance and plant growth ability of alfalfa at different growth stages were determined. The effects of hormone types and concentrations on the proliferation and nitrogen fixation of endophytic rhizobia were analyzed to provide a theoretical basis for accurately promoting the nodulation, nitrogen fixation and growth-promoting ability of endophytic rhizobia in seeds. The results showed that the optimal concentrations of 3-IAA, 6-BA and HBR were 12 mg·L⁻¹, 16 mg·L⁻¹ and 2.47 mg·L⁻¹, respectively. The nitrogen fixation performance of endophytic rhizobium plants containing three hormones was higher at the branching stage and budding stage. The growth ability of the plant was better at the flowering stage. The hormone 2.47 mg·L⁻¹ of HBR was beneficial to the proliferation, nodulation, nitrogen fixation and plant growth of endophytic rhizobia in alfalfa at the vegetative and reproductive growth stages, and the number of R.gn5 f in the seeds of HBR plants at the mature stage was the largest (281.25 CFU·g⁻¹). Therefore, the hormone 2.47 mg·L⁻¹ of HBR was better for the proliferation of endophytic rhizobia R.gn5 f and plant growth in alfalfa. These findings provide a theoretical basis for precisely leveraging the nodulation and nitrogen-fixing capabilities of seed-borne endophytic rhizobia, thereby laying a foundation for the symbiotic breeding of alfalfa and rhizobia. Full article

Legumes are important food crops and play a central role in sustainable agriculture through their ability to form symbiosis with rhizobia, soil bacteria that fix atmospheric nitrogen. Recent advances in single-cell and spatial transcriptomics, along with single-cell epigenomics, have enabled high-resolution analysis of gene expression dynamics and the prediction of cell-type-specific regulatory networks. In this review, we highlight recent progress in the use of single-cell omics in legumes, with a particular focus on how genes functioning in distinct cell types contribute to plant development, responses to pathogens, stress-induced plasticity, and the establishment of root nodule symbioses. Case studies in Medicago truncatula, Lotus japonicus, Glycine max, and Arachis hypogaea illustrate the shift from bulk to single-cell multi-omics. We conclude by outlining current limitations and future directions for building integrated legume cell atlases that will support translational research and crop improvement. Full article

Symbiosis between rhizobia and legumes can affect plant tolerance to abiotic and biotic stressors such as drought and herbivores. Yet few studies have assessed how soil rhizobia impact plants that face abiotic and biotic stress simultaneously. This is a major knowledge gap given that many aspects of plant growth and defense are affected by interacting stressors, and these interactions can affect legume–rhizobia symbiosis. Here we assessed rhizobia-mediated interactions between a legume host (Pisum sativum), a vector herbivore (pea aphid, Acyrthosiphon pisum), a plant virus (pea enation mosaic virus, PEMV), and soil water availability. We show that rhizobia promoted plant growth and mitigated osmotic stress caused by reduced soil water availability. Rhizobia also increased plant tolerance to PEMV under high soil moisture conditions but had no measurable effect on PEMV when plants were grown in soil with reduced water. To assess the mechanisms that mediated these complex interactions, we measured gene transcripts related to phytohormone signaling and found that salicylic acid, jasmonic acid, abscisic acid, and ethylene signaling were affected by interactions between rhizobia and water availability; each of these pathways affects PEMV transmission. Our study shows that beneficial effects of rhizobia on legumes are impacted by abiotic and biotic stress, and outcomes of symbiosis may be context-dependent in field settings. Full article

Our previous studies identified a new efficient and broad-spectrum rhizobium strain Bradyrhizobium elkanii Y63-1. This study evaluated the symbiotic effects of Y63-1 inoculation on Zhongdou 63 (ZD63) in native environments and under different nitrogen levels. The evaluation of symbiotic effects in native environments was conducted through pot experiments and field trials. Pot experiments were performed in greenhouse using three soil types. Field trials were conducted in three regions with different soil nitrogen levels. The symbiotic effect of soybean ZD63 inoculated with Y63-1 under different nitrogen levels was investigated through pot experiments in greenhouse. The results showed that Y63-1 is more competitive than the indigenous rhizobia of the three soil types in the nodulation of soybean ZD63. The nodulation ability and yield-related traits of soybean ZD63 were improved after inoculation with Y63-1 in the three regions, especially in Hanchuan, where the soil nitrogen level is relatively rich. The symbiotic effect of soybean ZD63 inoculated with Y63-1 in a pot experiment with four levels of N from 0 to 3.75 mmol/L was superior at N 2.81 mmol/L. Our findings provided technical support for the application of Y63-1 in China, and a theoretical basis for increasing the yield potential of soybean through inoculation with highly efficient rhizobia in agricultural production. Full article

Leguminous plants are critical global crops for food security, animal feed, and ecological sustainability due to their ability to establish nitrogen-fixing symbioses with rhizobia and their high nutritional value. Autophagy, a highly conserved eukaryotic catabolic process, mediates the degradation and recycling of cytoplasmic components through the fusion of autophagosome with vacuole/lysosome and plays essential roles in plant growth, stress adaptation, and cellular homeostasis. This review systematically summarizes current knowledge of autophagy in both Arabidopsis and leguminous plants. We first outline the conserved molecular machinery of autophagy, focusing on core autophagy-related (ATG) genes in Arabidopsis and key legume species such as Glycine max, Arachis hypogaea, Pisum sativum, Cicer arietinum, and Medicago truncatula. Furthermore, the review dissects the intricate molecular regulatory networks controlling autophagy, with an emphasis on the roles of phytohormones, transcription factors, and epigenetic modifications. We then highlight the multifaceted physiological functions of autophagy in these plants. Additionally, a preliminary analysis of the ATG8 gene family in peanut indicates that its members may be involved in seed development, biological nitrogen fixation, and drought resistance. Finally, it highlights key unresolved challenges in legume autophagy research and proposes future research directions. This review aims to provide a comprehensive theoretical framework for understanding the unique regulatory mechanisms of autophagy in legumes and to provide insights for molecular breeding aimed at developing stress-resilient, high-yielding, and high-quality legume cultivars. Full article

Selecting symbiotic rhizobia for use as inoculants in agriculture is a major challenge, though it is necessary for exploiting biological nitrogen fixation as an eco-friendly source of N in contrast to chemical N fertilizers which can pollute the environment. In addition to high symbiotic efficiency, bacterial strain ability to infect and effectively nodulate a wide range of host plants is also desired. Cross-infectivity studies are therefore important for identifying rhizobial strains that are highly effective with a broad host range. The legume/rhizobia symbiosis has the potential to contribute about 80% or more N to agricultural systems, thus providing a sustainable source of N in cropping systems. This study assessed the cross-nodulation, colony morphology, relative symbiotic effectiveness and N₂ fixation of native rhizobial isolates from Africa that nodulate diverse legume species. The results showed that the rhizobial isolates differed significantly in symbiotic performance and relative symbiotic effectiveness. As a result, they differed markedly in nodulation and shoot DM induced in their host plants. Full article

Nitrogen is an indispensable nutrient for plant growth and crop production, but it is not directly accessible to plants without the help of nitrogen-fixing bacteria. Legume plants can form root nodules in symbiosis with rhizobia. NODULE INCEPTION (NIN), a founding member of the NIN-like protein (NLP) family, is essential for nodulation in legume species. However, the knowledge of functional characteristics of the NLP family members in peanuts is limited. In this study, a genome-wide analysis of the NLP genes was carried out. A total of 16 NLP genes were identified in the peanut genome, including 2 AhNIN and 14 AhNLP, which were unevenly distributed on nine chromosomes of the peanut genome. Furthermore, transcriptomic profiles and expression pattern analysis showed that both AhNINa and AhNINb genes were specifically expressed in root nodules. Subcellar localization and transcriptional activity analysis revealed that both AhNINa and AhNINb encode transcriptional activators. In addition, the roots that down-regulated the expression of AhNINa and AhNINb genes failed to form nodules. These findings provide significant insights into the molecular functions of AhNINa and AhNINb genes in regulating peanut nodule development. Full article

Rhizobia have been used for decades as biopreparations, successfully replacing synthetic nitrogen fertilizers in legume cultivation. They have a beneficial effect on the growth and yield of these plants when cultivated in soils that are deficient in both nitrogen and indigenous rhizobia. However, such preparations, containing strains that are characterized by high effectiveness in reducing atmospheric dinitrogen, are not universal. Their use is ineffective when plants are grown in soils that are already rich in strains with low effectiveness, because such inoculant strains are unable to effectively compete with native soil populations. This review discusses issues related to the rhizobia–legume symbiosis, with particular emphasis on inter-strain competition occurring in the soil and in the colonized plant tissues. The importance of Nod factors (NFs) in symbiosis and their broad impact on plant physiological and developmental processes are also discussed. Research results on the effects of NF-containing biopreparations on legume growth and yield are summarized. Moreover, this review explains how such preparations can support the growth and yield of legumes growing in soils containing numerous populations of low-effectiveness rhizobia. Finally, the potential for the application of this technology to non-legume plants is presented. Full article