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• Several landraces of bambara groundnut (Vigna subterannea (L.) Verdc) exist in South Africa which are but, the most underutilized and un-researched legumes. • There is variations in the bambara groundnut landraces to the nodulation responses to a given species of rhizobium. • Bambara groundnut have promiscuous nodulation properties with different rhizobia species and host specificity rule does not apply for these legumes. • Bambara groundnut exhibit more symbiotic interaction with Rhizobia species belonging to the cowpea miscellany group. Bambara groundnut (Vigna subterranea) is one of the most underutilized and neglected legume crop used for human consumption worldwide. Unlike the common food and forage legumes, the symbiotic properties of this legume have not been studied sufficiently. This study is designed to investigate the nodulation compatibility and symbiotic performance of twelve landraces of V. subterranea with five different Rhizobia species isolated from the nodules of other legumes under glasshouse conditions. Pre-germinated seeds of each landrace planted in sterile river sand medium were inoculated with 108 cfu/ml of each rhizobium inoculum suspension and monitored with regular watering using nitrogen free Hoagland's solution for six weeks. The taxonomy and phylogeny of the five rhizobia species was determined using nucleotide sequence analysis of the 16S rRNA and recA (DNA recombination protein) genes. A concatenated multiple sequence alignment was used to construct an MLSA tree to further analyze the phylogeny of the strains. Significant differences were observed among individual bambara genotypes and rhizobia strains in terms of nodule numbers and dry weight, as well as plant biomass. Statistical analysis showed that Rhizobia strains XBD2 and XS34 identified as Bradyrhizobium zhangiangens and B. centrosematis respectively exhibited the highest nodulation compatibility in terms of nodule number and nodule dry weight with one or more bambara groundnut landraces. This study demonstrated that V. subterannea does not show preference to unique rhizobia, confirming that they are promiscuously nodulated by more than one species of rhizobium belonging mainly to the cowpea miscellany cross inoculation group. The findings of this study also provide insights into the selection and development of appropriate low cost rhizobia inoculants in the sustainable production of this underutilized legume for use by smallholder farmers in South Africa. [ABSTRACT FROM AUTHOR]

Herbicide applications worldwide generally intend to protect crop yields from weed interference while avoiding mechanical disturbance in the topsoil layer. Their intensive use often leads to cocktails of chemicals in soils, which may interfere with natural soil functions, and productivity. The effects of a sequence of herbicides typically used in soybean crops were tested on different endpoints related to the nitrogen cycle. The field experiment was repeated in 2020–2021 and 2021–2022, from fallow to harvest time of the soybean crop. The treatments were: a control without herbicides, a sequence of three herbicide applications at the label recommended rate, all the six possible combinations of the three herbicide applications, and a treatment with the typical, complete scheme but at twice the recommended rate. The first application was a mixture of glyphosate, dicamba, and clethodim; the second was a mixture of glyphosate, S-metolachlor, and flumioxazin, and the third herbicide application moment included fomesafen only. All the treatments remained weed-free, either by herbicides or manual removal. Significant negative effects were detected for nodulation in some treatments at the vegetative stage compared to the control, but no dose-dependent response was observed. Plant biomass and nodulation were not significantly related to herbicide mixtures at the reproductive stage, nor was the soybean yield at harvest time. These results engender a complex scenario for farmers to fully grasp the potential risks associated with the use of herbicides. However, potential nitrification was affected after the third herbicide application moment in the first year of the experiment, in all the treatments exposed to at least one herbicide application, while the abundance of ammonia oxidizers showed no effects. This comprehensive field assessment is relevant to evaluate herbicide environmental risks, accounting for plant-microbiome interactions under real pedo-climatic conditions and stress factors. [Display omitted] • Impacts of common herbicides schemes on nitrogen cycle endpoints were investigated. • Combinations evaluated: Glyphosate+dicamba+cletodim, glyphosate+S-metolachlor+flumioxazin, fomesafen. • Soybean nodulation was transiently affected by herbicide mixtures at label rate. • Abundance of ammonia oxidizers did not respond to different mixtures. • Potential nitrification in soil can be affected by herbicides under dry conditions. [ABSTRACT FROM AUTHOR]

[Display omitted] • The study presents chromosome-length genome assemblies of six legume species. • Evolutionary events that shaped the present day legumes are inferred. • Expansion of gene families contributing to unique traits in legumes is explored. • Demonstrated the utility of improved assemblies as better references. Legume crops are an important source of protein and oil for human health and in fixing atmospheric N 2 for soil enrichment. With an objective to accelerate much-needed genetic analyses and breeding applications, draft genome assemblies were generated in several legume crops; many of them are not high quality because they are mainly based on short reads. However, the superior quality of genome assembly is crucial for a detailed understanding of genomic architecture, genome evolution, and crop improvement. Present study was undertaken with an objective of developing improved chromosome-length genome assemblies in six different legumes followed by their systematic investigation to unravel different aspects of genome organization and legume evolution. We employed in situ Hi-C data to improve the existing draft genomes and performed different evolutionary and comparative analyses using improved genome assemblies. We have developed chromosome-length genome assemblies in chickpea, pigeonpea, soybean, subterranean clover, and two wild progenitor species of cultivated groundnut (A. duranensis and A. ipaensis). A comprehensive comparative analysis of these genome assemblies offered improved insights into various evolutionary events that shaped the present-day legume species. We highlighted the expansion of gene families contributing to unique traits such as nodulation in legumes, gravitropism in groundnut, and oil biosynthesis in oilseed legume crops such as groundnut and soybean. As examples, we have demonstrated the utility of improved genome assemblies for enhancing the resolution of " QTL-hotspot " identification for drought tolerance in chickpea and marker-trait associations for agronomic traits in pigeonpea through genome-wide association study. Genomic resources developed in this study are publicly available through an online repository, 'Legumepedia'. This study reports chromosome-length genome assemblies of six legume species and demonstrates the utility of these assemblies in crop improvement. The genomic resources developed here will have significant role in accelerating genetic improvement applications of legume crops. [ABSTRACT FROM AUTHOR]

Legumes coordinate nodulation and plant development to maximize reproductive success, but the underlying molecular mechanisms are not well understood. A recent study by Yun et al. has revealed that nodulation drives root-to-shoot movement of microRNA172 (miR172) to accelerate flowering time, thus building a new bridge between nodulation and plant growth regulation. [ABSTRACT FROM AUTHOR]

Node Inception (NIN) plays a crucial role in legume symbiosis by participating in both infection and nodule formation processes. However, its specific function in mungbean (Vigna radiata) remains poorly understood. This study aimed to functionally characterize the VrNIN1 gene in mungbean through an enhanced hairy root transformation approach. Examination of proVrNIN1: GUS hairy roots via GUS staining indicated the expression of VrNIN1 in later root promodia, nodule primordia, and nodules. Phenotypic evaluation revealed that overexpression or silencing of VrNIN1 led to a significant reduction in nodule numbers in hairy roots compared to controls. Additionally, interaction between VrNIN1 and VrNNC1 was confirmed through yeast two-hybrid, luciferase complementation and Co-immunoprecipitation assays. VrNNC1 expression was observed in the vascular bundle and cortex of roots and root nodules, where it notably suppressed nodule formation in transgenic hairy roots. Furthermore, gene expression analysis demonstrated the involvement of VrNIN1 and VrNNC1 in regulating root nodulation by modulating the expression of VrRIC1 and VrEDOD40. This study not only optimized the genetic transformation system for hairy roots in mungbean, but also provided mechanistic insights into the regulatory role of VrNIN1 in root nodule symbiosis in mungbean. • Overexpression or silencing of VrNIN1 suppresses mungbean nodulation in transgenic hairy roots using one-step method. • VrNNC1 inhibits the production of nodule in mungbean root. • VrNIN1 interacts with VrNNC1 to regulate the expression of VrRIC1 and VrEDOD40. [ABSTRACT FROM AUTHOR]

Mungbean (Vigna radiata L. Wilczek) is an economically important legume crop grown across India. The growth and yield of the crop have been declining over the recent years due to climate change which leads to decrease in soil moisture. Applications of drought-tolerant plant growth-promoting (PGP) rhizobial strains have been found to enhance crop productivity under water deficiency. Therefore, the objective of this study was to screen the bacterial strains from the mungbean root nodule that may help in improving the plant growth under drought condition. Bacteria were isolated from mungbean root nodules and screened for in vitro drought-tolerance using different concentrations of PEG 6000 at 10, 20, 30 and 40 %, and temperature-tolerance at 30, 35, 40 and 45 °C. In primary screening, out of 98 root nodule bacterial isolates tested, only 25 % showed drought-tolerance at 40 % polyethylene glycol (PEG)-6000 while 22 % of bacteria survived at 45 °C. During secondary screening on combined stress-tolerance, only 8 % of isolates showed tolerance of 40 % PEG-6000 at 45 °C. The in vitro drought-tolerance of bacteria varied significantly according to their sampling region/district. Various PGP traits, i.e., nitrogen fixation, phosphate solubilization, and production of indole acetic acid, ammonia, and 1-aminocyclopropane-1-carboxylate (ACC) deaminase, were analyzed in isolated stress-tolerant bacteria, which may contribute towards stress-tolerance and crop productivity in mungbean. The most promising drought-tolerant nodule bacterial isolates were identified as Rhizobium sp. and Pseudomonas indica , respectively by 16S rRNA sequencing. Moreover, bacterial isolates MuJs52b, MuJs53b, MuJs72a and MuBk32b, which exhibited drought-tolerance of 40 % PEG-6000 and different PGP activities, were used as bioinoculant on mungbean plants grown under moderate to severe drought at 50 and 25 % of field capacity (FC) in pot experiment. Bacteria inoculated plants showed maximum increase in nodule dry weight (56.5 %) and shoot dry weight (87.5 %) per plant even under severe drought at 25 % FC. The results indicated that application of four potential nodule bacterial isolates, which were able to tolerate drought stress of 40 % PEG-6000, and having multiple PGP traits, showed stimulation of the mungbean growth even up to 25 % FC. These plant growth-promoting nodule bacterial strains may be used for the enhancement of mungbean crop productivity under drought stress and could be used as biofertilizer. • Drought-tolerance of mungbean nodule bacteria varied with sampling regions. • About 25 % of isolates showed drought-tolerance at 40 % polyethylene glycol-6000. • Only 8 % of bacterial isolates showed tolerance of 40 % PEG-6000 at 45 °C. • 87.5 % increase in shoot biomass under 25 % field capacity in bacteria inoculation. • Promising drought-tolerant bacteria were Rhizobium sp. and Pseudomonas indica. [ABSTRACT FROM AUTHOR]

Vicia villosa (VV) and Vicia sativa (VS) are legume forages highly valued for their excellent nitrogen fixation. However, no research has addressed the mechanisms underlying their differences in nitrogen fixation. This study employed physiological, cytological, and comparative transcriptomic approaches to elucidate the disparities in nitrogen fixation between them. Our results showed that the total amount of nitrogen fixed was 60.45% greater in VV than in VS, and the comprehensive nitrogen response performance was 94.19% greater, while the nitrogen fixation efficiency was the same. The infection zone and differentiated bacteroid proportion in mature VV root nodules were 33.76% and 19.35% greater, respectively, than those in VS. The size of the VV genome was 15.16% larger than that of the VS genome, consistent with its greater biomass. A significant enrichment of the flavonoid biosynthetic pathway was found only for VV-specific genes, among which chalcone-flavonone isomerase, caffeoyl-CoA-O-methyltransferase and stilbene synthase were extremely highly expressed. The VV-specific genes also exhibited significant enrichment in symbiotic nodulation; genes related to nodule-specific cysteine-rich peptides (NCRs) comprised 61.11% of the highly expressed genes. qRT‒PCR demonstrated that greater enrichment and expression of the dominant NCR (Unigene0004451) were associated with greater nodule bacteroid differentiation and greater nitrogen fixation in VV. Our findings suggest that the greater total nitrogen fixation of VV was attributed to its larger biomass, leading to a greater nitrogen demand and enhanced fixation physiology. This process is likely achieved by the synergistic effects of high bacteroid differentiation along with high expression of flavonoid and NCR genes. • Vicia villosa surpasses Vicia sativa in nitrogen fixation. • Comparative transcriptome analysis reveals positive selection in nodulation. • Flavonoid biosynthesis enrichment in Vicia villosa enhances symbiosis. • Enhanced bacteroid differentiation in Vicia villosa due to NCR peptides. [ABSTRACT FROM AUTHOR]

Nanoparticles (NPs)-based growth stimulators have promising usage in agriculture. This research analyzed the impact of citric acid-coated magnetite nanoparticles (Fe 3 O 4 -NPs; 50 mg Fe L−1) added once at pre-sowing on soybean and alfalfa seedlings growing in association with their corresponding microsymbiont partners, Bradyrhizobium japonicum and Sinorhizobium meliloti ; also on the in vitro growth rate of these microorganisms. Fe-EDTA (50 mg Fe L−1) was used as a comparator. Fe 3 O 4 -NPs significantly augmented the growth rate constant (7–17%) and extracellular polysaccharides production of both microsymbionts (B. japonicum : 2-fold; S. meliloti : 43%), which probably favored bacterial adhesion to the root hairs. In both legumes, Fe 3 O 4 -NPs increased chlorophyll content (up to 56% in soybean) and improved plant growth, evidenced by a greater root biomass system (80–90% higher than the control), and increased shoot biomass (30–40%). Besides, Fe 3 O 4 -NPs addition resulted in earlier nodule formation and enhanced nodule biomass (about 2.5-fold in both species). Nodules were mainly located in the crown of the root in the NP50 treatment, while they were evenly distributed along lateral roots in the control and the comparator. Fe 3 O 4 -NPs also augmented significantly nodule leghemoglobin content (∼50–70%) and total N in legumes' shoots (ca. 20%). CAT activity increased only under NP50 treatment and no symptoms of oxidative damage were evidenced. In this work, we found that besides not being toxic neither to soybean and alfalfa plants nor to their microsymbiont partners, Fe 3 O 4 -NPs do not exert adverse effects on the symbioses establishment; oppositely, a more efficient nodulation pattern was verified in both plant species. • Fe 3 O 4 -NPs stimulated rhizobia multiplication rate and polysaccharides production. • Fe 3 O 4 -NPs increased nodule number and mass. • Fe 3 O 4 -NPs improved the spatial nodulation pattern. • Fe 3 O 4 -NPs enhanced plant growth and chlorophyll content in alfalfa and soybean. [ABSTRACT FROM AUTHOR]

Symbiotic nodules comprise two classes, indeterminate and determinate, defined by the presence/absence of apical meristem and developmental zonation. Why meristem and zonation are absent from determinate nodules remains unclear. Here, we define cell types in developing soybean nodules, highlighting the undifferentiated infection zones and differentiated nitrogen-fixation zones. Auxin governs infection zone maintenance. GRETCHEN HAGEN 3 (GH3) enzymes deactivate auxin by conjugation and promote cell differentiation. gh3 mutants increased undifferentiated cells and enlarged infection zones. The central symbiosis-transcription factor NIN2a activates GH3.1 to reduce auxin levels and facilitates cell differentiation. High auxin promotes NIN2a protein accumulation and enhances signaling, further deactivating auxin and depleting infection zones. Our findings shed light on the NIN2a-GH3-auxin module that drives soybean nodule cell differentiation. This study challenges our understanding of determinate nodule development and proposes that the regulation of nodule zonation offers valuable insights into broader mechanisms of cell differentiation across plant species. [Display omitted] • Developing soybean nodules are defined into infection and nitrogen-fixation zones • Auxin concentration determines the maintenance of infection zones • NIN2a triggers GH3.1 to reduce auxin levels, facilitating nodule cell differentiation • High auxin amplifies NIN2a-GH3 signal, depleting infection zones Tu and Gao et al. identify a mechanism involving NIN2a-GH3-mediated auxin deactivation and auxin-NIN2a-mediated symbiosis. High auxin feedback stabilizes NIN2a protein, further amplifying NIN2a-GH3-dependent auxin deactivation and promoting the disappearance of infection zones in soybean nodules. [ABSTRACT FROM AUTHOR]

Microplastics (MPs), widely presented in cultivated soil, have caused serious stresses on crop growth. However, the mechanism by which MPs affect legumes and rhizobia symbiosis is still unclear. Here, peanut seedlings were inoculated with Bradyrhizobium zhanjiangense CCBAU 51778 and were grown in vermiculite with 3 %/5 % (w/w) addition of PVC (polyvinyl chloride)-MPs/PBAT (polybutylene adipate)-MPs. PVC-MPs and PBAT-MPs separately decreased nodule number by 33–100 % and 2.62–80.91 %. Transcriptome analysis showed that PVC-MPs affected more DEGs (differentially expressed genes) than PBAT-MPs, indicating PVC-MPs were more devastating for the symbiosis than PBAT-MPs. Functional annotation revealed that PVC-MPs and PBAT-MPs enriched DEGs related to biosynthesis pathways such as flavonoid, isoflavonoid, and phenylpropanoid, in peanut. And when the dose increased from 3 % to 5 %, PVC-MPs mainly enriched the pathways of starch and sucrose metabolism, alanine, aspartate and glutamate metabolism, diterpenoid biosynthesis, etc. ; PBAT-MPs enriched cysteine and methionine metabolism, photosynthesis, MAPK signaling, and other pathways. These significantly enriched pathways functioned in reducing nodule number and promoting peanut tolerance to MPs stresses. This study reveals the effect of PVC-MPs and PBAT-MPs on peanut and rhizobium symbiosis, and provides new perspectives for legume production and environmental safety. [Display omitted] • Polyvinyl chloride (PVC)-MPs and polybutylene adipate (PBAT)-MPs significantly reduce peanut nodule number. • PVC-MPs is more devastating than PBAT-MPs for the symbiosis between peanut and rhizobium. • Peanut differential transcriptional response is existed according to the type and concentration of MPs. [ABSTRACT FROM AUTHOR]

The aim of this work was to investigate the impact of nano selenium (N–Se) and compost on the growth, photosynthesis, enzymes activity, compatible solutes and metals accumulation in soybean grown under tannery effluent polluted soil. The plants were exposed to compost application (no compost and compost addition) and foliar application of N–Se (0, 25, 50, and 75 mg L−1). The results showed the addition of compost in soil and foliar applied N–Se alleviated the toxic effect of tannery effluent polluted soil. Furthermore, foliar application of N–Se with basal compost supply significantly improved antoxidant enzymes activity in soybean grown in tannery effluent polluted soil. Addition of compost increased the root dry weight (46.43%) and shoot dry weight (33.50 %), relative water contents by (13.74 %), soluble sugars (15.99 %), stomatal conductance (gs) (83.33 %), intercellular CO 2 concentration (Ci) (23.34 %), transpiration rate (E) (12.10 %) and decreased the electrolyte leakage (27.96 %) and proline contents by (20.34 %). The foliage application of N–Se at the rate of 75 mg L−1 showed the most promising results in control and compost amended tannery effluent polluted soil. The determined health risk index (HRI) values were recorded less than 1 for both adults and children under the application of compost and N–Se. In summary, the combined use of N–Se at 75 mg L⁻1 and basal supply of compost is an effective strategy for enhancing soybean productivity while minimizing the potential risks of metal accumulation in soybean grains grown in tannery effluent polluted soil. [Display omitted] • N–Se and compost enhance plant resilience in polluted environments. • Synergistic effect of N–Se and compost enhance growth, antioxidative defenses and osmolyte accumulation in soyabean. • It is viable approach for reducing metal contamination which would further reduce the HRI. [ABSTRACT FROM AUTHOR]

Phosphorus (P), a macronutrient, plays key roles in plant growth, development, and yield. Phosphate (Pi) transporters (PHTs) and PHOSPHATE1 (PHO1) are central to Pi acquisition and distribution. Potentially, PHO1 is also involved in signal transduction under low P. The current study was designed to identify and functionally characterize the PHO1 gene family in chickpea (CaPHO1s). Five CaPHO1 genes were identified through a comprehensive genome-wide search. Phylogenetically, CaPHO1s formed two clades, and protein sequence analyses confirmed the presence of conserved domains. CaPHO1s are expressed in different plant organs including root nodules and are induced by Pi-limiting conditions. Functional complementation of atpho1 mutant with three CaPHO1 members, CaPHO1 , CaPHO1;like, and CaPHO1;H1, independently demonstrated their role in root to shoot Pi transport, and their redundant functions. To further validate this, we raised independent RNA-interference (RNAi) lines of CaPHO1 , CaPHO1;like , and CaPHO1;H1 along with triple mutant line in chickpea. While single gene RNAi lines behaved just like WT, triple knock-down RNAi lines (capho1/like/h1) showed reduced shoot growth and shoot Pi content. Lastly, we showed that CaPHO1s are involved in root nodule development and Pi content. Our findings suggest that CaPHO1 members function redundantly in root to shoot Pi export and root nodule development in chickpea. • PHOSPHATE1 (PHO1) is a conserved plant protein pivotal in mediating root to shoot Pi export. • CaPHO1 family members expressed differentially in vegetative, reproductive tissues and root nodules. • CaPHO1 , CaPHO1;like , and CaPHO1;H1 are low Pi responsive and restore the growth defects of atpho1 mutant. • CaPHO1 , CaPHO1;like , and CaPHO1;H1 function redundantly in chickpea for Pi export and root nodulation. [ABSTRACT FROM AUTHOR]

The global contribution of biological nitrogen fixation (BNF) to soybean production ranks Brazil as the leading country. In 2013/2014, a new technology based on soybean co-inoculation with Bradyrhizobium spp. and Azospirillum brasilense strains Ab-V5 and Ab-V6 was released, and here we report a five-year set of extension activities in Paraná state, southern Brazil, to demonstrate the benefits of co-inoculation. In total, 273 technical reference units (TRUs) were installed in two main soybean macro-regions, all showing naturalized populations of soybean bradyrhizobia. In each TRU, side-by-side plots consisting of soybean seeds non-inoculated or co-inoculated with Bradyrhizobium spp. and A. brasilense were installed, and 260 TRUs were evaluated for nodulation and 242 for grain yield. Consistent nodulation increases, of up to 350% were observed in every cropping season, with an average significant (p < 0.01) increase of 35% in the five-year period. Similarly, grain yield increased up to 80% due to co-inoculation, with an average significant (p < 0.01) increase of 8%, corresponding to 273 kg ha−1. The increases were confirmed in the two macro-regions and different levels of grain yield, from low (<3000 kg ha−1) to high (>4000 kg ha−1). In the five-year period, 3299 small farmers were reached (farms of ∼50 ha) and the average profit due to co-inoculation was estimated at US$ 111.5 ha−1 per cropping season. In addition, we discuss environmental benefits associated with the mitigation of greenhouse gases emissions, estimated at 350 kg ha−1 of CO 2 -e, in addition to soil N enrichment. [Display omitted] • Soybean can benefit from co-inoculation with Bradyrhizobium spp. and A, brasilense. • The technology was demonstrated to 3299 farmers in Brazil, for five cropping seasons. • Increases in nodulation, grain yield, and US$ 111.5 ha−1 in profit were confirmed. • Extension activities with farmers are needed for the adoption of microbial inoculants. • Soybean co-inoculation resulted in economic and environmental benefits. [ABSTRACT FROM AUTHOR]

Selective herbicides control weeds in cereal crops and break down over time, allowing safe planting of legumes in the following years. However due to climatic inconsistencies and changing farming practices, this is not always the case, and residues can inhibit formation of legume/rhizobia symbioses. The objectives were to determine whether: i) exposure to triasulfuron, even at extremely low levels, reduces shoot and root growth and nodulation of five diverse and widely sown legume pasture cultivars in Australian farming systems; and ii) sowing legumes prior to recommended plant-back criteria being met for chlorsulfuron, triasulfuron herbicide, clopyralid, and pyroxasulfone herbicides results in unacceptable damage to subsequently sown pasture and crop legumes, causing reduced root and shoot growth, nodulation and N fixation. A series of glasshouse and field experiments explored herbicide residue impact on commonly used legumes in dryland farming systems. A glasshouse study determined triasulfuron at concentration 0.000225 g a.i/ha, a (1/100,000) dilution of the label rate caused significant (p < 0.001) decrease in nodule count, root length, root, shoot weight for Trifolium spumosum cv. Bartolo and T. subterraneum cv. Dalkeith, and at 0.225 g a.i/ha and 2.25 g a.i/ha for all five cultivars tested. A bioassay assessed T. subterraneum cv. Dalkeith health when grown in field soil-cores taken 4, 7 and 10 months after herbicide application (chlorsulfuron, triasulfuron, clopyralid and pyroxasulfone) to a wheat crop. For all three, herbicide residues significantly decreased (p < 0.001) nodule number, shoot weight, root length and whole plant weight of T. subterraneum cv. Dalkeith compared to control. A field experiment assessed nodulation of five pasture and two crop legumes sown dry (dormant summer sowing), or following rainfall 10.5 months after initial herbicide application. Nodulation of all legume cultivars decreased in plots treated with clopyralid. Chlorsulfuron decreased nodulation for all cultivars except T. glanduliferum and T. subterraneum. Triasulfuron reduced nodulation for all cultivars except Ornithopus sativus and T. spumosum. Pyroxasulfone decreased nodulation of Biserrula pelecinus cv. Casbah and Lupinus angustifolius cv. Mandalup. Herbicide residues from preceding cereal crops reduced fitness and symbiotically fixed N in subsequently sown pasture or crop legumes. Our study highlighted label plant-back recommendations should be strictly adhered to, despite conflict with modern farming approaches of dry or early sowing) to combat climate change. This outcome may consequently lower profitability and increase the carbon footprint of farming systems. • Herbicide plant back recommendations may conflict with modern farming practices. • Herbicide residue reduced crop and pasture legume fitness. • Nodulation and subsequently symbiotically fixed N is reduced by herbicide residue. • Herbicide label plant-back recommendations should be strictly adhered to. [ABSTRACT FROM AUTHOR]

Bacillus sensu lato were screened for their capacity to mineralize organic phosphorus (P) and promote plant growth, improving nitrogen (N) and P nutrition of soybean. Isolates were identified through Type Strain Genome Server (TYGS) and Average Nucleotide Identity (ANI). ILBB95, ILBB510 and ILBB592 were identified as Priestia megaterium , ILBB139 as Bacillus wiedmannii , ILBB44 as a member of a sister clade of B. pumilus , ILBB15 as Peribacillus butanolivorans and ILBB64 as Lysinibacillus sp. These strains were evaluated for their capacity to mineralize sodium phytate as organic P and solubilize inorganic P in liquid medium. These assays ranked ILBB15 and ILBB64 with the highest orthophosphate production from phytate. Rhizocompetence and plant growth promotion traits were evaluated in vitro and in silico. Finally, plant bioassays were conducted to assess the effect of the co-inoculation with rhizobial inoculants on nodulation, N and P nutrition. These bioassays showed that B. pumilus, ILBB44 and P. megaterium ILBB95 increased P-uptake in plants on the poor substrate of sand:vermiculite and also on a more fertile mix. Priestia megaterium ILBB592 increased nodulation and N content in plants on the sand:vermiculite:peat mixture. Peribacillus butanolivorans ILBB15 reduced plant growth and nutrition on both substrates. Genomes of ILBB95 and ILBB592 were characterized by genes related with plant growth and biofertilization, whereas ILBB15 was differentiated by genes related to bioremediation. Priestia megaterium ILBB592 is considered as nodule-enhancing rhizobacteria and together with ILBB95, can be envisaged as prospective PGPR with the capacity to exert positive effects on N and P nutrition of soybean plants. [ABSTRACT FROM AUTHOR]

A major driving force behind sustainable agriculture and protection of the environment is effective management of nitrogen (N) in farming. Better understanding on the growth and functional adaptation of legumes under low nutrient savannah and grassland ecosystems remain crucial for food security. Therefore, this study examined if Vigna radiata (L.) R. Wilczek (Mung bean) establishes multiple symbiosis with soil microbes in KwaZulu-Natal (KZN) soils and how that symbiosis affects plant N nutrition and related-carbon growth costs. The study was conducted in the greenhouse using soils from four (Hluhluwe, Izingolweni, Bergville, and Ashburton) different geographical areas of KZN province. The soils were used as a natural inoculum and growth substrate thus treated as four treatments. Soil analysis of the four geographical areas showed marked differences with regard to phoshorus (P) and potassium (K) nutrient concentrations, exchange acidity and arbuscular mycorrhizal (AM) spore counts, while no significant differences were observed among the four treatments in term of N concentration and root colonization. Soils from the four sites were acidic and showed variation in nutrients especially with regard to P and N. Bergville soils had the highest P concentrations, exchange acidity and AM fungi spore counts, while Hluhluwe soils had the highest concentration of K, total cations and lowest spore count. Vigna radiata grown in Hluhluwe soils had higher biomass when compared to Bergville soil-grown plants. All plants nodulated with the exception of plants that were grown with Bergville soil. Despite differences in soil nutrient concentration, V. radiata plants established symbiosis with AM fungi, Rhizobium and numerous Bacillus species. Furthermore, the legume plants including the non-nodulated Bergville-grown V. radiata plants were able to switch N sources (atmospheric and soil N) to maintain their N nutrition and carbon construction costs. This observation suggests that non-nodulated Bergville-grown plants may have established symbiosis with other bacterial taxa such as Bacillus spp. and other endophytic bacterial spp. that fix atmospheric N. Overall, the symbiotic association of V. radiata with Rhizobium , AM fungi and various Bacillus species enhanced N utilization. In addition, V. radiata has the capacity to switch between soil N and atmospheric N while maintaining low carbon construction cost under low soil nutrient conditions. Vigna radiata thus can be adaptable to low soil nutrient savannah and grassland ecosystems in KZN province, South Africa. • Savannah and grassland soils are acidic and nutrient poor specifically with regard to N and P. • Vigna radiata formed symbiotic association with arbuscular mycorrhizal fungi, Rhizobium and Bacillus sp. • Legume–microbe symbiotic interaction enhanced V. radiata N nutrition and acquisition from the soil. • The interaction also maintained carbon construction costs under low nutrient soils. [ABSTRACT FROM AUTHOR]

Bradyrhizobium is thought to be the largest and most diverse rhizobial genus, but this is not reflected in the number of described species. Although it was one of the first rhizobial genera recognised, its taxonomy remains complex. Various contemporary studies are showing that genome sequence information may simplify taxonomic decisions. Therefore, the growing availability of genomes for Bradyrhizobium will likely aid in the delineation and characterization of new species. In this study, we addressed two aims: first, we reviewed the availability and quality of available genomic resources for Bradyrhizobium. This was achieved by comparing genome sequences in terms of sequencing technologies used and estimated level of completeness for inclusion in genome-based phylogenetic analyses. Secondly, we utilized these genomes to investigate the taxonomic standing of Bradyrhizobium in light of its diverse lifestyles. Although genome sequences differed in terms of their quality and completeness, our data indicate that the use of these genome sequences is adequate for taxonomic purposes. By using these resources, we inferred a fully resolved, well-supported phylogeny. It separated Bradyrhizobium into seven lineages, three of which corresponded to the so-called supergroups known for the genus. Wide distribution of key lifestyle traits such as nodulation, nitrogen fixation and photosynthesis revealed that these traits have complicated evolutionary histories. We present the first robust Bradyrhizobium species phylogeny based on genome sequence information for investigating the evolution of this important assemblage of bacteria. Furthermore, this study provides the basis for using genome sequence information as a resource to make important taxonomic decisions, particularly at the species and genus levels. [ABSTRACT FROM AUTHOR]

This is the first study that reports management of root-rot complex caused by Macrophomina phaseolina and Rhizoctonia solani concomitantly (104−6 CFU g−1 soil) in mungbean by Trichoderma spp. under field condition. Effectiveness of Trichoderma harzianum , T. hamatum , T. viride , T. polysporum and T. koningii against root-rot causing pathogens, M. phaseolina and R. solani was evaluated in vitro (dual inoculation test). The field performance of above Trichoderma spp. against root-rot disease complex caused by M. phaseolina and R. solani in mungbean was evaluated during two consecutive years. The farmyard manure colonized by T. harzianum , T. hamatum and T. viride was applied in the soil at 250 kg/ha (50 g/microplot) under field condition. The Trichoderma strains were characterized for fungicide sensitivity to distinguish from indigenous isolates, if they are present in the field soil. Mungbean cv. T44 expressed higher susceptibility to concomitant inoculations of M. phaseolina and R. solani , and exhibited significant suppression in plant growth (12–17%) and grain yield (26–30%) in two years. Treatments with Trichoderma species controlled root-rot, and improved mungbean yield, highest with T. viride, followed by T. harzianum and T. hamatum. Soil populations of M. phaseolina and R. solani decreased significantly in the plots receiving T. viride , T. harzianum or T. hamatum , whereas Trichoderma populations increased correspondingly. Soil application of T. viride or T. harzianum effectively controlled the root-rot disease complex (5–15%) and improved the grain yield of mungbean (14–19%) in diseased plots. Overall performance of T. viride was relatively better than carbendazim. • Rhizoctonia solani and Macrophomina phaseolina caused root-rot disease complex. • The pathogens significantly suppressed the seed germination and yield of mungbean. • Soil application of Trichoderma spp. controlled disease better than carbendazim. • T. viride checked the disease (46–61%) and improved the yield (9–17%) of mungbean. • Soil population of T. viride increased (57–60%), but of pathogens declined (57–60%). [ABSTRACT FROM AUTHOR]

Highlights • AhCYCLOPS is unique in having 10 exon as opposed to 11 of other homologs. • Under native promoter, AhCYCLOPS can complement Mtipd3-1 and Mtipd3-2 mutants. • RNAi of AhCYCLOPS affects nodulation in A. hypogaea. Abstract Root nodule symbiosis in legumes is established following interaction of compatible rhizobia that activates an array of genes, commonly known as symbiotic-pathway, resulting in nodule development. In model legumes, bacterial entry mainly occurs through infection thread involving the expression of transcription factor CYCLOPS/IPD3. Here we show the functional analysis of AhCYCLOPS in Arachis hypogaea where bacteria invade roots through epidermal cracks. Exploiting significant cross-species domain conservation, trans-complementation experiments involving ectopic expression of AhCYCLOPS in transgenic hairy-roots of Medicago truncatula ipd3 mutants resulted in functional complementation of Medicago nodules. Moreover, native promoter of AhCYCLOPS was sufficient for this cross-species complementation irrespective of the different modes of infection of roots by rhizobia and nodule ontology. To unravel the role of Ah CYCLOPS during 'crack-entry' nodulation in A. hypogaea , RNAi of AhCYCLOPS was performed which resulted in delayed nodule inception followed by drastic reduction in nodule number on transgenic hairy-roots. The infection zone of a significant number of RNAi nodules showed presence of infected cells with enlarged nucleus and rod shaped undifferentiated bacteria. Expression analysis showed downregulation of several nodulation responsible effectors endorsing the compromised condition of RNAi roots. Together, the results indicated that AhCYCLOPS plays an important role in A. hypogaea nodule development. [ABSTRACT FROM AUTHOR]

Selenium (Se) is an essential micronutrient to humans. Se biofortification in crops provides an effective means to enhance dietary Se intake. However, the effects of Se treatment on plant growth and development remain to be fully studied. In this study, we applied Se to soybean plants grown hydroponically and in soil. We observed that selenate treatment increased nodule number and fresh weight. Furthermore, Se supplementation increased isoflavone daidzein accumulation in roots and nodules. An exogenous supply of daidzein but not kaempferol was found to increase nodule number and fresh weight significantly, suggesting a role of daidzein in the Se-induced nodulation in soybean plants. In addition, the total sugar levels in nodules, roots, and leaves were significantly enhanced following selenate treatment. Subsequently, the N-compounds were greatly increased after Se treatment in all tissues examined. Transcriptome analysis revealed that Se treatment altered various metabolic and cellular processes to affect nodulation and nodule development. Se treatment upregulated GmNIN2b , an important nodule organogenesis gene, as well as genes associated with sugar metabolism and ureide transport. Our study provides insights underlying the Se-induced nodulation in soybean plants and further documents that Se biofortification in soybean can simultaneously improve not only the essential nutrient content but also nodulation for biological nitrogen fixation, a critically important agronomic trait in soybean plants. [Display omitted] • Selenate treatment promotes nodulation in soybean plants. • Isoflavone daidzein production is greatly increased by Se treatment in nodules and roots. • Exogenous supply of daidzein promotes nodulation. • Total sugar levels and N-compounds are elevated in plants exposed to selenate. • Transcriptome profiling reveals that selenate upregulates some important genes in nodulation. [ABSTRACT FROM AUTHOR]

Highlights • N 2 fixation can be affected by physical, chemical and biological factors of soil. • Soil tillage methods alter N 2 fixation by modification of these factors. • Conservation tillage enhances nodulation by increasing soil moisture. • A reduction of soil pH under conservation tillage reduces nodulation. • Soil compaction that may occur under conservation tillage can reduce N 2 fixation. Abstract Adopting conservation tillage practices such as zero tillage can enhance soil quality, compared with conventional tillage practices that disrupt soil structure. The benefits of maintaining soil structure through no tillage typically result in improved biological processes and increased microbial biodiversity. Rhizobia are considered here as an indicator for soil quality, as they are ubiquitous, present in high populations in many soils, rapidly respond to soil changes, and are crucial for legume productivity. The process of symbiotic nitrogen fixation, whereby rhizobia form a symbiotic association with leguminous plants and fix atmospheric nitrogen gas, can substantially improve agricultural system as, it has how environmental and economic costs for nitrogen supply. Tillage methods affect many soil characteristics such as aeration, structure, temperature and water use, all of which affect the microbial composition, nitrogen fixation and nodulation. This review systematically summarizes the effect of tillage systems such as conventional tillage and minimum tillage systems on nitrogen fixation by legumes. We identify that conservation tillage typically enhances nodulation and nitrogen fixation, through increased soil moisture retention and soil temperature, and increased soil microbial biomass. However, conservation tillage can lead to a reduction in soil pH and increased soil compaction, which can reduce nodulation. [ABSTRACT FROM AUTHOR]

Site-specific insertion plasmid pVO155 was used to knockout the genes involved in the alternation of host range of strain Bradyrhizobium diazoefficiens USDA 110 from its original determinate-nodule-forming host soybean ( Glycine max ), to promiscuous and indeterminate-nodule-forming shrubby legume sophora ( Sophora flavescens ). Symbiotic phenotypes of these mutants inoculated to these two legumes, were compared to those infected by wild-type strain USDA 110. Six genes of the total fourteen Tn 5 transposon mutated genes were broken using the pVO155 plasmid. Both Tn 5 and pVO155-inserted mutants could nodulate S. flavescens with different morphologies of low-efficient indeterminate nodules. One to several rod or irregular bacteroids, containing different contents of poly-β-hydroxybutyrate or polyphosphate were found within the symbiosomes in nodulated cells of S. flavescens infected by the pVO155-inserted mutants. Moreover, none of bacteroids were observed in the pseudonodules of S. flavescens , infected by wild-type strain USDA 110. These mutants had the nodulation ability with soybean but the symbiotic efficiency reduced to diverse extents. These findings enlighten the complicated interactions between rhizobia and legumes, i. e., mutation of genes involved in metabolic pathways, transporters, chemotaxis and mobility could alter the rhizobial entry and development of the bacteroid inside the nodules of a new host legume. [ABSTRACT FROM AUTHOR]

Highlights • Rehabilitation is required after iron mining in the Carajás Mineral Province (CMP). • Topsoil application during mineland revegetation may increase the initial growth of Fabaceae. • Fertilization and liming increase initial growth of five legume species used for revegetation. • Putative drought tolerance and metal accumulation qualify examined canga species for revegetation. • Although not occurring in the CMP, Bauhinia forficata showed the highest growth in all tested substrates. Abstract The main challenge of mineland revegetation is the establishment of species that rapidly accumulate biomass, organic matter and nutrients. Thus, the selection of promising species requires detailed knowledge of their growth performances in different mineland environments. Four Fabaceae species native to forests or metalliferous savannas, locally termed cangas, from the Carajás Mineral Province in the eastern Amazon of Brazil and the exotic Bauhinia forficata were cultivated under greenhouse conditions in different non-fertilized and fertilized (including liming) topsoils and mining wastes. After 45 days, the biomasses, specific leaf areas, leaf nutrient contents and nodulating root percentages were measured. Initial biomass accumulation and nodulation was higher in non-fertilized topsoils than in non-fertilized mining wastes; fertilization increased initial growth in all substrates. The canga species Mimosa acutistipula var. ferrea and Parkia platycephala showed lower biomass accumulation than other species, but their lower specific leaf areas indicated higher drought tolerance, an important adaptation in seasonal climates. Furthermore, the leaf nutrient contents indicated that both canga species might be hyperaccumulators of metal ions. Among the studied species, the highest biomass accumulation was detected in the exotic B. forficata in fertilized substrates. The patterns of initial biomass accumulation and nodulation of the examined species indicated that topsoils, fertilizers and lime should be applied whenever possible to enhance overall revegetation success. Putative drought tolerance and leaf metal ion accumulation of both canga species qualify them for use in revegetation projects, whereas the large biomass accumulation of the exotic B. forficata provides scientific support for its application in revegetation projects. However, risk assessments are required before it is introduced to the Carajás Mineral Province. [ABSTRACT FROM AUTHOR]

Upon immune challenge, insects recognize nonself. The recognition signal will propagate to nearby immune effectors. It is well-known that Toll signal pathway induces antimicrobial peptide (AMP) gene expression. Eicosanoids play crucial roles in mediating the recognition signal to immune effectors by enhancing humoral immune response through activation of AMP synthesis as well as cellular immune responses, suggesting a functional cross-talk between Toll and eicosanoid signals. This study tested a cross-talk between these two signals. Two signal transducing factors (MyD88 and Pelle) of Toll immune pathway were identified in Spodoptera exigua . RNA interference (RNAi) of either SeMyD88 or SePelle expression interfered with the expression of AMP genes under Toll signal pathway. Bacterial challenge induced PLA 2 enzyme activity. However, RNAi of these two immune factors significantly suppressed the induction of PLA 2 enzyme activity. Furthermore, RNAi treatment prevented gene expression of cellular PLA 2 . Inhibition of PLA 2 activity reduced phenoloxidase activity and subsequent suppression in cellular immune response measured by hemocyte nodule formation. However, immunosuppression induced by RNAi of Toll signal molecules was significantly reversed by addition of arachidonic acid (AA), a catalytic product of PLA 2 . The addition also significantly reduced the enhanced fungal susceptibility of S. exigua treated by RNAi against two Toll signal molecules. These results indicate that there is a cross-talk between Toll and eicosanoid signals in insect immunity. [ABSTRACT FROM AUTHOR]

Phaseolus vulgaris (common bean) was introduced to Kenya several centuries ago but the rhizobia that nodulate it in the country remain poorly characterised. To address this gap in knowledge, 178 isolates recovered from the root nodules of P. vulgaris cultivated in Kenya were genotyped stepwise by the analysis of genomic DNA fingerprints, PCR-RFLP and 16S rRNA, atpD , recA and nodC gene sequences. Results indicated that P. vulgaris in Kenya is nodulated by at least six Rhizobium genospecies, with most of the isolates belonging to Rhizobium phaseoli and a possibly novel Rhizobium species. Infrequently, isolates belonged to Rhizobium paranaense , Rhizobium leucaenae , Rhizobium sophoriradicis and Rhizobium aegyptiacum . Despite considerable core-gene heterogeneity among the isolates, only four nodC gene alleles were observed indicating conservation within this gene. Testing of the capacity of the isolates to fix nitrogen (N 2 ) in symbiosis with P. vulgaris revealed wide variations in effectiveness, with ten isolates comparable to Rhizobium tropici CIAT 899, a commercial inoculant strain for P. vulgaris . In addition to unveiling effective native rhizobial strains with potential as inoculants in Kenya, this study demonstrated that Kenyan soils harbour diverse P. vulgaris -nodulating rhizobia, some of which formed phylogenetic clusters distinct from known lineages. The native rhizobia differed by site, suggesting that field inoculation of P. vulgaris may need to be locally optimised. [ABSTRACT FROM AUTHOR]

Three bacteria, IC-59, IC-76A and IC-2002, isolated from the nodules of chickpea, were characterized for nodulation, nitrogen fixation, plant growth-promoting (PGP) and yield traits in five cultivars of chickpea such as BG256, RSG888, Subhra, K850 and ICCV2. All the bacteria produced cellulase, protease, β-1,3-glucanase, indole acetic acid, siderophore, hydro cyanic acid and 1-aminocyclopropane-1-carboxylate deaminase while none produced lipase and chitinase. The 16 S rDNA gene sequences of IC-59, IC-76A and IC-2002 were found to match closely with Rhizobium pusense , Paraburkholderia kururiensis and Stenotrophomonas maltophilia , respectively. The three bacteria nodulated all the cultivars of chickpea well, amplified nifH gene and fixed nitrogen. Under greenhouse conditions at 30 and 45 days after sowing, treatment of five cultivars of chickpea with bacterial cultures IC-59, IC-76A and IC-2002, enhanced the nodule number (up to 45%, 38% and 43%), nodule weight (up to 31%, 15% and 39%), shoot weight (11%, 16% and 14%) and root weight (37%, 48% and 62%), respectively, over the un-inoculated control. At crop maturity, IC-59, IC-76A and IC-2002 were found to enhance the shoot weight (16%, 40% and 26%), pod number (37%, 69% and 81%), pod weight (17%, 45% and 49%), seed number (21%, 31% and 39%) and seed weight (14%, 56% and 65%), respectively, over the un-inoculated control. Among the five cultivars, Subhra was found to enhance most of the PGP traits when treated with the three diazotrophic bacteria. It is concluded that the three diazotrophic bacteria could be potentially exploited for improving nodulation, nitrogen fixation, PGP and yields of chickpea. [ABSTRACT FROM AUTHOR]

The Chapada Diamantina in NE of Brazil is a biodiversity hotspot and a center of radiation for many Neotropical legume genera, such as Calliandra and Mimosa . The present study aimed to evaluate nodulation in Calliandra species endemic to various environments, and to characterize the diversity of their symbiotic rhizobia using housekeeping (16S rRNA, recA ) and plasmid-borne, symbiosis-related ( nifH and nodC ) genes. The nodulation ability of selected isolates was assessed. All of the 126 bacterial isolates from 18 Calliandra species collected in six different vegetation types were identified as Paraburkholderia according to their housekeeping and symbiosis gene phylogenies. They were grouped in seven clades in relation to the dominant vegetation type in their native environments. The majority, particularly those from highland “campo rupestre” vegetation, were similar to Paraburkholderia nodosa , but had nodC genes identical to the Mimosa symbiont Paraburkholderia tuberum sv. mimosae. The other smaller groups were related to Paraburkholderia diazotrophica and Paraburkholderia sabiae , and some single strains were not close to any known species. The symbionts of Calliandra spp. in NE Brazil are Paraburkholderia strains closely-related to Mimosa symbionts from the same region. NE Brazil is a reservoir of symbiotic Paraburkholderia that have an affinity for genera in the Mimosoid clade. [ABSTRACT FROM AUTHOR]

Caucasian clover (Trifolium ambiguum) is a perennial rooted and tillering leguminous forage with strong adaptability, outstanding stress tolerance and other preferable traits. However, the specificity with rhizobia limits the extended application of Caucasian clover. Therefore, it is important to study the changes of genes and metabolites in the early process of nodulation in Caucasian clover to improve its nodulation and nitrogen fixation ability. In this study, we used Caucasian clover as the experimental material to investigate its nodulation mechanism using transcriptomic and metabolomic approaches, such that to break the nitrogen fixation barrier for the promotion of Caucasian clover. Metabolomic and transcriptomic profiling revealed that both DAMs and DEGs were significantly enriched in the phenylpropanoid and flavonoid biosynthetic pathways, with DEGs showing up-regulation at 3 days and 6 days post inoculation (dpi) with rhizobia, and some DEGs showing down-regulation at 9 dpi. Accumulation of flavonoids was significantly increased at both 3 dpi and 6 dpi, and some compounds were significantly decreased at 9 dpi. A total of 35 DEGs were involved in flavonoid synthesis by WGCNA analysis, among which HCT, CCR, COMT and F3H played an important role. This study provides insights in understanding the molecular mechanism of nodulation and nitrogen fixation in Caucasian clover. • Transcriptomics and metabolomics techniques were applied to study the mechanism of early colonization of Caucasian clover, to understand the mechanism of nitrogen fixation in the early stage of colonization of Caucasian clover, and to provide a theoretical basis for the improvement of nitrogen fixation capacity in the later stage. • Significant changes in both root metabolites and genes after inoculation of Caucasian clover with rhizobia. • Genes regulating HCT, CCR, COMT and F3H may be key genes affecting nitrogen fixation in Caucasian clover nodules. • The rhizobium specificity of Caucasian clover has been one of the key factors restricting its popularization and cultivation, and the study of its nodulation and nitrogen fixation mechanism can provide a theoretical basis for the subsequent improvement of Caucasian clover nodulation and nitrogen fixation and the promotion of popularization and cultivation. [ABSTRACT FROM AUTHOR]

Unavailability of essential micronutrients is a major constrain for cowpea growth, nodulation and pod yield under acid soil condition. In this context a two year field experiment was conducted to assess the effect of boron, molybdenum and biofertilizers on growth, nodulation and pod yield of vegetable cowpea in acid soil of eastern Himalayan region. Treatments consisted of four levels of seed treatment with molybdenum and biofertilizers ( Rhizobium + PSB) and four levels of foliar spray of boron, laid out in split plot design. The result revealed that combined use of seed treatment with molybdenum (0.5 g/kg seed) and biofertilizers along with foliar spray of boron at 4 weeks of planting significantly enhanced the growth and yield attributes of cowpea and registered 42% and 54% improvement in number of pod and pod yield/plant respectively over control, whereas seed treatment with molybdenum (0.5 g/kg seed) and biofertilizers alone recorded 76% and foliar spray of boron at 4 weeks of planting alone produced 39% higher pod yield/plant over control. [ABSTRACT FROM AUTHOR]

Groundnut is an economically important N ​2 -fixing legume that can contribute about 100–190 kg N ha −1 to cropping systems. In this study, groundnut-nodulating native rhizobia in South African soils were isolated from root nodules. Genetic analysis of isolates was done using restriction fragment length polymorphism (RFLP)-PCR of the intergenic spacer (IGS) region of 16S-23S rDNA. A total of 26 IGS types were detected with band sizes ranging from 471 to 1415 bp. The rhizobial isolates were grouped into five main clusters with Jaccard's similarity coefficient of 0.00–1.00, and 35 restriction types in a UPGMA dendrogram. Partial sequence analysis of the 16S rDNA, IGS of 16S rDNA-23S rDNA, atpD , gyrB , gltA , glnII and symbiotic nifH and nodC genes obtained for representative isolates of each RFLP-cluster showed that these native groundnut-nodulating rhizobia were phylogenetically diverse, thus confirming the extent of promiscuity of this legume. Concatenated gene sequence analysis showed that most isolates did not align with known type strains, and may represent new species from South Africa. This underscored the high genetic variability associated with groundnut Rhizobium and Bradyrhizobium in South African soils, and the possible presence of a reservoir of novel groundnut-nodulating Bradyrhizobium and Rhizobium in the country. [ABSTRACT FROM AUTHOR]

Rooibos tea, Aspalathus linearis (Burm.f.), represents one of South Africa's most important indigenous crops, and monotypic plantations are rapidly replacing wild populations. Dwindling wild rooibos populations may drastically reduce possible, but hitherto overlooked, natural resources to bolster commercial productivity and long-term sustainability. Here, using next generation sequencing data, we seek to determine whether cultivation impacts on the diversity and community structure of mutualistic nitrogen fixing bacteria (rhizobia) associated with rooibos plants. We do this by generating operational taxonomic units (OTUs) from nodulation ( nodC ) and nitrogenase ( nifH ) DNA sequence data from rhizobia within root nodules of rooibos plants from cultivated and wild populations. For these rhizobial communities we found significant differences for various OTU diversity metrics due to geography (site), the interaction between site and status (cultivated vs. wild), but not for status. We also sequenced nodC soil microbiomes and found evidence for compositional differences in soil rhizobial communities due to geography, status (cultivated vs. wild), and the interaction between geography and status. Our data adds to existing evidence suggesting that tea cultivation in South Africa may have limited impacts on soil microbial community diversity and structure, and that such changes are mainly driven by larger geographic processes rather than human-mediated disturbances such as cultivation. [ABSTRACT FROM AUTHOR]

Synergism between beneficial rhizobacteria and fungal pathogens is poorly understood. Therefore, evaluation of co-inoculation of bacteria that promote plant growth by different mechanisms in pathogen challenged plants would contribute to increase the knowledge about how plants manage interactions with different microorganisms. The goals of this work were a) to elucidate, in greenhouse experiments, the effect of co-inoculation of peanut with Bradyrhizobium sp. SEMIA6144 and the biocontrol agent Bacillus sp. CHEP5 on growth and symbiotic performance of Sclerotium rolfsii challenged plants, and b) to evaluate field performance of these bacteria in co-inoculated peanut plants. The capacity of Bacillus sp. CHEP5 to induce systemic resistance against S. rolfsii was not affected by the inoculation of Bradyrhizobium sp. SEMIA6144. This microsymbiont, protected peanut plants from the S. rolfsii detrimental effect, reducing the stem wilt incidence. However, disease incidence in plants inoculated with the isogenic mutant Bradyrhizobium sp. SEMIA6144 V2 (unable to produce Nod factors) was as high as in pathogen challenged plants. Therefore, Bradyrhizobium sp. SEMIA6144 Nod factors play a role in the systemic resistance against S. rolfsii . Bacillus sp. CHEP5 enhanced Bradyrhizobium sp. SEMIA6144 root surface colonization and improved its symbiotic behavior, even in S. rolfsii challenged plants. Results of field trials confirmed the Bacillus sp. CHEP5 ability to protect against fungal pathogens and to improve the yield of extra-large peanut seeds from 2.15% (in Río Cuarto) to 16.69% (in Las Vertientes), indicating that co-inoculation of beneficial rhizobacteria could be a useful strategy for the peanut production under sustainable agriculture system. [ABSTRACT FROM AUTHOR]

Ensuring adequate populations of effective rhizobia in soil is essential to guarantee optimum nodulation and nitrogen fixation in legumes. The population of soybean-rhizobia and the proportion of slow and fast growers were enumerated in Vertisols of central India in different crop rotations for three years during 2013-15. Soils were from soybean-based (soybean-wheat and soybean-chickpea) and cereal-based rotations (maize-wheat, rice-wheat and maize-chickpea) rotations. Soybean-based rotations stimulated the rhizobial population by 22-fold compared to cereal rotations. Lowest populations were in the summer but increased in soybean rotations by 13.3-fold after the rainy season to 2743 cells g −1 soil at maximum vegetative growth. In the cereal rotations, the increase was by 1.7-fold to 61 cells g −1 soil. Long-term integrated nutrient management, by annual application of farmyard manure in soybean along with chemical fertilizers, improved the rhizobial numbers by 1.5-fold over chemical fertilization alone and by 2.9-fold over unfertilized treatments. Increased crop growth by chemical fertilizers also stimulated rhizobial populations by 1.9-fold over unfertilized soybean. The proportion of slow-growing soybean rhizobia was lower in soybean-based rotations (38%) compared to cereal-based rotations (62%), showing that continued soybean growth led to a greater proliferation of fast-growing rhizobia. Application of farmyard manure did not change the proportion of slow growers. The proportion of slow growers was ∼15% more in winter compared with the summer populations. The slow growers were symbiotically superior, producing greater dry matter and nodule mass (+12%), with more biologically fixed nitrogen (+18%) than the fast growers. Results highlight the importance of crop rotation with cereals, application of organic amendments along with chemical fertilizers and selection of slow-growing rhizobia as inoculants. [ABSTRACT FROM AUTHOR]

Studies on the role of nickel (Ni) in photosynthetic and antioxidant metabolism, as well as in flavonoid synthesis and biological fixation nitrogen in cowpea crop are scarce. The aim of this study was to elucidate the role of Ni in metabolism, photosynthesis and nodulation of cowpea plants. A completely randomized experiment was performed in greenhouse, with cowpea plants cultivated under 0, 0.5, 1, 2, or 3 mg kg−1 Ni, as Ni sulfate. In the study the following parameters were evaluated: activity of urease, nitrate reductase, superoxide dismutase, catalase and ascorbate peroxidase; concentration of urea, n-compounds, photosynthetic pigments, flavonoids, H 2 O 2 and MDA; estimative of gas exchange, and biomass as plants, yield and weight of 100 seeds. At whole-plant level, Ni affected root biomass, number of seeds per pot, and yield, increasing it at 0.5 mg kg−1 and leading to inhibition at 2–3 mg kg−1 (e.g. number of seeds per pot and nodulation). The whole-plant level enhancement by 0.5 mg Ni kg−1 occurred along with increased photosynthetic pigments, photosynthesis, ureides, and catalase, and decreased hydrogen peroxide concentration. This study presents fundamental new insights regarding Ni effect on N metabolism, and nodulation that can be helpful to increase cowpea yield. Considering the increasing population and its demand for staple food, these results contribute to the enhancement of agricultural techniques that increase crop productivity and help to maintain human food security. • Ni induces hormesis in yield and biomass endpoints in cowpea. • Among other physiological mechanisms revealed, low-dose Ni decreases ROS. • Low-dose Ni also increases chlorophylls, photosynthesis, ureides, and catalase activity. [ABSTRACT FROM AUTHOR]

[Display omitted] Inga vera and Lysiloma tree legumes form nodules with Bradyrhizobium spp. from the japonicum group that represent novel genomospecies, for which we describe here using genome data, symbiovars lysilomae, lysilomaefficiens and ingae. Genes encoding Type three secretion system (TTSS) that could affect host specificity were found in ingae but not in lysilomae nor in lysilomaefficiens symbiovars and uptake hydrogenase hup genes (that affect nitrogen fixation) were observed in bradyrhizobia from the symbiovars ingae and lysilomaefficiens. nolA gene was found in the symbiovar lysilomaefficiens but not in strains from lysilomae. We discuss that multiple genes may dictate symbiosis specificity. Besides, toxin-antitoxin genes were found in the symbiosis islands in bradyrhizobia from symbiovars ingae and lysilomaefficiens. A limit (95%) to define symbiovars with nifH gene sequences was proposed here. [ABSTRACT FROM AUTHOR]

This study assesses the effect of seed osmopriming with PEG (−0.6 MPa) on growth and physiological parameters in six symbiotic combinations involving two Moroccan alfalfa populations Adis-Tata (Ad) and Demnate2 (Dm2) and an American Moapa (Mo) variety inoculated with RcRh09 and Sinorhizobium meliloti (Rm1021) strains. Inoculated plants were submitted to water deficit consisting in 40% field capacity (FC) of substrate versus 80% FC for the controls during five weeks. The results showed that seed priming increased growth, leaf area, plant height and nodulation in the tested combinations under water deficit. Physiologically, the priming increased the photosystem II (PSII) efficiency, stomata closure, and relative water content as well as nitrogen fixation and P and K + uptake under this constraint. The combinations Ad-RcRh09, Ad-Rm1021 and Dm2-RcRh09 from primed seeds showed higher growth and K + accumulation than all of the other combinations. They maintained also important levels of F v /F m ratio, ETR and TF m as well as nitrogen and phosphorus in their leaves under drought stress, resulting in increase of their drought tolerance. Overall osmopriming was effective in the enhancement of nodulation and drought tolerance in almost all of the studied combinations. [ABSTRACT FROM AUTHOR]

Roots of leguminous plants perceive Nod factor signals, and then root hair deformation responses such as swelling and curling are activated. However, very little is known about the molecular mechanisms of such root hair deformation. We have previously shown that LjROP6, a member of the Rho family of small GTPases, was identified as an NFR5 ( N od F actor R eceptor 5 )-interacting protein and participated in symbiotic nodulation in Lotus japonicus . In this study, we identified ten LjROP GTPases including LjROP6, and they were distributed into groups II, III, IV but not group I by phylogenetic analysis. The expression profiles of ten LjROP genes during nodulation were examined. LjROP6 belonged to group IV and interacted with NFR5 in a GTP-dependent manner. Overexpression of either wild-type ROP6 or a constitutively active mutant (ROP6-CA) generated root hair tip growth depolarization, while overexpression of a dominant negative mutant (ROP6-DN) exhibited normal root hair growth. After inoculating with Mesorhizobium loti or adding Nod factors to hairy roots, overexpression of ROP6 and ROP6-CA exhibited extensive root hair deformation, while overexpression of ROP6-DN inhibited root hair deformation. The infection event and nodule number were increased in ROP6 and ROP6-CA overexpressing transgenic plants; but decreased in ROP6-DN overexpressing transgenic plants. These studies provide strong evidence that ROP6 GTPase, which binds NFR5 in a GTP-dependent manner, is involved in root hair development as well as root hair deformation responses induced by NFs in the early stage of symbiotic interaction in L. japonicus . [ABSTRACT FROM AUTHOR]

High sugar ryegrasses (HSG) have been developed to improve the uptake, digestion and nitrogen (N)-utilisation of grazing stock, with the potential to increase production yields and benefit climate by reducing methane (CH 4 ) and nitrous oxide (N 2 O) emissions from livestock farming. In this study, the effects of tropospheric ozone pollution on the seasonal growth dynamics of HSG pasture mesocosms containing Lolium perenne cv. AberMagic and Trifolium repens cv. Crusader were investigated. Species-specific ozone (O 3 ) dose-response relationships (seasonal means: 35, 41, 47, 51, 59 & 67 ppb) based on the Phytotoxic Ozone Dose (PODy) were constructed for above and below ground biomass, injury, N-fixation and forage quality. The dynamics of effects of ozone exposure on HSG pasture changed over the course of a season, with the strongest responses occurring in the first 4–8 weeks. Overall, strong negative responses to ozone flux were found for root biomass, root nodule mass and N-fixation rates, and ozone adversely impacted a range of forage quality parameters including total sugar content and relative and consumable food values. These results indicate that increasing ozone pollution could decrease the N-use efficiency and reduce the sugar content of managed pasture, and thereby partially detract from some of the suggested benefits of HSG. [ABSTRACT FROM AUTHOR]

Arbuscular mycorrhizal fungi (AMF) improve functioning of legume- Rhizobium symbiosis under salinity. However, plant responses to mycorrhization vary depending on the plant and fungal species. The current study aimed to compare the effectiveness of a native inoculum from saline soil and two exotic isolates, Funneliformis mosseae and Rhizophagus irregularis on two Cajanus cajan (pigeonpea) genotypes (Paras, Pusa 2002) subjected to NaCl stress. Salinity depleted nodulation and nutrient status in both genotypes with higher negative effects in Paras. Although all AM fungi improved growth, R. irregularis performed better by promoting higher biomass accumulation, nodulation, N 2 fixation and N, P uptake which correlated with higher AM colonization. R. irregularis inoculated plants also accumulated higher trehalose in nodules due to decreased trehalase and increased trehalose-6-P synthase, trehalose-6-phosphatase activities. The results suggest that higher stability of R. irregularis -pigeonpea symbiosis under salt stress makes it an effective ameliorator for overcoming salt stress in pigeonpea. [ABSTRACT FROM AUTHOR]

Despite the recognition that Rhizobium leguminosarum sv. viciae is the most common symbiont of Vicia species worldwide, there is no available information on rhizobia nodulating native Vicia species in Sweden. We have therefore studied the genetic diversity and phylogeny of root nodule bacteria isolated from V. cracca , V. hirsuta , V. sepium , V. tetrasperma and V. sylvatica growing in different locations in Sweden as well as an isolate each from V. cracca in Tromsø, Norway, and V. multicaulis in Siberia, Russia. Out of 25 isolates sampled from the six Vicia species in 12 different locations, there were 14 different genotypes based on the atpD , recA and nodA gene phylogenies. All isolates were classified into Rhizobium leguminosarum sv. viciae group based on the concatenated atpD and recA phylogeny and the nodA phylogeny. [ABSTRACT FROM AUTHOR]

Strigolactones (SLs) are multifunctional molecules acting as modulators of plant responses under nutrient deficient conditions. One of the roles of SLs is to promote beneficial association with arbuscular mycorrhizal (AM) fungi belowground under such stress conditions, mainly phosphorus shortage. Recently, a role of SLs in the Rhizobium -legume symbiosis has been also described. While SLs’ function in AM symbiosis is well established, their role in the Rhizobium -legume interaction is still emerging. Recently, SLs have been suggested to stimulate surface motility of rhizobia, opening the possibility that they could also act as molecular cues. The possible effect of SLs in the motility in the alfalfa symbiont Sinorhizobium meliloti was investigated, showing that the synthetic SL analogue GR24 stimulates swarming motility in S. meliloti in a dose-dependent manner. On the other hand, it is known that SL production is regulated by nutrient deficient conditions and by AM symbiosis. Using the model alfalfa- S. meliloti , the impact of phosphorus and nitrogen deficiency, as well as of nodulation on SL production was also assessed. The results showed that phosphorus starvation promoted SL biosynthesis, which was abolished by nitrogen deficiency. In addition, a negative effect of nodulation on SL levels was detected, suggesting a conserved mechanism of SL regulation upon symbiosis establishment. [ABSTRACT FROM AUTHOR]

Common bean ( Phaseolus vulgaris L.) has the capacity to fix atmospheric N 2 into the biosphere through its aptitude to establish a symbiosis with soil rhizobia. In order to search for environmental constraints that might limit this symbiosis a nodular diagnosis was performed in eighteen field sites chosen with farmers of the Setif agro-ecosystem. Common bean was used as a model grain-legume with six recombinant inbred lines (RILs) and one local genotype Djadida. At flowering stage, the biomass of plants and nodules was determined by excavating 20 cm in depth and around the root-system of ten plants per genotype and per site. The results indicate a large spatial variation in nodulation and growth between genotypes, and the distribution of soils in four soil clusters, based on physico-chemical properties. The inhibition of nodulation of all genotypes in soil of clusters A and B was associated with high residual soil mineral nitrogen (2.23 ± 0.49 g kg −1 soil). The low nodulation of all genotypes in the phosphorus (P) deficient soil of cluster C (6.73 ± 3.63 mg kg −1 soil) was partly compensated by increasing their efficiency in use of the rhizobial symbiosis (13%), estimated by the slope of the regression model of shoot biomass as a function of nodule biomass. Interestingly, significant correlations were found between nodulation of all genotypes and Olsen-P content in soils of clusters C (R 2 = 0.97, P < 0.001) and D (R 2 = 0.94, P < 0.05). It is concluded that the RILs selected for their efficient use of P for symbiotic nitrogen fixation show the highest nodulation and growth and that the nodular diagnosis can be used to assess the growth response of N 2 -dependent grain-legume to soils with low availabilities of N and P. [ABSTRACT FROM AUTHOR]

In a previous study, we identified the novel opa22 (DQ199621) gene in Mesorhizobium huakuii 7653R, which is required for nodulation. In this study, we determined that opa22 -homologous genes exist in the multiple species of bacteria in Rhizobiales. A conserved domain analysis revealed that the Opa22 homologues are a group of β-barrel outer membrane proteins, belonging to the surface antigen superfamily. A phylogenetic tree was constructed based on the Opa22 homologues and showed that Opa22 supports the validity of the 16S rRNA gene for phylogenic classification. Isogenic mutants were made for each homologue of Sinorhizobium medicae USDA1037, Rhizobium leguminosarum bv. trifolii LPR5045, and Bradyrhizobium japonicum USDA2110 via double-cross replacement. Plant experiments showed that the mutants had lost nodulation ability with their original host plants, and that this symbiotic phenotype could be restored by functional complementation. Interestingly, opa22 from M. huakuii 7653R partially restored nodulation ability of S. medicae isogenic mutant, but not that of B. japonicum isogenic mutant. Taken together, these results indicate that Opa22 is phylogenetically conserved in rhizobial families and is essential for root nodule formation in some species. [ABSTRACT FROM AUTHOR]

Nodular growth behavior with the inclusion of impurity particles in copper electrorefining was investigated herein by quantitative analyses of impurity elements inside nodules, observations of crystal structures, and numerical simulations of natural convection based on the tertiary current distribution. Impurity contents were higher in the upper half of the nodule than in either the lower half or electrolytic copper with non-nodulous growth. Impurity particles, such as suspended slime, were considered to be preferentially taken into the upper part of nodules due to frequent collisions with the upper part as they circulated along the convection vortex that emerged above the nodule. The inclusion of impurity particles changed the electrodeposition morphology and growth direction, and eventually produced granular irregularities and buds of new nodules on the upper surface of the initial nodule. [Display omitted] • Nodules contained high levels of impurities, especially in their upper half. • Each nodule evokes upward flow associated with a vortex in the solution. • Due to the vortex, slime particles are taken into the upper part of the nodule. • Inclusion of the particles promotes 3D growth and subsequent irregular deposition. [ABSTRACT FROM AUTHOR]

Noduler, an immune protein that mediates nodule formation by binding to specific bacteria and hemocytes was previously reported in the wild tasar silkworm, Antheraea mylitta . However, the molecular mechanism underlying nodulation in lepidopterans remains unclear. The present study is performed to investigate the functional connection between Noduler with various signalling pathways. It was observed that Noduler is an upstream factor in the phenoloxidase cascade and its knockdown has no direct effect on Toll/Imd pathway inducible genes. Additionally, Noduler was shown to stimulate cell proliferation via activation of p38 mitogen-activated protein kinase (MAPK). Inhibition of p38 in the infected hemocytes cultured in vitro resulted in reduced cell proliferation and melanization. These results suggest that Noduler mediates nodulation via p38/MAPK signalling. This is the first report implicating the p38 MAPK signalling pathway in the nodulation response of insects. [ABSTRACT FROM AUTHOR]

In order to better understand how mixed crop cultures mitigate stressful conditions, this study aims to highlight the beneficial effect of the intercropping legume-cereal in enhancing soil phosphorus (P) availability for plant growth and productivity in a P-deficient soil of a northern Algerian agroecosystem. To address this question, common bean ( Phaseolus vulgaris L. cv. El Djadida) and maize ( Zea mays L. cv. Filou), were grown as sole- and inter-crops in two experimental sites; S1 (P-deficient) and S2 (P-sufficient) during two growing seasons (2011 and 2012). Growth, nodulation and grain yield were assessed and correlated with the rhizosphere soil P availability. Results showed that P availability significantly increased in the rhizosphere of both species, especially in intercropping under the P-deficient soil conditions. This increase was associated with high efficiency in use of the rhizobial symbiosis (high correlation between plant biomass and nodulation), plant growth and resource (nitrogen (N) and P) use efficiency as indicated by higher land equivalent ratio (LER > 1) and N nutrition index (for maize) in intercropping over sole cropping treatments. Moreover, the rhizosphere P availability and nodule biomass were positively correlated ( r 2 = 0.71, p < 0.01 and r 2 = 0.62, p < 0.01) in the intercropped common bean grown in the P-deficient soil during 2011 and 2012. The increased P availability presumably improved biomass and grain yield in intercropping, though it mainly enhanced grain yield in intercropped maize. Our findings suggest that modification in the intercropped common bean rhizosphere-induced parameters facilitated P uptake, plant biomass and grain yield for the intercropped maize under P-deficiency conditions. [ABSTRACT FROM AUTHOR]

Soybean ( Glycine max (L.) Merr.) is able to fix atmospheric nitrogen in symbiosis with the bacteria Bradyrhizobium japonicum . Because these bacteria are not native in European soils, soybean seeds must be inoculated with Bradyrhizobium strains before sowing to fix nitrogen and meet their yield potential. In Central Europe soybean cultivation is still quite new and breeding of early maturing soybean varieties adapted to cool growing conditions has just started. Under these low temperature conditions in Central Europe the inoculation with different, commercially available Bradyrhizobium inoculants has resulted in unsatisfactory nodulation. The aim of this study was: (i) to test the ability of commercially available inoculants to maximize soybean grain yield, protein content and protein yield, (ii) to study the interaction of different inoculants with different soybean varieties for two different sites in Germany under cool growing conditions over three years and (iii) to determine the variability of biological nitrogen fixation. Field trials were set up on an organically managed site at the Hessische Staatsdomäne Frankenhausen (DFH) and on a conventionally managed site in Quedlinburg (QLB) for three consecutive seasons from 2011 to 2013. Three early maturing soybean varieties—Merlin, Bohemians, Protina—were tested in combination with four different Bradyrhizobium inoculants—Radicin No.7, NPPL-Hi Stick, Force 48, Biodoz Rhizofilm—and compared with a non-inoculated control. Effective inoculation with Bradyrhizobium strains increased grain yield, protein content and protein yield by up to 57%, 26% and 99%, respectively. Grain yield, protein content and protein yield were generally higher in DFH. Average grain yield was 1634 kg ha −1 in QLB (2012–2013) and 2455 kg ha −1 in DFH (2011–2013), average protein content was 386 g kg −1 in QLB and 389 g kg −1 in DFH and average protein yield was 650 kg ha −1 in QLB and 965 kg ha −1 in DFH. The percentage of nitrogen derived from air (Ndfa) ranged between 40% and 57%. Soybeans inoculated with Radicin No. 7 failed to form nodules, and crop performance was identical to the non-inoculated control. Biodoz Rhizofilm, NPPL Hi-Stick and Force 48 are suitable for soybean cultivation under cool growing conditions in Germany. Interactions between soybean variety and inoculant were significant for protein content and protein yield at both sites, but not for nodulation, grain yield, thousand kernel weight and Ndfa. The variety Protina in combination with the inoculant Biodoz Rhizofilm can be recommended for tofu for both tested sites, while Merlin and Protina in combination with Biodoz Rhizofilm are recommended for animal fodder production in DFH. Animal fodder production was not profitable in QLB due to low protein yields. [ABSTRACT FROM AUTHOR]