Nodulation Research Articles

Rhizobia-legume symbiosis mediates direct and indirect interactions between plants, herbivores and their parasitoids

Microorganisms associated with plant roots significantly impact the quality and quantity of plant defences. However, the bottom-up effects of soil microbes on the aboveground multitrophic interactions remain largely under studied. To address this gap, we investigated the chemically-mediated effects of nitrogen-fixing rhizobia on legume-herbivore-parasitoid multitrophic interactions. To address this, we initially examined the cascading effects of the rhizobia bean association on herbivore caterpillars, their parasitoids, and subsequently investigated how rhizobia influence on plant volatiles and extrafloral nectar. Our goal was to understand how these plant-mediated effects can affect parasitoids. Lima bean plants (Phaseoulus lunatus) inoculated with rhizobia exhibited better growth, and the number of root nodules positively correlated with defensive cyanogenic compounds. Despite increase of these chemical defences, Spodoptera latifascia caterpillars preferred to feed and grew faster on rhizobia-inoculated plants. Moreover, the emission of plant volatiles after leaf damage showed distinct patterns between inoculation treatments, with inoculated plants producing more sesquiterpenes and benzyl nitrile than non-inoculated plants. Despite these differences, Euplectrus platyhypenae parasitoid wasps were similarly attracted to rhizobia- or no rhizobia-treated plants. Yet, the oviposition and offspring development of E. platyhypenae was better on caterpillars fed with rhizobia-inoculated plants. We additionally show that rhizobia-inoculated common bean plants (Phaseolus vulgaris) produced more extrafloral nectar, with higher hydrocarbon concentration, than non-inoculated plants. Consequently, parasitoids performed better when fed with extrafloral nectar from rhizobia-inoculated plants. While the overall effects of bean-rhizobia symbiosis on caterpillars were positive, rhizobia also indirectly benefited parasitoids through the caterpillar host, and directly through the improved production of high quality extrafloral nectar. This study underscores the importance of exploring diverse facets and chemical mechanisms that influence the dynamics between herbivores and predators. This knowledge is crucial for gaining a comprehensive understanding of the ecological implications of rhizobia symbiosis on these interactions.

Differences in Fatty Acid and Central Carbon Metabolite Distribution among Different Tissues of Alfalfa–Rhizobia Symbiotic System

Fatty acid and central carbon metabolism are crucial energy metabolism reactions. However, to date, few studies have examined their distribution characteristics within the alfalfa–rhizobia symbiotic system. To clarify the distributional differences and accumulation rates of fatty acids and central carbon with this system, we measured the plant phenotype, nodule formation, nitrogen fixation capacity, and key nitrogen metabolism enzyme activities of Medicago sativa ‘Gannong No. 9’ 35 days post-inoculation (dpi) with Sinorhizobia meliloti LL11. Additionally, we employed targeted metabolomics to analyze central carbon and fatty acid metabolites in various tissue samples of symbiotic and control (C.K.) plants, as well as in S. meliloti LL11. We found that plant height; root length; aboveground fresh and dry weights; underground fresh and dry weights; and nitrate reductase, nitrogen reductase, glutamine synthetase, and glutamate synthase activities were significantly higher in the leaves and roots of symbiotic plants than in those of C.K. plants. Compared to symbiotic plants, C.K. plants exhibited higher total central carbon and fatty acid metabolite content, accounting for 38.61% and 48.17% of C.K. plants, respectively. We detected 32 central carbon and 40 fatty acid metabolites in S. meliloti LL11, with succinate (343,180.8603 ng·mL−1) and hexadecanoic acid (4889.7783 ng·mL−1) being the most. In both symbiotic and C.K. plants, central carbon metabolite was considerably higher than the fatty acid metabolite central. Moreover, the carbon metabolites found in symbiotic plants were primarily distributed in pink nodule roots (PNRs), with malate exhibiting the highest content (4,800,612.3450 ng·g−1), accounting for 53.09% of total central carbon metabolite content. Fatty acid metabolites were mainly found in pink root nodules (P.N.s), which are sites of nitrogen fixation. Trans-10-nonadecenoic acid and hexadecanoic acid exhibited the highest contents, comprising >15% of the total fatty acid metabolite content. We found that petroselaidic acid is only present in P.N., which seems to be closely related to the nitrogen fixation reaction in P.N. In general, symbiotic plants transfer central carbon metabolites to nodules via PNRs to drive nitrogen fixation. However, in P.N.s, these metabolites are limited, leading to accumulation in PNRs. Fatty acid metabolites, crucial for nitrogen fixation, are prevalent in P.N.s. Conversely, C.K. plants without nitrogen fixation distribute these metabolites primarily to the stems, emphasizing growth. This study provides new insights into the energy metabolism of symbiotic nitrogen fixation.

The influence of metal nanocarboxylates on the nitrogen-fixing activity of symbiotic soybean systems grown under field conditions

Background. Numerous scientific and industrial studies have proven the high effectiveness of using micronutrients in nanoscale form in agricultural crop cultivation technologies. Among them, special attention is drawn to soybeans, which hold a leading position in terms of sown areas among other leguminous crops in the country. They can provide up to 70 % of their own nitrogen needs through the fixation of its molecular form from the atmosphere in symbiosis with Bradyrhizobium japonicum nodulating bacteria. New methods of molecular biology, biotechnology, and genetic engineering, along with classical methods of microbiology, plant physiology, genetics, and agrochemistry, allow for addressing both fundamental questions regarding the characteristics of formation and functioning of legume-rhizobial systems, and practical approaches to correcting the interactions between symbiotic partners with the aim of creating highly effective symbioses. Therefore, research aimed at significant increasing the current level of biological nitrogen fixation and adapting symbiotic systems to negative environmental factors is currently relevant. The use of nanotechnology, in particular, the study of the effect of iron, germanium, and cobalt nanocarboxylates on the formation and functioning of the soybean-rhizobial symbiosis under field conditions in combination with seed inoculation with rhizobial bacteria may be promising. Materials and Methods. The objects of the investigation were symbiotic systems created with the participation of the Almaz variety of soybean and the Bradyrhizobium japonicum B1-20 rhizobacteria, and with the introduction of nanocarboxylates of iron (Fe), germanium (Ge) and cobalt (Co) into their cultivation medium. Physiological, microbiological, biochemical, and statistical research methods were used. Results. It was found that under field conditions, before the pod formation stage, the vegetative mass of soybean plants inoculated with rhizobial bacteria with the introduction of nanoparticles of carboxylates of iron, germanium, or cobalt into their cultivation medium was at the level of control plants or slightly exceeded them. It has been shown that under the effects of chelated micronutrients, the number of root nodules increased compared to control plants during the flowering and pod formation stages, and their mass was greater from the three trifoliate leaf stage, which ensured efficient functioning of the legume-rhizobial symbiosis. It has been noted that the used metal nanocarboxylates promote active functioning of the symbiotic apparatus in soybean plants, as an increase in nitrogen-fixing activity was observed at the stages of three trifoliate leaf development and flowering, ranging from 26–70 % depending on the microelement used. Conclusions. During field cultivation of soybeans, the effectiveness of pre-sowing seed inoculation with Bradyrhizobium japonicum B1-20 rhizobia was demonstrated through the introduction of iron, germanium, or cobalt nanocarboxylates into their cultivation medium. This opens up opportunities for increasing the efficiency of symbiotic systems of soybeans.

Effect of Organic Manures and Bio-Fertilizers on Growth, Yield and Quality of Kharif Cowpea [Vigna unguiculata (L.)

A field experiment was conducted at Agronomy Instructional Farm of SDAU, Sardarkrushinagar, Gujarat, India during kharif season of 2020-2021. The experiment consisting nine treatments viz., T1-Absolute control, T2-100% RDF (20 kg N + 40 kg P2O5 ha-1), T3- FYM @ 5.0 t ha-1, T4-FYM @ 2.5 t ha-1 + Rhizobium + PSB, T5-vermicompost @ 2.0 t ha-1, T6-vermicompost @ 1.0 t ha-1 + Rhizobium + PSB, T7-castor cake @ 2.0 t ha-1, T8-castor cake @ 1.0 t ha-1 + Rhizobium + PSB, T9-Ghan Jeevamrut @ 250 kg ha-1 at sowing time + Seed treatment with Beejamrut @ 200 ml kg-1 seed+ Jeevamrut @ 500 lit ha-1 with irrigation at sowing and 30 DAS were tested in randomized block design with four replications. The result revealed that the application of T8-castor cake @ 1.0 t ha-1 + Rhizobium + PSB showed significant improvement on plant height, number of branches per plant, dry matter accumulation, number of pods per plant, number of seeds per pod, length of pod and seed yield per plant whereas, application of T4-FYM @ 2.5 t ha-1 + Rhizobium + PSB gave significantly higher number of root nodules per plant, fresh and dry weight of root nodules. it is concluded that higher yield from kharif cowpea could be obtained by applying either castor cake @ 1.0 t ha-1 or FYM @ 2.5 t ha-1 along with Rhizobium + PSB in loamy sand soils of North Gujarat.

Cell-layer specific roles for gibberellins in nodulation and root development.

Gibberellins (GA) have a profound influence on the formation of lateral root organs. However, the precise role this hormone plays in the cell-specific events during lateral root formation, rhizobial infection and nodule organogenesis, including interactions with auxin and cytokinin (CK), is not clear. We performed epidermal- and endodermal-specific complementation of the severely GA-deficient na pea (Pisum sativum) mutant with Agrobacterium rhizogenes. Gibberellin mutants were used to examine the spatial expression pattern of CK (TCSn)- and auxin (DR5)-responsive promoters and hormone levels. We found that GA produced in the endodermis promote lateral root and nodule organogenesis and can induce a mobile signal(s) that suppresses rhizobial infection. By contrast, epidermal-derived GA suppress infection but have little influence on root or nodule development. GA suppress the CK-responsive TCSn promoter in the cortex and are required for normal auxin activation during nodule primordia formation. Our findings indicate that GA regulate the checkpoints between infection thread (IT) penetration of the cortex and invasion of nodule primordial cells and promote the subsequent progression of nodule development. It appears that GA limit the progression and branching of IT in the cortex by restricting CK response and activate auxin response to promote nodule primordia development.

Complete genome sequence of Bradyrhizobium sp. 62B, a native nitrogen-fixing rhizobium isolated from peanut nodules.

We present the complete genome sequence of Bradyrhizobium sp. 62B, a strain isolated from the root nodules of peanut plants that grow in central Argentina. The genome consists of 8.15 Mbp, distributed into a chromosome of 7.29 Mbp and a plasmid of 0.86 Mbp.

High Frankia abundance and low diversity of microbial community are associated with nodulation specificity and stability of sea buckthorn root nodule.

Actinorhizal symbioses are gaining attention due to the importance of symbiotic nitrogen fixation in sustainable agriculture. Sea buckthorn (Hippophae L.) is an important actinorhizal plant, yet research on the microbial community and nitrogen cycling in its nodules is limited. In addition, the influence of environmental differences on the microbial community of sea buckthorn nodules and whether there is a single nitrogen-fixing actinomycete species in the nodules are still unknown. We investigated the diversity, community composition, network associations and nitrogen cycling pathways of the microbial communities in the root nodule (RN), nodule surface soil (NS), and bulk soil (BS) of Mongolian sea buckthorn distributed under three distinct ecological conditions in northern China using 16S rRNA gene and metagenomic sequencing. Combined with the data of environmental factors, the effects of environmental differences on different sample types were analyzed. The results showed that plants exerted a clear selective filtering effect on microbiota, resulting in a significant reduction in microbial community diversity and network complexity from BS to NS to RN. Proteobacteria was the most abundant phylum in the microbiomes of BS and NS. While RN was primarily dominated by Actinobacteria, with Frankia sp. EAN1pec serving as the most dominant species. Correlation analysis indicated that the host determined the microbial community composition in RN, independent of the ecological and geographical environmental changes of the sea buckthorn plantations. Nitrogen cycle pathway analyses showed that RN microbial community primarily functions in nitrogen fixation, and Frankia sp. EAN1pec was a major contributor to nitrogen fixation genes in RN. This study provides valuable insights into the effects of eco-geographical environment on the microbial communities of sea buckthorn RN. These findings further prove that the nodulation specificity and stability of sea buckthorn root and Frankia sp. EAN1pec may be the result of their long-term co-evolution.

Occurrence of diverse plant growth promoting bacteria in soybean [Glycine max (L.) Merrill] root nodules and their prospective role in enhancing crop yield

Root nodules are the small nitrogen fixing factories housing endophytic bacteria. In this study, seventeen endophytic bacteria were isolated from the root nodules of soybean, which were subjected to the in vitro testing of plant growth-promoting characteristics. Bacterial isolates were able to produce indole acetate ranging from 0.7 to 18.3 μg ml−1. Five isolates were able to solubilize inorganic phosphate, in which NSB15 exhibited maximum solubilization potential. All bacterial isolates showed growth on nitrogen-free mineral media, except NSB7 and NSB11. Bacterial isolates were able to form biofilm, therein NSB10 displayed a maximum efficiency of 2.6 at OD570 nm. Seven isolates were positive for cellulase activity and five for pectinase activity. Based on the in vitro characterization, five efficient endophytic bacteria were phylogenetically identified by 16 S rRNA sequence analysis. NSB5 showed 99.52% identity with different species of Pseudomonas, and NSB9 showed 99.68% sequence identity with Bradyrhizobium. NSB15 and NSB16 showed maximum sequence identity with Comamonas terrigena, and NSB17 showed 100% sequence identity with Pseudomonas indica. This study represents the first international report of C. terrigena and P. indica in soybean host. In a pot experiment, inoculation of NSB9 and NSB17 significantly increased plant dry weight by 29% and 35%, respectively, compared to control. In a field trial, inoculation of NSB9, NSB15 and NSB17 significantly improved grain yield by 30%, 31% and 45%, respectively, compared to control. Conclusively, Bradyrhizobium sp. NSB9, C.terrigena NSB15 and P.indica NSB17 could be used as biofertilizers to improve the yield of soybean in a sustainable manner.

Phosphorylation of the alpha-I motif in SYMRK drives root nodule organogenesis

Symbiosis receptor-like kinase SYMRK is required for root nodule symbiosis between legume plants and nitrogen-fixing bacteria. To understand symbiotic signaling from SYMRK, we determined the crystal structure to 1.95 Å and mapped the phosphorylation sites onto the intracellular domain. We identified four serine residues in a conserved "alpha-I" motif, located on the border between the kinase core domain and the flexible C-terminal tail, that, when phosphorylated, drives organogenesis. Substituting the four serines with alanines abolished symbiotic signaling, while substituting them with phosphorylation-mimicking aspartates induced the formation of spontaneous nodules in the absence of bacteria. These findings show that the signaling pathway controlling root nodule organogenesis is mediated by SYMRK phosphorylation, which may help when engineering this trait into non-legume plants.

Multi-locus genome-wide association study reveal genomic regions underlying root system architecture traits in Ethiopian sorghum germplasm.

The identification of genomic regions underlying the root system architecture (RSA) is vital for improving crop abiotic stress tolerance. To improve sorghum (Sorghum bicolor L. Moench) for environmental stress tolerance, information on genetic variability and genomic regions linked to RSA traits is paramount. The aim of this study was, therefore, to investigate common quantitative trait nucleotides (QTNs) via multiple methodologies and identify genomic regions linked to RSA traits in a panel of 274 Ethiopian sorghum accessions. Multi-locus genome-wide association study was conducted using 265,944 high-quality single nucleotide polymorphism markers. Considering the QTN detected by at least three different methods, a total of 17 reliable QTNs were found to be significantly associated with root angle, number, length, and dry weight. Four QTNs were detected on chromosome SBI-05, followed by SBI-01 and SBI-02 with three QTNs each. Among the 17 QTNs, 11 are colocated with previously identified root traits quantitative trait loci and the remaining six are genome regions with novel genes. A total of 118 genes are colocated with these up- and down-streams of the QTNs. Moreover, five QTNs were found intragenic. These QTNs are S5_8994835 (number of nodal roots), S10_55702393 (number of nodal roots), S1_56872999 (nodal root angle), S9_1212069 (nodal root angle), and S5_5667192 (root dry weight) intragenic regions of Sobic.005G073101, Sobic.010G198000, Sobic.001G273000, Sobic.009G013600, and Sobic.005G054700, respectively. Particularly, Sobic.005G073101, Sobic.010G198000, and Sobic.009G013600 were found responsible for the plant growth hormone-induced RSA. These genes may regulate root development in the seedling stage. Further analysis on these genes might be important to explore the genetic structure of RSA of sorghum.

Melatonin mitigation of herbicide-induced injury to guar crop improves nodulation

The guar plant, or cluster bean, forms a weak symbiosis with rhizobia, and it is sensitive to herbicides. We hypothesized that application of melatonin to guar seeds, leaves, or both protect against metabolic injury from eight herbicides, and strengthening the symbiosis. Imazethapyr and 2,4-DB did not injure guar and its rhizobium partner. Root nodulation was severely damaged with pendimethalin and less with bentazon. A reduction in guar's total dry weight, which ranged from 14% with bentazon to 28% with bromoxynil, was observed, indicating metabolic stress. When no herbicide was applied, seeds coated with melatonin had no effect. When herbicides were applied, it partially mitigated herbicide-induced injury. Foliar application of melatonin protected guar completely against bentazon, bromoxynil, and oxyfluorfen, protected nodulation.

The peptide GOLVEN10 alters root development and noduletaxis in Medicago truncatula.

The conservation of GOLVEN (GLV)/ROOT MERISTEM GROWTH FACTOR (RGF) peptide encoding genes across plant genomes capable of forming roots or root-like structures underscores their potential significance in the terrestrial adaptation of plants. This study investigates the function and role of GOLVEN peptide-coding genes in Medicago truncatula. Five out of fifteen GLV/RGF genes were notably upregulated during nodule organogenesis and were differentially responsive to nitrogen deficiency and auxin treatment. Specifically, the expression of MtGLV9 and MtGLV10 at nodule initiation sites was contingent upon the NODULE INCEPTION transcription factor. Overexpression of these five nodule-induced GLV genes in hairy roots of M. truncatula and application of their synthetic peptide analogues led to a decrease in nodule count by 25-50%. Uniquely, the GOLVEN10 peptide altered the positioning of the first formed lateral root and nodule on the primary root axis, an observation we term 'noduletaxis'; this decreased the length of the lateral organ formation zone on roots. Histological section of roots treated with synthetic GOLVEN10 peptide revealed an increased cell number within the root cortical cell layers without a corresponding increase in cell length, leading to an elongation of the root likely introducing a spatiotemporal delay in organ formation. At the transcription level, the GOLVEN10 peptide suppressed expression of microtubule-related genes and exerted its effects by changing expression of a large subset of Auxin responsive genes. These findings advance our understanding of the molecular mechanisms by which GOLVEN peptides modulate root morphology, nodule ontogeny, and interactions with key transcriptional pathways.

Complete genome sequences of Rhizobium sp. strain SL42 and Hydrogenophaga sp. strain SL48, microsymbionts of Amphicarpaea bracteata

This study comprehensively analyzed two distinct rhizobacterial strains, Rhizobium sp. SL42 and Hydrogenophaga sp. SL48, through whole genome de novo sequencing. Isolated from root nodules of Amphicarpaea bracteata, a native legume related to soybean, they were selected to explore beneficial rhizobacteria from native plant relatives. Utilizing Illumina and Nanopore sequencers and MaSuRCA assembly, their complete genetic information was elucidated. Rhizobium sp. SL42 has a 4.06 Mbp circular chromosome and two plasmids with 60% GC content, while Hydrogenophaga sp. SL48 exhibits a 5.43 Mbp circular chromosome with 65% GC content. Genetic analysis identified them as new species, supported by ANI values (77.72% for SL42 and 83.39% for SL48) below the threshold. The genomic analysis unraveled a plethora of genes encoding diverse metabolic functions, secretion systems for substance transport, quorum sensing for coordination, and biosynthetic gene clusters suggesting the production of bioactive compounds. These functional properties contribute to plant growth stimulation, reflecting the symbiotic relationship of rhizobacteria with plants, potentially involving nitrogen fixation and growth-promoting compounds. This research contributes valuable knowledge about plant-microbe interactions and plant growth promotion by these two strains of rhizobacteria.

Born of fire, borne by water – Review of paleo-environmental conditions, floristic assemblages and modes of preservation as evidence of distinct silicification pathways for silcrete floras in Australia

Fossil plants in sub-basaltic andfluvial silcretes differ in their geological setting, silica source, taphonomy, preservation and the plants and communities represented: these factors collectively indicate distinct silicification pathways. This review shows that the floras in sub-basaltic silcretes are mostly autochthonous, being derived from the local vegetation, whereas the floras in inland fluvial silcretes are transported andallochthonous. The floras in both are three-dimensionally preserved. The plantsin sub-basaltic silcretes areusually permineralised, preserving internal anatomy and cellular morphology, whereas the plants in inland fluvial silcretes occur as moulds/impressions that may preserve epidermal andsurface features. Both types of silcrete floras offer insights into past environments and ecological drivers. Terrestrial (ground-dwelling) ferns are frequently preservedin situin sub-basaltic silcretes whilst in the inland fluvial silcretes they are represented only by pinnule fragments or abscised pinnules. The extraordinary anatomical preservation of soft tissues in sub-basaltic silcretes, e.g., exocarps of fruits, bark on wood, actively growing vegetative shoots (fern croziers) and root nodules, is evidence of rapid burial by volcanogenic sediments and subsequent silicification by silica-richgroundwaters. The source of silica was hydrothermal fluids released at the time of eruption and/or the weathering of overlying volcanics, and the acidic (humic) conditions resulting from buried plant material provided ideal geochemical conditions for silica precipitation and plantpermineralisation. The sub-basaltic silcrete floras formed contemporaneously with Eocene–Miocene volcanism in eastern Australia, whereas the formation of inland pedogenic and fluvial silcretes was probably initiated during the Paleocene–Eocene Thermal Maximum (PETM). The fine surface preservation of plants in inland fluvial silcrete floras indicates rapid burial but no organic material is preserved, probably because oxidising groundwaters stripped out the organics before silicification occurred. The comparatively less silica-rich groundwaters associated withfluvial silcretes and the sandy substrates would have further contributed to the loss of plant material.

Growth Response of Mucuna bracteata with the Application of Local Micro Organisms (LMO) of Banana Weevil

This research aims to determine the effect of concentration and duration immersion giving LOM banana weevil against the gowth of Mucuna bracteata. The research was conducted in the garden of Jalan Setia Bangun Pasar III, Sei Beras Sekata, Kecamatan sunggal, Kabupaten Deli Serdang, Sumatra utara and continued in the laboratory of the Indonesian Oil Palm Research Institute (IOPRI). This research was started in April-June 2020. This study used a randomized complete block design (RCBD) factorial. The first factor was the concentration of local microorganisms (LMO) of Banana Weevil consisting of 4 levels, namely: Without treatment, 15%, 30%, 45%. The second factor. The duration of immersion consists of 4 levels, namely: No immersion time, 15 minutes, 30 minutes, 45 minutes. Observation data were analyzed usingDuncan's Multiple Range Test with a significant 5%. The results showed that the LMO concentration of banana weevil was effective in increasing the gowth of the number of leaves 39.77, tendril length 83.14 cm, shoot fresh weight 28.54 g, and shoot dry weight 6.03 g. The duration of soaking had a significant effect on the highest number of leaves at week 3 (9.63 pieces). The interaction application of banana weevil concentration and soaking time affected the number of root nodules (40.50 gains) and root dry weight (0.73) g of theplant Mucuna bracteata.

Pea leaf weevil, Sitona lineatus (L.) (Coleoptera: Curculionidae), adult feeding preference and larval development on pulse crop varieties in Montana.

Montana accounts for approximately 45% of US dry pea production and the pea leaf weevil (PLW; Sitona lineatus (L.)) is the most common insect pest in this region. After crop emergence adult PLW feed on the foliage to mature and subsequently mate, and the soil-dwelling larvae feed and develop on the nitrogen-fixing root nodules. Producers commonly apply prophylactic insecticide treatments to the seed at planting as well as one or two post-emergent insecticide sprays to control PLW damage. To develop alternative management strategies based on integrated pest management (IPM), this field study evaluated pulse crops grown in Montana for adult feeding preference and larval development. Ten different field pea varieties, along with two faba bean, lentil and chickpea varieties, were evaluated during the 2020 and 2021 field seasons at the Montana State University Arthur H. Post Agronomy Farm. Significant PLW pest pressure was observed within the research plots during both experimental years. Field pea and faba bean were preferred by the foliage feeding adult stage, with all but one variety averaging 39.2 to 86.3 average notches per plant. The pea variety Lifter was significantly preferred over all other comparisons, averaging 142.4 and 95.0 notches per plant in 2020 and 2021, respectively. Adult PLW feeding on lentil and chickpea was minimal, averaging 3.3 to 8.2 and 0.5 to 1.6 notches per plant, respectively. Numbers of larvae were highest on the roots of pea varieties, a known reproductive host, and almost nil on lentil and chickpea roots. Faba bean is also known as reproductive host, but, unexpectedly, larval populations were also low on the two faba bean varieties. The results from this study provide some limited evidence for alternative IPM strategies for field peas based on host plant tolerance or resistance within the range of varieties tested. Adult preference and larval development of PLW varied between the different pulse crops with field peas and faba beans being the most susceptible and lentils and chickpeas being the least susceptible. Host plant resistance against PLW could provide more sustainable IPM approaches in the future. © 2024 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Pleiotropic Effects of PhaR Regulator in Bradyrhizobium diazoefficiens Microaerobic Metabolism.

Bradyrhizobium diazoefficiens can live inside soybean root nodules and in free-living conditions. In both states, when oxygen levels decrease, cells adjust their protein pools by gene transcription modulation. PhaR is a transcription factor involved in polyhydroxyalkanoate (PHA) metabolism but also plays a role in the microaerobic network of this bacterium. To deeply uncover the function of PhaR, we applied a multipronged approach, including the expression profile of a phaR mutant at the transcriptional and protein levels under microaerobic conditions, and the identification of direct targets and of proteins associated with PHA granules. Our results confirmed a pleiotropic function of PhaR, affecting several phenotypes, in addition to PHA cycle control. These include growth deficiency, regulation of carbon and nitrogen allocation, and bacterial motility. Interestingly, PhaR may also modulate the microoxic-responsive regulatory network by activating the expression of fixK2 and repressing nifA, both encoding two transcription factors relevant for microaerobic regulation. At the molecular level, two PhaR-binding motifs were predicted and direct control mediated by PhaR determined by protein-interaction assays revealed seven new direct targets for PhaR. Finally, among the proteins associated with PHA granules, we found PhaR, phasins, and other proteins, confirming a dual function of PhaR in microoxia.

Bio-Efficacy of New Herbicide Molecules for Weed Management in Grain Legumes

Grain legumes including pigeon pea, chickpea, peanut, soybean, lentil, cowpea, common bean, faba bean, pea, and horse gram are extensively cultivated globally. Higher protein content, coupled with symbiotic nitrogen-fixing bacteria in root nodules enabling nitrogen fixation, highlights their importance in minimizing fertilizer use for agricultural production systems. Legume cultivation is limited by prolonged weed interference which is managed either through mechanical, cultural, chemical, or biological methods separately or in combinations. Nevertheless, herbicides remain and will persist as a crucial and economical element in global crop cultivation. While first-generation herbicides benefit agriculture, their long-term persistence and off-target toxicity have significant negative consequences, causing harm to both the environment and humans. Moreover, weed resistance and similar chemistry enforce the demand for new modes of action. Therefore, continuous research into new herbicides is important for combating herbicide resistance and ensuring crop output. In recent years, a few herbicides with novel mechanisms of action have occurred. Plants treated with new-generation herbicides resulted in increased WCE (weed control efficiency), decreased weed dry matter, and seed yield. There were no or minimal phytotoxicity symptoms observed on the existing and succeeding crops. This review emphasizes the importance of newly formulated herbicides signifying high selectivity, low toxicity, target specificity, and minimal application rates, contributing to an enhanced understanding of human and environmental health. Furthermore, it emphasizes the significance of economic viability and environmental friendliness in these formulations.

The native distribution of a common legume shrub is limited by the range of its nitrogen-fixing mutualist.

Plant-microbe mutualisms, such as the legume-rhizobium symbiosis, are influenced by the geographical distributions of both partners. However, limitations on the native range of legumes, resulting from the absence of a compatible mutualist, have rarely been explored. We used a combination of a large-scale field survey and controlled experiments to determine the realized niche of Calicotome villosa, an abundant and widespread legume shrub. Soil type was a major factor affecting the distribution and abundance of C. villosa. In addition, we found a large region within its range in which neither C. villosa nor Bradyrhizobium, the bacterial genus that associates with it, were present. Seedlings grown in soil from this region failed to nodulate and were deficient in nitrogen. Inoculation of this soil with Bradyrhizobium isolated from root nodules of C. villosa resulted in the formation of nodules and higher growth rate, leaf N and shoot biomass compared with un-inoculated plants. We present evidence for the exclusion of a legume from parts of its native range by the absence of a compatible mutualist. This result highlights the importance of the co-distribution of both the host plant and its mutualist when attempting to understand present and future geographical distributions of legumes.

Genomic Insights into the Symbiotic and Plant Growth-Promoting Traits of "Candidatus Phyllobacterium onerii" sp. nov. Isolated from Endemic Astragalus flavescens.

A novel strain of Gram-negative, rod-shaped aerobic bacteria, identified as IY22, was isolated from the root nodules of Astragalus flavescens. The analysis of the 16S rDNA and recA (recombinase A) gene sequences indicated that the strain belongs to the genus Phyllobacterium. During the phylogenetic analysis, it was found that strain IY22 is closely related to P. trifolii strain PETP02T and P. bourgognense strain STM 201T. The genome of IY22 was determined to be 6,010,116 base pairs long with a DNA G+C ratio of 56.37 mol%. The average nucleotide identity (ANI) values showed a range from 91.7% to 93.6% when compared to its close relatives. Moreover, IY22 and related strains had digital DNA-DNA hybridization (dDDH) values ranging from 16.9% to 54.70%. Multiple genes (including nodACDSNZ, nifH/frxC, nifUS, fixABCJ, and sufABCDES) associated with symbiotic nitrogen fixation have been detected in strain IY22. Furthermore, this strain features genes that contribute to improving plant growth in various demanding environments. This study reports the first evidence of an association between A. flavescens and a rhizobial species. Native high-altitude legumes are a potential source of new rhizobia, and we believe that they act as a form of insurance for biodiversity against the threats of desertification and drought.