Rhizobial Nodulation Research Articles

The type III effector NopL interacts with GmREM1a and GmNFR5 to promote symbiosis in soybean

The establishment of symbiotic interactions between leguminous plants and rhizobia requires complex cellular programming activated by Rhizobium Nod factors (NFs) as well as type III effector (T3E)-mediated symbiotic signaling. However, the mechanisms by which different signals jointly affect symbiosis are still unclear. Here we describe the mechanisms mediating the cross-talk between the broad host range rhizobia Sinorhizobium fredii HH103 T3E Nodulation Outer Protein L (NopL) effector and NF signaling in soybean. NopL physically interacts with the Glycine max Remorin 1a (GmREM1a) and the NFs receptor NFR5 (GmNFR5) and promotes GmNFR5 recruitment by GmREM1a. Furthermore, NopL and NF influence the expression of GmRINRK1, a receptor-like kinase (LRR-RLK) ortholog of the Lotus RINRK1, that mediates NF signaling. Taken together, our work indicates that S. fredii NopL can interact with the NF signaling cascade components to promote the symbiotic interaction in soybean.

Two members of a Nodule-specific Cysteine-Rich (NCR) peptide gene cluster are required for differentiation of rhizobia in Medicago truncatula nodules.

Legumes have evolved a nitrogen-fixing symbiotic interaction with rhizobia, and this association helps them to cope with the limited nitrogen conditions in soil. The compatible interaction between the host plant and rhizobia leads to the formation of root nodules, wherein internalization and transition of rhizobia into their symbiotic form, termed bacteroids, occur. Rhizobia in the nodules of the Inverted Repeat-Lacking Clade legumes, including Medicago truncatula, undergo terminal differentiation, resulting in elongated and endoreduplicated bacteroids. This transition of endocytosed rhizobia is mediated by a large gene family of host-produced nodule-specific cysteine-rich (NCR) peptides in M. truncatula. Few NCRs have been recently found to be essential for complete differentiation and persistence of bacteroids. Here, we show that a M. truncatula symbiotic mutant FN9285, defective in the complete transition of rhizobia, is deficient in a cluster of NCR genes. More specifically, we show that the loss of the duplicated genes NCR086 and NCR314 in the A17 genotype, found in a single copy in Medicago littoralis R108, is responsible for the ineffective symbiotic phenotype of FN9285. The NCR086 and NCR314 gene pair encodes the same mature peptide but their transcriptional activity varies considerably. Nevertheless, both genes can restore the effective symbiosis in FN9285 indicating that their complementation ability does not depend on the strength of their expression activity. The identification of the NCR086/NCR314 peptide, essential for complete bacteroid differentiation, has extended the list of peptides, from a gene family of several hundred members, that are essential for effective nitrogen-fixing symbiosis in M. truncatula.

Root microbiomes of Zygophyllaceae in the Kazakhstan desert: a weak evidence for rhizobial nitrogen fixation

The plants of the Zygophyllaceae family are often considered to be capable of symbiotic atmosphere nitrogen fixation, forming rhizobial nodules similar to those of Fabaceae and Urticaceae. In four species of Zygophyllaceae and the related Peganum harmala (hereafter called Z-plants), collected in Dzungarian deserts (Kazakhstan), we analyzed the prokaryotic component of the root microbiome and the 15N and 13C content in the leaves of these Z-plants compared with neighboring dicots belonging to other families (R-plants). Among all studied Zygophyllum fabago root samples only one was found to have the root nodule, however the microbiome of this sample was similar to that found in other Z. fabago root samples where nodulation was not observed. If compared to Z-plants, the R-plants had a significantly higher relative abundance of bacteria of genera Glycomyces, Massilia and Streptomyces, while the Z-plants had a higher relative abundance of the representatives of genera Actinomadura, Nocardia and Pseudonocardia. Unidentified representatives of the family Rhizobiaceae were present in some of R and Z plants, being most abundant in soil samples. On average, the Z- and the R-plants did not differ in their δ13С and δ15N. Overall, the results do not allow us to consider the studied Zygophyllaceae plants as species with effective atmospheric nitrogen fixation due to rhizobial symbiosis – a characteristic feature of the most legumes.

A Comprehensive Process Of Nitrogen Fixation In Plants

Nitrogen is a component of several biomolecules that are essential for all organisms' growth and development. Nitrogen fixation is the biological process that converts molecular nitrogen to ammonia. Biological nitrogen fixation is mediated by diazotroph microorganisms that use nitrogenase enzymes to enhance atmospheric nitrogen. Much of this is accomplished through a symbiotic interaction between plants and diazotrophic bacteria. Microbiology and plant biology are discussed in symbiotic nitrogen fixation discussions. Some of the nitrogen fixation mechanisms mentioned in this paper begin with the formation of nodules, the action of the nitrogenase enzyme in reducing nitrogen to ammonia, and the presence of rhizobia in nodules. This study provides a comprehensive overview of the nodule formation process, the role of the nitrogenase enzyme in reducing nitrogen to ammonia, and the presence of rhizobia in nodules. A more complete literature review on biological nitrogen fixing in plants is required to obtain more specific information.

Role of a LORELEI- like gene from Phaseolus vulgaris during a mutualistic interaction with Rhizobium tropici

Reactive oxygen species (ROS), produced by NADPH oxidases known as RBOHs in plants, play a key role in plant development, biotic and abiotic stress responses, hormone signaling, and reproduction. Among the subfamily of receptor-like kinases referred to as CrRLK, there is FERONIA (FER), a regulator of RBOHs, and FER requires a GPI-modified membrane protein produced by LORELEI (LRE) or LORELEI-like proteins (LLG) to reach the plasma membrane and generate ROS. In Arabidopsis, AtLLG1 is involved in interactions with microbes as AtLLG1 interacts with the flagellin receptor (FLS2) to trigger the innate immune response, but the role of LLGs in mutualistic interactions has not been examined. In this study, two Phaseolus vulgaris LLG genes were identified, PvLLG2 that was expressed in floral tissue and PvLLG1 that was expressed in vegetative tissue. Transcripts of PvLLG1 increased during rhizobial nodule formation peaking during the early period of well-developed nodules. Also, P. vulgaris roots expressing pPvLLG1:GFP-GUS showed that this promoter was highly active during rhizobium infections, and very similar to the subcellular localization using a construct pLLG1::PvLLG1-Neon. Compared to control plants, PvLLG1 silenced plants had less superoxide (O2-) at the root tip and elongation zone, spotty hydrogen peroxide (H2O2) in the elongation root zone, and significantly reduced root hair length, nodule number and nitrogen fixation. Unlike control plants, PvLLG1 overexpressing plants showed superoxide beyond the nodule meristem, and significantly increased nodule number and nodule diameter. PvLLG1 appears to play a key role during this mutualistic interaction, possibly due to the regulation of the production and distribution of ROS in roots.

A rare non-canonical splice site in Trema orientalis SYMRK does not affect its dual symbiotic functioning in endomycorrhiza and rhizobium nodulation

BackgroundNitrogen-fixing nodules occur in ten related taxonomic lineages interspersed with lineages of non-nodulating plant species. Nodules result from an endosymbiosis between plants and diazotrophic bacteria; rhizobia in the case of legumes and Parasponia and Frankia in the case of actinorhizal species. Nodulating plants share a conserved set of symbiosis genes, whereas related non-nodulating sister species show pseudogenization of several key nodulation-specific genes. Signalling and cellular mechanisms critical for nodulation have been co-opted from the more ancient plant-fungal arbuscular endomycorrhizal symbiosis. Studies in legumes and actinorhizal plants uncovered a key component in symbiotic signalling, the LRR-type SYMBIOSIS RECEPTOR KINASE (SYMRK). SYMRK is essential for nodulation and arbuscular endomycorrhizal symbiosis. To our surprise, however, despite its arbuscular endomycorrhizal symbiosis capacities, we observed a seemingly critical mutation in a donor splice site in the SYMRK gene of Trema orientalis, the non-nodulating sister species of Parasponia. This led us to investigate the symbiotic functioning of SYMRK in the Trema-Parasponia lineage and to address the question of to what extent a single nucleotide polymorphism in a donor splice site affects the symbiotic functioning of SYMRK.ResultsWe show that SYMRK is essential for nodulation and endomycorrhization in Parasponia andersonii. Subsequently, it is revealed that the 5’-intron donor splice site of SYMRK intron 12 is variable and, in most dicotyledon species, doesn’t contain the canonical dinucleotide ‘GT’ signature but the much less common motif ‘GC’. Strikingly, in T. orientalis, this motif is converted into a rare non-canonical 5’-intron donor splice site ‘GA’. This SYMRK allele, however, is fully functional and spreads in the T. orientalis population of Malaysian Borneo. A further investigation into the occurrence of the non-canonical GA-AG splice sites confirmed that these are extremely rare.ConclusionSYMRK functioning is highly conserved in legumes, actinorhizal plants, and Parasponia. The gene possesses a non-common 5’-intron GC donor splice site in intron 12, which is converted into a GA in T. orientalis accessions of Malaysian Borneo. The discovery of this functional GA-AG splice site in SYMRK highlights a gap in our understanding of splice donor sites.

How strongly is rhizobial nodulation associated with bean cropping system?

How strongly is rhizobial nodulation associated with bean cropping system?

Tetracycline inhibits the nitrogen fixation ability of soybean (Glycine max (L.) Merr.) nodules in black soil by altering the root and rhizosphere bacterial communities

Tetracycline is a widely used antibiotic and may thus also be an environmental contaminant with an influence on plant growth. The aim of this study was to investigate the inhibition mechanisms of tetracycline in relation to soybean growth and ecological networks in the roots and rhizosphere. To this end, we conducted a pot experiment in which soybean seedlings were grown in soil treated with 0, 10, or 25 mg/kg tetracycline. The effects of tetracycline pollution on growth, productivity, oxidative stress, and nitrogenase activity were evaluated. We further identified the changes in microbial taxa composition and structure at the genus and species levels by sequencing the 16S rRNA gene region. The results showed that tetracycline activates the antioxidant defense system in soybeans, which reduces the abundance of Bradyrhizobiaceae, inhibits the nitrogen-fixing ability, and decreases the nitrogen content in the root system. Tetracycline was also found to suppress the formation of the rhizospheric environment and decrease the complexity and stability of bacterial networks. Beta diversity analysis showed that the community structure of the root was markedly changed by the addition of tetracycline, which predominantly affected stochastic processes. These findings demonstrate that the influence of tetracycline on soybean roots could be attributed to the decreased stability of the bacterial community structure, which limits the number of rhizobium nodules and inhibits the nitrogen-fixing capacity. This exploration of the inhibitory mechanisms of tetracycline in relation to soybean root development emphasises the potential risks of tetracycline pollution to plant growth in an agricultural setting. Furthermore, this study provides a theoretical foundation from which to improve our understanding of the physiological toxicity of antibiotics in farmland.

Phosphorus enrichment enabled Amorpha fruticosa to invade on the floodplain of the Tagliamento River, Italy

The North American nitrogen-fixing shrub Amorpha fruticosa (false indigo) is an aggressive invader of riverine habitats in Europe, though the reasons for its success are poorly understood. We hypothesized that its spread on the floodplain of the Tagliamento River in Northern Italy was enabled by anthropogenic phosphorus (P) enrichment. To investigate this hypothesis, we surveyed seed production at different locations along the river and performed a growth chamber experiment in which seedlings of three common floodplain shrubs (A. fruticosa, Salix eleagnos and Buddleja davidii) were grown at 10 levels of both nitrogen (N) and P. As a bioassay of N and P availabilities, we analyzed concentrations of these nutrients in Salix eleagnos leaves collected at different positions along the river. P availability was significantly higher in the lower reaches of the river, where A. fruticosa was abundant, than at its upstream limit. Numbers of A. fruticosa seeds per inflorescence increased strongly in a downstream direction and there was a trend for higher seed weight. In the growth experiment, A. fruticosa was more P-demanding than the other species, producing little biomass and no rhizobial nodules at low P. It also exhibited greater plasticity than the other species in both root mass fraction and ratio of longest root length to root mass. We conclude that anthropogenic P enrichment enabled A. fruticosa to invade what was originally a very oligotrophic environment. This N2-fixing shrub exhibits greater phenotypic plasticity than native S. eleagnos, giving it a competitive advantage under conditions of high P availability.

Red clover productivity under drought: Are soil microbes a burden or a treasure?

Drought-induced changes in plant traits are well-studied, e.g. building smaller and thicker leaves, reducing stomatal density or increasing root uptake. However, the extent to which these changes depend on plant-soil interactions remains unclear. Mutualistic soil microbes like arbuscular mycorrhizal fungi (AMF) and Rhizobium are known to enhance plant productivity, water and nutrient uptake and stress tolerance. Therefore, alterations in soil microbial loads are expected to affect not only plant productivity but also plant responses to drought through changing plant traits. In this study, we investigated the effects of plant-soil interactions on the productivity and traits of red clover (Trifolium pratense L.) under repeated drought. We conducted a pot experiment with two treatments: water treatment (wet versus drought) and microbial reduction by soil steam sterilization (native versus sterilized soil). We found that plants in native soil showed lower productivity and plant traits associated with slow-growing strategies (i.e. small and coarse leaves, lower stomatal density and higher root mass). However, the reduction of soil microbial load by soil steam sterilization increased plant productivity under wet conditions and led to plant traits associated with fast-growing strategies. Drought in sterilized soil decreased productivity, promoted earlier wilting and resulted in the development of plant traits associated with a more slow-growing strategy. Furthermore, roots became longer and thinner and rhizobial nodulation decreased, demonstrating the reduction of mutualists. Hence, our results show that soil microbes trigger plant traits, which suggests that they play an important role in plant responses to drought, in maintaining plant productivity and in prolonging plant vitality.

Investigation on microfloral association in the roots of Macrotyloma uniflorum (Lam.) Verdc., a medicinally important tropical pulse-crop and their possible applications for crop improvement: a review

Macrotyloma uniflorum (Lam.) Verdc., an economically important medicinal plant belongs to the Leguminosae family. Being Afro-Asian origin, the plant has long tradition of uses. It is primarily used for its antiurolithiatic property although it has other medicinal uses. Being Leguminosae member, this plant can form rhizobial nodules and mycorrhizal associations. The rhizobia obtained from this plant are mostly belonged to Bradyrhizobium sp. Although, Rhizobium pusence has also been reported. Microbes as biofertilizers can be used to increase yield of this plant, as well as there is great potential for utilizing the microbes derived from this plant. In this review we aim to describe the plant M. uniflorum - its taxonomic characteristics, economic uses, putative active constituents, and beneficial microflora along with their applications.

Mixed Enterobacter and Klebsiella bacteria enhance soybean biological nitrogen fixation ability when combined with rhizobia inoculation

Biological nitrogen fixation is a key process for nitrogen geochemical cycling and plant‒microbe interactions. At present, little is known about the possible effects of nonnodulating microbes on rhizobia nodulation in soils. Here, we show that Enterobacter sp. Z1 and Klebsiella sp. Z2 significantly improved soybean growth and nitrogen fixation in the presence of Bradyrhizobium diazoefficiens USDA110. Soil metabolomic analysis showed that the application of mixed strains Z1 and Z2 significantly increased the levels of flavonoids, indoleacetic acid (IAA), salicylic acid (SA), and taurine in rhizosphere soil. The addition of IAA, SA, or taurine increased nitrogenase activity, nodule production, and chlorophyll content in soybean. Flavonoids were the determinant of the interaction between soybeans and rhizobia. Moreover, strains Z1 and Z2 produced an abundance of IAA and SA, thus increasing the expression of flavonoid synthesis-related genes and eventually increasing the accumulation of flavonoids. Both strains Z1 and Z2 exhibited two metabolic pathways of taurine, and they catalyzed taurine to produce acetyl-CoA, a key flavonoid synthesis substrate in soybeans. This study revealed the mechanism by which rhizosphere microorganisms mediated soybean-rhizobium interactions, thus promoting soybean nitrogen fixation.

Rhizobium nodule diversity and composition are influenced by clover host selection and local growth conditions.

While shaping of plant microbiome composition through 'host filtering' is well documented in legume-rhizobium symbioses, it is less clear to what extent different varieties and genotypes of the same plant species differentially influence symbiont community diversity and composition. Here, we compared how clover host varieties and genotypes affect the structure of Rhizobium populations in root nodules under conventional field and controlled greenhouse conditions. We first grew four Trifolium repens (white clover) F2 crosses and one variety in a conventional field trial and compared differences in root nodule Rhizobium leguminosarum symbiovar trifolii (Rlt) genotype diversity using high-throughput amplicon sequencing of chromosomal housekeeping (rpoB and recA) genes and auxiliary plasmid-borne symbiosis genes (nodA and nodD). We found that Rlt nodule diversities significantly differed between clover crosses, potentially due to host filtering. However, variance in Rlt diversity largely overlapped between crosses and was also explained by the spatial distribution of plants in the field, indicative of the role of local environmental conditions for nodule diversity. To test the effect of host filtering, we conducted a controlled greenhouse trial with a diverse Rlt inoculum and several host genotypes. We found that different clover varieties and genotypes of the same variety selected for significantly different Rlt nodule communities and that the strength of host filtering (deviation from the initial Rhizobium inoculant composition) was positively correlated with the efficiency of symbiosis (rate of plant greenness colouration). Together, our results suggest that selection by host genotype and local growth conditions jointly influence white clover Rlt nodule diversity and community composition.

Advances in the study of the function and mechanism of the action of flavonoids in plants under environmental stresses.

This review summarizes the anti-stress effects of flavonoids in plants and highlights its role in the regulation of polar auxin transport and free radical scavenging mechanism. As secondary metabolites widely present in plants, flavonoids play a vital function in plant growth, but also in resistance to stresses. This review introduces the classification, structure and synthetic pathways of flavonoids. The effects of flavonoids in plant stress resistance were enumerated, and the mechanism of flavonoids in plant stress resistance was discussed in detail. It is clarified that plants under stress accumulate flavonoids by regulating the expression of flavonoid synthase genes. It was also determined that the synthesized flavonoids are transported in plants through three pathways: membrane transport proteins, vesicles, and bound to glutathione S-transferase (GST). At the same time, the paper explores that flavonoids regulate polar auxin transport (PAT) by acting on the auxin export carrier PIN-FORMED (PIN) in the form of ATP-binding cassette subfamily B/P-glycoprotein (ABCB/PGP) transporter, which can help plants to respond in a more dominant form to stress. We have demonstrated that the number and location of hydroxyl groups in the structure of flavonoids can determine their free radical scavenging ability and also elucidated the mechanism by which flavonoids exert free radical removal in cells. We also identified flavonoids as signaling molecules to promote rhizobial nodulation and colonization of arbuscular mycorrhizal fungi (AMF) to enhance plant-microbial symbiosis in defense to stresses. Given all this knowledge, we can foresee that the in-depth study of flavonoids will be an essential way to reveal plant tolerance and enhance plant stress resistance.

Extracts and Residues of Common Ragweed (Ambrosia artemisiifolia L.) Cause Alterations in Root and Shoot Growth of Crops.

Following the novel weapon hypothesis, the invasiveness of non-native species, such as common ragweed (Ambrosia artemisiifolia L.) can result from a loss of natural competitors due to the production of chemical compounds, which negatively affect native communities. Particularly the genus Ambrosia produces several types of organic compounds, which have the potential to inhibit germination and growth of other plants. Subsequent to an assessment of the chemical content of three different ragweed extracts (aqueous shoot and root extracts, as well as essential oil), two different trials on the effects of different concentrations of these extracts, as well as ragweed residues, were conducted on two different mediums (Petri dish vs. soil). In addition, we investigated the impact on the infection potential of Bradyrhizobium japonicum on soybean roots in three different soil types (arable soil, potting soil, and sand). The results showed that the exposure to common ragweed extracts and residues induced changes in the biomass and root production of crops and ragweed itself. Even though crops and ragweed differed in their response behavior, the strongest negative impact on all crops and ragweed was observed with ragweed residues, leading to reductions in biomass and root growth of up to 90%. Furthermore, we found a decrease in the number of rhizobial nodules of up to 48% when soybean was exposed to ragweed root extract.

Could conservation tillage increase the resistance to drought in Mediterranean faba bean crops?

Climate change, especially in Mediterranean countries, might have a detrimental effect on agro‑ecosystems and agricultural production, as well as on the price, quantity and quality of the products. This study assesses the potential impact of drought predictions on a faba bean crop, and evaluates the adoption of conservation tillage practices to reduce this effect. For this purpose, a rainfall exclusion experiment was carried out in a Mediterranean rotation in Southwest Spain, where a long-term tillage experiment was running since 2008. Soil water storage (SWS), crop productivity and mineral nutrition, plant ecophysiology and biomass quality, as well as the colonization of roots by arbuscular mycorrhizal fungi (AMF) and symbiotic Rhizobium bacteria were evaluated over one growth cycle to study the combined effect of different tillage systems - non-tillage (NT), reduced tillage (RT) and traditional tillage (TT)- and rainfall reduction. Rainfall reduction had a negative impact on faba bean germination on the TT system, and on its aboveground biomass across the three tillage systems, but did not affect grain production. The percentage of biomass yield reduction by rainfall exclusion was 30% for NT, 50% for RT and 20% for TT. In the case of RT, low yields were influenced by a high incidence of weeds under rainfall reduction. The negative effect of water exclusion was especially evident on photosynthesis rates and stomatal conductance across all tillage types, while leaf water potential was affected by drought only in the TT system. These ecophysiological indicators were positively associated to some variables of arbuscular mycorrhizal colonization and Rhizobium nodulation in roots. Changes in the patterns of symbiotic interactions in response to drought depended on the tillage type. We conclude that, despite no effect on soil water storage, in the conservation tillage systems the increase in the mycorrhizal colonization in roots, particularly under NT, could be beneficial for plants to face drought stress. However, in a scenario of reduced rainfall it will be necessary to invest more resources in weed control under RT.

Effects of different tillage on morpho-physiological traits of dryland chickpea (Cicer arietinum L.)

The study of different types of tillage can be effective in promoting conservation agriculture for chickpea cultivation. The present experiment was conducted to study the effects of different soil management (reduced tillage (RT), no-tillage (NT), and conventional tillage (CT)) on morpho-physiological characteristics of chickpea in a complete randomized block design field experiment with three replications during the 2017–2019 cropping seasons. In this experiment effects of soil management on mycorrhizal colonization and sporulation, rhizobium nodules, relative leaf water content, leaf area index, chlorophyll and carotenoids, chlorophyll fluorescence, canopy temperature, enzymes, proline, hydrogen peroxide, malondialdehyde, leaf soluble proteins, carbohydrates, and leaf P and N content were investigated in early grain filling were evaluated. The highest activity of antioxidant enzymes including catalase (0.066 U/mg−1Protein min−1), peroxidase (1.22 U/mg−1Protein min−1), and superoxide dismutase (0.69 U/mg−1Protein min−1) were observed in the plants grown under CT practice, while the lowest were observed under NT system. In NT, the lowest amounts of malondialdehyde and carotenoids were retrieved compared to the conventional tillage. CT determined a reduction in chlorophyll in leaves compared to RT (13 %) and NT (36.2 %), respectively. The highest rate of canopy temperature depression occurred in no-tillage system. The highest remobilization from stems to seeds was respectively obtained from conventional tillage, reduced tillage and no-tillage treatments. In no-tillage, leaf area index, quantum efficiency of PSII (chlorophyll fluorescence), relative water content, leaf nitrogen, and leaf phosphorus increased compared to reduced tillage and conventional tillage, respectively. The rate of colonization and sporulation of mycorrhizal fungi and the number of rhizobium nodules significantly increased under NT compared to RT and CT systems. The results in this experiment showed that the NT system improved relative leaf water content, reduced antioxidant enzymes, and positive effects on measured morpho-physiological traits increased the yield and stability of chickpea compared to RT and CT systems under rainfed conditions.

Characterization of endophytic bacteria isolated from root nodules of lentil in intercropping with durum wheat

Legumes improve soil fertility by interacting symbiotically with nitrogen-fixing rhizobia allocated in root nodules. Some bacterial endophytes can coexist with rhizobia in nodules and might help legumes by enhancing stress tolerance, producing hormones stimulating plant growth, and increasing plant nutrient intake. Twenty-six bacterial endophytes from Lens culinaris root nodules cultivated in intercropping with Triticum durum were identified and characterized molecularly and biochemically. Potential plant growth-promoting strains have been selected according to the indole acetic acid and 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase production, and for their inorganic phosphate solubilization ability. The presence of genes associated to ACC deaminase and nitrogenase was evaluated. Six selected strains were grown with varying NaCl and polyethylene glycol concentrations to test their salt and osmotic stress tolerance. Priestia megaterium 11NL3 and Priestia aryabhattai 19NL1, resulted to be tolerant to salinity and osmotic stress, were tested on four genotypes of T. durum seeds in different stress conditions. The effect of strain inoculation on seed germination, vigor, and root-to-shoot ratio varied depending on the type of stress and on the durum wheat genotypes. For future research, it will be necessary to test the selected bacterial strains at different plant phenological stages and to clarify the mechanisms involved in the different outcomes of plant-microbe interactions.

Influence of blended NPSB fertilizer on nodulation and yield performance of Rhizobium inoculated common bean varieties in acidic soil, western Ethiopia

The decline of soil fertility and limited adaptive cultivars are some of the factors that affect crop production. This study aimed to examine the response of Rhizobium inoculated common bean varieties to NPSB fertilizer application for nodulation, yield, and yield related traits. Three varieties of common bean (Local, Loko, and Nasir) were combined with four rates of blended NPSB (0, 50, 100, and 150 kg ha−1) fertilizers in randomized complete block design with three replications arranged factorially. The result revealed significantly highest number of total nodules (53.7), effective nodules per plant (35.54), number of pods per plant (7.4), plant stand count (87%), biomass (17.5 t ha1), seed yield (2996 kg ha1), and harvest index (16.67%) were recorded at the rate of 100 kg ha−1 NPSB which was 183%, 60%, 100%, 19%, 56%, 112%, and 33.3% increment over the control, respectively. Nodules fresh weight and nodules dry weight per plant showed 188% and 344.8% improvement over control, respectively. Nassir variety was higher in nodulation and yield, while Loko variety had long rooting which has implication on nitrogen fixation and plant nutrition. Thus, the result suggests that highest seed yield was achieved from variety Nasir (2996 kg ha−1) with 100 kg ha−1 blended NPSB combination producing net benefit ha−1 of 79,245.78 ETB (Ethiopian Birr).

Interplay between rhizobial nodulation and arbuscular mycorrhizal fungal colonization inLotus japonicusroots

This study aims to identify main factors that influence the tripartite association of legumes with arbuscular mycorrhiza fungi (AMF) and nitrogen-fixing rhizobia. Concurrent inoculations with Mesorhizobium loti and four AMF strains were performed on the model legume Lotus japonicus. Nodulation was significantly enhanced by all AMF strains, under normal conditions, and by specific AMF strains under heat-stress conditions. The impact of rhizobia on mycorrhizal colonization was AMF strain dependent. Co-inoculation trials, where either AMF or rhizobia were restricted outside the root, showed that the symbiotic phenotypes are not influenced by microbial interactions at the pre-symbiotic stage. External application of nutrients showed that P enhances nodulation, while N application does not enhance mycorrhizal colonization. Nodulation and mycorhization affect one another during advanced stages of the symbiosis. AMF strains may enhance nodulation under both normal and high environmental temperatures. Rhizobium-AMF compatibility is critical, as rhizobium may positively affect specific AMF strains, an effect that does not derive from increased N uptake.