Rhizobial Strains Research Articles

Diversity of rhizobia and non-rhizobia endophytes isolated from root nodules of Trifolium sp. growing in lead and zinc mine site Guelma, Algeria

High concentrations of heavy metals in mine soil disturb the interactions between legumes and microorganisms leading to select strains adapted to these specific conditions. In this work, we analyzed the diversity of fifty strains isolated from Trifolium sp. nodules growing on Pb-Zn mine soil, in the Northeastern of Algeria and highlighted their potential symbiotic traits. The phylogeny of the 16S rRNA gene sequences revealed a high bacterial diversity with a predominance of non-rhizobial endophytes. The identified isolates belong to the thirteen following genera Cupriavidus, Pseudomonas, Bacillus, Acinetobacter, Enterobacter, Roseomonas, Paracoccus, Frondihabitans, Microbacterium, Kocuria, Providencia, Micrococcus and Staphylococcus. Regarding rhizobial strains, only isolates affiliated to Rhizobium genus were obtained. The symbiotic gene nodC and the nitrogen fixation gene nifH present showed that Rhizobium isolates belonged to the symbiovar trifolii. In addition to bacterial, one yeast strain was isolated and identified as Rhodotorula mucilaginosa by sequencing the internal transcribed spacer (ITS) region.

Deciphering the phylogenetic affiliation of rhizobial strains recommended as chickpea inoculants in Argentina

Chickpea (Cicer arietinum L.) is globally cultivated due to its high nutritional value. As with other legumes, its success depends greatly on its inoculation with effective symbiotic rhizobial strains. Since its agricultural importance as an alternative winter crop in Argentina is very recent, there are limited phylogenetic studies on the affiliation and origin of the two strains used for its inoculation here. We attempted to define their specific identity through a multilocus sequence approach on seven housekeeping genes (phylogeny and average nucleotide identity), as well as on the basis of 16S rRNA gene sequence and nodC gene analysis. The strains were accurately and conclusively corroborated as M. ciceri and M. mediterraneum species, and their denominations were found to be associated to originally described chickpea-nodulating strains.

Native Rhizobia Strains Enhance Seed Yield of Groundnut Varieties in Northern Ghana

Rhizobia inoculation with effective strains is an environmentally friendly approach for enhancing nodulation and yield of legumes. To obtain an ideal strain for inoculant production, the strain's performance must be matched to the environmental conditions. A 2 × 9 cross-factorial experiment laid in a randomized complete block design with three replications on farmers' fields in the northern part of Ghana was set up to evaluate the rhizobia's performance. The factors were groundnut varieties (Chinese and Samnut 22) and nine strains consisting of five native rhizobia (KNUST 1001, 1002, 1003, 1032, and 1031), two commercial strains (Biofix and BR3267), and a positive (N+) and absolute control (N–). In addition, the population of the strains was assessed after a cropping season. The strains' performance on groundnut was location and variety dependent. At Cheshegu, KNUST 1031 and 1002 significantly increased seed yield of the Chinese variety compared to other strains; however, KNUST 1031 elicited a 24% yield increase while KNUST 1002 caused a 16% yield increase over the control. Strain KNUST 1031 increased the seed yield of the Chinese variety by 24% while KNUST 1002 increased the seed yield of Samnut by 16%. Only KNUST 1002 elicited a significant seed yield increase in Samnut 22 at Cheshegu. At Binduri, strain KNUST 1003 significantly increased the seed yield of the Chinese variety by 35% relative to the control. Samnut 22 did not show a clear preference for any of the strains. The Chinese variety did not show a clear response to the strains at Tanina. However, Samnut 22 responded to KNUST 1002 as it increased seed yield by 45% relative to the control. On average, the seed yield at Tanina (846.15 kg ha−1) was less than the seed yield recorded at Binduri (1,077.66 kg ha−1) and Cheshegu (1,502.78 kg ha−1). Inoculation with strains KNUST 1002, 1003, and 1031 was all profitable under the current experimental conditions as they recorded value cost ratios (VCRs) above the threshold of 3–4. The study has shown that strains KNUST 1002, 1003, and 1031 have the potential to be used in inoculant formulation to increase groundnut production and enhance the income of smallholder groundnut farmers in northern Ghana.

Conditional sanctioning in a legume–Rhizobium mutualism

Legumes are high in protein and form a valuable part of human diets due to their interaction with symbiotic nitrogen-fixing bacteria known as rhizobia. Plants house rhizobia in specialized root nodules and provide the rhizobia with carbon in return for nitrogen. However, plants usually house multiple rhizobial strains that vary in their fixation ability, so the plant faces an investment dilemma. Plants are known to sanction strains that do not fix nitrogen, but nonfixers are rare in field settings, while intermediate fixers are common. Here, we modeled how plants should respond to an intermediate fixer that was otherwise isogenic and tested model predictions using pea plants. Intermediate fixers were only tolerated when a better strain was not available. In agreement with model predictions, nodules containing the intermediate-fixing strain were large and healthy when the only alternative was a nonfixer, but nodules of the intermediate-fixing strain were small and white when the plant was coinoculated with a more effective strain. The reduction in nodule size was preceded by a lower carbon supply to the nodule even before differences in nodule size could be observed. Sanctioned nodules had reduced rates of nitrogen fixation, and in later developmental stages, sanctioned nodules contained fewer viable bacteria than nonsanctioned nodules. This indicates that legumes can make conditional decisions, most likely by comparing a local nodule-dependent cue of nitrogen output with a global cue, giving them remarkable control over their symbiotic partners.

Microbial Sensing and Removal of Heavy Metals: Bioelectrochemical Detection and Removal of Chromium(VI) and Cadmium(II).

The presence of inorganic pollutants such as Cadmium(II) and Chromium(VI) could destroy our environment and ecosystem. To overcome this problem, much attention was directed to microbial technology, whereas some microorganisms could resist the toxic effects and decrease pollutants concentration while the microbial viability is sustained. Therefore, we built up a complementary strategy to study the biofilm formation of isolated strains under the stress of heavy metals. As target resistive organisms, Rhizobium-MAP7 and Rhodotorula ALT72 were identified. However, Pontoea agglumerans strains were exploited as the susceptible organism to the heavy metal exposure. Among the methods of sensing and analysis, bioelectrochemical measurements showed the most effective tools to study the susceptibility and resistivity to the heavy metals. The tested Rhizobium strain showed higher ability of removal of heavy metals and more resistive to metals ions since its cell viability was not strongly inhibited by the toxic metal ions over various concentrations. On the other hand, electrochemically active biofilm exhibited higher bioelectrochemical signals in presence of heavy metals ions. So by using the two strains, especially Rhizobium-MAP7, the detection and removal of heavy metals Cr(VI) and Cd(II) is highly supported and recommended.

Genetic characterization at the species and symbiovar level of indigenous rhizobial isolates nodulating Phaseolus vulgaris in Greece

Phaseolus vulgaris (L.), commonly known as bean or common bean, is considered a promiscuous legume host since it forms nodules with diverse rhizobial species and symbiovars. Most of the common bean nodulating rhizobia are mainly affiliated to the genus Rhizobium, though strains belonging to Ensifer, Pararhizobium, Mesorhizobium, Bradyrhizobium, and Burkholderia have also been reported. This is the first report on the characterization of bean-nodulating rhizobia at the species and symbiovar level in Greece. The goals of this research were to isolate and characterize rhizobia nodulating local common bean genotypes grown in five different edaphoclimatic regions of Greece with no rhizobial inoculation history. The genetic diversity of the rhizobial isolates was assessed by BOX-PCR and the phylogenetic affiliation was assessed by multilocus sequence analysis (MLSA) of housekeeping and symbiosis-related genes. A total of fifty fast-growing rhizobial strains were isolated and representative isolates with distinct BOX-PCR fingerpriniting patterns were subjected to phylogenetic analysis. The strains were closely related to R. anhuiense, R. azibense, R. hidalgonense, R. sophoriradicis, and to a putative new genospecies which is provisionally named as Rhizobium sp. I. Most strains belonged to symbiovar phaseoli carrying the α-, γ-a and γ-b alleles of nodC gene, while some of them belonged to symbiovar gallicum. To the best of our knowledge, it is the first time that strains assigned to R. sophoriradicis and harbored the γ-b allele were found in European soils. All strains were able to re-nodulate their original host, indicating that they are true microsymbionts of common bean.

Effect of Some Rhizobium Strains on Fenugreek Growth and Biological Control of Sclerotinia Stem Rot of Fenugreek Caused by Sclerotinia trifoliorum

Effect of Some Rhizobium Strains on Fenugreek Growth and Biological Control of Sclerotinia Stem Rot of Fenugreek Caused by Sclerotinia trifoliorum

Isolation and properties of antimicrobial substance produced by Sinhorhizobium melilloti from root nodules of Medicago sativa

The symbiotic association of alfalfa (Medigaco sativa) with Sinorhizobium melilloti contributes to the production of inoculum to improve plant growth and increase yield. The competitiveness of the introduced strains is a very important factor in the performance of an inoculum which is based on the use of rhizobial strains. This competitiveness is due to the production of anti-microbial substances, among them, bacteriocines. In this study, the totals of 30 rhizobial strains were isolated from M. sativa nodules sampled from sa-line soils of Algeria. Twenty strains were nodulated the host plant M. sativa. The antimicrobial activity producing strains SW16 and SW15 were identified as Sinorhizobium melliloti based on 16S rRNA sequance analysis. Partial puri-fication of this inhibitorys substances by ammonium sulfate were precipitat-ed with 75% saturation. These antimicrobial activitys showed the maximum activity against the strain SW10 estimated at 1800 with the strain SW16 and 2500 AU/ml for the strain SW15. The physicochemical properties of these antimicrobial activitys reveals thier thermoresistant nature and sensitive to protease, but theire were resistant to a wide range of pH and also at differ-ent concentrations of Nacl. This inhibitory agent display primary metabolite kinetics as its maximal production was detected in the growth phase. Antimi-crobial substances produced by sinorhizobium mielilloti SW15 and SW16 exhibited inhibitory activity against the phytopathogen (Aspergillus sp., Fusarium sp., Cladosporium sp. and Alternaria altterna).

Nitrogen accumulated and biologically fixed by uninoculated Anadenanthera peregrina (L.) Speg trees under monospecific stands in the Atlantic Forest biome

Nitrogen-fixing legumes are widely used to improve ecosystems. However, N accumulation in biomass, N2 amounts biologically fixed, and the effects on soil N status are poorly understood for plantations with slow-growing N2-fixing legume trees in seasonally dry environments. In this study, we assessed these questions in monospecific stands of uninoculated Anadenanthera peregrina (L.) var. peregrina (angico) trees established in the Atlantic Forest biome. Nine experimental plots with a stand density of 1111 tree ha−1 were examined about five to six years after tree planting. N content in the leaves, branches, bark, and wood was estimated using allometric equations and N concentration in the tissues. To assess the N content, the topsoil layer was sampled in each plot and in one pasture area. The annual N2 fixation rate at the stand scale was estimated by the natural abundance of 15N, using leaves of angico and a mix of leaves of herbs and shrubs growing in the understory in each plot. N accumulation in aboveground biomass was estimated at 260 kg ha−1 and N allocated in the leaves and branches was four-fold that in the tree stem. N derived from biological N2 fixation was estimated at 50% on average, with an annual rate of N fixed in the aboveground biomass of 22 kg ha−1 year−1. Soil N storage was similar between A. peregrina stands and the pasture area at six years after planting. Long-term gains of N2 fixation may be greatly improved by the adoption of breeding programs for this slow-growing species and the use of an adequate rhizobium strain.

Co-inoculations with rhizobia and arbuscular mycorrhizal fungi alters mycorrhizal composition and lead to synergistic growth effects in cowpea that are fungal combination-dependent

Cowpea can effectively form tripartite symbiotic associations with nitrogen-fixing bacteria (NFB) and arbuscular mycorrhizal fungi (AMF) although the selection of compatible AMF species and rhizobial strains which are promoting cowpea growth remains a challenge. The aims of the current study were 1) to evaluate the response of cowpea plants to a symbiotic NFB and a multi-AMF inoculum and 2) to explore any interaction between the symbiotic NFB and the different AMF isolates. In a pot gnotobiotic trial, cowpea plants grown under limited N supply, were inoculated with or without a symbiotic nitrogen-fixing bacterium, Sinorhizobium meliloti, and combinations of three different AMF species namely Dominikia disticha, Claroideoglomus etunicatum and Rhizophagus irregularis. Experimental evaluation was determined through the measurement of above ground biomass, nutrient content and AMF root colonization. The presence of AMF species on cowpea roots was also determined with cloning and sequencing. Inoculation with both AMF and S. meliloti led to increased cowpea biomass production compared to inoculation with AMF only, but the presence of a positive effect depended on the specific AMF partners used. Inoculation with AMF alone had a highly positive impact on the growth and P uptake of cowpea, but the NFB inoculation was needed to address N deficiency in planta. The presence of both symbionts generally led to increased AMF colonization of the cowpea roots, however, plant colonization depended on the AMF species, and became even negative, when all three AMF inocula were used together. The AMF composition in plant roots was also altered in the presence of the S. meliloti. Plant nitrogen content of cowpea plants significantly increased under the presence of both symbionts compared to AMF alone, while phosphorus content was hardly affected by dual inoculations. The results show positive synergistic effects of the different AMF species and S.meliloti. Inoculation with all AMF isolates and S. meliloti led to high above ground biomass production and accumulation of N. The presence of S. meliloti increased P content in plants not inoculated with AMF. Finally, the efficiency of synergism depends on the specific AMF partners used and it is not related to their colonization levels.

Comparative genomic analysis of diverse rhizobia and effective nitrogen-fixing clover-nodulating Rhizobium strains adapted to Egyptian dry ecosystems

Rhizobium strains that nodulate Egyptian winter clover belong to two symbiotic species, Rhizobium aegyptiacum sv. trifolii and Rhizobium bangladeshense sv. trifolii. Rhizobia from Egyptian clover are often tolerant of extreme environmental conditions and are generally poorly characterized, despite the importance of this crop species. Here, we report on the comparative genomic analysis of four stress-tolerant, highly effective nitrogen-fixing, Egyptian-clover-nodulating rhizobia, R. aegyptiacum sv. trifolii strain Rhiz950 and Rhizobium bangladeshense sv. trifolii strains Rhiz1002, Rhiz1017 and Rhiz1024, as well as other diverse Rhizobium strains. While Rhizobium bangladeshense sv. trifolii strains Rhiz1002, Rhiz1017, and Rhiz1024 had similar genome sizes of around 6.6 Mb, the salt tolerant strain Rhiz950 had a slightly larger genome size of 7.4 Mb. All four strains lacked genes responsible for methylation and sulfation of nod factors (nodS and nodHPQ). They also lacked nodZ, and instead had the functionally-equivalent nod factor fucosylation gene nolK. No strains contained homocitrate synthase (encoded by nifV) that is essential for free-living nitrogen fixing by diazotrophs. A number of genes unique to the Egyptian clover strains and to other rhizobia are potential candidates for variation in stress tolerance and host-range.

Diversity and phylogenetic affinities of Bradyrhizobium isolates from Pampa and Atlantic Forest Biomes

In this work, we investigated Bradyrhizobium strains isolated from soils collected from the rhizosphere of native and exotic legumes species inhabiting two ecoclimatic zones – asubtropical-lowland pasture (Pampa Biome) and a volcanic plateau covered by Araucaria Moist Forests (Atlantic Forest Biome). The rhizobial strains were isolated from the nodules of seven native and one exotic legume species used as rhizobium traps. Single-gene (recA, glnII, dnaK) and combined-gene MLSA analyses (dnaK-glnII-gyrB-recA-rpoB) revealed that nearly 85% of the isolates clustered in B. elkanii supergroup, while the remaining (except for two isolates) in B. japonicum supergroup, albeit, in most cases, separately from the type strains of Bradyrhizobium species. As a symbiotic gene marker, a portion of nifD gene was sequenced for 194 strains. In the nifD-tree, an American branch III.3D (104 isolates), was the most numerous among the isolates. A significant portion of the isolates clustered in American groups; subclade III.4 (40 strains), Clade VII (3 strains), and a new Clade XX (4 strains). Most of the remaining strains belonged to a pantropical III.3C branch (39 isolates). On the other hand, identification of isolates belonging, respectively, to Clade I and Clade II may result of spreading of the Australian (Clade I) and European (Clade II) bradyrhizobia following the introduction of their legume hosts. Our study indicated that the American groups predominated in the symbiotic Bradyrhizobium communities in southern Brazil. However, there is a significant component of exotic lineages, resulting from the dispersal of pantropical Fabaceae taxa and the introduction of exotic legumes.

Genome-wide analysis and expression profiling of H-type Trx family in Phaseolus vulgaris revealed distinctive isoforms associated with symbiotic N2-fixing performance and abiotic stress response

Thioredoxins (Trxs) are implicated in plant development and stress tolerance through redox regulation of target proteins. Trxs of Type h (Trxhs) constitute the largest and the most complicated cluster in the Trx family because of their unknown individual functions. Here, we identified and characterized the Phaseolus vulgaris Trxh family during development, mutualistic interactions and in response to abiotic stress. P. vulgaris (common bean) Trxh gene family (PvTrxh) encompasses 12 isoforms (PvTrxh1-h12), subdivided into 3 groups according to their amino acid sequence features. In silico RNA-seq -based expression analysis showed a differential expression of PvTrxh genes during development. RT-qPCR analysis of PvTrxh genes during nodule organogenesis revealed their highest expression in the nodule primordium (NP). Interestingly, in response to symbiosis, specific PvTrxh isoforms (PvTrxh3 and h5) were found to be highly upregulated compared to mock-inoculated plants. In addition, their expression patterns in the NP positively correlated with the symbiotic N2-fixing efficiency of the Rhizobium strain, as revealed by a number of symbiotic efficiency parameters (ARA, leghemoglobin content, biomass, and total soluble proteins), concomitantly with increased amounts of hydrogen peroxide (H2O2). On the other hand, distinctive PvTrxh isoforms were found to be upregulated in plant leaves, where H2O2 amounts were elevated, in response to both salt and drought constraints. When exogenously applied, H2O2 upregulated specific PvTrxh isoforms in plant leaves and roots. These findings point to a specific, rather than redundant, function for Trxh proteins in common bean beside the association of distinctive Trxh isoforms with symbiosis and abiotic stress response.

Ensifer. meliloti sv. lancerottense nodulates Lotus creticus in alkaline soils of Northern Morocco

Lotus spp. are a plant of great importance as a forage to improve pastures, to restore degraded soils and the inoculation with best rhizobial strains is widely used in many countries. The aim of this work was to analyze the phylogeny of bacteria nodulating Lotus creticus collected from sandy alkaline saline soil in Tangier province Northern Morocco and determine their identity. Out of 44 bacterial isolates, 21 strains were selected for the phenotypic characterization and symbiotic efficiency evaluation. The enterobacterial repetitive intergenic consensus (ERIC)-polymerase chain reaction (PCR) fingerprinting showed different patterns at 40% similarity, and the amplified ribosomal DNA restriction analysis (ARDRA) generated one ribotype. Based on both the ERIC-PCR and the ARDRA results, 2 isolates, LcT51 and LcA30, were then chosen for molecular analysis. The 16S rRNA gene sequences showed that the 2 strains are closely related to Ensifer meliloti LMG 6133T with similarity values of 99.69%% to 99.93%. The analysis of concatenated atpD, glnII, gyrB, rpoB and dnaK housekeeping genes sequences confirmed the affiliation of the two strains to E. meliloti LMG 6133T. The phylogenic analysis of the nodC and nifH symbiotic genes, confirmed that L. creticus is nodulated in Tangier alkaline soils by the symbiovar lancerottense of E. meliloti.

Beneficial traits of root endophytes and rhizobacteria associated with plants growing in phytomanaged soils with mixed trace metal-polycyclic aromatic hydrocarbon contamination

The diversity of cultivable bacteria associated with plants from phytomanaged soils with mixed trace metal (TM) and polycyclic aromatic hydrocarbon (PAH) contamination in Pierrelaye (France) was evaluated. The emphasis was on the cultivable bacterial community since the overall objective is to obtain inoculants to improve the remediation of this type of contaminated site. Root endophytic and rhizosphere soil bacterial counts were determined, and isolates were pooled by amplified rDNA restriction analysis and identified by 16S rDNA sequencing. Isolates were further characterized for the production of plant growth-promoting (PGP) substances, and resistance to TM. The selected strains were evaluated for their ability to degrade PAHs. The potential of cell-free microbial supernatant to increase the mobilisation of PAHs from the polluted soil of Pierrelaye was also evaluated. Proteobacteria and Actinobacteria dominated the collection of isolates, and differences in taxonomic diversity were observed between plant species (Populus or Zea mays) and depending on the remediation treatment (Populus inoculation with mycorrhizae or Populus intercropping with Alnus). The majority of isolates exhibited at least one of the tested PGP traits, as well as resistance to more than one TM. Several rhizosphere, endophyte and even one bulk soil isolate showed high rates of fluoranthene and pyrene reduction. The endophyte Rhizobium strain MR28 isolated from maize and degrading pyrene produced bioemulsifying molecules capable of improving the availability of PAHs from the soil of Pierrelaye. A selection of the most interesting strains was made for further re-inoculation experiments in order to assess their potential in rhizoremediation processes.

Selección de un consorcio microbiano promotor del crecimiento de plántulas de cebolla en condiciones de umbráculo

The practice of producing more vigorous seedlings represents a competitive advantage at the time of transplanting a crop, and the use of combined biofertilizers are a sustainable ecological alternative. The objective of this research was to select a microbial consortium for the production of F1 2000 hybrid onion seedbeds under shade-house conditions. Five rhizobacterial strains of the genera Rhizobium (ME01 strain), Bradyrhizobium (Leu2A and YE1 strains), Ochrobactrum (ES1 strain) and Pseudomonas (Alf strain), which have shown favorable effects on pepper and lettuce seedlings. These rhizobacteria were inoculated in a mixed manner (microbial consortium) in onion as follows: Alf+ES1, ME01+ES1, ES1+Leu2A, Alf+Leu2A, YE1+ES1, ME01+Alf, YE1+Alf, ME01+YE1, YE1+Leu2A, ME01+Leu2A, using a soil from San Juan de Lagunillas-Mérida, Venezuela under shade-house conditions for 60 days. The following variables were determined: number of leaves, pseudostem base diameter, aerial and root length, aerial and root fresh and dry weight. Additionally, a CO2 assimilation curve under different light levels was carried out on the seedlings of the selected consortium to observe their photosynthetic response. The consortium ME01 + Leu2A (Rhizobium tropici + Bradyrhizobium japonicum) increased all studied variables, especially the pseudostem base diameter, essential for onion cultivation, and yielded higher seedlings CO2 assimilation rates. The use of this microbial consortium is recommended as an option for agricultural production under seedbed conditions.

Will Phosphate Bio-Solubilization Stimulate Biological Nitrogen Fixation in Grain Legumes?

Biological nitrogen fixation (BNF) refers to a bacterially mediated process by which atmospheric N2is reduced, either symbiotically or non-symbiotically, into ammonia (NH3) in the presence of the enzyme complex nitrogenase. In N2-fixing grain legumes, BNF is often hampered under low phosphorus (P) availability. The P status of legumes, particularly nodules, as well as P availability in the rhizosphere, play a vital role in regulating BNF. Aside from increasing P availability via fertilization, other plant traits (i.e., extensive rooting system and their spatial distribution, hyper-nodulation, root exudates, rhizosphere acidification, and heterogeneity) contribute to greater P uptake and hence more effective BNF. The positive interaction between P availability and BNF can be exploited through beneficial soil P solubilizing microorganisms (PSM). These microorganisms can increase plant-available P by modifying either rhizosphere soil processes or promoting plant traits, which lead to increased P uptake by the production of plant growth-promoting substances, both of which could indirectly influence the efficiency of BNF in legumes. In this review, we report on the importance of microbial P bio-solubilization as a pathway for improving BNF in grain legumes via PSM and P solubilizing bacteria (PSB). Because BNF in legumes is a P-requiring agro-ecological process, the ability of soil PSB to synergize with the rhizobial strains is likely a key belowground process worth investigating for advanced research aiming to improve rhizosphere biological functions necessary for sustainable legume-based cropping systems.

The leguminous trees Vachellia seyal (Del.) and Prosopis juliflora (Swartz) DC and their association with rhizobial strains from the root-influence zone of the grass Sporobolus robustus Kunth

This study focused on the genetic, symbiotic and phenotypic diversity of a collection of 12 Vachellia seyal and Prosopis juliflora rhizobial strains that were isolated from soils influenced by the roots of the grass Sporobolus robustus. Phylogenetic trees were constructed based on data from the 16S rRNA gene, from a multi-locus sequence analysis (MLSA) of the housekeeping genes recA, atpD, glnA and gyrB, as well as from the symbiotic genes nodA, nodC and nifH. Most of the mesorhizobial strains were clustered with the M. plurifarium type strain ORS 1032T and the 16S rRNA gene was as discriminatory as the other housekeeping genes. The Ensifer collection was closely related to E. alkalisoli YIC 4027T and E. fredii LMG 6217T using 16S rRNA and MLSA. Amplification of the Rhizobium collection was only observed with the 16S rRNA gene, where the strains were clustered with Rhizobium sp. 1B, Rhizobium sp. SEMIA 6411, Rhizobium sp. AS1-101a and Rhizobium sp. ORS 3441. The phylogeny of the nifH gene from Mesorhizobium and Ensifer strains were similar to those of nodulation genes (nodA and nodC). The nodA-nodC and nifH gene phylogenies were not consistent with those of 16S rRNA and the housekeeping genes. Ensifer genospecies tolerated high salinity better than the other genotypes after testing on a salt content gradient up to 49‰. We conclude that the rhizosphere of Sporobolus tussocks harbors a rhizobial microbiota, which could be capable of helping V. seyal and P. juliflora to grow better in saline soils.

The effect of native strains of nodule bacteria on the development of symbiotic apparatus and on the productivity of new soybean cultivars

In 2018 and 2019, we studied new strains of nodule bacteria of soybean (Bradyrhizobium japonicum) in comparison with the standard (Noktin A) in field experiments on the experimental field of V.S. Pustovoit All-Russian Research Institute of Oil Crops (VNIIMK), Krasnodar on a leached extra heavy loam and weakly humus chernozem. The new strains were the strain 5/1, isolated from the meadow-chernozem soil of the Amur region and the strain 7p, isolated from the leached chernozem of the Krasnodar region. The aim of the research was to evaluate their effectiveness on promising soybean cultivars Slavia, Bars, Irbis and Opus by their influence on the development of symbiotic apparatus, development of root system and above-ground vegetative mass of plants in the phase of soybean vegetation, flowering and seed-filling, as well as on the seed yield and its quality.For 2 years, on average, all strains to varying degrees contributed to a more intensive development of a root system and an increase of above-ground mass of soybean plants at the beginning of the growth season. We observed the maximum increase in biomass by the seedfilling phase in the Bars cultivar with strains 5/1 and in the standard – by 45 and 48 %, respectively. However, the Slavia cultivar with bacterization variants in this phase had less dry above-ground plants mass than the control, by 30-51 %.Overall, the bacterization provided an increase in soybean productivity but to varying degrees by year and with different combinations of symbiotic partners (soybean cultivar – rhizobia strain). We observed the highest increase in seed productivity in Slavia and Opus cultivars: on average over 2 years - by 0.17-0.27 t/ha (8.7-13.0 %) and by 0.06-0.35 t/ha (2.6-15.1 %), respectively. The cultivars Bars and Irbis were less responsive to bacterization. We noted a certain cultivar-strain relation of preliminary complementary pairs: the Slavia cultivar – strains 5/1 and 7p; the Bars cultivar – strain 5/1; the Irbis cultivar – strains 5/1 and the standard; the Opus cultivar – strains 7p and the standard.

Sourcing Rhizobium leguminosarum biovar viciae strains from Mediterranean centres of origin to optimize nitrogen fixation in forage legumes grown on acid soils

AbstractOver the last three decades, farming systems in Europe and Australia have seen a decline in legume plantings, leading to reduced soil carbon and fertility, and an increase in plant disease, reliance on industrial nitrogen fertilizer and herbicides. In Australia, one reason for this decline has been the movement towards sowing crops and forages into dry soil, before the opening rains, as a consequence of climate variability. This practice predicates against the survival of rhizobial inoculants, and hence generates uncertainty about legume performance. The research reported here was initiated to improve the robustness of a specific forage legume/rhizobia symbiosis to increase nitrogen fixation in low pH, infertile soils. Rhizobial strains (Rhizobium leguminosarum biovar viciae) from Pisum sativum L. were sourced from acid soils in southern Italy and southern Australia. Strains were evaluated for N fixation on the forage legumes P. sativum, Vicia sativa and Vicia villosa, then for survival and persistence in acid soils (pHCa 4.6). Fourteen of the strains produced a higher percentage of nitrogen derived from the atmosphere (%Ndfa) compared to commercial comparator strain SU303 (<78%). Twenty‐two strains survived sufficiently into the second season to form more nodules than SU303, which only achieved 3% of plants nodulated. Elite strains WSM4643 and WSM4645 produced six times more nodulated plants than SU303 and had significantly higher saprophytic competence in acid soil. These strains have the ability to optimize symbiotic associations with field peas and vetch in soils with low fertility, carbon and pH that are restrictive to the current commercial strain SU303.