Indigenous Rhizobia Research Articles

Inoculation of Erythrina brucei with plant-beneficial microbial consortia enhanced its growth and improved soil nitrogen and phosphorous status when applied as green manure

Erythrina brucei has been applied as a green manure to improve soil fertility in southern Ethiopia. It has been nodulated by indigenous rhizobia. The objectives of this study were to evaluate the effects of E. brucei inoculation with microbial consortia consisted of Bradyrhizobium shewense, Acinetobacter soli and arbuscular mycorrhizal fungi (AMF)on E.brucei growth, soil nitrogen and phosphorous status after application as a green manure.A field experiment was conducted by inoculating E. Brucei with different microbial consortia. E. brucei inoculated with the microbial consortia were grown for 150 days. Its shoot length was measured at 60, 90, 120 and 150 days after planting. Then, plants were uprooted and mulched as a green manure. The soil nitrogen, available phosphorous and soil organic matter analysis were done. The experimental design was completely randomized block design with eight treatments comprised of three replications. Inoculated treatments did not show a significant (p < 0.05) difference in shoot length in the first 60 days. However, shoot length was increased between 19.1 and 41.3 %, 10.5–43.4 % and 8.7–37.6 %, respectively at 90, 120 and 150 days. The soil organic matter was improved in both inoculated and un-inoculated treatments. The improvements in the soil organic matter of un-inoculated treatments may be due to the decomposition of un-inoculated plants biomass in the soil. The B. shewense inoculation improved the soil nitrogen by 17 %. The soil phosphorous was improved in 57 % of inoculated treatments. The inoculation of E. brucei with microbial consortia enhanced its growth and improved soil fertility when applied as a green manure. Inoculating the green manure legumes with symbiotically effective rhizobia and plant-beneficial microbes can enhance the growth of E. brucei and its nutrient uptake.

Impact of microbial consortium of Rhizobium tropici and Rhizobium mayense on the growth of Phaseolus vulgaris L.

The main objectives of the present investigation was to characterize and recognize potential indigenous Rhizobium spp. associated with red clover nodules, as well as to evaluate the influence of prospective rhizobia inoculation (individual and consortia) on common bean plant growth. Total of 8 rhizobia like bacteria were isolated and were investigated for their specific PGP traits, production of hydrolytic enzymes. Results revealed, four isolates synthesize IAA (22.3 ± 1.45 to 88.6 ± 1.45 μg mL−1), three isolates solubilized phosphate (40.69 ± 1.25 to 216.3 ± 1.31 μg mL−1), three isolates solubilized potassium, produced siderophore, and showed chitinase production, two isolates possess ACC deaminase activity, one isolate was able to solubilize zinc, 5 isolates produced β- 1, 3-glucanase (0.38 ± 0.005 to 2.82 ± 0.011 % units) and four isolates produced cellulase. Two bacterial isolates found to exhibit most of the PGP activities, were selected and identified on the basis of phenotypic, biochemical tests and 16S rRNA sequencing, as Rhizobium tropici IHTF-1 and Rhizobium mayense IHTF-2. Interaction of these potential rhizobium strains individually and consortia with common bean plants under greenhouse conditions boosted root and shoot length, fresh and dry biomass compared to un-inoculated control plants. SEM study revealed that both the strains, IHTF-1 and IHTF-2 colonized common bean roots. These results imply that Rhizobium spp., identified in this work, can be used as bio-inoculants to increase common bean plant production in a sustainable way.

Evaluation of Rhizobium along with Multifunctional Rhizobacteria for Improving the Growth and Yield of Black Gram [Vigna mungo (L.) Hepper

Background: Indigenous rhizobial populations may be unable to achieve successful symbiosis in the field due to rare population and unfavourable soil environment. Introduced plant growth promoting rhizobacteria (PGPR) are frequently linked to faster growth, development, and yield of plant with synergetic effect on indigenous Rhizobium bacteria. Furthermore, co-inoculating legumes with both Rhizobium and PGPR is proven more effective for improving nodulation as well as growth and development of legumes. Methods: The experiment was conducted at research farm of TCA, Dholi Muzaffarpur a campus of Dr. Rajendra Prasad Central Agriculture University, Pusa, Bihar during kharif season of 2021 to investigate the “Evaluation of Rhizobium along with multifunctional Rhizobacteria for improving the growth and yield of black gram [Vigna mungo (L.) Hepper]”. There were eight number of treatments and replicated thrice in a randomized block design. The treatment comprised as T1- control, T2- Rhizobium (Bradyrhizobium spp.), T3- Rhizobium + PUK-171 (Stenotrophomonas rhizophila), T4- Rhizobium + NE 10 (Bacillus cereus), T5-Rhizobium + Pseudomonas spp., T6-Rhizobium + LMSR 45 (Pantoea agglomerans), T7-Rhizobium + Methylobacterium, T8-N as per RDF. Result: The result revealed that co-inoculation of Rhizobium + PUK-171 (Stenotrophomonas rhizophila) significantly increase the plant height, number of leaves plant-1, number of branches plant‑1, plant dry weight, crop growth rate, and in nodule studies number of nodules plant-1, dry weight of nodules recoded significantly higher result as compare to T1, T2, and T8 and found at par with rest of treatment. In yield attributing character number of pods plant-1 recorded significantly higher result in co-inoculation of Rhizobium + PUK-171 (Stenotrophomonas rhizophila) and rest of character did not produce significant effect, in case of seed yield similar trends was followed, while in case of stover yield co-inoculation of Rhizobium along with Rhizobium + NE 10 (Bacillus cereus) recorded significantly higher result as compare to T1 and T8 and at par with rest of treatments. Harvest index did not produce significant effect.

Effectiveness of indigenous Rhizobium sp. isolates from peatland soils on soybean (Glycine max L. Merril) growth and production

The low productivity of soybeans can be overcome by cultivating them on peatlands, accompanied by the provision of indigenous Rhizobium strains derived from peatlands. Isolating Rhizobium sp. from peatlands is believed to enhance soybean productivity on such land. This study aims to determine the effectiveness of local Riau Rhizobium sp. isolates for soybean cultivation in Riau peatlands. Six isolates of Rhizobium sp. were used in this study, obtained from plants growing on peatlands: IIMB4, IIRM1, IIRM2 from the rhizosphere of Mucuna bracteata, and IIRA4, IIRA2, IIRA6 from the rhizosphere of Acacia crassicarpa. The experiment followed a completely randomized design (CRD), with each treatment replicated four times. The treatments included control, commercial Rhizobium sp., isolates IIMB4, IIRA2, IIRA6, IIRM2, IIRA4, and IIRM1. The results demonstrated that all indigenous Rhizobium sp. isolates from peatlands, particularly IIMB4, effectively formed symbiotic associations with soybean plant roots, improving growth parameters and increasing soybean production. Nevertheless, it is also necessary to assess the effectiveness of these Rhizobium sp. isolates on various other leguminous plant species to identify the most efficient symbiotic isolates across different leguminous crops.

Selected indigenous drought tolerant rhizobium strains as promising biostimulants for common bean in Northern Spain.

Drought is the most detrimental abiotic stress in agriculture, limiting crop growth and yield and, currently, its risk is increasing due to climate change. Thereby, ensuring food security will be one of the greatest challenges of the agriculture in the nearest future, accordingly it is essential to look for sustainable strategies to cope the negative impact of drought on crops. Inoculation of pulses with biostimulants such as rhizobium strains with high nitrogen fixation efficiency and drought-tolerance, has emerged as a promising and sustainable production strategy. However, some commercial inoculums are not effective under field conditions due to its lower effectiveness against indigenous rhizobium strains in the establishment of the symbiosis. Thus, in the present study, we evaluated the ability to improve drought tolerance in common bean plants of different indigenous rhizobia strains isolated from nearby crop fields in the Basque Country either affected by drought or salinity. The plants in this trial were grown in a climatic chamber under controlled conditions and exposed to values of 30% relative soil water content at the time of harvest, which is considered a severe drought. From the nine bacteria strains evaluated, three were found to be highly efficient under drought (namely 353, A12 and A13). These strains sustained high infectiveness (nodulation capacity) and effectiveness (shoot biomass production) under drought, even surpassing the plants inoculated with the CIAT899 reference strain, as well as the chemically N-fertilized plants. The tolerance mechanisms developed by plants inoculated with 353, A12 and A13 strains were a better adjustment of the cell wall elasticity that prevents mechanical damages in the plasma membrane, a higher WUE and an avoidance of the phenological delay caused by drought, developing a greater number of flowers. These results provide the basis for the development of efficient common bean inoculants able to increase the yield of this crop under drought conditions in the Northern Spain and, thus, to be used as biostimulants. In addition, the use of these efficient nitrogen fixation bacteria strains is a sustainable alternative to chemical fertilization, reducing cost and minimizing its negative impact on environment.

Mechanism of Cr(VI) reduction by an indigenous Rhizobium pusense CR02 isolated from chromite mining quarry water (CMQW) at Sukinda Valley, India.

Toxicological assessment of CMQW generated due to chromite mining activities at Sukinda Valley has revealed high chromium contamination along with Zn and Fe. The present study focused on the mechanism of chromate reduction by an indigenous multi-metal tolerant bacterium, Rhizobium pusense CR02, isolated from CMQW. The isolated strain has shown resistance up to 520 mg/L of Cr(VI) with an IC50 value of 385.4 mg/L. The highest reduction rate 8.6 × 10-2/h was recorded with 20 mg/L of initial concentration of Cr(VI). Extracellular (3.06 ± 0.012 U/mL), intracellular (3.60 ± 0.13 U/mL), and membrane (1.89 ± 0.01 U/mL) associated chromate reductases were found to be involved for reduction. The extracellular polymeric substances (EPS) produced by the isolate also enhanced reduction activity of 46.32 ± 1.69 mg/L after 72 h with an initial concentration of 50 mg/L. FTIR analysis revealed the involvement of functional groups -OH, -CO, and -NH for Cr(VI) biosorption whereas P=O, -CO-NH- and -COOH interacted with Cr(III). Zeta potential with less negative surface charge favored reduction of Cr(VI). Treatment of CMQW by bacterial isolate detoxified Cr(VI) minimizing chromosomal aberrations in root cells of Allium cepa L., suggesting the role of Rhizobium pusense CR02 as a promising bio-agent for Cr(VI) detoxification.

Effect of nano-formulated indigenous Rhizobium sp. on nodulation, growth, and yield of Edamame soybean

The isolates of indigenous Rhizobium sp. are compatible with Edamame soybean, but the inoculum formulation using a carrier material from ordinary peat has not been optimal. The study was aimed to evaluate the effects of the nano-formulation of indigenous Rhizobium sp. inoculum on the growth and yield of Edamame soybean. The research was arranged in a randomized complete block design using a single factor treatment, namely the inoculum formulae, consisting of Nano Peat 95% + Nano Biochar 5%, Nano Peat 95% + Nano Bone 5%, Nano Peat 90% + Nano Biochar 5% + Nano Bone 5%, and Peat 50% + Charcoal 49% + Lime 1% (control). Each treatment consisted of three replications, producing 12 experimental units. Observations were made on the population dynamics of indigenous Rhizobium sp., nodulation, growth, and yield of Edamame soybean. The inoculation of nano-formulated indigenous Rhizobium sp. was significantly effective in nodulation, accelerating flowering period, and increasing the yield. The treatment of Nano Peat 90% + Nano Biochar 5% + Nano Bone 5% produced the highest yield (10.28 tons/ha), indicating an increase of 2.3% compared to the control

Competitiveness of Bradyrhizobium japonicum inoculation strain for soybean nodule occupancy

The competitiveness of Bradyrhizobium japonicum inoculation strain against indigenous rhizobia was examined in a soil pot experiment. The effect of inoculation strain was evaluated under different soil conditions: with or without previously grown soybean and applied commercial inoculant. Molecular identification of inoculation strain and investigated rhizobial isolates, obtained from nodules representing inoculated treatments, was performed based on 16S rDNA and enterobacterial repetitive intergenic consensus (ERIC) sequencing. Inoculation strain showed a significant effect on the investigated parameters in both soils. Higher nodule occupancy (45% vs. 18%), nodule number (111% vs. 5%), nodule dry weight (49% vs. 9%), shoot length (15% vs. 7%), root length (31% vs. 13%), shoot dry weight (34% vs. 11%), shoot nitrogen content (27% vs. 2%), and nodule nitrogen content (9% vs. 5%) was detected in soil without previously grown soybean and applied commercial inoculant. Soil had a significant effect on the shoot, root and nodule nitrogen content, while interaction of experimental factors significantly altered dry weight and nitrogen content of shoots, roots and nodules, as well as number of nodules. Nodulation parameters were significantly related with shoot dry weight, shoot and nodule nitrogen content. Symbiotic performance of inoculation strains in the field could be improved through co-selection for their competitiveness and effectiveness.

A new function of white-rot fungi Ceriporia lacerata HG2011: improvement of biological nitrogen fixation of broad bean (Vicia faba)

The inoculation of plant growth-promoting microbes with multifarious functions is a simple, economic, and effective way to improve nodulation and biological nitrogen fixation (BNF) of legumes. Broad bean (Vicia faba) is commonly grown in the winter in tropics and subtropics for increasing soil N and farmers’ income. The new functions of Ceriporia lacerata HG2011, a white-rot fungus, in nodulation and BNF (measured by 15N natural abundance) were studied with the broad bean in liquid culture, soil incubation, and greenhouse pot experiments. The results showed that this fungus released IAA, GA, and Fe-binding ligands into culture solutions, increased lateral roots and root surfaces, and mobilized phosphorus and iron into bioavailable forms in the soil. These performances may be beneficial to nodulation and BNF. The indigenous rhizobia that infect broad been were long-lived in the experimental soil. The efficiency of exogenous rhizobium inoculation may be unsatisfactory in the soils for frequently growing broad beans because of fierce competition with native rhizobia. Compared with no inoculation, the fungal inoculant increased nutrient (nitrogen, phosphorus, and potassium) availability in the fertilized soil, nodule mass, and plant BNF and nutrient uptake, leading to higher plant biomass and grain yield. Thus, C. lacerata HG2011 provided more potential sites for rhizobia infection in nodulation, increased nodule size, and improved nodule mineral nutrient (particularly phosphorus and iron) and photosynthate acquisitions, resulting in better nodulation and increased plant BNF. These significant findings firstly proved a new function of C. lacerata HG2011 in improving the inoculation and BNF of legume plants.

Abundance and Symbiotic Rhizobia Colonizing Soybean (Glycine max) in Soils of Kakamega County, Western Kenya

Identification of effective indigenous rhizobia strain nodulating soybean (Glycine max) was conducted in Kakamega County, Western Kenya. This study was carried out to establish the abundance and symbiotic efficiency of native rhizobia strains in soil samples collected from 12 sites in four agroecological zones within the region. The MPN enumeration technique was used to estimate the indigenous rhizobia numbers and showed that 54% of the sampled sites had high abundance. Rhizobia number in the soil collected from the six regions varied from 2.5 × 102 to 3.12 × 103 cells·g− soil. Thirty isolates from the soil collected in the four regions were tested for efficiency using soybean as the trap plant in Leonard jars containing sterilized vermiculite irrigated with nitrogen-free media. Determination of the relationship between rhizobial abundance and symbiotic efficiency with respect to the soil chemical conditions was performed using ANOVA, and the means were compared using Tukey’s honest significant difference test. Inoculation with bacterial isolates significantly ( P &lt; 0.05 ) increased the nodule number and shoot dry weight, while weight of the seeds showed variations across the groups. The soil pH across the 4 regions ranged between 5.41 and 6.52.

The relative contribution of indigenous and introduced arbuscular mycorrhizal fungi and rhizobia to plant nutrient acquisition in soybean/maize intercropping in unsterilized soils

It has been demonstrated that intercropped crops may benefit from inoculation with rhizobia or arbuscular mycorrhizal (AM) fungi in soybean/maize intercropping systems under sterilized conditions. Little is known about the relative contribution of indigenous and introduced AM fungi and rhizobia to nutrient acquisition of intercropped soybean and maize in unsterilized soils. In this study, we evaluated the effectiveness of indigenous and introduced AM fungi and rhizobia in a soybean/maize intercropping system under unsterilized soil conditions. The results show that introduced rhizobial inoculation promoted soybean nodulation and growth. Single AM fungal inoculation promoted indigenous rhizobial nodulation and increased maize AM root colonization, but had little effect on maize growth. Co-inoculation strongly increased plant dry weight, and nitrogen (N) and phosphorus (P) content of the intercropped soybean compared to those with only indigenous rhizobial and AM fungal communities, but had no effect on those of maize in the same intercropped system. These results indicate that AM fungal inoculation promoted nodulation by indigenous rhizobia. Effective rhizobial inoculation combined with introduced AM fungi may not only promote symbiotic N2 fixation, but also enhance rhizosphere processes, which has the potential to improve nutrient acquisition in the field. Soybean is a weak competitor compared with maize in intercropping systems. Inoculation with introduced AM and rhizobia ameliorated the growth suppression of intercropped soybean, but inhibited growth of intercropped maize, indicating that inoculation of introduced AM fungi and/or rhizobia partly shifted the competitive advantage from maize to soybean. In conclusion, introduced AM fungi and rhizobia contributed more than indigenous populations to promoting growth and nutrient acquisition of the intercropped soybean in unsterilized soils.

Characterization of Rhizobium Indigenous Isolates and Their Compatibility with Edamame Soybean

Three isolates were isolated from edamame soybean nodules and characterized as indigenous Rhizobium sp. compatible with Edamame soybean, showing the potential to be developed as an inoculum for biological fertilizers that can increase the efficiency of nitrogen fertilizers. All isolates grew on YMA + Congo Red medium, with colony characteristics of a circular shape, pink color, 1-3 mm in diameter with convex elevation, and slightly translucent (Opaque). The results of microscopic characterization showed that the bacilli-shaped cells were gram-negative. The growth curve showed that all isolates could grow optimally after 48 hours of culture. Physiologically, the three isolates were aerobic and catalase-producing bacteria. The re-inoculation of these Rhizobium isolates on edamame seeds proved its compatibility indicated by effective nodule formation up to 48.03 - 66.23%.

Phylogenetic diversity of indigenous Rhizobium trapped from the natural habitat of Pisum sativum L. in eastern and central Algeria

The nitrogen-fixing symbiosis fixation between legumes and Rhizobium helps the plant to survive and to compete effectively on nitrogen poor soils. The soil environment attached to the root system is characterized by intense microbial activity. This work aimed to study the diversity of indigenous rhizobia living in the rhizosphere of forage pea in eastern and central Algeria. Bacteria were trapped in vitro from collected soils. They were isolated from nodules by direct isolation or by bacterial trapping, and tested for nodulation. Further characterization was carried out to identify the isolates. Ninety-four isolates were obtained. Thirty-four were rhizobial strains that could, with two exceptions, establish root-nodule symbioses with the host plant. Different profiles of susceptibility to rhizobiophages indicated that the majority of isolates were likely to be members of the Rhizobium leguminosarum group of species. The strains revealed diverse plasmid profiles, and diverse restriction patterns of cpn60 gene amplicons and on Southern blot analysis of nodABC genes. Sequences of 16S rRNA gene showed that all isolates exhibited 99.85% identity with R. leguminosarum sv. viciae USDA 2370T, R. laguerreae FB206T and R. anhuiense CCBAU 23252T. Analysis of cpn60 sequences revealed two groups. One of them clustered with ≤99% identity with R. laguerreae FB403. The second was clustered with ≤99% identity with R. laguerreae FB206T. Our findings suggest that the isolates may belong to the species R. laguerreae.

Towards sustainable yield improvement: field inoculation of soybean with Bradyrhizobium and co-inoculation with Azospirillum in Mozambique.

The effects of sole inoculation of soybean (Glycine max L. Merrill) with Bradyrhizobium and co-inoculation with Bradyrhizobium and Azospirillum on nodulation, plant growth and yields were investigated in the 2013/2014 and 2014/2015 cropping seasons under field conditions in Mozambique. The treatments included (1) Control (non-inoculated control, with symbiosis depending on indigenous rhizobia), (2) Urea (non-inoculated, receiving 200kgha-1 of N), (3) Sole inoculation with B. diazoefficiens strain USDA 110, and (4) Co-inoculation with B. diazoefficiens strain USDA 110 and A. brasilense strains Ab-V5 and Ab-V6, evaluated in a randomized complete block design with five replications. Nodule number and dry weight, shoot dry weight, biological and grain yields, grain dry weight, and harvest index were evaluated. In general, both sole inoculation and co-inoculation enhanced nodulation in relation to control. Sole inoculation increased grain yield by 22% (356kgha-1), the same enhancement magnitude attained under mineral N treatment, suggesting that Bradyrhizobium inoculation provides ecological and economic sustainability to the soybean crop in Mozambique or other countries with similar agro-climatic conditions. Co-inoculation did not increase grain yields in relation to neither the control nor sole inoculation, indicating that further research with adapted and high yielding soybean varieties along with effective rhizobial strains is required in Mozambique to attune the beneficial Azospirillum-plant cultivar-rhizobia interactions that have been reported in other countries for several legumes, including soybean.

Nitrogen uptake and growth of white clover inoculated with indigenous and exotic Rhizobium strains

Little information is available on investigating the effectiveness of indigenous and exotic rhizobia in enhancing nitrogen uptake and growth of white clover. This study aimed to evaluate the nitrogen fixation effectiveness of native rhizobia isolated from white clover grown in Taiwan as compared to an exotic strain, Rhizobium leguminosarum bv. trifolii BCRC 14266. Indigenous rhizobia were isolated from nodules in roots of white clover, and 16S rRNA gene sequences were used to identify their taxonomy. To compare the symbiotic effectiveness of indigenous and exotic rhizobia, white clover plants were inoculated respectively with two indigenous isolates (CHB 1120 and CHB 1121), BCRC 14266, and a non-inoculated control. Based on 16S rRNA gene sequences, CHB 1120 and CHB 1121 could be identified as Rhizobium species. Compared with the non-inoculated control and BCRC 14266, CHB 1120 and CHB 1121 significantly increased the dry weight of shoots and roots at 75 days after planting (DAP). Additionally, CHB 1120 and CHB 1121 significantly enhanced the amount of chlorophyll present in leaves estimated by SPAD readings, increasing nitrogen contents in shoots by 38.1 and 49.2%, respectively. In comparison with BCRC 14266, CHB 1120 and CHB 1121 significantly increased the nodule number and nitrogenase activity at both 45 and 75 DAP. In conclusion, the two indigenous strains significantly outperform the exotic strain and non-inoculated control in promoting nitrogen uptake and growth of white clover.

THE EFFECTIVENESS OF INDIGENOUS ENDOMYCORRHIZA AND RHIZOBIUM INOCULUM IN INCREASING NUTRIENT UPTAKE AND YIELD OF SOYBEAN IN DRY LAND

Increasing the productivity of soybeans in dry land can be done by designing a package of fertilizer technology based on biological materials using indigenous endomycorrhiza and Rhizobium. The application of indigenous endomycorrhizal biofertilizer combined with Rhizobium is expected to be able to improve nitrogen and phosporus uptake so as to increase the productivity of soybeans in dry land. The experiment used two-factor factorial randomized block design. The first factor was dose of endomycorrhizal spores of Glomus that consisted of four levels, namely, treatment without endomycorrhiza inoculation, dose of 50endomycorrhizal spores, dose of 100 endomycorrhizal spores, and dose of 150 endomycorrhizal spores. The second factor was inoculation of Rhizobium inoculum that consisted of two levels, namely, treatment without Rhizobium inoculation and Rhizobium inoculation. The results showed that combination of 50 endomycorrhizal spores with Rhizobium inoculation gave the best effect on the number of effective root nodules per plant, endomycorrhizal infection per plant, nutrient uptake by plant, number of pods per plant, number of seeds per plant, and oven-dry weight of seeds per plant.

Genomic insight into the origins and evolution of symbiosis genes in Phaseolus vulgaris microsymbionts

BackgroundPhaseolus vulgaris (common bean) microsymbionts belonging to the bacterial genera Rhizobium, Bradyrhizobium, and Ensifer (Sinorhizobium) have been isolated across the globe. Individual symbiosis genes (e.g., nodC) of these rhizobia can be different within each genus and among distinct genera. Little information is available about the symbiotic structure of indigenous Rhizobium strains nodulating introduced bean plants or the emergence of a symbiotic ability to associate with bean plants in Bradyrhizobium and Ensifer strains. Here, we sequenced the genomes of 29 representative bean microsymbionts (21 Rhizobium, four Ensifer, and four Bradyrhizobium) and compared them with closely related reference strains to estimate the origins of symbiosis genes among these Chinese bean microsymbionts.ResultsComparative genomics demonstrated horizontal gene transfer exclusively at the plasmid level, leading to expanded diversity of bean-nodulating Rhizobium strains. Analysis of vertically transferred genes uncovered 191 (out of the 2654) single-copy core genes with phylogenies strictly consistent with the taxonomic status of bacterial species, but none were found on symbiosis plasmids. A common symbiotic region was wholly conserved within the Rhizobium genus yet different from those of the other two genera. A single strain of Ensifer and two Bradyrhizobium strains shared similar gene content with soybean microsymbionts in both chromosomes and symbiotic regions.ConclusionsThe 19 native bean Rhizobium microsymbionts were assigned to four defined species and six putative novel species. The symbiosis genes of R. phaseoli, R. sophoriradicis, and R. esperanzae strains that originated from Mexican bean-nodulating strains were possibly introduced alongside bean seeds. R. anhuiense strains displayed distinct host ranges, indicating transition into bean microsymbionts. Among the six putative novel species exclusive to China, horizontal transfer of symbiosis genes suggested symbiosis with other indigenous legumes and loss of originally symbiotic regions or non-symbionts before the introduction of common bean into China. Genome data for Ensifer and Bradyrhizobium strains indicated symbiotic compatibility between microsymbionts of common bean and other hosts such as soybean.

Response of Indigenous Rhizobia to the Inoculation of Soybean [&amp;lt;i&amp;gt;Glycine max&amp;lt;/i&amp;gt; (L.) Merrill] Varieties Cultivated under Controlled Conditions in C&amp;#244;te d’Ivoire

Soybean [Glycine max (L.) Merrill] is an important crop known to improve population nutritional status and increase soil fertility and its productivity through biological nitrogen fixation. In Cote d’Ivoire, the introduced Bradyrhizobium japonicum used as inoculum had slight compatibility to several soybean varieties compromising their vulgarization. Therefore, the present study was conducted to examine the infectiveness and the effectiveness of indigenous rhizobial isolates on three soybean varieties (Canarana, Doko and Piramana) cultivated in Cote d’Ivoire. The experiment was conducted with potted plant filled with sterilized sand and was statistically laid in Completely Randomized Design (CRD) with sixteen (16) natives rhizobia, one (01) reference strain and uninoculated control (with or without nitrogen) with three replications. The results showed that inoculation significantly improved nodule number, nodule dry weight, plant height and total dry matter of soybean over the negative control treatment. Among the inoculated treatments, five indigenous rhizobia RSC119, RSC324, RSC502, RSC504 and RSC508 significantly (P -1) compared to IRAT FA3 strain (95 mg·plant-1) on Doko. The higher effectiveness was recorded with RSC119, RSC504 and RSC502 with 206.73%; 201.79% and 200.45% respectively compared to TN (100%). The correlation analysis indicated significant association of nodule number and total biomass indicating the importance of symbiotic nitrogen fixation. Based on their infectiveness and their effectiveness, the isolates RSC119, RSC324, RSC502, RSC504 and RSC508 could be used as elite local rhizobia and tested in field conditions to establish their potential contribution on soybean productivity.

Vegetation cover affects rhizobia-tree legume symbiosis in the semi-arid region of Brazil

Biological nitrogen fixation (BNF) is the main form of introducing nitrogen into systems with low fertilizer input, which prevail in the semi-arid region of Brazil. BNF was evaluated in leucena and sabia grown in samples of a soil collected under different vegetation cover: native vegetation; capoeira (area abandoned for the restoration); agricultural use; sabia grove; and leucena grove. Nodulation was abundant in soil under all the types of cover. Leucena grown in soil under capoeira exhibited the highest dry biomass of nodules, while the same cover provided the lowest dry biomass of nodules for sabia. Growth and shoot biomass were higher in plants grown in soil under caatinga. BNF was high in leucena and sabia, reaching rates higher than 97% in plants grown in soil under capoeira. The highest amounts of fixed nitrogen (N) were found in leucena plants grown in soil under caatinga. It is the first estimate of the potential to fixed N for sabia and leucena in soils of the semi-arid region, providing an initial estimate of the amounts of N that can be fixed in the field by these tree legumes in the Brazilian semi-arid. Key words: Indigenous rhizobia, isotope, Leucaena leucocephala (Lam.) de Wit, Mimosa caesalpiniifolia Benth, N-15 natural abundance method, tropical dry forest.

Response of dry bean (Phaseolus vulgaris L.) to inoculation with indigenous and commercial Rhizobium strains under organic farming systems in Minnesota

Organic farmers recognize the importance of using Rhizobium to meet crop N fertility needs and to reduce use of chemical fertilizers. Field experiments were conducted during the 2015 and 2016 seasons at different organic fields to assess the effect of indigenous Rhizobium leguminosarum bv. phaseoli (OrgK9) and commercial R. tropici (CIAT899) strains on symbiotic performance and grain yield of bean varieties, Eclipse and Redhawk. Averaged for both varieties, nodule numbers on plants inoculated with CIAT899 (35.2 ± 3.7 and 26.3 ± 2.6 /plant) and OrgK9 (29.6 ± 2.5 and 26.8 ± 2.1 /plant) were significantly greater (P < 0.0001) than the control (18.9 ± 2.2 and 10.5 ± 3.1) in 2015 and 2016, respectively. Bean genotype Eclipse cultivated at Lamberton and inoculated with OrgK9 had (P < 0.0001) greater number of nodules compared with CIAT899-inoculated or non-inoculated plants. The N-content (3.3 ± 0.04%) of plants inoculated with CIAT899 was greater (P < 0.0001) compared with plants inoculated with OrgK9. Strain CIAT899 increased nodule occupancy by 29 and 62% and 4 and 26% on Red Hawk cultivated in the Lamberton and Farmington fields compared with the control in season 2015 and 2016, respectively. The majority of nodules formed on Red Hawk (76%) and Eclipse (64%) at Farmington were occupied by CIAT899 and OrgK9 in 2015 and 2016, respectively. Eclipse inoculated with OrgK9 had a significantly greater seed yields (2683 ± 402 and 2546 ± 247 kg/ha) compared with control (2265 ± 996 and 2058 ± 51 kg/ha) in both years, respectively. These results clearly indicate that symbiotic performance and grain yield of dry bean can be significantly increased by using Rhizobium inoculation under organic farming systems.