Identification of Rhizobia Isolated from Nodules of Mexican Commercial Soybean Varieties

Rhizobia, crucial for nitrogen fixation in leguminous plants, play a vital role in soybean cultivation. This study, conducted in Mexico, a major soybean importer, aimed to identify bacteria from nodules of five soybean varieties in high-production regions. Multilocus sequence analysis (MLSA) was employed for enhanced species resolution. The study identified six Bradyrhizobium species: Bradyrhizobium japonicum USDA 110, Bradyrhizobium japonicum USDA 6, Bradyrhizobium elkanii USDA 76, Bradyrhizobium neotropicale, Bradyrhizobium lablabi, and Bradyrhizobium icense. Bradyrhizobium japonicum USDA 110 predominated in the soils, displaying symbiotic preference for the Huasteca 400 variety. However, phylogenetic analysis didn't reveal a clear association between strains, soil, and soybean variety. This research sheds light on the diversity of rhizobia in Mexican soybean cultivation, contributing to the understanding of symbiotic relationships in soybean production systems.

Morpho-Physiological and Biochemical Characterization of Soybean-Associated Rhizobia and Effect of Their Liquid Inoculant Formulation on Nodulation of Host Plants in the Cameroon Cotton Fields Zone

The aim of this research was to assess the diversity of the Cameroon cotton zone in soybean associated rhizobia in order to formulate the most efficient elite inoculant to boost both the cotton and soybean production. Therefore, soybean associated rhizobia were isolated and characterized morphologically, physiologically and biochemically on YEMA culture media. For each of the two soybean varieties (Houla1 and TGX1910 14F) used, the trials were laid out in two IRAD-fields of North Cameroon (Sanguere-Paul) and Far-North (Soukoundou) respectively, under a complete randomized complete block design, the isolate formulations representing the treatments. The six isolated strains (IS1, IS2, IS3, IS4, IS5, IS6) from which seven liquid inoculant were formulated were revealed to belong to the same slow growing group of rhizobia, with a high level of tolerance to temperature, pH, and salinity, with optimum growth at respectively 28˚C, pH (7 - 9), salt (1% - 5%). Not surprisingly, root nodules were formed by both inoculated and uninoculated soybean plants. However, the most efficient soybean-rhizobia symbiosis for nodulations were isolate IS6 associated to TGX1910 14F variety, and isolate IS5 associated to Houla1variety at Sanguere-Paul. Whereas isolate M was associated to TGX1910 14F variety, Houla 1 variety had affinity with native rhizobia isolates at Soukoundou. The present results suggest the adaptability of rhizobia isolates to a particular soybean variety at a particular cotton fields zone. These findings should be taken into consideration for commercial inoculant formulation.

Isolation and Authentication of Local Rhizobia Nodulating Common Bean (Phaseolus vulgaris L.) in Different Agro-Ecological Zones of Côte d’Ivoire

Legumes such as common bean (Phaseolus vulgaris L.) have been introduced into cropping systems for sustainable soil management. Consequently, the loss of fertility of the latter remains a major constraint to bean production because this legume is rarely fertilized, yet it is considered to be a poor nitrogen fixer in the absence of inoculation. To overcome this, this study was undertaken with the objective of seeking efficient local rhizobia in order to propose a bean inoculum formulation. To do this, soil samples taken from twelve localities in the Centre, North and West areas of C?te d’Ivoire were used to trap bean nodulating rhizobia. The ROBA1 bean accession used was sown in pots containing the sampled soils. Seedlings were uprooted at the start of flowering and nodulation was assessed. The isolates obtained were purified and then characterized phenotypically. The infectivity and symbiotic efficacy of these isolates were determined in vitro by the authentication test in which the purified isolates were reinoculated to their original host plant. A total of 24 rhizobium isolates were obtained from the soils of six localities. During morphological characterization, the isolates showed typical characteristics of Rhizobium. With the exception of RPC501, RPC505 and RPC522, all isolates were authenticated and able to nodulate the host plant in controlled culture. Isolates RPC502, RPC507, and RPC508 were effective and significantly increased (P < 0.05) nodule number and weight, height, and plant biomass. This study has, therefore, revealed the presence of effective local rhizobia in Ivorian soils and capable of nodulating common beans. A genetic characterization of efficient rhizobia identified after experimentation in different environmental conditions should be considered before being recommended as bean rhizobia inoculant.

Isolation and Characterization of Nitrogen Fixing Rhizobia from Cultivated and Uncultivated Soils of Northern Tanzania

Soil bacteria1 called rhizobia are gram-negative capable to colonize the soil immediately surrounding roots under the influence of the plant “rhizosphere” and reduce atmospheric nitrogen into the form available to plants through nitrogen fixation process. Nitrogen is the most limiting and supplied nutrient to most plants, and the determinant of plant growth. Legumes differ with most plants because they have access to nitrogen from both mineral and symbiotic sources. Small-scale farmers who are the major legume producers in Africa rarely apply fertilizers during legume production. Hence, the crop is largely dependent on fixed nitrogen from native nitrogen fixers. Isolation of rhizobia for legume production has been given a little attention in Africa due to inadequate research or negligence of researchers and unawareness of its potential in legume production as well as lack of an intention from skilled personnel to popularize the technology. Evaluation of effectiveness of isolated rhizobia is essential for inoculants preparation, host specificity recommendation and symbiotic effectiveness. The isolation, determination of their population in the soil and assessing factors affecting their population and testing the effectiveness of native nitrogen fixers with respect to right trap host crop are given a special attention in this review.

Phenotypic, Stress Tolerance and Plant Growth Promoting Characteristics of Rhizobial Isolates from Selected Wild Legumes of Semiarid Region, Tirupati, India

Rhizobia are vital for nitrogen input, fertility of soil and legume plant growth. Knowledge on rhizobial diversity from arid and semiarid areas is important for dry land agriculture in the context of climatic change and for economic utilization. This study provides morphological, biochemical, stress tolerance and plant growth promoting characteristics of fifteen rhizobial isolates from the nodules of same number of wild legumes and one isolate from cultivated Arachis hypogea from semi-arid region, Tirupati. The bacterial isolates were confirmed as rhizobia based on colony morphology and biochemical tests. Based on the colour change of YMA-BTB medium, eight isolates were identified as slow growers and six were fast growers. The isolates differed in growth pattern, colony morphology, antibiotic resistance at higher concentrations and uniformity in utilization of carbon and nitrogen sources. The isolates are tolerant to NaCl up to one percent, displayed normal growth at temperatures 28℃ - 30℃, at neutral pH and poor growth at pH 5and 9. The isolates varied in the production of EPS and IAA, positive for phosphate solubilization and siderophore formation. This functional diversity displayed by the isolates can be utilised for the legume crop production by cross inoculation.

Comparative analysis of symbiotic phenotypes of soybean ’’Tianlong 1’’ with two different rhizobia and co-inoculation at different developmental stages

Symbiotic nitrogen fixation between soybean and rhizobia, which directly catalyze reduction of atmospheric nitrogen into ammonia, has critical importance in agricultural economy and environment. However, soybean symbiotic nitrogen efficiency, which changes with growth stage, largely relies on symbiotic host-specificity and nodule development. In this report, symbiotic phenotypes of soybean ‘Tianlong 1’ with different inoculation (inoculated with Bradyrhizobium japonicum strain 113-2, Sinorhizobium fredii USDA205 and co-inoculated with 113-2 and USDA205) were comparatively studied at different developmental stages. Without additional nitrogen, chlorophyll content, above ground fresh weight,plant height, nodule number and nodule dry weight changed with different rhizobia at various developmental stages. 113-2 had more advantages than USDA205 in promoting plant growth and nodulation. Nodulation morphology of co-inoculation was more similar to 113-2 than USDA205. Competitive nodulation between two rhizobia promoted plant growth, which had significant agricultural application prospect. For the first time, this study provided evidence for co-inoculation with different rhizobia having positive effect on plant growth, and shed new light on the competitive relationship between different rhizobia.

Phenotypic and Genetic Characterization of Trifolium Rhizobia Isolated from Temperate and Subtropical Regions of China

The clovers that comprise Trifolium genus are naturalized in the subtropical and tropical zones in China. They are valuable bioresources as important green manures and pasture grass, which contribute biologically fixed dinitrogen (N_2) and provide nutrition to farming systems. However, there are very few effective strains available for inoculant production and there is little information available about symbiotic rhizobia in Chinese legume clover root nodules. In this study, 139 root nodule bacteria were isolated from two clover species (Trifolium repens and Trifolium pretense) growing in the subtropical and temperate regions of China, 16S rRNA gene sequence analysis, BOX-PCR, whole cell protein SDS-PAGE, and nodulation tests were performed to characterize these strains.The results showed that phenotypic and genetic diversities among 139 isolates were large, with 83 protein patterns and 66 BOXAIR profiles, respectively. The rhizobial strains were first divided into two large phenotypic protein groups. The sequencing strains representing the two groups were related to Rhizobium leguminosarum USDA2370~T and R. sophorae CCBAU03386~T and had 99.6%-100% similarities. The phylogeny specificity of the rhizobia from clover was elucidated, while showed a large variation in the fingerprints of the phenotypes and genotypes and genetic diversity was high (revealed by Shannon diversity index, H'). The rhizobial isolates from subtropical regions, such as Anhui Province, Yunnan Province and Hubei Province, had higher diversities than those from temperate areas, such as Hebei Province and Shanxi Province, which could be used to identify rhizobial strains from clover and screen efficient inoculum strains. A number of diverse rhizobial strains had been identified and a pool of currently available clover rhizobial strains were increased. This would ultimately increase the likelihood of identifying more efficient strains suited for developing a successful inoculation strategy for the production of white clover.

Phosphorus Fertilizer Rating and Rhizobia Inoculation for Improved Productivity of Cowpea in Northern Uganda

Cowpea (Vigna unguiculata) is an important legume crop in the tropics and subtropical regions of the world. It is mainly grown for its leaves and grains, and to a lesser extent as a fodder crop. Cowpea is considered as the most important food grain legume in the dry savannas of tropical Africa. This study compared the yield of local (Agondire) and improved (SECOW 2W) cowpea varieties grown on an Oxisol. Inorganic P at levels of 0, 10, 20, and 40 kg·ha-1 was tested on each variety with or without rhizobia inoculation. The experiments were set up in a randomized complete block design and replicated thrice during the short and long rains of the 2015/2016 seasons on fifteen fields in Arua district, northern Uganda. Agondire responded significantly (P < 0.05) better than SECOW 2W when high rates of inorganic phosphorus (40 kg P ha-1) were applied. A significant increase of 26.4% and 28.4% in grain yield of Agondire and SECOW 2W, respectively was obtained after inoculation with rhizobia. We concluded that inoculation and P fertilizer application increased the yield of both varieties, but with inoculation, SECOW 2W performs much better at lower P fertilizer rates than Agondire. Therefore, we recommend growing of SECOW 2W under inoculation with 20 kg P ha-1 and an application of 40 kg P ha-1 for Agondire local cowpea variety in northern Uganda.

Evidence of Fungicides Degradation by Rhizobia

Fungicides which are not easily degradable have the greatest adverse effects on soil microbes. These pesticides negatively affect the growth and multiplication of fungi and bacteria and consequently cause the disturbance of the natural soil microbial balance. In this study two fungicide tolerant isolates of rhizobia;clover isolate (TA1) and peanut isolate (8) were assessed in their capacity to degrade Vitavax and Rizolex. The performance of these isolates in fungicides degradation was tested using the colorimetric assay for Rizolex and the HPLC analysis for Vitavax to detect the degradation products. Using HPLC analyses, the control sample showed specific peak indicating the Vitavax presence in the medium. The specific peak did not change in the control samples throughout the experiment.With the strainTA1 the specific peak of the Vitavax fungicides started to reduce as the incubation time goes on. The Vitavax fungicide did not degrade completely after 240 hours of incubation with rhizobial isolate. The Rizolex used in this study contained blend of Thiram (active ingredient of Rizolex) and Tolcofs methyl fungicides in 1:1 ratio. The biodegradation of Rizolex in the liquid media showed the formation of two new intermediates which were released into the medium indicating the degradation of the tested fungicide by peanut rhizobial isolate No. 8 in 48 hrs of incubation 45% of this compound was degraded. This work shows that the selection of fungicides tolerant rhizobial strains is important to protect the rhizobial inoculants from the toxic effect of the pesticides.

Resistance to Abiotic Stress and Effectiveness of Native Rhizobia on Bambara Groundnut [Vigna subterranea (L.) Verdc.] in Benin

Bambara groundnut [Vigna subterranea (L.) Verdc.], as a legume, can establish relationships with nitrogen-fixing bacteria such as Rhizobium. However, Rhizobium efficacy is not always optimal due to the lack or poor efficient strains in the soil. This study aimed to evaluate symbiotic efficiency of endogenous Rhizobia nodulating Bambara groundnut and their resistance to abiotic conditions. Root nodules were randomly sampled from three agroecological zones across the country, surface sterilized, ground and paste plated on YEMA media. After 24 hours, the bacterial colonies were purified. The pure cultures were further characterized using morphological and biochemical methods and their resistance to antibiotics and heavy metals was evaluated. Lastly, the symbiotic efficiency of the isolates was assessed through a greenhouse experiment. A total of eighty-five presumptive strains were isolated from Bambara groundnut roots nodules obtained from the farms. The physiological characterization of the isolated showed a decrease in isolates growth when NaCl concentration was more than 7%. In addition, 47% of the isolates were tolerant to a temperature of 40°C. Most of the isolates were highly resistant to Erythromycin in all its concentration levels and to Kanamycin, Spectinomycin, Neomycin and Ampicillin at 10 μg⋅mL−1. Most of them showed resistance to Cu and Zn at 10 μg⋅mL−1. Results of the effectiveness test on two Bambara groundnut varieties yielded dry shoot matter varying from 3.33 g⋅plant−1 to 7.21 g⋅plant−1 for variety 1 and from 4.38 g⋅plant−1 to 8.38 g⋅plant−1 on variety 2. N uptake ranged between 0.09 g⋅plant−1 and 0.29 g⋅plant−1 for variety 1 and between 0.12 and 0.29 g⋅plant−1 for variety 2. The isolates yielding higher shoot dry weight and N uptake were LMSEM312, LMSEM338, LMSEM307, LMSEM351 for variety 1 and LMSEM338, LMSEM309, LMSEM307 for variety 2. The isolates showing better performance can be used to develop bio-fertilizer for sustainable Bambara groundnut production in Benin.

Response of Indigenous Rhizobia to the Inoculation of Soybean[Glycine max(L.)Merrill]Varieties Cultivated under Controlled Conditions in Cote 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 C?te 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 C?te 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.

Adsorption of Cadmium by Soil Colloids and Minerals in Presence of Rhizobia

Experiments were conducted to study the adsorption of Cd on two soil colloids (red soil and yellow- brown soil) and three variable-charge minerals (goethite, noncrystalline Fe oxide and kaolin) in the absence and presence of rhizobia. The tested strain Rhizobium fredii C6, tolerant to 0.8 mmol L-1 Cd, was selected from 30 rhizobial strains. Results showed that the isotherms for the adsorption of Cd by examined soil colloids and minerals in the presence of rhizobia could be described by Langmuir equation. Within the range of the numbers of rhizobial cells studied, the amount of Cd adsorbed by each system increased with increasing rhizobial cells. Greater increases for the adsorption of Cd were found in red soil and kaolin systems. Rhizobia influence on the adsorption of Cd by examined soil colloids and minerals was different from that on the adsorption of Cu. The presence of rhizobia increased the adsorption sanity of soil colloids and minerals for Cd, particularly for the goethite and kaolin systems. The discrepancies in the influence of rhizobia on the adsorbability and affinity of selected soil colloids and minerals for Cd suggested the different interactions of rhizobia with various soil components. It is assumed that bacterial biomass plays an important role in controlling the mobility and bioavailability of Cd in soils with kaolinite and goethite as the major colloidal components, such as in variable-charge soil.

Phylogenetically clustering of rhizobia by genome structure:application to unclassified Rhizobium

Previous research reveals that the genome structures of rhizobial type strains and reference strains can reflect their phylogenetic relationships. In order to further explore the potential application of genome structure as a phyl ogenetic marker in rhizobial natural taxonomy, this study analyzed the genome st ructures of 29 unclassified nodule bacteria isolated from the root nodules of le guminous trees, Robinia sp., Dalbergia spp., and Albizia spp. and 7 rhizobial re ference strains by I-CeuI cleavage, then clustered these bacteria phylogenetical ly based on their genome structures and compared these clusters with those based on numerical taxonomy and 16S rDNA PCR-RFLP. Eleven phylogenetic clusters were obtained. The clusters were in large part consistent with those based on numeric al taxonomy and 16S rDNA PCR-RFLP. Also there are inconsistent clusters based on the above three methods. But results are completely consistent with 16S rRNA cl usters. This suggested that the genome structure clustering method can be used t o fastly identify root nodule isolates and detect their phylogenetic relationshi ps. The credibility and repeatability of the results, together with the simplici ty and possibility to analyze a large number of strains in a short time of the m ethod, indicates the broad potential application of genome structure as phylogen etic marker to categorize rhizobial isolates and should in the future facilitate biodiversity studies.

Selection of rhizobial strains differing in their nodulation kinetics under low temperature in four temperate legume species

Background:Winter climate change including frequent freeze-thaw episodes and shallow snow cover will have major impacts on the spring regrowth of perennial crops.Non-bloating perennial forage legume species including sainfoin,birdsfoot trefoil,red clover,and alsike clover have been bred for their adaptation to harsh winter conditions.In parallel,the selection of cold-tolerant rhizobial strains could allow earlier symbiotic nitrogen(N)fixation to hasten spring regrowth of legumes.Methods:To identify strains forming nodules rapidly and showing high N-fixing potential,60 rhizobial strains in association with four temperate legume species were evaluated over 11 weeks under spring soil temperatures for kinetics of nodule formation,nitrogenase activity,and host yield.Results:Strains differed in their capacity to form efficient nodules on legume hosts over time.Strains showing higher nitrogenase activity were arctic strain N10 with sainfoin and strain L2 with birdsfoot trefoil.For clovers,nitrogenase activity was similar for control and inoculated plants,likely due to formation of effective nodules in controls by endophyte rhizobia present in seeds.Conclusions:Selection based on nodulation kinetics at low temperature,nitrogenase activity,and yield was effective to identify performant rhizobial strains for legume crops.The use of cold-tolerant strains could help mitigate winter climatic changes.

Physical and Microbiological Properties of Alfalfa-Established Soil in the Semiarid Horqin Sandy Land in Northern China

In a previous article, we reported that a local variety of alfalfa (Medicago sativa L. cv. Aohan) had high potential to be a pioneer plant for ecological restoration in the Horqin Sandy Land, China. The plantation of Aohan significantly improved the organic matter, clay, total carbon and nitrogen contents of the soils. In this study, we investigated the physical properties such as dispersion ratio, water-stable aggregates content, and the soil microbiomes, five years after alfalfa establishment in the same study site. We found no significant difference in the dispersion ratios between the soils before and after alfalfa establishment, and all the soils at the study site were erosive. Water stable aggregates mainly distributed in 96%, suggesting that it would take longer time for improving soil structure. However, large-size aggregates (2 - 5 mm) content was slightly higher in the alfalfa planting plots. This slight increase is presumed to have long-term importance for soil and ecosystem recovery in semi-arid areas like Horqin Sandy Land. Moreover, we also found that Actinomycetes dominated the microbial community in both bulk and rhizosphere soils, and two kinds of rhizobia, Bradyrhizobium and Sinorhizobium fredii, were identified in the rhizosphere soil.

楚雄南苜蓿根瘤菌的鉴定及其耐酸耐铝特性研究

为了获得耐酸铝性强的楚雄南苜蓿(Medicago polymorpha L.)共生根瘤菌菌株,本研究对从不同地区采集到的5份根瘤样品进行分离、纯化和鉴定。对鉴定得到的根瘤菌进行菌体形态观察、低氮回接以及耐酸、铝特性的研究。结果表明:YS-8,YS-10,DH-9,DH-31属于根瘤菌属根瘤菌、CX-44属于中华根瘤菌属苜蓿中华根瘤菌,5个菌株均符合根瘤菌基本形态特征。接种5株根瘤菌后,楚雄南苜蓿的干重、鲜重、株高、结瘤数均显著高于对照(P<0.05);pH值在4.5~7.5范围内,5株菌株均能正常生长,当pH值=3.5时,5株菌株全部死亡;当Al3+浓度在100~1 500 mg·L^(-1)之间,随着Al3+浓度的升高,菌株生长逐渐缓慢,Al3+浓度达到2 000 mg·L^(-1)时,5株菌株全部死亡。分离出的5株根瘤菌均能与楚雄南苜蓿共生结瘤并促进其生长,且具有较强的耐酸铝性。筛选出的5株根瘤菌均能在pH值大于3.5且铝离子浓度(pH值=5)小于1 500 mg·L^(-1)的条件下推广使用,菌株CX-44的效果最佳。

Cd胁迫下接种根瘤菌对紫花苜蓿氮代谢的影响

为探讨接种根瘤菌对Cd胁迫下紫花苜蓿氮代谢的影响,采用盆栽试验,以2种紫花苜蓿(维多利亚、WL525HQ)为植物材料,研究Cd(0 mg·kg^(-1)和50 mg·kg^(-1))处理土壤接种根瘤菌对两种紫花苜蓿的氮代谢关键酶活性和含氮化合物的影响。结果表明,Cd胁迫影响紫花苜蓿氮代谢,50 mg·kg^(-1)Cd胁迫对未接种根瘤菌紫花苜蓿WL525HQ地上部硝酸还原酶(NR)活性的影响最大,NR活性较0 mg·kg^(-1)Cd处理降低85.01%。0 mg·kg^(-1)Cd处理时,WL525HQ接种根瘤菌后地上部谷氨酸合成酶(GOGAT)活性较未接种组提高95.53%,维多利亚接种根瘤菌后地上部天冬酰胺合成酶(AS)活性增加33.30%。50 mg·kg^(-1)Cd胁迫时,与不接种根瘤菌相比,接种根瘤菌的WL525HQ地上部NR活性增幅最大(164.66%),接种根瘤菌后维多利亚地下部NR活性与未接种处理相比提高99.46%。50 mg·kg^(-1)Cd处理中,接种根瘤菌缓解了Cd胁迫对紫花苜蓿含氮物质积累的抑制,维多利亚、WL525HQ的可溶性蛋白含量分别比未接种组显著提高6.24%和5.82%,游离氨基酸含量增加16.10%和18.70%,维多利亚总氮含量显著提高9.48%。研究表明,接种根瘤菌可通过调节氮代谢关键酶活性来促进Cd胁迫下紫花苜蓿的氮素向蛋白质合成的方向转运积累,一定程度上缓解Cd对紫花苜蓿的伤害。

皖豫高效抗逆大豆根瘤菌Y2-4的选育

为筛选适合安徽、河南两地的大豆高效抗逆根瘤菌,从安徽和河南两地选取7个采样点采集大豆根瘤并分离根瘤菌,通过系统发育分子鉴定、回接大豆筛选、抗逆境胁迫能力测定筛选高效抗逆大豆根瘤菌,并通过初步田间接种试验对其促生效果进行了评估。结果显示:共分离得到621株大豆根瘤细菌,其中Sinorhizobium属菌株418株(67.3%),是该地区的优势大豆根瘤菌,Bradyrhizobium属菌株198株(31.9%),Rhizobium属菌株5株(0.8%,回接大豆不能结瘤)。筛选得到1株具有应用潜力的高效抗逆根瘤菌S.fredii Y2-4,与参比菌株CCBAU 45436相比,Y2-4菌株接种的大豆叶绿素含量、根瘤数、地上干重分别提高了1.8%、15.5%和9.8%,且在3%NaCl盐胁迫及38℃高温胁迫条件下仍具有生长能力。田间接种试验结果显示,在全氮(225 kg·hm^(-2)复合肥,氮磷钾比例15∶15∶15)、减氮26.6%(225 kg·hm^(-2)复合肥,氮磷钾比例11∶15∶15)、不施氮(225 kg·hm^(-2)复合肥,氮磷钾比例0∶15∶15)3种氮肥水平下接种Y2-4菌株均可以提高大豆产量,“减氮26.6%+接种Y2-4”处理较“全氮+不接种”处理条件下,大豆产量增加了25.5%。综上所述,Y2-4菌株可以作为皖豫两省部分地区的大豆高效抗逆根瘤菌接种菌株进行推广应用。