Bradyrhizobia Isolates Research Articles

Features of Local Bradyrhizobia Populations after Long-Term Period in the Soil without a Host Plant

In previous years, the serological and genetic diversities of soybean nodule bacteria in agrocenoses of Ukraine have been researched. Less attention was paid to the study of their survival in the soil. Taking into account the natural heterogeneity of bacteria of the genus Bradyrhizobium, the aim of this work was to evaluate the diversity of bradyrhizobia in local populations of different soils after a long-term period without leguminous plants, to obtain new isolates of nodule bacteria and to study their properties. Methods. Microbiological (isolation of bradyrhizobia from the nodules of trap plants, study of the properties of strains), serological (study of the diversity of rhizobia in nodule populations, study of the serological affiliation of strains), vegetation and field experiments (study of plant infecting with bradyrhizobia). Results. Local populations of bradyrhizobia in sod-podzolic soil and leached chornozem were studied using trap plants of the genera Glycine, Vigna, and Lupinus. It was established that after a 7 to 8-year period without leguminous plants, active nodule bacteria remained in both types of soil, which nodulated cultivated and wild soybeans, cowpeas, mung beans, adzuki beans, and lupine. The main microsymbionts of plants of the genera Glycine and Vigna on different types of soil were soybean bradyrhizobia belonging to 6 serological groups: 46, M8, КВ11, 634b, HR, and B1. The representatives of 4 serogroups corresponded to the inoculant strains of Bradyrhizobium japonicum 46, M8, 634b, and КВ11, which were periodically used in the studied areas. In addition to B. japonicum, cowpea plants trapped microsymbionts of B. lupini serogroup 367a (4.2%) from the soil. Bradyrhizobia of serogroup B1 were detected both in nodules of cowpea (6.3%) and wild soybean (12.5%). 45.8% of lupine nodules were formed by bacteria B. lupini of serogroup 367a. The appearance in populations of representatives of serogroups HR and B1 along with a group of unidentified microsymbionts requires further research. Cultivation of trap plants of wild soybeans and various types of cowpea made it possible to identify saprophytic strain B. japonicum M8 (formed 25.0% to 83.4% of nodules) in the sod-podzolic soil, which did not infect the roots of cultivated soybeans. 70 isolates of bradyrhizobia were obtained from nodules of trap plants, which were preliminarily identified as B. japonicum, B. lupini, and Bradyrhizobium sp. Conclusions. The results confirm the importance of using different leguminous trap plants for a more complete characterization of the local rhizobial community. Cultivation of plants of the genera Glycine, Vigna, and Lupinus, capable of cross-infection, made it possible to detect bacteria B. japonicum (serogroups 46, M8, КВ11, 634b, HR), B. lupini (serogroup 367a), and Bradyrhizobium sp. (serogroup B1), which exist for a long-term period as saprophytes in sod-podzolic soil and leached chornozem. 70 isolates of bradyrhizobia were obtained, 35 of which were serologically related to the inoculant strains of B. japonicum introduced into the agrocenosis at the beginning of the research.

Exploring potential soybean bradyrhizobia from high trehalose-accumulating soybean genotypes for improved symbiotic effectiveness in soybean.

Drought is the most important factor limiting the activity of rhizobia during N-fixation and plant growth. In the present study, we isolated Bradyrhizobium spp. from root nodules of higher trehalose-accumulating soybean genotypes and examined for moisture stress tolerance on a gradient of polyethylene glycol (PEG 6000) amended in yeast extract mannitol (YEM) broth. In addition, the bradyrhizobial strains were also evaluated for symbiotic effectiveness on soybean. Based on 16S rDNA gene sequences, four bradyrhizobial species were recovered from high trehalose-accumulating genotypes, i.e., two Bradyrhizobium liaoningense strains (accession number KX230053, KX230054) from EC 538828 and PK-472, respectively, one Bradyrhizobium daqingense (accession number KX230052) from PK-472, and one Bradyrhizobium kavangense (accession number MN197775) from Valder genotype having low trehalose. These strains, along with two native strains, viz., Bradyrhizobium japonicum (JF792425), Bradyrhizobium liaoningense (JF792426), and one commercial rhizobium, were studied for nodulation, leghaemoglobin, and N-fixation abilities on soybean under sterilized sand microcosm conditions in a completely randomized design. Among all the strains, D-4A (B. daqingense) followed by D-4B (B. liaoningense) was found to have significantly higher nodulation traits and acetylene reduction assay (ARA) activity when compared to other strains and commercial rhizobia. The bradyrhizobia isolates showed plant growth promotion traits such as indole acetic acid (IAA), exopolysaccharide (EPS), and siderophore production, phosphate-solubilizing potential, and proline accumulation. The novel species B. daqingense was reported for the first time from Indian soil and observed to be a potential candidate strain and should be evaluated for conferring drought tolerance in soybean under simulated stress conditions.

Genetic and phenotypic diversity of microsymbionts nodulating promiscuous soybeans from different agro-climatic conditions

BackgroundGlobal food supply is highly dependent on field crop production that is currently severely threatened by changing climate, poor soil quality, abiotic, and biotic stresses. For instance, one of the major challenges to sustainable crop production in most developing countries is limited nitrogen in the soil. Symbiotic nitrogen fixation of legumes such as soybean (Glycine max (L.) Merril) with rhizobia plays a crucial role in supplying nitrogen sufficient to maintain good crop productivity. Characterization of indigenous bradyrhizobia is a prerequisite in the selection and development of effective bioinoculants. In view of this, bradyrhizobia were isolated from soybean nodules in four agro-climatic zones of eastern Kenya (Embu Upper Midland Zone, Embu Lower Midland Zone, Tharaka Upper Midland Zone, and Tharaka Lower Midland Zone) using two soybean varieties (SB8 and SB126). The isolates were characterized using biochemical, morphological, and genotypic approaches. DNA fingerprinting was carried out using 16S rRNA gene and restricted by enzymes HaeIII, Msp1, and EcoRI. ResultsThirty-eight (38) bradyrhizobia isolates obtained from the trapping experiments were placed into nine groups based on their morphological and biochemical characteristics. Most (77%) of the isolates had characteristics of fast-grower bradyrhizobia while 23% were slow-growers. Restriction digest revealed significant (p < 0.015) variation within populations and not among the agro-climatic zones based on analysis of molecular variance. Principal coordinate analysis demonstrated sympatric speciation of indigenous bradyrhizobia isolates. Embu Upper Midland Zone bradyrhizobia isolates had the highest polymorphic loci (80%) and highest genetic diversity estimates (H’ = 0.419) compared to other agro-climatic zones. ConclusionThe high diversity of bradyrhizobia isolates depicts a valuable genetic resource for selecting more effective and competitive strains to improve promiscuous soybean production at a low cost through biological nitrogen fixation.

Dual inoculation of soybean with &lt;i&gt;Rhizophagus irregularis&lt;/i&gt; and commercial &lt;i&gt;Bradyrhizobium japonicum&lt;/i&gt; increases nitrogen fixation and growth in organic and conventional soils

<abstract> Soil amendment with beneficial microorganisms is gaining popularity among farmers to alleviate the decline of soil fertility and to increase food production and maintain environmental quality. However, farm management greatly influence soil microbial abundance and function, which overly affects crop growth and development. In this work, greenhouse experiments involving soybeans were conducted to evaluate the effects of bradyrhizobia and arbuscular mycorrhizal fungi (AMF) dual inoculation on nodulation, AMF root colonization, growth and nutrient acquisition under contrasting farming systems. The experimental treatments were AMF and/or bradyrhizobia inoculation and dual inoculation on SC squire soybean variety. The exotic AMF inoculants used were <italic>Funneliformis mosseae</italic> (BEG 12) and <italic>Rhizophagus irregularis</italic> (BEG 44) while bacteria were commercial <italic>Bradyrhizobium japonicum</italic> (USDA110) and native bradyrhizobia isolates. Experiments with soil samples from organic and conventional farms were set out using a completely randomized design with three replicates. The results demonstrated that bradyrhizobia and AMF dual inoculation consistently and significantly enhanced soybean nodule dry weight (NDW), shoot dry weight (SDW) and AMF root colonization compared with individual bradyrhizobia<italic>, </italic> AMF and non-inoculated control. Moreover, organic soil significantly (p = 0.001) increased soybean SDW, NDW and AMF root colonization compared to conventional soil. Remarkably, shoot nutrients content differed in organic and conventional farming where, shoot nitrogen, phosphorus, potassium and organic carbon were higher in organic farming than the latter. Among individual inoculants, <italic>Rhizophagus irregularis</italic> out-performed <italic>Funneliformis mosseae, </italic> while commercial <italic>Bradyrhizobium japonicum</italic> showed higher performance than native bradyrhizobia. Our results demonstrated the importance of organic farming, AMF and bradyrhizobia dual inoculation in enhancing soybean growth and nutrient acquisition. However, field trials should be assessed to determine the good performance of bradyrhizobia and AMF dual inoculation in organic farming before being popularized and adopted by farmers as a sustainable agronomical management strategy to increase soil fertility and food productivity. </abstract>

Rescue and genetic assessment of soybean-nodulating Bradyrhizobium strains from an experimental field thirty years after inoculation

As the long-term phenotype and genetic stability of bacteria used as inoculant are important parameters in their ecology and for agricultural purposes, this study aimed genotypically characterize several-rescued bradyrhizobia of an experimental field thirty years after the first inoculation. A high genetic diversity of 30 bradyrhizobia isolates was observed, either by AFLP (H = 4.87) or rep-PCR (H = 4.18). The results indicate that the Bradyrhizobium population that persists in the Eldorado soil is genetically very diverse and different from the parental strains. All isolates were infective and trapped in IAS-5 soybean variety maintaining their nodulation and nitrogen fixation properties. Given that many rhizobia in a soil can lost the infective capacity and that the host genotype can affect the spectrum of rhizobial genotype selected from a soil, the genetic diversity of the complete bradyrhizobia population in Eldorado soil could be even higher than the identified in this work.

Superior symbiotic performance ofnative bradyrhizobia isolates over foreign inoculants with cowpea cultivars in India

Efficiency of symbiotic interactions of native and foreign inoculants bradyrhizobia isolates with six cowpea varieties (CO1, CO3, CO4, CO6, Paiyur 1 and Vamban 1) were evaluated under field conditions. Based on sequence analysis of 16S-23S rRNA intergenic spacer (IGS) region, three native isolates were classified as B. yuanmingense . Cowpea varieties inoculated with bradyrhizobia showed significantly superior nodulation, nitrogenase activity, dry matter accumulation, and seed yield compared to uninoculated treatments. The native B. yuanmingense strains CR03 and CR09 exhibited host-cultivar specificity with CO3, and Paiyur 1, respectively. Plants inoculated with native B. yuanmingense isolates produced higher plant dry matter accumulation and seed yield compared to foreign B. japonicum inoculated plants. Correlation coefficients analysis revealed that plant dry matter accumulation emerged as the best criterion for selection of effective cowpea-bradyrhizobia associations in given physical and biological conditions.

Host range, symbiotic effectiveness and nodulation competitiveness of some indigenous cowpea bradyrhizobia isolates from the transitional savanna zone of Ghana

Host range, symbiotic effectiveness and nodulation competitiveness of some indigenous cowpea bradyrhizobia isolates from the transitional savannah zone of Ghana

Molecular evidence for shifts in polysaccharide composition associated with adaptation of soybean Bradyrhizobium strains to the Brazilian Cerrado soils.

Pyrolysis mass spectrometry (PyMS) and DNA fingerprinting (RAPD and RSalpha hybridization) were used to characterize soybean inoculant strains and root nodule isolates of bradyrhizobia from the Brazilian Cerrado soils. Most isolates were shown to be derived from the inoculant strains on the basis of genotype comparisons by DNA fingerprinting. Phenotypic analysis (using PyMS) of the strains and separately of the polysaccharides derived from them showed that the nodule isolates differed from the parental strains, suggesting adaptation to the Cerrado soil environment. The extent of the differences between the derivatives and inoculant strains was similar for comparisons made on the basis of whole-cell preparations or from the isolated polysaccharides, indicating that the adaptation was caused by changes in the composition of the polysaccharides produced.

Specificity of Rhizobia Nodulating Genista monspessulana and Genista linifolia In Vitro and in Field Situations

Genista monspessulana and Genista linifolia are woody legumes with a high potential value for the rehabilitation of degraded soils , although field establishment of the plantlets in nonnative soils is very difficult because of the lack of specific rhizobial strains . In this work the rhizobia that nodulate the two species were tenta tively classified as a Bradyrhizobium sp . Only those soils with naturally occurring G. monspessulana or G. linifolia, now or in the past , had specific bradyrhizobia . Out of the six rhizobial strains analyzed , only Bradyrhizobium sp . ISLU21 , iso lated from Lupinus luteus, nodulated with the species studied . Out of the 11 legumes inoculated with the strains isolated from G. monspessulana and G. linifolia, only L. luteus produced infective nodules . In a field experiment , plants inocu lated with the specific bradyrhizobia isolates showed higher survival , growth rates , and N content than the noninoculated controls .

Symbiotic interactions of Phaseolus acutifolius and P. acutifolius × P. vulgaris hybrid progeny in symbiosis with Bradyrhizobium spp. And Rhizobium leguminosarum bv. phaseoli

The rhizobial requirements and the N2-fixing potential of Phaseolus acutifolius and P. acutifolius × P. vulgaris hybrid progeny were investigated in glasshouse experiments. Although P. acutifolius was promiscuous, effective nodulation and N2 fixation occurred only with a few Bradyrhizobium isolates, especially those that were isolated from P. acutifolius, P. limensis, P. penduratus, P. lunatus, Canavalia ensiformis, Calopogonium mucunoides, and Psophocarpus tetragonolobus. Strong host × Bradyrhizobium interactions were detected in four genotypes of P. acutifolius tested against eight isolates of bradyrhizobia and a commercial mixed inoculant. All seven progeny tested nodulated with Bradyrhizobium isolates and Rhizobium leguminosarum bv. phaseoli, but there was a highly specific rhizobial requirement for effective nodulation and N2 fixation. The progeny × rhizobial interaction accounted for 83% of the total phenotypic variation. Two (P-6 and P-7) and five (P-1, P-2, P-3, P-4, and P-5) progeny nodulated and fixed N2 effectively with R. l. bv. phaseoli and Bradyrhizobium spp., respectively. The R. l. bv. phaseoli – progeny symbiosis had a greater N2-fixing potential than the Bradyrhizobium isolate – progeny symbiosis. In a soil (oxisol) test, progeny P-6 and P-7 showed significant response to inoculation with R. l. bv. phaseoli. Strain R. l. bv. phaseoli TAL 182 was the most competitive strain, occupying 84% of the nodules in both the progeny. Key words: rhizobial requirements, Phaseolus acutifolius × Phaseolus vulgaris hybrids.

Intrinsic antibiotic resistance and serological characterization of populations of indigenous Bradyrhizobium isolated from nodules of Desmodium intortum and Macroptilium atropurpureum in three soils of S.E. Queensland

A collection of 1275 isolates of bradyrhizobia from three sites was made in the first (early) and 5th or 6th (late) growing seasons of uninoculated field plots of Desmodium intortum and Macroptilium atropurpureum. Isolates were characterized by intrinsic antibiotic resistance (IAR) and serological techniques. Non-hierarchial pattern analysis was used to group the isolates into antiobiotic inhibition response (IAR) types. Antisera were prepared for representative isolates of the most populous IAR types representing both early and late growing seasons. The data were used to test the hypothesis that under the influence of the soil root-rhizosphcre environment one or two IAR or serological types may dominate in the formation of nodules after several growing seasons. The IAR inhibition response patterns indicated a range of heterogeneity within and between sites and there was no significant increase of any IAR type in proportion of nodules formed in the late growing season samples. Most isolates at a site were accounted for by 2 or 3 of the IAR groups but the proportions of these types were different between sites. Serological grouping did not agree with the IAR groups, was more heterogeneous, and identified only 37–68% of isolates. However, there were serological types at each site that increased their proportion in the nodule population during the period of the experiment. Although the proportion of IAR types did not change between growing seasons the IAR screening provided a mechanism of selecting a representative dominant type for serological characterization and thus an avenue for selecting dominant strains that intrinsically may have the survival and competitive qualities required of a good inoculum strain.