Differential effect of various endomycorrhizal fungi on nodulating ability of green gram by Bradyrhizobium sp. (Vigna) strain S24

Bradyrhizobium sp. (Vigna) strain S24 interacted differentially with eight vesicular-arbuscular mycorrhizal (VAM) fungi and caused significant variations in nodulation and growth parameters of green gram. Coinoculation with Scutellospora calospora resulted in the highest nitrogenase activity and dry biomass. The nodulation competitiveness of strain S24 was significantly higher (60–63%) in the presence of Glomus mosseae, G. fasciculatum and Scutellospora calospora when compared to treatment with single inoculation of S24 (51%). Percentage VAM colonization was higher in treatments having higher nocule occupancy of introduced strain (S24). Received: 26 June 1995     

Stimulation of nodulation and plant growth of chickpea (Cicer arietinum L.) by Pseudomonas spp. antagonistic to fungal pathogens

Two strains of Pseudomonas MRS23 and CRP55b showed antagonistic activity towards the pathogenic fungi Aspergillus sp., Fusarium oxysporum f. sp. ciceri, Pythium aphanidermatum and Rhizoctonia solani under culture conditions. Larger growth inhibition zones were obtained on nutrient agar (NA) and King's B media in comparison to potato dextrose agar and pigment production media. Both the strains produced siderophore in agar plates as well as in liquid cultures. Fungal inhibition zones were reduced in size and abolished in iron-supplemented NA medium by Pseudomonas strains MRS23 and CRP55b, respectively, indicating that some other metabolites along with siderophores are involved in growth inhibition of fungi by strain MRS23, whereas CRP55b produced only siderophores. Only Pseudomonas strain MRS23 was found to produce hydrocyanic acid (HCN). Seed bacterization with Pseudomonas strains of two chickpea (Cicer arietinum L.) cultivars, H8618 and C235, showed root-stunting effects at 5 days, whereas this inhibitory effect was overcome at 10 days of seedling growth in cv. H8618. Coinoculation of chickpea with Pseudomonas strains MRS23 and CRP55b, and Mesorhizobium sp. Cicer strain Ca181 resulted in the formation of 68.2-115.4% more nodules at 80 and 100 days after planting as compared to single inoculation with the Mesorhizobium strain under sterile conditions. The shoot dry weight ratios of coinoculated treatments at different stages of plant growth varied from 1.18 to 1.35 times that of Mesorhizobium-inoculated and 3.25 to 4.06 times those in uninoculated controls. The plant N contents were also increased significantly on coinoculation. Coinoculation effects of HCN-producing strain MRS23 were significantly lower than those of non-HCN-producing strain CRP55b in terms of shoot dry weight and shoot N. The results demonstrated the potential benefits of using rhizosphere bacteria as coinocula in nodule promotion and plant growth in chickpea.     

Antifungal and Plant Growth Promoting Activities of Indigenous Rhizobacteria Isolated from Maize (Zea mays L.) Rhizosphere

Plant growth promoting rhizobacteria (PGPR) enhance the plant growth directly by assisting in nutrient acquisition and modulating plant hormone levels, or indirectly by decreasing the inhibitory effects of various pathogens. The aim of this study was to select effective PGPR from a series of indigenous bacterial isolates by plant growth promotion and antifungal activity assays. This study confirmed that most of the isolates from maize rhizosphere were positive for PGPR properties by in vitro tests. Azotobacter and Bacillus isolates were better phosphate solubilizers and producers of lytic enzymes, hydrocyanic acid (HCN), and siderophores than Pseudomonas. Production of indole-3-acetic acid (IAA) and antifungal activity were the highest in Azotobacter, followed by Bacillus and Pseudomonas. The most effective Azotobacter isolates (Azt₃, Azt₆, Azt₁₂) and Bacillus isolates (Bac_10, Bac₁₆) could be used as PGPR agents for improving maize productivity. Further selection of isolates will be necessary to determine their efficiency in different soils.     

Arbuscular mycorrhizal fungal spore-associated bacteria affect mycorrhizal colonization,plant growth and potato pathogens

Arbuscular mycorrhizal (AM) fungi and their bacterial associates are essential living components of the soil microbiota. From a total of 385 bacteria previously isolated from spores of AM fungi (AMB), 10 were selected based on ability to inhibit growth of plant pathogens. Effects of these isolates on AM fungal colonization, plant growth in potato (Solanum tuberosum L.) and inhibition of pathogens was investigated. AM fungal root colonization of potato was 7-fold higher in the presence of the Pseudomonas FWC70 isolate in a greenhouse and was 6–9-fold higher in the presence of the three isolates Pseudomonas FWC70, Stenotrophomonas FWC94 and Arthrobacter FWC110 in an outdoor pot experiment. Several growth traits of potato were stimulated by the Pseudomonas isolates FWC16, FWC30 and FWC70 and by the Stenotrophomonas isolate FWC14. All three Pseudomonas isolates showed inhibition against Erwinia carotovora, Phytophthora infestans and Verticillium dahliae but Stenotrophomonas isolates were variable. Protease(s), siderophores and indole acetic acid were produced by all isolates. Chitinase(s) were produced by all Stenotrophomonas and phosphate-solubilizing activity by all Pseudomonas isolates, the Stenotrophomonas FWC14 isolate and the Arthrobacter FWC110 isolate. We conclude that some AMB are multifunctional and production of extracellular enzymes and bioactive compounds are likely mechanisms for their multifunctional activities. Our results show that some AMB are likely to contribute to the often described ability of AM fungi to inhibit pathogens, acquire mineral nutrients and modify plant root growth.     

Seed Bacterization with Fluorescent Pseudomonas spp. Enhances Nutrient Uptake and Growth of Cajanus cajan L.

Among plant-growth-promoting rhizobacteria (PGPR), fluorescent Pseudomonas spp. are an important group affecting plant growth. Pigeon pea is an important pulse crop and most of the studies were aimed at using Pseudomonas spp. for pest management in pigeon pea. Seventy-five fluorescent Pseudomonas spp. were isolated from diverse agroecosystems of India and evaluated for their plant-growth-promoting ability, primarily by the paper cup method. Seventeen selected isolates were further evaluated by short-term pot assay for plant growth promotion. Seeds treated with bacteria showed greater nutrient concentration and growth than the control. Isolate P17 showed significant growth promotion in terms of root length (54.5 cm), dry mass (323 mg), chlorophyll (24 spad units), carbohydrates (21.2 percent), nitrogen (2.45 percent), calcium (1.82 percent), iron (984 ppm), and manganese (564 ppm). Pseudomonas sp. P17 strain was identified as a potential PGPR for nutrient uptake and plant growth promotion in pigeon pea, and this finding paves a way for integrated plant nutrient management in rainfed agroecosystems.     

抗重金属植物根际细菌的植物促生长特征以及它们对黑芥种子萌发的影响

Phytoremediation is an emerging technology that uses plants and their associated microbes to clean up pollutants from the soil, water, and air. In order to select the plant growth-promoting rhizobacteria(PGPR) for phytoremediation of heavy metal contamination, 60 bacterial strains were isolated from the rhizosphere of two endemic plants, Prosopis laevigata and Spharealcea angustifolia, in a heavy metal-contaminated zone in Mexico. These rhizobacterial strains were characterized for the growth at different pH and salinity, extracellular enzyme production, solubilization of phosphate, heavy metal resistance, and plant growth-promoting(PGP) traits, including production of siderophores and indol-3-acetic acid(IAA). Overall, the obtained rhizobacteria presented multiple PGP traits. These rhizobacteria were also resistant to high levels of heavy metals(including As as a metalloid)(up to 480 mmol L(-1)As(V), 24 mmol L(-1)Pb(Ⅱ), 21 mmol L(-1)Cu(Ⅱ), and 4.5 mmol L(-1)Zn(Ⅱ)). Seven rhizobacterial strains with the best PGP traits were identified as members of Alcaligenes, Bacillus, Curtobacterium, and Microbacterium, and were selected for further bioassay.The inoculation of Brassica nigra seeds with Microbacterium sp. CE3R2, Microbacterium sp. NE1R5, Curtobacterium sp. NM1R1,and Microbacterium sp. NM3E9 facilitated the root development; they significantly improved the B. nigra seed germination and root growth in the presence of heavy metals such as 2.2 mmol L(-1)Zn(Ⅱ). The rhizobacterial strains isolated in the present study had the potential to be used as efficient bioinoculants in phytorremediation of soils contaminated with multiple heavy metals.     

Characterization of phosphate solubilizing fluorescent pseudomonads from the rhizosphere of Aloe vera (L.)

Soil phosphorous (P) deficiency is a major constraint to plant production which is overcome by adding inorganic-phosphate as chemical fertilizers. Fluorescent pseudomonads are the diverse group of bacteria able to mobilize sparingly soluble phosphate form. Total three hundred seven fluorescent Pseudomonas isolates were obtained from the Aloe barbadensis (Miller) rhizosphere. These Pseudomonas strains were further evaluated in vitro for their ability to solubilize phosphate and to produce indole acetic acid (IAA), hydrogen cyanide (HCN), siderophore and 1-aminocyclopropane 1- carboxylate (ACC) deaminase. Fifty three (36.8%) isolates produced IAA and 52 (36.1%) isolates produced siderophores whereas 36 (25.0%) and 31 (21.5%) isolates produced HCN and ACC deaminase, respectively. A positive correlation existed between siderophore and ACC deaminase producers. Cluster analysis showed rhizosphere as the major factor influencing the ecological distribution and physiological characterization of phosphate solubilizing bacteria (PSB). Based on partial 16S rRNA gene sequencing PSB were identified as Pseudomonas putida, Pseudomonas sp. and Pseudomonas plecoglossicida with highest phosphate solubilization ability. In conclusion, these phosphate solubilizing fluorescent pseudomonads would help in understanding their role in phosphorus solubilization and identification of potent phosphorus solubilizers from the rhizosphere of commercially grown A. barbadensis.     

A sensitive method for detecting the depletion of nonexchangealble potassium in the rhizosphere using a sequential extraction with 0.01 molar hydrochloric acid

Twenty-one strains of fluorescent pigment-producing Pseudomonas (abbreviated to FPP-Pseudomonas) species were isolated from soil and roots of apple and peach trees using selective media. FPP-Pseudomonas strains were identified as Pseudomonas fluorescens. Moreover, on the basis of the utilization of several organic compounds, these strains were divided into three groups.

P. fluorescens strains isolated from the roots were assigned to mainly groups 1 and 2, and most of the isolates from the soil to group 3. All the strains of group 2 exhibited antifungal activity (in vitro) against three soilborne plant pathogenic fungi: Rhizoctonia solani, Verticillium dahliae, and Rosellinia necatrix. These results suggest that the strains of group 2 play an important role as antifungal rhizobacteria.     

Population size,distribution, and symbiotic characteristics of indigenous Bradyrhizobium spp. that nodulate TGx soybean genotypes in Africa

Soils of many potential soybean fields in Africa are characterized by low levels of biological nitrogen fixation (BNF) activities and often cannot support high soybean yields without addition of inorganic N fertilizers or external application of soybean rhizobia. The most probable number (MPN) technique was used to determine the bradyrhizobial populations that nodulate TGx soybean genotypes (a cross between nonpromiscuous North American soybean genotypes and promiscuous Asian soybean genotypes), cowpea or North American soybean cv. Clark IV, in soils from 65 sites in 9 African countries. The symbiotic effectiveness of isolates from these soils was compared to that of Bradyrhizobium japonicum strain USDA110. The bradyrhizobial population sizes ranged from 0 to 10⁴ cells g⁻¹ soil. Bradyrhizobium sp. (TGx) populations were detected in 72% and B. japonicum (Clark) in 37% of the soil samples. Bradyrhizobium sp. (TGx) populations were generally low, and significantly less than that of the cowpea bradyrhizobial populations in 57% of the samples. Population sizes of less than 10 cells g⁻¹ soil were common as these were detected in at least 43% of the soil samples. B. japonicum (Clark) occurred in higher population densities in research sites compared to farmers’ fields. Bradyrhizobium sp. (TGx) populations were highly correlated with biotic but not abiotic factors. The frequent incidence of low Bradyrhizobium sp. (TGx) populations is unlikely to support optimum BNF enough for high soybean yields while the presence of B. japonicum (Clark) in research fields has the potential to compromise the selection pressure anticipated from the indigenous Bradyrhizobium spp. (Vigna) populations. Bradyrhizobium isolates could be placed in four symbiotic phenotype groups based on their effectiveness on a TGx soybean genotype and the North American cultivar Clark IV. Symbiotic phenotype group II isolates were as effective as B. japonicum strain USDA110 on both soybean genotypes while isolates of group IV were effective on the TGx soybean genotype but not on the Clark IV. The group IV isolates represent a unique subgroup of indigenous bradyrhizobia that can sustain high soybean yields when available in sufficient population densities.     

Co-inoculation of selected nodule endophytic rhizobacterial strains with Rhizobium tropici promotes plant growth and controls damping off in common bean

Production of common bean(Phaseolus vulgaris)is limited by the occurrence of damping off(rhizoctoniosis),which is caused by the fungus Rhizoctonia solani.However,the co-inoculation of plant growth-promoting rhizobacteria(PGPR)involved in biological control along with diatomic nitrogen(N2)-fixing rhizobia can enhance N nutrition and increase production.In this context,finding microorganisms with synergistic effects that perform these two roles is of fundamental importance to ensure adequate yield levels.The aim of this study was to evaluate the effects of co-inoculation of nodule endophytic strains of the genera Bacillus,Paenibacillus,Burkholderia,and Pseudomonas with Rhizobium tropici CIAT 899,an N2-fixing rhizobial strain,on the biocontrol of damping off and growth promotion in common bean plants.Greenhouse experiments were conducted under axenic conditions using the common bean cultivar Pérola.The first experiment evaluated the potential of the 14 rhizobacterial strains,which were inoculated alone or in combination with CIAT 899,for the control of R.solani.The second experiment evaluated the ability of these 14 rhizobacterial strains to promote plant growth with three manners of N supply:co-inoculation with CIAT 899 at low mineral N supply(5.25 mg N mL^-1),low mineral N supply(5.25 mg N mL^-1),and high mineral N supply(52.5 mg N mL^-1).The use of rhizobacteria combined with rhizobia contributed in a synergistic manner to the promotion of growth and the control of damping off in the common bean.Co-inoculation of the strains UFLA 02-281/03-18(Pseudomonas sp.),UFLA 02-286(Bacillus sp.),and UFLA 04-227(Burkholderia fungorum)together with CIAT 899 effectively controlled damping off.For the common bean,mineral N supply can be replaced by the co-inoculation of CIAT 899 with plant growth-promoting strains UFLA 02-281/02-286/02-290/02-293.Nodule endophytes UFLA02-281/02-286 are promising for co-inoculation with CIAT 899 in the common bean,promoting synergy with rhizobial inoculation and protection against disease.     

Phosphate-solubilization activity of bacterial strains in soil and their effect on soybean growth under greenhouse conditions

The efficiency of 13 phosphate-solubilizing bacteria (PSB; four Burkholderia sp., five Enterobacter sp., and four Bradyrhizobium sp.) was assessed in a soil plate assay by evaluating soil phosphorus (P) availability. A commercial argentine strain, Pseudomonas fluorescens, was used for comparing solubilizing activity. Burkholderia sp. PER2F, Enterobacter sp. PER3G, and Bradyrhizobium sp. PER2H strains solubilized the largest quantities of P in the soil plate assay after 60 days as compared with the other strains, including the commercial one. The effect of PSB inoculation on growth and nutrient uptake of soybean plants was also studied under greenhouse conditions. Plants inoculated with Burkholderia sp. PER2F had the highest aerial height and showed an appropriate N/P ratio. However, none of the PSB increased P uptake by plants. This suggests that PSB inoculation does not necessarily improve P nutrition in soybean, nor was there any relationship between P availability in the soil plate assay and P content in the soybean shoot in the greenhouse. We concluded that the selection of efficient PSB strains as possible inoculation tools for P-deficient soils should focus on the integral interpretation of soil assays, greenhouse experiments, and field trials.     

Dual inoculation of peanut with Glomus sp. and Bradyrhizobium sp. enhanced the symbiotic nitrogen fixation as assessed by 15N-Technique

Abstract

The response of peanut (Arachis hypogaea L.) to inoculation with vesicular-arbuscular mycorrhizal (VAM) fungi (Glomus etunicatum) and Bradyrhizobiurn sp. was studied in pots by the acetylene reduction activity (ARA) and ‘A-value’ methods. The soil used was a Light-coloured Andosol and the treatments consisted of the inoculation of VAM fungi only, inoculation of Bradyrhizobium only, dual inoculation of VAM fungi and Bradyrhizobium and control, under non-sterilized and sterilized soil conditions.

In the non-sterilized soil the ARA and nitrogen fixation determined by the ‘A-value’ method increased significantly only by dual inoculation of VAM fungi and Bradyrhizobium at 100 days after planting (DAP), but no significant difference was observed at 70 DAP. In the case of dual inoculation, 75% of the nitrogen of the plant was derived from fixation whereas the plants inoculated only with Bradyrhizobium derived 68% of their nitrogen from fixation and the control plants, 64%. Amount of P in plant increased significantly only by dual inoculation with VAM fungi and Bradyrhizobium.

In the sterilized soil a highly significant increase in the ARA was observed of the dual inoculation at all the sampling times. Nitrogen fixation determined by the A-value technique and N and P contents in plant also increased significantly by dual inoculation. Results obtained by the A-value method showed that plants with dual inoculation derived 68% of their nitrogen from fixation while the plants inoculated only with Bradyrhizobium, 38%.

From our this study we conclude that nitrogen fixation as well as N and P contents in peanut increased significantly only by dual inoculation with VAM fungi and Bradyrhizobium.     

Arbuscular mycorrhizal fungus and rhizobacteria affect the physiology and performance of Sulla coronaria plants subjected to salt stress by mitigation of ionic imbalance

Salt stress has become a major menace to plant growth and productivity. The main goal of this study was to investigate the effect of inoculation with the arbuscular mycorrhizal fungi (AMF; Rhizophagus intraradices) in combination or not with plant growth‐promoting rhizobacteria (PGPR; Pseudomonas sp. (Ps) and Bacillus subtilis) on the establishment and growth of Sulla coronaria plants under saline conditions. Pot experiments were conducted in a greenhouse and S. coronaria seedlings were stressed with NaCl (100 mM) for 4 weeks. Plant biomass, mineral nutrition of shoots and activities of rhizosphere soil enzymes were assessed. Salt stress significantly reduced plant growth while increasing sodium accumulation and electrolyte leakage from leaves. However, inoculation with AMF, whether alone or combined with the PGPR Pseudomonas sp. alleviated the salt‐induced reduction of dry weight. Inoculation with only AMF increased shoot nutrient concentrations resulting in higher K⁺: Na⁺, Ca²⁺: Na⁺, and Ca²⁺: Mg²⁺ ratios compared to the non‐inoculated plants under saline conditions. The co‐inoculation with AMF and Pseudomonas sp. under saline conditions lowered shoot sodium accumulation, electrolyte leakage and malondialdehyde (MDA) levels compared to non‐inoculated plants and plants inoculated only with AMF. The findings strongly suggest that inoculation with AMF alone or co‐inoculation with AMF and Pseudomonas sp. can alleviate salt stress of plants likely through mitigation of NaCl‐induced ionic imbalance, thereby improving the nutrient profile.     

Molecular characterization and PCR detection of a nitrogen-fixing Pseudomonas strain promoting rice growth

Nitrogen-fixing plant growth-promoting rhizobacteria (PGPR) from the genus Pseudomonas have received little attention so far. In the present study, a nitrogen-fixing phytohormone-producing bacterial isolate from kallar grass (strain K1) was identified as Pseudomonas sp. by rrs (16S ribosomal RNA gene) sequence analysis. rrs identity level was high with an uncharacterized marine bacterium (99%), Pseudomonas sp. PCP2 (98%), uncultured bacteria (98%), and Pseudomonas alcaligenes (97%). Partial nifH gene amplified from strain K1 showed 93% and 91% sequence similarities to those of Azotobacter chroococcum and Pseudomonas stutzeri, respectively. The effect of Pseudomonas strain K1 on rice varieties Super Basmati and Basmati 385 was compared with those of three non-Pseudomonas nitrogen-fixing PGPR (Azospirillum brasilense strain Wb3, Azospirillum lipoferum strain N4 and Zoogloea strain Ky1) used as single-strain inoculants. Pseudomonas sp. K1 was detected in the rhizosphere of inoculated plants by enrichment culture in nitrogen-free growth medium, which was followed by observation under the microscope as well as by PCR using a rrs-specific primer. For both rice varieties, an increase in shoot biomass and/or grain yield over that of noninoculated control plants was recorded in each inoculated treatment. The effect of Pseudomonas strain K1 on grain yield was comparable to those of A. brasilense Wb3 and Zoogloea sp. Ky1 for both rice varieties. These results show that nitrogen-fixing pseudomonads deserve attention as potential PGPR inoculants for rice.     

Ectomycorrhiza formation and willow growth promotion as affected by associated bacteria: role of microbial metabolites and use of C sources

Biotic interactions affect the impact of potential plant growth promoting microorganisms in the rhizosphere, but their magnitude and fundamentals are often hardly known. In a pot experiment, two physiologically different strains of the ectomycorrhizal fungus Paxillus involutus (GUL and FRA) were tested separately and in combination with associated bacteria (Sphingomonas paucimobilis 1 L, Ralstonia pickettii 16 B, Sphingomonas sp. 23 L) on their effects on the growth of willows (Salix viminalis). Both P. involutus strains significantly increased the growth of the willows compared with non-inoculated plants, but the magnitude of this effect was significantly affected by the fungal strain. The P. involutus strain GUL with higher synthesis of auxin-like substances, acid phosphatases, siderophores and faster utilisation of yeast extract in vitro increased the willow growth in situ more effectively than strain FRA. Additionally, dual inoculation with the P. involutus strains GUL and FRA in combination with the associated bacteria promoted the willow growth, especially the combination with S. paucimobilis 1 L. This bacterial strain used effectively C sources which are common components of plant root exudates, e.g. glucose, sucrose, maltose and mannose as well as compounds synthesized by fungi, e.g. trehalose in vitro. We conclude that the analyses of fungal metabolites and of C source use of associated bacteria can successfully contribute to accelerate the selection of capable plant growth promoting combinations.     

Co-inoculation of Acacia mangium with Glomus intraradices and Bradyrhizobium sp. in aeroponic culture

Acacia mangium grown in aeroponic culture was co-inoculated with selected strains of Bradyrhizobium sp. and Glomus intraradices. A single-step technique using alginate as an embedding and sticking agent for an inoculum composed of arbuscular mycorrhiza (AM)-infected sheared roots was used to infect plants. This method resulted in the successful establishment of AM in 100% of the inoculated plants after 7 weeks. The results indicated that dual microbial inoculation with Glomus intraradices strain S-043 and Bradyrhizobium strain AUST 13C stimulated the growth of A. mangium in aeroponic culture. The effects of single and dual microbial inoculations were also evaluated at two levels of P in the nutrient medium. A concentration of 5 mg P kg^–1 stimulated the development of AM without affecting plant development or establishment of Bradyrhizobium symbiosis. In contrast, saplings supplemented with a higher concentration of P (25 mg kg^–1) alone or co-inoculated with Bradyrhizobium had lower AM frequencies.     

Response of alfalfa (Medicago sativa L.) to single and mixed inoculation with phosphate-solubilizing bacteria and Sinorhizobium meliloti

The objectives of this work were to phenotypically and genetically characterize alfalfa rhizosphere bacteria and to evaluate the effect of single or mixed inoculation upon nodulation and biological nitrogen fixation. Thirty-two strains showed tricalcium phosphate solubilization ability, and two of them caused bigger or equal solubilization halos than the control strain P. putida SP22. The comparison of the 16S ribosomal DNA sequences indicated that these strains are phylogenetically related to Bacillus spp. and Pseudomonas spp. A beneficial effect of both isolates on alfalfa growth was observed in coinoculation assays. Pseudomonas sp. FM7d caused a significant increase in root and shoot dry weight, length, and surface area of roots, number, and symbiotic properties of alfalfa plants. The plants coinoculated with Sinorhizobium meliloti B399 and the Bacillus sp. M7c showed significant increases in the measured parameters. Our results indicating that strains Pseudomonas sp. FM7d and Bacillus sp. M7c can be considered for the formulation of new inoculants.     

Isolation and characterization of plant growth promoting endophytic bacterial isolates from root nodule of Lespedeza sp.

Thirty-nine endophytic bacterial strains were isolated from the nodule of Lespedeza sp. grown in two different locations of South Korea. All strains were checked for their plant growth promoting (PGP) abilities under in vitro conditions. Most of the isolates showed multiple PGP activity, i.e., indole acetic acid production, ACC deaminase activity, siderophore production, and phosphate solubilization. The strains were identified by using 16S rRNA gene sequence analysis as belonging to Alphaproteobacteria, Betaproteobacteria, Actinobacteria, and Firmicutes phylum with nine different genera Arthrobacter, Bacillus, Bradyrhizobium, Burkholderia, Dyella, Methylobacterium, Microbacterium, Rhizobium, and Staphylococcus. Gene nodA amplification showed positive results only for strains from Bradyrhizobium and Rhizobium genera. The strains from Bradyrhizobium and Rhizobium genera enhanced plant growth, nodulation, and acetylene reduction activity when inoculated on Vigna unguiculata L. (cowpea), whereas other strains did not induce nodule formation but enhanced plant growth. Herbaceous legume Lespedeza sp. formed root nodules with diverse bacterial group, and probably, these bacteria can be used for stimulating plant growth.     

Isolation and characterization of a mycorrhiza helper bacterium from rhizosphere soils of poplar stands

If mycorrhizal formation could be enhanced by co-inoculation with mycorrhiza helper bacteria (MHB) which promote rapid root colonization by specific ectomycorrhizal fungi, this would be of advantage to the poplar forest industry. A number of poplar rhizobacterial strains were isolated from 11 regions of the eastern China. Four of the isolates, SY15, DZ18, HLJ4, and PY10, were characterized as MHB potential strains based on their positive effect on growth of ectomycorrhizal fungi Pisolithus tinctorius (Pers.) and Lactarius insulsus (Fr.). Under greenhouse conditions, one of the bacterial isolate, DZ18, significantly promoted the poplar trees growth and ectomycorrhizal colonization of P. tinctorius and L. insulsus on Populus deltoides Marsh. In contrast, the other three isolates SY15, HLJ4, and PY10 promoted fungal growth in vitro experiments but did not enhance ectomycorrhizal (ECM) formation in the greenhouse experiment. Therefore, it was concluded that DZ18 can be considered as an MHB strain. DZ18 was identified as Bacillus sp. based on morphological, physiological, and biochemical analyses in combination with analysis of 16S rDNA gene sequences.     

Phylogeny and nitrogen fixation potential of Bradyrhizobium species isolated from the legume cover crop Pueraria phaseoloides (Roxb.) Benth. in Eastern Cameroon

Pueraria is an herbaceous, perennial legume crop originating in Asia. Pueraria phaseoloides (Roxb.) Benth. (tropical kudzu) is frequently introduced into production systems and is used as green manure, a cover crop and a forage plant, making it important economically. We used P. phaseoloides as a trap crop to study and characterize soil rhizobia in Eastern Cameroon. Bacteria were isolated from fresh nodules collected from field-grown P. phaseoloides roots. The 16S-23S rRNA internal transcribed spacer (ITS) sequences from 30 bacterial isolates were amplified by polymerase chain reaction (PCR) and the reaction products were sequenced. Phylogenetic analysis revealed that all isolates were ascribed to the genus Bradyrhizobium and were grouped into three clusters of Bradyrhizobium sp. strains, one cluster of B. yuanmingense strains, and one cluster of B. elkanii strains. Acetylene reduction assay (ARA) results indicated that the B. yuanmingense strains had significantly higher nitrogen fixation potential and that they could be used as inoculants to enhance nitrogen fixation in Pueraria grown in Eastern Cameroon.