Co-inoculations of arbuscular mycorrhizal fungi and rhizobia under salinity in alfalfa

Alfalfa (Medicago sativa L.) is cultivated in arid and semi-arid regions where salinity is one of the main limiting factors for its production. Thus, this experiment was conducted to evaluate the efficacy of arbuscular mycorrhizal fungus (AMF), Glomus mosseae, alfalfa rhizobia Sinorhizobium meliloti (R) seed inoculation in the development of salinity tolerance of different alfalfa cultivars (Rehnani, Pioneer and Bami) under a variety of salinity levels. The results revealed that under non-stress condition, root mycorrhizal infection, nodulation (the number and weight of nodules per plant), potassium (K), calcium (Ca), phosphorus (P), zinc (Zn), copper (Cu) and magnesium (Mg) contents of the root and shoot, the value of the K/Na ratio, protein [calculated from the nitrogen (N) content] and proline contents of the shoot and the alfalfa yield were found to be the highest while Na contents of the root and shoot were seen to be the lowest when seeds were double inoculated followed by mycorrhizae, rhizobium and control treatments, respectively. Similarly, under salinity condition, the greatest amounts of mycorrhizal infection, nodulation, root and shoot P contents, the value of K/Na ratio, the shoot proline content and the root Ca content were enhanced with the least amount of leaf Na content related to the cases of seeds which were double inoculated, followed by mycorrhizae, rhizobium and control treatments respectively. The results suggested that inoculation of alfalfa seed with AMF or R, especially double inoculation, causes a considerable increase in alfalfa yield under both saline and non-saline conditions by increasing colonization, nodulation and nutrient uptake.     

Evaluation of rhizobial strains nodulating lespedeza cuneata for improving n input into minesoil revegetation systems

Abstract

This study was designed to identify strains of Bradyrhizobium sp. (lespedeza) which could improve the plant performance and N status of Lespedeza cuneata (Dumont) G. Don (sericea lespedeza). Based upon preliminary screening for nodulation capability and acetylene reducing activity (ARA), six strains of rhizobia were chosen to be evaluated in the greenhouse for plant growth effects and N₂‐fixing ability.

The L. cuneata symbiosis with two strains, VPI 142 and VPI 163, resulted in the greatest plant growth, total N accumulation, and highest nodule nitrogenase activity (acetylene reduction activity). The high correlation (significant at the 1% level) of shoot dry weight with root dry weight (r = .94), nodule dry weight (r = .92), total shoot N (r = .98), total root N (r = .92), as related to nitrogenase activity of the nodule mass (r = .71), indicates that plant dry weight could be used as an easily determined measurement for screening isolates to be used with L. cuneata.

The identification of efficient rhizobial strains capable of increasing N input should benefit revegetation systems using L. cuneata as the principal legume.     

Effect of combined inoculation strains on growth of lupin on newly reclaimed land in Egypt

Inoculation studies with Bradyrhizobium isolates were investigated in a glasshouse and field experiment to compare the effects of single and multiple rhizobium inoculations on growth and symbiotic performance in lupin cultivation. A clear difference in host-strain compatibility was observed 120 days after sowing (greater number and dry weight of nodules, higher shoot dry weight and total N accumulation). To confirm the results from the glasshouse, combined inoculations with a different level of N fertilizer and six lupin cultivars were tested on newly reclaimed land at Tahreer Governorate, Egypt. N fertilizer application significantly decreased nodulation status of white lupin, but increased seed and straw yields compared with the non-fertilized control. Two combined inoculations were superior to the other strains in terms of infection and development of nodules in four accessions (1, 20, 30 and 32) and the cultivar Giza 1. All combinations of rhizobium strains tested enhanced the growth and total N accumulation of the lupin cultivars. Rhizobium inoculation increased seed and straw yield compared with the non-inoculated control. Reactions of the tested strain inoculations and interaction between Rhizobium strains and host plant in the glasshouse were almost identical to their reaction in the field. The results from this study suggest that the improvement through development of combined inoculation strains could be possible and would offer security for nodulation. High yields were accomplished with seed inoculation, particularly when lupin was cultivated for the first time and indigenous populations of rhizobia in the soil were low.     

酸性紫色土上紫花苜蓿的结瘤性能与养分吸收

盆栽试验表明,在pH.5.45的酸性紫色土接种苜蓿根瘤菌,可显著提高紫花苜蓿地上部和地下部生物量。根瘤菌不同株系的结瘤性能和对宿主生长的影响存在显著差异,且不同紫花苜蓿品种的结瘤性能也存在显著差异。结瘤性能良好的菌株显著提高地上部氮、磷和钙的含量,而降低地上部钾含量和铝含量。紫花苜蓿地上部的氮、磷、钾和钙含量高于地下部,镁含量差异不大,而铝含量在接种后地下部含量高于地上部。相关分析表明,紫花苜蓿根瘤重和根瘤数与地上部生物量和地上部氮含量之间存在显著正相关关系;而地下部铝含量与地上部生物量、结瘤性能和植株氮含量呈显著负相关关系。说明酸性土壤良好的结瘤性能可提高生物固氮效率、促进紫花苜蓿生长,但根系铝的过量吸收影响紫花苜蓿的生长、结瘤与氮素吸收。     

Analysis of regulation site and manner of abundant nodulation in a soybean (Glycine max (L.) Merr.) cultivar,kitantusunte, using grafting techniques

To characterize the regulation site and manner of the abundant nodulation in the soybean (Glycine max (L.) Merr.) cv. Kitamusume, three grafting eperiments were carried out as follows: reciprocal wedge grafting and inter-cultivar approach grafting between Kitamusume and a normal nodulating cultivar, Toyosuzu, as well as wedge grafting of scions of the supernodulating mutant En6500 onto either Kitamusume or Toyosuzu rootstock. In the reciprocal wedge grafting, the number of nodules per shoot dry weight and average weight per nodule in the grafted plants were consistent with those exhibited by the genotype of their rootstocks. Approach grafting did not affect the number of nodules per shoot dry weight on either side of the inter-cultivar approachgrafted plant. Although grafting of the mutant scion resulted in the loss of the autoregulatory response from the roots of both cultivars, difference in the number of nodules per g shoot dry weight still remained between the two cultivars. These results suggested that the abundant nodulation in Kitamusume is controlled by the root in a non-systemic manner and is independent of the autoregulation mechanism.     

Nodulation and growth of common bean (Phaseolus vulgaris) under water deficiency

Three experiments were conducted in order to investigate the effect of water deficiency on nodulation, rhizobial diversity and growth of common bean. In the first experiment, the effect of water deficiency was studied on two soil samples under glasshouse conditions. A significant decrease in nodulation and shoot dry weight production was observed. The molecular characterization of the root nodule isolates by PCR-RFLP of 16S rRNA and nodC genes showed that the nodulation by Rhizobium etli was severely inhibited. The in vitro analysis of salt tolerance indicated that drought stress favoured nodulation by salt-tolerant strains. In the second experiment, the effect of water deficiency was studied on sterilized sand using Rhizobium tropici CIAT899^T and Ensifer meliloti bv. mediterranense 4H41 as inoculants. The results showed that strain 4H41, which is the more salt tolerant, was more competitive and more effective under water deficiency than strain CIAT899^T. In the third experiment, the strain 4H41 was used to inoculate four fields. A significant increase in nodule number, shoot dry weight and grain yield was observed even in the non-irrigated soils. This work constitutes the first report of a strain enhancing the growth and the grain yield of common bean under water deficiency.     

Root-temperature effects on competition for nodule occupancy between two Rhizobium meliloti strains

Summary Axenically grown alfalfa (Medicago sativa L. var. Peace) was simultaneously inoculated with Canadian commercial Rhizobium meliloti strains NRG-185 and BALSAC. The plants were grown for 7 weeks in sealed units at five different root temperatures (8°, 13°, 17°, 21°, and 25°C) and at a relatively constant air temperature (24°–30°C). Nodule occupancy by each strain was determined by enzyme-linked immunosorbent assay (ELISA). Nitrogenase activity, nodule fresh weight, and plant dry weight were also measured. The lowest root-temperature regime (8°C) resulted in substantially lower nodule numbers and weights, and plant dry weights, than the higher temperature regimes. Development of nitrogenase activity was completely inhibited at 8°C. The immunoassay of nodule-strain occupancy showed markedly different strain-nodulation responses to the various root-temperature regimes. At 8°C, 63% of nodules were occupied by both strains. Dual strain occupancy decreased from 63% to 2% with increasing root-growth temperature, while the proportion of nodules containing only strain NRG-185 increased from 9% to 75%. Nodules containing only strain BALSAC remained relatively constant at 25% from 8° to 21°C, decreasing slightly at 25°C. The results suggest that root-environment temperatures during the period of nodule formation may have major differential effects on the success of competing rhizobial strains. If this is so, then selection of Rhizobium strains with enhanced low-temperature nodulation capabilities should be possible.     

Nodulation response to molybdenum supplementation in alfalfa and its correlation with root and shoot growth in low pH soil

Molybdenum (Mo) is a critical micronutrient for nitrogen (N) fixation in legumes. Low pH limits the availability of Mo, thereby reducing nodulation and N fixation. This study investigates the effect of Mo supplementation on alfalfa nodulation and its correlation with root and shoot biomass in low-pH soil. Three experiments were conducted in the greenhouse, involving 14 genotypes of alfalfa subjected to four different treatments, unlimed low-pH soil (5.2) with Mo applied (lithium (Li)^?Mo⁺), low-pH soil (5.2) without Mo (Li^?Mo^?), limed soil (pH 7.3) with Mo applied (Li⁺Mo⁺), and limed soil (pH 7.3) without Mo (Li⁺Mo^?). Foliar application of Mo resulted in a significant increase in nodule counts in the 14 alfalfa cultivars grown in low-pH soil (5.2) even though to a lesser extent than in limed soil with neutral pH (7.3). The increase in number of nodules correlated positively with plant root weight and upper plant biomass.     

The diversity of rhizobia nodulating chickpea (Cicer arietinum) under water deficiency as a source of more efficient inoculants

Chickpea is an important pulse crop grown mainly in the arid and semi-arid regions. The effect of water deficiency on nodulation, biomass production, and competition for nodule occupancy was evaluated in three different soils with two chickpea cultivars, Amdoun I and Chetoui. Two watering regimes were considered; a control that was irrigated three times per week and a water-deficient treatment that was irrigated only one time a week. Results showed that water deficiency significantly decreased the nodule number and the shoot dry weight for both cultivars. Root-nodule bacteria were isolated and characterized by PCR-RFLP of 16S rDNA and nifD-K intergenic spacer. The results show that water deficiency affects the diversity of nodulating rhizobia. The nodulation by Mesorhizobium mediterraneum was reduced while inefficient nodulation by Ensifer meliloti was favoured. In both treatments, chickpea was preferentially nodulated by nifD-K type N6. Analysis for NaCl tolerance showed that most of rhizobia nodulating chickpea under water deficiency are NaCl tolerant. Inoculation with the selected salt-tolerant strain of M. mediterraneum LILM10 increased significantly nodule number and grain yield in the field.     

Biocontrol strain Pseudomonas fluorescens CHA0 and its genetically modified derivative with enhanced biocontrol capability exert comparable effects on the structure of a Sinorhizobium meliloti population in gnotobiotic systems

The impact of biocontrol strain Pseudomonas fluorescens CHA0 and of its genetically modified, antibiotic-overproducing derivative CHA0/pME3424 on a reconstructed population of the plant-beneficial Sinorhizobium meliloti bacteria was assessed in gnotobiotic systems. In sterile soil, the final density of the reconstructed S. meliloti population decreased by more than one order of magnitude in the presence of either of the Pseudomonas strains when compared to a control without addition of P. fluorescens. Moreover, there was a change in the proportion of each individual S. meliloti strain within the population. Plant tests also revealed changes in the nodulating S. meliloti population in the presence of strains CHA0 or CHA0/pME3424. In both treatments one S. meliloti strain, f43, was significantly reduced in its root nodule occupancy. Analysis of alfalfa yields showed a slight but statistically significant increase in shoot dry weight when strain CHA0 was added to the reconstructed S. meliloti population whereas no such effect was observed with CHA0/pME3424.     

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.     

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.     

Cu-tolerant Sinorhizobium meliloti strain is beneficial for growth,Cu accumulation,and mineral uptake of alfalfa plants grown in Cu excess

In this work, we have compared the physiological responses of alfalfa plants inoculated with either Sinorhizobium meliloti strain S412 (Cu-tolerant) or S112 (Cu-sensitive) in the presence or absence of 0.5 mM of CuSO₄. The addition of copper (Cu) introduced a decrease of nodule number and their dry weight (DW) in both symbioses. The interaction established with the Cu-sensitive strain is more affected by Cu than that with the tolerant one. In fact, plants inoculated with the sensitive strain revealed a decrease of shoot and root DW, larger than that found in plants inoculated with the tolerant strain. However, under copper supply, Medicago sativa with the Cu-tolerant strain did not show any significant changes in both shoot and root biomass production. Under Cu excess, high levels of Cu were detected in different parts of the plant in the two symbioses and a high translocation of Cu to aerial parts was shown with the strain S412. Plants with S412 were able to accumulate large quantities of calcium (Ca) in their roots and nodules. While Ca content decreased drastically in shoot at 0.5 mM of Cu treatment. Moreover, nodulation with S412 allowed plants to maintain high levels of magnesium (Mg) in all tissues and high iron (Fe) levels in nodules. Results suggest that this symbiotic pair could be used in phytostabilization of Cu-contaminated soils.     

Interaction Effects of Nitrogen and Phosphorus on Nodulation in Red Clover (Trifolium pratense L.)

Red clover (Trifolium pratense L.) is one of the most important plants in forage production, especially in northern areas. Fertilisation practices are focused on high yield and forage quality but effects of nutrients on nodulation and N₂ fixation are poorly understood. The aim of this work was to study how nitrogen (N) and phosphorus (P) separately as well as in combination affected nodulation. Red clover plants were grown in pots with gravel in a greenhouse for 11 weeks. To resemble field conditions the root temperature was kept lower than the shoot temperature. Plants were given five different combinations of N and P concentrations during growth. The result showed that at high N concentrations P had a counteracting effect on the N inhibition. The N₂-fixation parameters, nodule number, nodule dry matter and specific nitrogenase activity, were six times higher in plants grown with high N and high P than in plants with high N and low P. When the N₂-fixation parameters and the dry matter of roots and shoots were related to total plant dry matter, there was a stronger effect of P on nodulation parameters than on roots and shoots. This indicates that P has a direct effect on the N₂-fixation parameters, rather than an indirect effect via increased plant growth. These results demonstrate the importance to studying the effects of more than one nutrient at a time.     

PLANT GROWTH PROMOTING RHIZOBACTERIA INCREASE GROWTH,YIELD AND NITROGEN FIXATION IN PHASEOLUS VULGARIS

Nitrogen (N) fixation by legume-Rhizobium symbiosis is important to agricultural productivity and is therefore of great economic interest. Growing evidence indicates that soil beneficial bacteria can positively affect symbiotic performance of rhizobia. The effect of co-inoculation with plant growth-promoting rhizobacteria (PGPR) and Rhizobium, on nodulation, nitrogen fixation, and yield of common bean (Phaseolus vulgaris L.) cultivars was investigated in two consecutive years under field conditions. The PGPR strains Pseudomonas fluorescens P-93 and Azospirillum lipoferum S-21 as well as two highly effective Rhizobium strains were used in this study. Common bean seeds of three cultivars were inoculated with Rhizobium singly or in a combination with PGPR to evaluate their effect on nodulation and nitrogen fixation. A significant variation of plant growth in response to inoculation with Rhizobium strains was observed. Treatment with PGPR significantly increased nodule number and dry weight, shoot dry weight, amount of nitrogen fixed as well as seed yield and protein content. Co-inoculation with Rhizobium and PGPR demonstrated a significant increase in the proportion of nitrogen derived from atmosphere. These results indicate that PGPR strains have potential to enhance the symbiotic potential of rhizobia.     

Cultivable heterotrophic N<Subscript>2</Subscript>-fixing bacterial diversity in rice fields in the Yangtze River Plain

Heterotrophic N₂-fixing bacteria are a potentially important source of N₂ fixation in rice fields due to the moist soil conditions. This study was conducted at eight sites along a geographic gradient of the Yangtze River Plain in central China. A nitrogen-free solid malate-sucrose medium was used to isolate heterotrophic N₂-fixing bacteria. Numbers of the culturable N₂-fixing bacteria expressed as CFU (colony forming units) ranged between 1.41ǂ.42᎒⁶ and 1.24ǂ.23᎒⁸ in the sampled paddy field sites along the plain. Thirty strains with high ARA (acetylene reduction activity) were isolated and purified; ARA of the strains varied from 0.9 to 537.8 nmol C₂H₄ culture^-1 h^-1, and amounts of ¹⁵N fixed ranged between 0.008 and 0.4866 mg·culture^-1·day^-1. According to morphological and biochemical characteristics, 14 strains were identified as the genus Bacillus, 2 as Burkholderia, 1 as Agrobacterium, 4 as Pseudomonas, 2 as Derxia, 1 as Alcaligenes, 1 as Aeromonas, 2 as Citrobacter, and 3 strains belonged to the corynebacter-form group.     

Effect of inoculum rate on the performance of chickpea (Cicer arietinum L.) Rhizobium strains in the field

Summary The influence of three inoculum rates on the performance of three chickpea (Cicer arietinum L.) Rhizobium strains was examined in the field on a Mollisol soil. Increasing amounts of inoculum improved the performance of the strains. A normal dose (10⁴ cells per seed) applied at different intervals gave non-significant increases in nodulation, nitrogenase activity (acetylene reduction assay), nitrogen uptake and grain yield. A ten-fold increase in inoculum increased nodule number, shoot dry weight, nitrogenase activity (ARA) and grain yield, but increases over the control were significant only for nodule dry weight and nitrogen uptake by shoot and grain. The highest level of inoculum (100 × normal) significantly increased nodule dry weight, grain yield, total nitrogenase activity (ARA) and nitrogen uptake by shoot and grain. Strain TAL 620 was more effective than the other two. Combined nitrogen (60 kg N ha^–1) suppressed nodulation and nitrogenase activity (ARA).Research paper No. 4345 from the Experiment Station, G. B. P. U. A. & T., Pantnagar, Nainital, U. P.     

N2-fixing bacteria in the rhizosphere: Quantification and hormonal effects on root development

The paper summarizes the results of a series of experiments on enumeration of N₂-fixing bacteria (diazotrophs) and hormonal effects of Azospirillum on root development. Numbers of N₂-fixing and N-heterotrophic bacteria were determined on the root (rhizoplane plus “inner” root surface) and in the rhizosphere soil (0–3 mm from the root surface) of Arrhenatherum elatius, other forage grasses and some herbaceous plant species. Pot experiments involved freshly collected soil from an unfertilized grassland area containing its natural population of N₂-fixing bacteria. The MPN (most probable number) of diazotrophs in relation to the MPN of the total bacterial population was always lower on the root than in the rhizosphere soil, suggesting that diazotrophs were not selectively advantaged at the root surface. Supply of mineral nitrogen (NH₄NO₃) decreased the proportion of N₂-fixing bacteria at the rhizoplane as well as in the rhizosphere soil. Similar results were obtained when N was supplied via the leaves. The data suggest that N₂-fixing bacteria in the rhizosphere are poor competitors once they loose their competitive advantage of binding dinitrogen. Correspondingly, the increase in the MPN of the diazotrophs found during plant development was interpreted as a result of decreased available combined N in the rhizosphere. The proportion of N₂-fixing bacteria relative to the total number of bacteria was generally below 1%. Considering the potential amount of substrate released from the roots and the substrate requirement of the bacterial population, N₂-fixation was considered insignificant for plant growth under the given conditions. For the investigations on possible beneficial effects on plant development by bacterial hormones, Azospirillum brasilense was chosen because evidence suggests that amongst the soil bacteria releasing hormones, especially IAA, certain strains of this species are more important than other bacteria. Application of A. brasilense Cd (ATCC 29710) onto the roots of young wheat plants grown in soil increased the number of lateral roots, the total root length and the number of root hairs. Similar results were obtained after application of IAA. This suggests that IAA is an important factor responsible for the effects observed after inoculation with A. brasilense. The increase in root surface may improve acquisition of nutrients and enhance growth of plants. Another hormonal effect of A. brasilense was an increase in nodulation of Medicago sativa grown on agar. Again pure IAA resulted in a similar increase in nodule number. Increases in nodule number were only in part associated with a change in root morphology. Therefore an effect of IAA on the plant immanent regulation system for nodulation is likely.     

紫花苜蓿“Vector”品种高效根瘤菌筛选及其田间竞争结瘤能力研究

Seventeen Sinorhizobium meliloti strains from seven provinces in China were used to screen highly effective strains for alfalfa cultivar in a greenhouse study and their symbiotic relationship and competitive ability were studied in the field. CCBAU30138 was the most effective strain, as evidenced by increase in dry weights. A field experiment showed that the inoculation of alfalfa with CCBAU30138 resulted in increases of 11.9% and 19.6% of dry matter production and crude protein production, respectively, in forage of monocultured plants. The total dry matter yields of alfalfa and tall fescue in binary culture were increased by 16.3% by inoculation of alfalfa with this strain. These results showed that S. rneliloti strain CCBAU30138 was an effective inoculant both in the greenhouse and in the field. The analysis of randomly amplified polymorphic DNA （RAPD） by polymerase chain reaction （PCR） from nodule extracts showed that the strain CCBAU30138 had high competitiveness in the field. It occupied 47.5% of nodules in alfalfa monoculture and 44.4% of nodules in alfalfa-tall fescue binary culture after 20 weeks of growth. In conclusion, a simple system to select highly effective and competitive symbiotic strains specific to alfalfa was established. Using this system, a s.train suitable for the alfalfa cultivar ‘Vector＇ grown in Wuqiao County of Hebei Province was obtained.     

Competition between effective and less effective strains of Bradyrhizobium spp. for nodulation on Vigna radiata

Local and exotic cowpea bradyrhizobial strains were examined for their effectiveness and competitive ability on the cultivated Vigna radiata (mungbean) variety NM-51. The seven most efficient N₂-fixing strains were then evaluated for their competitiveness against two less effective strains in a pair-wise inoculation experiment. Nodule occupancy was determined using fluorescent antibodies. The most efficient strain, Vr-2, could not compete with less effective strains for nodule occupancy, so the biomass and N yield were low. Bradyrhizobial strain M-55 had good competitive ability, as it occupied almost 50% of nodules in comparison with less effective strains and improved the biomass and N yield of mungbean significantly. Competitiveness/compatibility is one of the vital parameters for the selection of inocula strains, therefore, M-55, K-92 and Vr-6 are recommended as good inocula of commercial quality because of their competitiveness along with their highly efficient N₂-fixation.