Leghaemoglobin Content Research Articles

Enhancement of rhizosphere citric acid and decrease of NO3−/NH4+ ratio by root interactions facilitate N fixation and transfer

Cereal can stimulate legume N fixation through competition for soil mineral N. In addition, organic acids in the rhizosphere can mobilize external nutrients, which may help nodulation. However, how much NO3− and NH4+ competition and organic acids in the rhizosphere of intercropped crops contribute to N fixation remains unclear and requires study. Field and greenhouse experiments were conducted to quantify effects of N competition and organic acids on N fixation in a maize/alfalfa intercropping system. Intercropping increased nitrogen derived from the atmosphere (%Ndfa), nodules number, and leghemoglobin content by 43.66%, 85.53%, 141.05%, respectively, leading to significantly improved total N uptake and yield, compared to monoculture. The improved %Ndfa was not only due to the depletion of NO3−, but also significantly correlated with the decrease of NO3−/NH4+ ratio and the increase of citric acid in rhizosphere of alfalfa, which could mobilize soluble resources for N fixation under no N addition. Overall, 15.4%–21.5% of N fixed by alfalfa was transferred to associated maize, and the improved N fixation enhanced N transfer. Our findings provide a mechanism for how root interactions facilitate N fixation, highlighting the importance of NO3−/NH4+ ratio and citric acid in nutrient mobilization for N fixation.

Evaluation of biocontrol agents for the management of root-rot of mung bean caused by Macrophomina phaseolina

Present study was undertaken to evaluate the effectiveness of various biocontrol agents through seed treatment against root-rot of mung bean caused by Macrophomina phaseolina under pot condition. Maximum control of the disease was observed on treatment with T. viride (46.7%) and P. aeruginosa (44.4%) which improved the yield parameters by 28.6 and 25.9%; and functional nodules by 51.9–57.0% with 22.4–22.9% greater leghemoglobin content in the nodules (P < 0.05). Their treatment also improved the leaf chlorophylls (30.2–35.8%) and carotenoids (31.3–32.0%). Soil population of M. phaseolina in the pots treated with antagonists was 40.8–67.3% lesser, being greatest with T. viride and P. aeruginosa.

Arbuscular mycorrhizal fungi and biochar improves drought tolerance in chickpea.

Arbuscular mycorrhizal fungi (AMF) inoculation and biochar amendment has been reported to improve growth of several crop plants however their role in stress amelioration individually as well as in combination has not been worked out. This experiment was conducted to evaluate the application of AMF and biochar on the performance of chickpea under drought stress. The treatments included the individual as well as combined treatment of AMF and biochar to drought stressed and normal chickpea plants. Plants inoculation improved growth in terms of shoot and root length, leaf area and number of branches which was observed to show a steep decline due to drought stress. Drought declined the AMF colonization potential though biochar amendment ameliorated the negative effects of drought significantly by improving the spore population, number of mycelium, vesicle and arbuscules and the percentage of colonization as well. Increased chlorophyll synthesis in biochar and AMF treated plants was obvious, which lead to significant enhancement in the net photosynthetic efficiency. Drought stress also declined the relative water content (RWC) and membrane stability index (MSI), while treatment of biochar and AMF either individually or in combination mitigated the deleterious effects to considerable extent and caused a significant enhancement in RWC and MSI under normal conditions. Amendments with biochar and AMF inoculation increased the nitrogen fixation attributes including the number and weight of nodules, leghemoglobin content and activity of nitrate reductase enzyme leading to greater uptake and assimilation of nitrogen in them when compared to drought stressed plants. Drought stressed chickpea plants exhibited considerable reduction in uptake of nitrogen and phosphorous which was ameliorated by biochar and AMF treatments. It could be suggested that increase in growth and physiological attributes in chickpea due to biochar amendments and AMF inoculation under drought stress were plausibly due to their involvement in nitrogen and phosphorous uptake, chlorophyll synthesis and photosynthesis.

Symbiotic parameters, growth, nutrient accumulation, productivity and profitability as influenced by integrated nutrient management in lentil (Lens culinaris)

ABSTRACTField experiments evaluated the effects of integrated nutrient management on symbiotic parameters, growth, nutrient accumulation, productivity and profitability of lentil (Lens culinaris Medikus). Application of recommended dose of nutrients (RDN, 12.5 kg N ha−1 + 40 kg P2O5 ha−1) + 25 kg ZnSO4 ha−1 + seed inoculation with biofertilizers [Rhizobium + phosphate solubilizing bacteria (PSB) + plant growth promoting rhizobacteria (PGPR)] + 1.0 g ammonium molybdate kg−1 seed recorded the highest number & dry weight of nodules, leghaemoglobin content, root & shoot dry weight, plant height, number of pods plant−1 and 100-seed weight. The next best treatment was RDN + seed inoculation with biofertilizers + 1.0 g ammonium molybdate kg−1 seed. On the basis of mean of three-year data, the treatment of RDN + 25 kg ZnSO4 ha−1 + seed inoculation with biofertilizers + 1.0 g ammonium molybdate kg−1 seed proved the best in realizing the highest grain yield (34.0%), gross returns (34.0%) and net returns (54.8% higher over control). Nitrogen, phosphorus and potassium in the grains and straw were significantly improved where RDN was applied in combination with seed inoculation, basal application of ZnSO4 and seed treatment with 1 g ammonium molybdate than their single applications.

Quantification of leghaemoglobin content in pea nodules based on near infrared hyperspectral imaging spectroscopy and chemometrics

Leghaemoglobin content in nodules is closely related to the amount of nitrogen fixed by the legume–rhizobium symbiosis. It is, therefore, commonly measured in order to assess the effect of growth-promoting parameters such as fertilisation on the symbiotic nitrogen fixation efficiency of legumes. The cyanmethaemoglobin method is a reference method in leghaemoglobin content quantification, but this method is time-consuming, requires accurate and careful technical operations and uses cyanide, a toxic reagent. As a quicker, simpler and non-destructive alternative, a method based on near infrared (NIR) hyperspectral imaging was tested to quantify leghaemoglobin in dried nodules. Two approaches were evaluated: (i) the partial least squares (PLS) approach was applied to the full spectrum acquired with the hyperspectral device and (ii) the potential of multispectral imaging was also tested through the preselection of the most relevant wavelengths and the building of a multiple linear regression model. The PLS approach was tested on mean spectra acquired from samples containing several nodules and acquired separately from individual nodules. Peas (Pisum sativum L.) were cultivated in a greenhouse. The nodules were harvested on four different dates in order to obtain variations in leghaemoglobin content. The leghaemoglobin content measured with the cyanmethaemoglobin method in fresh nodules ranged between 1.4 and 4.2 mg leghaemoglobin g–1 fresh nodule. A PLS regression model was calibrated on leghaemoglobin content measured with the reference method and mean NIR spectra of dried nodules acquired with a hyperspectral imaging device. On a validation dataset, the PLS model predicted the leghaemoglobin content in nodule samples well (R2 = 0.90, root mean square error of prediction = 0.26). The multispectral approach showed similar performance. Applied to individual nodules, the PLS model highlighted a wide variability of leghaemoglobin content in nodules harvested from the same plant. These results show that NIR hyperspectral imaging could be used as a rapid and safe method to quantify leghaemoglobin in pea nodules.

Exploring Crop–Microbiome Interactions Towards Improving Symbiotic Performance of Chickpea (Cicer arietinum) Cultivars Using Cyanobacterial Inoculants

The significance of integrated nutrient management practices is well established in improving the productivity of chickpea (Cicer arietinum); however, the effects of the inoculation of cyanobacterial inoculants on nodule metabolism, microbiome and associated genes are less explored. In the present investigation, cyanobacterium Anabaena laxa (A. laxa) and biofilm developed using Anabaena torulosa, with Mesorhizobium ciceri as a partner (An-M. ciceri), were evaluated along with Mesorhizobium ciceri (M. ciceri) alone, in three chickpea cultivars. Microbial inoculation led to 40–70% enhancement in nitrogen fixation, leghaemoglobin and ureide content, and two- to threefold increment in nitrate reductase and phosphoenolpyruvate carboxylase activity of the nodules. An enhancement of 30–50% in the soil available macro- and micronutrients and plant growth attributes was also observed. A significant correlation between the soil microbiological and plant parameters was recorded, particularly in relation to the nitrogen dynamics. Increases in the leghaemoglobin content in nodules due to An-M. ciceri, A. laxa and M. ciceri ranged from 18 to 40%, particularly in chickpea cv. BG372 in which 60–80% enhancement was recorded. Whereas the nifH gene copies in the nodule tissues ranged from 5.00 × 106 to 3.35 × 107 g−1, the application of A. laxa led to higher abundances of nifH gene copies in desi chickpea cv. BG372 and kabuli BG1053 cultivars. An-M. ciceri, followed closely by A. laxa, was the top-ranking treatment, and chickpea cv. BG372 was the best performing cultivar; An-M. ciceri—chickpea cv. BG372 proved to be the superior combination for higher plant growth and soil nutrient-related traits.

Nodulation and Delayed Nodule Senescence: Strategies of Two Bradyrhizobium Japonicum Isolates with High Capacity to Fix Nitrogen.

The purpose of this work was to study further two Bradyrhizobium japonicum strains with high nitrogen-fixing capacity that were identified within a collection of approximately 200 isolates from the soils of Argentina. Nodulation and nitrogen-fixing capacity and the level of expression of regulatory as well as structural genes of nitrogen fixation and the 1-aminocyclopropane-1-carboxylate (ACC) deaminase gene of the isolates were compared with that of E109-inoculated plants. Both isolates of B. japonicum, 163 and 366, were highly efficient to fix nitrogen compared to commercial strain E109. Isolate 366 developed a higher number and larger biomass of nodules and because of this fixed more nitrogen. Isolate 163 developed the same number and nodule biomass than E109. However, nodules developed by isolate 163 had red interiors for a longer period, had a higher leghemoglobin content, and presented high levels of expression of acdS gene, that codes for an ACC deaminase. In conclusion, naturalized rhizobia of the soils of Argentina hold a diverse population that might be the source of highly active nitrogen-fixing rhizobia, a process that appears to be based on different strategies.

Optimized nitrogen application methods to improve nitrogen use efficiency and nodule nitrogen fixation in a maize-soybean relay intercropping system

In China, the abuse of chemical nitrogen (N) fertilizer results in decreasing N use efficiency (NUE), wasting resources and causing serious environmental problems. Cereal-legume intercropping is widely used to enhance crop yield and improve resource use efficiency, especially in Southwest China. To optimize N utilization and increase grain yield, we conducted a two-year field experiment with single-factor randomized block designs of a maize-soybean intercropping system (IMS). Three N rates, NN (no nitrogen application), LN (lower N application: 270 kg N ha−1), and CN (conventional N application: 330 kg N ha−1), and three topdressing distances of LN (LND), e.g., 15 cm (LND1), 30 cm (LND2) and 45 cm (LND3) from maize rows were evaluated. At the beginning seed stage (R5), the leghemoglobin content and nitrogenase activity of LND3 were 1.86 mg plant−1 and 0.14 mL h−1 plant−1, and those of LND1 and LND2 were increased by 31.4 and 24.5%, 6.4 and 32.9% compared with LND3, respectively. The ureide content and N accumulation of soybean organs in LND1 and LND2 were higher than those of LND3. The N uptake, NUE and N agronomy efficiency (NAE) of IMS under CN were 308.3 kg ha−1, 28.5%, and 5.7 kg grain kg−1 N, respectively; however, those of LN were significantly increased by 12.4, 72.5, and 51.6% compared with CN, respectively. The total yield in LND1 and LND2 was increased by 12.3 and 8.3% compared with CN, respectively. Those results suggested that LN with distances of 15–30 cm from the topdressing strip to the maize row was optimal in maize-soybean intercropping. Lower N input with an optimized fertilization location for IMS increased N fixation and N use efficiency without decreasing grain yield.

Yield enhancement and phosphorus economy in lentil (Lens culinaris Medikus) with integrated use of phosphorus, Rhizobium and plant growth promoting rhizobacteria

ABSTRACTThe study evaluated the effects of phosphorus (0, 20, 30, and 40 kg P2O5 ha−1) and biofertilizers [Rhizobium (Rhizobium leguminosarum bv viciae), plant growth promoting rhizobacteria (PGPR) (Pseudomonas fluorescens), Rhizobium + PGPR, and uninoculated control] in lentil. Application of 40 kg P2O5 ha−1 resulted in the highest number of nodules, nodule dry weight, leghemoglobin content in nodules, chlorophyll content, yield attributes, and grain yield. Coinoculated treatment performed better than uninoculated control, and individual inoculations of Rhizobium and PGPR in terms of all above mentioned parameters. Application of 20 kg P2O5 ha−1 + Rhizobium inoculation gave statistically similar and 20 kg P2O5 ha−1 + Rhizobium + PGPR inoculation gave significantly higher grain yield than that by 40 kg P2O5 ha−1 alone. The use of Rhizobium alone and Rhizobium + PGPR consortium can save not only 20 kg P2O5 ha−1 but also increase the grain yield of lentil.

Phenotypic Analysis and Molecular Markers of Plant Nodule Senescence.

Leguminous crops can form nodules to fix atmospheric nitrogen (N2). Senescence of nodules is associated with a rapid decline in N fixation. During the process of nodule senescence, a number of visible or detectable changes on morphology, biochemistry, and physiology occur. Here we describe several methods for examining the senescing phenotypes of nodules, including rhizobium inoculation, nitrogenase activity determination with the acetylene reduction assay, leghemoglobin content determination, and apoptotic cell identification with TdT-mediated dUTP-biotin nick end-labeling (TUNEL) staining.

Efficacy of post-emergence herbicides for weed control in soybean

A field experiment was conducted at Punjab Agricultural University, Ludhiana to study the efficacy of post-emergence herbicides for weed control in soybean. The herbicides (pendimethalin, imazethapyr, imazethapyr + imazamox and quizalofop-p-ethyl) did not show any significant adverse effects on the number, dry weight and leghaemoglobin content of nodules. Application of pendimethalin 0.45 kg/ha as pre-emergence (PE) + hand weeding (HW) at 40 days after sowing (DAS) recorded significantly higher seed yield than other treatments, however, it was at par with two hand weeding. Among the herbicides, imazethapyr at 75 g/ha applied at 3 weeks after sowing (WAS) recorded significantly higher seed yield than pendimethalin 0.45 kg/ha (PE) and weedy check and was at par with imazethapyr + imazamox 70 g/ha and quizalofop-p-ethyl 50 g/ha applied at 3 WAS. Application of pendimethalin 0.45 kg/ha (PE) + HW at 40 DAS provided the highest net returns (` 49496/ha) followed by two hand weedings. However, application of post-emergence herbicides imazethapyr at 75 g/ha and imazethapyr + imazamox 70 g/ha at 3 WAS were found promising in controlling weeds, providing optimum seed yield and higher B: C ratio. In case of scarcity of labour, post-emergence herbicides can play an important role in controlling weeds effectively.

Inoculant rhizobia suppressed root-knot disease, and enhanced plant productivity and nutrient uptake of some field-grown food legumes

ABSTRACTThe potential effect of rhizobial inoculation on root knot nematodes in chickpea, mungbean and pigeonpea were studied under field condition. The seed treatment with respective rhizobium strains increased the nodulation, leghemoglobin content, bacteriod population, plant growth, yield and nitrogen uptake of three three food legumes compared to the plants without the rhizobium treatment. The nematode (1500 juveniles/kg soil) incited oval galls on the roots of the three legumes, and suppressed plant growth and yield. The galling, egg mass production and soil population of the nematode was greater on the plants without the rhizobium treatment. The pure culture and culture filtrate of the rhizobium strains suppressed the egg hatching and induced mortality to the juveniles of M. incognita over control. The nematode infection reduced the nodulation, bacteroid population and leghemoglobin contents of the nodules and NPK uptake by the plants. Hence, the rhizobia treatment shall be integrated to common agronomic practice of food legume cultivation so as to enhance crop productivity and to protect roots from nematode attack.

Cyanobacterial and rhizobial inoculation modulates the plant physiological attributes and nodule microbial communities of chickpea.

The present investigation aimed to understand the influence of two plant growth promoting cyanobacterial formulations (Anabaena-Mesorhizobium ciceri biofilm and Anabaena laxa), along with Mesorhizobium ciceri, on the symbiotic performance of five each of desi- and kabuli-chickpea cultivars. Inoculation with cyanobacterial formulations led to significant interactions with different cultivars, in terms of fresh weight and number of nodules, the concentration of nodular leghemoglobin, and the number of pods. The inoculant A. laxa alone was superior in its performance, recording 30-50% higher values than uninoculated control, and led to significantly higher nodule number per plant and fresh root weight, relative to the M. ciceri alone. Highest nodule numbers were recorded in the kabuli cultivars BG256 and BG1003. The kabuli cultivar BG1108 treated with the biofilmed Anabaena-M. ciceri inoculant recorded the highest concentration of leghemoglobin in nodules. These inoculants also stimulated the elicitation of defense- and pathogenesis-related enzymes in both the desi and kabuli cultivars, by two to threefolds. The analyses of Denaturing Gradient Gel Electrophoresis (DGGE) profiles revealed that microbial communities in nodules were highly diverse, with about 23 archaeal, 9 bacterial, and 13 cyanobacterial predominant phylotypes observed in both desi and kabuli cultivars, and influenced by the inoculants. Our findings illustrate that the performance of the chickpea plants may be significantly modulated by the microbial communities in the nodule, which may contribute towards improved plant growth and metabolic activity of nodules. This emphasizes the promise of cyanobacterial inoculants in improving the symbiotic performance of chickpea.

Symbiotic Parameters, Growth, Nutrient Uptake as Influenced by Biofertilizers under Conservation Agriculture Practices

A field experiment was conducted during rainy season 2014 and 2015 at Research Farm of the Punjab Agricultural University, Ludhiana, Punjab, India to study the effect of conservation agriculture practices (Happy Seeder sowing, Straw Chopper + Zero Tillage and Conventional tillage) and biofertilizers [Bradyrhizobium and plant growth promoting rhizobacteria (PGPR)] on growth, symbiotic parameters and productivity of soybean. The results showed that Happy Seeder sowing and Straw Chopper + Zero Tillage sowing improved the emergence count, leaf area index, photosynthetic active radiation interception, plant height of soybean and symbiotic traits (number and dry weight of nodules and leghaemoglobin content). Highest pods plant−1 and 100-seed weight were recorded in Happy Seeder sowing, followed by Straw Chopper + Zero Tillage sowing and conventional sowing. Based on the mean of two years, Happy Seeder sowing recorded 14.6 and 17.0% higher seed yield than Straw Chopper + Zero Tillage sowing and conventional sowing, respectively. Total nitrogen, phosphorus and potassium uptake were significantly higher in Happy Seeder sowing than the other planting methods. Single and dual inoculation of Bradyrhizobium and PGPR did not influence the growth parameters, symbiotic traits, yield attributes, biological, straw and seed yields, nutrient uptake and protein content of soybean significantly. Therefore, retention of crop residues with zero tillage (Happy Seeder sowing) proves to be the best planting method for sustainable productivity of soybean.

Elevated carbon dioxide level along with phosphorus application and cyanobacterial inoculation enhances nitrogen fixation and uptake in cowpea crop

ABSTRACTClimate change, as a result of increase in the concentration of greenhouse gases, influences growth and productivity of leguminous crops. A study was carried out to analyse the impacts of elevated carbon dioxide (CO2) and cyanobacterial inoculation on growth, N2 fixation and N availability and uptake in cowpea crop, under different doses of phosphorus. Cowpea crop was grown under ambient (400 µmol mol−1) and elevated (550 ± 20 µmol mol−1) CO2 levels using Free-Air Carbon dioxide Enrichment facility. Elevated CO2 level increased chlorophyll content in leaves, improved nodulation and nitrogen fixation by the crop. Increase in P dose up to 16 mg kg−1 soil enhanced nodule development and N2 fixation under high CO2 condition. Cyanobacterial inoculation increased nodule weight, leghaemoglobin content in nodules and total nitrogenase activity. Although nitrogen concentration in cowpea seeds decreased in high CO2 treatment, higher N uptake was recorded. Under elevated CO2 condition, cyanobacterial inoculation and higher P doses led to enhanced root growth and N2 fixation and availability of soil nitrogen. The study illustrated the synergistic effect of high CO2 and cyanobacterial inoculation in enhancing crop growth and availability of soil N, mediated by biological N2 fixation in cowpea under different levels of P.

Comparing symbiotic performance and physiological responses of two soybean cultivars to arbuscular mycorrhizal fungi under salt stress.

The presented experiments evaluated the symbiotic performance of soybean genotypes with contrasting salt stress tolerance to arbuscular mycorrhizal fungi (AMF) inoculation. In addition, the physiological stress tolerance mechanisms in plants derived from mutualistic interactions between AMF and the host plants were evaluated. Plant growth, nodulation, nitrogenase activity and levels of endogenous growth hormones, such as indole acetic acid and indole butyric acid, of salt-tolerant and salt-sensitive soybean genotypes significantly decreased at 200 mM NaCl. The inoculation of soybean with AMF improved the symbiotic performance of both soybean genotypes by improving nodule formation, leghemoglobin content, nitrogenase activity and auxin synthesis. AMF colonization also protected soybean genotypes from salt-induced membrane damage and reduced the production of hydrogen peroxide, subsequently reducing the production of TBARS and reducing lipid peroxidation. In conclusion, the results of the present investigation indicate that AMF improve the symbiotic performance of soybean genotypes regardless of their salt stress tolerance ability by mitigating the negative effect of salt stress and stimulating endogenous level of auxins that contribute to an improved root system and nutrient acquisition under salt stress.

Interactive effects of salinity and two phosphorus fertilizers on growth and grain yield of Cicer arietinum L.

ABSTRACTChickpea is considered among the most sensitive grain legumes to salinity. The improvement of tolerance of lines in combination with tolerant rhizobial strains depends on various environmental and cultural conditions such as soil properties. This investigation was undertaken to evaluate the effect of phosphorus fertilization (0, 90 and 200 kg ha−1 of P2O5) on biomass, nodular traits and grain yield (GY) of chickpea (cv. Flip 84-79C) growing under salinity (0 and 150 mM NaCl). The trial was laid out following a randomized block design with three replicates during 2010–2012, at the experimental farm of Oued Smar (Algiers). Salinity did not significantly decrease the dry biomass of the plants but the relative shoot growth was more affected than control, P and SP1 treatments. Besides, salinity significantly reduced GY (−20%) and nodulation traits compared to the control plants while an inversely proportional relationship was found between protein, leghemoglobin and MDA content, K/Na ratio and the increase in salt concentration. Application of two P levels to saline soil enhanced growing conditions of plants. Particularly, the (90 kg ha–1 of P × 150 mM NaCl) combination significantly increased leghemoglobin (92%), reduced proline content (−69%) and protected membranes against peroxydation compared to saline conditions. A significant increase was observed in the GY (about 30%) of plants at both P doses combined with salt stress compared to other cases. Statistically, the low P level combined with salinity induced similar responses of plants and sometimes better responses to control plants. Finally, our results support the roles of phosphorus fertilizer in the alleviation of salt stress and enhancing the soil quality for better symbiosis efficiency and yield of chickpea.

Effect of saline water irrigation and seed inoculation with rhizobium on nodulation and leghemoglobin content in fenugreek(Trigonella foenum-greacum L.)

The present study was undertaken to know the effects of salinity on nodulation and leghemoglobin content in two cultivars (NDM-17 and Pusa Kasauri) of fenugreek (Trigonella foenum-greacum L.) treated with rhizobium. The pot experiments were conducted following completely randomized block design method. Two sets of pots were maintained with one set treated with rhizobium and other without. The sets were irrigated with saline water of different electrical conductivities (0.2, 3.2, 6.2, 7.2, 10.2, 12.2 and 14.2 dSm-1) created with NaCl, Na2SO4, NaHCO3 and CaCl2 salts. Observations on nodules number, weight and leghemoglobin content were recorded 30, 60, 90 and 120 days after sowing . The nodules growth decreased with increasing levels of salinity. Seeds treated with rhizobium ameliorated the deleterious effect of salinity at all levels besides improving the fertility of soil and growth of root nodules by nitrogen fixation. Present findings revealed that maximum number, weight and leghemoglobin content in cv. NDM-17 was higher as compared to cv. Pusa Kasauri in both treated and non-treated with rhizobium indicating it be the tolerant of the two cultivars.

The Interaction between Arbuscular Mycorrhizal Fungi and Endophytic Bacteria Enhances Plant Growth of Acacia gerrardii under Salt Stress.

Microbes living symbiotically in plant tissues mutually cooperate with each other by providing nutrients for proliferation of the partner organism and have a beneficial effect on plant growth. However, few studies thus far have examined the interactive effect of endophytic bacteria and arbuscular mycorrhizal fungi (AMF) in hostile conditions and their potential to improve plant stress tolerance. In this study, we investigated how the synergistic interactions of endophytic bacteria and AMF affect plant growth, nodulation, nutrient acquisition and stress tolerance of Acacia gerrardii under salt stress. Plant growth varied between the treatments with both single inoculants and was higher in plants inoculated with the endophytic B. subtilis strain than with AMF. Co-inoculated A. gerrardii had a significantly greater shoot and root dry weight, nodule number, and leghemoglobin content than those inoculated with AMF or B. subtilis alone under salt stress. The endophytic B. subtilis could alleviate the adverse effect of salt on AMF colonization. The differences in nitrate and nitrite reductase and nitrogenase activities between uninoculated plants and those inoculated with AMF and B. subtilis together under stress were significant. Both inoculation treatments, either B. subtilis alone or combined with AMF, enhanced the N, P, K, Mg, and Ca contents and phosphatase activities in salt-stressed A. gerrardii tissues and reduced Na and Cl concentration, thereby protecting salt-stressed plants from ionic and osmotic stress-induced changes. In conclusion, our results indicate that endophytic bacteria and AMF contribute to a tripartite mutualistic symbiosis in A. gerrardii and are coordinately involved in the plant adaptation to salt stress tolerance.

Native Pseudomonas spp. suppressed the root-knot nematode in in vitro and in vivo, and promoted the nodulation and grain yield in the field grown mungbean

The study describes the effects of Pseudomonas aeruginosa, Pseudomonas fluorescens, Pseudomonas stutzeri and Pseudomonas striata on root nodulation (Bradyrhizobium sp.), root-knot disease (Meloidogyne incognita), and on the plant growth and yield of field grown mungbean (Vigna radiata). In vitro the Pseudomonas spp. produced hydrogen cyanide (P. fluorescens), ammonia, siderophore and indole acetic acid, and solubilized phosphorus. The bacterial cells and cell free culture filtrate of Pseudomonas spp. suppressed egg hatching and induced mortality to the juveniles of M. incognita with overall greater effects of P. fluorescens and P. striata. The seeds of mungbean cv. T-44 treated with Pseudomonas spp. (1011–12colony formingunits/ml) and Bradyrhizobium (109–10CFU/ml, 5ml/kg seeds) were sown at 45 spots in every field plot (4×2m) with or without the nematode inoculation of 2000juveniles/spot. In the plots without nematodes, grain yield and NPK acquisition of mungbean plants were significantly higher with P. fluorescens or P. striata treatments (P⩽0.05). The Pseudomonas treatments synergized with Bradyrhizobium sp., leading to significant enhancements in the root nodulation, leghemoglobin contents, and the population of rhizobia in the nodule as well as in the soil. The nematode infection caused severe galling on the roots and decreased the yield of mungbean by 21% in the absence of Pseudomonas spp. The nematode infection also suppressed the nodulation, leghemoglobin contents and rhizobia population. However, treatments with Pseudomonas spp. improved the nodulation and other parameters of nematode infected plants. Among the four Pseudomonas spp., P. fluorescens was found more effective against the root-knot nematode, and its application reduced the gall formation, reproduction and soil population of M. incognita (P⩽0.05). The suppressive effect of P. fluorescens on the nematode was relatively less than carbofuran (5g active ingredient/kg seed), but the yield of nematode infected plants with the bacterial treatment was 14% (P⩽0.05) greater than the chemical treatment. Hence, seed treatment with P. fluorescens offers a better substitute of the nematicide in mungbean cultivation.