Yield and N assimilation of winter wheat (Triticum aestivum L., var. Norstar) inoculated with rhizobacteria

The effects of bacterial inoculants on the growth of winter wheat were studied in a growth chamber. Azospirillum brasilense, Azotobacter chroococcum, Bacillus polymyxa, Enterobacter cloacae, or a mixture of the four rhizobacteria were the inoculants tested. Inoculation effects on yield, yield components, and N-derived from fertilizer (Ndff) were assessed. The response of plants inoculated with individual bacteria was inconsistent and varied with treatment. At the first harvest (58 days after planting-DAP) plants inoculated with the mixture exhibited increases in plant dry weight, total-N and Ndff. At the second harvest (105 DAP), plants inoculated with A. brasilense and the mixture exhibited increases in shoot biomass, whereas at maturity (170 DAP), the inoculated plants showed no differences in total-N or shoot dry matter yield, as compared to the uninoculated controls. Inoculation with A. brasilense, however, increased the Ndff in the shoots, and B. polymyxa tended to enhance grain yield. Practical use of these rhizobacteria as inoculants for winter wheat may have limited value until such time as we better understand factors which influence rhizosphere competence of bacterial inoculants.     

Inoculation of field-grown wheat (Triticum aestivum) with Azospirillum spp. in Brazil

Summary Three field experiments with wheat were conducted in 1983, 1984, and 1985 in Terra Roxa soil in Paraná, the major Brazilian wheat-growing region, to study inoculation effects of various strains of Azospirillum brasilense and A. amazonense. In all three experiments inoculation with A. brasilense Sp 245 isolated from surface-sterilized wheat roots in Paraná produced the highest plant dry weights and highest N% in plant tops and grain. Grain yield increases with this strain were up to 31 % but were not significant. The application of 60 or 100 kg N ha^–1 to the controls increased N accumulation and produced yields less than inoculation with this strain. Another A. brasilense strain from surface-sterilized wheat roots (Sp 107st) also produced increased N assimilation at the lower N fertilizer level but reduced dry weights at the high N level, while strain Sp 7 + Cd reduced dry weights and N% in the straw at both N levels. The A. amazonense strain isolated from washed roots and a nitrate reductase negative mutant of strain Sp 245 were ineffective. Strains Sp 245 and Sp 107st showed the best establishment within roots while strain Cd established only in the soil.     

The flavonoid naringenin enhances intercellular colonization of rice roots by<Emphasis Type="Italic"> Azorhizobium caulinodans</Emphasis>

The intercellular colonization of rice roots by Azorhizobium caulinodans and other diazotrophic bacteria has been studied using strains marked with the lacZ reporter gene. A. caulinodans were able to enter the roots of rice at emerging lateral roots (lateral root cracks) by crack entry and this was observed by light microscopy. After colonization of lateral roots, bacteria moved into intercellular space within the cortical cell layer of roots. Naringenin at 1×10^-5 and 5×10^-5 M concentration significantly enhanced root colonization. The role of nodABC and regulatory nodD genes was also studied; lateral root crack (LRC) colonization of rice was shown to be Nod factor and NodD independent. Lateral root crack colonization of rice was also observed with similar frequency following inoculation with Azospirillum brasilense and the colonization by A. brasilense was stimulated by naringenin and other flavonoid molecules.     

Effect of nitrogen on the yield response of Pennisetum americanum,Triticum aestivum and Zea mays to inoculation with Azospirillum brasilense under temperate conditions

Summary A nitrate-respiring strain, a denitrifying strain, and a non-nitrogen-fixing strain of Azospirillum brasilense were compared for their effect on the growth of pearl millet (Pennisetum americanum), wheat (Triticum aestivum) and maize (Zea mays) under temperate conditions in nitrogen-limited pot cultures. Increases in yield of Z. mays shoots occurred with all three strains when inoculation coincided with the addition of low levels of combined nitrogen. The inoculation of A. brasilense did not show any effect on the yield of P. americanum and T. aestivum. Increased numbers of A. brasilense became associated with Z. mays roots following the addition of low levels of combined nitrogen. Low and very variable rates of acetylene reduction activity were observed from excised roots of inoculated Z. mays plants without preincubation. Results indicate that inoculation of cereals with A. brasilense under temperate conditions has only a limited effect on plant growth.     

植物促生菌接种对中国芥蓝根际固有微生物群落结构的影响

Plant growth-promoting rhizobacteria (PGPR) have been widely recognized as an important agent,especially as a biofertilizer,in agricultural systems.The objectives of this study were to select efective PGPR for Chinese kale (Brassica oleracea var.alboglabra) cultivation and to investigate the efect of their inoculation on indigenous microbial community structure.The Bacillus sp.SUT1 and Pseudomonas sp.SUT19 were selected for determining the efficiency in promoting Chinese kale growth in both pot and field experiments.In the field experiment,PGPR amended with compost gave the highest yields among all treatments.The Chinese kale growth promotion may be directly afected by PGPR inoculation.The changes of microbial community structure in the rhizosphere of Chinese kale following PGPR inoculation were examined by denaturing gradient gel electrophoresis (DGGE) and principal coordinate analysis.The DGGE fingerprints of 16S rDNA amplified from total community DNA in the rhizosphere confirmed that our isolates were established in the rhizosphere throughout this study.The microbial community structures were slightly diferent among all the treatments,and the major changes depended on stages of plant growth.DNA sequencing of excised DGGE bands showed that the dominant species in microbial community structure in the rhizosphere were not mainly interfered by PGPR,but strongly influenced by plant development.The microbial diversity as revealed by diversity indices was not diferent between the PGPR-inoculated and uninoculated treatments.In addition,the rhizosphere soil had more influence on eubacterial diversity,whereas it did not afect archaebacterial and fungal diversities.     

Effect of Azospirillum inoculants on arbuscular mycorrhiza establishment in wheat and maize plants

Plant growth-promoting rhizobacteria and arbuscular mycorrhizal (AM) fungi represent two main groups of beneficial microorganisms of the rhizosphere. The role of different strains of Azospirillum on AM fungi development was evaluated by measuring the percentage of AM colonisation of the root system in durum wheat and maize plants, grown under both greenhouse and field conditions. The effect of wild-type Azospirillum brasilense strain Sp245 and genetically modified (GM) derivatives overproducing indole-3-acetic acid was assessed at greenhouse level in (1) three different cultivars of durum wheat, in the presence of indigenous AM fungi and (2) maize plants artificially inoculated with Glomus mosseae and Glomus macrocarpum. In addition, the establishment of natural AM fungal symbiosis was evaluated using Azospirillum lipoferum CRT1 in maize plants at field level. Despite the stimulatory effect of the different Azospirillum inocula on root growth, no significant differences in AM colonisation were found, independently of the AM fungus involved, either in wheat or in maize plants. Similarly, GM A. brasilense, which strongly stimulates root development, did not affect AM formation. Although these results were obtained in conditions in which the mycorrhization rate was moderate (15–30%), overall considered they indicate that the use of wild-type or GM Azospirillum phytostimulators does not alter mycorrhization.     

Influence of soluble phosphorus fertilizer on the interaction between a vesicular-arbuscular mycorrhizal fungus and Azospirillum brasilense in barley (Herdeum vulgare L.)

Summary Pot-culture studies were carried out to examine the response of barley (Hordeum vulgare L.) to inoculation with Azospirillum brasilense and Glomus versiforme, singly and/or in combination, under varying levels of nitrogenous [(¹⁵NH₄)₂SO₄] and soluble phosphatic (single superphosphate) fertilizers. The interaction between both the endophytes led to increased growth and nutrition of the barley plants. Roots from plants inoculated with Azospirillum brasilense and Glomus versiforme exhibited very low acetylene reduction activity. N₂ fixation in the plants increased with the increase in plant growth but the mycorrhiza alone gave a low level of N₂ fixation in the plants compared to combined inoculation with both the endophytes.     

Using the spermosphere model technique to describe the dominant nitrogen-fixing microflora associated with wetland rice in two Egyptian soils

Summary This study is an attempt to describe the dominant N₂-fixing microflora associated with the roots of wetland rice. Rice cultivar Giza 171 was grown in a phytotron on two alluvial Egyptian soils for 8 days, a stage when the nitrogenase activity of undisturbed plants reached a level of 245 × 10^–6 mol C₂H₄ h^–1 g^–1 dry weight of leaf. The roots and rhizosphere soils were then used for counting and isolating dominant diazotrophs. Counts and initial enrichment steps were carried out on a selective medium made of an axenic rice plantlet, the spermosphere model, incubated under 1 % acetylene. The counts were very high, exceeding 10⁸ bacteria g^–1 dry weight of rhizosphere soil. Enterobacteriaceae were dominant; most isolates were Enterobacter cloacae belonging to different biotypes in the two soils. Enterobacter agglomerans, Citrobacter freundii and Klebsiella planticola were also present as members of the dominant microflora. Azospirillum brasilense and Azospirillum lipoferum were present as well, but less abundant.     

Infectivity and acetylene reduction of diazotrophic rhizosphere bacteria in wheat (Triticum aestivum) seedlings under gnotobiotic conditions

Summary Wheat seedlings were inoculated with rhizosphere nitrogen-fixing bacteria and grown gnotobiotically for 15 days. The growth medium consisted of semisolid agar with or without plant nutrients. The bacteria, isolated from roots of field-grown wheat, were three unidentified Gram-negative rods (A1, A2, E1), one Enterobacter agglomerans (C1) and two Bacillus polymyxa (B1, B2). A strain of Azospirillum brasilense (USA 10) was included for comparison.Nitrogenase activity (acetylene reduction activity, ARA) was tested on intact plants after 8 and 15 days of growth. In semisolid agar without plant nutrients, five isolates showed ARA of 0.01–0.9 nmol C₂H₄ plant^–1 h^–1, while the two strains of B. polymyxa had higher ARA of 3.3–10.6 nmol C₂H₄ plant^–1 h^–1.Plant development was not affected by inoculation with bacteria, except that inoculation with B. polymyxa resulted in shorter shoots and lower root weight.Transmission electronmicroscopy of roots revealed different degrees of infection. A. brasilense, A1 and A2, occurred mainly in the mucilage on the root surface and between outer epidermal cells (low infectivity). B. polymyxa strains and E1 were found in and between epidermal cells (intermediate infectivity) while E. agglomerans invaded the cortex and was occasionally found within the stele (high infectivity).     

Responses of native legume desert trees used for reforestation in the Sonoran Desert to plant growth-promoting microorganisms in screen house

Three slow-growing legume trees used for desert reforestation and urban gardening in the Sonoran Desert of Northwestern Mexico and the Southwestern USA were evaluated whether their growth can be promoted by inoculation with plant growth-promoting bacteria (Azospirillum brasilense and Bacillus pumilus), unidentified arbuscular mycorrhizal (AM) fungi (mainly Glomus sp.), and supplementation with common compost under regular screenhouse cultivation common to these trees in nurseries. Mesquite amargo (Prosopis articulata) and yellow palo verde (Parkinsonia microphylla) had different positive responses to several of the parameters tested while blue palo verde (Parkinsonia florida) did not respond. Survival of all tree species was over 80% and survival of mesquite was almost 100% after 10 months of cultivation. Inoculation with growth-promoting microorganisms induced significant effects on the leaf gas exchange of these trees, measured as transpiration and diffusive resistance, when these trees were cultivated without water restrictions.     

The fate of markerAzospirillum lipoferum inoculated into rice and its effect on growth,yield and N2 fixation of plants studied by acetylene reduction,15N2 feeding and15N dilution techniques

Summary A spontaneous mutant ofAzospirillum lipoferum, resistant to streptomycin and rifampicin, was inoculated into the soil immediately before and 10 days after transplanting of rice (Oryza sativa L.). Two rice varieties with high and low nitrogen-fixing supporting traits, Hua-chou-chi-mo-mor (Hua) and OS4, were used for the plant bacterial interaction study. The effect of inoculation on growth and grain and dry matter yields was evaluated in relation to nitrogen fixation, by in situ acetylene reduction assay,¹⁵N₂ feeding and¹⁵N dilution techniques. A survey of the population of marker bacteria at maximum tillering, booting and heading revealed poor effectivety. The population of nativeAzospirillum followed no definite pattern. Acetylene-reducing activity (ARA) did not differ due to inoculation at two early stages but decreased in the inoculated plants at heading. In contrast, inoculation increased tiller number, plant height of Hua and early reproductive growth of both varieties. Grain yield of both varieties significantly increased along with the dry matter. Total N also increased in inoculated plants, which was less compared with dry matter increase.¹⁵N₂ feeding of OS4 at heading showed more¹⁵N₂ incorporation in the control than in the inoculated plants. The ARA,¹⁵N and N balance studies did not provide clear evidence that the promotion of growth and nitrogen uptake was due to higher N₂ fixation.     

Biological nitrogen fixation at elevated temperature in different Azospirillum species and strains

Nitrogenase activity, nitrogenase synthesis, and the growth of four species of Azospirillum were examined at 30°C and 42°C. Azospirillum brasilense Sp 7 did not synthesize nitrogenase at 42°C nor was the enzyme stable at this temperature. In A. lipoferum 708 and A. brasilense 12S the nitrogenase activity was stable at 42°C but the synthesis of nitrogenase was reduced. In A. brasilense Sp 9 the nitrogenase activity was stable and showed the highest C₂H₂ reduction activity at 42°C.     

Synergistic effects of plant-growth promoting rhizobacteria and Rhizobium on nodulation and nitrogen fixation by pigeonpea (Cajanus cajan)

Plant‐growth promoting rhizobacteria (PGPR), in conjuction with efficient Rhizobium, can affect the growth and nitrogen fixation in pigeonpea by inducing the occupancy of introduced Rhizobium in the nodules of the legume. This study assessed the effect of different plant‐growth promoting rhizobacteria (Azotobacter chroococcum , Azospirillum brasilense, Pseudomonas fluorescens, Pseudomonas putida and Bacillus cereus) on pigeonpea (Cajanus cajan (L) Milsp.) cv. P‐921 inoculated with Rhizobium sp. (AR‐2–2 k). A glasshouse experiment was carried out with a sandy‐loam soil in which the seeds were treated with Rhizobium alone or in combination with several PGPR isolates. It was monitored on the basis of nodulation, N₂ fixation, shoot biomass, total N content in shoot and legume grain yield. The competitive ability of the introduced Rhizobium strain was assessed by calculating nodule occupancy. The PGPR isolates used did not antagonize the introduced Rhizobium strain and the dual inoculation with either Pseudomonas putida, P. fluorescens or Bacillus cereus resulted in a significant increase in plant growth, nodulation and enzyme activity over Rhizobium‐inoculated and uninoculated control plants. The nodule occupancy of the introduced Rhizobium strain increased from 50% (with Rhizobium alone) to 85% in the presence of Pseudomonas putida. This study enabled us to select an ideal combination of efficient Rhizobium strain and PGPR for pigeonpea grown in the semiarid tropics.     

Agronomical Performance of Upland Rice Cultivars Inoculated with Azospirillum brasilense Depends on the Plant Genotype

Plant growth–promoting bacteria may play an important role on rice development; however, its interaction with different genotypes is still uncertain. This work aimed to assess the effect of inoculation of Azospirillum brasilense AbV5 strain on the agronomical performance of different rice cultivars under field conditions during two consecutive years and to determine the response of rice cultivars to indole-acetic acid (IAA) rates under in vitro conditions using for both conditions a randomized block design. Field experiments evaluated the productivity components and grain yield of inoculated and noninoculated cultivars and in vitro assays monitored the plantlet growth under different IAA rates. Field experiments showed that the general average grain yield of rice cultivars inoculated with A. brasilense AbV5 strain was significantly greater. Fifty percent of the evaluated cultivars had statistically significant increase in yield varying from 40 to 108 percent upon inoculation with A. brasilense AbV5 strain, while 35 percent showed no significant change in yield (?6 to ?28 percent). In vitro assays showed rate- and cultivar-dependent responses of upland rice to exogenous IAA. These results show a cultivar-dependent response of rice to inoculation with A. brasilense AbV5 strain, which can be related with IAA production by AbV5 strain.     

Improving Strategic Growth Stage-based Drought Tolerance in Quinoa by Rhizobacterial Inoculation

ABSTRACT

Climate change is imposing high temperature resulting in prolonged drought episodes and shrinking of fresh water resources across the globe. In this scenario, even drought tolerant crops like quinoa are also losing significant yield. However, this study was planned to investigate the impact of drought on quinoa at critical growth stages and bacterial inoculation to improve drought tolerance. Drought was imposed by maintaining 25% pot water holding capacity (PWC) at multiple leaf, flowering, and seed filling stage (DSFS), while 80% PWC was considered as control. Three strains of plant growth promoting rhizobacteria (PGPR) named as: Bacillus licheniformis, Pseudomonas fluorescens, and Azospirillum brasilense were inoculated with quinoa seeds before sowing with respect to drought treatments. PGPR inoculation mitigated the drastic effects of drought by improving crop growth, net assimilation rate, water use efficiency, leaf chlorophyll, and phenolic contents, all of these ultimately contributed to improvement in grain yield and its contributing attributes. Moreover, PGPR markedly improves the grain quality attributes including protein, phosphorus, and potassium contents. Principal component analysis linked the different scales of study and demonstrated the potential of physio-biochemical traits to explain the quinoa yield variations under drought condition with response to PGPR inoculation. Among different PGPR, A. brasilense was found most effective both under normal and drought conditions. Overall, DSFS has more detrimental effects among critical growth stages of quinoa and A. brasilense can be used as a shotgun tactic to ameliorate drought stress in quinoa.     

Effect of inoculation with different strains of Azospirillum brasilense on cotton (Gossipium barbadense)

Summary The response of the cotton plant to inoculation with six strains of Azospirillum brasilense was investigated under subtropical conditions in Egypt. Azospirilla populations and activities were increased as a result of root inoculation with liquid inoculum of Azospirillum sp. Highest C₂H₂ — reduction activities on roots were obtained with strains S631 and Sp Br 14 (means of 216.85 and 209.50 nmol C₂H₄g^–1 root h^–1 respectively) while strain M4 gave the lowest activity (mean of 100.8 nmol C₂H₄g^–1 root h^–1). Statistical analysis showed that Azospirillum strains 5631, Sp Br 14, E15 and SC22 significantly increased the plant dry weight and nitrogen uptake while inoculation with strains M4 and SE had no significant effect in that respect.     

Biostimulant effects of rhizobacteria on wheat growth and nutrient uptake depend on nitrogen application and plant development

The capacity of plant growth-promoting rhizobacteria (PGPR) – Bacillus amyloliquefaciens GB03 (BamGB03), B. megaterium SNji (BmeSNji), and Azospirillum brasilense 65B (Abr65B) – to enhance growth and nutrient uptake in wheat was evaluated under different mineral N fertilizer rates, in sterile and non-sterile soils, and at different developmental stages. In gnotobiotic conditions, the three strains significantly increased plant biomass irrespective of the N rates. Under greenhouse conditions using non-sterile soil, growth promotion was generally highest at a moderate N rate, followed by a full N dose, while no significant effect was observed for the inoculants in the absence of N fertilizer. At 50N, plant biomass was most significantly increased in roots (up to +45% with Abr65B) at stem-elongation stage and in the ears (+19–23% according to the strains) at flowering stages. For some nutrients (N, P, Mn, and Cu), the biomass increases in roots and ears were paralleled with reduced nutrient concentrations in the same organs. Nevertheless, growth stimulation resulted in a higher total nutrient uptake and higher nutrient uptake efficiency. Furthermore, Abr65B and BmeSNji counteracted the reduction of root development caused by a high N supply. Therefore, combining PGPR with a proper cultivated system, N rate, and plant stage could enhance their biostimulant effects.     

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.     

Infection and colonization of aseptically micropropagated sugarcane seedlings by nitrogen-fixing endophytic bacterium, Herbaspirillum sp. B501gfp1

In this study, we used Herbaspirillum sp. B501gfp1 (B501gfp1), an isolate from wild rice, to investigate the interaction between a non-host nitrogen-fixing endophytic bacterium and micropropagated sugarcane plants under aseptic condition. Two Japanese sugarcane plants (Saccharum sp.) cultivars (cvs) NiF8 and Ni15 were inoculated using B501gfp1 in two inoculum doses of 10⁸ and 10² bacterial-cells-per-milliliter suspension. The results showed that bacterial cells colonized both the root and stem tissues, and colonization was apparent in the intercellular spaces. Higher bacterial numbers were detected in plant tissues inoculated with the higher inoculum concentration treatment. Bacterial numbers also varied between the two cultivars, with the higher values determined in cv Ni15. This study provides evidence that Herbaspirillum sp. B501gfp1, a rice isolate, could colonize sugarcane tissues, suggesting non-specificity of host plant among endophytes.     

The effect of Azospirillum brasilense Sp7 and Azotobacter chroococcum on nitrogen balance in soil under cropping with oats (Avena sativa L.)

Summary Pot experiments with oats were carried out to study the effect of Azospirillum brasilense Sp 7 and Azotobacter chroococcum 94K on the yield of plants, the N content of soil and the ¹⁴N balance. The plants were grown on gray forest soil under irrigation with deionized water and application of ¹⁵N-labelled fertilizer at a rate of 4 mg N 100 g^-1 soil. Inoculation of plants with Azospirillum spp. and Azotobacter spp. failed to increase the plant yield. However, the increase in total N in the soil at the end of the experiment and the positive ¹⁴N balance in the soil-plant system due to increased nitrogenase activity in the rhizosphere were statistically significant. The amount of N accumulated in the soil was comparable with the rate of N applied as fertilizer.