Comparative Analysis of Various Strains of Plant Growth Promoting Rhizobacteria on the Physiology of Garlic (Allium sativum)

Garlic is a most important medicinal herb belonging to the family Liliaceae. Both its leaves and bulb are edible. The current study was based on evaluating the growth promoting potential of plant growth promoting rhizobacteria (PGPR) on garlic (Allium sativum L.) growth and biochemical contents. Garlic cloves were inoculated with 3 kinds of PGPRs, Pseudomonas putida (KX574857), Pseudomonas stutzeri (Kx574858) and Bacillus cereus (ATCC14579) at 108 cells/mL prior to sowing. Under natural conditions, plants were grown in the net house. The PGPR significantly enhanced % germination, leaf and root growth and their biomass also increased the diameter of bulb and fresh and dry weight. The flavonoids, phenolics, chlorophyll, protein and sugar content were also significantly increased due to PGPR inoculation. The Pseudomonas stutzeri was found most effective for producing longer leaves with moderate sugar, high flavonoids (129%) and phenolics (263%) in bulb over control (Tap). The Pseudomonas putida exhibited a maximum increase in bulb diameter and bulb biomass with maximum phenolics and flavonoid contents.

Acid-Phosphorus Activity of Wheat Varieties Rhizobacteria of Uzbekistan

In this work, local strains of phosphate-solubilizing microorganisms were isolated and identified from the wheat rhizosphere and exogenous acid phosphatase enzymes of locally active phosphate- and potassium-mobilizing rhizobacteria belonging to the genera Escherichia, Rahnella, Bacillus, Enterobacter, Pseudomonas, and Pantoea were studied. The efficiency of the physiological properties of rhizobacteria is determined by the production of soluble phosphorus, and the amount of phosphorus depends on the activity and biomass of bacteria that secrete phosphorus. This is done by phosphate solubilizing bacteria, and the habitat ecosystem is enriched with beneficial micronutrients. In these studies, active rhizobacteria activity of acid phosphatase in nutrient liquid was studied at different temperatures. Optimum pH activity index and temperature variability of enzymes were determined. It should be noted that in the most active phosphate-solubilizing strains the maximum enzymatic activity was observed in the culture fluid of R. aquatilis strain 17, which produced 1.086 μmol p-nitrophenol μmol/min/ml. P. agglomerans 22, P. agglomerans 20 and Ps. kilonensis 32 cultures phosphatase activity was 0.143 - 0.680 p-nitrophenol μmol/min/ml. It should be noted that the phosphatase activity of bacteria belonging to the same genus and species was very different from each other. That is, the enzyme activity of Rahnella aquatilis strain 17 was 9 times higher than the enzyme activity of Rahnella aquatilis strain 9. The pH optimum of sour phosphatase enzymes in Rahnella aquatilis strain 16 was 6.0. The optimum temperature of acid phosphatase activity was 45˚C and 50˚C. The reason for this may be that the strains were isolated in different soil and climate conditions. When the acid phosphatase activity of R. aquatilis 3, 9, E. cloacae 8 and P. agglomerans 22 cultures was determined at a temperature of 45˚C, it was observed that the enzyme activity increased by 2 - 4 times. Es. hermannii 1, Ps. kilonensis 26 and B. simplex 28 bacteria acid phosphatase activity was not significantly affected by temperature rise.

Research Progress of Mechanism of Action of Plant Growth Promoting Rhizobacteria

The paper first introduces the definition and classification of plant growth promoting rhizobacteria （PGPR）, then reviews the research achievements on the mechanism of action of plant growth promoting rhizobacteria, including growth pro-moting mechanism and bio-control mechanism, subsequently lists the use of excel-lent plant growth promoting rhizobacteria strains in recent years, especial y Pseu-domonas and Bacil us strains, and final y discusses problems existing in this area and points out issues requiring further exploration, including PGPR screening meth-ods, preservation methods, mechanism of action, in order to commercialize PGPR as soon as possible and practical y realize its application to production.

Role of soil rhizobacteria in phytoremediation of heavy metal contaminated soils

Heavy metal pollution of soil is a significant environmental problem and has its negative impact on human health and agriculture. Rhizosphere, as an important interface of soil and plant, plays a significant role in phytoremediation of contaminated soil by heavy metals, in which, microbial populations are known to affect heavy metal mobility and availability to the plant through release of chelating agents, acidification, phosphate solubilization and redox changes, and therefore, have potential to enhance phytoremediation processes. Phytoremediation strategies with appropriate heavy metal-adapted rhizobacteria have re-ceived more and more attention. This article paper reviews some recent advances in effect and significance of rhizobacteria in phytoremediation of heavy metal contaminated soils. There is also a need to improve our understanding of the mechanisms in-volved in the transfer and mobilization of heavy metals by rhizobacteria and to conduct research on the selection of microbial isolates from rhizosphere of plants growing on heavy metal contaminated soils for specific restoration programmes.

Suppression of Meloidogyne javanica by antagonistic and plant growth-promoting rhizobacteria

Four rhizobacteria selected out of over 500 isolates from rhizosphere of the vegetables in China were further studied for suppression of the root-knot nematode and soil-borne fungal pathogens in laboratory and greenhouse in Belgium. They were identified as Brevibacillus brevis or Bacillus subtilis by Biolog test and partial 16s rDNA sequence comparison. They not only inhibited the radial growth of the root-infecting fungi Rhizoctonia solani SX-6, Pythium aphanidermatum ZJP-1 and Fusarium oxysporum f.sp. cucumerinum ZJF-2 in vitro, but also exhibited strong nematicidal activity by killing the second stage larvae of Meloidogyne javanica to varying degrees in the greenhouse. The toxic principles of bacterium B7 that showed the highest juvenile mortality were partially characterized. The active factors were heat stability and resistance to extreme pH values. B7 used either as seed dressing or soil drench significantly reduced the nematode populations in the rhizosphere and enhanced the growth of mungbean plants over the controls in the presence or absence of R. solani.

Isolation, characterization and effect of plant-growth-promoting rhizobacteria on pine seedlings(Pinus pseudostrobus Lindl.)

In this study,10 bacterial strains were isolated from the rhizosphere of coniferous trees on Mount Tla′loc in Mexico.The strains were characterized by their capacity to produce auxins,solubilize phosphates and stimulate mycelial growth of the ectomycorrhizal fungus Suillus sp.All isolates were identified at the molecular level.Moreover,an experiment was established to evaluate the response of Pinus pseudostrobus seedlings to inoculation with the rhizobacteria strains.The isolated strains belonged to the species Cupriavidus basilensis,Rhodococcus qingshengii,R.erythropolis,Pseudomonas spp.,P.gessardii,Stenotrophomonas rhizophila and Cohnella sp.All of the strains produced auxins;the best producer was R.erythropolis CPT9(76.4 lg mL^-1).P.gessardii CPT6 solubilized phosphate at a significant level(443 lg mL^-1).The strain S.rhizophila CPT8 significantly increased the radial growth of the ectomycorrhizal fungus Suillus sp.by 18.8%.Five strains increased the dry mass of the shoots;R.qingshengii CPT4 and R.erythropolis CPT9 increased growth the most,by more than 20%.Inoculation with plant-growth-promoting rhizobacteria can be a very useful practice in a forest nursery to produce healthy,vigorous plants.

The role of rhizobacteria in rice plants: Growth and mitigation of toxicity

Allelopathic compounds reduce the growth and productivity of upland rice plants, especially in consecutive plantations. The rhizobacteria Pseudomonas fluorescens BRM-32111 and Burkholderia pyrrocinia BRM-32113 have been recorded as growth promoters in rice. This study was developed to understand the effect of the application of rhizobacteria on upland rice plants in consecutive plantations. Experiments were conducted in a completely randomized design with four replications of four treatments: rice seed inoculated with P. fluorescens BRM-32111, rice seed inoculated with B. pyrrocinia BRM-32113(both sown on soil with rice residue), non-inoculated plants sown on soil with rice residue(control with residue(WR)), and non-inoculated plants on soil with no residue(NR). Roots and seedling growth were adversely affected by allelopathic compounds in control WR plants. Plants inoculated with rhizobacteria P. fluorescens BRM-32111 or B. pyrrocinia BRM-32113 induced an increase of 88% in biomass, 3% in the leaf area, 40% in length, 67% in root biomass, 21% in chlorophyll a, 53% in chlorophyll(a+b), 50% in rate of carbon assimilation(A), 227% in A/rubisco carboxylation efficiency(Ci) and 63% in water use efficiency(WUE) compared to control WR plants. These results indicate that rhizobacteria P. fluorescens BRM-32111 and B. pyrrocinia BRM-32113 increase the tolerance of rice plants to stress from allelochemicals. There are possible practical agricultural applications of these results for mitigating the effects of environmental allelochemistry on upland rice.

Plant growth-promoting rhizobacteria(PGPR)and its mechanisms against plant diseases for sustainable agriculture and better productivity

Plant growth-promoting rhizobacteria(PGPR)are specialized bacterial communities inhabiting the root rhizosphere and the secretion of root exudates helps to,regulate the microbial dynamics and their interactions with the plants.These bacteria viz.,Agrobacterium,Arthobacter,Azospirillum,Bacillus,Burkholderia,Flavobacterium,Pseudomonas,Rhizobium,etc.,play important role in plant growth promotion.In addition,such symbiotic associations of PGPRs in the rhizospheric region also confer protection against several diseases caused by bacterial,fungal and viral pathogens.The biocontrol mechanism utilized by PGPR includes direct and indirect mechanisms direct PGPR mechanisms include the production of antibiotic,siderophore,and hydrolytic enzymes,competition for space and nutrients,and quorum sensing whereas,indirect mechanisms include rhizomicrobiome regulation via.secretion of root exudates,phytostimulation through the release of phytohormones viz.,auxin,cytokinin,gibberellic acid,1-aminocyclopropane-1-carboxylate and induction of systemic resistance through expression of antioxidant defense enzymes viz.,phenylalanine ammonia lyase(PAL),peroxidase(PO),polyphenyloxidases(PPO),superoxide dismutase(SOD),chitinase andβ-glucanases.For the suppression of plant diseases potent bio inoculants can be developed by modulating the rhizomicrobiome through rhizospheric engineering.In addition,understandings of different strategies to improve PGPR strains,their competence,colonization efficiency,persistence and its future implications should also be taken into consideration.

Synergistic combination of arbuscular mycorrhizal fungi and plant growth-promoting rhizobacteria modulates morpho-physiological characteristics and soil structure in Nitraria tangutorum bobr.Under saline soil conditions

Nitraria tangutorum Bobr.,a typical xero-halophyte,can be used for vegetation restoration and reconstruction in arid and semiarid regions affected by salinity.However,global climate change and unreasonable human activity have exacerbated salinization in arid and semi-arid regions,which in turn has led to the growth inhibition of halophytes,including N.tangutorum.Arbuscular mycorrhizal fungi(AMF)and plant growth-promoting rhizobacteria(PGPR)have the potential to improve the salt tolerance of plants and their adaptation to saline soil environments.In this study,the effects of single and combined inoculations of AMF(Glomus mosseae)and PGPR(Bacillus amyloliquefaciens FZB42)on N.tangutorum were evaluated in severe saline soil conditions.The results indicate that AMF and PGPR alone may not adapt well to the real soil environment,and cannot ensure the effect of either growth promotion or salt-tolerance induction on N.tangutorum seedlings.However,the combination of AMF and PGPR significantly promoted mycorrhizal colonization,increased biomass accumulation,improved morphological development,enhanced photosynthetic performance,stomatal adjustment ability,and the exchange of water and gas.Co-inoculation also significantly counteracted the adverse effect of salinity on the soil structure of N.tangutorum seedlings.It is concluded that the effectiveness of microbial inoculation on the salt tolerance of N.tangutorum seedlings depends on the functional compatibility between plants and microorganisms as well as the specific combinations of AMF and PGPR.

Increased ammonification,nitrogenase,soil respiration and microbial biomass N in the rhizosphere of rice plants inoculated with rhizobacteria

Azospirillum brasilense and Pseudomonas fluorescens are well-known plant growth promoting rhizobacteria.However,the effects of A.brasilense and P.fluorescens on the N cycles in the paddy field and rice plant growth are little known.This study investigated whether and how A.brasilense and P.fluorescens contribute to the N transformations and N supply capacities in the rhizosphere,and clarified the effects of A.brasilense and P.fluorescens on the N application rate in rice cultivation.Inoculations with A.brasilense and P.fluorescens coupled with N application rate trials were conducted in the paddy field in 2016 and 2017.The inoculations of rice seedlings included four treatments:sterile saline solution(M_(0)),A.brasilense(M_(b)),P.fluorescens(M_(p)),and co-inoculation with a mixture of A.brasilense and P.fluorescens(M_(bp)).The N application rate included four levels:0 kg N ha^(–1)(N_(0)),90 kg N ha^(–1)(N_(90)),180 kg N ha^(–1)(N_(180)),and 270 kg N ha^(–1)(N_(270)).The results indicated that the M_(bp) and M_(p) treatments significantly enhanced the ammonification activities in the rhizosphere compared with the M_(0) treatment,especially for higher N applications,while the Mbp and M_(b) treatments greatly enhanced the nitrogenase activities in the rhizosphere compared with the M_(0) treatments,especially for lower N applications.Azospirillum brasilense and P.fluorescens did not participate in the nitrification processes or the denitrification processes in the soil.The soil respiration rate and microbial biomass N were greatly affected by the interactions between the rhizobacteria inoculations and the N fertilizer applications.In the M_(bp) treatment,N supply capacities and rice grain yields showed no significant differences among the N_(90),N_(180),and N_(270) applications.The N application rate in the study region can be reduced to 90 kg N ha^(–1) for rice seedlings co-inoculated with a mixture of A.brasilense and P.fluorescens.

Effect of Plant Growth-Promoting Rhizobacteria at Various Nitrogen Rates on Corn Growth

Plant growth-promoting rhizobacteria (PGPR) colonize plant roots and promote plant growth by producing and secreting various chemical regulators in the rhizosphere. With the recent interest in sustainable agriculture, an increasing number of researchers are investigating ways to improve the efficiency of PGPR use to reduce chemical fertilizer inputs needed for crop production. Accordingly, greenhouse studies were conducted to evaluate the impact of PGPR inoculants on biomass production and nitrogen (N) content of corn (Zea mays L.) under different N levels. Treatments included three PGPR inoculants (two mixtures of PGPR strains and one control without PGPR) and five N application levels (0%, 25%, 50%, 75%, and 100% of the recommended N rate of 135 kg N ha−1). Results showed that inoculation of PGPR significantly increased plant height, stem diameter, leaf area, and root morphology of corn compared to no PGPR application under the same N levels at the V6 growth stage, but few differences were observed at the V4 stage. PGPR with 50% of the full N rate produced corn biomass and N concentrations equivalent to or greater than that of the full N rate without inoculants at the VT stage. In conclusion, mixtures of PGPR can potentially reduce inorganic N fertilization without affecting corn plant growth parameters. Future research is needed under field conditions to determine if these PGPR inoculants can be integrated as a bio-fertilizer in crop production nutrient management strategies.

Potential of Biostimulants Based on PGPR Rhizobacteria Native to Benin’s Soils on the Growth and Yield of Maize (<i>Zea mays </i>L.) under Greenhouse Conditions

The application of biostimulants in agriculture represents an environmentally friendly alternative while increasing agricultural production. The aims of the study were to develop solid biostimulants based on five rhizobacteria native to Benin’s soils and to evaluate their efficacy on the growth and biomass yield of maize under greenhouse conditions on ferrallitic and ferruginous soils. Clay and peat were used as a conservation binder for the preparation of the biostimulants. These binders were used alone or combined in the different formulations with maize flour and sucrose. 10 g of biostimulants were applied at sowing in pots containing five kilograms of sterilised soil. The experimental design was a completely randomised block of 24 treatments with three replicates. The results obtained showed significant improvements (P < 0.001) in height (49.49%), stem diameter (32.7%), leaf area (66.10%), above-ground biomass (97.12%) and below-ground biomass (53.98%) on ferrallitic soil with the application of the clay + Pseudomonas putida biostimulant compared to the control. On the other hand, the use of the peat biostimulant + Pseudomonas syringae was more beneficial for plant growth on ferruginous soil. The height, stem diameter, leaf area, above-ground biomass and below-ground biomass of the plants under the influence of this biostimulant were improved by 83.06%, 44.57%, 102.94%, 86.84% and 42.68%, respectively, compared to the control. Therefore, these results confirm that Rhizobacteria express their potential through biostimulants formulated on maize. The formulated biostimulants can later be used by producers to improve crop productivity for sustainable agriculture.

Potential seed germination-enhancing plant growth-promoting rhizobacteria for restoration of Pinus chiapensis ecosystems

Rhizosphere soil samples of three Pinus chiapensis sites were analyzed for their physicochemical properties,soil bacteria isolated and screened in vitro for growthpromoting abilities.Nine isolates that showed promise were identified to five genera Dyella,Luteimonas,Euterobacter,Paraburkholderia and Bacillus based on the sequences of16 S rRNA gene.All the strains were isolated from nondisturbed stands.These bacteria significantly decreased germination time and increased sprout sizes.Indole acetic acid and gibberellin production and phosphate solubilisation were detected.Results indicate that these biochemicals could be essential for P.chiapensis distribution and suggest the possibility that PGPR inoculation on P.chiapensis seeds prior to planting could improve germination and possibly seedling development.

Isolation, Screening and Molecular Characterization of Multifunctional Plant Growth Promoting Rhizobacteria for a Sustainable Agriculture

The use of PGPR as a multifunctional biofertilizer or biostimulant is an alternative way to prevent soil pollution and preserve agricultural for sustainable economy. In this study, 102 bacterial strains were isolated from rhizospheric soil of different crop fields. Among them, 15 bacterial isolates rich of NPK were selected to screen for PGP activity. It was found that 4 out 15 isolates were able to fix atmospheric nitrogen, 14 could solubilize phosphate and 5 could solubilize potassium. They were further examined for the production of hydrolytic enzymes (amylase, cellulose, chitinase, etc.), plant hormone (IAA) and plant defense substances (HCN, siderophore, etc.). All PGPR isolates were able to produce IAA, siderophore and ammonia while 2 isolates could produce HCN. Among them, 73.33% of selected isolates produced amylase, 80% produced cellulase, 66.67% produced pectinase, 93.33% produced chitinase and β-glucanase. For salt stress tolerance, all the isolates grew well in 5% NaCl while only 4 tolerated 9% NaCl. Among all isolates, 2 have antifungal activity and 5 have antibacterial activity. The best 6 isolates and consortium were tested to promote plant growth in green-gram and maize germination. Seed germination of green-gram and maize was observed the best in Acromobacter insolitus S3 compared with other treatments. Pseudomonas plecoglossicida B3 was found the best in fresh weight for both crops. The highest root formation was observed in Acromobacter insolitus S3 treatment in maize and Enterobacter hormaechei W1 treatment in green-gram.

Plant Growth Promoting Rhizobacteria as Biological Control Agent in Rice

The use of agrochemical products to combat diseases in crops has adverse effects on the environment and human health. Plant growth promoting rhizobacterium (PGPR) has been increasingly proposed as an eco-friendly alternative in agriculture. PGPRs have beneficial effects not only in promoting plant growth but also have shown their potential as biological control agent, being able to inhibit plant pathogens. Here, we investigated the use of PGPR Paraburkholderia sp. strain SOS3 to provide disease protection in rice (Oryza sativa L.). The antagonistic activity of SOS3 against five fungal pathogens of rice was assessed by dual culture on plates and on rice seedlings. The results showed that on plate assay, SOS3 inhibits the growth of Curvularia lunata, Rhizoctonia solani, Pyricularia oryzae, Helminthosporium oryzae, and Fusarium moniliforme by 17.2%, 1.1%, 8.3%, 32.5%, and 35.4%, respectively. When inoculated on rice seeds, SOS3 promotes seed germination and significantly reduces disease symptoms in plants infected with R. solani. These results suggest that SOS3 has a great potential to be used in rice agriculture to combat the “Sheath Blight” disease.

Applying Rhizobacteria on Maize Cultivation in Northern Benin:Effect on Growth and Yield

The aim of the study was to investigate the effects of five plant growth-promoting rhizobacteria (PGPR) (Bacillus panthothenicus;Pseudomonas Cichorii;Pseudomonas Putida;Pseudomonas syringae and Serratia marcescens) on the growth and yield of maize on a ferruginous soil under field condition. Maize seeds were inoculated with 10 ml of bacterial suspension. Study was conducted in a completely randomized design with fifteen treatments and three replicates. A half-dose of recommended (13, 17, 17 kg?ha?1) NPK was applied 15 days after emergence. The results show that the Serratia marcescens + 50% NPK treatment yielded the best results for height, fresh underground biomass, dry aboveground biomass, dry underground biomass, and grain yield with respective increases of 41.09%, 217.5%, 213.34%, 93.82%, and 39.05% compared to the control. Maximum stem diameter (increases of 49.65%) was recorded in the plants treated with 100% NPK (full dose NPK) while the highest leaf area (466.36 ± 9.57 cm2), obtained on plant treated with Pseudomonas putida + 50% NPK was 32.08% greater than in the non-inoculated control. Our results suggest the use of these rhizobacteria as biological fertilizers for enhancing the growth and maize seed yield in ferruginous soil in the North of Benin.

Plant Growth Promoting Rhizobacteria Having 1-Aminocyclopropane-1-Carboxylic Acid Deaminase to Induce Salt Tolerance in Sunflower (<i>Helianthus annus L.</i>)

Soil salinity badly affects agriculture productivity through accumulation of salts in upper layers of soils. The harmful effects of salts in arable lands have influenced modern as well as ancient civilizations. A pot study was carried out to test the performance of two PGPR isolates (KS 8, KS 28) on sunflower (SMH-0917) under different salinity levels (8, 10 and 12 dS·m-1). These salinity levels were developed by adding calculated amount of salts (NaCl, Na2SO4, CaCl2 and MgSO4) with ratio of 3:4:2:1. The bacterial strains KS 8 and KS 28 were applied separately in two treatments while third treatment was co-inoculation (KS mix). Completely randomized experimental design (CRD) was used and data were collected at flowering stage about pre-decided plant growth parameters (plant height, shoot dry weight and root dry weight). The bacterial isolate KS 8 showed an increase of 26, 102% and 83% in plant height, shoot dry weight and root dry weight at EC 8 dS·m-1, while this improvement was 67%, 163% and 296% at EC 10 dS·m-1, however an increase of 100%, 74% and 382% was recorded over control respectively at EC 12 dS·m-1. Similarly isolate KS 28 exhibited an increase of 14%, 69% and 54% in plant height;shoot dry weight and root dry weight at EC 8 dS·m-1, whereas this improvement was 56%, 163% and 188% at EC 10 dS·m-1, while an increase of 60%, 41% and 282% was registered respectively over control at EC 12 dS·m-1. The increase due to mixture treatments was 4%, 41% and 16% in plant height, shoot dry weight and root dry weight at EC 8 dS·m-1, while an increase of 33%, 57% and 100% at EC 10 dS·m-1, whereas an improvement of 53%, 33% and 164% respectively was noted at EC 12 dS·m-1 over un-inoculated. The isolate KS 8 performed better than KS 28 and mixture treatment. These two PGPR strains could be used to mitigate the adverse impact caused by salinity stress on sunflower.

Isolation and Screening of Rhizobacteria from Scirpus Grossus Plant after Lead （Pb） Exposure

Phytoremediation is one of method which can be applied to remediate the contaminated environment. In most cases, microorganisms bacteria and fungi, living in the rhizosphere closely associated with plants, may contribute to mobilize metal ions by increasing the bioavailable fraction. Some studies have evidenced that heavy metal-resistant bacteria can enhance metal uptake by hyperaccumulator plants. Lead-resistant bacteria which could help to increase the lead uptake by Scirpus grossus was isolated and screened. The samples were taken from plant roots after being exposed in a range finding test by spiking analytical grade of Pb（NO3）2 solution in variation of Pb concentrations. The results of rhizobacteria isolation showed that there were several colonies having resistance to grow and survive in contaminated environment even the host plant had withered. Only a few of rhizobacteria colonies were affected by high concentrations of lead exposure during screening test. The screening test was conducted by growing the isolated colonies on plates containing tryptic soy agar （TSA） medium containing of 200, 400 and 600 mg/L Pb solution including the plate with only TSA media without any lead exposure acting as a control medium, and incubating them at 30℃ for 72 hours. Isolation of bacteria from rhizosphere had found 47 colonies including several colonies from the withered plants. These all 47 colonies then become 28 after characterization by using color and colony morphology, followed by Gram stain, catalase, oxidase and motility test. The screening test of lead resistant bacteria colonies resulted 3 groups which is scored high, medium and low. The screened colonies will then be used for further study.

微生物肥料新型功能作用机理与根际定殖增强策略

微生物肥料是支撑农业绿色发展的重要投入品,根际益生菌是微生物肥料菌种的主要来源。我国农业发展对促进作物根系发育、增强作物耐盐胁迫能力等新型功能的微生物肥料提出了需求,然而目前对根际益生菌促进作物根系发育和增强耐盐胁迫的分子机理研究仍然薄弱,成为制约优异菌种选育的瓶颈。另一方面,微生物肥料的根际定殖能力低也是导致其田间应用效果差的重要因素。本文综述了根际益生菌调控根系发育、增强植物耐盐的活性物质和作用机理,分析其根际定殖的过程和菌植互作机制,提出了增强根际定殖的策略,以期为微生物肥料研究提供参考。

垂穗披碱草根际促生菌的分离鉴定及促生作用研究

优良的根际生长促生菌(Plant growth-promoting rhizobacteria, PGPR)是生产优质微生物菌肥的重要物质基础。本研究以广布于青藏高原的垂穗披碱草(Campeiostachys nutans Griseb.)为材料,采用平板划线法分离其PGPR,探究菌株的促生特性,通过16S测序确定菌株的分类地位,并进行盆栽试验验证PGPR的促生效果。结果表明,从垂穗披碱草根际土筛选出14株促生特性优良的PGPR,其中,有11株兼具产IAA,ACC脱氨酶以及铁载体的能力。经16S rDNA鉴定,以假单胞菌属为优势菌属,6株属于假单胞菌属(Pseudomonas),2株属于芽孢杆菌属(Bacillus),2株属于葡萄球菌属(Staphylococcus),其他四株分别属于类节杆菌属(Paenarthrobacter)、微杆菌属(Microbacterium)、不动杆菌属(Acinetobacter)和考克氏菌属(Kocuria)。盆栽试验表明,接种14株菌株对多年生黑麦草具有良好的促生效果,并能够提高其光合效率。研究结果丰富了植物根际促生菌菌种资源库,为实现农业“绿色增产”提供优质菌肥种质资源。