Role Of Plant Growth Promoting Rhizobacteria Research Articles

Plant Growth-Promoting Rhizobacteria: Context, Mechanisms of Action, and Roadmap to Commercialization of Biostimulants for Sustainable Agriculture.

Microbes of the phytomicrobiome are associated with every plant tissue and, in combination with the plant form the holobiont. Plants regulate the composition and activity of their associated bacterial community carefully. These microbes provide a wide range of services and benefits to the plant; in return, the plant provides the microbial community with reduced carbon and other metabolites. Soils are generally a moist environment, rich in reduced carbon which supports extensive soil microbial communities. The rhizomicrobiome is of great importance to agriculture owing to the rich diversity of root exudates and plant cell debris that attract diverse and unique patterns of microbial colonization. Microbes of the rhizomicrobiome play key roles in nutrient acquisition and assimilation, improved soil texture, secreting, and modulating extracellular molecules such as hormones, secondary metabolites, antibiotics, and various signal compounds, all leading to enhancement of plant growth. The microbes and compounds they secrete constitute valuable biostimulants and play pivotal roles in modulating plant stress responses. Research has demonstrated that inoculating plants with plant-growth promoting rhizobacteria (PGPR) or treating plants with microbe-to-plant signal compounds can be an effective strategy to stimulate crop growth. Furthermore, these strategies can improve crop tolerance for the abiotic stresses (e.g., drought, heat, and salinity) likely to become more frequent as climate change conditions continue to develop. This discovery has resulted in multifunctional PGPR-based formulations for commercial agriculture, to minimize the use of synthetic fertilizers and agrochemicals. This review is an update about the role of PGPR in agriculture, from their collection to commercialization as low-cost commercial agricultural inputs. First, we introduce the concept and role of the phytomicrobiome and the agricultural context underlying food security in the 21st century. Next, mechanisms of plant growth promotion by PGPR are discussed, including signal exchange between plant roots and PGPR and how these relationships modulate plant abiotic stress responses via induced systemic resistance. On the application side, strategies are discussed to improve rhizosphere colonization by PGPR inoculants. The final sections of the paper describe the applications of PGPR in 21st century agriculture and the roadmap to commercialization of a PGPR-based technology.

Role of plant growth-promoting rhizobacteria in reducing the harmful effect of water stress on some physiological traits of popcorn

A field experiment was conducted in the experimental field of field crops, College of Agriculture, University of Baghdad during the autumn season of 2017. In order to know the role of plant growth-promoting rhizobacteria in improving the physiological traits of popcorn crop under water stress, the split plot design was used with three replicates. The main plots included water stress treatments with three levels of irrigation, which were depletion 50% (Control), 60% and 70% of water availability, which were symbolized by S1, S2 and S3, respectively. The secondary plots included four treatments of bacterial vaccine (Control, Azotobacter, Azospirillum, Azotobacter+Azospirillum) which were symbolized by F0, F1, F2 and F3, respectively. The results showed that the water stress treatment when irrigation by depletion 70% had a significant effect on the decrease in auxin content by 36.44%, gibberellic acid 11.14%, cytokinin 47.55%, chlorophyll 20.07%, relative water content 18.09% and turgor pressure 20.64%. Vaccination with plant growth-promoting rhizobacteria (PGPRs) significantly increased physiological characteristics, Azospirillum treatment gave the highest average of auxin and gibberellic acid content of 66.28 and 43.72 μM sequentially, the mixture treatment of Azotobacter+Azospirillum significantly increased chlorophyll and proline content, relative water content and turgor pressure of the leaves. Vaccination with types of PGPRs achieved the best contribution to a small effect of water stress when treated with Azospirillum and Azotobacter+Azospirillum. Therefore, we suggest that the vaccination of popcorn seeds is used with water stress.

Investigating the mechanisms underlying phytoprotection by plant growth-promoting rhizobacteria in Spartina densiflora under metal stress.

Pollution of coasts by toxic metals and metalloids is a worldwide problem for which phytoremediation using halophytes and associated microbiomes is becoming relevant. Metal(loid) excess is a constraint for plant establishment and development, and plant growth promoting rhizobacteria (PGPR) mitigate plant stress under these conditions. However, mechanisms underlying this effect remain elusive. The effect of toxic metal(loid)s on activity and gene expression of ROS-scavenging enzymes in roots of the halophyte Spartina densiflora grown on real polluted sediments in a greenhouse experiment was investigated. Sediments of the metal-polluted joint estuary of Tinto and Odiel rivers and control, unpollutred samples from the Piedras estuary were collected and submitted to ICP-OES. Seeds of S.densiflora were collected from the polluted Odiel marshes and grown in polluted and unpolluted sediments. Rhizophere biofilm-forming bacteria were selected based on metal tolerance and inoculated to S.densiflora and grown for 4months. Fresh or frozen harvested plants were used for enzyme assays and gene expression studies, respectively. Metal excess induced SOD (five-fold increase), whereas CAT and ascorbate peroxidase displayed minor induction (twofold). A twofold increase of TBARs indicated membrane damage. Our results showed that metal-resistant PGPR (P.agglomerans RSO6 and RSO7 and B.aryabhattai RSO25) contributed to alleviate metal stress, as deduced from lower levels of all antioxidant enzymes to levels below those of non-exposed plants. The oxidative stress index (OSI) decreased between 50 and 75% upon inoculation. The results also evidenced the important role of PAL, involved in secondary metabolism and/or lignin synthesis, as a pathway for metal stress management in this halophyte upon inoculation with appropriate PGPR, since the different inoculation treatments enhanced PAL expression between 3.75- and five-fold. Our data confirm, at the molecular level, the role of PGPR in alleviating metal stress in S.densiflora and evidence the difficulty of working with halophytes for which little genetic information is available.

Role of Plant Growth-Promoting Rhizobacteria (PGPR), Biochar, and Chemical Fertilizer under Salinity Stress

ABSTRACTPot experiment was conducted under axenic conditions in a growth chamber with 14 h photoperiod at 22/26°C to evaluate the role of biochar, phosphate-solubilizing rhizobacteria (Pseudomonas sp.), and chemical fertilizer under induced salt stress (150 mM sodium chloride (NaCl)). Factorial randomized complete plot designs with three replications were used. Biochar and fertilizer were mixed in soil (5:1) while Pseudomonas sp. was applied as seed soaking. Salt stress applied at 3 leaf stage significantly reduced (27%) soil moisture and increased electrolyte leakage, Na and potassium (K) uptake, proline, and antioxidant enzymes. Biochar and Pseudomonas sp. decreased the sodium by 24% and 50%, respectively, and increased proline, soil moisture content, and peroxidase (POD) activity. Fertilizer treatment increased the electrolyte leakage by 73%. The effect of fertilizer was 3–4× higher for proline and POD activity in combined treatment with biochar and Pseudomonas. The fertilizer effect can be augmented by the application of Pseudomonas sp. and biochar to alleviate salt stress.

Deciphering the role of plant growth-promoting rhizobacteria in the tolerance of the invasive cordgrass Spartina densiflora to physicochemical properties of salt-marsh soils

Background and aims A glasshouse experiment was conceived to assess the role of a bacterial consortium (Pseudomonas composti SDT3, Aeromonasaquariorum SDT 13 and Bacillus sp. SDT14) isolated from the rizhosphere of S. densiflora on its growth and physiological tolerance to the physicochemical properties of marsh soils.

In vitro antagonistic activity, plant growth promoting traits and phylogenetic affiliation of rhizobacteria associated with wild plants grown in arid soil

The role of plant growth-promoting rhizobacteria (PGPR) in adaptation of plants in extreme environments is not yet completely understood. For this study native bacteria were isolated from rhizospeheric arid soils and evaluated for both growth-promoting abilities and antagonistic potential against phytopathogenic fungi and nematodes. The phylogentic affiliation of these representative isolates was also characterized. Rhizobacteria associated with 11 wild plant species from the arid soil of Almadinah Almunawarah, Kingdom of Saudi Arabia (KSA) were investigated. From a total of 531 isolates, only 66 bacterial isolates were selected based on their ability to inhibit Fusarium oxysporum, and Sclerotinia sclerotiorum. The selected isolates were screened in vitro for activities related to plant nutrition and plant growth regulation as well as for antifungal and nematicidal traits. Isolated bacteria were found to exhibit capabilities in fix atmospheric nitrogen, produce ammonia, indoleacetic acid (IAA), siderophores, solubilize phosphate and zinc, and showed an antagonistic potential against some phytopathogenic fungi and one nematode species (Meloidogyne incognita) to various extent. Isolates were ranked by their potential ability to function as PGPR. The 66 isolates were genotyped using amplified rDNA restriction analysis (ARDRA) and 16S rRNA gene sequence analysis. The taxonomic composition of the representative genotypes from both rhizosphere and rhizoplane comprised Bacillus, Enterobacter and Pseudomonas. Out of the 10 genotypes, three strains designated as PHP03, CCP05, and TAP02 might be regarded as novel strains based on their low similarity percentages and high bootstrap values. The present study clearly identified specific traits in the isolated rhizobacteria, which make them good candidates as PGPR and might contribute to plant adaption to arid environments. Application of such results in agricultural fields may improve and enhance plant growth in arid soils.

Plant growth-promoting rhizobacteria reduce adverse effects of salinity and osmotic stress by regulating phytohormones and antioxidants in Cucumis sativus

We assessed the role of plant growth-promoting rhizobacteria (PGPR) strains viz. Burkholdera cepacia SE4, Promicromonospora sp. SE188 and Acinetobacter calcoaceticus SE370 in counteracting salinity and drought stress to cucumber plants. The control plants had stunted growth, while PGPR-treated plants had significantly higher biomass and chlorophyll contents under salinity and drought stress. The ameliorative effects of PGPR-application were also evidenced by the increased water potential and decreased electrolytic leakage. The PGPR-applied plants had reduced sodium ion concentration, while the potassium and phosphorus were abundantly present as compared to control under stress. Oxidative stress was mitigated by PGPR through reduced activities of catalase, peroxidase, polyphenol oxidase, and total polyphenol as compared to control. The control plants showed up-regulation of stress-responsive abscisic acid as compared to PGPR application, while salicylic acid and gibberellin 4 were significantly higher in PGPR. In conclusion, the PGPR application might be used in marginalized agricultural lands to increase crop productivity.

Role of plant growth-promoting rhizobacteria and their exopolysaccharide in drought tolerance of maize

The present study deals with the isolation and characterization of exopolysaccharides (EPS) produced by the plant growth-promoting rhizobacteria (PGPR) from arid and semiarid regions of Pakistan, and to investigate the drought tolerance potential of these PGPR on maize when used as bioinoculant alone and in combination with their respective EPS. Three bacterial strains Proteus penneri (Pp1), Pseudomonas aeruginosa (Pa2), and Alcaligenes faecalis (AF3) were selected as EPS-producing bacteria on the basis of mucoid colony formation. All these strains were gram negative, motile, and positive for catalase. Strain Pp1 was positive for oxidase test and was phosphate solubilizing, while Pa2 and AF3 were negative. The isolated strains were sequenced using 16SrRNA. Total soluble sugar, protein, uronic acid, emulsification activity, and Fourier-transformed infrared spectroscopy of EPS were determined. Drought stress had significant adverse effects on growth of maize seedlings. Seed bacterization of maize with EPS-producing bacterial strains in combination with their respective EPS improved soil moisture contents, plant biomass, root and shoot length, and leaf area. Under drought stress, the inoculated plants showed increase in relative water content, protein, and sugar though the proline content and the activities of antioxidant enzymes were decreased. The Pa2 strain isolated from semiarid region was most potent PGPR under drought stress. Consortia of inocula and their respective EPS showed greater potential to drought tolerance compared to PGPR inocula used alone.

Rice Sheath Blight: A Review of Disease and Pathogen Management Approaches

Rice is an important food grain and is a staple food for majority of the world’s population. To meet increasing global demand and consumption, rice productivity must be enhanced. However, biotic stresses such as diseases have impeded rice cultivation both in the tropics and subtropics. Of them, sheath blight is a major soil borne disease causing economic losses to rice cultivation. This article summarizes sheath blight (ShB) of rice, disease etiology and economics. Elaborative and updated accounts of various management options and their efficacy for ShB control are given. Specifically, the effects of popular cultural practices influencing ShB incidence, various chemical fungicides, and biological control individually and their combined effect on ShB are presented. The role of Plant Growth-Promoting Rhizobacteria (PGPR) and various genera of PGPR in ShB suppression are discussed. The present review also showed various aspects relating to ShB suppression by PGPR such as antagonism, competition for space and essential nutrients, and induction of systemic resistance. Integrated management of ShB involving all the compatible combinations is included in this review.

Paddy plants inoculated with PGPR show better growth physiology and nutrient content under saline conditions

The possible role of plant growth-promoting rhizobacteria (PGPR) to alleviate salt stress during plant growth has been studied on paddy rice ( Oryza sativa L.) 'GJ-17' under greenhouse conditions; the study included growth parameters, mineral concentration, and antioxidant enzyme level. Salinity reduced plant growth, but PGPR inoculation reduced its harmful effect up to 1% salinity. Plants inoculated with PGPR under saline conditions showed 16% higher germination, 8% higher survival, 27% higher dry weight, and 31% higher plant height. Similarly, PGPR inoculated plants showed increased concentrations of N(26%), P (16%), K (31%), and reduced concentrations of Na (71%) and Ca (36%) as compared to non-inoculated control plants under saline conditions. Plants inoculated with PGPR under saline conditions also showed significant variations in antioxidant levels and growth physiology. Results suggested that inoculation with PGPR Bacillus pumilus and Pseudomonas pseudoalcaligenes in salt-stressed plants could help to alleviate salt stress in the paddy.

Soil microbes and plant fertilization

With respect to the adverse effects of chemical fertilization on the environment and their related expenses, especially when overused, alternative methods of fertilization have been suggested and tested. For example, the combined use of chemical fertilization with organic fertilization and/or biological fertilization is among such methods. It has been indicated that the use of organic fertilization with chemical fertilization is a suitable method of providing crop plants with adequate amount of nutrients, while environmentally and economically appropriate. In this article, the importance of soil microbes to the ecosystem is reviewed, with particular emphasis on the role of plant growth-promoting rhizobacteria, arbuscular mycorrhizal fungi, and endophytic bacteria in providing necessary nutrients for plant growth and yield production. Such microbes are beneficial to plant growth through colonizing plant roots and inducing mechanisms by which plant growth increases. Although there has been extensive research work regarding the use of microbes as a method of fertilizing plants, it is yet a question how the efficiency of such microbial fertilization to the plant can be determined and increased. In other words, how the right combination of chemical and biological fertilization can be determined. In this article, the most recent advances regarding the effects of microbial fertilization on plant growth and yield production in their combined use with chemical fertilization are reviewed. There are also some details related to the molecular mechanisms affecting the microbial performance and how the use of biological techniques may affect the efficiency of biological fertilization.

Isolation and characterization of a plant growth-promoting rhizobacterium, Serratia sp. SY5.

The role of plant growth-promoting rhizobacteria (PGPR) in the phytoremediation of heavy-metal-contaminated soils is important in overcoming its limitations for field application. A plant growth-promoting rhizobacterium, Serratia sp. SY5, was isolated from the rhizoplane of barnyard grass (Echinochloa crus-galli) grown in petroleum and heavy-metal-contaminated soil. This isolate has shown capacities for indole acetic acid production and siderophores synthesis. Compared with a non-inoculated control, the radicular root growth of Zea mays seedlings inoculated with SY5 can be increased by 27- or 15.4-fold in the presence of 15 mg-Cd/l or 15 mg-Cu/l, respectively. The results from hydroponic cultures showed that inoculation of Serratia sp. SY5 had a favorable influence on the initial shoot growth and biomass of Zea mays under noncontaminated conditions. However, under Cd-contaminated conditions, the inoculation of SY5 significantly increased the root biomass of Zea mays. These results indicate that Serratia sp. SY5 can serve as a promising microbial inoculant for increased plant growth in heavy-metal-contaminated soils to improve the phytoremediation efficiency.