Plant Growth Promoting Rhizobacteria Interaction Research Articles

Synergistic interactions of nanoparticles and plant growth promoting rhizobacteria enhancing soil-plant systems: a multigenerational perspective.

Sustainable food security and safety are major concerns on a global scale, especially in developed nations. Adverse agroclimatic conditions affect the largest agricultural-producing areas, which reduces the production of crops. Achieving sustainable food safety is challenging because of several factors, such as soil flooding/waterlogging, ultraviolet (UV) rays, acidic/sodic soil, hazardous ions, low and high temperatures, and nutritional imbalances. Plant growth-promoting rhizobacteria (PGPR) are widely employed in in-vitro conditions because they are widely recognized as a more environmentally and sustainably friendly approach to increasing crop yield in contaminated and fertile soil. Conversely, the use of nanoparticles (NPs) as an amendment in the soil has recently been proposed as an economical way to enhance the texture of the soil and improving agricultural yields. Nowadays, various research experiments have combined or individually applied with the PGPR and NPs for balancing soil elements and crop yield in response to control and adverse situations, with the expectation that both additives might perform well together. According to several research findings, interactive applications significantly increase sustainable crop yields more than PGPR or NPs alone. The present review summarized the functional and mechanistic basis of the interactive role of PGPR and NPs. However, this article focused on the potential of the research direction to realize the possible interaction of PGPR and NPs at a large scale in the upcoming years.

The role of plant growth promoting rhizobacteria in strengthening plant resistance to fluoride toxicity: a review.

A wide variety of bacteria are present in soil but in rhizospheric area, the majority of microbes helps plant in defending diseases and facilitate nutrient uptake. These microorganisms are supported by plants and they are known as plant growth-promoting rhizobacteria (PGPR). The PGPRs have the potential to replace chemical fertilizers in a way that is more advantageous for the environment. Fluoride (F) is one of the highly escalating, naturally present contaminants that can be hazardous for PGPRs because of its antibacterial capacity. The interactions of F with different bacterial species in groundwater systems are still not well understood. However, the interaction of PGPR with plants in the rhizosphere region reduces the detrimental effects of pollutants and increases plants' ability to endure abiotic stress. Many studies reveal that PGPRs have developed F defense mechanisms, which include efflux pumps, Intracellular sequestration, enzyme modifications, enhanced DNA repair mechanism, detoxification enzymes, ion transporter/antiporters, F riboswitches, and genetic mutations. These resistance characteristics are frequently discovered by isolating PGPRs from high F-contaminated areas or by exposing cells to fluoride in laboratory conditions. Numerous studies have identified F-resistant microorganisms that possess additional F transporters and duplicates of the well-known targets of F. Plants are prone to F accumulation despite the soil's low F content, which may negatively affect their growth and development. PGPRs can be used as efficient F bioremediators for the soil environment. Environmental biotechnology focuses on creating genetically modified rhizobacteria that can degrade F contaminants over time. The present review focuses on a thorough systemic analysis of contemporary biotechnological techniques, such as gene editing and manipulation methods, for improving plant-microbe interactions for F remediation and suggests the importance of PGPRs in improving soil health and reducing the detrimental effects of F toxicity. The most recent developments in the realm of microbial assistance in the treatment of F-contaminated environments are also highlighted.

Genomic content of wheat has a higher influence than plant domestication status on the ability to interact with Pseudomonas plant growth-promoting rhizobacteria.

Plant evolutionary history has had profound effects on belowground traits, which is likely to have impacted the ability to interact with microorganisms, but consequences on root colonization and gene expression by plant growth-promoting rhizobacteria (PGPR) remain poorly understood. Here, we tested the hypothesis that wheat genomic content and domestication are key factors determining the capacity for PGPR interaction. Thus, 331 wheat representatives from eight Triticum or Aegilops species were inoculated under standardized conditions with the generalist PGPR Pseudomonas ogarae F113, using an autofluorescent reporter system for monitoring F113 colonization and expression of phl genes coding for the auxinic inducing signal 2,4-diacetylphloroglucinol. The interaction with P. ogarae F113 was influenced by ploidy level, presence of genomes AA, BB, DD, and domestication. While root colonization was higher for hexaploid and tetraploid species, and phl expression level higher for hexaploid wheat, the diploid Ae. tauschii displayed higher phl induction rate (i.e., expression:colonisation ratio) on roots. However, a better potential of interaction with F113 (i.e., under non-stress gnotobiotic conditions) did not translate, after seed inoculation, into better performance of wheat landraces in non-sterile soil under drought. Overall, results showed that domestication and especially plant genomic content modulate the PGPR interaction potential of wheats.

Zinc oxide nanoparticles (ZnO NPs) stabilized by phytocellulose derived biopolymer and their bipartite interaction studies with agriculturally important microbes/Raphanus sativus (L.) seeds

Zinc oxide nanoparticles (ZnO NPs) are one of the most studied metal oxide NPs (MONPs) owing to their unique physiochemical properties. The last few years have witnessed a growing interest among researchers in adopting the green chemistry approach to fabricate MONPs. We herein report the synthesis of ZnO NPs stabilized by carboxymethyl cellulose (CMC) derived from noxious aquatic weed, i.e., Eichhornia crassipes biomass (EC-CMC). The UV–Vis spectra showed maximum absorbance at ∼380 nm, and the XRD crystallite size of EC-CMC capped ZnO NPs (c-ZnO NPs) (∼26 nm) was smaller as compared to virgin ZnO NPs (v-ZnO NPs) (∼29 nm). The value of apparent strain (εA x 10−3), root mean square strain (ERMS x 10−3), stress (MPa), and energy density (KJm−3) for c-ZnO NPs obtained from the SSP plot was ∼0.893, ∼0.173, ∼116 and ∼51.83 respectively. The study also examined the differential effects of c-ZnO NPs treatment on the growth of two plant growth-promoting rhizobacteria (PGPR), i.e., Pseudomonas fluorescens (Gram -ve), and Bacillus subtilis (Gram +ve). The findings revealed that P. fluorescens (PFL) was more susceptible to c-ZnO NPs than B. subtilis (BST). Furthermore, R. sativus seeds treated with c-ZnO NPs (10–50 ppm) exhibited notable improvements in plumule length, radicle length, vigor index, and biomass content over other treatments and control. The biopriming of R. sativus seeds with PFL and BST showed synergistic effects with 10-ppm c-ZnO NPs treatment and promoted overall seedling growth. The bacterial kinetics and seed germination studies manifest that the c-ZnO NPs at lower doses have growth-promoting effects. The combination of PFL + BST+10-ppm c-ZnO NPs showed substantial improvements in the germination indices of R. sativus. The present work has demonstrated the potential of utilizing positive bipartite interaction of PGPRs and bio-stabilized ZnO NPs to develop nanoformulations promoting plant growth management.

The Biosynthesis and Functions of Polyamines in the Interaction of Plant Growth-Promoting Rhizobacteria with Plants.

Plant growth-promoting rhizobacteria (PGPR) are members of the plant rhizomicrobiome that enhance plant growth and stress resistance by increasing nutrient availability to the plant, producing phytohormones or other secondary metabolites, stimulating plant defense responses against abiotic stresses and pathogens, or fixing nitrogen. The use of PGPR to increase crop yield with minimal environmental impact is a sustainable and readily applicable replacement for a portion of chemical fertilizer and pesticides required for the growth of high-yielding varieties. Increased plant health and productivity have long been gained by applying PGPR as commercial inoculants to crops, although with uneven results. The establishment of plant-PGPR relationships requires the exchange of chemical signals and nutrients between the partners, and polyamines (PAs) are an important class of compounds that act as physiological effectors and signal molecules in plant-microbe interactions. In this review, we focus on the role of PAs in interactions between PGPR and plants. We describe the basic ecology of PGPR and the production and function of PAs in them and the plants with which they interact. We examine the metabolism and the roles of PAs in PGPR and plants individually and during their interaction with one another. Lastly, we describe some directions for future research.

Symbiotic Variations among Wheat Genotypes and Detection of Quantitative Trait Loci for Molecular Interaction with Auxin-Producing Azospirillum PGPR.

Crop varieties differ in their ability to interact with Plant Growth-Promoting Rhizobacteria (PGPR), but the genetic basis for these differences is unknown. This issue was addressed with the PGPR Azospirillum baldaniorum Sp245, using 187 wheat accessions. We screened the accessions based on the seedling colonization by the PGPR and the expression of the phenylpyruvate decarboxylase gene ppdC (for synthesis of the auxin indole-3-acetic acid), using gusA fusions. Then, the effects of the PGPR on the selected accessions stimulating Sp245 (or not) were compared in soil under stress. Finally, a genome-wide association approach was implemented to identify the quantitative trait loci (QTL) associated with PGPR interaction. Overall, the ancient genotypes were more effective than the modern genotypes for Azospirillum root colonization and ppdC expression. In non-sterile soil, A. baldaniorum Sp245 improved wheat performance for three of the four PGPR-stimulating genotypes and none of the four non-PGPR-stimulating genotypes. The genome-wide association did not identify any region for root colonization but revealed 22 regions spread on 11 wheat chromosomes for ppdC expression and/or ppdC induction rate. This is the first QTL study focusing on molecular interaction with PGPR bacteria. The molecular markers identified provide the possibility to improve the capacity of modern wheat genotypes to interact with Sp245, as well as, potentially, other Azospirillum strains.

Wheat (Triticum aestivum L.) inoculation through characterization and identification of soil bacteria

Rhizobacteria stimulate plant growth, and are profoundly known for increasing crop production and lowering crop input costs by replacing chemical fertilizer applications. The application of PGPR (Plant growth promoting rhizobacteria) not only regulates the nutritional and hormonal balance of plants, but also increases resistance against plant pathogens. The interaction of PGPR with bulk soil or with microbes in the rhizosphere indirectly boosts plant growth rates, and PGPR can be declared a biofertilizer. Therefore, the intent of the study was to analyze the influence of indigenous rhizospheric bacteria and the mode of action of PGPR on improved yield (Triticum aestivum L.) as a biofertilizer under both in vivo and in vitro conditions. Based on their engagement in producing ACC (Aminocyclopropane-1-carboxylic acid) deaminase, phosphorus solubilization, indole acetic acid (IAA), siderophore, potential strains have been identified. PGPR with the recommended dose urea, Diammonium phosphate (DAP) and Muriate of potash (MOP) were utilized. Inoculants of wheat seeds with urea (CH4N2O), DAP [(NH4)2HPO4] and MOP enhanced the growth drastically. For half of the suggested doses of synthetic fertilizers and a strain consortium, the strains were used in various combinations to achieve a maximum yield compared to the single use of the recommended fertilizer dose and a strain consortium.16Sr RNA gene sequencing, fatty acid profile, and biology further established certain strains. An inoculated bacterium has greater capacity and leads to improved crop production, enhanced yield when spread in conjunction under field conditions and therefore can reduce chemical fertilizer use.

An OsNAM gene plays important role in root rhizobacteria interaction in transgenic Arabidopsis through abiotic stress and phytohormone crosstalk.

Overexpression of Bacillus amyloliquefaciens SN13-responsive OsNAM gene in Arabidopsis reveals its important role in beneficial plant and plant growth promoting rhizobacteria interaction by conferring stress tolerance and phytohormone modulation. Salinity is one of the major constraints that affect crop development and yield. Plants respond and adapt to salt stress via complex mechanisms that involve morpho-physiological, biochemical, and molecular changes. The expression of numerous genes is known to alter during various abiotic stresses and impart stress tolerance. Recently, some known rhizospheric microbes have also been used to mitigate the effects of abiotic stresses; however, the molecular basis of such interactions remains elusive. Therefore, the present investigation was aimed to elucidate the plant growth-promoting rhizobacteria (PGPR; Bacillus amyloliquefaciens-SN13) -induced crosstalk among salinity and phytohormones in OsNAM-overexpressed Arabidopsis plants. Transgenic plants showed increased germination percentage compared to wild-type (WT) seeds under 100mM of NaCl. Phenotypic data showed increased root length, rosette diameter, leaf size, and biomass in transgenics than WT plants. Transgenic plants can also better maintain membrane integrity and osmolyte concentration under salinity as compared to WT. Further, gene expression analysis of AP2/ERF, GST, ERD4, and ARF2 genes showed differential expression and their positive modulation in transgenic Arabidopsis exposed to salt stress in the presence of SN13 as compared to uninoculated WT. Modulation in IAA, ABA, and GA content in inoculated plants showed the more pronounced positive effects of SN13 on transgenic plants that supported our findings on Arabidopsis-SN13 interaction. Overall, the study concludes that SN13 positively modulated expression of stress-responsive genes under salinity and alter phytohormones levels in OsNAM-overexpressed plants suggesting its extensive role in cross-talk among salinity and phytohormones in response to PGPR.

Microbiome Management by Biological and Chemical Treatments in Maize Is Linked to Plant Health.

The targeted application of plant growth-promoting rhizobacteria (PGPR) provides the key for a future sustainable agriculture with reduced pesticide application. PGPR interaction with the indigenous microbiota is poorly understood, but essential to develop reliable applications. Therefore, Stenotrophomonas rhizophila SPA-P69 was applied as a seed coating and in combination with a fungicide based on the active ingredients fludioxonil, metalaxyl-M, captan and ziram. The plant performances and rhizosphere compositions of treated and non-treated maize plants of two field trials were analyzed. Plant health was significantly increased by treatment; however, overall corn yield was not changed. By applying high-throughput amplicon sequencing of the 16S rRNA and the ITS genes, the bacterial and fungal changes in the rhizosphere due to different treatments were determined. Despite the fact that treatments had a significant impact on the rhizosphere microbiota (9–12%), the field site was identified as the main driver (27–37%). The soil microbiota composition from each site was significantly different, which explains the site-specific effects. In this study we were able to show the first indications how PGPR treatments increase plant health via microbiome shifts in a site-specific manner. This way, first steps towards a detailed understanding of PGPRs and developments of consistently efficient applications in diverse environments are made.

Mechanistic Insights of the Interaction of Plant Growth-Promoting Rhizobacteria (PGPR) With Plant Roots Toward Enhancing Plant Productivity by Alleviating Salinity Stress.

Agriculture plays an important role in a country’s economy. The sector is challenged by many stresses, which led to huge loss in plant productivity worldwide. The ever-increasing population, rapid urbanization with shrinking agricultural lands, dramatic change in climatic conditions, and extensive use of agrochemicals in agricultural practices that caused environmental disturbances confront mankind of escalating problems of food security and sustainability in agriculture. Escalating environmental problems and global hunger have led to the development and adoption of genetic engineering and other conventional plant breeding approaches in developing stress-tolerant varieties of crops. However, these approaches have drawn flaws in their adoption as the process of generating tolerant varieties takes months to years in bringing the technology from the lab to the field. Under such scenario, sustainable and climate-smart agricultural practices that avail bacterial usage open the avenues in fulfilling the incessant demand for food for the global population. Ensuring stability on economic fronts, bacteria minimizes plant salt uptake by trapping ions in their exopolysaccharide matrix besides checking the expression of Na+/H+ and high-affinity potassium transporters. Herein we describe information on salinity stress and its effect on plant health as well as strategies adopted by plant growth-promoting rhizobacteria (PGPR) in helping plants to overcome salinity stress and in mitigating loss in overall plant productivity. It is believed that acquisition of advanced knowledge of plant-beneficial PGPR will help in devising strategies for sustainable, environment-friendly, and climate-smart agricultural technologies for adoption in agriculture to overcome the constrained environmental conditions.

Isolation, characterization and screening of PGPR capable of providing relief in salinity stress

Environmental stresses such as drought, temperature, salinity, air pollution, heavy metals, pesticides, and soil pH are major limiting factors in crop production because they affect almost all plant functions. Soil salinization is a serious stress condition causing major problem for crop productivity. To combat this salinity stress, Plant growth promoting rhizobacteria (PGPR) is considered as innovative, effective and ecofriendly approach. Plant growth promoting rhizobacteria (PGPR) have various direct and indirect mechanisms which can be correlated with their ability to form biofilms, chemotaxis, and the production of exopolysaccharide, indole-3-acetic acids (IAA) and aminocyclopropane-1- carboxylate (ACC) deaminase Investigations on the interaction of PGPR with other microbes and their effect on the physiological response of crop plants under different soil salinity regimes are still at an incipient stage. An experiment was conducted to investigate the effect of PGPR on lowering down the salt stress. Treatments were control (T 1 ), Salt tolerant isolate KH-1 (T 2 ), Salt tolerant isolate KH-2 (T 3 ), Salt tolerant isolate KH-3 (T 4 ), PGPR-I (Pseudimonas) (T 5 ), PGPR-II (Azotobacter) (T 6 ). Rice was sown under saline conditions at Soil Salinity Research Institute, Pindi Bhattian. With the inoculation of salt tolerant PGPR, plant growth and yield was improved. Result showed significant increase in plant height, biomass and yield over control. Inoculation of salt tolerant isolate KH-2 produced maximum grain yield in rice (4267 kg/ha) followed by PGPR-II and it was statistically significant from all other treatments along with control. It is concluded that with the application of salt tolerant isolate (KH-2), there is significant increase in rice production.

Evaluation of multifarious plant growth promoting traits, antagonistic potential and phylogenetic affiliation of rhizobacteria associated with commercial tea plants grown in Darjeeling, India.

Plant growth promoting rhizobacteria (PGPR) are studied in different agricultural crops but the interaction of PGPR of tea crop is not yet studied well. In the present study, the indigenous tea rhizobacteria were isolated from seven tea estates of Darjeeling located in West Bengal, India. A total of 150 rhizobacterial isolates were screened for antagonistic activity against six different fungal pathogens i.e. Nigrospora sphaerica (KJ767520), Pestalotiopsis theae (ITCC 6599), Curvularia eragostidis (ITCC 6429), Glomerella cingulata (MTCC 2033), Rhizoctonia Solani (MTCC 4633) and Fusarium oxysporum (MTCC 284), out of which 48 isolates were antagonist to at least one fungal pathogen used. These 48 isolates exhibited multifarious antifungal properties like the production of siderophore, chitinase, protease and cellulase and also plant growth promoting (PGP) traits like IAA production, phosphate solubilization, ammonia and ACC deaminase production. Amplified ribosomal DNA restriction analysis (ARDRA) and BOX-PCR analysis based genotyping clustered the isolates into different groups. Finally, four isolates were selected for plant growth promotion study in two tea commercial cultivars TV-1 and Teenali-17 in nursery conditions. The plant growth promotion study showed that the inoculation of consortia of these four PGPR isolates significantly increased the growth of tea plant in nursery conditions. Thus this study underlines the commercial potential of these selected PGPR isolates for sustainable tea cultivation.

Identification of Root-Secreted Compounds Involved in the Communication Between Cucumber, the Beneficial Bacillus amyloliquefaciens, and the Soil-Borne Pathogen Fusarium oxysporum.

Colonization of plant growth-promoting rhizobacteria (PGPR) is critical for exerting their beneficial effects on the plant. Root exudation is a major factor influencing the colonization of both PGPR and soil-borne pathogens within the root system. However, the tripartite interaction of PGPR, plant roots, and soil-borne pathogens is poorly understood. We screened root exudates for signals that mediate tripartite interactions in the rhizosphere. In a split-root system, we found that root colonization of PGPR strain Bacillus amyloliquefaciens SQR9 on cucumber root was significantly enhanced by preinoculation with SQR9 or the soil-borne pathogen Fusarium oxysporum f. sp. cucumerinum, whereas root colonization of F. oxysporum f. sp. cucumerinum was reduced upon preinoculation with SQR9 or F. oxysporum f. sp. cucumerinum. Root exudates from cucumbers preinoculated with SQR9 or F. oxysporum f. sp. cucumerinum were analyzed and 109 compounds were identified. Correlation analysis highlighted eight compounds that significantly correlated with root colonization of SQR9 or F. oxysporum f. sp. cucumerinum. After performing colonization experiments with these chemicals, raffinose and tryptophan were shown to positively affect the root colonization of F. oxysporum f. sp. cucumerinum and SQR9, respectively. These results indicate that cucumber roots colonized by F. oxysporum f. sp. cucumerinum or SQR9 increase root secretion of tryptophan to strengthen further colonization of SQR9. In contrast, these colonized cucumber roots reduce raffinose secretion to inhibit root colonization of F. oxysporum f. sp. cucumerinum.

Amelioration of drought tolerance in wheat by the interaction of plant growth-promoting rhizobacteria.

Drought stress adversely affects the growth and yield of wheat. The present study was planned to investigate the effect of inoculation of plant-growth promoting rhizobacteria (PGPR) strains IG 3 (Klebsiella sp.), IG 10 (Enterobacter ludwigii) and IG 15 (Flavobacterium sp.) in improving drought tolerance in wheat. These PGPR strains were screened for drought tolerance in nutrient broth supplemented with different concentrations (0-25%) of polyethylene glycol (PEG6000). Effect of PGPR inoculation on various physiological, biochemical parameters and gene expression of stress responsive genes were studied under drought stress. Root colonization at the surface and interiors of roots was demonstrated using scanning electron microscopy (SEM) and tetrazolium staining, respectively. Drought stress significantly affected various growth parameters, water status, membrane integrity, osmolyte accumulation and stress-responsive gene expressions, which were positively altered by PGPR-inoculation in wheat. Quantitative real-time (qRT)-PCR analysis revealed the up regulation of some stress-related genes (DREB2A and CAT1) in un-inoculated wheat plants exposed to drought stress. PGPR-inoculated plants showed attenuated transcript levels suggesting improved drought tolerance due to interaction of PGPRs. The PGPR strain IG 3 was found to be the best in terms of influencing biochemical and physiological status of the seedlings under drought stress. Our report demonstrates the role of PGPRs Enterobacter ludwigii and Flavobacterium sp. in plant growth promotion of wheat plants under drought stress. The study reports the potential of PGPR in alleviating drought stress in wheat which could be used as potent biofertilizers.

Biocontrol by plant growth promoting rhizobacteria against black scurf and stem canker disease of potato caused by Rhizoctonia solani

Non-pathogenic soil bacteria living in association with roots of higher plants enhance their adaptive potential and thus could be beneficial for their growth. Here, we present the current status of the use of Bacillus subtilis in biocontrol. Rhizobacteria are found in the rhizosphere. Plant growth promoting rhizobacteria (PGPR) strains, such as Bacillus and Pseudomonas, were isolated by using Nutreint dextrose Agar medium or Potato Dextrose Agar medium. The selection of PGPR strains was done by duel culture methods against the potato pathogens. The interaction of PGPR (Bacillus) with potato seeds or vegetative parts show promising antagonism by virtue of producing siderophore and antibiotics against black scurf and stem canker diseases of potato caused by Rhizoctonia solani, thereby resulting in increase of potato yield. The effectiveness of PGPR strain (Bacillus spp.) in improving the yield of potato in greenhouse conditions and in the field was observed.