Plant Growth-promoting Rhizobacteria Bacteria Research Articles

Effects of PGPR Bacteria Applications on Soil Properties, Plant Growth and Yield Values in Karaerik and Narince Grape Varieties

Plant growth-promoting rhizobacteria (PGPR) are beneficial bacteria that promote plant growth by adhering to the root surfaces in the rhizosphere region of plants. In addition to improving the physical properties of soils, these bacteria increase plant growth and yield by positively affecting nitrogen fixation, phosphorus solubility, water and nutrient uptake of plants. In this study, the effects of bacteria applications on the vegetative development and yield levels of Karaerik and Narince grape varieties, which are important table varieties of Erzincan and Tokat regions, grown in greenhouses in Erzurum central conditions were investigated. In the study, 4 different bacterial combinations (Pseudomonas chlororaphis + Paenibacillus pabuli + Bacillus simplex + Pseudomonas fluorescens) that promote plant growth were applied to the plant root zone as a solution. In the study, the effects of PGPR applications on the vegetative growth of vines, some pomological characteristics, yield levels, macronutrient contents of leaves and physical and chemical properties of greenhouse soils were determined. While aggregate stability and porosity values of PGPR treated soils increased, water permeability and bulk density values decreased. Bacterial applications in both grape varieties showed a positive effect on shoot length, shoot diameter, number of nodes, berry width, berry length, cluster width, cluster length, number of seeds, number of clusters, cluster weight, number of berries, berry weight, total yield and macronutrient content of leaves. According to the control group, PGPR applied soils; organic matter content increased by 76.2%, aggregate stability values increased by 49.5% and porosity by 5.5%, while water permeability decreased by 18.3% and bulk density by 3.9%. Depending on the application, it was determined that the yield increased by 42.8% in Karaerik grape variety and 35.7% in Narince grape variety.

Microbially modified effect of exogenous organic matter on soil chemical and biological indices and plant responses

PurposeExogenous Organic Matter (EOM) enriches and regenerates the soil, while solving the problem of landfilling waste such as sewage sludge and bottom sediments. The main purpose of the presented study was to estimate the influence of type and dosage of applied EOM on soil biological characteristics and supporting plant growth, with consideration of inoculation with PGPR (plant growth-promoting rhizobacteria).Materials and methodsThe soil samples were characterized by measuring key enzyme activities, determining the community-level physiological profiling (CLPP) using Biolog EcoPlates, abundance of microorganisms and evaluation physical and chemical properties.Results and discussionApplication of EOM mostly increased enzyme activity as well as overall metabolic activity compared to control sample. Increasing the dose of poultry manure and sewage sludge from 20 to 40 t ha−1 increased dehydrogenase, acid and alkaline phosphatase activity. Moreover, the addition of EOM affected the metabolic activity and the number of selected groups of bacteria and fungi.ConclusionsIn the research it was proven that application of EOM leads to relatively rapid and positive changes in soil biological activity. The research also confirmed that the supporting factor for plant growth was the inoculation with PGPR bacteria. This approach, together with the reuse of organic wastes may become an attractive approach in sustainable cropping systems in a circular economy system.Graphical

Endophytic bacteria improve jute growth through induction of phytohormones-related gene expression

Plants coexist with complex populations of microorganisms, including Plant Growth-Promoting Rhizobacteria (PGPR). PGPR bacteria help in plant development by secreting numerous plan growth-promoting compounds like IAA, gibberellin, siderophore, and cytokinin. They also provide resistance to plants against different pathogens. Jute fibre is the second most important fibre next to cotton, obtained from the bark of plant through microbial retting process. Hence, increased plant growth means increased bark i.e., increased fibre. This study aims to identify the molecular, physiological and growth promotion characteristics of non-rhizobial bacterial specie from the surface-sterilized root of healthy and biotic stressed (nematode-infested) jute (Corchorus capsularis; Corchorus olitorius and an advanced variety of C. olitorius, Robi-1). We have identified 62 culturable bacterial isolates from healthy and nematode-infected jute plant using bacterial 16S rDNA sequencing. All the isolates were distributed to Bacillus, Staphylococcus and Ensifer genera, respectively. B. cereus, S. hominis and a consortium increased the growth phenotype (Root length, shoot length, germination rate, root and shoot biomass) of C. capsularis (CVL-1), C. olitorius (O-9897), and an advanced variety of C. olitorius (Robi-1), respectively. Increased expression (qRT-PCR analysis) of growth hormones GA-20 and GA-03 oxidase corroborates plant growth induction by increased production of the growth hormone gibberellin. Taken together, our results suggest that plant-growth promotion by endophytic bacteria may involve the increased expression of growth hormone gibberellin and nutrient uptake. B. cereus and S. hominis having plant growth-promoting traits could be useful in sustainable agriculture practice.

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.

Investigating PGPR bacteria for their competence to protect hybrid maize from the factor drought stress

Drought and heat are severe environmental stresses that constantly affect plant growth and development. Maize (Zea mays L.) is known for its sensitivity to abiotic stresses, which often causes significant yield losses. With plant growth-promoting rhizobacteria (PGPR), the harmful effects of drought and heat stress on plants can be alleviated. The aim of the present study was to investigate the physiological traits of plants affected by drought stress in a treatment including four PGPR bacteria, two regimes of irrigation and two stages of phenophases, and the analysis of the influence of the individual factors and their combined effects, respectively. In addition, the investigations covered the testing of the nutrient acquisition ability and nutrient use efficiency, the plant growth stimulating effect of PGPR bacteria, and the analysis of the performance trials. The largest amount of soluble orthophosphate was produced by Pseudomonas putida (51.636 µg/cm3). This is significantly more than the amount of phosphate solubilized by Bacillus pumilus (15.601 µg/cm3), Pseudomonas fluorescens (14.817 µg/cm3) and Bacillus megaterium (14.621 µg/cm3). The germination vigour of the seedlings in the treatment with Pseudomonas putida was 55% higher, represented by the value of 15,237.125, in comparison with the control, with the value of 9792.188. The Pseudomonas putida treatment resulted in the most outstanding fresh/dry weight ratio (7.312) compared to the control (7.780), when the interaction between all factors was taken into account under stressed conditions at 50% female flowering stage. The highest dry matter content of the plants (18.344%) compared to the control (17.344%) was measured in the case of the Pseudomonas putida treatment during the milk stage of development under stressed conditions. In the field trial, the plants treated with KD2 (Bacillus pumilus and Pseudomonas putida) presented significantly higher results in the aspect of grain yield (6.278 t/ha) compared to the control (5.468 t/ha).

Brassicaceae, Chenopodiaceae ve Urticaceae Familyalarına Ait Bazı Bitki Türlerinin Arbusküler Mikorhizal Fungus (AMF) ve Rhizobacteria Arasındaki İlişki

This study was conducted to investigate the effects of some plant growth-promoting rhizobacteria (PGPR) on the arbuscular mycorrhizal fungi (AMF) formation on [Brassica oleracea (cauliflower), Spinacia oleracea (spinach) ,and Urtica urens (stinging nettle)] belonging to Brassicaceae, Chenopodiaceae and Urticaceae families, which are known to have a negative influence on the symbiotic life formation with AMF. Two PGPR isolates that contributed to the plant's growth and served as a “mycorrhizal helper” in various hosts were predetermined at the initial stage; then they were applied to three plant species with AMF species [Gigaspora margarita and commercial AMF (ERS)]. The obtained results revealed that combined AMF x PGPR treatments improved the growth and morphological development parameters of cauliflower, spinach, and nettle plants. PGPR bacteria had different effects on AMF root colonization depending on the plant species. The highest root colonization rate was achieved in spinach plants with the commercial AMF treatments. Commercial AMF isolate, alone or in combination with PGPR strains, was also found to increase AMF spore density and mycorrhizal dependency in cauliflower and spinach plants. There was no significant difference in total phosphorus content in cauliflower and nettle compared to the control group, and only one application group (G. margarita x PGPR) in spinach plants had an increase in phosphorus content.

Wheat plant –Plant Growth Promoting Rhizobacteria (PGPR) interaction to alleviate the salt stress in vitro and in vivo

The current work studied the mechanistic basis of salt tolerant PGPR bacteria in alleviating salinity stress in wheat.Two experiments were conducted at the Agricultural Research Center (ARC), 2021-2022, to evaluate the interaction between wheat var. Misr1 and two salt tolerant PGPR bacterial strains, Azospirillum (A.) brasilense NO40 and Bacillus thuringiensis (Bt) under saline conditions. The staining technique used to detect the colonization effectiveness of applied bacteria. Images of 30-day wheat seedlings were captured and subjected to the following measurements: root area, leaf area, root length, shoot length, and dark green color index (DGCI). TEM was used to look for bacterial colonization in wheat seedling. Chlorophyll, proline, peroxidase activity, rhizosphere dehydrogenase activity and electrical conductivity (EC) were all quantified. Results revealed that the wheat seedling roots inoculated with the salt tolerant bacterial strains produced a highly intense red colour. The colonized bacteria appeared on the outer surface of the root and intercellular space of root tissue. The data showed a significant rise in all measured parameters in the inoculated wheat seedlings with the salt tolerant bacterial strains compared to the non-inoculated wheat seedlings. Additionally, the wheat seedlings inoculated with a mixture of NO40 and Bt showed the best results as compared to that inoculated with only NO40 or with only Bt. Finally, EC values before and after planting with the inoculated wheat seeds revealed a decrease in the salinity of the soil rhizosphere (9.27 mmhos/cm vs. 5.1 mmhos/cm). In conclusion: Salt stress in wheat saline soils was alleviated by bacterial strains studied. Optimum results were obtained from the mixture of A. brasilense and Bt. Results must later be verified in field trials.

Plant Growth-Promoting Rhizobacteria With ACC Deaminase Activity Enhance Maternal Lateral Root and Seedling Growth in Switchgrass.

Switchgrass, a C4 plant with high potential as a bioenergy source, is unsteady in yield under sub-optimal conditions. Bacteria containing 1-aminocyclopropane-1-carboxylate synthase (ACC) deaminase can promote plant growth. We isolated bacteria containing ACC deaminase activity from switchgrass rhizosphere using an orthogonal matrix experimental design with four factors (bacterial liquid concentration, bacterial liquid treatment time, nitrogen content, and NaCl) to quantitatively investigate the effects and pairwise interactions on the seedling growth. Pseudomonas sp. Y1, isolated from the switchgrass cv. Blackwell rhizomes was selected. We optimized the inoculation bacterial concentration, treatment time, NaCl, and nitrogen concentration for the seedling growth. The optimal bacterial concentration, treatment time, NaCl, and nitrogen content was 0.5–1.25 OD at 600 nm, 3 h, 60–125 mM and 158 mg L−1, respectively. Pseudomonas sp. Y1 significantly increased the total root length, root surface, shoot length, and fresh and dry weight through an effective proliferation of the number of first-order lateral roots and root tips. This indicated that Pseudomonas sp. Y1 has a higher potential to be used as a plant growth-promoting rhizobacteria bacteria.

Plant Growth Promotion and Biocontrol Properties of Aneurinibacillus migulanus Isolated from Maize Roots (Zea mays)

Aims: To isolate Plant Growth Promoting Bacillus strain from maize roots, to evaluate its biocontrol potentials and to characterize the isolate using16S rRNA sequencing.
 Place and Duration of Study: Department of Applied Microbiology and Brewing, Nnamdi Azikiwe University, Awka, between February 2019 and March 2020.
 Methodology: The isolation of Plant Growth Promoting Rhizobacteria (PGPR) from maize roots was done using Pikovskaya (PVK) agar. Quantitative determination of phosphate was carried out using PVK broth. Evaluations of other plant growth promoting properties were carried out such as IAA, etc. Fusarium and Enterobacter plant pathogens were isolated from diseased maize plants. The in vitro antagonism effects of the PGPR isolates against the pathogens were analyzed using the dual culture plate technique. The pot experiment was carried out in a completely randomized design. Plant characteristics such as plant height, shoot and root weight, chlorophyll content, as well as disease assessment were recorded accordingly. The organisms were identified using phenotypic and molecular methods.
 Results: Seven PGPR bacteria were isolated from maize (Zea mays) roots using PVK agar. Aneurinibacillus migulanus gave the highest solubilization index of 4.21 while isolate IS48 gave the lowest solubilization index of 1.47. A. migulanus produced IAA, ammonia and cellulase enzyme but no hydrogen cyanide. The organism showed antagonism activity against the two tested phytopathogens. In the pot experiment, A. migulanus treated plants showed a statistically insignificant difference in maize plant height at P=0.05 but gave significant increases in shoot and root wet weights. The organism offered 83.33% and 71.43% protection against Enterobacter and Fusarium pathogens respectively in the pot experiment.
 Conclusion: A. migulanus solubilized phosphate in addition to other plant growth promoting properties. It showed biocontrol potentials both in vitro and in vivo and thus can be used as substitute for synthetic agrochemicals.

Phenotypic display of plant growth-promoting traits in individual strains and multispecies consortia of plant growth promoting rhizobacteria and rhizobia under salinity stress

The use of multispecies plant growth promoting rhizobacteria (PGPR) in conjunction with rhizobia is a favourable tool for mitigating salt stress to legumes. However there is a need to understand the synergistic effect of PGPR in consortia, while also demonstrating the PGP effect under salinity. In this study, we have evaluated PGPR bacteria belonging to Enterobacter, Pseudomonas and rhizobia, individually as well as in consortia for plant growth promoting traits viz. indole acetic acid (IAA), biofilm and siderophore production, under salt stress. Interestingly, several consortia demonstrated better stress tolerance and responded with increased PGPR effect suggesting synergy between these multispecies combinations. Present work reports promising novel combinations of soil isolates which show enhanced PGP traits in consortia that could mitigate salt stress.

Role of Local Biofertilizer in Enhancing the Oxidative Stress Defence Systems of Date Palm Seedling (Phoenix dactylifera) against Abiotic Stress

Among the abiotic stresses, drought is the first environmental stress responsible for a decrease in agricultural production worldwide; it affects plants in various ways, including slowing down plant growth and disrupting its general physiology. Arbuscular mycorrhizal symbiosis and plant growth-promoting rhizobacteria (PGPR) are considered to be the bioameliorators of the plant’s resistance to water stress. The present study investigated the effects of inoculation with arbuscular mycorrhizal fungi (AMF) and PGPR on the water status and antioxidant enzyme activities of date palm seedlings grown under water stress conditions. The parameters related to the plant’s water status were significantly ( p < 0.05 ) higher in the plants treated with mycorrhizae and mycorrhizae + bacteria compared with their respective controls, especially under water stress conditions. The maximum proline content was obtained in plants inoculated with the AMF species and PGPR (combined) under severe water stress conditions reaching a value of 2.588 ± 0.034 in 25% field capacity, compared with 0.978 ± 0.024 for the control. In addition, the inoculated seedlings showed notably lower activities of superoxide dismutase (SOD), catalase (CAT), peroxidase (POX), and glutathione S-transferase (GST) in response to severe water stress compared with nonmycorrhizal seedling. Overall, the arbuscular mycorrhizal symbiosis and PGPR bacteria inoculation could be promising methods to enhance date palm resistance against oxidative stress.

Evaluation of the Effects of Plant Growth Promoting Rhizobacteria (PGPR) on Yield and Quality Parameters of Tomato Plants in Organic Agriculture by Principal Component Analysis (PCA)

Our research was carried out to determine the effects of plant growth promoting rhizobacteria (PGPR) on the yield and quality parameters of tomato plants in organic farming conditions. In our study, Bacillus megaterium M‑3, Paenibacillus polymxa, Burkholderia cepacia, Azospirillum sp-245 bacterial strains were applied by three different applications methods such as to the soil, root region and leaves. The research was carried out as field experiment in 37 plots and 10 plants per plot. As a result of the study, it was determined that different PGPR applications significantly affect the yield and quality parameters of tomato plant in organic agriculture. When the results were evaluated, the highest yield was obtained as 1533 kg da−1 with foliar application of B. megaterium M‑3 bacteria. B. megaterium M‑3 bacteria application to leaves increased that yield by about 20% compared to the control. It was determined that the bacteria applications did not have any significant effect on fruit size, fruit width and fruit weight. However, PGPR applications increased the amount of plant nutrients in the leaf, and pH, soluble solid contents (SSC), the rate of titratable acidity and the vitamin C values in the fruit. In conclusion, some PGPR bacteria as B. megaterium M‑3, P. polymxa, B. cepacia, A. sp-245 increased the yield of the product and have a positive effect on quality parameters. As a result of the PCA (principal component analysis), PC1 alone explained 35% of the total variance and PC2 explained 24%. PC1 was found to be associated with soluble solid matter, vitamin C, titratable acidity, pH and EC, PC2 was found to be fruit yield and marketable yield, and PC3 was found to be scrap yield and marketable yield ratio.

Biodiversity and Plant Growth Promoting Potential of Bacteria from Soybean Rhizosphere of Saline Soil

PGPR are root-associated bacteria that form symbiotic relationships with many plants. These are the Bacteria that colonize plant roots and promote plant growth are referred to as plant growth-promoting rhizobacteria (PGPR). PGPR are highly diverse and are important in plant growth promotion and increase in yield of crops. Almost all of the PGPR bacteria produce phytohormones, some fixes atmospheric nitrogen, some solublizes the phosphates and some resist phytopathogens by production of siderophores. An understanding of microbial diversity is important in agricultural contest, it is important and useful to know soil quality in terms of PGPR bacteria which is helpful for taking measures for soil management and increased plant productivity. It is also important to understand the relationship of soil and plants with the diversity of associated bacteria for their better exploitation. Therefore, it is important to know the soil micro flora and their diversity. Most of the rhizospheric bacterial diversity from normal soil have been studied and organisms explored for their use as bioinoculents. However, saline soil rhizospheric microfloras remain unexplored. By considering this, in the present study fifty two bacterial isolates including PGPR have been isolated from saline soil of Kolhapur district of southern Maharashtra, India. Isolates were identified up to genus and species level. Few isolates were studied their nitrogen fixing and phosphate solublizing activity. Present study showed that amongst nitrogen fixing bacteria Azotobacter chroococcum found to be most dominant and Bacillus megaterium was found to be most dominant phosphate solublizer. Study indicated the importance of these organism as bioinoculents for saline soil and can be explored for biofertilizer production.

Effect of Soil Physicochemical Properties on PGPR Density at A Coffee Plantation in Malang, Indonesia

The objective of this research was to determine the effect of physicochemical properties of coffee plantation soil on density of plant growth-promoting rhizobacteria (PGPR). The PGPR bacteria were isolated from rhizosphere of Coffea arabica and Coffea canephora soil using serial dilution method. The number of IAA-producing, phosphate-solubilizing, and nitrogen-fixing bacteria were determined by Tryptic Soy Agar, Pikovskaya Agar and Nitrogen-free-Bromothymol Blue Agar medium, respectively. The density of IAA producing bacteria and nitrogen-fixing bacteria of Coffea arabica soil 1.5×105 cfu/g and 2×104 cfu/g, respectively were higher than Coffea canephora soil. The density of phosphate-solubilizing bacteria 1.7×105 cfu/g of Coffea canephora was higher than Coffea arabica soil. Environmental parameters of both coffee species were significantly influenced by latitude, light intensity and tree height (p<0.05). The C/N ratio was significantly higher of Coffea arabica soil 11.33 % than Coffea canephora soil 8.66 %. The highest correlation (correlation > 0.86) was between nitrogen-fixing bacteria and IAA-producing bacteria. This analysis can be performed that the density of PGPR may vary due to some soil properties, environment factors, and plant characteristics.

Metatranscriptomics and nitrogen fixation from the rhizoplane of maize plantlets inoculated with a group of PGPRs

Plant roots are inhabited by a large diversity of microbes, some of which are beneficial for the growth of plants and known as plant growth promoting rhizobacteria (PGPR). In this work, we designed a multispecies inoculum of PGPRs containing Rhizobium phaseoli, Sinorhizobium americanum and Azospirillum brasilense nitrogen-fixing strains and other plant-growth promoting bacteria such as Bacillus amyloliquefaciens and Methylobacterium extorquens. We evaluated the effect of this group of bacteria on the growth of one-month-old maize plants. The multispecies inoculum exerted a beneficial effect on maize plants that was greater than that obtained with single-bacteria. Using the same multispecies inoculant, acetylene reduction was recorded in 5-day-old roots indicating active nitrogen fixation by bacteria in maize. Azospirillum nitrogen fixation was lower than that obtained with the multispecies inoculum. We focused on the analysis of R. phaseoli gene expression in presence of other PGPRs. Many R. phaseoli up- regulated genes in roots in the presence of other bacteria are hypothetical, showing our poor knowledge of bacteria-bacteria interactions. Other genes indicated bacterial nutrient competition and R. phaseoli stress. Differentially expressed transcriptional regulators were identified that may be key in bacteria-bacteria interaction regulation. Additionally, gene expression was analyzed from Azospirillum but not from sinorhizobia and methylobacteria due to the low number of transcripts obtained from maize roots. The metatranscriptomic analysis from maize roots showed expression of Azospirillum nif genes in the presence of PGPR bacteria. Our hypothesis is that other bacteria stimulate Azospirillum capacity to fix nitrogen and this should be further explored.

In vitro study of plant growth promoting rhizobacteria (PGPR) and endophytic bacteria antagonistic to Ralstonia solanacearum formulated with graphite and silica nano particles as a biocontrol delivery system (BDS)

Abstract Antagonistic Lysinibacillus sp., Bacillus subtilis, and Pseudomonas fluorescens were proven to control Ralstonia solanacearum that causes bacterial wilt on potatoes. Present study reports in vitro evaluation of a formulation containing PGPR and endophytic bacteria with the novel biocontrol delivery system (BDS) consisted of graphite and silica NPs. Crystal structure, morphology, elemental analysis and size distribution of particles in the suspension were respectively observed by XRD, SEM, EDS, and PSA. While the morphology and bacterial existence were observed by SEM, UV–vis, and photoluminescence spectroscopy. The ability of above BDS to form synergistic effect and inducing antagonistic interactions against R. solanacearum was evaluated by measuring the diameter of inhibition zone (DIZ). It is highlighted that the widest inhibition zones were resulted from biocontrol with graphite + silica NPs, indicating that BDS significantly affects the biocontrol mechanism. Compared to control, the inhibition zones caused by Lysinibacillus sp. were widest in the formulation with 3% graphite +5% silica NPs; by B. subtilis were in the formulation with 5% graphite +5% silica NPs, and 5%; by P. fluorescens were in the formulation with 5% graphite +5% silica NPs.

REUSE OF WASTE DRAINAGE WATER AFTER ITS TREATMENT USING PGPRS TO IRRIGATE SOME HORTICULTURAL CROPS

Natural sources of water are limited in Egypt. The rapidly growing populations necessitate continuous expansion of the cultivated area. This means an increase of the gap between the demands of water for irrigation and the limited water supply. Looking for other sources such as low quality water like (industrial effluent, drainage and sewage) must be used in irrigation of some garden and wood plants. This investigation was conducted on agricultural drainage wastewater from El Mohete drain (Marioteya Canal) west of Cairo; the samples were collected from different places during (Summer and Winter seasons). The wastewater contaminated with pathogenic microorganisms, the excess of fertilizers (inorganic & organic), heavy metals, and the residuals of pesticides. Plant Growth Promoting Rhizobacteria (PGPR) could remediate the wastewater as biological bioremediation to remove some pollutants such as pathogenic microorganisms, heavy metals and pesticides. Chemical remediation was used as nitrification inhibitor to stop transformation of ammonia to nitrate. This work was conducted to study the ability of PGPR strains e.g. Bacillus megaterium, Bacillus subtillis, Bacillus circulans, Paenibacillus polymyxa, Pseudomonas floresense, Serratia sp. and Azotobacter chroococcum 5, 9 and 23 to treat the drainage water for irrigation the Mentha viridis cv. and Gladiolas grandiflorus cv. plants. Two pot experiments were conducted in greenhouse. The treatments were applied as follows; Natural water, treated water and drainage water to irrigate the plant. Use the PGPR as inoculants and thiourea as nitrification inhibitor, Heavy metal treated was (Copper, Cobalt, Zinc, Cadmium and Mercury) the result showed us heavy metals removal by PGPR from drainage water. The characterizations of PGPRs as shown in the obtained results are they could enhance plant growth by using their own metabolism (solublizing phosphate, producing hormones or fixing nitrogen) as well as correlation of them with the potenit of effects on the growth of plants in unfavorable conditions in order to improve the efficiency of phytoremdiation of contarinated soils. The removal of heavy metals and the elimination of pesticides residues were markedly noticed in this investigation. Results also confirmed the ability of PGPRs in suppressing the effect of pathogenic bacteria like Salmonellasp and E.coli. These abilities are of great importance in terms of plant and soil health. Consequently, the role of PGPRs bacteria associated with plant rhizosphere in remediation of water and soil contaminations due to its biochemical activity and thus, stimulate plant growth is a great important subject in phytoremediation process nowadays.

Improvement of Sorghum (Sorghum bicolor l. Moench) growth and yield under drought stress by inoculation with Bacillus cereus and foliar application of potassium silicate

TEN plant growth promoting rhizobacteria (PGPRs) isolated from the rhizosphere of sorghum plants were screened for production of Indole acetic acid (IAA), exopolysaccharide (EPS), phosphate solubilizing, siderophore production and Hydrogen cyanide (HCN), in addition to the ability to withstand drought and heat stresses. The best performing isolate was identified by both biochemical and molecular methods as Bacillus with 99% similarity to B. cereus strain. The in vivo plant growth promoting activity of identified strain on Sorghum growth (Sorghum bicolor l. Moench) under drought stress was evaluated at a field experiment in combination with different levels of potassium silicate. Treatments included inoculation of seeds by B. cereus and three levels of K silicate (50.150 and 200 ppm) as foliar spray. Drought stress was achieved by spacing between irrigation times (20 days between each irrigation). Results showed that, supplementation of K silicate (50,150 and 200 ppm) plus PGPRs inoculation increased vegetative growth, RWC% and improved electrolyte leakage, recorded 76.2 %, 82.2 % and 80.2 % respectively. Proline content recorded 23.6%, 32.1% and 34.14% respectively under deficit water. As well as the combined treatment between inoculation and K silicate improved photosynthetic pigments, chlorophyll stability index, osmotic potential, plant K+, Ca2+ and Mg2+ accumulation, while reduced Na+ uptake besides that enhanced Na/K ratio compared to control under drought. Also, K silicate only or with PGPRs bacteria increased the total number of bacteria and actinomycetes in rhizosphere but reduced the number of soil fungi. Antioxidant enzymes were reduced affected by the combined action of inoculation with B. cereus and K silicate spraying. The results proved that the combination of PGPRs plus foliar application of K silicate is favorable treatment under drought stress.

The Potential Use of Plant Growth-Promoting Rhizobacteria (PGPR) as Antagonists and Biocontrol Agents in Hevea Diseases

The rhizosphere related bacterial species have a significant capability in plant growth promotion, referred to as Plant Growth Promoting Rhizobacteria (PGPR). Several substances produced by antagonistic rhizobacteria have been related to pathogen control and indirect promotion of growth in many plants. The objectives of this study were to identify effective PGPR bacteria in rubber soils of Sri Lanka, determine the potential use as antagonists and biocontrol agents to control economically important Hevea diseases in nurseries, and identify effective novel inoculant formulations. Soil samples were collected from the root rhizozphere of cover crops in Hevea fields in Rubber Research Institute of Sri Lanka (RRISL), Dartonfield. Bacteria were isolated by TSA plate method. Isolated PGPR bacteria were subjected to test the enzyme secretion ability. Pectinase, Lipase, and Amylase secretion ability of PGPR were tested in specifically developed media. Auxin production of PGPR were measured using freshly prepared Salkowsky reagent. Phosphorous solubilizing ability of PGPR was tested using Pikovskaya (PVK) medium. Antagonistic ability of PGPR was tested against the Rigidoporous microporus, Fusarrium sp. and Pythium sp. causing white root disease and Patch Canker disease in rubber respectively. Paper disc diffusion method was used to test the antagonism of selected bacteria and the percentage growth inhibition was calculated. Plasmid DNA extraction of antagonistic PGPR was done following the alkaline SDS method. Gene sequencing of selected bacteria was further carried out. Among 13 selected PGPR bacterial species, 3 bacteria were showing significant antagonism towards R. microporus. (Percentage growth inhibition by 51.2%, 46.8% and 44.3% respectively) Fusarium sp. was controlled by 7 PGPR species. Pythium sp. was controlled by 2 PGPR (Percentage growth inhibition by 41.6% and 38.7% respectively) 5 types of combinations of bacteria were tested. Among 5 types, 2 types were highly effective in control of R. microporus (Percentage growth inhibition by 79.8% and 72.6% respectively). All 5 combinations were moderately effective in control Fusarium sp. and 1 type was highly effective in control of Pythium sp. (Percentage growth inhibition by 67.8%). PGPR can be used as effective biocontrol agents in control of Hevea pathogens. The combinations of PGPR are more effective than the individual bacterial species. This will be leading to improve the productivity of Hevea plantations in Sri Lanka. Keywords: Plant Growth Promoting Rhizobacteria, Antagonism, Hevea pathogens

Inoculation with Azospirillum sp. and Herbaspirillum sp. Bacteria Increases the Tolerance of Maize to Drought Stress.

Stress drought is an important abiotic factor that leads to immense losses in crop yields around the world. Strategies are urgently needed to help plants adapt to drought in order to mitigate crop losses. Here we investigated the bioprotective effects of inoculating corn grown under drought conditions with two types of plant growth-promoting rhizobacteria (PGPR), A. brasilense, strain SP-7, and H. seropedicae, strain Z-152. Plants inoculated with the bacteria were grown in a greenhouse with perlite as a substrate. Two hydric conditions were tested: normal well-watered conditions and drought conditions. Compared to control non-inoculated plants, those that were inoculated with PGPR bacteria showed a higher tolerance to the negative effects of water stress in drought conditions, with higher biomass production; higher carbon, nitrogen, and chlorophyll levels; and lower levels of abscisic acid and ethylene, which are plant hormones that affect the stress response. The oxidative stress levels of these plants were similar to those of non-inoculated plants grown in well-watered conditions, showing fewer injuries to the cell membrane. We also noted higher relative water content in the vegetal tissue and better osmoregulation in drought conditions in inoculated plants, as reflected by significantly lower proline content. Finally, we observed lower gene expression of ZmVP14 in the inoculated plants; notably, ZmVP14 is involved in the biosynthesis of abscisic acid. Taken together, these results demonstrate that these bacteria could be used to help plants cope with the negative effects of drought stress conditions.