Plant Growth Promoting Rhizobacteria Properties Research Articles

Characterization and performance evaluation of plant growth promoting bacteria in tomato rhizosphere

An acute and compelling need to replace chemical fertilizers has shifted our focus towards plant growth-promoting rhizobacteria (PGPR) that rapidly colonize the rhizosphere. In the present investigation, two isolates from tomato rhizosphere, TS4 and TS6, were screened for various PGPR properties. Both isolates expressed different properties such as enzyme production and hydrogen sulfide (H2S) production. Production of Indole-3-Acetic Acid (IAA) was 13.33 μg mL−1 for both TS4 and TS6. Ammonia excretion was 75.0 μg mL−1 for TS4 and 82.5 μg mL−1 for TS6. Both isolates tolerated salt stress up to 10% sodium chloride (NaCl), drought stress tolerated by isolate TS4 was up to -0.30 MPa and TS6 survived up to -0.49 MPa osmotic pressure. To assess the colonization potential of the isolates, their biofilm potential and chemotactic behavior towards the tomato root exudates were studied. Colonization of the tomato rhizosphere by TS4 and TS6 was observed quantitatively and found that root tips were more profusely colonized as compared to the root base. Nethouse studies to test their influence on tomato revealed a positive influence in some plant aspects. All the results led to the conclusion that isolates TS6 identified as Micrococcus luteus and TS4 belonging to genera Lactobacillus were efficient PGPR. This paper highlights the efficacy of PGPR as a component of sustainable agriculture for improved productivity. However, the need of risk assessment and rigorous surveillance of bacteria before developing them as a bioformulation is also emphasized.

Study of the plant growth-promoting capacity of Pseudomonas putida 1046 in a model plant system

Plant Growth Promoting Rhizobacteria (PGPR) represent a microbial community that exerts growth-promoting capabilities in plants by various mechanisms. Among the PGPR genera, Pseudomonas spp. deserves special attention. It is due to its characteristic traits, like the production of phytohormones and siderophores, solubilization of minerals and phosphates, and plant protection from biotic and abiotic stress. These PGPR properties depend on the microorganism and its plant counterpart. The use of microbial strains as bioinoculants must consider the physiological and economic aspects of the process, and the plant growth stimulating effect has to be checked and proved. This study aimed to explore the PGP capacity of Pseudomonas putida 1046 strain in a model plant system of the economically important corn culture (Zea mays). The effect of the strain’s metabolic status on the plant germination capacity was evaluated. Bacterial cultures, grown 16 h and 48 h, were explored for the treatment of the corn seeds at three experimental concentrations: 0.1, 0.2, and 0.4%, and monitoring of their germination capacity through the growth indicators length of the radicle, length of the coleoptile, and the number of lateral roots. The data obtained outline the positive effect of Pseudomonas putida 1046 on the germination capacity of corn when applied at 0.2% concentration. The in vitro treatment of the model plants with 0.2% suspension resulted in a 22.87%–28.33% increase in the length of the radicle, a 35.96%–49.56% increase in the length of the coleoptile, and a 5.41–16.67% increase in the number of the lateral roots. High values of the vigour index (2125 for 16 h and 2721 for 48 h culture) were also registered. The strain’s ability to produce siderophores of hydroximate type and exhibit phosphate solubilizing activity is proved. The optimal treatment parameters of the corn seeds comprise the application of 0.2% suspension of 16 h grown Pseudomonas putida 1046 strain for five days.

Isolation and molecular characterization of plant growth promoting bacteria from the rhizosphere of orchids in Turkey

The objective of the study was to isolate and identify bacteria having plant growth promoting rhizobacteria (PGPR) characteristics from the rhizosphere of wild orchids. Orchid plants belonging to the species of Anacamptis pyramidalis, Himantoglossum caprinum, Limodorum abortivum, Platanthera bifolia, Serapias vomeracea subsp. laxiflora, Spiranthes spiralis, Ophrys apifera, Ophrys sphegodes, Orchis coriophora, Orchis laxiflora, Orchis provincialis, Orchis tridentata from the Black Sea region (Samsun, Turkey). Rhizobacteria were isolated from the rhizosphere of orchids and assayed for phosphate solubilization, 1 aminocyclopropane-1-carboxylate (ACC) deaminase activity and indole-3-acetic acid (IAA) production. Out of 111 rhizobacteria, 65 solubilized phosphate, 32 had ACC deaminase activity, 83 produced IAA. Sixteen of the isolates showed all the traits. Comparing sequences of 16S rDNA against the database with BLAST, the most common genera were Bacillus, Paenibacillus, Pseudomonas, Acinetobacter, Agrobacterium and Stenotrophomonas. This is the first study to comprehensively evaluate the PGPR properties of strains isolated from wild orchid rhizosphere.

Inoculation of Pseudomonas mutant strains can improve growth of soybean and corn plants in soils under salt stress

In the last decades, the applications of Plant Growth Promoting Rhizobacteria (PGPR) as inoculants for enhancing crops yield under different stress conditions have reached enormous interest. Pseudomonas putida KT2440 is a well-known rhizobacteria capable of colonizing roots of agronomically important crops. This work aims to evaluate three P. putida KT2440 mutants (mus-20, mus-42, and EU206), which have non-biofilm producing and exopolysaccharide overproducing phenotypes, for their potential as PGPR on soybean and corn plants under saline stress. Experimental studies showed that KT2440 and its mutants were effective in three main PGPR properties: solubilization of phosphates and synthesis of indolic compounds and siderophores. Notably, indolic compounds synthesis increased in mus-20 and EU206 strains. Furthermore, all evaluated strains were tolerant to saline stress. Bacterial inoculation of soybean and corn seeds was effective both in vitro and in vivo tests, even at high salt concentrations (80 and 120 mM NaCl). Among mutant bacteria, EU206 strain seems to be the most efficient PGPR by significantly increasing seed germination, shoot and root lengths, and fresh and dry weights of plants compared to non-inoculated controls, in in vivo tests under saline condition, mainly in both corn plants. These results suggest that inoculation with the P. putida KT2440 mutant strains is an appropriate strategy to enhance the growth of soybean and corn plants, so they might be employed for promoting regional crops growth at field scale using natural saline soils.

IMPACT OF PLANT GROWTH PROMOTING RHIZOBACTERIA AS BIO-CONTROL AGENTS ON CITRUS NEMATODE, TYLENCHULUS SEMIPENETRANS INFECTING BALADY ORANGE (CITRUS SINENSIS L.) AND IMPROVING ITS PRODUCTIVITY

Three bacterial species of plant growth promoting rhizobacteria (PGPR) namely Paenibacillus polymyxa, Methylobacterium mesophilicum and Methylobacterium radiotolerans were tested alone or combined with humic acid as bio-control agents against the citrus nematode Tylenchulus semipenetrans under laboratory and field conditions. Results cleared that; all tested PGPR species produced IAA, HCN, ammonia, chitinase and protease enzymes and also solubilized phosphate in laboratory. P. polymyxa emphasized the superiority among other species in all PGPR properties except for phosphate solubilization, whereas M. radiotolerans showed highest amount of phosphorus solubilized in culture media. On the other hand, the results of the nematode survey conducted on orange, Citrus sinensis L. cv Balady grown in different localities of Ismailia and Sharkia Governorates during season 2019, revealed the presence of seven genera and species of plant-parasitic nematodes. Among which, T. semipenetrans occurred in all examined samples (100% frequency of occurrence) with a relatively high population density of 2330 and 2640 infected juveniles (J2) /250 g soil in Ismailia and Sharkia Governorates, respectively. Field experiments were conducted in two different locations, at Ismailia and Sharkia Governorates to assess the effectiveness of PGPR strains alone or combined to reduce the numbers of T. semipenetrans during season 2019. It was found that, all treatments caused significant (P≤0.05) reduction in T. semipenetrans population, compared to control treatment. The nematicide, Nemathorin® 10% G followed by P. polymyxa (20 L.fed-1 ) + foliarspraying of M. mesophilicm (5 L.fed-1 ) gave the highest efficacy in controlling the citrus nematode. Percentage reduction in numbers of J2/250g soil and adult females/1g roots for these treatments in Ismailia Governorate were 91% (85.7%) and 91.4% (89.5%), respectively. While the parallel values in Sharkia Governorate were 90% (87%) and 94% (90%), respectively. The combination of P. polymyxa and humic acid (20 L.fed-1 ) with foliar spraying of M. mesophilicm (5 L.fed-1 ) gained the third position. All treatments increased the fruit yield compared to control treatment. The highest percentages of increase were determined with Nemathorin (160% and 206%) followed by P. polymyxa + Humic acid (20 L.fed-1 ) + foliar spraying of M. mesophilicum (155.7% and 193%) and M. radiotolerans + P. polymyxa + foliar spraying of M. mesophilicum (153% and182%) in Ismailia, and Sharkia Governorates respectively.

A rhizosphere isolate from Oryza sativa, Enterobacter cloacae VITTPN2, as a potential plant growth promoting rhizobacteria; an in vitro study

The increasing need for Plant Growth Promoting Rhizobacteria (PGPR) for biofertilizer development is warranted owing to the environmental hazards caused by chemical fertilizers. Our investigation was to isolate, screen and characterize PGPR from rhizospheric soil with potential PGPR properties. Oryza sativa and Saccharum officinarum rhizosphere were collected from the agricultural research station, Virinjipuram, Vellore (12.9202N, 79.1333E), Tamil Nadu, India for PGPR isolation. Eleven distinct isolates of bacteria were grown on Jensen’s (seven) and Pikovskaya’s media (four). Among these, four isolates (TPN1 to TPN4) showed phosphate solubilisation activity. And one isolate TPN2 particularly showed both nitrogen fixation and phosphate solubilization with other PGPR properties. Furthermore, the isolate TPN2 demonstrated promising results in Indole 3-Acetic Acid production (99.29±0.945µg ml-1). Since the isolate TPN2 displayed all PGPR characteristics under study, it was selected for pot culture studies. The seeds treated with TPN2 revealed an increase of 63.6% in shoot length and 14.63% in root length of the okra plant. There was a 74.6% increase in shoot length and a 16% increase in the root length of the tomato plant. Additionally, there was extensive development of lateral roots in okra plant. Henceforth TPN2 was identified as Enterobacter cloacae VITTPN2 (ku951582). This report produced remarkable results which promise the bacterial strain Enterobacter cloacae strain VITTPN2 can be further studied as a prospective biofertilizer.

Plant-mediated restriction of Salmonella enterica on tomato and spinach leaves colonized with Pseudomonas plant growth-promoting rhizobacteria

Reducing Salmonella enterica association with plants during crop production could reduce risks of fresh produce-borne salmonellosis. Plant growth-promoting rhizobacteria (PGPR) colonizing plant roots are capable of promoting plant growth and boosting resistance to disease, but the effects of PGPR on human pathogen-plant associations are not known. Two root-colonizing Pseudomonas strains S2 and S4 were investigated in spinach, lettuce and tomato for their plant growth-promoting properties and their influence on leaf populations of S. enterica serovar Newport. Plant roots were inoculated with Pseudomonas in the seedling stage. At four (tomato) and six (spinach and lettuce) weeks post-germination, plant growth promotion was assessed by shoot dry weight (SDW) and leaf chlorophyll content measurements. Leaf populations of S. Newport were measured after 24h of leaf inoculation with this pathogen by direct plate counts on Tryptic Soy Agar. Root inoculation of spinach cv. ‘Tyee’, with Pseudomonas strain S2 or S4 resulted in a 69% and 63% increase in SDW compared to non-inoculated controls (p<0.005 and p<0.01, respectively). Similarly, Romaine lettuce cv. ‘Parris Island Cos’ responded positively to S2 and S4 inoculation (53% and 48% SDW increase, respectively; p<0.05), and an increase in leaf chlorophyll content (p<0.001), compared to controls. Tomato cv. ‘Nyagous’ yielded significantly greater SDW (74%, p<0.01 and 54%, p<0.05 for S2 and S4, respectively), and also higher leaf chlorophyll content (19% and 29%, p<0.001, respectively) relative to controls. Leaf chlorophyll content only increased in S4-inoculated tomato cv. ‘Moneymaker’ plants (27%, p<0.001), although both S2 and S4 promoted plant growth by over 40% compared to controls (p<0.01 and p<0.05, respectively). No significant growth promotion was detected in tomato cv. ‘BHN602’, but S2-inoculated plants had elevated leaf chlorophyll content (13%, p<0.01). Root inoculation with Pseudomonas S4 restricted S. Newport populations inoculated on leaves of spinach (p<0.001) and all three tomato cultivars (p<0.05), compared to controls, 24h post Salmonella inoculation. Impairment of S. Newport leaf populations was also observed on spinach when plant roots were inoculated with S2 (p<0.01). With an initial leaf inoculum of approximately 6.0logCFU of S. Newport/plant, the significantly greater reduction of S. Newport populations on Pseudomonas-treated plants than those on non-inoculated control plants after 24h was modest with differences of one log or less. By contrast, the survival of S. Newport on the leaves of Romaine lettuce was not influenced by Pseudomonas root colonization. These findings provide evidence that root inoculation of certain specialty crops with beneficial Pseudomonas strains exhibiting PGPR properties may not only promote plant growth, but also reduce the fitness of epiphytic S. enterica in the phyllosphere. Plant-mediated effects induced by PGPR may be an effective strategy to minimize contamination of crops with S. enterica during cultivation.

Biochemical Characterization and Molecular Fingerprinting of Plant Growth Promoting Rhizobacteria

Plant growth promoting rhizobacteria (PGPR) are a heterogeneous group of bacteria that can be found in the rhizosphere, which can improve the extent or quality of plant growth directly or indirectly. However, screening strategies for selecting the best rhizobacterial strain for rhizosphere competence with other microbial species in the plant rhizosphere will require more comprehensive knowledge. In present investigation nine different strains were tested for their PGPR properties by using RFLP analysis on 16S rRNA gene or amplified rDNA restriction analysis (ARDRA). 16 S rDNA amplification was done and restriction profiling was done using two endonuclease i.e. msp1 and taq1. Depending upon banding pattern of all the nine strains dendogram was created using NTsys software. A clear cut difference was seen in genetic diversity among the strains. Pseudomonas was found to be the most effective strain among all. Depending upon the outcome we can conclude that ARDRA can be effective tool for analyzing the genetic diversity among different bacteria and PGPR starin e.g. Pseudomonas, Bacillus can be used as a potent biofertilizer.