Iron facilitates the RetS-Gac-Rsm cascade to inversely regulate protease IV (piv) expression via the sigma factor PvdS in Pseudomonas aeruginosa

Pseudomonas aeruginosa produces several proteases, such as an elastase (LasB protease), a LasA protease, and protease IV (PIV), which are thought as significant virulence factors during infection. Regulators of LasA and LasB expression have been identified and well characterized; however, the molecular details of this regulation of protease IV (PIV) remained largely unknown. Here, we describe the interaction between protease IV and the RetS/Rsm signalling pathway, which plays a central role in controlling the production of multiple virulence factors and the switch from planktonic to biofilm lifestyle. We show that the expression of piv was reduced in ΔretS or ΔrsmA strain grown under restrictive conditions but was induced in ΔretS or ΔrsmA mutant grown under rich conditions as compared with wild-type parent. We compare the expression of piv under various conditions and found that iron facilitates RetS/Rsm system to lead this inverse regulation. Moreover, we reveal that the RetS/Rsm pathway regulates PIV production dependent on the alternative sigma factor PvdS. Collectively, this study extends the understanding of the RetS/Rsm regulatory cascade in response to environmental signals and provides insights into how P. aeruginosa adapts to the complex conditions.     

Characterization of <Emphasis Type="Italic">Pseudomonas aeruginosa</Emphasis> RM-3 as a Potential Biocontrol Agent

Molecular characterization of rhizobacterial isolate RM-3, based on sequencing of a partial 1,313-bp fragment of 16S rDNA amplicon, validated the strain as Pseudomonas aeruginosa. The strain showed significant growth inhibition of different phytopathogenic fungi in dual plate and liquid culture assays. Maximum growth inhibition was found in case of Macrophomina phaseolina in plate assay (68%), whereas it was 93% in Dreschlera graminae in dual liquid assay. Microscopic studies (light and scanning electron) showed morphological abnormalities such as perforation, fragmentation, swelling, shriveling and lysis of hyphae of pathogenic fungi. The strain also exhibited production of siderophore and hydrogen cyanide (HCN) on chrome azurol S and King’s B media, respectively. Besides, this strain also produced extracellular chitinase enzyme and an important antibiotic, phenazine. Seed bacterization with RM-3 showed a significant (P < 0.05) increase in seed germination, shoot length, shoot fresh and dry weight, root length, root fresh and dry weight and leaf area. It was also able to colonize the rhizosphere of plants and reduced percent disease incidence in M. phaseolina-infested soil by 83%. Yield parameters such as pods, number of seeds and grain yield per plant also enhanced significantly (P < 0.05) in comparison to control. Thus, the secondary metabolites producing Pseudomonas aeruginosa strain RM-3 exhibited innate potential of plant growth promotion and biocontrol potential in vitro and in vivo.     

Stimulation of the growth of <Emphasis Type="Italic">Jatropha curcas</Emphasis> by the plant growth promoting bacterium <Emphasis Type="Italic">Enterobacter cancerogenus</Emphasis> MSA2

A novel Enterobacter cancerogenus MSA2 is a plant growth promoting gamma-proteobacterium that was isolated from the rhizosphere of Jatropha cucas a potentially important biofuel feed stock plant. Based on phenotypic, physiological, biochemical and phylogenetic studies, strain MSA2 could be classified as a member of E. cancerogenus. However, comparisons of characteristics with other known species of the genus Enterobacter suggested that strain MSA2 could be a novel PGPB strain. In vitro studies were carried for the plant growth promoting attribute of this culture. It tested positive for ACC (1-aminocyclopropane-1-carboxylic acid) deaminase production, phytase, phosphate solubilization, IAA (Indole acetic acid) production, siderophore, and ammonia production. The isolate was then used as a inoculant for the vegetative study of Jatropha curcas plant. Enterobacter cancerogenus MSA2 supplemented with 1% carboxymethylcellulose showed overall plant growth promotion effect resulting in enhanced root length (124.14%), fresh root mass (81%), fresh shoot mass (120.02%), dry root mass (124%), dry shoot mass (105.54%), number of leaf (30.72%), chlorophyll content (50.41%), and biomass (87.20%) over control under the days of experimental observation. This study was designed for 120 days and was in triplicate and the data was collected at every 30 days.     

Effects of Pseudomonas fluorescens F113 on Ecological Functions in the Pea Rhizosphere Are Dependent on pH

Abstract The aim of this microcosm study was to determine influence of the antibiotic 2,4-diacetylphloroglucinol (DAPG) on the effect of wild-type and functionally modified Pseudomonas fluorescens F113 strains in a sandy loam soil of pH 5.4 planted with pea (Pisum sativum var Montana). The functional modification of strain F113 was a repressed production of DAPG, useful in plant disease control, creating the DAPG negative strain F113 G22; both were marked with a lacZY gene cassette. Lowering the soil pH to 4.4 significantly reduced the plant shoot and root weights and the root length, whereas the bacterial inocula had no significant effect. Both inocula significantly reduced the shoot/root ratio at pH 5.4, but this effect was not evident at the lowered or elevated (6.4) pH levels. The decrease in pH significantly increased the fungal and yeast colony-forming units from the rhizosphere (root extract), but did not affect the total bacterial c.f.u.'s. Inoculatioin with strain F113 in the pH 4.4 soil resulted in a significantly greater total bacterial population. The fungal and yeast c.f.u.'s were not significantly affected by the inocula at any pH studied. Increasing the pH significantly increased the indigenous Pseudomonas population in comparison to the reduced pH treatment and significantly increased both the introduced and total Pseudomonas populations. The antibiotic producing strain significantly reduced the total bacterial population and the NAGase activity (related to fungal activity) at pH 6.4 where the inocula population was the greatest. Alkaline phosphatase, phosphodiesterase, aryl sulfatase, β-glucosidase, alkaline β-galactosidase, and NAGase activities significantly increased with increasing in pH. The F113 inocula reduced the acid phosphatase activity at pH 5.4 and increased the acid β-galactosidase activity over all the pH treatments. The results presented illustrate the variation in impact with soil pH, with implications for variability in efficacy of Pseudomonas fluorescens biocontrol agents with soil pH. Received: 26 June 1998; Accepted: 1 February 1999     

Biological control of onion leaf blight disease by bulb and foliar application of powder formulation of antagonist mixture

Abstract

Three antagonists: Pseudomonas fluorescens (Pf1), Bacillus subtilis and Trichoderma viride, were tested alone and in combination for suppression of onion leaf blight (Alternaria palandui) disease under glasshouse and field conditions. The average mean of disease reduction was 24.81% for single strains and 42.44% for mixtures. In addition to disease suppression, treatment with a mixture of antagonists promoted plant growth in terms of increased plant height and ultimately bulb yield. Though seed treatment of either single strain or strain mixtures alone could reduce the disease, subsequent application to root, leaves or soil further reduced the disease and enhanced the plant growth. The mixture consisting of Pseudomonas fluorescens Pf1 plus Bacillus subtilis plus Trichoderma viride was the most effective in reducing the disease and in promoting plant growth and bulb yield in greenhouse and field tests.     

Improvement of fitness and biocontrol properties of Pseudomonas putida via an extracellular heme peroxidase

The extracellular 373-kDa PehA heme peroxidase of Pseudomonas putida KT2440 has two enzymatic domains which depend on heme cofactor for their peroxidase activity. A null pehA mutant was generated to examine the impact of PehA in rhizosphere colonization competence and the induction of plant systemic resistance (ISR). This mutant was not markedly hampered in colonization efficiency. However, increase in pehA dosage enhanced colonization fitness about 30 fold in the root and 900 fold in the root apex. In vitro assays with purified His-tagged enzymatic domains of PehA indicated that heme-dependent peroxidase activity was required for the enhancement of root tip colonization. Evaluation of live/dead cells confirmed that overexpression of pehA had a positive effect on bacterial cell viability. Following root colonization of rice plants by KT2440 strain, the incidence of rice blast caused by Magnaporthe oryzae was reduced by 65% and the severity of this disease was also diminished in comparison to non-treated plants. An increase in the pehA dosage was also beneficial for the control of rice blast as compared with gene inactivation. The results suggest that PehA helps P. putida to cope with the plant-imposed oxidative stress leading to enhanced colonization ability and concomitant ISR-elicitation.     

Amino Acids, Iron, and Growth Rate as Key Factors Influencing Production of the Pseudomonas Putida BTP1 Benzylamine Derivative Involved in Systemic Resistance Induction in Different Plants

The biological control bacterium Pseudomonas putida BTP1 exerts its protective effect mostly by inducing an enhanced state of resistance in the host plant against pathogen attack [induced systemic resistance (ISR)]. We previously reported that a specific compound derived from benzylamine may be involved in the elicitation of the ISR phenomenon by this Pseudomonas strain. In this article, we provide further information about the N,N-dimethyl-N-tetradecyl-N-benzylammonium structure of this determinant for ISR and show that the benzylamine moiety may be important for perception of the molecule by root cells of different plant species. We also investigated some regulatory aspects of elicitor production with the global aim to better understand how in situ expression of these ISR elicitors can be modulated by physiological and environmental factors. The biosynthesis is clearly related to secondary metabolism, and chemostat experiments showed that the molecule is more efficiently produced at low cell growth rate. Interestingly, the presence of free amino acids in the environment is necessary for optimal production, and a specific positive effect of phenylalanine was evidenced in pulsed continuous cultures. The influence of other abiotic factors, such as mineral content, oxygen concentration, or pH, on elicitor production is also reported and discussed with respect to the specific conditions that the producing strain undergoes in the rhizosphere environment.     

Growth-Promoting Ability of Rhodopseudomonas palustris G5 and Its Effect on Induced Resistance in Cucumber Against Salt Stress

The objective of this study was to investigate the potential of Rhodopseudomonas palustris G5 in promoting growth and inducing salt resistance in cucumber (Cucumis sativus L.). In this study, the growth-promoting potential of the bacteria was studied by measuring the ability to produce indole-3-acetic acid (IAA) and 5-aminolevulinic acid (ALA), fix nitrogen, and solubilize potassium and phosphate. The greenhouse pot experiments were set up to study how strain G5 affected growth and salt resistance of cucumber seedlings. The results showed that strain G5 exhibited plant growth-promoting attributes such as the production of IAA and ALA, as well as nitrogen-fixing, potassium-solubilizing, and phosphorus-solubilizing ability. In pot trials, strain G5 increased shoot height, root length, fresh weight, dry weight, total chlorophyll content, and soluble sugar content of cucumber seedlings under salt stress, compared to the seedlings that were exposed to salt stress in the absence of the strain G5. Furthermore, antioxidant enzyme activity analysis showed that strain G5 strongly increased the activity of superoxide dismutase, peroxidase, and polyphenol oxidase in cucumber seedlings under salt stress. In addition, strain G5 treatment decreased H₂O₂ and malondialdehyde contents of salt-stressed seedling. In sum, these results showed that strain G5 enhanced growth and induced systemic resistance in cucumber seedlings under salt stress by the production of IAA, ALA, and soluble sugars, the induction of antioxidant enzymes as well as nutrient adjustment of nitrogen, phosphorus, and potassium.

     

Rhizosphere Competent Pseudomonas aeruginosa GRC1 Produces Characteristic Siderophore and Enhances Growth of Indian Mustard (Brassica campestris)

Pseudomonas aeruginosa GRC₁, an isolate of potato rhizosphere, was known to have several plant growth–promoting activities, including production of phytohormone and antibiotic substance. The isolate was found to have prolific production ability of hydroxamate siderophore in iron-deficient conditions. The siderophore of GRC₁ was purified and characterized. The purified siderophore appeared to be of pyoverdin type with typical amino acid composition. In field trials, P. aeruginosa GRC₁ enhanced the growth of Brassica campestris var Pusa Gold (Indian mustard). Significant increase in root and shoot weight, length, grain yield per plant, and total grain yield was recorded. Root colonization was studied with Tn5-induced streptomycin-resistant transconjugants of spontaneous rifampicin-resistant GRC₁ (designated GRC₁^rif+strep+) after different durations. The strain was significantly rhizopheric competent and stabilized in the rhizosphere, without disturbing the normal indigenous bacterial population.     

Growth promotion and root colonisation in pepper plants by phosphate‐solubilising Chryseobacterium sp. strain ISE14 that suppresses Phytophthora blight

Previously, we selected bacterial strain ISE14 through a sequential selection procedure that included radicle, seedling, and in planta assays and field tests. This strain not only suppressed a destructive soilborne disease, Phytophthora blight, caused by Phytophthora capsici but also increased fruit yields of pepper plants in the fields. This study was conducted to identify strain ISE14 by 16S rRNA gene sequence analysis and to characterise biocontrol and plant growth promotion activities of the strain in pepper plants. Strain ISE14, identified as Chryseobacterium sp., significantly reduced disease severity in plants inoculated with Ph. capsici and promoted plant growth (lengths and dry weights of shoots and roots) compared with those in plants treated with Escherichia coli DH5α (negative control) or MgSO₄ solution (untreated control). This strain effectively colonised pepper plant roots as assessed by bacterial population analysis and confocal laser scanning microscopy; it enhanced soil microbial activity and biofilm formation, but not the production of indole acetic acid. Strain ISE14 also solubilised organic or inorganic phosphate by production of acid and alkaline phosphatases or reduction in pH, resulting in enhanced pepper plant growth. This strain exhibited similar or greater activity in disease control and plant growth promotion tests compared with positive control strains Paenibacillus polymyxa AC‐1 (biocontrol) and Bacillus vallismortis EXTN‐1 (plant growth). Therefore, Chryseobacterium sp. ISE14 may be a phosphate‐solubilising and plant growth‐promoting rhizobacterium (PGPR) strain that suppresses Phytophthora blight of pepper. To our knowledge, this is the first report of a phosphate‐solubilising PGPR strain of Chryseobacterium sp. that suppresses the pepper disease.     

Quorum quenching by Bacillus cereus U92: a double-edged sword in biological control of plant diseases

In the present survey, quorum quenching activity was examined from a biocontrol point of view. Acyl-homoserine lactone (AHL) degrading bacteria were isolated from tomato rhizosphere using two standard bioreporter strains and different synthetic AHLs and then identified according to 16S rDNA sequences. Five isolates capable of inactivating both short and long 3oxo-substituted AHLs showed high similarity with the genera Bacillus, Microbacterium and Arthrobacter, and thereby Bacillus cereus U92 was determined as the most efficient quorum quencher strain. In the quantitative experiments, this strain remarkably inactivated all synthetic AHLs up to 80%. In the laboratory co-cultures, B. cereus U92 efficiently quenched QS-regulated phenotypes in Agrobacterium tumefaciens, Pseudomonas aeruginosa, Pseudomonas chlororaphis and Chromobacterium violaceum. The strain successfully reduced the frequency of Ti-plasmid conjugal transfer in A. tumefaciens by about 99% in the binary cultures. Meanwhile, in a more natural environment, this strain acted as a biocontrol agent, efficient in alleviating QS-regulated crown gall incidence on tomato roots (up to 90%) as well as attenuating Pectobacterium soft rot on potato tubers (up to 60%). On the other hand, reducing phenazine production in P. chlororaphis operated as a suppressor of its QS-regulated biocontrol activity and also inhibited pyocyanin production in P. aeruginosa, a plant growth-promoting bacterium, by 75%. In general, B. cereus U92 seems very promising in the biological control of pathogenic bacteria; however, its broad AHL-degrading activity has a detrimental role on beneficial microbes which should not be neglected.     

The Rhizobium sp. strain NGR234 systemically suppresses arbuscular mycorrhizal root colonization in a split‐root system of barley (Hordeum vulgare)

Nitrogen‐fixing bacteria (rhizobia) form a nodule symbiosis with legumes, but also induce certain effects on non‐host plants. Here, we used a split‐root system of barley to examine whether inoculation with Rhizobium sp. strain NGR234 on one side of a split‐root system systemically affects arbuscular mycorrhizal (AM) root colonization on the other side. Mutant strains of NGR234 deficient in Nod factor production (strain NGRΔnodABC), perception of flavonoids (strain NGRΔnodD1) and secretion of type 3 effector proteins (strain NGRΩrhcN) were included in this study. Inoculation resulted in a systemic reduction of AM root colonization with all tested strains. However, the suppressive effect of strain NGRΩrhcN was less pronounced. Moreover, levels of salicylic acid, an endogenous molecule related to plant defense, were increased in roots challenged with rhizobia. These data indicate that barley roots perceived NGR234 and that a systemic regulatory mechanism of AM root colonization was activated. The suppressive effect appears to be Nod factor independent, but enhanced by type 3 effector proteins of NGR234.     

Inhibition of primary roots and stimulation of lateral root development in Arabidopsis thaliana by the rhizobacterium Serratia marcescens 90–166 is through both auxin-dependent and -independent signaling pathways

The rhizobacterium Serratia marcescens strain 90–166 was previously reported to promote plant growth and induce resistance in Arabidopsis thaliana. In this study, the influence of strain 90-166 on root development was studied in vitro. We observed inhibition of primary root elongation, enhanced lateral root emergence, and early emergence of second order lateral roots after inoculation with strain 90–166 at a certain distance from the root. Using the DR5::GUS transgenic A. thaliana plant and an auxin transport inhibitor, N-1-naphthylphthalamic acid, the altered root development was still elicited by strain 90–166, indicating that this was not a result of changes in plant auxin levels. Intriguingly, indole-3-acetic acid, a major auxin chemical, was only identified just above the detection limit in liquid culture of strain 90–166 using liquid chromatography-mass spectrometry. Focusing on bacterial determinants of the root alterations, we found that primary root elongation was inhibited in seedlings treated with cell supernatant (secreted compounds), while lateral root formation was induced in seedlings treated with lysate supernatant (intracellular compounds). Further study revealed that the alteration of root development elicited by strain 90–166 involved the jasmonate, ethylene, and salicylic acid signaling pathways. Collectively, our results suggest that strain 90–166 can contribute to plant root development via multiple signaling pathways.     

Establishment of transformed root cultures of Perezia cuernavacana producing the sesquiterpene quinone perezone

Summary The sesquiterpene quinone currently known as perezone is abundantly produced by the roots of Perezia cuernavacana. This compound is of biotechnological interest since it may be used as a pigment and has several pharmacological properties. In this work we demonstrate that perezone is also produced in transformed root cultures of P. cuernavacana. Hairy roots were induced by inoculation of internodal segments of sterile plants of P. cuernavacana with Agrobacterium rhizogenes AR12 strain. The axenic liquid MS medium cultures of the hairy roots isolated from the internodes showed active growth in the absence of growth regulators. The transformed nature of the tissue was confirmed by genomic integration (PCR and slot blot hybridization) and expression (enzyme activity) of the marker gus-gene. The production of perezone by a transformed root culture was evidenced by IR spectroscopy. Our results offer an alternative for enhanced production of perezone and represent an advantage over its extraction from natural plant populations which present problems in their agronomic culture.     

Aeromonas punctata PNS-1: a promising candidate to change the root morphogenesis of Arabidopsis thaliana in MS and sand system

A model system of sand, comprising Arabidopsis plants inoculated with Aeromonas punctata PNS-1 strain, was used to evaluate the bacterial effect in modulation of plant root structure at second-order lateral root level. In MS media, the root morphogenesis was changed only at first-order lateral root level when inoculated with PNS-1 strain. Inoculation with PNS-1 strain was subjected to significant (P < 0.01) increase in primary root length and lateral root density in both MS and sand system. However, this strain modulated the root structure in the sand environment in a complex manner that may be helpful for incitation of the plant–microbe interaction close to natural environment. In order to determine whether this change in root morphology was due to bacterial auxin, Arabidopsis transgenic line (DR5:GUS) was used to reveal the change in homeostasis of endogenous auxin. In PNS-1 inoculated transgenic seedlings of Arabidopsis plant (DR5:GUS), endogenous auxin in primary root apices and lateral roots was enhanced. For confirmation, PNS-1 was evaluated for auxin production in vitro, showed an increase in auxin production after supplementation of l-tryptophan. The presence of ACC deaminase activity in PNS-1 showed its possible involvement in primary root elongation. In the present study Aeromonas punctata PNS-1 is the potential candidate for triggering the change in root morphogenesis of Arabidopsis thaliana with the involvement of auxin and ACC deaminase production.     

Growth enhancement of black pepper (<Emphasis Type="Italic">Piper nigrum</Emphasis>) by a newly isolated <Emphasis Type="Italic">Bacillus tequilensis</Emphasis> NII-0943

A Gram positive, rod-shaped potential strain was selected from the pool of bacterial isolates obtained from the Western Ghats forest (India) on the basis of zone of P-solubilization activity. Identification based on 16S rRNA gene sequence revealed that the strain is of Bacillus species, sharing highest sequence similarity to Bacillus tequilensis NRRL B-41771^T (99.5%). Strain NII-0943 was able to produce good amount of indole acetic acid (IAA) and was positive for siderophore production. In addition to IAA and siderophore attributes, strain NII-0943 also possessed the characteristics like Ca₃(PO₄)₂ solubilization and growth in nitrogen-free medium. Seed inoculation with the strain NII-0943 resulted in significantly higher root initiation in black pepper cuttings grown under pots. The contents of nitrogen and phosphorus in both soil and plant were also enhanced significantly in treatments inoculated with these bacterial inocula. Hence, based on this evidence it is proposed that strain NII-0943 could be deployed as a plant growth-promoting inoculant to attain the desired results of bacterization.     

Effect of introduced Pseudomonas fluorescens strains on the uptake of nitrogen by wheat from 15N-enriched organic residues

The effects of an antibiotic-producing Pseudomonas fluorescens strain (F113) carrying the marker gene cassette lacZY and a marked, non-producing strain (F113G22) on the uptake of nitrogen from ¹⁵N-enriched organic residues incorporated into a sandy soil were investigated in microcosm studies. Strain F113 produces the antibiotic 2,4-diacetylphloroglucinol (DAPG), whilst its modified derivative strain F113G22 has DAPG production deleted by Tn5 mutagenesis. Uptake of nitrogen by wheat (Triticum aestivum) from ¹⁵N-enriched organic residues was estimated using stable isotope-ratio mass spectrometry of shoot and root material of 17-day-old plants. In addition, plant growth and active microbial biomass in soil were monitored. In contrast to results obtained in our previous study on pea (Pisum sativum), it was found that in wheat, inoculation with either strain F113 or F113G22 decreased the proportion of nitrogen derived from ¹⁵N-labelled organic residues incorporated into soil as compared to non-inoculated controls. It is therefore suggested that these strains decreased mineralization of organic residues in the rhizosphere of wheat, making less inorganic N (¹⁵N) available for plant uptake. The results of this study indicate that the effects of introduced Pseudomonas fluorescens strains on nitrogen mineralization in the rhizosphere are plant-species dependent, and highlight the importance of testing microbial inocula on a range of plant species.     

Effects of above- and belowground herbivory on growth,pollination, and reproduction in cucumber

Plants experience unique challenges due to simultaneous life in two spheres, above- and belowground. Interactions with other organisms on one side of the soil surface may have impacts that extend across this boundary. Although our understanding of plant–herbivore interactions is derived largely from studies of leaf herbivory, belowground root herbivores may affect plant fitness directly or by altering interactions with other organisms, such as pollinators. In this study, we investigated the effects of leaf herbivory, root herbivory, and pollination on plant growth, subsequent leaf herbivory, flower production, pollinator attraction, and reproduction in cucumber (Cucumis sativus). We manipulated leaf and root herbivory with striped cucumber beetle (Acalymma vittatum) adults and larvae, respectively, and manipulated pollination with supplemental pollen. Both enhanced leaf and root herbivory reduced plant growth, and leaf herbivory reduced subsequent leaf damage. Plants with enhanced root herbivory produced 35% fewer female flowers, while leaf herbivory had no effect on flower production. While leaf herbivory reduced the time that honey bees spent probing flowers by 29%, probing times on root-damaged plants were over twice as long as those on control plants. Root herbivory increased pollen limitation for seed production in spite of increased honey bee preference for plants with root damage. Leaf damage and hand-pollination treatments had no effect on fruit production, but plants with enhanced root damage produced 38% fewer fruits that were 25% lighter than those on control plants. Despite the positive effect of belowground damage on honey bee visitation, root herbivory had a stronger negative effect on plant reproduction than leaf herbivory. These results demonstrate that the often-overlooked effects of belowground herbivores may have profound effects on plant performance.     

Vermicompost-based bioformulation for the management of sugarbeet root rot caused by Sclerotium rolfsii

Vermicompost-based bioformulations of bacterial and fungal biocontrol agents were examined against sugarbeet root rot caused by Sclerotium rolfsii. The result showed that the Pseudomonas fluorescens strain Pf1 in combination with either Trichoderma asperellum strain TTH1 or Bacillus subtilis strain EPCO-16 performed better in reducing disease next to the chemical difenoconazole. Similarly, enhanced yield was observed in the same combination treatments under both pot and field conditions.     

Evaluation of Pseudomonas chlororaphis subsp. aurantiaca SR1 for growth promotion of soybean and for control of Macrophomina phaseolina

Pseudomonas chlororaphis subsp. aurantiaca SR1 was evaluated for control of Macrophomina phaseolina in vitro and in soybean plants, for growth promotion of soybean plants and for production of antifungal compounds. Strain SR1 caused a significant inhibition of M. phaseolina in vitro and reduced damping-off in the in vivo assays. In addition, strain SR1 significantly increased shoot and root length and shoot and root dry weight of soybean plants in M. phaseolina infested soil, as compared to control plants in infested soil. Fragments for the phenazine-1-carboxylic acid, pyrrolnitrin and hydrogen cyanide encoding genes were amplified from the DNA of strain SR1 after polymerase chain reaction (PCR) assays with specific primers. Thus, this study establishes that P. chlororaphis subsp. aurantiaca SR1 provides control of M. phaseolina in vivo and suggests that strain SR1 might be applied as an effective biocontrol agent to protect soybean plants from this phytopathogen.