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Arabidopsis thaliana accession Col-0 seedlings were transferred into an autoclaved soil/sand mixture amended with either 10 or 20% (wt/wt) soil from fields in Washington State that are suppressive to take-all or Rhizoctonia root rot of wheat. Three weeks after transplanting, these plants had population sizes of 2,4-diacetylphloroglucinol (DAPG) or phenazine-1-carboxylic acid (PCA)-producing pseudomonads of greater than 5 × 105 colony forming units per gram fresh weight of root with rhizosphere soil. When the plants were challenge-inoculated with Pseudomonas syringae pv. tomato DC3000, both soils induced systemic resistance in the leaves against bacterial speck to a level similar to that induced by P. simiae WCS417r, P. fluorescens Q2-87 (DAPG+), P. brassicacearum Q8r1-96 and L5.1-96 (both DAPG+), and P. synxantha 2-79 (PCA+). Pasteurization of the soils before adding them into the soil/sand mixture eliminated DAPG- and PCA-producing pseudomonads from the Arabidopsis rhizosphere and significantly reduced induced systemic resistance activity. However, populations of total culturable aerobic bacteria were similar in the rhizosphere of plants grown in soil/sand mixes amended with untreated or pasteurized suppressive soils. This is the first report of induction of systemic resistance in Arabidopsis by take-all and Rhizoctonia-suppressive soils and the ability of PCA-producing P. synxantha 2-79 to induce resistance. [Figure: see text] The author(s) have dedicated the work to the public domain under the Creative Commons CC0 “No Rights Reserved” license by waiving all of his or her rights to the work worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law, 2024.

Concerning sustainable agriculture, plant growth promoting rhizobacteria (PGPR), which are a subgroup of “fluorescent pseudomonads,” are crucial. They are widely known for supporting plant health through a variety of methods. The use of fluorescent pseudomonads in agri-biotechnology has gained traction due to their potential for safeguarding plants from a variety of phytopathogens. Fluorescent pseudomonads being commercialized as bioinoculants for the treatment of various plant diseases is currently regarded as highly successful on a global scale. Fluorescent pseudomonads are being employed as efficient bio-control agents (BCAs) against an array of phytopathogens. Due to their capacity to generate a wide range of secondary metabolites, they offer enormous promise as BCA. Thus, this review’s goal is to outline and evaluate the functions of fluorescent pseudomonads’ secondary metabolites in reducing phytopathogens and improving plant health. Prominent secondary metabolites linked to biocontrol through fluorescent pseudomonads include phenazines (PHZ), 2, 4-diacetylphloroglucinol (DAPG), pyoluteorin (PLT), pyrrolnitrin (PRN), cyclic lipopeptides (CLPs), and volatile organic compounds (VOCs), including hydrogen cyanide (HCN). The antifungal, antibacterial, antiviral, antitumor, and antinematicidal effects of these metabolites are well-established.

Concerning sustainable agriculture, plant growth promoting rhizobacteria (PGPR), which are a subgroup of "fluorescent Pseudomonads," are crucial. They are widely known for supporting plant health through a variety of methods. The use of fluorescent Pseudomonads in agri-biotechnology has gained traction due to their potential for safeguarding plants from a variety of phytopathogens. Fluorescent pseudomonads being commercialized as bioinoculants for the treatment of various plant diseases is currently regarded as highly successful on a global scale. Fluorescent Pseudomonads are being employed as efficient bio-control agents (BCAs) against an array of phytopathogens. Due to their capacity to generate a wide range of secondary metabolites, they offer enormous promise as BCA. Thus, this review's goal is to outline and evaluate the functions of fluorescent Pseudomonads' secondary metabolites in reducing phytopathogens and improving plant health. Prominent secondary metabolites linked to biocontrol through fluorescent Pseudomonads include phenazines (PHZ), 2, 4-diacetylphloroglucinol (DAPG), pyoluteorin (PLT), pyrrolnitrin (PRN), cyclic lipopeptides (CLPs), and volatile organic compounds (VOCs), including hydrogen cyanide (HCN). The antifungal, antibacterial, antiviral, antitumor, and antinematicidal effects of these metabolites are well-established. [ABSTRACT FROM AUTHOR]

The article presents a study which investigated the fluorescent Pseudomonads against coriander powdery mildew under in vitro conditions. Topics discussed include identification of fluorescent Pseudomonads, biochemical characterization of fluorescent Pseudomonads, and assessment of fluorescent Pseudomonads under in vitro condition.

Chickpea wilt caused by Fusarium oxysporum f. sp. ciceris is a devastating soil-borne disease with a significant impact on yields and affecting chickpea production worldwide. Fluorescent pseudomonads are utilized as effective biocontrol agents (BCA) against a variety of phytopathogens and they play a key role in pathogen suppression through various processes. In the present study, twenty indigenous fluorescent pseudomonads were isolated from twenty soil samples collected from different districts of North Eastern Karnataka. The isolates were tested in vitro for their ability to resist the pathogen by using a dual culture approach. Further, morphological and biochemical characters were studied by growing these isolates on King’s B agar medium. All twenty isolates showed inhibition of the test pathogen, with isolate PF-19 showing the highest inhibition of 88.89%. All the isolates developed slimy, irregular colonies with light yellowish green pigmentation, fluorescence under UV light and rod-shaped cells under the microscope, as well as gram negative in reaction. All isolates except PF-2, Pf-9 and PF-10 revealed positive results for KOH, catalase, gelatin liquefaction and starch hydrolysis. [ABSTRACT FROM AUTHOR]

The present study was aimed at the evaluation of soil temperature, pH and carbon dioxide evolution on the number and efficiency of fluorescent pseudomonads around the root system of Pokkali rice at Vytilla in Ernakulam district of Kerala. Two plots (40 m2) comprising control (without application of Pseudomonas fluorescens) and P. fluorescens treated plants were used for the field experiment. The isolates of fluorescent Pseudomonads or Pseudomonas fluorescence were counted and their efficiency was assessed for IAA, ammonia, HCN and siderophore production. Simultaneously, soil temperature, pH, and carbon dioxide evolution were also recorded. A total of 6 fluorescent pseudomonads (VPJU, VPJL, VPAU1, VPAU2, VPAU3 and VPAU4) were found during the crop period. All the isolates produced IAA and ammonia with varying degrees of intensity. Three isolates (VPAU1, VPAU3 and VPAU4) produced HCN, and no microbial isolates produced siderophore. The effect of soil temperature, pH, EC and carbon dioxide evolution was correlated with the number of fluorescent pseudomonads in the soil. The bacteria were significantly afflicted by pH and EC, whereas soil temperature and CO2 evolution did not show any effect on the number of fluorescent pseudomonads. There was no significant influence of soil temperature, pH, EC and carbon dioxide evolution on indole acetic acid production, ammonia, and HCN production. Inoculated Pseudomonas fluorescence did not survive in Pokkali rice fields. However, further studies are needed for at least three seasons in Pokkali soils to confirm the results of the present study. [ABSTRACT FROM AUTHOR]

In the present study, different fluorescent pseudomonads isolates from agricultural soil were characterized and identified as plant growth promoting bacteria. On the basis of specific biochemical tests, 42 were confirmed as fluorescent Pseudomonas spp. Simultaneously, when all isolates were evaluated for their biocontrol traits, 21 isolates were good HCN producers, 23 isolates were siderophore producers and 28 isolates were also identified as phosphate solubilizers. Further, all the 42 isolates were evaluated for their antagonistic activity against the four major pathogens using dual culture assay viz., Sclerotium rolfsii, Rhizoctonia solani, Pyricularia grisea and Helminthosporium nodulosum, of which 10 isolates viz., UUHF Psf-4, 11, 12, 15, 17, 20, 28, 35, 40 and 41 showed maximum per cent inhibition against all the four tested pathogens. Among all the isolates, UUHF Psf-4 exhibited maximum per cent inhibition with 83.75 % towards S. rolfsii, 85.00 % inhibition towards R. solani, 80.00 % inhibition towards P. grisea and 78.57 % inhibition towards H. nodulosum, respectively. Results of plant growth-promoting (PGP) activities in finger millet, under laboratory and glass house conditions, revealed that all the 10 putative candidates were found effective in significantly increasing most of the planting value parameters (first count, germination per cent, root length, shoot length, seedling length, fresh and dry weight, vigour index I and II) under both laboratory and glass house conditions. UUHF Psf-4 was found to be best followed by UUHF Psf-15 and UUHF Psf-41 in most of the characters studied, all being superior to control. [ABSTRACT FROM AUTHOR]

Maize (Zea mays L.) is a major cereal crop grown in a large number of countries. Loss in maize yield due to biotic stresses including fungal phytopathogens is a matter of immense concern. Control measures applied for eradication of fungal phytopathogens in maize are not up to the mark and more often involve harsh chemical(s)/pesticide(s) that cause deleterious effects both in humans and soil biota. Greener alternatives, such as the use of rhizosphere microbes in the form of bioinoculants, have proven to be very successful in terms of enhancing crop yield and suppressing fungal phytopathogens. In the present study, fluorescent pseudomonads were isolated from the maize rhizosphere and monitored for their plant growth-promoting (PGP) and biocontrol activities against Fusarium moniliforme. Based on various PGP traits and biocontrol potential, isolate JM-1 was found to be most effective and as per 16S rRNA gene sequencing analysis was identified as Pseudomonas fluorescens. Further experiments showed that the biocontrol potential of JM-1 against ear rot fungus involved the production of antifungal compound 2,4-diacetylphloroglucinol (DAPG). When examined for antagonistic interaction under scanning electron microscopy (SEM), structural abnormality, hyphal lysis, and deformity in fungal mycelium were observed. In the pot experiment, application of talc-based JM-1 containing bioformulation (in pot trials) showed significant enhancement in maize growth parameters (including the seed number and weight) in comparison to control even in presence of the phytopathogen. Ear fresh weight, dry weight, number of seeds per plant, and 100-grain weight were found to increase significantly by 34, 34, 52, and 18% respectively, in comparison to control. P. fluorescens JM-1 can therefore be used as a bioinoculant for ear rot disease control and sustainably enhancing maize yield. [ABSTRACT FROM AUTHOR]

Fluorescent pseudomonads drawn broad attention as production of secondary metabolites, phytohormones, siderophores, enzymes, antibiotics, hydrogen cyanide and volatile compounds. The present study was to exhilarate traits of plant growth promotion by fluorescent pseudomonads under drought stress. Fifty one efficient bacterial isolates were taken to evaluate their growth in different concentrations of polyethylene glycol 6000 (PEG) at 0 % (-0.05 MPa), 10 % (-0.65 MPa), 20 % (-1.57 MPa), 30 % (-2.17 MPa) and 40 % (-2.70 MPa). On the basis of growth at higher PEG (40 %) concentration, four efficient bacteria were preferred. Plant growth promoting traits such as IAA, exopolysachharides (EPS) production, ACC deaminase activity, phosphate solubilization and potassium releasing characters were tested for the selected drought tolerant fluorescent pseudomonads. Among four efficient strains, two strains i.e., PCKR-2 showed P-solubilization Index was (3.80 mm), followed by AGVS (4.33 mm), PCKS (4.12 mm) and PVAS (2.28 mm). Data on potassium solubilization activity show that out of two isolates, PCKR-2 showed the highest solubilization zone (3.50 mm), followed by PCKS (3.17 mm), AGVS (2.83 mm) and PVAS (2.50 mm). The findings suggests that the use of fluorescent pseudomonads will aid better plant growth promotion under drought stress. [ABSTRACT FROM AUTHOR]

During the 2016 growing season, melon fruits were severely affected by rind necrosis and rot and nearly 80% of the fruits were unmarketable in a field in Koçarlı district of Aydın. In order to determine occurrences of the fruit infections in the following year, surveys were conducted in 2017. Isolations were made from the symptomatic fruits and bacterial growths were observed consistently. In this study, we identified the causal agents of melon fruit necrosis and rot. Pathogenicity of the bacterial strains was determined on melon fruit by needle injection method and thirteen strains were further characterized with phenotypic characterization, analysis of 16S rRNA gene sequences and specific PCR assays. As a result of the pathogenicity tests, brown spots and necrosis formation was observed initially and in the later stage, inoculated fruit burst out by the fermentative strains. The oxidative strains produced limited necrosis on the rind. Fermentative bacterial agents isolated from the melon necrosis and rot were identified as Enterobacter cloacae, Klebsiella pneumoniae and Kosakonia cowanii. Enterobacter cloacae strains were further tested with tDNA-PCR using T5A/T3B primers. The oxidative bacteria were phenotypically grouped within the fluorescent pseudomonads. Homology search of the oxidative strains using the sequence information of partial 16S rRNA gene identified the strains as Pseudomonas spp. The oxidative strain 413-Si2-L2 and the reisolate 06R2K were the most similar to strains of Pseudomonas putida and P. reidholzensis including the type strains. The strain, 413-MKV-3 and the reisolate 03R2K were the most related to Pseudomonas fluorescens, P. baetica, P. syringae, and Pseudomonas sp. strains. The ability of Enterobacter cloacae, Klebsiella pneumoniae and Kosakonia cowanii to cause disease on melon fruit was shown for the first time in this study by fulfilling Koch postulate. Furthermore, although limited rind necrosis was produced, pathogenicity of the fluorescent pseudomonads on melon fruit was also confirmed. [ABSTRACT FROM AUTHOR]

A total of 87 FPs have been isolated from tomato (Lycopersicon esculentum) rhizosphere and evaluated by dual plate assay method for the antimicrobial activity of Ralstonia solanacearum. Of which, 30 FPs showed antagonistic activity against R. solanacearum with the zone of inhibitions (ZOI) ranging from 19 mm to 28 mm. Similarly, antagonistic FPs significantly controlled various fungal phytopathogens such as Rhizoctonia solani (6.3 mm−20 mm), Macrophomina phaseolina (8.7 mm−19.3 mm), Fusarium oxysporum (7.3 mm−30.7 mm), and Sclerotium rolfsii (5.3 mm−21 mm). The cell-free culture filtrate of Pseudomonas sp VSMKU3054 significantly suppressed the fungal pathogens and increased the root and shoot length of the tomato seedlings compared to the control. Furthermore, the antagonistic FPs effectively produced lytic enzymes and antimicrobial traits such as amylase (6), protease (30), cellulase (28), pectinase (12), chitinase (22), gelatinase (27), siderophore (28), hydrogen cyanide (25), phosphate solubilization (30), and Indole acetic acid (IAA) (23). Genetic diversity of FPs was assessed by BOX-PCR with specific primers revealed that two distinct clusters were observed, whereas, RFLP analyses were showed that 5 to 16 bands ranged from 75 bp to 1.2 bp with two major clusters using restriction enzyme HaeIII. The antibiotic encoding genes were detected from FPs, of which 10 FPs were positive for 2,4-diacetylphloroglucinol (DAPG), 9 FPs were positive for pyoleuterin (PLT), 10 FPs were positive for hydrogen cyanide (HCN) and none of them obtained pyrrolnitrin (PRN) with respective primers. Based on the superior antagonistic isolates against R. solanacearum and phytofungal pathogens and other antimicrobial traits, the isolate VSMKU3054 was selected for further studies. Based on the morphological, physiological and 98% of 16 s rDNA sequence similarity, the selected isolate VSMKU3054 was identified as Pseudomonas fluorescens. Further, the potential isolate P. fluorescens VSMKU3054 and cell free culture filtrate remarkably enhance tomato seedling growth such as root and shoot length, fresh and dry weight and vigor index compared to control. This study indicated that rhizospheric isolates of FPs have more potential for plant growth promotion and plant protection from plant pathogenic microbes.

Phytopathogenic Verticillia cause Verticillium wilt on numerous economically important crops. Plant infection begins at the roots, where the fungus is confronted with rhizosphere inhabiting bacteria. The effects of different fluorescent pseudomonads, including some known biocontrol agents of other plant pathogens, on fungal growth of the haploid Verticillium dahliae and/or the amphidiploid Verticillium longisporum were compared on pectin-rich medium, in microfluidic interaction channels, allowing visualization of single hyphae, or on Arabidopsis thaliana roots. We found that the potential for formation of bacterial lipopeptide syringomycin resulted in stronger growth reduction effects on saprophytic Aspergillus nidulans compared to Verticillium spp. A more detailed analyses on bacterial-fungal co-cultivation in narrow interaction channels of microfluidic devices revealed that the strongest inhibitory potential was found for Pseudomonas protegens CHA0, with its inhibitory potential depending on the presence of the GacS/GacA system controlling several bacterial metabolites. Hyphal tip polarity was altered when V. longisporum was confronted with pseudomonads in narrow interaction channels, resulting in a curly morphology instead of straight hyphal tip growth. These results support the hypothesis that the fungus attempts to evade the bacterial confrontation. Alterations due to co-cultivation with bacteria could not only be observed in fungal morphology but also in fungal transcriptome. P. protegens CHA0 alters transcriptional profiles of V. longisporum during 2 h liquid media co-cultivation in pectin-rich medium. Genes required for degradation of and growth on the carbon source pectin were down-regulated, whereas transcripts involved in redox processes were up-regulated. Thus, the secondary metabolite mediated effect of Pseudomonas isolates on Verticillium species results in a complex transcriptional response, leading to decreased growth with precautions for self-protection combined with the initiation of a change in fungal growth direction. This interplay of bacterial effects on the pathogen can be beneficial to protect plants from infection, as shown with A. thaliana root experiments. Treatment of the roots with bacteria prior to infection with V. dahliae resulted in a significant reduction of fungal root colonization. Taken together we demonstrate how pseudomonads interfere with the growth of Verticillium spp. and show that these bacteria could serve in plant protection.

Phytopathogenic Verticillia cause Verticillium wilt on numerous economically important crops. Plant infection begins at the roots, where the fungus is confronted with rhizosphere inhabiting bacteria. The effects of different fluorescent pseudomonads, including some known biocontrol agents of other plant pathogens, on fungal growth of the haploid Verticillium dahliae and/or the amphidiploid Verticillium longisporum were compared on pectin-rich medium, in microfluidic interaction channels, allowing visualization of single hyphae, or on Arabidopsis thaliana roots. We found that the potential for formation of bacterial lipopeptide syringomycin resulted in stronger growth reduction effects on saprophytic Aspergillus nidulans compared to Verticillium spp. A more detailed analyses on bacterial-fungal co-cultivation in narrow interaction channels of microfluidic devices revealed that the strongest inhibitory potential was found for Pseudomonas protegens CHA0, with its inhibitory potential depending on the presence of the GacS/GacA system controlling several bacterial metabolites. Hyphal tip polarity was altered when V. longisporum was confronted with pseudomonads in narrow interaction channels, resulting in a curly morphology instead of straight hyphal tip growth. These results support the hypothesis that the fungus attempts to evade the bacterial confrontation. Alterations due to co-cultivation with bacteria could not only be observed in fungal morphology but also in fungal transcriptome. P. protegens CHA0 alters transcriptional profiles of V. longisporum during 2 h liquid media co-cultivation in pectin-rich medium. Genes required for degradation of and growth on the carbon source pectin were down-regulated, whereas transcripts involved in redox processes were up-regulated. Thus, the secondary metabolite mediated effect of Pseudomonas isolates on Verticillium species results in a complex transcriptional response, leading to decreased growth with precautions for self-protection combined with the initiation of a change in fungal growth direction. This interplay of bacterial effects on the pathogen can be beneficial to protect plants from infection, as shown with A. thaliana root experiments. Treatment of the roots with bacteria prior to infection with V. dahliae resulted in a significant reduction of fungal root colonization. Taken together we demonstrate how pseudomonads interfere with the growth of Verticillium spp. and show that these bacteria could serve in plant protection. [ABSTRACT FROM AUTHOR]

Aims: This study aimed to isolate and evaluate the indigenous fluorescent Pseudomonas spp. with bio-control potential against Rhizoctonia solani and promoting growth in chilli seedlings. Methodology: A total of 120 fluorescent bacterial were isolated from the healthy chilli rhizosphere soil from the seven major chilli cultivation localities in Terengganu, Malaysia. Only 115 Gram negative fluorescent isolates were further invitro screened for antagonistic activities against R. solani and plant growth-promoting properties. The 50 most effective fluorescent Pseudomonads antagonist against R. solani with minimum percentage inhibition of radial growth (PIRG) of 65% were selected. Hierarchical cluster analysis was further conducted with two dendrograms derived from SPSS Statistic 20 to facilitate the comparison between these 50 isolates for antagonistic and growth-promoting properties. A total of 40 fluorescent isolates within the most potential cluster were further selected and identified using 16S rRNA sequencing. Thirty four fluorescent isolates were identified as Pseudomonas spp. and six isolates as Burkholderia spp. The top 13 ranked fluorescent Pseudomonas spp. from the scoring index were evaluated for seed germination and vigor index in chilli seedlings. There was no significant difference in germination rate between fluorescent Pseudomonas inoculated with control. However, vigor index of chilli seeds pre-inoculated with fluorescent P. putida (B5C1), P. aeruginosa (B3C56) and P. putida (B5C7) were significantly increased with 4684.9, 4657.3 and 4401.0 over control (P = 0.05). Conclusion, significance and impact of study: These selected fluorescent isolates: P. putida (B5C1), P. aeruginosa (B3C56) and P. putida (B5C7) have the potential to be developed as biofungicide against R. solani and as growthpromoter in chilli production system. [ABSTRACT FROM AUTHOR]

We have shown, the outcome of antifungal activity of phenazine derivatives which is produced by fluorescent pseudomonads (FPs) for the control of sheath blight of rice. A total of 50 fluorescent pseudomonads (FPs) were isolated from rice rhizosphere. Off which, 36 FPs exhibited antagonistic activity against Rhizoctonia solani , Macrophomina phaseolina , Fusarium oxysporum , Alternaria alternata and Sclerotium rolfsii up to 70–80% compared to control by dual culture method. BOX-PCR analyses of antagonistic isolates indicated that two phylogenetic group, where group I consisted of 28 isolates and eight isolates belongs to group II. Among 36 FPs, a total of 10 FPs revealed that the presence of phenazine derivatives on thin layer chromatography (TLC), which is coincided with that of authentic phenazine with R f value 0.57. Similar to TLC analysis, antibiotic encoding gene phenazine-1-carboxamide (PCN) was detected in 10 FPs by PCR analysis with respective primer. Among, PCN detected isolates of FPs, a significant biocontrol potential possessing isolate designated as VSMKU1 and it was showed prominent antifungal activity against R. solani and other tested fungal pathogens. Hence, the isolate VSMKU1 was selected for further studies. The selected isolate VSMKU1 was identified as Pseudomonas aeruginosa by 16S rDNA sequence analysis. The antifungal metabolite phenazine like compound produced by VSMKU1 was confirmed by UV, FT-IR and HPLC analysis. The phenazine compound from VSMKU1 significantly arrest the growth of R. solani compared to carbendazim by well diffusion method. The detached leaf assay showed remarkable inhibition of lesion height 80 to 85% by the treatments of culture (VSMKU1), cell free culure filtrate and phenazine like compound compared to control and other treatments was observed in detached leaves of rice. These results emphasized that VSMKU1 isolate can be used as an alternative potential biocontrol agent against sheath blight of rice, instead of using commercial fungicide such as validamycin and carbendazim which cause environmental pollution and health hazards. [ABSTRACT FROM AUTHOR]

Possibility of manipulating some of the efficient strains of fluorescent pseudomonads to manage the root-infecting pathogens of maize was studied throughout this study. Out of 110 isolates 24 of Pseudomonas species, recovered from the plant rhizosphere showed to have inhibitory effect against two major root-infecting pathogens of maize, namely Cephalosporium maydis and Fusarium verticillioides in vitro. Pot experiment revealed that just 4 isolates could reduce infection with both pathogens and enhance the plant growth as well. Based on the genotypic identifications of these four isolates showed that they were: Pseudomonas putida strain Pau9, P. putida strainPau11, P. putida strain Psf3 and P. aeruginosa strain Psf9.

Native fluorescent Pseudomonas isolates from the rhizosphere of various crops grown in the state of Karnataka in southern India were isolated, identified and screened for their ability to act as biological control agents for economically important fungal plant pathogens. Ninety two Pseudomonas isolates were isolated from the rhizosphere soil of different crop plants from the farms of the University of Agricultural Sciences, Raichur (India) and surrounding villages, Dharwad and IIHR, Bangalore using specific medium. All the isolates were found to be gram-negative rods. Among these, 66 isolates produced the characteristic yellow pigmentation and showed fluorescence. The isolates were categorized into four groups based on siderophore production (high, moderate, low and no production) and evaluated for the presence of pvdA, phl and plt genes associated with siderophore production, DAPG and pyoluteorin respectively. None of them appeared to carry the pvdA and plt genes. However, one isolate RPF-13 was found to carry the phl gene based on gene specific PCR results. This DAPG+ve isolate was identified as Pseudomonas putida by 16s r DNA sequence analysis. This paper reports the identification of one of the few highly effective DAPG producing Pseudomonas isolates from southern India that can be used biological control in addition to the identification and characterization of several other fluorescent Pseudomonads with potential to serve as bio-control agents against a number of important pathogenic fungal species.

Fusarium wilt caused by Fusarium oxysporum f. sp. niveum (FON) is a destructive soilborne disease commonly found in watermelon producing areas throughout the world. At present, the control of Fusarium wilt depends heavily on host resistance and chemical fungicide application. In this study, we isolated fluorescent pseudomonads from the rhizosphere of healthy watermelon and evaluated their biocontrol capacity against FON race 2. Biochemical assays indicated that all 14 fluorescent Pseudomonas strains were able to produce indole-3-acetic acid and at least one type of biosurfactants. Both sulphur oxidising and proteolytic activities were exhibited in 2 of the 14 strains. However, none of them could synthesise phenazine antibiotics. Seven strains with different morphological and biochemical characteristics were identified by sequencing the rpoB gene. Among those, one was Pseudomonas resinovorans (WMT16-1-1), two were P. putida (WMC16-1-1 and WMC16-2-5), one was P. fluorescens (WMC16-1-8) and others were Pseudomonas sp. In vitro studies indicated that WMC16-1-1, WMC16-1-8 and WMC16-2-5 inhibited mycelial growth of FON significantly. Detection of biosynthetic loci of 2,4-diacetylphloroglucinol (DAPG), pyrrolnitrin and pyoluteorin using specific primers indicated that the three strains could not produce the antibiotics. In greenhouse studies, WMC16-1-1, WMC16-1-8 and WMC16-2-5 reduced the severity of Fusarium wilt significantly with WMC16-1-1 being the most effective. Inoculation with WMC16-2-5 resulted in the significantly greater weight of both stems and roots compared to the nontreated control, while WMC16-1-1 resulted in greater stem weight. Pseudomonas strains WMC16-1-1, WMC16-1-8 and WMC16-2-5 are potential candidates for controlling Fusarium wilt and promoting the growth of watermelon. [ABSTRACT FROM AUTHOR]

Introduction:Fluorescent pseudomonads produced a variety of siderophores in which the pyoverdine type siderophore is the main one. These bacteria employ siderophores to increase availability of Iron for their own and plants consumption. Siderophores have a special role in the biological control activity of these bacteria against plant pathogens. Materials and methods: Siderophore production was checked in 21 indigenous Pseudomonads strains, two reference strains and one Bacillus sp. strain by qualitative CAS-Agar, semi-quantitative CAS-AD and quantitative spectrophotometric methods. Results: Colony growth in some of isolates such as UTPF93 has been inhibited in CAS-Agar method because of the detergent compound HDTMA. So, siderophore production was low in these strains. All strains produced siderophore by the CAS-AD method. The highest and the lowest siderophore production were recorded in UTPF76 and UTPF45 with 1.005 and 0.0026 mM of defroxamin equivalent, respectively. The Pyoverdine mutant strain MPFM1 and the Bacillus sp. strain also produce low amounts of siderophore in two recent methods. So, these methods are non-selective to the type of siderophore. In quantitative method only Pyoverdine type siderophore was detectable and the strains MPFM1 and Bacillus sp. did not produce this type of siderophore. The highest amount of pyoverdine was recorded in non-indigenous strain 7NSK2 with 625.29 mM/L followed by UTPF65, UTPF81 and UTPF87. Discussion and conclusion: CAS-AD was the best method for total siderophore measurement and spectrophotometric was the accurate and efficient method for detection of pyoverdine type siderophore in fluorescent pseudomonads.

Pseudomonas sp. are known to be good Plant Growth Promoting Rhizobacteria (PGPR). In this study, Pseudomonas sp. were isolated from soil planted with kuini (Mangifera odorata) using soil dilution method and spread onto King's B media. Five isolates of Pseudomonas sp. were observed to give promising results in the phytohormone and antimicrobial test conducted. These isolates are Pseudomonas sp. isolate K24pf, K29pf, K32pf, K33pf and K37pf. From the 5 potential isolates, Pseudomonas sp. isolate K29pf was chosen because it showed potential activity in producing marked amounts of Indole-3-Acetic Acid and gibberellic acid. Pseudomonas sp. isolate K29pf also produced antimicrobial activities towards Ralstonia solanacearum, Erwinia caratovora, Erwinia mallotivora and Colletotrichum gloeosporioides. Seed germination test showed that Pseudomonas sp. isolate K29pf was able to promote approximately 90% growth of Brassica chinensis seeds. Pot trial conducted showed that Treatment 3 (+OF+PGPR) was able to increase Brassica chinensis root by 36.5% and 28.4% of its biomass compared to treatment using Treatment 1 (+OF). [ABSTRACT FROM AUTHOR]

Soil phosphorous (P) deficiency is a major constraint to plant production which is overcome by adding inorganic-phosphate as chemical fertilizers. Fluorescent pseudomonads are the diverse group of bacteria able to mobilize sparingly soluble phosphate form. Total three hundred seven fluorescent Pseudomonas isolates were obtained from the Aloe barbadensis (Miller) rhizosphere. These Pseudomonas strains were further evaluated in vitro for their ability to solubilize phosphate and to produce indole acetic acid (IAA), hydrogen cyanide (HCN), siderophore and 1-aminocyclopropane 1- carboxylate (ACC) deaminase. Fifty three (36.8%) isolates produced IAA and 52 (36.1%) isolates produced siderophores whereas 36 (25.0%) and 31 (21.5%) isolates produced HCN and ACC deaminase, respectively. A positive correlation existed between siderophore and ACC deaminase producers. Cluster analysis showed rhizosphere as the major factor influencing the ecological distribution and physiological characterization of phosphate solubilizing bacteria (PSB). Based on partial 16S rRNA gene sequencing PSB were identified as Pseudomonas putida, Pseudomonas sp. and Pseudomonas plecoglossicida with highest phosphate solubilization ability. In conclusion, these phosphate solubilizing fluorescent pseudomonads would help in understanding their role in phosphorus solubilization and identification of potent phosphorus solubilizers from the rhizosphere of commercially grown A. barbadensis. [ABSTRACT FROM AUTHOR]

Plant growth promoting rhizobacteria (PGPR) belonging to the group “fluorescent pseudomonads” play very important role in sustainable agriculture. They are well known to assist plants’ health by diverse mechanisms. Potential of fluorescent pseudomonads to protect plants from a range of phytopathogens is of prime importance and gained momentum in agri-biotechnology. At global level commercialization of fluorescent pseudomonads in the form of bioinoculants for the management of several plant diseases is now considered to be very effective. Fluorescent pseudomonads are being used as effective biocontrol agents (BCA) against an array of phytopathogens. They have great potential as BCA because of the ability to produce a variety of secondary metabolites. Therefore, the objective of this review is to describe and assess the roles of secondary metabolites produced by fluorescent pseudomonads in controlling the phytopathogens and enhancing the plant health. Prominent secondary metabolites involved in biocontrol by fluorescent pseudomonads include phenazines (PHZ), 2, 4-diacetylphloroglucinol (DAPG), pyoluteorin (PLT), pyrrolnitrin (PRN), cyclic lipopeptides (CLPs) and volatile organic compounds (VOCs) such as hydrogen cyanide (HCN). These metabolites are known for antifungal, antibacterial, antiviral, antitumor and anti-nematicidal properties. Better contemporary techniques for extraction, purification and characterization may unveil the mechanisms of action of these metabolites and enable to utilize them in future bioformulations so as to replace harmful synthetic chemicals (in agriculture). [ABSTRACT FROM AUTHOR]

Fluorescence-based reporter systems are valuable tools for studying gene expression dynamics in living cells. Here we describe a dual-fluorescence reporter system carrying the red fluorescent marker mCherry and the blue fluorescent protein EBFP2 enabling the simultaneous analysis of two promoters in broad-host range autofluorescent Gram-negative bacteria. [ABSTRACT FROM AUTHOR]

Possibility of manipulating some of the efficient strains of fluorescent pseudomonads to manage the root-infecting pathogens of maize was studied throughout this study. Out of 110 isolates 24 of Pseudomonas species, recovered from the plant rhizosphere showed to have inhibitory effect against two major root-infecting pathogens of maize, namely Cephalosporium maydis and Fusarium verticillioides in vitro. Pot experiment revealed that just 4 isolates could reduce infection with both pathogens and enhance the plant growth as well. Based on the genotypic identifications of these four isolates showed that they were: Pseudomonas putida strain Pau9, P. putida strain Pau11, P. putida strain Psf3 and P. aeruginosa strain Psf9. [ABSTRACT FROM AUTHOR]

Native fluorescent Pseudomonas isolates from the rhizosphere of various crops grown in the state of Karnataka in southern India were isolated, identified and screened for their ability to act as biological control agents for economically important fungal plant pathogens. Ninety two Pseudomonas isolates were isolated from the rhizosphere soil of different crop plants from the farms of the University of Agricultural Sciences, Raichur (India) and surrounding villages, Dharwad and IIHR, Bangalore using specific medium. All the isolates were found to be gram-negative rods. Among these, 66 isolates produced the characteristic yellow pigmentation and showed fluorescence. The isolates were categorized into four groups based on siderophore production (high, moderate, low and no production) and evaluated for the presence of pvdA, phl and plt genes associated with siderophore production, DAPG and pyoluteorin respectively. None of them appeared to carry the pvdA and plt genes. However, one isolate RPF-13 was found to carry the phl gene based on gene specific PCR results. This DAPG+ve isolate was identified as Pseudomonas putida by 16s r DNA sequence analysis. This paper reports the identification of one of the few highly effective DAPG producing Pseudomonas isolates from southern India that can be used biological control in addition to the identification and characterization of several other fluorescent Pseudomonads with potential to serve as bio-control agents against a number of important pathogenic fungal species [ABSTRACT FROM AUTHOR]

In soil, plant roots coexist with bacteria and fungi that produce siderophores capable of sequestering the available iron. Microbial cyanogenesis has been demonstrated in many species of fungi and in a few species of bacteria (e.g., Chromobacterium and Pseudomonas). Fluorescent Pseudomonas isolates P29, P59, P144, P166, P174, P187, P191 and P192 were cyanogenic and produced siderophores in the presence of a strong chelater 8-Hydroxyquinoline (50 mg/l). A simple confrontation assay for identifying potential antagonists was developed. Fluorescent Pseudomonas isolates P66, P141, P144, P166 and P174 were antagonistic against both Rhizoctonia solani and Sclerotium rolfsii. Vigorous plant growth was observed following seed bacterization with P141, P200 and P240. In field experiments, seed bacterization with selected bacterial isolates resulted in reduced collar rot ( S. rolfsii) incidence. [ABSTRACT FROM AUTHOR]

Many species or strains of the genus Pseudomonas have been characterized as plant growth promoting rhizobacteria (PGPR). We used a combination of phenotypic and genotypic techniques to analyze the community of fluorescent Pseudomonas strains in the rhizosphere of commercially grown Mentha piperita (peppermint). Biochemical techniques, Amplified rDNA Restriction Analysis (ARDRA), and 16S rRNA gene sequence analysis revealed that the majority of the isolated native fluorescent strains were P. putida. Use of two Repetitive Sequence-based PCR (rep-PCR) techniques, BOX-PCR and ERIC-PCR, allowed us to evaluate diversity among the native strains and to more effectively distinguish among them. PGPR activity was tested for the native strains and reference strain P. fluorescens WCS417r. Micropropagated M. piperita plantlets were exposed to microbial volatile organic compounds (mVOCs) emitted by the bacterial strains, and plant biomass parameters and production of essential oils (EOs) were measured. mVOCs from 11 of the native strains caused an increase in shoot fresh weight. mVOCs from three native strains (SJ04, SJ25,SJ48) induced changes in M. pierita EO composition. The mVOCs caused a reduction of metabolites in the monoterpene pathway, for example menthofuran, and an increase in menthol production. Menthol production is the primary indicator of EO quality. The mVOCs produced by native strains SJ04, SJ25,SJ48 and strain WCS417r were analyzed. The obtained mVOC chromatographic profiles were unique for each of the three native strains analyzed, containing varying hydrocarbon, aromatic, and alogenic compounds. The differential effects of the strains were most likely due to the specific mixtures of mVOCs emitted by each strain, suggesting a synergistic effect occurs among the compounds present.

Orfamide-type cyclic lipopeptides (CLPs) are biosurfactants produced by Pseudomonas and involved in lysis of oomycete zoospores, biocontrol of Rhizoctonia and insecticidal activity against aphids. In this study we compared the biosynthesis, structural diversity, in vitro and in planta activities of orfamides produced by rhizosphere-derived Pseudomonas protegens and related Pseudomonas species. Genetic characterization together with chemical identification revealed that the main orfamide compound produced by the P. protegens group is orfamide A, while the related strains Pseudomonas sp. CMR5c and CMR12a produce orfamide B. Comparison of orfamide fingerprints led to the discovery of two new orfamide homologues (orfamide F and orfamide G) in Pseudomonas sp. CMR5c. The structures of these two CLPs were determined by nuclear magnetic resonance (NMR) and mass spectrometry (MS) analysis. Mutagenesis and complementation showed that orfamides determine the swarming motility of parental Pseudomonas sp. strain CMR5c and their production was regulated by luxR type regulators. Orfamide A and orfamide B differ only in the identity of a single amino acid, while orfamide B and orfamide G share the same amino acid sequence but differ in length of the fatty acid part. The biological activities of orfamide A, orfamide B and orfamide G were compared in further bioassays. The three compounds were equally active against Magnaporthe oryzae on rice, against Rhizoctonia solani AG 4-HGI in in vitro assays, and caused zoospore lysis of Phytophthora and Pythium. Furthermore we could show that orfamides decrease blast severity in rice plants by blocking appressorium formation in M. oryzae. Taken all together, our study shows that orfamides produced by P. protegens and related species have potential in biological control of a broad spectrum of fungal plant pathogens.

Thirty isolates of fluorescent pseudomonads were obtained from rhizosphere of different crops in Raichur, India. The fluorescent pseudomonad strains were characterized in vitro for biochemical traits, antimicrobial traits, and pyoluteorin antibiotic production. All the isolates that showed fluorescent pigment production under UV light were rod shaped, Gram negative, positive for oxidase, catalase and citrate utilization tests, and negative for indole test. Out of 30 isolates, 07 isolates were positive for HCN production, 15 isolates were positive for HS production, and all the isolates were positive for siderophore production. Among all the isolates, RFP-22 showed the maximum percent inhibition of mycelium (46.66 %) of Rhizoctonia solani, the pathogen, and the remaining isolates showed the moderate to least inhibition of mycelium growth of R. solani. The 16S rRNA analysis confirmed that the antibiotic positive isolates belonged to genus Pseudomonas. The amplification of 779 bp region in isolates RFP- 4 and RFP-19 corresponded to pyoluteorin antibiotic-coding pltB gene. Further characterization of pyoluteorin antibiotic through TLC and TOF-MS analysis confirmed the presence of pyoluteorin at 274.26 (g/mol) peak and 2.10 min retention time. Biochemical and molecular analyses confirmed the antagonism of Pseudomonas and isolate through pyoluteorin production. [ABSTRACT FROM AUTHOR]

Verticillium wilt of olive (Olea europea L.) caused by Verticillium dahliae is difficult to manage and control in Algeria and worldwide. The present investigation was undertaken to search indigenous pseudomonads population in the Algerian habitats for isolates with potential antagonism against V. dahliae. Twenty one indigenous isolates of fluorescent pseudomonads were obtained from the rhizosphere and non-rhizosphere field soil under healthy and Verticillium-infected olive orchards at different locations in Algeria (Boumerdes, Tizi ouzou, Bouira). The phenotypic diversity of those isolates was characterized according to their biochemical and physiological properties and their genotypic div ersity was ascertained on the basis of their repetitive extragenic palindromic patterns by PCR technology. Numerical analysis of that Characterization showed clustering of those isolates and high level of similarity (80%) among all of them. Their antagonistic activity in vitro against two pathogenic isolates of V. dahliae belonging to defoliating and non-defoliating pathotypes, respectively was bio-assayed on two types of culture media (KB and PDA). Seven isolates caused total inhibition of mycelium growth and microsclerotia formation on KB medium. Ten isolates caused only inhibition of microsclerotia formation on PDA medium. [ABSTRACT FROM AUTHOR]

Soil samples were collected from different rhizosphere plants grown in SEKEM farm, Bilbis, El-Sharkyia governorate, Egypt. Four fluorescent pseudomonads isolates, out of seventy one, were selected according to their efficiency to produce IAA, cyanide, antagonistic effect and high ability to solubilize potassium and phosphorus. These isolates were identified using 16S rRNA gene sequencing technique to be different strains of Pseudomonas otitidis . Growth curve and growth kinetics were determined on king’s broth medium. Ps. otitidis SE8 gave the highest specific growth rate, multiplication rate and number of generation being 0.287 h −1 , 0.4147 h −1 and 4.98 h −1 , respectively. This strain also showed the lowest of doubling time. Ps. otitidis SE8 and OL2 had higher activity to solubilize phosphorus than other tested strains. Bacterial strain SE8 also gave a considerable amount of soluble potassium as compared with other strains being 80.7 ppm. The maximum IAA and gibberellic acid production was also recorded by Pseudomonas SE8 and OL2. A remarkable quantity of siderophores was detected in the case of Ps. otitidis SE8 being 28.20 mM DFOM. Application of these isolates as inoculants for tomato plants in green house was performed. The results showed that inoculation of tomato seedling with Pseudomonas strains led to suppress the soil-borne pathogen, increased of NPK uptake and supported tomato plant growth. [ABSTRACT FROM AUTHOR]

Many Pseudomonas species promote plant growth and colonize a wide range of environments. The annotation of a Coffea arabica ESTs database revealed a considerable number of Pseudomonas sequences. To evaluate the genomic and physiology of Pseudomonas that inhabit coffee plants, fluorescent Pseudomonas from C. arabica root environment were isolated. Two of them had their genomes sequenced; one from rhizospheric soil, named as MNR3A, and one from internal part of the root, named as EMN2. In parallel, we performed biochemical and physiological experiments to confirm genomic analyses results. Interestingly, EMN2 has achromobactin and aerobactin siderophore receptors, but does not have the genes responsible for the production of these siderophores, suggesting an interesting bacterial competition strategy. The two bacterial isolates were able to degrade and catabolize plant phenolic compounds for their own benefit. Surprisingly, MNR3A and EMN2 do not contain caffeine methylases that are responsible for the catabolism of caffeine. In fact, bench experiments confirm that the bacteria did not metabolize caffeine, but were resistant and chemically attracted to it. Furthermore, both bacteria, most especially MNR3A, were able to increase growth of lettuce plants. Our results indicate MNR3A as a potential plant growth promoting bacteria. [ABSTRACT FROM AUTHOR]

Aims: Pseudomonas sp. CMR12a is an effective biocontrol agent that produces various antifungal metabolites including phenazine antibiotics and cyclic lipopeptides. In this study, we wanted to investigate the influence of substrate composition on the role of phenazines and the cyclic lipopeptide (CLP) sessilin in biocontrol of bean root rot caused by Rhizoctonia solani AG 2-2. Methods: Disease severity and spreading rate of R. solani were determined in three substrates, containing different ratios of potting soil and sand, inoculated with Pseudomonas sp. CMR12a or its mutants impaired in phenazine and/or sessilin biosynthesis. Results: In the mixtures containing 50 or 75 % of potting soil, the presence of either phenazines or sessilin was sufficient to suppress bean root rot. However, in the mixture containing only 25 % of potting soil, the involvement of both compounds was required to provide better protection. The ratio between potting soil and sand also determined the spreading rate of Rhizoctonia hyphae. The mixture containing 75 % of potting soil was the most suppressive against R. solani invasion. Conclusions: The use of various potting soil/sand combinations affected the development of bean root rot disease but Pseudomonas sp. CMR12a effectively controlled the disease in all substrates. Depending on the disease pressure, however, the production of either phenazines or sessilin, or both compounds is required for effective biocontrol. [ABSTRACT FROM AUTHOR]

Genetic systems of salicylate catabolism were studied in 75 strains of fluorescent pseudomonads and in 30 exogenously isolated SAL plasmids. All exogenously isolated SAL plasmids were found to contain the classical nahG gene in combination with the genes of the meta-pathway of catechol cleavage. In most studied strains, salicylate catabolism was controlled by the chromosomal genes, the nahU gene being the key gene of salicylate utilization and subsequent catechol cleavage occurring via the ortho-pathway. It is suggested that the nahU-like sequences play a key role in occurrence of the Sal phenotype in strains degrading salicylate, but not naphthalene. [ABSTRACT FROM AUTHOR]

The System of Rice Intensification (SRI) is an innovative method of rice (Oryza sativa) cultivation that combines many farm practices. Though the benefits of SRI are obvious, the underlying principles in enhanced yields are not yet scientifically analyzed. Two important components of SRI are keeping the rice field moist without flooding and frequent weeding out practices that enhance the aerobic conditions which in turn improve soil biological activity including enhanced root growth and activity of aerobic soil organisms. We have taken up the present investigations, with the premise that soil microorganisms especially fluorescent pseudomonads (FLPs), whose role in enhancement of plant growth is unequivocal, may contribute to the enhanced growth and yield of rice cultivated under SRI.The results of present investigations revealed that rice cultivated under SRI harboured more the population of FLPs in rhizosphere than non-rhizosphere soil. Screening of rhizospheric FLPs isolates has revealed that many of the isolates possessed the ability of producing growth promoting substances like IAA, GA, siderophores, 'p'solubilization. Some selected strains have also shown resistance towards heavy metals, salts and pH. They have also exhibited significant antifungal activity and enhanced the seed germination and efficient root colonization. Further, artificial inoculations have also clearly shown to enhance the growth in terms of height, dry weight of shoot and root. Thus, the results substantiate the role of FLPs for the enhanced growth and yield of rice cultivated under SRI. [ABSTRACT FROM AUTHOR]

Chili (Capsicum annuum L.) is one of the vegetable commodities with high economic value. Until now, the necessity rate of chili is still high but the production is still low. One of the obstacles, which highly influence chili production, is wilt disease due to Ralstonia solanacearum and Fusarium oxysporum. This study aims at identifying the best fluorescent pseudomonads isolate in suppressing the development of the primary wilt disease due to Ralstonia solanacearum and F. oxysprorum in the field. This study employs Completely Randomized Design that comprises 3 treatments. The three treatments are the type of fluorescent pseudomonads which is Pf-122 isolate, Pf-160 isolate, and Pf-B isolate. The observation parameter on suppressing the disease development is perceived from incubation period of the initial appearance of symptoms, disease index and the change of stem tissue color. The result of the study shows that the longest incubation period is treatment with fluorescent pseudomonads of Pf-122 isolate and Pf-160 isolate. The chili is treated with fluorescent pseudomonads of Pf-122 isolate and Pf-160 isolate, the initial appearance of symptoms at the 8th day after inoculation. In the treatment with fluorescent pseudomonads of Pf-122 isolate and Pf-160 isolate compared to control, is able to delay the appearance of symptom for 3 days. The disease development starts from 10th to 30th day, the treatment with Pf-122 isolate shows the slowest development compared to other treatment and control. In the last observation, the disease index with treatment of Pf-122 isolate is the lowest which is 37%, then it is followed by Pf-B and Pf-160 which are 39% and 40% respectively, whereas in the control it reaches 67%. For the color change on stem tissue, there is no real difference of the three treatments of fluorescent pseudomonads application but it differs and smaller from the control.

Highlights: [•] Fed-batch strategies were used for simultaneous production of pseudomonad bioinoculants and DAPG. [•] Exponential feeding caused substrate inhibition during cultivation. [•] pH-signal based feeding resulted in high biomass production as well as DAPG. [•] The dual use of pH signals for substrate feeding as well as for pH control was successfully carried out. [ABSTRACT FROM AUTHOR]

Some Pseudomonas fluorescens strains, consistently isolated from the rhizosphere of wild plants grown in a soil that was highly polluted with illegal waste of smelter residues, were utilised for Mirabilis jalapa seed bioinoculation to verify their effects on seed germination and on promoting a higher heavy metal accumulation in the plant rhizosphere and/or uptake in the leaves. The high content of heavy metals in the soil induced a decrease in either the leaf dry weight or photosynthetic pigment concentration during all vegetative phase of M. jalapa. Bioinoculation with P. fluorescens strains significantly increased the germination of seeds and the root length in the contaminated soil. In some bacterial strain/seed combination, bioinoculation significantly increased the accumulation of heavy metals in M. jalapa rhizosphere. For Cd, the concentration of this metal in the rhizospheres of bioinoculated plants ranged from 270 to 910 μg g of dry weight compared with 200 μg g of dry weight for the non-coated plants. Two P. fluorescens strains, AA27 and MO49, which were isolated from Artemisia annua and Melilotus officinalis, respectively, induced a significantly higher rhizosphere availability also for Cr, Cu, Ni and Zn. However, despite the relevant accumulation of the heavy metals in the plant rhizosphere, generally the metal uptake into the leaves was rather low. Both analysis of variance and principal component analysis confirmed this finding. However, one P. fluorescens strain, CD1, which was isolated from the multi-metal accumulator Cynodon dactylon, significantly promoted the M. jalapa leaf uptake for Cr, Cu and Zn. The plant metal uptake assessment, confirmed the per se capability of M. jalapa to effectively uptake Cd (30 %) and Cu (12.72 %) from the rhizosphere to the leaves, whereas the uptake for the other metals was low: Ni (2.66 %), Zn (2.46 %), Cr (1.75 %), Pb (0.73 %). [ABSTRACT FROM AUTHOR]

Despite the importance of antibiosis in biological control, little is known about the genes involved in antifungal activity. Therefore, the present study was aimed at identifying the location of the antagonistic gene(s) in Pseudomonas aeruginosa FP6 towards Rhizoctonia solani and Colletotrichum gloeosporioides using a PCR-based approach. A new bacterial strain, designated as FP6, was isolated from rhizospheric soil and identified as a member of Pseudomonas aeruginosa based on 16S rRNA analysis. The secondary metabolites produced by this strain have shown broad-spectrum antifungal activity against Rhizoctonia solani and Colletotrichum gloeosporioides. Antifungal metabolites of a nonenzymatic nature were found to be responsible for the antagonism. Hyphal malformation was also observed in both of the fungal pathogens. PCR analysis of the genomic DNA with antibiotic specific primers detected phenazine-1-carboxylic acid, 2,4-diacetylphloroglucinol, and pyoluteorin. Plasmid isolation and plasmid curing of the strain exhibited varied antagonistic activity. A chromosomal gene was found to be involved in the production of a fungal antagonistic compound as demonstrated by the gel elution technique using antibiotic gene-specific primers. The study speculates that antimetabolites play an important role in the control of phytopathogens. [ABSTRACT FROM AUTHOR]

Abstract: The overall objective of the current study was to test two hypotheses: (1) application of the systemic fungicide Benlate to leatherleaf fern results in long-term increases in populations of deleterious fluorescent pseudomonads that endophytically colonize rhizomes; (2) such endophytic colonization, resulting from Benlate treatment, is associated with damage to leatherleaf fern and development of symptoms of fern distortion syndrome (FDS). Mean populations of fluorescent pseudomonads and total aerobic bacteria in the rhizosphere were significantly increased 3 months after the application of Benlate 50 WP and Benlate 50 DF as foliar sprays and drenches, compared to populations in the non-treated control. In another test, at 5 months after treatment, endophytic populations of fluorescent pseudomonads inside rhizomes of plants treated with Benlate 50 WP and Benlate 50 DF (both from DuPont) were significantly higher than populations in rhizomes of plants treated with three different generic sources of Benlate 50 WP, the active ingredient benomyl, and MBC. In the same test, treatments with the two DuPont sources of Benlate, but not the generic sources, benomyl, or MBC resulted in reduced overall growth of plants, including reductions weight of fronds, roots and rhizomes and caliper of rhizomes. Three long-term experiments examined the effect of Benlate 50 WP and Benlate 50 DF on populations of fluorescent pseudomonads and development of distortions of frond growth and other symptoms associated with FDS. In two tests at 24 months after application, treatment with both formulations of Benlate increased endophytic populations of fluorescent pseudomonads inside rhizomes, compared to controls, in both experiments, and endophytic populations inside petioles of fronds arising from rhizomes were significantly greater with both Benlate treatments in one test where this parameter was measured. Also at 24 months after application, the Benlate treatments were associated with significant increases in severity of FDS, using a previously reported rating scale and by measuring several other parameters associated with FDS. In the third long-term test, the first crop of fronds was cut 24 months after treatment. Four weeks later, the numbers of actively growing rhizomes (that had produced new fronds) were significantly reduced on Benlate-treated plants, compared to the controls. At 6 months after cutting (30 months after Benlate treatments), weights of fronds were lower on Benlate-treated plants than on controls. Characterization of fluorescent pseudomonads isolated from inside rhizomes and petioles at 24 months after treatment revealed that applications of Benlate resulted in a marked increase in pectinolytic activity. DNA sequencing of 150 strains of fluorescent pseudomonads from inside rhizomes and 60 from inside petioles at 24 months after application of Benlate indicated low matches to type strains in the ribosomal data base. Phylogenetic characterization of the strains indicated the existence of 10 clusters. Pronounced shifts in frequency of strains in the various clusters were noted with Benlate treatment: over 70% of strains from rhizomes of Benlate-treated plants belonged to cluster E3, compared to only 2% of the strains from control rhizomes, and 98% of the control strains belonged to clusters C, D2, F, and G, while none of the strains from petioles or rhizomes of Benlate-treated plants belonged to these four clusters. In summary, treatment of leatherleaf fern with Benlate 50 WP and Benlate 50 DF from DuPont led to a progression of long-term deleterious effects on leatherleaf fern that were associated with increased populations of fluorescent pseudomonads that were functionally and phylogenetically different from pseudomonads from control plants. [Copyright &y& Elsevier]

Fourteen bacterial isolates from the rhizosphere of potato plants growing near Sétif, (Algeria) were characterised as fluorescent Pseudomonads by phenotypical methods and one was identified as Pseudomonas chlororaphis by sequencing ribosomal DNA. In dual culture, this isolate inhibited the growth of the phytopathogenic fungi Fusarium oxysporum f. sp. lycopersici, F. oxysporum f. sp. albedinis, F. solani and Rhizoctonia solani and the oomycete Pythium ultimum. Extracts of supernatants from liquid cultures of the Ps. chlororaphis isolate completely inhibited these organisms when incorporated into potato dextrose agar at a rate equivalent to 0.31 ml culture filtrate/ml, or greater. In a disc assay, extracts equivalent to 0.31 ml supernatant gave inhibition zones of 15 mm and 25 mm for the Gram-positive bacteria Bacillus subtilis and Paracoccus paratrophus, respectively. Fractionation of extracts of supernatants by TLC and HPLC with diode array detection allowed the identification of phenazine carboxylic acid as one of the antimicrobial compounds and the tentative identification of two others as 2-hydroxy phenazine carboxylic acid and 2-hydroxy phenazine. [ABSTRACT FROM AUTHOR]

Occurrence of phase variation phenomenon in fluorescent pseudomonads resulted from the Sss and XerD recombinase activities that are encoded by sss and xerD genes, respectively. In this research, the effects of sss gene in enabling colonizing bacterial strains of fluorescent pseudomonads were investigated. Only 25 bacterial strains of fluorescent pseudomonads subjected to examined, 7 bacterial strains Um141, Um11, Um138, Um70, Um115, UmCHN5 and Pseudomonas fluorescens F113 were able to adopt themselves to root under various growing conditions and colonized the totality of wheat root parts. Finally, these strains reached to the end part of roots both in complete sterilized condition and in presence of Gaeumannomyces graminis var. tritici, the causal agent of take-all disease. The laboratory cultivation of these strains on King B and SA media, resulted in the appearance of colonies with various morphology. The polymeras chain reaction(PCR) experiment to monitore sss gene in 25 bacterial strains revealed that this gene was present in seven bacterial strains representing considerable root colonization. [ABSTRACT FROM AUTHOR]

ntagonistic fluorescent pseudomonads isolated from rice rhizospheric soil were characterized using biochemical, taxonomical and molecular tools. Production of cyclopropane fatty acid (CFA) was correlated with their antagonistic potential. Strains were grouped into 18 different genotypes on the basis of amplified ribosomal DNA restriction analysis (ARDRA) and repetitive (rep)-PCR based genotypic fingerprinting analyses. High phylogenetic resolution among antagonistic fluorescent pseudomonad strains was obtained based on the DNA gyrase B subunit ( gyrB) and RNA polymerase sigma factor 70 ( rpoD) gene sequence analyses. Combined gyrB and rpoD sequence analysis resulted in the accurate estimation of molecular phylogeny and provided a significant correlation between the genetic distances among strains. Present study demonstrated the genetic and functional relationship of fluorescent pseudomonads. The knowledge on genetic and functional potential of fluorescent pseudomonads associated with rice rhizosphere is useful to understand their ecological role and for their utilization in sustainable agriculture. [ABSTRACT FROM AUTHOR]

Abstract: Talc and aluminum silicate powders were used to develop inorganic carrier-based formulations of fluorescent pseudomonad strains R62 and R81. The aerobically cultivated cell-free broth of both the strains contained a hydroxamate-type siderophore and an antibiotic 2,4-diacetylphloroglucinol (DAPG). The formulations of these bioinoculants were able to bring the natural contaminants in the non-sterile carriers to acceptable limits in the presence of 54.6μgg−1 of siderophore and 10μgg−1 of DAPG. The shelf life of talc powder-based formulation was about 1 year in comparison to about 100 days for aluminum silicate-based formulation. Both sterile and non-sterile carrier formulations worked significantly well in comparison to their controls for growth of Vigna mungo and Triticum aestivum crops. Sterile talc powder-based formulation of strain R81 showed maximum increase in dry root weight, dry shoot weight, and root volume of Vigna mungo over that with aluminum silicate-based formulation. On Triticum aestivum, the growth response was better in the case of R62-treated seeds in comparison to treatment with R81. However, a consortium of talc powder formulation of R62 and R81 gave the best increase of 46% for sterile and non-sterile carriers in grain yield of Triticum aestivum over respective controls. [ABSTRACT FROM AUTHOR]

Although Rhizoctonia solani is a cosmopolitan soilborne pathogen, the genus includes isolates with different pathogenicity ranging from high virulence to avirulence. The biocontrol strain Pseudomonas fluorescens P190r and the arbuscular mycorrhizal (AM) fungus Glomus mosseae BEG12 were inoculated alone or in combination in tomato plants infested by the mildly virulent pathogen R. solani #235. Plant growth as well as root morphometric and topological parameters were evaluated. The infection of R. solani was significantly reduced by all the combinations of the beneficial microorganisms. Root systems of R. solani-infected plants were weakly developed but highly branched with a herring-bone pattern, while those inoculated with the AM fungus, alone or in combination with the bacterial strain, were longer and more developed, and displayed a dichotomous pattern. The interactions among these three microorganisms affected plant growth and root architecture of tomato plants. [ABSTRACT FROM AUTHOR]

Bacterial canker of tomato, caused by Clavibacter michiganensis subsp. michiganensis, continues to be a problem for tomato growers in the Souss-Massa Draa valley, South of Morocco. Assuming that biological control is an alternative for the management of this disease, a total of 303 fluorescent pseudomonads strains isolated from roots and rhizospheric soil of tomato plants were in vitro tested against C. michiganensis subsp . michiganensis. Fluorescent pseudomonads strains which showed the highest antagonistic properties were thereafter investigated for their ability to colonize tomato roots. Our results showed that fluorescent pseudomonads are more represented in rhizospheric soils. However, the most efficient fluorescent pseudomonads isolates were found in the rhizoplane soil and the endorhizosphere. Among 42 spontaneous antibiotic resistant mutants obtained by treatment of the wild-type isolates with five antibiotics (rifampicine, nalidixic acid, ampicilline and chloramphenicol), 28 completely colonized the roots of all tomatoes seedlings used in this investigation. The 42 wild type isolates were then used for in vivo screening with the cotyledon test. Using this test, eight isolates from 42 tested induced a significant decrease of disease incidence and disease symptoms. The eight efficient isolates were then tested for their effectiveness in the protection of tomato plants in pots under greenhouse conditions. Results obtained showed that all tested isolates applied as seed and root treatments reduced significantly ( P ≤ 0.001) the incidence of bacterial canker. [ABSTRACT FROM AUTHOR]