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Acta Phytopathologica et Entomologica Hungarica
Authors: A. Kamalakannan, L. Mohan, K. Kavitha, S. Harish, R. Radjacommare, S. Nakkeeran, V. K. Parthiban, R. Karuppiah and T. Angayarkanni

Five isolates of Trichoderma viride, Pseudomonas fluorescens and four isolates of Bacillus subtilis were evaluated for their ability to control Rhizoctonia solani, the causal agent of stem and stolon rot of peppermint (Mentha piperita Lin.). Of the various isolates of T. viride, P. fluorescens and B. subtilis tested, TVUV10, PFMMP and BSG3 showed the maximum inhibition of mycelial growth of R. solani. Among these isolates, P. fluorescens, PFMMP recorded the highest inhibition zone against R. solani in vitro and was very effective in reducing disease incidence in greenhouse condition. The effective isolates were evaluated for their ability to induce defense related enzymes and chemicals in plants. Increased activity of phenylalanine ammonia lyase (PAL), peroxidase (PO), polyphenoloxidase (PPO) and total phenolics were recorded in the biocontrol agents pretreated peppermint plants challenged with R. solani. P. fluorescens isolate PFMMP recorded early and increased synthesis of all defense related enzymes and total phenol. Thus, the present study shows that application of biocontrol agents; induce defense related enzymes involved in phenyl propanoid pathway in addition to direct antagonism which collectively contribute for enhanced resistance against invasion of R. solani in M. piperita.

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Changes in activities of phenylalanine ammonia-lyase,chitinase,ß-1,3-glucanase and phenolic content in rice leaves were measured at different times after treatment of leaves with Pseudomonas fluorescens strain Pf1.When rice leaves were sprayed with P.fluorescens,substantial increase in the phenylalanine ammonia-lyase activity was observed 1 day after treatment.Following increase of the first enzyme of the phenylpropanoid pathway,phenolic content of rice leaves also increased to a maximum at 4 days after P.fluorescens treatment.Chitinase activity increased in rice leaves in response to application of P.fluorescens and the maximum enzyme activity was observed 3 days after treatment.ß-1,3-Glucanase activity also increased significantly from 1 day after P.fluorescens treatment and continued to increase through 7 days.A five-fold increase in glucanase activity was observed 7 days after P.fluorescens treatment.

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Twenty strains of Pseudomonas fluorescens were evaluated for their potential in promoting plant growth and in the control of late leaf spot caused by Cercosporidium personatum in groundnut under greenhouse conditions. Seed treatment with P. fluorescens strain Pf1 recorded the highest germination percentage and the maximum plant height. Seed treatment with P. fluorescens Pf1 significantly controlled late leaf spot disease of groundnut and increased the pod yield. When the treated seeds were sown in soil, the antagonist colonized well in the groundnut rhizosphere. P. fluorescens Pf1 showed the maximum production of indole acetic acid in in vitro.

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Pseudomonads, including P. fluorescens strain MKB 158, can inhibit the development of Fusarium seedling blight disease on wheat and barley. Application of this and other pseudomonads as head sprays inhibits the development of Fusarium head blight disease (FHB) disease on wheat and barley under both field and glasshouse conditions. P. fluorescens strains MKB 158 and MKB 249 also reduced DON contamination of grain under field conditions. Evidence suggests that P. fluorescens does not directly inhibit the growth of Fusarium , but that it potentiates host resistance against this disease. Transcriptome profiling identified barley genes differentially expressed as early events in (a) bacterium-induced resistance to seedling blight and (b) heads following P. fluorescens and Fusarium culmorum co-inoculation. Bacterium-potentiated resistance to Fusarium affects the transcription of many genes that are involved in diverse processes, including cell rescue and defence, metabolism, cell cycle and DNA replication and signalling.

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Psychrotrophic Pseudomonas species P. fluorescens, P. fragi and P. lundensis were found as predominant bacteria of chicken meat stored at chill temperature, which showed high level of molecular diversity, while isolates of the psychrotrophic yeasts Candida zeylanoides, Metschnikowia pulcherrima, Rhodotorula glutinis and Rhodotorula mucilaginosa formed clusters of high level similarity within the different species as revealed by RAPD-PCR analysis.Combination of multiplex PCR and sequencing of the rpoB gene resulted correct identification of the Pseudomas isolates, while the routine diagnostic tests led to improper identification in case of half of the isolates, which indicated the extended biochemical and physiological heterogeneity of the food-borne pseudomonads. Majority of P. fluorescens and P. lundensis isolates were strong protease and lipase producers, while P. fragi strains were week or negative from this respect. Proteolytic and lipolytic activities of the isolated yeast strains were species specific and protease production was less frequent than lipolytic activities.

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Acta Alimentaria
Authors: M.Y. Jiang, Z.R. Wang, K.W. Chen, J.Q. Kan, K.T. Wang, Zs. Zalán, F. Hegyi, K. Takács and M.Y. Du

After suffering from mechanical injury and fungal infection, grapes are perishable. Botrytis cinerea, the causal agent of gray mould, is a critical pathogen for grapes. In this study, the inhibitory effect of Pseudomonas fluorescens on the formation of gray mould on grapes during the postharvest storage was investigated on “Kyoho” grape. The results suggest that a living cell suspension of P. fluorescens significantly inhibited spore germination of B. cinerea, and significantly reduced the incidence of grape gray mould. Moreover, compared with the control, the fruit inoculated with P. fluorescens had elevated activities of polyphenol oxidase (PPO), peroxidase (POD), catalase (CAT), phenylalanine ammonia-lyase (PAL), chitinase (CHI), and β-1,3-glucanase (GLU). Increase in enzyme activity correlated with enhanced host resistance. In addition, there was little difference in storage quality between the treated group and control group, indicating no adverse effects of the induced defence response on fruit quality.

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Acta Phytopathologica et Entomologica Hungarica
Authors: S. Mathiyazhagan, K. Kavitha, G. Chandrasekar, S. Nakkeeran, K. Manian, A. S. Krishnamoorthy, A. Sankaralingam and W. G. D. Fernando

The commercial cultivation of Phyllanthus amarus (Schum and Thonn) has led to the outbreak of stem blight caused by Corynespora cassiicola (Berk and Curt) Wei. Infection of C. cassiicola is reported on P. amarus for the first time. C. cassiicola produced glycoproteinaceous toxin responsible for the symptoms simirlarly produced by the pathogen. B. subtilis (CBE4), P. chlororaphis (PA23), endophytic P. fluorescens (ENPF1)  and T. viride (Tv-MNT7) degraded the toxin of C. cassiicola.

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Downy mildew of maize caused by Peronosclerospora sorghi was significantly controlled by seed treatment and foliar sprays of a talc-based formulation of a Pseudomonas fluorescens strain under greenhouse and field conditions. Leaf extracts of Prosophis chilensis and Azadirachta indica were found to be equally effective as P. fluorescens in controlling maize downy mildew, although the extracts were not as effective at inhibiting conidial germination as the pseudomonad or as metalaxyl. These treatments also suppressed sporulation of P. sorghi on diseased foliage. Enhanced induction of defense enzymes, chitinase and β-1,3-glucanase appeared to be associated with control mechanism and metalaxyl did not show such induction. The reduction in disease incidence under field condition resulted in increased yield. The inhibitory effect of P. fluorescens and extracts of P. chilensis or A. indica make them potential alternatives to metalaxyl for control of maize downy mildew, although their efficacy, practical application and cost needs to be explored in greater detail before they can be incorporated into an integrated pest management programme.

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Treatment of acibenzolar-S-methyl (bionTM), salicylic acid and the saprophytic bacterium Pseudomonas fluorescens exhibited induced systemic resistance in Sorghum bicolor (cv. Rio) to Sugarcane mosaic virus (SCMV) isolates from sugarcane. The treatments significantly slowed down the SCMV titre in plants during the initial growth phase. The enhanced induction of total phenols, phenylalanine ammonia lyase (PAL), peroxidase (PO) and polyphenol oxidase (PPO) might have contributed for the induced systemic resistance triggered by various biotic and abiotic inducers. More induction of PO and PPO isozymes were noticed upon application of these inducers. In the present studies, there was a significant decrease of SCMV titre as evidenced by ELISA in these treatments. Among the treatment methods, foliar application was highly effective in case of the abiotic elicitors bion and salicylic acid whereas with P. fluorescens seed treatment was effective.

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Journal of Radioanalytical and Nuclear Chemistry
Authors: Y. Suzuki, T. Nankawa, T. Yoshida, T. Ozaki, T. Ohnuki, A. J. Francis, S. Tsushima, Y. Enokida and I. Yamamoto

Summary  

We have investigated the structure of Eu(III)-citrate complexes in aqueous solution and their degradability by Pseudomonas fluorescens. Analysis of 1:1, 1:2, and 1:5 Eu(III):citrate solutions at pH 7 by electrospray ionization mass spectrometry (ESI-MS) showed that the 2:2 Eu(III)-citrate complex is the predominant complex species at a low citrate/Eu(III) ratio, while at a high ratio, a 1:2 Eu(III)-citrate complex is formed preferably. Studies on the biodegradation of Eu(III)-citrate complex by P. fluorescens have shown that a 2:2 Eu(III)-citrate complex is resistent to degradation while a 1:2 complex transforms to a 2:2 complex with the degradation of excess citric acid.

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