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Aragno, Michel

Nom
Aragno, Michel
Affiliation principale
Email
Michel.Aragno@unine.ch
Identifiants
https://libra.unine.ch/handle/123456789/753

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  • Publication
    Accès libre
    Plant growth stage, fertiliser management and bio-inoculation of arbuscular mycorrhizal fungi and plant growth promoting rhizobacteria affect the rhizobacterial community structure in rain-fed wheat fields
    (2006)
    Roesti, David
    ;
    Gaur, Rachna
    ;
    Johri, B. N.
    ;
    Imfeld, G.
    ;
    Sharma, S.
    ;
    Kawaljeet, K.
    ;
    Aragno, Michel 
    The goal of this study was first to assess the dynamics of the bacterial community during a growing season in three Indian rain-fed wheat fields which differ mainly through their fertilizer management and yield and then to study the effects of PGPR/AMF bio-inoculations on the bacterial community structure and wheat growth. The bacterial community structure of the rhizosphere soil (RS) and the rhizoplane/endorhizosphere (RE) was determined by PCR-denaturing gradient gel electrophoresis. Seed treatments consisted of consortia of two PGPR strains alone or combined with AMF or AMF alone. The PGPR strains were Pseudomonas spp. which included some or all of the following plant growth promoting properties: phosphate solubilisation and production of indole-3-acetic acid, siderophores, 1-aminocyclopropane-1-carboxylate deaminase and diacetyl-phloroglucinol. The mycorrhizal inoculum was an indigenous AMF consortium isolated from the field with the lowest level of fertilization and yield. Variation partitioning analysis of the DGGE data indicated a predominant effect of the wheat growth stage (30.4% of the variance, P=0.001) over the type of field (9.0%, P=0.027) on the bacterial community structure in the RE. The impact of plant age in the RS was less than in the RE and the bacterial community structure of the field with the highest input of fertilization was very different from the low input fields. The bio-inoculants induced a significant modification in the bacterial community structure. In the RS, the bacterial consortia explained 28.3% (P=0.001) and the presence of AMF 10.6% (P=0.02) of the variance and the same trend was observed in the RE. Plant yield or grain quality was either increased or remained unaffected. For example, protein content was significantly higher in the treated plants' grain compared to the control plants; maximum values were obtained when the PGPR were co-inoculated with the AMF. The percentage of root colonization by AMF was significantly higher in the treatments containing a mycorrhizal inoculum than in the untreated control and remained unaffected by the PGPR treatments. In conclusion, the wheat rhizobacterial community structure is highly dynamic and influenced by different factors such as the plant's age, the fertilizer input and the type of bio-inoculant. In addition, there is a distance-related effect of the root on the bacterial community. Finally, a combined bio-inoculation of diacetyl-phloroglucinol producing PGPR strains and AMF can synergistically improve the nutritional quality of the grain without negatively affecting mycorrhizal growth.
  • Publication
    Accès libre
    Réponse des populations de "Pseudomonas" à une augmentation de la concentration de CO2 atmosphérique dans la rhizosphère de "Lolium perenne" et "Molinia coerulea"
    (2004)
    Tarnawski, Sonia
    ;
    Aragno, Michel 
    Cette thèse a pour objectif d'évaluer la réponse des Pseudomonas à une augmentation de la concentration en CO2 atmosphérique (pCO2) dans la rhizosphère de deux graminées pérennes: Lolium perenne et Molinia coerulea. La première partie de ce travail s'intéresse au développement d'outils méthodologiques pour l'étude de la diversité des Pseudomonas dans le sol et la rhizosphère. Nous avons mis au point un protocole d'amplification d'une partie de l'ADNr 16S et de l'intergène 16S-23S de l'ADNr (séquences 16S-ITS1) spécifique au genre Pseudomonas. L'analyse PCR-RFLP des séquences d'ADNr 16S-ITS1 a ensuite été utilisée pour la caractérisation des populations de Pseudomonas associées à la rhizosphère de M. coerulea par approche culturale et amplification directe des séquences 16S-ITS1. Les Pseudomonas représentaient jusqu'à 10% de la microflore cultivable du sol et de la rhizosphère, et leur diversité était plus faible dans la fraction racinaire que dans le sol. Les Pseudomonas fluorescents dominaient dans la fraction racinaire alors que des organismes proche de P. alcaligenes étaient plus fréquemment retrouvés dans le sol. La seconde partie de cette étude est consacrée à l'influence d'une augmentation du pCO2 sur les populations de Pseudomonas associés à la rhizosphère des graminées pérennes. L'analyse de caractères en relation avec la plante (production d'auxine, sidérophores, de cyanure d'hydrogène, et réduction des nitrates) de 1228 isolats montrait que la structure phénotypique des populations de Pseudomonas était altérée sous fort pCO2 dans la rhizosphère, les deux plantes influençant différemment leur microflore. La fréquence des Pseudomonas réducteurs de nitrate était stimulée sous pCO2 élevée avec la proximité de la racine. La diversité génotypique des Pseudomonas dissimilant les nitrates, basée sur l'analyse des séquences ITS1, et des gènes de nitrate réductase narG et napA n'était pas significativement modifiée sous pCO2 élevée ou à proximité de la racine. Les Pseudomonas réducteurs de nitrates semblaient contre-sélectionnés dans la rhizosphère de L. perenne, et limités dans leur réponse au pCO2 élevée par la disponibilité en azote. L'étude des formes de nitrate réductases présentes dans les souches correspondantes, a révélé une modification de la diversité fonctionnelle parmi les souches de Pseudomonas associés à la rhizosphère sous pCO2 élevée. Ce changement dans les populations de Pseudomonas est discuté en relation avec les possibles modifications des conditions physico-biochimiques de la rhizosphère sous fort pCO2., The objective of this thesis was to assess the response of Pseudomonas to an increase atmospheric CO2 concentration (pCO2) in the rhizosphere of the two perennial grasses: Lolium perenne and Molinia coerulea. The first part of this work was interested in the development of methodological tools for studying Pseudomonas diversity in the soil and in the rhizosphere. We proposed a protocol for the specific Pseudomonas amplification of the partial 16S rDNA and 16S-23S rDNA spacer (16S-ITS1 sequences). PCR-RFLP analysis of 16S-ITS1 rDNA sequences was used for the characterization of Pseudomonas associated with the rhizosphere of M. coerulea by culture approach and direct amplification of the 16S-ITS1 sequences. Pseudomonas accounted for up to 10% of the cultivable microflora in soil and rhizosphere, and its diversity was lower in the root fraction. Fluorescent Pseudomonas dominated in the rhizosphere whereas organisms close to P. alcaligenes were more frequently found in the soil. The second part this study was devoted to the influence of an increase in pCO2 on Pseudomonas populations associated with the rhizosphere of the perennial grasses. Analysis of characters in relation with the plant (auxin, siderophores, hydrogen cyanide production and nitrate reduction) among 1228 isolates showed that the phenotypic structure of Pseudomonas populations was altered under elevated pCO2 in the rhizosphere, the two plants influencing their microflora differently. Nitrate reducers Pseudomonas were stimulated under elevated pCO2 at the root proximity. The genotypic diversity of nitrate dissimilating Pseudomonas, based on 16S-ITS1 rDNA sequences and narG and napA nitrate reductase genes analysis, was not significantly modified by plant or by elevated pCO2. Nitrate reducing Pseudomonas seemed to be counter-selected in the rhizosphere of L. perenne, and limited in their response to elevated pCO2 by nitrogen availability. The study of nitrate reductase forms present in the corresponding strains revealed a modification of functional diversity among rhizospheric Pseudomonas under elevated pCO2. This change among Pseudomonas populations is discussed in relation with possible modifications of the rhizosphere physico-biochemical conditions under elevated pCO2.