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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
    Diacetylphloroglucinol-producing pseudomonads do not influence AM fungi in wheat rhizosphere
    (2004)
    Gaur, Rachna
    ;
    Shani Noam
    ;
    Kawaljeet
    ;
    Johri, B. N.
    ;
    Rossi, Pierre
    ;
    Aragno, Michel 
    Natural agroecosystems are directly dependent on bene-ficial microorganisms present in bulk soil and rhizo-sphere for soil health and plant productivity. With the current thrust on use of microbial inoculants, espe-cially the biological control agents, it is necessary to assess their negative influence on such beneficial forms as AM fungi since they help the plant withstand various stresses. Among other molecules, pseudomonads pre-sent in the rhizosphere secrete the antifungal, 2,4-dia-cetylphloroglucinol (DAPG) and are currently in great demand as bioinoculants. Based on the cultural, bio-chemical, and molecular tools we show that DAPG producing pseudomonads recovered from wheat rhizo-sphere do not adversely affect AM colonization. Eva-luation of such effects on non-target organisms will help early acceptance of microbial inoculants in future.