Mutational Disruption of the Biosynthesis Genes Coding for the Antifungal Metabolite 2,4-Diacetylphloroglucinol Does Not Influence the Ecological Fitness of Pseudomonas fluorescens F113 in the Rhizosphere of Sugarbeets

Carroll, Heather W.; Moënne‐Loccoz, Yvan; Dowling, David N.; O’Gara, Fergal

doi:10.1128/aem.61.8.3002-3007.1995

Cited by 64 publications

(29 citation statements)

References 29 publications

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“…Pythium ultimum causes dampingoff of pea seedlings, and the Phl-producing strains inhibit Pythium growth in plate assays (Fenton et al 1992). Deletion of the biosynthetic locus for Phl production showed that the ability to produce Phl in strain F113 was responsible for the biocontrol properties of this strain, but did not contribute to its rhizosphere competence (Fenton et al 1992;Carroll et al 1995).…”

Section: Introductionmentioning

confidence: 99%

Biocontrol of Pythium in the pea rhizosphere by antifungal metabolite producing and non-producing Pseudomonas strains

et al. 2001

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Aims: Four well-described strains of Pseudomonas¯uorescens were assessed for their effect on pea growth and their antagonistic activity against large Pythium ultimum inocula. Methods and Results: The effect of Pseudomonas strains on the indigenous soil micro¯ora, soil enzyme activities and plant growth in the presence and absence of Pythium was assessed. Pythium inoculation reduced the shoot and root weights, root length, and the number of lateral roots. The effect of Pythium was reduced by the Pseudomonas strains. Strains F113, SBW25 and CHAO increased shoot weights (by 20%, 22% and 35%, respectively); strains Q2-87, SBW25 and CHAO increased root weights (14%, 14% and 52%). Strains SBW25 and CHAO increased root lengths (19% and 69%) and increased the number of lateral roots (14% and 29%). All the Pseudomonas strains reduced the number of lesions and the root and soil Pythium populations, while SBW25 and CHAO increased the number of lateral roots. Pythium inoculation increased root and soil microbial populations but the magnitude of this effect was Pseudomonas strain-speci®c. Pythium increased the activity of C, N and P cycle enzymes, while the Pseudomonas strains reduced this effect, indicating reduced plant damage. Conclusions: Strains SBW25 and CHAO had the greatest bene®cial characteristics, as these strains produced the greatest reductions in the side effects of Pythium infection (microbial populations and enzyme activities) and resulted in signi®cantly improved plant growth. Strain SBW25 does not produce antifungal metabolites, and its biocontrol activity was related to a greater colonization ability in the rhizosphere. Signi®cance and Impact of the Study: This is the ®rst critical comparison of such important strains of Ps.¯uorescens showing disease biocontrol potential.

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Section: Introductionmentioning

confidence: 99%

Biocontrol of Pythium in the pea rhizosphere by antifungal metabolite producing and non-producing Pseudomonas strains

et al. 2001

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“…It is widely recognized that successful root colonization is an important prerequisite for effective biocontrol (Weller, 1988;Bull et al, 1991). Biocontrol agents introduced as soil or seed inoculants colonize the root system in competition with the indigenous soil microbiota (Weller, 1988;Parke, 1990;Weller & Thomashow, 1994;Carroll et al, 1995). Strains of the Pseudomonas fluorescens-putida group are often aggressive root-colonizers and can constitute half or more of the total number of culturable rhizosphere bacteria following their introduction into the rhizosphere (Bowen & Rovira, 1976;Smiley, 1979;Schroth & Hancock, 1982;Carroll et al, 1995).…”

Section: Introductionmentioning

confidence: 99%

“…Introduced rhizobacteria tend to colonize primarily the older parts of the root and consequently are found at comparatively lower numbers in the root tip area (Russo et al, 1996). Often, the population size of biocontrol inoculants has been monitored by colony counts, at the scale of the whole root system (Natsch et al, 1994;Carroll et al, 1995) or particular root segments (Bull et al, 1991;Russo et al, 1996). However, these determinations do not yield any information on the distribution of individual cells of the inoculant in the rhizosphere and their physical interaction with the target fungal pathogen, which are poorly understood (Fukui et al, 1994).…”

Section: Introductionmentioning

confidence: 99%

**Interactions between the biocontrol agent Pseudomonas fluorescens CHA0 and Thielaviopsis basicola in tobacco roots observed by immunofluorescence microscopy**

et al. 1997

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Pseudomonas fluorescens CHA0 protects plants from damage caused by several soilborne fungi. In this work, immunofluorescence microscopy was used to investigate the colonization of tobacco roots by CHA0 and its physical relationship with the black root rot fungus Thielaviopsis basicola. The pseudomonad colonized the rhizoplane shortly after planting of tobacco seedlings in sterile soil microcosms, in which it had been introduced as soil inoculant. CHA0 was found between and inside cells in the epidermis and the cortex, as well as in the xylem vessels, within 4-7 days after planting of seedlings. The presence of CHA0 delayed the colonization of the interior of tobacco roots by T. basicola compared with the treatment in which only the fungus had been inoculated. Likewise, the pseudomonad reduced the extent of black root rot from 82% to 28%. However, CHA0 was seldom found in contact with the mycelium of T. basicola or in its vicinity, indicating that direct colonization of the mycelium of T. basicola by CHA0 was not required for protection of tobacco against black root rot. Overall, the results suggest that the interior of the root is a key site for implementation of the strain's biocontrol activity against soilborne plant-pathogenic fungi.

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“…For strains such as Pseudomonas fluorescens 2-79 and P. aureofaciens 30-84, the production of phenazine antibiotics contributes to competitiveness on the roots of wheat (Mazzola et al 1992). In contrast, for P. fluorescens F113, the production of the antibiotic 2,4-diacetylphloroglucinol does not appear to be a factor in the competitiveness of the strain on the roots of sugarbeet (Carroll et al 1995). Metabolites that directly suppress plant-pathogenic fungi could also have some other function, such as serving as a siderophore for the uptake of iron.…”

Section: Special Featurementioning

confidence: 98%

“…These tools include isogenic mutants of rhizobia whose altered symbiotic function is linked to alteration of a single gene (Tirichine et al 2000). Fine-structure genetic analyses (Raaijmakers and Weller 2001) and genetic modification (Carroll et al 1995) of Pseudomonas fluorescens also are providing insights into its ecological role.…”

Section: New Research Toolsmentioning

confidence: 99%

Cooperation in the Rhizosphere and the “Free Rider” Problem

Denison

Bledsoe

Kahn

et al. 2003

Ecology

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Rhizobial bacteria, endomycorrhizal fungi (also known as arbuscular mycorrhizas), and pseudomonad bacteria associated with plant roots can provide substantial benefits to the plants by fixing nitrogen, supplying phosphorus, or controlling root pathogens, respectively. A significant fraction of plant photosynthetic carbon may be used by these associated microorganisms, both to support their beneficial activities and for microbial growth and reproduction. Because many microbial individuals are associated with each individual plant, the individual benefit to a microbe that allocates more resources to its own reproduction (thereby allocating less to fixing N2, supplying P, or producing antifungal metabolites) would exceed its individual loss from any resulting reduction in collective benefits (mainly plant carbon substrates). An initially rare “free rider” mutant strain might therefore be expected to displace its more cooperative parental strain. Yet, the mycorrhizal and legume–rhizobium mutualisms have persisted (often coexisting with “cheating”) for millions of years. This paper discusses the importance of microbial cooperation (with plants and with other microbes) and possible reasons for its evolutionary persistence in the rhizosphere. In undisturbed soils, spatial structure can favor kin selection, but this may be counterbalanced by the increased likelihood that future competitors will be among the beneficiaries of current cooperation. In loose associations, direct fitness benefits to microorganisms may explain the evolutionary persistence of activities (e.g., production of antifungal compounds) that can benefit plants as a side effect. In closer, more symbiotic, relationships, host sanctions against individuals or clones that fail to perform their symbiotic function may be more important. New molecular methods and other research tools are facilitating research on this topic, and some of these conclusions soon may be revised. Corresponding Editor: D. A. Phillips. For reprints of this Special Feature, see footnote 1, p. 815

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Mutational Disruption of the Biosynthesis Genes Coding for the Antifungal Metabolite 2,4-Diacetylphloroglucinol Does Not Influence the Ecological Fitness of Pseudomonas fluorescens F113 in the Rhizosphere of Sugarbeets

Cited by 64 publications

References 29 publications

Biocontrol of Pythium in the pea rhizosphere by antifungal metabolite producing and non-producing Pseudomonas strains

Biocontrol of Pythium in the pea rhizosphere by antifungal metabolite producing and non-producing Pseudomonas strains

**Interactions between the biocontrol agent Pseudomonas fluorescens CHA0 and Thielaviopsis basicola in tobacco roots observed by immunofluorescence microscopy**

Cooperation in the Rhizosphere and the “Free Rider” Problem

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