Direct and Specific Assessment of Colonisation of Wheat Rhizoplane by Pseudomonas fluorescens Pf29A     

Alain Chapon  Morgane Boutin  Delphine Rimé  Laurie Delalande  Anne-Yvonne Guillerm  Alain Sarniguet 《European journal of plant pathology / European Foundation for Plant Pathology》2003,109(1):61-70

The efficacy of fluorescent pseudomonads as suppressors of soil-borne diseases is linked to their ability to colonise plant roots. Monitoring the dynamics of biocontrol agents in the rhizosphere should improve the irreliability. We designed a pair of Sequenced Characterised Amplified Region (SCAR) primers specific to Pseudomonas fluorescens Pf29A, based on a specific 700 bp RAPD product selected in a previous work. Primer specificity was tested with DNA samples extracted from rhizospheric soil and rhizoplane of wheat plants grown in two different non-sterile soils. We assessed the total population of Pf29A by PCR and the culturable population by counting a tetracycline-resistant Pf29A transformant producing Green Fluorescent Protein (GFP), on selective medium 5 days after inoculation of non-sterile soil. SCAR primers were specific for Pf29A in both soils. We evaluated the limit of detection to 14.2 fg of target DNA, equivalent to 242 Pf29A cells per cm of wheat root. Culturable populations of Pf29A transformant accounted for 13% and 4% of the total populations 5 days after treatment with 10³ and 10⁷ CFU of transformed Pf29A per gram of soil. The SCAR derived sequence is a good candidate to develop a strain specific and sensitive PCR-quantification of Pf29A available for population dynamic studies in fields. We confirm that only a small proportion of the total Pf29A rhizosphere population is culturable.  相似文献   

Dominant Colonisation of Wheat Roots by Pseudomonas fluorescens Pf29A and Selection of the Indigenous Microflora in the Presence of the Take-all Fungus     

A. Chapon  A.-Y. Guillerm  L. Delalande  L. Lebreton  A. Sarniguet 《European journal of plant pathology / European Foundation for Plant Pathology》2002,108(5):449-459

Increases in populations of fluorescent pseudomonads on wheat roots are usually associated with take-all decline, natural control of take-all, a disease caused by the fungus Gaeumannomyces graminis var. tritici (Ggt). Colonisation by Pseudomonas fluorescens strain Pf29A was assessed on the roots of healthy plants and of plants with take-all, and the effect of this bacterium on indigenous populations of fluorescent pseudomonads was studied. The efficacy of Pf29A as an agent for the biocontrol of take-all on five-week-old wheat seedlings was tested in non-sterile conducive soil in a growth chamber. RAPD (random amplification of polymorphic DNA) fingerprinting with a decamer primer was used to monitor strain Pf29A and culturable indigenous rhizoplane populations of fluorescent pseudomonad. Pf29A decreased disease severity and accounted for 44.6% of the culturable fluorescent pseudomonads on healthy plant rhizoplane and 75.8% on diseased plant rhizoplane. Fewer RAPD patterns were obtained when Pf29A was introduced into the soil with Ggt. In the presence of Ggt and necrotic roots, Pf29A became the dominant root coloniser and dramatically changed the diversity and the structure of indigenous fluorescent pseudomonad populations. The results show that Ggt and reduced lesion size on roots can trigger a specific increase in antagonist populations and that the introduction of a biocontrol agent in soil influences the structure of indigenous bacterial populations.  相似文献   

Sensitivity to pH and ability to modify ambient pH of the take‐all fungus Gaeumannomyces graminis var. tritici     

L. Lebreton  S. Daval  A.‐Y. Guillerm‐Erckelboudt  C. Gracianne  K. Gazengel  A. Sarniguet 《Plant pathology》2014,63(1):117-128

pH is one of the major ambient factors affecting life history traits of soilborne phytopathogenic fungi. The diversity of phenotypic responses to pH changes has not been extensively explored within fungal populations. To investigate this question, the ability of 82 strains of a worldwide collection of the take‐all agent Gaeumannomyces graminis var. tritici (Ggt) to grow in controlled pH conditions, reflecting their pH sensitivity, was measured. Of these 82 strains, 37 belonged to the G1 type and 45 to the G2 type, the two main genetic groups identified in Ggt populations. The experiments were conducted in Petri dishes on Fahraeus solid media buffered at pH 4·6, 6·0 or 7·0 with citrate–disodium phosphate solutions. The 82 strains exhibited a wide range of hyphal growth rates at the three pH levels. Ten statistically different pH profiles were described. The G2 strains grew significantly better than the G1 on the slightly acidic (pH 6·0) and the neutral (pH 7·0) buffered media. The ability of three strains to change ambient pH was also measured on unbuffered Fahraeus solid media initially adjusted to pH 5·6 or 8·0. All three strains were able to alkalinize the acidic medium. However, important variations between strains in the intensity, range and persistence of this alkalinization were measured. These results provide the first evidence of intraspecific variability in pH sensitivity within soilborne fungal species.  相似文献