Prevalence of fluorescent pseudomonads producing antifungal phloroglucinols and/or hydrogen cyanide in soils naturally suppressive or conducive to tobacco black root rot

• Published in: FEMS microbiology ecology 2003-05, Vol.44 (1), p.35-43
• Main Authors: Ramette, Alban, Moënne-Loccoz, Yvan, Défago, Geneviève
• Format: Article
• Language: English
• Subjects: 2,4‐Diacetylphloroglucinol; Agronomy. Soil science and plant productions; Alleles; Animal, plant and microbial ecology; Biochemistry and biology; Biocontrol; Biological and medical sciences; Biological control; Black root; Chemical, physicochemical, biochemical and biological properties; Ecology; Fluorescence; Fundamental and applied biological sciences. Psychology; Fungicides; Hydrogen cyanide; Inoculation; Metabolites; Microbial ecology; Microbiology; Physics, chemistry, biochemistry and biology of agricultural and forest soils; Population number; Pseudomonas; Rhizosphere; Root rot; Roots; Soil science; Soils; Thielaviopsis basicola; Tobacco; Various environments (extraatmospheric space, air, water)
• ISSN: 0168-6496; 1574-6941
• DOI: 10.1111/j.1574-6941.2003.tb01088.x

Abstract Certain soils from Morens, Switzerland, are naturally suppressive to Thielaviopsis basicola-mediated black root rot of tobacco, and fluorescent pseudomonads are involved in this suppressiveness. Here, we compared two conducive, one moderately suppressive and one suppressive soil from Morens. Disease levels on tobacco after heavy T. basicola inoculation varied from 29% to 85% for the two conducive soils, 10% to 78% for the moderately suppressive soil and 11% to 42% for the suppressive soil, depending on time of the year. In the absence of T. basicola inoculation, disease levels were between 0% and 40% and varied also in time. Fluorescent pseudomonads were isolated from the rhizosphere and roots of tobacco subjected to T. basicola inoculation and characterized for production of the biocontrol metabolites 2,4-diacetylphloroglucinol (Phl) and HCN. No difference in population size was found between the suppressive and the conducive soils for total, Phl+ and HCN+ fluorescent pseudomonads colonizing the rhizosphere or roots of tobacco. Yet, the percentage of Phl+ isolates was significantly higher (30–32% vs. 6–11%) in the rhizosphere and roots for plants grown in the suppressive soil compared with the moderately suppressive and conducive soils. Different restriction profiles for phlD, one of the Phl biosynthetic genes, were often found when analyzing Phl+ isolates colonizing the same plant. Most phlD alleles were recovered from both suppressive and conducive soils, except one allele found only in root isolates from the suppressive soil.