Submitted to: International Congress of Plant Pathology Abstracts and Proceedings
Publication Type: Other
Publication Acceptance Date: 1/20/2003
Publication Date: 2/20/2003
Citation: Weller, D.M., Thomashow, L.S. 2003. Take-all decline: a model for biocontrol of soilborne pathogens. International Congress of Plant Pathology Abstracts and Proceedings. p. 48-49.
Technical Abstract: Take-all, caused by Gaeumannomyces graminis, is an important root disease of wheat. Take-all decline (TAD) is the spontaneous decrease in the incidence and severity of take-all that occurs with monoculture wheat or barley after a severe disease outbreak. The suppressiveness of TAD soils in Washington State USA results from the build-up of 2,4 diacetylphlorogluinol (DAPG)-producing fluorescent Pseudomonas spp. DAPG producers were present above the threshold density (10 5/g root) required for take-all control or wheat roots grown in TAD soils but were below the threshold on roots from conducive soils. TAD soils lost suppressiveness when DAPG producers were eliminated by pasteurization, and conducive soils gained suppressiveness when DAPG producers werin introduced via mixing in small amounts of TAD soil. DAPG was isolated from roots of wheat grown in TAD soil but not from conducive soil. DAPG producers inhibit many pathogens and are enriched in other suppressive soils, especially those with a history of crop monoculture. They exhibit considerable genetic and phenotypic diversity, which is a resource of improving biocontrol of plant pathogens. For example, the rhizosphere competence of BOX-PCR genotype D strains (exemplified by P. fluorescens Q8r1-96) on wheat and pea was far superior to that of other genotypes. Application of very low doses of D genotype strains resulted in the establishment of high rhizosphere population densities that were stable throughout the gowing season. By matching genotypes of DAPG producers with crops for which they have a colonization preference, root colonization and biocontrol can be increased without increasing the amount of inoculum.