Submitted to: ASA-CSSA-SSSA Annual Meeting Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 11/12/2006
Publication Date: N/A
Technical Abstract: Plants have evolved strategies of stimulating and supporting groups of antagonistic microorganisms in the rhizosphere as a defense against diseases caused by soilborne pathogens owing to a lack of genetic resistance to many common soilborne pathogens. Some of the best examples of natural microbial defense of plant roots occur in disease suppressive soils. Soil suppressiveness against many different diseases has been described. Take-all is the most important root disease of wheat and soils become suppressive to take-all when wheat or barley is grown continuously in a field following a disease outbreak; this phenomenon is called take-all decline (TAD). In the U.S and The Netherlands, TAD results from the enrichment during monoculture of populations of 2,4-diacetylphloroglucinol (DAPG)-producing Pseudomonas fluorescens. DAPG-producing P. fluorescens also are enriched by monoculture of other crops (i.e., pea and flax), and evidence is accumulating that DAPG producers contribute to the defense of plant roots in many different agroecosystems. Twenty two genotypes of DAPG producers have been identified. The genotype of an isolate is predictive of its rhizosphere competence on wheat and pea. Multiple genotypes often occur in a soil and the crop grown enriches for certain genotypes and modulates the outcome of the competition among genotypes.