Submitted to: Microbial Ecology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/22/2004
Publication Date: 8/24/2004
Citation: Mazzola, M., Funnell, D., Raaijmakers, J.M. 2004. Wheat cultivar-specific selecton of 2,4-diacetylphloroglucinol-producing fluorescent pseudomonas species from resident soil populations. Microbial Ecology. 48:338-348. DOI:10.1007/S00248-003-1062y. Interpretive Summary: Certain soils possess a natural ability to suppress the activity of soilborne plant pathogens. In most instances this "suppressiveness" functions through specific microorganisms resident to the soil. The natural suppression of take-all disease of wheat was previously shown to operate through the activity of bacteria, specifically fluorescent pseudomonads, which produce the antibiotic 2, 4-diacetylphloroglucinol (2,4-DAPG). These bacteria increase in response to continuous cropping of soils with wheat, and induce a decline in the incidence of take-all. In our study, we demonstrated that the increase in populations of these bacteria can vary depending upon the wheat cultivar that is planted. In addition, certain genotypes of these bacteria appear to be preferentially selected by specific wheat genotypes. These data indicate that the interactions between 2,4-DAPG-producing bacteria and plants is not a random event. In addition, the data suggest that the use of certain wheat cultivars, which more rapidly enhance populations of 2, 4-DAPG-producing bacteria may also reduce the time necessary to develop a soil suppressive to take-all. Should this prove true, the management of soil suppressiveness may ultimately develop into an effective and environmentally sound tool for the control of soilborne plant diseases such as take-all of wheat.
Technical Abstract: Fluorescent Pseudomonas spp. that produce the antibiotic 2, 4-diacetylphloroglucinol (2,4-DAPG) are known to provide biological control of several soilborne diseases and have a central role in the development of take-all decline, a spontaneous reduction in the severity of take-all in response to continuous wheat monoculture. Based on restiction fragment length polymorphism and sequence analyses of ph1D, a key gene involved in 2,4-DAPG production, two previously undefined ph1D+ genotypes, referred to as genotypes PfZ and PfY, were discovered. Wheat cultivar Lewjain was the primary source of genotype PfY while cultivar Penawawa yielded the majority genotype PfZ. Based on 16S rDNA sequence analysis, both new ph1D genotypes were classified as P. fluorescens. When strain LR3-AI, originally isolated from cultivar Lewjain, was applied as a soil inoculant, this strain was recovered at higher populations from the rhizosphere of Lewjain than the rhizosphere of two other cultivars. No cultivar effects were shown for the 2,4-DAPG-producing strain Q2-87. These results add further to evidence indicating a degree of specificity in interactions between plant cultivars and specific members of the saprophytic microbial community. As Lewjain exhibited a superior capacity to enhance resident soil populations of 2,4-DAPG-producing fluorescent pseudomonads, we postulate that use of specific cultivars may have potential to reduce the length of the monoculture period required to induce suppressiveness of soils to take-all disease.