Accumulation of Pseudomonas-derived 2,4-diacetylphloroglucinol on wheat seedling roots is influenced by host cultivar

Production of antifungal metabolites, including the polyketide 2,4-diacetylphloroglucinol (2,4-DAPG), is one mechanism by which biocontrol strains of Pseudomonas fluorescens suppress soilborne fungal pathogens. P. fluorescens strains vary in ability to produce 2,4-DAPG, but the role of the host in modulating metabolite accumulation in the rhizosphere is not well defined. To examine 2,4-DAPG production and accumulation during early stages of rhizoplane interactions, we compared metabolite production by two P. fluorescens strains in culture and on seedling roots of three Triticum aestivum L. (wheat) cultivars, Buchanan, Finley, and Tara, in a soil-free system. P. fluorescens strain Q8r1-96, an aggressive colonizer of the wheat rhizosphere, produced 1850 μg mL−1 2,4-DAPG after 48 h of growth in King’s Medium B, significantly (P > 0.05) more than 19.4 μg mL−1 metabolite produced by the moderately aggressive strain Q2-87V1 under the same conditions. Rhizoplane levels of 2,4-DAPG after 4 d of Q8r1-96 colonization were 1946, 1650, and 2767 ng g−1 for Buchanan, Finley, and Tara, respectively. Metabolite levels obtained for Q2-87V1 colonization were 1468, 366, and 80 ng g−1 on the respective cultivars. Strain Q8r1-96 deposited significantly (P < 0.05) more 2,4-DAPG than Q2-87V1 on Tara and Finley roots, whereas both strains produced similar (P > 0.05) amounts of the metabolite on Buchanan roots. In greenhouse experiments, take-all damage was reduced only on Tara roots inoculated with Q8r1-96. To our knowledge, this is the first report to compare 2,4-DAPG accumulation in the rhizoplanes of different cultivars, and to demonstrate that rhizoplane 2,4-DAPG accumulation depends on a cultivar–bacterial strain interaction.