Antibiosis has been proposed to contribute to the beneficial bacteria-mediated biocontrol against pea Aphanomyces root rot caused by the oomycete pathogen Aphanomyces euteiches. However, the antibiotics required for disease suppression remain unknown. In this study, we found that the wild type strains of Pseudomonas protegens Pf-5 and Pseudomonas fluorescens 2P24, but not their mutants that lack 2,4-diacetylphloroglucinol, strongly inhibited A. euteiches on culture plates. Purified 2,4-diacetylphloroglucinol compound caused extensive hyphal branching and stunted hyphal growth of A. euteiches. Using a GFP-based transcriptional reporter assay, we found that expression of the 2,4-diacetylphloroglucinol biosynthesis gene phlAPf-5 is activated by germinating pea seeds. The 2,4-diacetylphloroglucinol producing Pf-5 derivative, but not its 2,4-diacetylphloroglucinol non-producing mutant, reduced disease severity caused by A. euteiches on pea plants in greenhouse conditions. This is the first report that 2,4-diacetylphloroglucinol produced by strains of Pseudomonas species plays an important role in the biocontrol of pea Aphanomyces root rot.
Keywords: 2,4-DAPG; Aphanomyces euteiches; Pseudomonas spp.; antibiotics; biocontrol.