2009), disruption of the organization of cytoskeletal filamentous actin in Aphanomyces cochlioides hyphae (Islam and Fukushi 2010), and impairment of mitochondrial function in the yeast Saccharomyces cerevisae (Gleeson et al. 2008), improvement of crop health by seed treatment with DAPG (Raudales et al. The toxicity of DAPG to diverse groups of organisms suggests that its targets may include varities of cellular processes such as lysis of bacterial cells by novel antibiotic mechanisms (Kamei and Isnansetyo 2003), alterations of plant root development (Brazelton et al. fluorescens is largely linked to the production of DAPG (Dwivedi and Johri 2003 Paulsen et al. A large body of literature suggests that the biocontrol efficacy of P. 2003a Kamei and Isnansetyo 2003 Islam and Fukushi 2010).
The polyketide antibiotic, 2,4-diacetylphloroglucinol (DAPG) produced by several strains of the biocontrol bacterium, Pseudomonas fluorescens, has been shown a broad-spectrum toxicity to organisms such as bacteria, fungi, protists, nematodes and peronosporomycetes (Bender and Rangaswamy 1999 Bangera and Thomashow 1999 Isnansetyo et al. This is the first report of inhibitory activities of DAPG and its derivatives against zoosporogenesis and motility of zoospores of two important peronosporomycete phytopathogens. This revealed that the degree of hydrogen atoms substitution in the benzene ring by acyl groups and the length of substituted acyl groups were related to the level of bioactivity. Among them, 2,4-dipropylphloroglucinol exerted the highest inhibitory activity against both zoosporogenesis and motility of zoospores. All derivatives of DAPG had similar inhibitory activities but at varying doses. cochlioides zoospores formed round cystospores instead of lysis and then germinated with excessively-branched germ tubes. Generally, zoospores became immotile shortly after exposure to DAPG followed by lysis. In both cases, DAPG inhibited zoosporogenesis (5 μg/ml) and the motility of zoospores (10 μg/ml) in a dose-dependent manner. The aim of this study was to test the effects of DAPG and its derivatives on zoosporogenesis and motility of zoospores of a downy mildew pathogen, Plasmopara viticola, and a damping-off pathogen, Aphanomyces cochlioides.
Zoosporogenesis and motility of zoospores are critical for a complete disease cycle and pathogenicity of the peronosporomycete phytopathogens. 2,4-Diacetylphloroglucinol (DAPG) produced by Pseudomonas fluorescens, shows toxicity to many microorganisms including fungi, bacteria, and peronosporomycetes.
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