phlF− mutant of Pseudomonas fluorescens J2 improved 2,4-DAPG biosynthesis and biocontrol efficacy against tomato bacterial wilt

• The phlF, negatively regulating 2,4-DAPG synthesis was deleted to obtain J2-phlF−.
• Mutant J2-phlF− produced more 2,4-DAPG than wild strain J2.
• Mutant J2-phlF− colonization ability increased in rhizosphere soil.
• Biocontrol efficacy against tomato bacterial wilt was improved by J2-phlF−.

Pseudomonas fluorescens J2 can produce 2,4-diacetylphloroglucinol (2,4-DAPG) as the main antibiotic compound and effectively inhibits the wilt pathogens Ralstonia solanacearum and Fusarium oxysporum. The phlF which negatively regulates the 2,4-DAPG synthesis in strain J2 was disrupted by homologous recombination to construct a mutant strain J2-phlF−. The mutant J2-phlF− produced much more 2,4-DAPG and showed higher inhibitory effect on R. solanacearum than the wild type strain J2 in vitro. The mutant J2-phlF− also showed more colonization of tomato roots and higher inhibition to R. solanacearum in soil than wild type strain J2. The biocontrol efficiency of mutant J2-phlF− was higher against tomato bacterial wilt than wild type strain J2, but the differences were not significant. However, the application of both strains with organic fertilizer improved the colonization and biocontrol efficiency against tomato bacterial wilt and mutant strain J2-phlF− showed higher biocontrol efficiency against tomato bacterial wilt than wild type strain J2. Both strains, J2 and J2-phlF−, could also promote the growth of tomato plants.

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