Biocontrol of Tomato Fusarium Wilt by a Novel Genotype of 2,4-Diacetylphloroglucinol-producing Pseudomonas sp. NJ134

The rhizobacterium NJ134, showing strong $in$ $vitro$ antifungal activity against $Fusarium$ $oxysporum$ , was isolated from field grown tomato plants and identified as $Pseudomonas$ sp. based on 16S ribosomal DNA sequence and biochemical analyses. The antifungal compound purified by gas chromatography-mass spectrometry, infrared, and nuclear magnetic resonance analyses from NJ134 cultures was polyketide 2,4-diacetylphloroglucinol (DAPG). Analysis of the sequence of part of one of the genes associated with DAPG synthesis, $phlD$ , indicated that the DAPG producer NJ134 was a novel genotype or variant of existing genotype termed O that have been categorized based on isolates from Europe and North America. A greenhouse study indicated that about 10⁸ CFU/g of soil NJ134 culture application was required for effective biocontrol of Fusarium wilt in tomato. These results suggest that a new variant genotype of a DAPG-producing strain of $Pseudomonas$ has the potential to control Fusarium wilt under the low disease pressure conditions.