Genetic diversity of phlD from 2,4-diacetylphloroglucinol-producing fluorescent Pseudomonas spp.

Fluorescent Pseudomonas spp. that produce 2,4-diacetylphloroglucinol (2,4-D APG) have biocontrol activity against damping-off, root rot, and wilt disea ses caused by soilborne fungal pathogens, and play a key role in the natura l suppression of Gaeumannomyces graminis var. tritici, known as take-all de cline. Diversity within phlD, an essential gene in the biosynthesis of 2,4- DAPG, was studied by restriction fragment length polymorphism (RFLP) analys is of 123 2,4-DAPG-producing isolates from six states in the United States and six other:locations worldwide. Clusters defined by RFLP analysis of phl D correlated closely with clusters defined previously by BOX-polymerase cha in reaction (PCR) genomic fingerprinting, indicating the usefulness of phlD as a marker of genetic diversity and population structure among 2,4-DAPG p roducers. Genotypes defined by RFLP analysis of phlD were conserved among i solates from the same site and cropping history. Random amplified polymorph ic DNA analyses of genomic DNA revealed a higher degree of polymorphism tha n RFLP and BOX-PCR analyses. Genotypic diversity in a subset of 30 strains representing all the phlD RFLP groups did not correlate with production in vitro of monoacetylphloroglucinol, 2,4-DAPG, or total phloroglucinol compou nds. Twenty-seven of the 30 representative strains lacked pyrrolnitrin and pyoluteorin biosynthetic genes as determined by the use of specific primers and probes.