FREQUENCY OF ANTIBIOTIC-PRODUCING PSEUDOMONAS SPP IN NATURAL ENVIRONMENTS

The antibiotics phenazine-1-carboxylic acid (PCA) and 2,4-diacetylphlo roglucinol (Phl) are major determinants of biological control of soilb orne plant pathogens by various strains of fluorescent Pseudomonas spp . In this study, we described primers and probes that enable specific and efficient detection of a wide variety of fluorescent Pseudomonas s trains that produce various phenazine antibiotics or Phl. PCR analysis and Southern hybridization demonstrated that specific genes within th e biosynthetic loci for Phl and PCA are conserved among various Pseudo monas strains of worldwide origin, The frequency of Phl- and PCA-produ cing fluorescent pseudomonads was determined on roots of wheat grown i n three soils suppressive to take-all disease of wheat and four soils conducive to take-all by colony hybridization followed by PCR. Phenazi ne-producing strains were not detected on roots from any of the soils, However, Phl-producing fluorescent pseudomonads were isolated from al l three take-all-suppressive soils at densities ranging from approxima tely 5 x 10(5) to 2 x 10(6) CFU per g of root. In the complementary co nducive soils, Phl-producing pseudomonads were not detected or were de tected at densities at least 40-fold lower than those in the suppressi ve soils. We speculate that fluorescent Pseudomonas spp. that produce Phl play an important role in the natural suppressiveness of these soi ls to take-all disease of wheat.