Submitted to: International Plant Growth Promoting Rhizobacteria Workshop
Publication Type: Abstract Only
Publication Acceptance Date: February 16, 2009
Publication Date: N/A
Technical Abstract: Strains of the rhizosphere bacterium Pseudomonas fluorescens produce redox-active phenazine antibiotics that suppress a wide variety of soilborne plant pathogens. Our laboratory recently detected these bacteria a population levels up to 106 colony-forming units (cfu) per gram of root (fresh weight) on dryland wheat and barley from commercial fields in central Washington State. A regional survey has indicated the high populations are limited to non-irrigated cereals grown within an area roughly bound by 46.3º and 47.9 º and 117.5º to 119º W (ca three million acres). An average yearly precipitation level below 15 inches and lack of irrigation appear to be major population level determinants. In 2007 and 2008, we recovered 396 phenazine-producing Pseudomonas isolates from wheat and barley roots grown in this area. These isolates comprise 30 genotypes based on DNA fingerprinting , with and additional genotype fromed by P. fluorescens 2-79 isolated from the same area in 1979. According to 16S rDNA and house keeping gene sequence analysis, the majority of our isolates from a unique group separate from previously characterized pathogen-suppressing phenazine-producers. However, the isolates show close association to a different fluorescent Pseudomonas species, P orientalis CIP 105540 (unknown as to its phenazine–producing ability) as well as P. gessardii CIP 105469 and P. synxantha IAM 2356. The specific biogeographic limits and robust diversity indicate a wide distribution of phenazine production within strains of different fluorescent Pseudomonas species limited to non-irrigated dryland wheat.