Submitted to: Meeting Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 8/20/2013
Publication Date: N/A
Citation: Interpretive Summary:
Technical Abstract: We recently discovered large populations of phenazine-producing (Phz+) Pseudomonas strains and concentrations of the antibiotic phenazine-1-carboxylic acid (PCA) of up to 1.6 µg g-1 of root plus rhizosphere soil on roots of non-irrigated cereals grown over more than a million hectares of the Columbia Plateau of central Washington State. To test the hypothesis that these Phz+ populations are enriched specifically under dryland conditions, we established adjacent irrigated and nonirrigated plots of wheat at the WSU Dryland Research Station at Lind, Washington in 2011. We monitored population densities and rhizosphere colonization frequencies of indigenous Phz+ bacteria, as well as rhizosphere concentrations of PCA, seven times during two growing seasons. With or without irrigation, Phz+ bacterial populations and colonization frequencies followed the same trend till the fifth and third samplings, and then populations and colonization frequencies in the irrigated plots declined significantly as compared to those in the nonirrigated plots. PCA recovered from roots followed the bacterial population trend. Water potential of soil at 10 and 20 cm depth reached -500 and -400 Kpa in the dryland plots, respectively, and soil was fully saturated in the irrigated plots. As a first step towards understanding the molecular mechanisms involved in survival of Phz+ bacteria under dryland conditions, we have sequenced P. fluorescens 2-79, a well-studied biocontrol strain isolated over 30 years ago from the Lind site. Samples for a global analysis of bacterial community structure in the rhizosphere of wheat from isolated rhizosphere DNA are currently being processed. The expected results of these analyses will provide insight into the major phylogenetic groups represented in each community, reveal how dryland and irrigated samples differ in species diversity and composition, and enable us to determine whether these differences can be correlated with soil moisture and wheat growth stage.