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Survival of Pseudomonas putida, a Biological Control Agent, in Soil. Marcella Dupler, Research associate, Department of Botany and Plant Pathology, Colorado State University, Fort Collins 80523; Ralph Baker, professor, Department of Botany and Plant Pathology, Colorado State University, Fort Collins 80523. Phytopathology 74:195-200. Accepted for publication 17 August 1983. Copyright 1984 The American Phytopathological Society. DOI: 10.1094/Phyto-74-195.

When cells of Pseudomonas putida were added to soil, suppressiveness to Fusarium wilt of flax was induced. Survival characteristics of this bacterium were determined. A rifampin-resistant mutant of the bacterium was used to monitor population densities in soil. Recovery of P. putida as reflected by the number of colony-forming units (cfu) detected immediately after the addition of P. putida to soil was greatest at high matric potential. When added at - 100 bars, no P. putida were detected; however, when soils were dried slowly to - 100 bars, the bacterium survived. When different initial concentrations of P. putida were added to nonsterile soil, subsequent increase of bacteria was greater when soil received the lower inoculum level. P. putida survived through winter under ambient environmental conditions in two Colorado soils, with population densities increasing after January. Rhizosphere colonization of radish plants by P. putida was lower in soils that were biologically active (incubated 1 wk at near - 0.3 bars before the introduction of P. putida) compared to soils that were previously air-dry. Population densities of the bacterium in the rhizospheres of cucumber and radish plants remained high throughout field trials.