Survival ofPseudomonas putida,a Biological Control Agent, in Soil

Abstract

When cells of P. putida were added to soil, suppressiveness to Fusarium wilt [Fusarium oxysporun f. sp. lini] 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 2 Colorado [USA] soils, with population densities increasing after Jan. 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.