EFFECT OF A GENETICALLY-MODIFIED PSEUDOMONAS-AUREOFACIENS ON INDIGENOUS MICROBIAL-POPULATIONS OF WHEAT

An isolate of Pseudomonas aureofaciens from the phylloplane of sugar beet which was chromosomally modified for monitoring purposes by the insertion of two gene cassettes (km(r)-xylE and lacZY) was introduced to the phytosphere of spring wheat in a number of experiments and the resulting microbial perturbations quantified. Such studies involving innocuous bacterial isolates can serve as a guide in the assessment of risk associated with the release of functionally modified microorganisms. Introductions of P. aureofaciens on seeds caused large microbial perturbations (up to 2 log units) at the seedling stage on seeds and roots. As the inoculated plants matured (tillering, flowering and ripening), perturbations of total microbial populations were found to be non-significant. Microbial perturbation on maturing wheat roots as a result of seed inoculations with P. aureofaciens could only be detected using more sensitive monitoring procedures describing the Pseudomonas community in terms of colony appearance rate on a selective Pseudomonas medium. Spray applications of the marked P. aureofaciens isolate onto the leaf surface of wheat caused no significant perturbations of the indigenous microbial populations present on the phylloplane.