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

An isolate of Pseudomonas aureofaciens from the phylloplane of sugar b eet which was chromosomally modified for monitoring purposes by the in sertion of two gene cassettes (km(r)-xylE and lacZY) was introduced to the phytosphere of spring wheat in a number of experiments and the re sulting microbial perturbations quantified. Such studies involving inn ocuous bacterial isolates can serve as a guide in the assessment of ri sk associated with the release of functionally modified microorganisms . Introductions of P. aureofaciens on seeds caused large microbial per turbations (up to 2 log units) at the seedling stage on seeds and root s. As the inoculated plants matured (tillering, flowering and ripening ), perturbations of total microbial populations were found to be non-s ignificant. Microbial perturbation on maturing wheat roots as a result of seed inoculations with P. aureofaciens could only be detected usin g more sensitive monitoring procedures describing the Pseudomonas comm unity in terms of colony appearance rate on a selective Pseudomonas me dium. Spray applications of the marked P. aureofaciens isolate onto th e leaf surface of wheat caused no significant perturbations of the ind igenous microbial populations present on the phylloplane.