IMPACT OF FIELD RELEASE OF GENETICALLY-MODIFIED PSEUDOMONAS-FLUORESCENS ON INDIGENOUS MICROBIAL-POPULATIONS OF WHEAT

In a field release experiment, an isolate of Pseudomonas fluorescens, which was chromosomally modified with two reporter gene cassettes (lac ZY and Kan(r)-xylE), was applied to spring wheat as a seed coating and subsequently as a foliar spray. The wild-type strain was isolated fro m the phylloplane of sugar beet but was found to be a common colonizer of both the rizosphere and phylloplane of wheat as well. The impact o n the indigenous microbial populations resulting from release of this genetically modified microorganism (GMM) was compared with the impact of the unmodified, wild-type strain and a nontreated control until 1 m onth after harvest of the crop. The release of the P. fluorescens GMM and the unmodified, wild-type strain resulted in significant but trans ient perturbations of some of the culturable components of the indigen ous microbial communities that inhabited the rhizosphere and phyllopla ne of wheat, but no significant perturbations of the indigenous cultur able microbial populations in nonrhizosphere soil were found. Fast-gro wing organisms that did not produce resting structures (for example, f luorescent pseudomonads and yeasts) seemed to be most sensitive to per turbation. In terms of hazard and risk to the environment, the observe d microbial perturbations that resulted from this GMM release may be c onsidered minor for several reasons. First, the recombinant P. fluores cens strain caused changes that were, in general, not significantly di fferent from those caused by the unmodified wild-type strain; second, perturbations resulting from bacterial inoculations were mainly small; and third, the release of bacteria had no obvious effects on plant gr owth and plant health.