Effects of Pseudomonas putida WCS358r and its genetically modified phenazine producing derivative on the Fusarium population in a field experiment, as determined by 18S rDNA analysis

We measured effects of Pseudomonas putida WCS358r and its genetically modified phenazine producing derivative on the Fusarium population in the soil of a wheat field in the Netherlands. We used 18S rDNA analysis to study the Fusarium population through a strategy based on screening clone libraries by using amplified ribosomal DNA restriction analyses (ARDRA). After screening a total of 1000 clones, 70 clones had a Fusarium-like ARDRA pattern. Phylogenetic analysis showed that 51 out of 70 of these clones cluster in a monophyletic group together with the Fusarium isolates that were also obtained from the experimental field, suggesting that these clones originated from fungal strains belonging to the genus Fusarium. Both the introduced Pseudomonas parental strain and the GMM inhibit the development of the Fusarium and probably account for the higher diversity of Fusarium-like clone types at day 40 compared to day 13 and 27. While the antagonistic properties of P. putida WCS358r appear to suppress the Fusarium population, the introduced genetic modification does not seem to play a great additional role. [KEYWORDS: Genetically modified microorganisms; Pseudomonas putida; Fusarium; Amplified ribosomal DNA restriction analyses; 18S rDNA; Wheat rhizosphere; Soil