The targeted application of plant growth promoting rhizobacteria (PGPR) provides the key for a future sustainable agriculture with reduced pesticide application. PGPR interaction with the indigenous microbiota is poorly understood but essential to develop reliable applications. Therefore, Stenotrophomonas rhizophila SPA-P69 was applied as seed coating and in combination with a fungicide based on the active ingredients fludioxonil, metalaxyl-M, captan and ziram. Plant performance and rhizosphere composition of treated and non-treated maize plants of two field trials were analyzed. Plant health was significantly increased by treatment; however overall corn yield was not changed. By applying high-throughput amplicon sequencing of the 16S rRNA and the ITS genes, the bacterial and fungal changes in the rhizosphere due to different treatments were determined. Despite treatments had a significant impact on the rhizosphere microbiota (9- 12%), the field site was identified as main driver (27- 37%). Soil microbiota composition from each site was significantly different, which explains the site-specific effects. In this study we were able to show first indications how PGPR treatments increase plant health via microbiome shifts in a site-specific manner. This way first steps towards a detailed understanding of PGPRs and developments of consistently efficient applications in diverse environments are set.