The development of Fusarium culmorum structures growth of Pseudomonas fluorescens 2137 gus-marked strain and interactions between them in rhizospheric soil and on barley rhizoplane were monitored. Immunofluorescent staining was used for F. culmorum identification. P. fluorescens suppressed growth of F. culmorum mycelia and macroconidia but stimulated forming of its chlamydospores in rhizospheric soil. P. fluorescens did not suppress F. culmorum on barley root surface. In turn F. culmorum could suppress P. fluorescens growth in barley rhizosphere and on rhizoplane. In certain periods the quantity of P. fluorescens on barley root surface was decreased significantly when F. culmorum presented on roots. Nevertheless the treatment of barley grain with P. fluorescens led to decrease of root rot intensity of plants in soil with F. culmorum addition.