Effects of Rhizoctonia solani on Root Colonization of Canola by Pseudomonas fluorescens Strain UTPF86

Root colonization by antagonist bacteria has been considered as a prerequisite for a successful biocontrol. For an effective suppression of plant disease, an efficient and fast colonization is necessary to prevent the establishment of pathogen on the root system. Colonization of canola root by strain UTPF86 were investigated with and without Rhizoctonia solani AG-4, under greenhouse conditions. Among 14 strains of Pseudomonas fluorescens, strain UTPF86 was selected on the basis of biocontrol and root colonization activity. Chloramphenicol and tetracycline resistant mutants of this strain, were used in all experiments. The roots were sampled at 1, 2, 3 and 4 weeks after planting. Bacterial population was determined using dilution procedure. Bacteria enumerated on selective S1 medium. This study demonstrated that in the presence of R. solani, root colonization was significantly increased by strain UTPF86. Furthermore, the rate of root colonization increased during the first two weeks and then it began to decrease during the third and fourth weeks post planting.