Impact of a beneficial and of a pathogenic Fusarium strain on the fingerprinting-based structure of microbial communities in tomato ( Lycopersicon esculentum Milll.) rhizosphere

Fusarium solani strain FsK (FsK), isolated from a plant pathogen-suppressive compost, grows endophytically in tomato roots and controls infestations by Fusarium oxysporum f.sp. radicis-lycopersici (FORL). The effect of root colonization by the two fungi on the diversity of rhizosphere microbial community was studied. Tomato plants were inoculated with FsK and/or FORL and rhizosphere soil was collected 8, 15 and 30 days post inoculation (dpi) and analyzed by denaturating gradient gel electrophoresis (DGGE) of PCR-amplified internal transcribed spacer (ITS) sequences of fungi and 16S rRNA gene sequences of common rhizosphere bacterial guilds like alpha-proteobacteria and pseudomonads. Cluster analysis of DGGE fingerprints showed that FsK had a transient impact on the fungal and alpha-proteobacterial community only during its endophytic stage (15 dpi), while FORL had a readily distinguished and persistent effect on the fungal community. The changes observed in the rhizosphere fungal and bacterial communities may depict the interactions of the two fungal inocula with the plant. Cloning of selected DGGE bands stimulated by FsK showed that the responsive bacteria were closely related to species known to include biological control agents (BCA). Overall, the inoculation of FsK in tomato rhizosphere did not appear to have a significant impact on the diversity of non-target microbial groups inhabiting plant rhizosphere.