Microbial succession in the rhizosphere of live and decomposing barley roots as affected by the antagonistic strain Pseudomonas fluorescens DR54-BN14 or the fungicide imazalil

The protocol used in the present study was a long-term mesocosm experiment where the microbial succession around live barley roots and subsequent decomposing roots was assessed after seed coating with either the antagonistic strain Pseudomonas fluorescens DR54-BN14 or the fungicide imazalil. Four diversity measures were used: community level physiological profiles (CLPP), Bacteria-specific polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE), actinomycete-specific PCR-DGGE and phospholipid fatty acid (PLFA), as well as total cell counts, colony-forming units (CFU) and culturable spore formers, and spore counts of the Bacillus cereus group. Analysis of non-treated plants provided a baseline description of the natural microbial succession from which effects of the treatments could be evaluated. A microbial succession occurred both in the rhizosphere and around decomposing roots, shown with all three diversity measures. A clear response to root death was found, and a clear distinction between root tip and root base samples. Using the recommended concentration of imazalil and a realistic number of DR54-BN14 for seed coating, transient, initial effects of both treatments on the microbial communities were observed at the root base with the PLFA analysis only. The lack of lasting significant side effects of DR54-BN14 is in agreement with an initial fast reduction in culturable DR54-BN14.