Endophytic colonization of spruce by plant growth-promoting rhizobacteria

We evaluated internal tissue colonization of hybrid spruce (Picea glauca X P. engelmannii) seedlings by two plant growth-promoting rhizobacteria (PGPR ) strains, Bacillus polymyxa strain Pw-2R and Pseudomonas fluorescens strai n Sm3-RN, using surface sterilization-dilution plating and immunofluorescen t antibody staining assays. Both strains were consistently detected inside spruce root and stem tissues 5 months after seed inoculation according to a surface sterilization-dilution plating assay. Internal tissue population s izes ranged from log 3.9 to log 5.0 cfu g(-1) plant tissue. Visualization o f bacteria using immunofluorescent antibody staining suggested that these m icroorganisms colonized root hair and cortical cells as well as stem vascul ar tissues. Our results confirm the capability of these two plant growth-pr omoting rhizobacterial strains to enter spruce root tissues after soil inoc ulation and ultimately colonize stem vascular tissue without causing visibl e symptoms of disease. (C) 1999 Federation of European Microbiological Soci eties. Published by Elsevier Science B.V. All rights reserved.