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Rhizobacterial colonization of bermudagrass by Bacillus spp. in a Marvyn loamy sand soil

Richard Murphey Coy, David W. Held, Joseph W. Kloepper
Applied soil ecology 2019 v.141 pp. 10-17
Bacillus pumilus, Bacillus sphaericus, Cynodon dactylon, bacteria, endophytes, grasses, growth promotion, loamy sand soils, nitrogenase, phosphates, phyllosphere, population density, population dynamics, rhizoplane, siderophores, solubilization, turf management
Rhizobacterial inoculants have been previously shown to demonstrate growth promotion in bermudagrass, yet mechanisms for growth promotion and colonization of bermudagrass are unknown. Using rifampicin-resistant strains of Bacillus spp., colonization and persistence of bacteria were assessed under field conditions in the rhizoplane, rhizosphere, endorhiza, and endophytic phyllosphere. Strains of Bacillus pumilus and B. sphaericus were determined to have nitrogenase and phosphate solubilization activity and to produce siderophores. These results showed differences between strains of the same species, and phosphate solubilization was greatest under alkaline conditions. The characteristics of the rhizobacterial strains provide greater insights into the growth promotion demonstrated in bermudagrass. All bacterial strains tested were detectable in plant and soil within 24 h after inoculation and persisted through 12 week post inoculation. Colonization occurred on both external and internal plant structures, but was typically higher in rhizoplane and rhizosphere samples. Populations remained stable for 2 week after inoculation with drastic declines occurring after 6 week. Bacillus sphaericus was the most prolific colonizer, having the greatest population density per sample and least drastic population decline 12 week after inoculation. These results provide better understanding of plant-microbe-interactions in amenity grasses and can aid in determining application frequencies and intervals of biostimulants for turfgrass management.