Suppression of summer patch by rhizosphere competent bacteria and their establishment on Kentucky bluegrass

Several hundred bacteria isolated from the turfgrass rhizosphere were evaluated for the suppression of summer patch, caused by the fungus, Magnaporthe poae, and for rhizosphere competence on Kentucky bluegrass cv. Baron. Three isolates, identified as Pseudomonas sp. 105-2, Comamonas acidovorans HF42 and Enterobacter sp. BF14, significantly suppressed summer patch symptoms compared to untreated control plants in a greenhouse-growth chamber assay. All three were present in populations greater than log5 cfu g−1 f.w. turfgrass rhizosphere 2 wk after application. The three isolates established and maintained detectable populations in turfgrass when repeatedly applied to field plots during the summer months of 1992, 1993 and 1994. Strains were detected in field turfgrass samples that consisted of thatch, root and soil at up to 103–104 cfu g−1 f.w. sample. Populations of the three isolates were higher in the rhizosphere than in the turf thatch layer when compared on a g−1 sample basis. In 1994, pathogen-inoculated field plots treated with the C. acidovorans HF42 or Pseudomonas sp. 105-2 significantly reduced summer patch symptoms compared to untreated controls.