Selection of Bacterial Antagonists Using Enrichment Cultures for the Control of Summer Patch Disease in Kentucky Bluegrass

A continuous enrichment culture procedure was used to isolate bacteria from various soil sources capable of suppressing summer patch disease of turfgrass. Cultures consisted of a minimal salts medium supplemented with the mycelium of Magnaporthe poae, the causal agent of summer patch, as the sole carbon source. Percentages of chitinolytic bacteria increased in all enrichments over time. Approximately 30% of randomly selected isolates from enrichment cultures significantly reduced summer patch symptom development compared with untreated controls. Six isolates consistently suppressed summer patch in Kentucky bluegrass by more than 50% compared with controls in repeated experiments. All six isolates colonized the turfgrass rhizosphere in high populations. The six isolates ranged in the spectrum of extracellular enzymes that they expressed. The best disease-suppressing isolate, N4-7, expressed chitinase, glucanase, lipase, and protease activity, and inhibited the growth of M. poae in vitro.