Evaluation of bacterial antagonists for reduction of summer patch symptoms in Kentucky bluegrass

Ten bacterial strains previously identified for their ability to control soilborne pathogens on agronomic crops were evaluated for their ability to suppress summer patch disease caused by Magnaporthe poae in Kentucky bluegrass (Pen pratensis L). Bacterial strains varied in the ability to inhibit the growth of M. poae in agar plate bioassays, although most strains inhibited the fungus to some degree. Three strains originally isolated from wheat, Pseudomonas fluorescens 2-79, P. fluorescens 13-79, and Bacillus subtilis D-39Sr, and two strains originally isolated from cotton, Enterobacter cloacae EcH-1 and EcCT-501, significantly reduced summer patch symptoms by between 29 and 46% compared to untreated control plants after a S-week period in the growth chamber. The live strains did not reduce summer patch disease in field trials in 1990. However, in 1991, B. subtilis D-39Sr and E. cloacae EcH-1 reduced summer patch severity by 53 and 49%, respectively, over the entire season compared to untreated control plots. In 1994, both B. subtilis D-39Sr and E. cloacae EcH-1 also reduced summer patch severity over the entire season by up to 39 and 34%, respectively, compared to the untreated control in field plots, All five bacteria that reduced summer patch in growth chamber studies were present in the rhizosphere of greenhouse/growth chamber grown turfgrass at 10(4) to 10(6) CFU/g of fresh weight sample 2 weeks after application to plants. A single sampling of field plots during 1991 and four separate samplings of field plots during 1994 indicated that introduced bacteria were present within the turf at populations above 10(3) CFU/g of sample.