A MINIATURIZED AND RAPID BIOASSAY FOR THE SELECTION OF SOIL BACTERIA SUPPRESSIVE TO PYTHIUM BLIGHT OF TURFGRASSES

A miniaturized plant assay was developed to screen bacterial strains for their ability to suppress Pythium blight of turfgrasses caused by Pythium aphanidermatum. Bacteria were recovered from soil and thatch from both high-maintenance and low-maintenance turfgrass sites and tested on creeping bentgrass plants grown in wells of tissue culture plates (TCP) and then in pots of perennial ryegrass in the growth chamber (GC). Of the 200 strains screened in TCP assays, 86 significantly suppressed Pythium blight (disease rating < 3.0 after 7 days) as compared with untreated plants. The highest frequency of antagonist recovery (54.5%) was from the thatch of both low- and high-maintenance turfgrass sites, while the lowest frequency of antagonist recovery (27.3%) was from rhizosphere soil in both types of maintenance sites. Of the strains from thatch that were suppressive in TCP assays, 45% also were effective in GC assays. The lowest frequency of suppressive bacterial strains in both TCP assays and GC assays (24.1%) was with strains recovered from rhizosphere soil under high-maintenance (i.e., golf course) turf. Bacterial strains recovered from thatch were more suppressive than those recovered from rhizosphere soil in TCP assays but not in GC assays. Antagonistic bacteria recovered from media selective for enteric bacteria and Pseudomonas spp. were as suppressive to Pythium blight of creeping bentgrass as those recovered from a nonselective medium. However, enteric bacteria were more suppressive to Pythium blight of perennial ryegrass than were general heterotrophic bacteria or Pseudomonas spp. Only two strains of Enterobacter cloacae tested were effective in TCP assays and only one of these was effective in GC assays. All bacterial strains that were ineffective in TCP assays also were ineffective in GC assays. The TCP assay developed in this study proved to be an effective means of rapidly screening large numbers of bacterial strains in plant assays for the suppression of Pythium blight.