ISOLATION OF THE CHITINOLYTIC BACTERIA XANTHOMONAS-MALTOPHILIA AND SERRATIA-MARCESCENS AS BIOLOGICAL-CONTROL AGENTS FOR SUMMER PATCH DISEASE OF TURFGRASS

A mycelial baiting method was used to isolate chitinolytic bacteria fr om soils known to harbor Magnaporthe poae, the causal agent of summer patch on Kentucky bluegrass. Two bacterial isolates, identified as Xan thomonas maltophilia 34S1 and Serratia marcescens 9M5, suppressed summ er patch symptom development in Kentucky bluegrass cv. Baron by more t han 70 and 50%, respectively, when compared to untreated control plant s in growth chamber studies. Further studies indicated that time of ap plication and concentration of bacteria influenced the degree of disea se suppression. In general, bacteria were least effective in suppressi ng disease when they were applied to plants at dates closest to planti ng, and were most effective when applied up to 4 wk after planting. In bacterial concentration experiments, the highest degree of disease su ppression was observed when plants were treated with the highest conce ntration of X. maltophilia 34S1. In contrast, the highest concentratio n of S. marcescens 9M5 did not provide the highest amount of disease c ontrol. Instead, less disease suppression was observed for plants trea ted with bacterial concentrations greater than the observed optimal co ncentration of 10(9) cfu ml(-1). Survival of both bacteria was monitor ed in soil and the rhizosphere after application of three different ba cterial concentrations. Populations of both bacteria in the rhizospher e stabilized 18 days after the final bacterial application, regardless of the concentration. For both bacteria, however, significant differe nces in non-rhizosphere soil populations, which steadily declined over time, were observed between the highest and lowest concentrations use d throughout the sampling period.