ISOLATION AND CHARACTERIZATION OF PSEUDOMONAS AERUGINOSA WITH ANTAGONISTIC ACTIVITY AGAINST PYTHIUM APHANIDERMATUM

A study was conducted to isolate and characterize bacterial strains from greenhouse soils with potential for suppression of Pythium damping-off of cucumber. Out of 100 bacterial isolates collected from greenhouse soils, 20 isolates were found to be antagonistic to Pythium aphanidermatum in in vitro studies. The size of the growth inhibition zone of P aphanidermatum on potato dextrose agar varied from 4 to 9 mm, with an average of 6.2 mm. Identification of these bacterial isolates to the species level using API20NE as well as sequences of the 16S ribosomal RNA confirmed their identity as Pseudomonas aeruginosa. Bacterial isolates showed optimum growth at 30 degrees C, whereas a temperature of 37 degrees C favored bacterial antagonistic activity. Bacterial growth and antagonistic activity were not affected at high salinity levels (10 dS m(-1)) known to be stressful to cucumber production. This provides evidence for tolerance to salinity among the isolated bacteria. In vivo assays provided evidence for inhibition of Pythium damping-off at 28 degrees C, with no effect on growth of cucumber seedlings. This is the first report of occurrence of Ps. aeruginosa with antagonistic activity against P aphanidermatum in greenhouse soils in Oman.