ABSTRACT:
150 bacterial isolates were isolated from rhizosphere of cucumber. Among them,19 isolates showing inhibition percentagegreater than 25% against Pythium ultimum in vitro were chosen for further studies. Four known strains namely 2-79, CHA0, CHA89, and PF-5 were screened as controls. These strains also showed varied levels of PGPR traits –siderophore and HCN. Detection of PCA gene was evaluated with a PCR-based assay. The PCA gene was detected in strains 2-79, Y-21, F141, F10, M80-3, T37, M8-10, CHN4, and T30-1. Strain 2-79 was used as positive control for the detection of this gene. Colonies of four strains including 2-79, Y-21, F141, and F10 showed production of PCA with presence of crystalline deposits after one week development. Greenhouse screens showed all nine strains contain PCA gene can control pre-emergence damping-off. In addition, four strains 2-79, Y-21, F141, and F10 controlled better both pre and post-emergence damping-off. Positive activation were found in strains which produced high levels of siderophore and HCN. There were two strains CHA0 and PF5 that showed high levels of biological control in vivo. No obvious strains CHA0 and PF-5with PCA gene were found, but screening showed these strains produce siderophore and HCN well. Results showed a meaningful correlation between production of PCA, siderophore, and HCN from one side and inhibition of post and pre-emergence damping-off in vivo from the other side.