IN VITRO CHARACTERIZATION OF SELECTED INDIGENOUS RHIZOBACTERIAL STRAINS AS BIOCONTROL AGENT OF BACTERIAL WILT DISEASE ON CHILI

Abstract

Bacterial wilt caused by Ralstonia solanacearum is the important dangerous diseases in chili. Until now this disease has been difficult to control; while the bacteria attack the xylem vessel they cannot be reached by any bactericide. Biocontrol is potential for controlling this disease. One group of important biocontrol agents is the plant growth promoting rhizobacteria (PGPR). Based on in planta screening method, we have found 13 indigenous rhizobacterial strains from healthy chili’s rhizosphere, which have the ability to control bacterial wilt and to increase growth and yield of chili. This research is aimed at characterizing the direct mechanisms of selected indigenous rhizobacterial strains as biocontrol agents of R. solanacearum in vitro. The physiological characters of indigenous rhizobacterial strains as biocontrol agents had been observed, including production of antibiotic, siderophore, HCN, haemolysine, protease, and biosurfactan. For root colonization rifampicin mutants of indigenous rhizobacterial strains had been the results of in vitro analysis showed that those selected rhizobacterial strains had various physiological characters as biocontrol agents. Not all biocontrol tested characters have been produced by indigenous rhizobacterial strains. Only RZ2.1AP4 strains showed the positive on 3 characters. All indigenous rhizobacterial strains produced biosurfactant but only Pseudomonas hibiscicola strain RZ1.1AG4 showed the highest viscosity. All rifampicin mutants of indigenous rhizobacterial strains have colonized chili roots on rhizoplane and in the root tissues (endophyte) from nursery until 9 days after planting. RZ2.1AP2 and Klebsiela michiganensis strain RZ1.3AG4 showed the highest bacterial population on chilli roots. The bacterial population was higher in root tissue (endophytes) than on the root surface (rhizoplane) from seedling stage until 9 days after transplanting.