Potential of Indigenous Rhizobacteria as Biocontrol Agents of Xanthomonas sp.

Bacterial leaf blight (BLB) disease caused by Xanthomonas sp. is one of the main diseasesof eucalypt plants. The utilization of rhizobacteria to manage diseases in other agriculturalecosystems has been reported. This study aims to select and characterize rhizobacteria fromthe rhizospheric zones of Eucalyptus pellita with antagonistic nature against Xanthomonas sp.and to identify isolates that have the best potential as biocontrol agents in the Eucalyptus–Xanthomonas pathosystem. The research was conducted in-vitro. The antagonism test wasarranged in a completely randomized design with three replications. Characteristics ofantagonistic rhizobacteria were examined based on their ability as plant growth-promotingbacteria (PGPR). Identification of potential rhizobacteria was performed based on 16S rRNAsequences. There were 14 isolates showing antagonistic activities against Xanthomonas sp. Theresults showed that the rhizobacteria had significant antagonistic impacts against the pathogen.Characterization of the 14 isolates indicated that all isolates produced siderophores and indoleacetic acid (IAA). As many as 13 isolates produced protease, eight isolates were able to dissolvephosphate, and three isolates synthesized hydrogen cyanide (HCN). The isolate with the highestinhibitory effect was isolate RE081, whose activity was classified as very strong. The RE81isolate also showed the best properties in the HCN test (+++), IAA production (19,29 mg L–1),and the ability to dissolve phosphates. Molecular analysis of the 16S rRNA gene disclosed thatRE81 is Pseudomonas aeruginosa (100%).