Potential of Endophytic and Rhizobacteria as an Effective Biocontrol for Ralstonia syzygii subsp. syzygii

Abstract

Background and Objective: Sumatra disease caused by Ralstonia syzygii subsp. syzygii is reported to generate severe damage to clove plantation in Indonesia. The chemical control of insect vector has partially been successful yet impacted on environmental problems. Endophytic and rhizobacteria have been reported as potential biocontrol agents for many plant diseases due to safety of human and non-target organisms. The objective of this study was to find the potential endophytic and rhizobacteria for biocontrol of Ralstonia syzygii subsp. syzygii. Methodology: The endophytic and rhizobacteria were screened for their indole acetic acid (IAA) production, phosphate solubility, antibiosis activity and followed by molecular characterization. The experiment was arranged in a Completely Randomized Design (CRD) with 3 replications. The data were subjected to statistical analysis using one-way ANOVA and means were separated by DMRT (p<5%). Results: Forty six bacterial endophytes were successfully recovered from roots, stems, leaves and flowers of the healthy clove. Also, 66 isolates were isolated from the rhizospheric soil. Among them, 24 endophytic and 21 rhizobacteria produced indole acetic acid (IAA). Only rhizobacterial isolates but not endophytes indicated phosphatase activities. The in vitro antibiosis assay against Ralstonia syzygii subsp. syzygii showed that 23 endophytic and 14 rhizobacteria produced inhibition zone. Furthermore, 16S rDNA analysis confirmed that such endophytic and rhizobacteria were identified as Bacillus subtilis subsp. subtilis and Bacillus cereus, respectively. Conclusion: Endophytic and rhizobacteria could produce IAA, dissolve phosphate and generate the biggest inhibition zones against R. syzygii subsp. syzygii while molecular assay identified them as B. subtilis subsp. and B. cereus.