SELECTION AND CHARACTERIZATION OF SIDEROPHORE-PRODUCING RHIZOBACTERIA AND POTENTIAL ANTAGONISTIC ACTIVITY TOWARD Ralstonia solanacearum

Ralstonia solanacearum is an important disease of tomato.  An alternative method to control the disease is the application of biocontrol agents.  Plant Growth-Promoting Rhizobacteria (PGPR) could be used as potential biocontrol agents.  PGPR with siderophores is among compounds having important role in disease suppression.  This experiment was conducted to select and characterize the siderophore-producing rhizobacteria from tomato and to determine their potential as antagonistic agents for R. solanacearum.  Candidates of the PGPR were isolated from tomato grown in West Java Province, Indonesia. The isolates were detected as siderophore-producing bacteria using CAS medium. Among 29 isolates producing siderophore and having negative result on hypersensitivity reaction, two isolates provided the widest diameter of inhibition zone toward R. solanacearum.  Both isolates were CP1C and CP2D with diameter of inhibition zone up to 3.6 and 7.0 mm, respectively.  Based on the sequence of 16S rDNA, isolate CP1C was identified as Brevundimonas sp., while isolate CP2D was identified as Enterobacter sp.  Both bacteria did not cause negative effect on the increasing plant height and dry weight of the plants, compared with control.