Antagonistic rhizobacteria, more specifically fluorescent pseudomonads, are known to control fungal root
diseases of agronomic crops. In this study, Pseudomonas aeruginosa bacteria were isolated from Hibiscus
sabdariffa (roselle) rhizosphere. Bacterial isolate was assayed by dual culture technique for potential biological
control agent against Rhizoctonia solani, Fusarium oxysporum, Sclerotium rolfsii and Macrophomina
phaseolina as phytopathogenic fungi in vitro. Among P. fluorescens isolates, isolate No 9 exhibited the highest
activity and produced blue green pigment. Based on biochemical and physiologic tests and MicroScan, this
isolate identified as P. fluorescens No 9. Isolate No 9 was shown to have broad spectrum in vitro antibiotic
activity against fungal plant pathogens. It was able to produce considerable amount of dark blue colour pigment
(2.3g), which yielded 14 mg of purified greenish-yellow metabolite exhibiting effect on spore production and
hyphal morphology of F. oxysporum. phzE gene, which is part of the phenazine biosynthetic pathway, was used
as universal and to detect the ability of bacteria to produce phenazine. Results from this study provide
comprehensive information on biocontrol mechanisms that can be used for commercial use and appropriate
application of this bacterium.