Rhamnolipid biosurfactant against Fusarium sacchari--the causal organism of pokkah boeng disease of sugarcane.

Pokkah boeng disease on sugarcane caused by the fungus Fusarium sacchari results considerable damage to the crop leading to top rot, the most serious and advanced stage of pokkah boeng, where the growing point is killed and the entire top of the plant dies. In the present study, the effect of rhamnolipid biosurfactant as an antifungal agent against F. sacchari to control pokkah boeng disease was investigated. On the basis of surface tension reduction, 12 bacterial isolates were selected as potent biosurfactant producers and eight of them showed antagonistic effect against F. sacchari. Among the eight, the isolate DS9 was found as the effective inhibitor of the fungus in vitro which was further evaluated using its biosurfactant present in whole culture, cell-free culture supernatant and crude biosurfactant at various concentrations. Reductions of fungal growths were found more with crude biosurfactant. By sequencing 16S rRNA, DS9 was identified as P. aeruginosa and the produced biosurfactant was characterized as rhamnolipid by Liquid Chromatography-Mass Spectrometry (LC-MS) analysis. The rhamnolipid biosurfactant inhibits phytopathogenic fungi F. sacchari and therefore seems to be a good biocontrol agent to control pokkah boeng disease of sugarcane.