Colonization study of antagonistic Pseudomonas sp. in Vanilla planifolia using green fluorescent protein (GFP) as a marker

Vanilla (Vanilla planifolia Andrews) is a high value crop cultivated for the production of Vanillin, one of the most valuable flavoring commodities in the food and beverage industry worldwide. Vanilla cultivation is severely hampered by the prevalence of various fungal diseases. Fusarium oxysporum, Rhizoctonia solani and Sclerotium rolfsii were isolated from naturally infected vanilla plants and an attempt was made to curtail the spoilage caused by the isolated fungal pathogens using biocontrol agents. Pseudomonas fluorescens P7 and Pseudomonas putida P4 were isolated from vanilla rhizosphere soil and checked for their capability to control fungal pathogens of vanilla both under In vitro and in vivo conditions. The endophytic colonisation ability of the selected rhizosphere bacteria were evaluated after genetically tagging them with a constitutively expressing green fluorescent protein gene (gfp). The green fluorescent endophytic bacteria were observed within the plant tissue when cross sections of the petiole were viewed under the confocal laser scanning microscope. The bacterial isolates were effectual in controlling the selected fungal pathogens of vanilla. The gfp- tagged Pseudomonas sp.   was populated within the intercellular spaces of the vanilla leaves one week after its foliar spraying. Key words: Biocontrol, confocal laser scanning microscope, endophytic bacteria, Fusarium oxysporum, Rhizoctonia solani, Sclerotium rolfsii.