Validation of endophytic bacteria colonisation in tissue culture-derived oil palm plantlets via green fluorescent visualization

Abstract

This study aimed to validate the colonisation capability of endophytic bacteria (EB) isolates, Bacillus cereus EB2 and Pseudomonas aeruginosa EB35, that previously exhibited their potentials as biological control agents (BCAs) against the Ganoderma spp., a pathogen for Ganoderma disease in oil palm. Here, we demonstrated a rapid method to determine the colonisation capacity of the selected EB using oil palm tissue culture plantlets and a green fluorescent protein (GFP) visual marker. Wounded plantlet roots were inoculated with GFP-tagged B. cereus EB2 and P. aeruginosa EB35 while the plantlets without EB inoculation served as controls. The GFP signals appeared as bright green spots or lines in the inoculated GFP-tagged EB cells in root and leaf plantlet tissues, respectively, under the confocal laser scanning microscopy (CLSM) 5 days post-inoculation. In contrast, there was no intense GFP spots in neither the control root nor leaf tissues. The cracks in the roots by wounding facilitated the entry of the GFP-tagged EB cells into root tissues, allowing for endophytically colonisation of the root and above-ground tissues. Subsequent result of polymerase chain reaction (PCR)-GFP analysis further displayed the endophytic nature and early chronological colonisation of the tested EB. This is a preliminary report on root colonisation by a Gram-positive endophyte, B. cereus EB2 and leaf tissues colonisation by both EB isolates as internal colonisers, demonstrating their potential as BCAs to protect oil palm against Ganoderma spp. for a sustainable disease management.