ABSTRACT

Endophytes are organisms living as symptomless colonies within host plants. Endophytic microorganisms, including bacteria and fungi, have gained significant attention in recent years due to their fascinating ecological relationships with host plants.They produce several metabolites, which have found wide applications in agriculture, medicine, and other industries. This thesis was aimed at the molecular characterisation of endophytic microorganisms present in the stems of tomato (Solanum lycopersicum L.) plants, exploring their antimicrobial activity to evaluate their potential as sources of antimicrobial compounds. The research was carried out in two dimensions simultaneously. Bacterial and fungal endophytes were isolated from a healthy tomato stem, while their phytopathogen counterparts were isolated from a diseased tomato stem. The identity of microorganisms (endophytes and phytopathogens) isolated from tomato stem were investigated using phenotypic characteristics. Antagonistic co-culture method was used to observe the antagonistic effect of the endophytes on phytopathogens. Using molecular techniques, the identities of the bacterium and fungus that had antimicrobial properties were determined, the identity of a pathogenic fungus was also confirmed. Cell filtrate was extracted from the endophytes and tested on the pathogens using the poison plate method. The results of the phenotypic tests showed Enterobacter spp., Pseudomonas spp., and Pantoea spp. as the suspected endophytic bacteria, while species of Fusarium, Rhizopus, and Botrytis were obtained as the suspected endophytic fungi. Pseudomonas spp. and Aspergillus spp. were also observed as the suspected bacterial and fungal pathogens respectively. Among the screened endophytes, Pantoea spp. had antibacterial activity against Pseudomonas spp., while Rhizopus spp. had an antifungal effect on Aspergillus spp. The molecular analysis confirmed the identity of the endophytic bacterium and fungus as Pantoea agglomerans and Rhizopus stolonifer, the identity of the pathogenic fungus was also confirmed to be Aspergillus niger. Cell filtrate of Pantoea agglomerans showed antibacterial activity against the test pathogen (Pseudomonas syringae), while that of Rhizopus stolonifer exhibited antifungal property against Aspergillus niger. The findings from the study revealed that products from Pantoea agglomerans and Rhizopus stolonifer can be used to produce antimicrobial agents. The future direction to the study is to investigate how secondary metabolites from these organisms can be explored as antimicrobial agents.