The objectives of the present work were to determine which fruit peel extracts inhibit the growth of Agrobacterium tumefaciens and also whether they can reduce or prevent crown gall disease in plants. Four fruit peel extracts (lemon, banana, passionfruit, rambutan) were compared and evaluated in terms of their antibacterial effects on Agrobacterium tumefaciens.

Three experiments (Direct Inhibition, Zone of Inhibition and Tumour Formation Assay) were carried out in our project. In the Direct Inhibition experiment, 100 microlitre of Agrobacterium tumefaciens and fruit peel extract were plated onto nutrient agar then incubated at 30 degree celsius for 48 hours before the Colony Forming Units (CFU) were counted. For the Zone of Inhibition experiment, five wells were punched using a glass hole punch and 100 microlitre of Agrobacterium tumefaciens and fruit peel extract were transferred into each well before the diameter of inhibition was measured. Lastly, 3ml of Agrobacterium tumefaciens and 3ml of fruit peel extract were transferred onto each carrot stick in a petri dish while their respective masses were measured over 10 days in the Tumour Formation Assay experiment.

Results showed that rambutan peel extract had the greatest effect on Agrobacterium tumefaciens, followed by banana, lemon then passionfruit. Furthermore, it was also concluded that only rambutan peel extracts active and small molecules were able to diffuse through the nutrient agar from the Zone of Inhibition experiment. Lastly, we also found that that the protective effects of host-pathogen interactions between the carrot and Agrobacterium tumefaciens inhibited the antimicrobial effects of the fruit peels extracts. As such, our results imply that rambutan peel extract is most effective against Agrobacterium tumefaciens and thus would be most the most viable alternative against the crown gall disease.

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