Antibacterial Activity of Japanese Honeysuckle (Lonicera Japonica) Against Plant Pathogenic Bacteria

Liew, Xiao Ying (2025) Antibacterial Activity of Japanese Honeysuckle (Lonicera Japonica) Against Plant Pathogenic Bacteria. Final Year Project (Bachelor), Tunku Abdul Rahman University of Management and Technology.

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Abstract

Plant pathogens in soil are culprits of extensive yield losses in many crops worldwide. Ralstonia solanacearum is one of the soil-borne plant pathogens that result in destructive crop illness worldwide due to its extreme aggressiveness and broad host range. The pathogen causing green-wilting symptoms affecting approximately 43 plant species in Malaysia, is particularly important affecting solanaceous crops like chili (Capsicum annum). Chili is one of the most cultivated crops in Malaysia where bacterial wilt caused by R. solanacearum can lead to substantial yield loss. Management of this disease using chemical pesticides has yield inconclusive results due to its soil dwelling capability. Alternatives in managing this bacterium are urgently needed. The present study aimed to evaluate in vitro and in vivo antibacterial activity of L. japonica crude extract against the R. solanacearum isolated using TZC medium. The findings indicate indiscernible antibacterial activity of the L. japonica extract against R. solanacearum. The crude extract showed no inhibition up to 400 mg/mL, compared to positive control that exhibited a clear zone of 22.00 ±0.0 mm. However, bacterial inhibition was observed in wells containing 50 mg/mL to 100 mg/mL crude extracts via broth microdilution assay. As the research progressed to nursery trials, phytotoxicity of the plant extracts against the chili seedlings was observed even at the lowest concentration. Population count of R. solanacearum in the treated soils was performed instead, to observe effects of plant extracts against the pathogen. The pathogen population in the control seedlings was recorded to have 3.11 x107 CFU/g 1-week after application and the CFU count was not significantly reduced in the following week. Similar observations were recorded for treatment A (25% commercial extract), B (50% commercial extract), C (100 mg/mL crude extract) and D (combination of commercial and crude extract), with average population of 3.22 x107, 2.33 x107, 5.56 x107, 3.56 x107 CFU/g respectively 1-week after application, indicating that plant extracts have shown no effect in suppressing the pathogen. Further studies on confirming identity of R. solanacearum and purification of L. japonica crude extract would be needed to draw more conclusive results.