African Journal of

  • Abbreviation: Afr. J. Biotechnol.
  • Language: English
  • ISSN: 1684-5315
  • DOI: 10.5897/AJB
  • Start Year: 2002
  • Published Articles: 12481

Full Length Research Paper

Efficacy of thymol and eugenol against bacterial wilt bacterium Ralstonia solanacearum

George Oluoch
  • George Oluoch
  • Institute for Basic Sciences Technology and Innovation, Pan African University, Kenya.
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Edward George Mamati
  • Edward George Mamati
  • Department of Horticulture and Food Security, Jomo Kenyatta University of Agriculture and Technology, Kenya.
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Viviene Matiru
  • Viviene Matiru
  • Department of Botany, Jomo Kenyatta University of Agriculture and Technology, Kenya.
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Moses Nyongesa
  • Moses Nyongesa
  • National Potato Research Centre, Kenya Agricultural and Livestock Research Organization, Kenya.
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  •  Received: 28 April 2021
  •  Accepted: 10 June 2021
  •  Published: 30 June 2021


Bacterial wilt caused by Ralstonia solanacearum is a major constraint to production of potatoes (Solanum tuberosum L). To date, there are no known conventional bactericides which provide effective control of this soil borne pathogen. This study aimed at investigating the antibacterial activity of eugenol and thymol which are the major components of thyme and clove essential oils, respectively against R. solanacearum. The pathogen was isolated from potato tubers exhibiting bacterial wilt symptoms. The inhibitory effect of these compounds was assayed by disc diffusion and minimal inhibition concentration (MIC) methods. Combinational test was also performed using chequerboard assay. At a concentration of 100 mg mL-1, thymol and eugenol had inhibition zones of 27 and 17 mm, respectively. The MIC of eugenol and thymol were determined as 275 and 175 µg mL-1, respectively and both had bactericidal effect against R. solanacearum. Combinational test revealed an additive effect indicating that their combined use does not significantly enhance inhibition. Both compounds have a potential to be exploited as antibiotic for the management of bacterial wilt disease albeit thymol at a lower concentration. Exploitation of these volatile compounds in vivo however faces challenges which can be overcome through nanoencapsulation by an appropriate nanocarrier.
Key words: Essential oils, inhibitory effect, combinational test, chequerboard assay, bactericidal effect.