In-vitro Antibacterial Activity of Thymol and Eugenol against Ralstonia solanacearum Isolated from Potato

Ralstonia solanacearum-caused bacterial wilt is a serious limitation to potato output (Solanum tuberosum L.). R. solanacearum is mainly spread through infected seed stocks but can also spread from infested to healthy fields by farm equipment, irrigation water and plant-to-plant through the rhizosphere. There are no known conventional bactericides that can effectively control this soil-borne pathogen at this time. This study aimed to investigate 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. Disc diffusion and minimum inhibition concentration (MIC) techniques were used to test the inhibitory impact of these substances. Chequerboard assay was used to conduct a combinational test. Thymol and eugenol had 27 mm and 17 mm inhibition zones, respectively, at a dosage of 100 mg mL-1. Both eugenol and thymol displayed bactericidal effects against R. solanacearum, and their MICs were determined to be 275 and 175 g mL-1, respectively. An additive effect was found in a combinational test, demonstrating that their use together did not considerably improve inhibition. Both chemicals have the potential to be used as antibiotics to treat bacterial wilt disease, albeit thymol has a lower concentration than the other. However, in vivo use of these volatile chemicals encounters difficulties that can be overcome by encapsulating them in a suitable nanocarrier.