English

Oluoch George,George Mamati Edward,Nyongesa Moses,Matiru Viviene

doi:10.5897/ajb2021.17353

Abstract

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.

Highlights

Potato (Solanum tuberosum L.) is one of the most important food crops which provides a greater potential for food security and incomes around the world (Gildemacher et al, 2009)
This is caused by Ralstonia solanacearum, a Gram-negative bacterium which causes bacterial wilt disease in potato and on more than 200 other plant species that include tomato, eggplant, tobacco, geranium, pepper and banana
The identity of the virulent isolates was further confirmed by Polymerase chain reaction (PCR) using primers specific to R. solanacearum species (Figure 1) (Fegan and Prior, 2005)

Summary

Introduction

Potato (Solanum tuberosum L.) is one of the most important food crops which provides a greater potential for food security and incomes around the world (Gildemacher et al, 2009). Bacterial wilt has no known bactericide commercially released for use which can efficiently manage to control the disease and it leads to high reduction in crop yields This is caused by Ralstonia solanacearum, a Gram-negative bacterium which causes bacterial wilt disease in potato and on more than 200 other plant species that include tomato, eggplant, tobacco, geranium, pepper and banana Damaged roots arising from wounds caused by soil borne organisms like the nematodes or wounds formed by the emergence of lateral roots can spread R. solanacearum by acting as an avenue for infection (Karim and Hossain, 2018) Once it gets into the roots, it colonizes the xylem in the vascular bundles and blocks water uptake resulting in wilting and eventual death (Meng, 2013). The bacteria can survive in water and in residues of infected plants for a long period of time making its control very difficult (Pradhanang et al, 2000)

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