In vitro antibacterial activity of selected plant extracts against potato bacterial wilt (Ralstonia solanacearum Smith) in Rwanda

Abstract: Bacterial wilt caused by Ralstonia solanacearum Smith is the most severe potato disease in Rwanda because there is no known pesticide for it and cultural control methods seem almost impossible to implement. Therefore, use of plant extracts with antibacterial activities which are locally available, economically affordable and environmental friendly could be an alternative in the management of the disease. This research focused on in vitro screening of the antibacterial activity of methanol, water and chloroform extracts of ten local plant materials against the pathogen. From this screening, methanol and water extracts of three promising plant species, i.e., tobacco, wild marigold and garlic were also used for determination of minimal inhibitory concentration (MIC). The results showed higher inhibition zone of methanol extracts (16.85 mm) against bacteria followed by water (14.42 mm) and chloroform (14.19 mm) extracts. All ten plant extracts inhibited the growth of the pathogen. Higher antibacterial activity was found in tobacco, wild marigold and garlic extracts (19.61, 18.56, and 18.3 mm inhibition zones, respectively). Minimal inhibitory concentration (MIC) of methanol extracts from tobacco and wild marigold was 6.25 mg mL^-1 whereas, garlic methanol extract was 12.5 mg mL^-1. Furthermore, MIC of water extract was 12.5 mg/mL^-1 in all three plant species. The findings revealed that tobacco, garlic and wild marigold extracts are the best in the control of potato bacterial wilt. Moreover, methanol extracts are the most efficient in management of potato bacterial wilt in comparison to water and chloroform extracts.