Effect of Solvent Extracts of Some Plants on Ralstonia solanacearum

Aims: To study the efficacy of different solvent extracts (chloroform, ethanol, methanol and hexane) of ten plants on Ralstonia solanacearum the causal organism of bacterial wilt of tomato.
Place and Duration of Study: Departments of Crop Production, Soil and Environmental Management and Biological Sciences, Bowen University, Iwo, Nigeria from August 2011 to April 2012.
Methodology: Ten plants namely Ocimum gratissimum, Vernonia amygdalina, Allium sativum, Zingiber officinale, Cymbopogon citratus, Azadirachta indica, Jatropha curcas, Senna obtusifolia, Senna occidentalis and Senna alata were collected from Iwo, air dried and pulverized. Chloroform, ethanol, methanol and hexane were used to extract active ingredients from the ten plants. The solvent extracts were tested against R. solanacearum the causal organism of bacterial wilt of tomato and other plants using the disc diffusion method on Mueller Hinton agar. The minimum inhibitory concentration (MIC) of the effective extracts was determined.
Results: The plant extracts from chloroform were the most active and this was followed by methanol and ethanol, the lowest activity was recorded from the hexane extracts. The chloroform extracts of J. curcas had the widest zone of inhibition of 15mm followed by O. gratissimum (13mm). All the solvent extracts of A. sativum were active except the hexane extract. The means and standard error of triplicate tests were recorded. The MIC of the active extracts were studied, the MIC of the A. sativum ethanolic extract was 0.25 mg/ml while it was 0.5mg/ml for the V. amygdalina ethanol extract. The MIC of the A. sativum chloroform extract was 0.25mg/ml; J. curcas chloroform extract MIC was 0.125mg/ml, and the MIC for methanolic extract of both extracts were 0.5mg/ml and 0.25mg/ml respectively.
Conclusion: The activities of the different solvent extracts are remarkable when compared with the water extracts. Hence, solvent extracts will enhance the efficacy of these phytochemicals in the management of R. solanacearum infections as opposed to water extracts.