Effects of Selected Plants Extracts on in vitro Growth of Ralstonia slanacearum (Smith), the Causal Agent of Bacterial Wilt of Irish Potatoes

The antibacterial effect of crude medicinal plant extracts of Ocimum gratissimum, Brassica oleracea var. botrytis and Ipomoea batatas on Ralstonia solanacearum (Smith) extracted from infected potato tubers was determined by in vitro study using ethyl acetate and methanol solvents. The extracts were used at concentrations of 0.4, 0.2, 0.1, 0.05 and 0.025 mg mL-1. It was found that all the plant extracts used at their different concentrations except methanol extracts of Ipomea batatas at 0.025 mg mL-1 were effective to varying degrees in controlling the growth of bacterial colonies. The best results were observed with ethyl acetate extracts of Ipomoea batatas at concentration of 0.4 mg mL-1 giving mean inhibition zone of 4.2 mm followed by ethyl acetate extract of Brassica oleracea at concentration of 0.05 mg mL-1 that was 4.12 mm.