IN VITRO EVALUATION OF AKANDA (Calotropis procera) AND CASTOR (Ricinus communis) LEAF EXTRACTS AGAINST Ralstonia solanacearum CAUSING BACTERIAL WILT OF BRINJAL PLANT

Abstract

Bacterial wilt of brinjal, caused by Ralstonia solanacearum is a most devastating disease in humid tropic. The isolated bacterium from brinjal plant was found to produce pink or light red color or characteristic red center and whitish margin on nutrient agar medium after 24 hours of incubation. Biochemical characterization including gram’s staining, catalase oxidase test, levan production from sucrose, lipase activity on tween 80 agar, arginine dihydrolase reaction, Nacl tolerance test, starch hydrolysis test, nitrate reduction test, gas production from nitrate (demystification) and potassium hydroxide solubility test revealed that the isolated bacterium was R. solanacearum. Pathogenicity test revealed that the isolated bacterium can cause wilt disease in brinjal plant. All biochemical tests in combination with the pathogenicity test confirmed the isolate as R. solanacearum. The present study was conducted to develop effective antibacterial agent without any residual effect, and to analyze the in-vitro antibacterial potential of Calotropis procera (Akanda), Ricinus communis (Castor) against the isolate Ralstonia solanacearum. The antibacterial activity of the methanol, water and petroleum ether extracts was assayed by using disc diffusion method. The results of antibacterial activity revealed that the average zone of inhibition of the Akanda leaf extracts was more in the methanol extract (4.83 cm) than in the water extract which showed zero zone of inhibition. In case of Castor the maximum zone of inhibition was found using methanol extract (2.1 cm) where, both petroleum ether and water showed same zone of inhibition (1.5 cm).Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) was determined by two fold micro broth serial dilution method with methanol solvent as the solvent reported the best result against the bacteria in zone of inhibition. The result of Minimum Inhibitory Concentration and Minimum Bactericidal Concentration was found best at 67.5μg/ml using Akanda leaf extract than Castor leaf extract (125 μg/ml) with methanol solvent. In viable cell counting test both of the plant, Akanda leaf extract and Castor leaf extract with methanol inhibited 100% of the bacterial growth at 200 min time exposure that means both of the plants are effective against the growth of R. solanacearum.