ASSESSMENT OF ACTIVITY OF ATA (Annona squamosa) AND BAEL (Aegle marmelos) LEAF EXTRACTS IN IN VITRO AGAINST Pectobacterium carotovorum subsp. carotovorum CAUSING BACTERIAL SOFT ROT OF POTATO

Abstract

Bacterial soft rot of potato caused by a gram-negative bacterium Pectobacterium carotovorum is sirious storage disease of potato in humid and subtropical region like Bangladesh. The bacterium was isolated from a symptomatic diseased potato tuber. Biochemical characterization including gram’s staining test, potassium hydroxide test (KOH), catalase oxidase test, oxidation/fermentation of glucose, nitrate reduction test lecithinase activity test confirmed the isolated bacterium as Pectobacterium sp. Pathogenicity test showed more confirmative result that the isolated bacterium was P. carotovorum. In vitro antibacterial potential of Annona squamosa (Ata) and Aegle marmelos (Bael) leaf extract were also studied to evaluate their efficacy against the isolated P. carotovorum. The antibacterial activities of methanol and water extracts of the test plants were determined using disc diffusion method on nutrient agar medium. The tested results of antibacterial activity exhibited that the average zone of inhibition of Ata leaf was higher in water extract (2.53cm) than methanol extract which showed less zone of inhibition (2.00cm). On the other hand, in case of Bael, the maximum zone of inhibition (2.43 cm) was also found in water extract compared to methanol (1.43 cm). As the water extract reported the best result against the bacterium in zone of inhibition, two fold micro broth serial dilution methods with water solvent was used to determine minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC). This result showed that minimum inhibitory concentration and minimum bactericidal concentration was found the best at 62.5 μg/ml using Ata leaf extract than Bael leaf extract (125 μg/ml) with water solvent. Following that cell viability test was done where both Ata and Bael leaf extract with water inhibited 100% of the bacterial growth at 240 min time exposure i.e. the biological evaluation resulted that both of the plant extracts are effective against the growth of P. carotovorum.