Bioassay-guided characterization of antifungal principles from blue gum tree (Eucalyptus globulus)

Secondary metabolites present in the plants can be used as pathogen growth reducing agents and can act as crop plant growth enhancer so this has led the researchers to investigate their mechanisms of action and isolation of active compounds. In the present study antifungal activity of the petroleum ether extract of Eucalyptus globulus leaves was detected by direct bioautography on silica gel thin layer chromatography plates against Alternaria solani. The active metabolites were further isolated by bioassay-directed fractionation using column chromatography and followed by Gas-chromatography Mass Spectrometryanalysis. Separation of active antifungal principle was done by silica gel column chromatography which produced total 7 fractions. Antifungal activity of these fractions was once again checked against Alternaria solani by poison food technique, among them Column fractions 6, 7 and 1 showed a higher zone of inhibition than the standard fungicides bavistin and mancozeb. Fraction no. 6 was found to be most active with 83.40% inhibition of A. solani. Morphological and cytological changes in A. solani were also observed by Scanning electron microscopic study. After treatment mycelium width of Alternaria solani increased as 69.52% and conidia size of the Alternaria solani was reduced 72.17% as compared to control. Column fraction 6 was further analyzed by gas chromatography-mass spectrometry. Total 25 compounds was identified. The dominant compounds were Bicyclo, 2-Ethyl-5-methylfuran and Valerenol and these are the main factors of antifungal nature of Eucalyptus glogulus Labill leaf So, it can be concluded that Plant extracts naturally and significantly inhibit the conidial size and mycelia growth hence could be a safer alternative to chemical fungicides to control plant diseases. © 2022, Indian Phytopathological Society.