Control of foliar diseases of tea with Xanthium strumarium leaf extract

Tea industry forms the backbone of economy in the sub-Himalayan agro-climatic region of north east India where it is normally grown extensively in large plantations. The study was aimed to develop a bio-rational alternative to the harmful chemical fungicides for controlling foliar fungal diseases which limit tea production. An antifungal compound from benzene extract of adult leaves from Xanthium strumarium L. was purified and characterized and the in vitro antifungal activity was evaluated against a broad spectrum of plant pathogens. The sesquiterpene lactone which was purified by bioassay guided fractionation using repeated column chromatography and thin layer chromatography was identified as xanthatin by ultraviolet, infrared and nuclear magnetic resonance spectroscopic analysis. The minimum inhibitory concentration of the isolated compound tested by microdilution method ranged from <0.0097 to 0.325 mg ml−1 against 8 tea pathogens and 12 other plant pathogens. The most susceptible fungi were Colletotrichum camelliae, Curvularia eragrostidis and Rhizoctonia solani among tea pathogens and Colletotrichum gloeosporioides, Fusarium moniliforme and Rhizopus stolonifer among other tested pathogens. Subsequently the in vivo antifungal activity was tested in detached leaves against four foliar tea pathogens, C. camelliae, C. eragrostidis, Lasidiplodia theobromae and Pestalotiopsis theae. The purified compound completely inhibited lesion development at 0.1 mg ml−1 concentration against C. camelliae and C. eragrostidis. The purified compound and the crude extract were further tested for their ability to control foliar diseases in young tea plants of two clonal varieties, TV-18 and TV-30 in the greenhouse. The water insoluble extracts emulsified in water effectively controlled brown blight (C. camelliae), leaf spot (C. eragrostidis), grey blight (P. theae) and leaf blight (L. theobromae). Highest percentage efficacy of disease control was exhibited against leaf spot followed by brown blight. The disease control efficacy was comparable to the fungicide bavistin. The results show that the adult leaves of X. strumarium may be used as a source of botanical fungicidal preparation for controlling foliar fungal diseases of tea.

► A sesquiterpene lactone was purified from leaf extract of Xanthium strumarium.
► The purified compound was identified as xanthatin following spectroscopic analysis.
► Xanthatin possessed antifungal activity against twenty plant pathogens in vitro.
► Lesion development was inhibited by xanthatin in detached leaves of tea.
► Emulsified extract preparations protected tea plants against major foliar diseases.