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Management of brown blight in tea caused by Colletotricum gloeosporioides by crude and purified leaf extract of Xanthium strumarium

Dipanwita Saha: University of North Bengal

<div>Tea (<em>Camellia sinensis</em>) is an economically important plantation crop of India but is susceptible to attack by several fungal pathogens. The study was aimed to develop botanical fungicides which could be a safer alternative to the harmful chemical fungicides. A fungal pathogen was isolated from the leaves of tea plants showing symptoms of brown blight from the tea plantations in Darjeeling. The pathogen was identified as <em>Colletotricum gloeosporioides</em> following PCR amplification and sequencing of the ITS region (Gen Bank accession Number KC493156) and its pathogenicity was confirmed through verification of Koch’s Postulates. For controlling the disease, crude leaf extracts of <em>Xanthium strumarium</em> was tested for antifungal activity <em>in vitro</em> against the pathogenic isolate by agar cup assay method. Bioassay guided fractionation of the crude extract led to the isolation of two antifungal compounds, 8<em>-epi-</em>xanthatin (<strong>1</strong>) and 8<em>-epi-</em>xanthatin-1β,5β-epoxide (<strong>2</strong>). The structures were elucidated by IR, NMR and ESI-MS spectroscopy data analysis. Determination of MIC of the pure compounds by micro-dilution bioassay method revealed that antifungal activity of <strong>1</strong> was higher than <strong>2</strong>. The water insoluble extracts emulsified in water effectively controlled brown blight of tea in the green-house and its efficacy was comparable to the fungicide bavistin. The results show that <em>X. strumarium</em> leaves may be used as a source of botanical fungicidal preparation for controlling brown blight in tea.</div>