BIOLOGICAL CONTROL (in vitro) OF THE PATHOGEN CAUSING LEAF BLIGHT DISEASE OF MINT (Mentha arvensis L.)

Mentha arvensis L (Menthol mint) is very important aromatic and medicinal crop for its menthol oil production and uses in food, medical, cosmetic and others. This herb is being infected and damaged by many fungal diseases. The leaf blight is one of the destructive diseases of many crops. We conducted one year survey for leaf blight disease in the cultivated fields of mints in representative areas of four districts (North 24-Parganas, South 24 Parganas, Nadia and Kolkata (Sealdah) of West Bengal. Diseased leaves of mint plants were collected and 12 fungal isolates of pathogen were isolated in PDA medium. All isolates were characterized and identified by morphological and microscopical methods. We attempted to control it in vitro by biocontrol agent Trichoderma asperellum and for this purpose we employed dual culture plate method. The mechanism of biocontrol by T. asperellum was studied by light compound microscopy. The result of morphological and microscopical study showed that all 12 isolates of pathogen were Alternaria alternata (Fr.) Keissler, but they were clubbed into 2 strains (1 and 2) on the basis of similarity and dissimilarity of cultural, spore production capacity and level of pathogenicity. The growth of this pathogen (strain1) was inhibited and was completely controlled within 7 days in dual culture plate. Microscopic study of interaction between pathogen and biocontrol agent showed that hypha of T. asperellum coiled around the pathogen hyphae (A. alternata) along with cellular distortion and vacuolation. In conclusion, this study reported first time the leaf blight of mints in West Bengal and causal pathogen is A. alternata and this pathogen can be controlled by biocontrol agent T. asperellum. This study may encourage scientists for application of T asperellum against A. alternata in agrifield trial for ecofriendly biocontrol of this destructive disease.