Folia Microbiol.39 (5), 409-414 (1994) Accumulation of Antifungal Compounds in Tea Leaf Tissue Infected with Bipolaris carbonum B.N. CHAKRABORTYand A. SAttA Plant Pathology Laboratory, Departmentof Botany, University of North Bengal P.O. - N.B.U. 734 430, Dr. - Darjeelin~ WestBenga~India ReceivedMay 13, 1994 ABSTRACT. Varietal resistance of tea towards Bipolaris carbonum was tested following detached leaf inoculationtechnique. Amongthe fourteenvarieties tested, three were found to be highly susceptible,while other three were resistant. Leaf exudates and diffusates collected from the resistantvarietieswere more fungitoxic than those from the susceptibleones. Two antifungal compounds isolated from healthy and B. carbonum-infected tea leaves exhibited clear inhibition zones at RF 0.8 and 0.65, respectively,in a chromatographic bioassay.On the basis of their color reaction on TLC and UV-spectra these were identified to be catechinand pyrocatechol.Resistantand susceptiblevarietiesaccumulated 439-510 and 187-212 lag/g fresh mass tissue of pyrocatechol, respectively, 2 d after inoculationwith B. carbonum, whilea low concentration(45 -58 lag/g)of this compound was detectedin healthyleaf tissue. Tea (Camellia sinensis (L.) O. KUNTZE) is one of the most important plantation crops of India. It forms the backbone of the economy of North-East India. Foliar diseases (Sarmah 1960; Chakraborty 1987) drastically reduce the quality and quantity of tea production. Besides being peren- nial, it is likely that the tea plant in the course of its adjustment to varying environments, has also evolved a very effective defense mechanism which successfully wards off most of the fungal pathogens (Chakraborty et al. 1994). The biochemical mechanisms responsible for containment of fungal patho- gens in the resistant interactions are undoubtedly multifold. Oligophenols are the major constituents of tea leaves (Wang 1991) and their antifungal activity against Pestalotiopsis theae has been reported (Chakraborty et al. 1989). In this communication, the involvement of antifungal compounds in determining resistance of tea to Bipolaris carbonum is discussed. MATERIALS AND METHODS Plant material. Fourteen varieties of tea plants (TV-1, TV-9, TV-14, TV-16, TV-17, TV-18, TV-19, TV-20, TV-23, TV-25, TV-26, Teenali-17/1/54, TS-449, CP-1) produced at the Tocklai Experi- mental Station, Jorhat (Assam) were collected from the clone house of Mohurgong and Gulma Tea Estate, Darjeeling (West Bengal) and grown in the Phytopathological Experimental Garden of the department as described by Chakraborty and Saha (1994). Fungal cultures. A virulent strain of Bipolaris carbonum (syn. Helminthosporium carbonum), anamorph of Cochliobolus carbonum NELSON (IMI 298762), was obtained from the departmental stock culture collection. It was originally isolated from the naturally infected leaves of tea plants grown in Gayabari Tea Estate, Darjeeling (Chakraborty 1987). Glomerella cingulata and Pestalotiopsis theae were obtained from the Tocklai Experimental Station, Jorhat. Helminthosporium oryzae, H. Maydis and H. sativum were obtained from the Indian Agricultural Research Institute, New Delhi. Inoculation technique and disease assessment. Detached leaf inoculation technique of Dickens and Cook (1989) was followed with modification for artificial inoculation of tea leaves. Fully expanded young tea leaves were detached from plants, washed with sterile distilled water, blotted and then placed in plastic trays lined with moist blotting paper. Conidial suspension of B. carbonum was prepared from 10-d-old culture and the conidia concentration was adjusted to 1/nL (i.e. 106/mL) by serial dilution and hemocytometer count. Twenty ttL droplets (2-4 per leaf) of conidial suspension of the fungus were placed on the adaxial surface of each leaf with a hypodermic syringe. In control sets, drops of sterile distilled water were placed on leaves. Each tray was covered with a glass lid and sealed with petroleum jelly in order to minimize the drying of drops during incubation. Assessment of inoculum infectivity and symptom development were done on the basis of percent drops that resulted in lesion production after 3 d of inoculation (Chakraborty and Saha 1989a). Observations were based on 50 inoculated leaves for each treatment and average of three separate experiments.