Indian Phytopath. 58 (3) : 298-304 (2005) Defense enzymes triggered by Exobasidium vexans Massee induce resistance in tea plants B.N. CHAKRABORTY*, M. SHARMA and R. DAS-BISWAS Immuno-Phytopathology Laboratory, Department of Botany, University of North Bengal, P.O. NBU, Siliguri 734 013 ABSTRACT: Involvement of defense related enzymes such as chitinase (CHT), b-1,3-glucanase (bGLU) and peroxidase (POX) in developing resistance in tea plants against Exobasidium vexans causing blister blight disease was evaluated. Among the ten tea varieties tested against E. vexans, B-668 and T-135 were found to be most susceptible while P-1258 and TV-26 were resistant under identical conditions. Screening for resistance of these varieties towards E. vexans based on plate trapped antigen (PTA) format of ELISA using polyclonal antibodies of the pathogen (PAb-EV) also confirm the results. Changes in the levels of enzyme activities were noticed in tea varieties exhibiting compatible and incompatible interactions against E. vexans. Disease free leaf samples exhibited greater accumulation of CHT and bGLU than infected ones. However, considerable increase in POX activity was evident in plants showing resistant reaction against E. vexans after overcoming the disease in the field condition. Time course accumulation of defense enzymes in tea plants triggered by inoculation with E. vexans showed a general increase in CHT and bGLU within 24 h of inoculation whereas the activity of POX increased 48 h post-inoculation. Elicitation of these defense enzymes was also evident in plants induced with salicylic acid (SA). Induced resistance occurs when an early synergistic increase in CHT and bGLU activity is coupled with POX. Key words: Tea, blister blight, PR-proteins, Exobasidium vexans Plants resist pathogen infection through physical and chemical defenses that may be either preformed or induced after pathogen penetration. Induced responses include rapid production of reactive oxygen species, enhancement of preformed structural barriers, hypersensitive cell death, production of phytoalexins, peroxidases and pathogenesis-related (PR) proteins. The accumulation of PR-proteins upon infection with microbial pathogens is well documented in plants (Van Loon, 1997). Among PR-proteins plant hydrolases such as b-1,3- glucanases and chitinases have been suggested to be involved in plant resistance against fungal pathogens (Kim and Hwang, 1994). It has also been demonstrated that chitinases probably play an active role in the development of healthy plants and b-1,3-glucanase is similarly expressed in unstressed plants (Garcia-Garcia et al., 1994). The biochemical function of PR-proteins has only been established for some groups but the implication of these enzymes in disease resistance has been supported by the demonstration that they all have been shown to possess antimicrobial activity (Van Loon, 1999). Blister blight caused by Exobasidium vexans Massee is one of the most serious foliar diseases of tea. It has been documented that the disease is more serious in bushes recovering from pruning as they have greater proportions of succulent and tender material that makes it more susceptible to the disease. However, tea plants overcome the infection and recover from the disease by exhibiting resistant reactions. This study was carried out with an aim to delineate the association of defense enzymes in tea plants during its resistant reactions against E. vexans. *Corresponding author: bnc_nbu@hotmail.com