Induction of Systemic Resistance by Trichoderma Asperellum against Bacterial Wilt of Tomato Caused by Ralstonia Solanacearum

Trichoderma asperellum was used as a biological control agent against bacterial wilt disease caused by Ralstonia solanacearum. The present investigation is focused on the role of defense- related enzymes in imparting resistance to tomato against bacterial wilt pathogen Ralstonia solanacearum. Two isolates of Trichoderma asperellum (T4 and T8) exhibiting high antagonistic activity against a virulent strain of Ralstonia solanacearum (RS) were selected during screening for studies on several biocontrol mechanisms under greenhouse conditions. Seed treatment with T. asperellum isolates significantly improved the quality of seed germination and seedling vigor. Efficacy of T4 and T8 isolates, evaluated under greenhouse conditions exhibited suppression by about 50% in disease incidence of bacterial wilt and promoted growth in tomato plant. The isolates T4 and T8 were further tested for their ability to induce the production of defense-related enzymes in plants. The seed application with T4 and T8 isolates induced a significant increase in the activities of peroxidase (POX), Polyphenol oxidase (PPO), phenylalanine ammonia lyase (PAL), and â.1, 3-glucanase in treated tomato plants. Increased activities of phenylalanine ammonia lyase, peroxidase, Polyphenol oxidase, â-1, 3-glucanase were observed in T4 and T8 pre-treated tomato plants challenged with Ralstonia solanacearum. Trichoderma asperellum treatment also triggered the defense related enzymes involved in synthesis of phenols. Higher accumulation of phenolics was noticed in plants pre-treated with T4 and T8 challenged with Ralstonia solanacearum. Native PAGE analysis of both peroxidase (POX) and Polyphenol oxidase (PPO) was carried out for the time course of enzyme activities. The present study shows that in addition to direct antagonism and plant growth promotion; induction and increased activity of defense related enzymes involved in the phenyl propanoid pathway collectively contributed to enhanced resistance against invasion of bacterial wilt in tomato caused by Ralstonia solanacearum.