Induction of Systemic Resistance in Tomato against Ralstonia solanacearum by Pseudomonas fluorescens

The biological control agent Pseudomonas fluorescens was used against the bacterial wilt causing Ralstonia solanacearum. The present investigation focuses on the role of defense related enzymes in imparting resistance in tomato against R. solanacearum. A total of ten rhizobacterial isolates were screened against R. solanacearum, of which three isolates (Pf3, Pf5 & Pf8) showed a maximum inhibition against the pathogen and were further identified as P. fluorescens by 16S rRNA analysis. Seedling treatment with P. fluorescens isolates significantly enhanced the quality of seed germination and seedling vigor. The three P. fluorescens strains were further tested for their ability to induce the production of defense-related enzymes in plants. Involvement of defense related enzymes in bacterial wilt pathogenesis was studied in susceptible tomato cultivar (Arka Meghali). Root dip inoculation was performed with bacterial suspensions of R. solanacearum and P. fluorescens (1 × 108 cfu/ml) on ten days old seedlings and harvested at different time intervals (0, 3, 6, 9, 12, 15, etc. up to 72 h) and assayed for the defense related enzyme activity. The seedling treatment of P. fluorescens isolates induced a significant increase in the activities of peroxidase (POX), Polyphenol oxidase (PPO), phenylalanine ammonia lyase (PAL), and β-1, 3-glucanase in treated tomato plants and the same trend of increase in enzyme activity was observed in P. fluorescens treated tomato seedlings challenged with R. solanacearum. The activities of the enzymes PAL, POX, PPO and β-1, 3-glucanase reached maximum at 24, 18, 24 and 24 h after inoculation respectively. Higher accumulation of phenolics was noticed in plants pre-treated with P. fluorescens and challenge inoculated with R. solanacearum. Native PAGE analysis of both Peroxidase (POX) and Polyphenol oxidase (PPO) was carried out for the time course of enzyme activities and the isoforms of POX and PPO were examined. Corresponding author. RE TR AC TE D