Among the various biocontrol agents, Pseudomonas fluorescens Migula, a strain of Plant Growth Promoting Rhizobacteria (PGPR) is being exploited commercially for plant protection to induce  systemic resistance against various insect pests and diseases. The foliar application of P. fluorescens has been reported to enhance the activity of defense related enzymes viz., Peroxidase (POD),

Polyphenoloxidase (PPO) and Phenylalanine Ammonia-lyase (PAL) in the plant system. The experiment was conducted to know the effect of induced resistance in onion through foliar application of P. fluorescens on onion thrips, Thrips tabaci. Onion thrips is the major insect pest of onion and it is identified as a pest of national importance which causes an annual yield loss of about 10 to 15 per cent in India. The results indicated that the highest activity of POD (0.70 mg protein/min), PPO (0.54 mg protein/min) and Phenylalanine Ammonia-lyase (0.30 mg/100 mg) was recorded in P. fluorescens treated onion plants. The activity of these enzymes was negatively correlated with thrips population. The minimum activity of all three enzymes was observed from untreated check. These enzymes involved in the production of phytoalexins and phenolics in onion plant and thus, the induced resistance played an important role in the management of Thrips tabaci.