Induced resistance in potato against Phytophthora infestans using chemicals and bio- agents

Induced resistance in potato against Phytophthora infestans was studied using inducer chemicals (salicylic acid, benzothiadiazol, fosetyl-Al, calcium chloride, ethylene, hydrogen peroxide, potassium hydrogen phosphate) and bio-agents (Pseudomonas fluorescens, Trichoderma viride, Trichoderma harzianum). Treatments were given as tuber dip for ten minutes before sowing, spray application and combined tuber treatment and spray application. Challenge inoculations by P. infestans were done at 10 days intervals of each treatment. Observations were recorded in terms of per cent disease severity. Leaves from treated plants were used to study changes in total phenols, o - dihydroxy phenol, defense related enzymes (PAL, PPO, PO) and chitinase activity. Minimum disease severity (2.0%) was recorded in case of plants sprayed with salicylic acid @ 100μg/ml and it was completely controlled when observed after 7 days of first inoculation where combined tuber treatment and spray application of salicylic acid were given. It was followed by benzothiadiazole @ 100μg/ml and fosetyl-Al @ 1000μg/ml. Disease severity started increasing after subsequent challenge inoculations. There was increase in total phenols, o-dihydroxy phenols, PAL in treated plants after challenge inoculations. Maximum increase (52.4%) in peroxidase and chitinase activity was observed in salicylic acid treated plants. Comparatively, lower induction of resistance was observed with the bio-agents tested.