Effect of salicyclic acid on defence related enzymes and late blight in potato

Effect of foliar and tuber treatment of salicylic acid (SA) @ 0.5 and 1.0 mM, on defence related enzymes and potato late blight incidence in Kufri Jyoti (Tolerant, T) and Kufri Pukhraj (Highly susceptible, HS) was studied. Tubers were treated for 10 minutes before sowing. Foliar application was done at 24 and 34 days after planting (DAP). Leaf samples were collected after 24 (1^st collection) and 34 (2^nd collection) DAP in both treatments and used for estimation of defence related enzymes, total sugars and total soluble proteins. Sporangial solution (10⁴spores/ml) was sprayed after 2^nd sample collection. Per cent disease incidence and severity were recorded at 7, 14 and 21 day post inoculation. SA @ 0.5mM caused statistically significant (at 5% level) increase in chitinase, glucanase, peroxidase (POD), catalase (CAT), polyphenol oxidase (PPO), phenylalanine ammonia lyase (PAL), total sugars and total soluble protein in Kufri Jyoti via both the treatments. Least disease incidence and severity were recorded in Kufri Jyoti @ 0.5mM SA, although both the treatments were effective against late blight in both the varieties. The second foliar spray acted as a booster dose on the basis of higher increase in activities of defense enzymes. All the biochemical parameters were found to be significantly negatively correlated with disease severity. PPO and PAL registered high r² values. Foliar application of SA was more effective. Both varieties responded to SA treatment positively. The response was higher in tolerant variety but susceptible variety also showed better response as evidenced by decreased disease incidence and severity. Integration of disease tolerance and SA spray thus proved effective against P. infestans in potato.