Systemic acquired resistance in muskmelon plants induced by different sar compounds in response to challenge inoculation by downy mildew pathogen

In India, muskmelon crop is attacked by many bacterial, fungal and viral pathogens causing various diseases among which, downy mildew of cucurbits caused by Pseudoperonospora cubensis, an oomycete is most severe one. The present investigations were conducted to minimize fungicide load by testing alternate method of disease control. Different SAR compounds were tested as foliar sprays. Salicylic acid, Jasmonic acid and Bion (Benzothiadiazole-BTH) @ 50μM, 250μM, 500μM, 1000μM and β-amino butyric acid of 20 mM, 30mM, 50 mM, 100mM were sprayed for inducing resistance in mushmelon against downy mildew pathogen. Salicylic acid, Jasmonic acid and Bion @ 500 μM, and a-amino butyric acid @50 mM concentration gave best control of disease. Protein content in plants ranged between 10.5 to 12.7 mg/g fresh weight compared to 5.2 mg/g fresh weight in control. Induction of proteins and defense related enzymes was systemic in nature. The SAR compounds also spiked the activities of pathogenesis related proteins (Pr-proteins) i.e. β-1, 3 glucanase, Peroxidase (POD), and defense related proteins i.e. Polyphenol oxidase (PPO), Phenylalanine ammonia lyase (PAL) from 18 to 180 per cent indicating induction of resistance. Protein profiling of treated muskmelon plants was also done electrophoreticaly, which further confirmed the induction of pathogenesis-related proteins ranging from 15–75 kDa along with some other proteins. Total chlorophyll and carotenoids levels were raised from 3 per cent to 55 per cent in response to SAR compounds treatment. Salicylic acid showed best results with 77.27 per cent disease control followed by Jasmonic acid with 76.6 per cent; whereas both, Bion and Aeta amino butyric almost gave 66 per cent disease control as compared to control plants. Integration of disease tolerance in muskmelon varieties and spray of salicylic acid proved to be very economical for controlling downy mildew of muskmelon.