Biochemical basis of systemic acquired resistance induced by different Systemic Acquired Resistance (SAR) elicitors in Brassica cultivars challenge inoculated with downy mildew pathogen

Abstract

In India, Brassica is attacked by many bacterial, fungal and viral pathogens causing various diseases among which, downy mildew caused by Hyaloperonospora brassicae, an oomycete is the most severe one. The present investigation was conducted to reduce fungicide load on Brassica by testing an alternate method of disease control. Different Systemic Acquired Resistance (SAR) compounds were tested as foliar sprays like Salicylic acid, Jasmonic acid and Bion (Benzothiadiazole-BTH) for inducing resistance in different genotypes of Raya (Brassica juncea) against downy mildew pathogen. Protein content in plants ranged between 43.5 to 57.7 mg/g fresh weight compared to 37.2 mg/g fresh weight in control. Induction of proteins and defense related enzymes was systemic in nature. The SAR compounds also surged the levels of defense related proteins, i.e. Polyphenol oxidase (PPO), Phenylalanine ammonia lyase (PAL) and pathogenesis related Pr- proteins i.e. ?-1,3 glucanase, Peroxidase (POD), from 21 to 130 per cent indicating induction of resistance. Protein profiling of treated Brassica plants was also done electrophoreticaly, which further confirmed the induction of pathogenesis-related proteins ranging from 15- 75 kDa along with some other proteins. Salicylic acid @ 500µM showed best results with 71.27 per cent disease control followed by Jasmonic acid with 69.6 per cent; whereas both, Bion and ?eta amino butyric acid gave almost 63 per cent disease control as compared to control plants. Integration of disease tolerance in Brassica varieties/genotypes combined with prophylactic spray of salicylic acid proved to be very economical for managing downy mildew disease.