Inhibition potential of rhamnolipid biosurfactant against Corynespora cassiicola – a phytopathogen of king chilli

Background. The king chilli, Capsicum chinense Jacq., is a chilli variant well-known as one of the world’s hottest chillies while Corynespora cassiicola is a fungal pathogen that causes severe rotting in different parts of the crop and affects the fruit yield and market values. This study was attempted for management of C. cassiicola by applying rhamnolipid biosurfactant extracted from bacterial strain Pseudomonas aeruginosa SR17. Materials and Methods. The antifungal potential of crude and column-purified biosurfactant was studied against C. cassiicola; EC50 and IC50 values were calculated accordingly. The in vivo action of rhamnolipid on germination of king chilli seeds infected by the fungus was assayed by calculating the percentage of germination and vigour index of the seedling. The in planta antifungal efficacy of crude rhamnolipid was investigated by preventive and curative treatments. Management of post-harvest infection of ripe king chilli fruit was evaluated by measuring the percentage of disease index of rhamnolipid. Results and Discussion. The EC50 values for crude and column purified biosurfactant were calculated as 489.39±1.58 mg/L and 438.18±2.55 mg/L, respectively, against the mycelia of C. cassiicola. The minimum inhibitory concentrations (MIC) for crude and column-purified biosurfactants were 400 mg/L and 200 mg/L, respectively, against the spores of C. cassiicola. The germination percentage of seedlings increased up to 55 % after biosurfactant treatment of C. cassiicola infected seeds. The disease percentages reduced up to 49±1 % and 51.3±1.55 % after performing curative and preventive in planta experiments in king chilli plants infected with C. cassiicola. The IC50 value of rhamnolipid was calculated as 895.74mg/L in post-harvest disease management of king chilli fruits. Conclusions. The rhamnolipid extracted from P. aeruginosa SR17 exhibited in vitro and in-planta efficacy against C. cassiicola. The application of rhamnolipid was also found to be effective in reducing post-harvest loss of stored king chilli fruit.