Lactic acid bacteria mediated induction of defense enzymes to enhance the resistance in tomato against Ralstonia solanacearum causing bacterial wilt

Abstract

The biocontrol agent Lactic acid bacterium (LAB) was used against the bacterial wilt caused by Ralstonia solanacearum. The present investigation focuses on the role of defense related enzymes in imparting resistance to tomato plants against R. solanacearum. The LAB isolate was tested for its ability to induce the production of defense-related enzymes in treated tomato seedlings. Tomato seedlings were raised from LAB pretreated seeds, were challenge inoculated with R. solanacearum, harvested at different time intervals (0–72h) and assayed for defense enzyme activity. The LAB treated seeds showed increase in germination percentage (6%) and seedling vigour index (259) compared with control. Treatment of tomato seedlings with LAB isolate induced a significant amount of Peroxidase (POX), Polyphenol oxidase (PPO), Phenylalanine ammonialyase (PAL), total phenolics and β-1,3-glucanase activities. The activities of PAL, POX, PPO and β-1,3-glucanase reached maximum at 24h, 24h, 32h and 24h respectively after challenge inoculation. Increased accumulation of phenolics was noticed in plants pre-treated with LAB. Native PAGE analyses of POX and PPO were carried out for the time course of enzyme activities and the isoforms of POX and PPO were examined. In field study, ten isolates of R. solanacearum treated plots yielded an average of 32.4–50kg/m2 and LAB treated plots an average of 153.5kg/m2. As compared to the control, LAB increased the yield by 15.3% (8.2kg/m2) and the pathogen infected plants and pre-treated with LAB gave an average of 55% (28.3kg/m2 compared to the infected plots). Field experiment results indicated that LAB exhibited 61.1% of disease reduction of bacterial wilt in tomato.