Effect of plant compounds on induced activities of defense-related enzymes and pathogenesis related protein in bacterial blight disease susceptible rice plant

Induction of resistance to control bacterial blight in rice was studied after treatment with various plant extracts by measuring activities of polyphenol oxidase (PPO), peroxidase (PO), beta-1,3-glucanase and a pathogen related (PR) protein. Extracts of four plants (Azardirachta indica, Ages mermelos, Cassia auriculata and Vitex negundo) against bacterial blight were analyzed. Bacterial blight was more effectively controlled by the water and methanol extracts of V. negundo than the other plant extracts. The extracts induced the defense related enzymes such as PPO, PO and beta-1,3-glucanase in both pre and post inoculation of Xanthomonas oryzae. The pathogenesis related (PR) protein bands were clearly visible at 33 kDa and 14 kDa in methanol and water extract treated leaves of V. negundo. Elevated enzyme activities and PR protein levels indicate that defense enzymes are responsible for the control the bacterial blight disease rather than antagonism by extracts. The methanol and water extracts of V. negundo suppressed the bacterial blight disease about 73% and 76% over control respectively, under field condition. The plants grown in extract-treated plots were healthy and their leaf surface area was found to be higher than the control and standard. V. negundo effectively controlled the bacterial blight disease under in vitro and in vivo conditions through induced systemic resistance which can be used as an effective biocontrol agent in rice field. (C) 2012 Elsevier Ltd. All rights reserved.