Production of hydrogen peroxide and physiological changes in tomato after infection of alternaria alternata

Plant defense mechanisms against necrotrophic pathogens such as Alternaria alternata are considered to be complex and different from those that are effective against biotrophs. Tomato is an economically important vegetable crop affected severely by A. alternata that causes leaf spot, stem canker and fruit rot diseases. In the present work physiological parameters were found to be decreased in tomato plants after infection by the pathogen. The infection also leads to production of reactive oxygen species which are involved in antimicrobial activities for restricting pathogen’s ingression in plants. Hydrogen peroxide production was observed by 3, 3'-diaminobenzidine staining, which showed reddish-brown color precipitation in leaves. Estimation of hydrogen peroxide showed highest level of production of H2O2 after 48 hours after infection and then declined after 48 hour up to 96 hours. Following H2O2 production activities of different antioxidant enzymes namely ascorbate peroxidase, catalase and glutathione s-transferase level were checked which were found to be altered due to ROS production.