Evaluation of biochemical and molecular changes of tomato plants interacted with Alternaria solani

Early blight disease is one of the most common foliar diseases of tomato, which causes a great reduction in the quantity and quality of its yield. Regarding the use of fungicides in controlling this disease, identification of plant defense mechanism against the pathogen can be useful in introducing resistant cultivars and controlling the damage of the pathogen. In this research, several biochemical changes and expression patterns of PR1b1 and WRKY33 genes were investigated by qRT-PCR in a resistant cultivar Super 2270 and a susceptible cultivar CH Flat infected with the fungus Alternaria solani. Sampling was done during five intervals with three replications. The hydrogen peroxide accumulation, activity of defense enzymes Guacul peroxidase, Catalase and Superoxide dismutase enzymes, and the number of transcripts of genes was found to be increased in a challenge with the pathogen. The activity of these enzymes and genes were higher in the resistant cultivar. H2O2 accumulated rapidly in the resistant cultivar leaf tissues and peaked during the early stages of infection, whereas accumulation was stronger and more intense in the susceptible cultivar tissues in later stages.These results indicated that the induction of oxidant/antioxidant responses and the activity of genes in this study are a part of the tomato defense mechanism against the necrotrophic fungus A.solani.