Evaluation of Antioxidant Activity and Physiological Changes in Pear After Inoculation by Erwinia amylovora, Causing Agent of Fire Blight Disease

In order to evaluate the antioxidant activity in the pear cultivars including Dargazi and William Duchesse after inoculation with E. amylovora, an experiment carried out in factorial randomized complete block design with three replications. The resistance level has been determined with calculation of the length of lesion to the overall sheet length percentage. In order to find out the plant resistance mechanisms to the pathogen, ascorbate peroxidase (APX), catalase (CAT), guaiacol peroxidase (POX), H2O2 accumulation and total antioxidant capacity (TAC) were measured at zero, 3, 6, 9, 12 and 15 days after the inoculation by E. amylovora. According to the data obtained all biochemical parameters are affected by pathogen attack. In addition, most of the biochemical parameters showed a significant increase on the leaves of Dargazi cultivar compared with William Duchesse cultivar after pathogen infection. Catalase and peroxidase enzymes activity in the Dargazi cultivar were significantly different (P≤ 0.01) with William Duchesse cultivar during inoculation, and the highest activity were obtained at the sixth to 12 days after the treatment. Investigation of disease progression in shoot showed that the progression rate of necrosis in pear shoots was related with index of varietal susceptibility, so that William Duchesse with high index of varietal susceptibility, had higher rate of necrosis.