Biochemical basis of Benzothiadiazole-mediated defense in quince under orchard condition

Based on the recent results on the efficacy of Bion elicitor in increasing quince (Cydonia oblanga) resistance to fire blight caused by Erwinia amylovora bacterium, the biochemical basis of this induced defense was studied for the first time. The experiment was conducted on quince cv. Isfahan seedlings grafted on quince rootstocks under orchard condition.  In early spring, three-years-old young plants were sprayed twice with Bion (400 mg/l) in 4-days intervals and four days after the last spray, young leaves were collected for enzymes extraction and quantification. Also, phytotoxic effects of Bion were studied throughout the time course of the study in orchard. Based on the results, Bion did not induce any phytotoxicity effects on quince. Bion treatment increased polyphenol oxidase and peroxidase activities but did not affect on catalase activity. It is concluded that elevation of oxidative enzymes are a part of biochemical mechanism of Bion-mediated defense in quince but catalase enzyme activity, which dismutase reactive oxygen species, does not change.