University of Tehran Iranian Journal of Horticultural Science 2008-482X 48 3 2017 12 22 Study on enzymatic and biochemical changes in cucumber plant treated with potassium phosphite under Fusarium oxysporum f. sp. radicis-cucumerinum stress Study on enzymatic and biochemical changes in cucumber plant treated with potassium phosphite under Fusarium oxysporum f. sp. radicis-cucumerinum stress 601 611 64523 10.22059/ijhs.2017.138752.897 FA Sahar Heidarzade Former M.Sc. Student, Faculty of Agriculture, Shahrood University of Technolgy, Iran Shahrokh Gharanjik Assistant Professor, Faculty of Agriculture, Shahrood University of Technolgy, Iran Ali Dehestani Assistant Professor, Genetics & Agricultural Biotechnology Institute of Tabarestan (GABIT), Iran Darioush Shahriari Instructor, Agriculture and Natural Resources Research Center of Tehran Province, Iran Journal Article 2015 12 26 In this study, we evaluated the effects of five levels of potassium phosphite (KH₂PO₃) on Induced Systemic Resistance (ISR), and also defense related enzymes and metabolites activities during different days in cucumber plants inoculated with <em>Fusarium oxysporum</em>. The experiment was designed as a split-plot in time based on a completely randomized design with three replications. The activity of defense-related enzymes including, catalase (CAT), guaiacol peroxidase (GPX), superoxide dismutase (SOD) and also the accumulation of secondary metabolites such as lipid peroxidation (MDA) and hydrogen peroxide (H₂O₂), were evaluated in a period of 11 days after pathogen inoculation. Results revealed that defense enzymes activities and metabolites accumulations were significantly increased in plants treated with potassium phosphite in comparison to control. The highest concentration of CAT enzyme (18.7 U mg^-1 protein) was measured in plants treated with 4 gr l^-1 potassium phosphite (KPhi4) and 5 days after inoculation, that showed 2.81 fold increase in comparison with control (no inoculate with the pathogen). Also the highest concentration of enzymes GPX (233 U mg^-1 protein) and SOD (10.8 U mg^-1 protein) were recorded at 3 days after inoculation in plants treated with KPhi4 in comparison with control plants. Results showed that accumulation of H2O2 in plant tissues and it's time was in accordance with increasing of defense enzymes CAT, GPX and SOD and it would indicate that the H2O2 production is the prerequisite for production of defense-related enzymes. It was also revealed that MDA accumulation in KPhi4 treatment was less than other treatments, indicating reduced tissue damage and alleviated disease symptoms. In this study, we evaluated the effects of five levels of potassium phosphite (KH₂PO₃) on Induced Systemic Resistance (ISR), and also defense related enzymes and metabolites activities during different days in cucumber plants inoculated with <em>Fusarium oxysporum</em>. The experiment was designed as a split-plot in time based on a completely randomized design with three replications. The activity of defense-related enzymes including, catalase (CAT), guaiacol peroxidase (GPX), superoxide dismutase (SOD) and also the accumulation of secondary metabolites such as lipid peroxidation (MDA) and hydrogen peroxide (H₂O₂), were evaluated in a period of 11 days after pathogen inoculation. Results revealed that defense enzymes activities and metabolites accumulations were significantly increased in plants treated with potassium phosphite in comparison to control. The highest concentration of CAT enzyme (18.7 U mg^-1 protein) was measured in plants treated with 4 gr l^-1 potassium phosphite (KPhi4) and 5 days after inoculation, that showed 2.81 fold increase in comparison with control (no inoculate with the pathogen). Also the highest concentration of enzymes GPX (233 U mg^-1 protein) and SOD (10.8 U mg^-1 protein) were recorded at 3 days after inoculation in plants treated with KPhi4 in comparison with control plants. Results showed that accumulation of H2O2 in plant tissues and it's time was in accordance with increasing of defense enzymes CAT, GPX and SOD and it would indicate that the H2O2 production is the prerequisite for production of defense-related enzymes. It was also revealed that MDA accumulation in KPhi4 treatment was less than other treatments, indicating reduced tissue damage and alleviated disease symptoms. https://ijhs.ut.ac.ir/article_64523_d2de34e0ede5a7cd570b234069bc622d.pdf