Study on enzymatic and biochemical changes in cucumber plant treated with potassium phosphite under Fusarium oxysporum f. sp. radicis-cucumerinum stress

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 Fusarium oxysporum. 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.