Induction of Early Oxidative Events in Soft Wheat Leaves Inoculated with Septoria tritici and their Relationship to Resistance of Moroccan Cultivars

The inoculation of soft wheat by Septoria tritici induces a foliar necrosis and an important modifications in the oxidative metabolism of which the time course clearly distinguishes the studied cultivars according to their behaviour to this disease. In the resistant cultivars (Mahdia, Achtar), the inoculation was accompanied by an early and localized necrosis and a fast and intense increase of the peroxidase (POD) and the superoxide dismutase (SOD) activities and of a fast, weak and transient accumulation of the malonydialdehyde (MDA). In the susceptible cultivars (Nasma & Marchouch), the necrotic symptoms appears tardily and preceded by a late increase of the activities of polyphenol oxidase (PPO), SOD and catalase (CAT) and an important accumulation of the MDA. These results suggest that the fast and localized necrosis reaction in resistant cultivars was related to the intervention of the POD, whereas the late and generalized necrosis in the susceptible cultivars was associated to the PPO. In addition, the differential responses of the SOD activity in the resistant and susceptible cultivars suggest a key role of the SOD in soft wheat defense.