Evidence for the importance of hydrogen peroxide in wheat infected by the hemibiotrophic pathogen Septoria triciti

ROS production. We studied the role of hydrogen peroxide (H2O2) in defence as well as a pathogenesis factor for S. tritici. In Stakado (resistant), pathogen growth was arrested just after penetration, resulting in absence of pycnidia and symptoms. The growth arrest coincided with a significantly higher number of autofluorescing cells and accumulation of H2O2 than in the susceptible cv. Sevin. In Sevin, very little H2O2 accumulated, except during sporulation, where tissue degradation occurred. This accumulation probably represents a stress response coinciding with tissue collapse. This pattern of H2O2 accumulation supports the dogma that pathogens with a necrotrophic phase benefit from accumulation of ROS. However, infiltration of catalase (to remove H2O2), water (control) or H2O2 showed that H2O2 was etrimental during all stages of the interaction. Thus, both early (during the initial, biotrophic, stage of infection) and late (during the necrotrophic phase) infiltration of catalase enhanced fungal growth and resulted in faster s