Reactive oxygen species (ROS) play a central role in plant immune responses. The chief enzymes that generate ROS are plasma-membrane NADPH oxidase and apoplast peroxidases. Today it is known that ROS perform signaling functions and serve as a trigger for the induction of plant defense systems at an early stage of disease development. The most important virulence factors of the Stagonospora nodorum are multiple fungal necrotrophic effectors (NEs) (SnTox) that affect the redox-status and cause necrosis and/or chlorosis on wheat lines possessing dominant susceptibility genes (Snn). However, the effect of NEs on ROS generation in the early stages of infection has not been studied. The pathosystem wheat–S. nodorum is mediated by multiple fungal NEs – host sensitivity gene interactions that include SnToxA–Tsn1, SnTox1–Snn1, and SnTox3–Snn3 and others. In this study, combinations of different genotypes of several varieties of soft spring wheat (Triticum aestivum L.) with different allelic states of susceptibility genes and several S. nodorum isolates, characterized by presence or absence of SnToxA, SnTox1, SnTox3 effector genes expression (SnB, Sn9MN, Sn4VD) were studied. In the compatible interaction Zhnitsa/ SnB or Sn9MN, suppression of hydrogen peroxide generation was found, which occurred due to high activity of catalase, low activity of peroxidase and reduce of expression of genes encoding NADPH-oxidase (TaRboh), anionic peroxidase (TaPrx) and superoxide dismutase (TaSod) at the early stage of infection (24 hours), which further led to the formation of extensive lesions. The greatest accumulation of hydrogen peroxide was found in the incompatible interaction Omskaya35/ SnB or Sn4VD. S. nodorum effectors SnToxA, SnTox1, SnTox3 reduced hydrogen peroxide generation at the initial stage of infection, most likely due to the regulation of peroxidase activity. This work was supported by the RFBR in the framework of the research project no. 20-316-80047 and no. 18-04-00978.