Influence of Agroclimatic Conditions, Life Form, and Host Species on the Species Complex of Wheat Septoria Pathogens

—Currently, Septoria is the basis of the pathogenic complex on wheat crops in Russia, occupying the predominant position among harmful fungal diseases. In case of severe wheat damage, the crop loss caused by the fungus Zimoseptoria tritici constitutes from 10–25 to 40–60%. Crop loss caused by the parasitizing of the fungus Parastagonospora nodorum ranges from 10–20 to 30–50% during the years of epiphytoty. The question of the economic significance of Parastagonospora avenae has not yet been examined completely. However, depending on the area of wheat cultivation and the year of observation, its part in the Septoria population can reach 76.9%. It was of interest to study in detail the influence of the conditions of the specific year, life form, and species of wheat on the formation of the species composition of Septoria in the pathogenic complex of wheat. Among the complex set of factors included in the concept of the environment, a significant role belongs to its abiotic components, namely, climate and weather, but the variety as an environment-forming factor has a decisive role. Our studies were carried out in 2010–2017. During the research period, the weather conditions varied significantly over the years and were not always favorable for the development of plants and the formation of a good wheat crop. During the study, deviations from the long-term average annual values in the amount of precipitation during the vegetation period, and, in general, over the year, were noted. The years 2012, 2014, and 2015 were characterized by the highest moisture supply during the vegetation season. It has been shown that cooler days of April and May promote better development of P. avenae and P. nodorum . P. nodorum obtains its predominant development during the years with more humid weather within the vegetation period of wheat, in contrast to Z. tritici , which is more resistant to low humidity. These data demonstrate the adaptation of the pathogen to the conditions of an increased temperature regime and reduced amount of rainfall.