Abstract
The objective of this study was to evaluate populations of the fungi Parastagonospora nodorum and P. pseu-donodorum from the Leningrad, Tambov, and Amur regions of the Russian Federation for the presence of the effector genes SnToxA, SnTox1, SnTox3, SnTox5, and SnTox267. Leaf samples showing symptoms of septoria were collected in 2025 from various spring wheat cultivars at the milk-wax ripeness stage of grain. The investigations were carried out using light micros-copy, PCR, and CTAB methods. Screening of 165 P. nodorum isolates and 19 P. pseudonodorum isolates revealed significant inter- and intraspecific differences in the distribution of effector genes. It was established that SnTox3 had the highest preva-lence among P. nodorum genotypes (53 %), whereas the distribution of SnTox5 was strictly linked to the geographic origin of the samples (European part of Russia – up to 100 %; Amur region – 0 %). Isolates of P. pseudonodorum from the Tambov region were characterized by the presence of SnToxA (79 %), SnTox3 (79 %), and SnTox5 (100 %), while SnTox267 occurred less frequently (58 %), and SnTox1 was absent. Upon summarization of the data obtained from a five-year monitoring (2021–2025) of P. nodorum and P. pseudonodorum populations from different regions of the Russian Federation, a high het-erogeneity in the distribution of the necrotrophic effector genes SnToxA, SnTox1, SnTox3, SnTox267, and SnTox5 was revealed. Species-specific and geographic differentiation in gene occurrence frequencies, as well as their temporal dynamics, were established. The research presents for the first time the results of applying the primer pair SnTox5_qPCR_F/ SnTox5_qPCR_R for testing Russian populations of Parastagonospora spp. for the presence of the SnTox5 gene. As part of the initiated work on studying the species composition of wheat septoria pathogens from the Blagoveshchensk district of the Amur region, P. nodorum was identified as the predominant species in the phytopathogenic complex.