Abstract
The causative agent of Septoria leaf spot of wheat - Zimoseptoria tritici is one of the most harmful and common Septoria pathogens in Russia. Its great intraspecific variability provides the potential for selection of races with increased virulence to resistant varieties. The aim of the research was to reveal the frequency of occurrence of potentially dangerous races in the regional Z. tritici populations on wheat. The investigations were conducted from 2003 to 2018 on the basis of All-Russian Research Institute of Phytopathology. 304 monospores isolates from 7 regions of Russia were tested. The analysis of combinations of the interaction cultivar-isolate and of the diversity of morphological types of colonies of the fungus was discovered 260 races. The potential danger of the race was determined by the aggressiveness degree and the virulence genes spectrum. On these characteristic Z. tritici races were divided into 6 groups. The proportion of potentially dangerous races in regional populations ranged from 5.4 to 16.9%. The highest frequency of potentially dangerous races was observed in the North Caucasus and Central-Chernozem regions. The Volga region was the second most likely to detect such races. In other regions, the numbers of such races was 2-3 times lower, and in Siberia were not observed. The races, virulent to effective resistance Stb-genes, were discovered in all regions, except West-Siberian. Their share in populations was 16-28.6%, and they were more common among races with a wide range of virulence genes. These studies have concluded that the greatest probability of occurrence of potentially dangerous races Z. tritici exists in regions where favorable conditions and this species dominate in the Septoria complex. Expansion of the Z. tritici areal due to changing climatic conditions may lead to an increase in the proportion of aggressive and widely virulent races in other regions.
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