Seedling resistance of winter and spring bread wheat cultivars to Pyrenophora tritici-repentis

   Background. The fungus causing tan spot on wheat leaves, Pyrenophora tritici-repentis (Ptr), continues to expand its range and inflict severe damage to the crop. Development of resistant cultivars remains the most effective and environmentally friendly way of disease control.   The objective was to characterize modern domestic cultivars of bread wheat (Triticum aestivum L.) according to their seedling resistance to geographically different Ptr populations, identify sources of Ptr resistance, locate the presence of dominant Tsn1 alleles in cultivars, and assess their relationship with Ptr susceptibility.   Materials and methods. Ptr resistance was assessed in 76 winter bread wheat cultivars from the VIR collection, and 4 winter and 43 spring bread wheat cultivars from the Volga region. Isolates from the Krasnodar, Tambov, Tatarstan and Altai Ptr populations (2022) served as the inoculum. Dominant Tsn1 alleles were identified by PCR using the Xfcp623 marker.   Results. Bread wheat cultivars were characterized for the type of response in the leaves of their seedlings to isolates from Ptr populations and the presence/absence of dominant Tsn1 alleles. Resistance to isolates from two or three Ptr populations was observed in 11 winter and 13 spring cultivars. Differences between winter and spring forms in their resistance levels wereshown. Dominant Tsn1 alleles were identified in 26 cultivars. No statistically significant association was found between the presence/absence of dominant Tsn1 alleles and the manifestation of resistance/susceptibility to Ptr.   Conclusion. The disclosed diversity of bread wheat cultivars in their responses to the infection with isolates of different Ptr populations may be due to their differences in the alleles of Ptr resistance/susceptibility genes as well as the presence of still unknown effector genes in the pathogen’s genome. Cultivars resistant to two or three Ptr populations can be used by breeders as sources of seedling resistance.