Wheat (Triticum L.) cultivars from GRIN collection (USA) selected for durable resistance to septoria tritici and stagonospora nodorum blotch

Septoria tritici blotch (STB) or Stagonospora nodorum blotch (SNB) are among the most harmful and economically significant diseases of wheat in the grain growing regions of the world, especially in the countries with a temperate climate. In epiphytotic years the losses from the disease can reach 30-40 %. In Russia the diseases holds a dominant position in a pathogenic complex of fungus diseases of grain crops. In this paper we first determined the parameters of partial resistance in the cultivars of wheat (genus Triticum ) from the collection of the Germplasm Resources Information Network (GRIN, USA) using the stable strains of Septoria tritici and Stagonospora nodorum pathogens. The aim of our study was to select wheat varieties with long-term resistance to blotch based on field and laboratory tests. A long-term study (2009-2015) of the disease development on the wheat cultivars from GRIN Collection were conducted at artificial infection in infection nursery (Central region of Russia, Moscow Province). The samples studied belonged to various genetic groups. A total of 20 samples were diploids (2 n = 14), 409 samples were tetraploids (2 n = 28), 1688 samples were hexaploids (2 n = 42), and also 397 lines derived from crossing of Triticum aestivum with Aegilotriticum were tested. The area under disease progress curve was determined, and the index of resistance (IR) was calculated. The cultivars, that characterized by slow development of the disease in the field, i.e. with high-and middle IR, were selected for laboratory studies. The plants were grown in artificial climate chambers till the 3rd leaf fully unfolded. Pieces of leaves were inoculated by a drop of spore suspension of S. tritici (4 isolates) or St. nodorum (4 isolates), 10 replications per each variety-to-pathotype combination. The samples were grouped according to the latent period length and size of infectious spots. As a result, 191 samples of T. aestivum subsp. aestivum and a sample of T. aestivum subsp. spelta with a high index of resistance to the disease were selected among hexaploid wheat; 16 samples were found in tetraploid wheat, including 8 samples of T. turgidum subsp. durum, 2 samples of T. turgidum subsp. turgidum, 3 samples of T. turgidum subsp. dicoccon, 3 samples of T. timopheevii subsp. timopheevii ; and 4 samples were selected from diploid wheat T. monococcum subsp. aegilopoides. Eleven lines derived from crossing of T. aestivum and Aegilotriticum sp. showed the slowed-down in the disease development. The selected hexaploid wheat cultivars were mostly from North American ecology-geographical group of T. aestivum subsp. aestivum, including 77 cultivars from the USA and 18 - from Canada (34.5 % in total). Selected tetraploid wheat samples of T. turgidum subsp. durum were from North and Central America, and those of T. turgidum subsp. turgidum, T. timopheevii subsp. timopheevii and T. turgidum subsp. dicoccon from Europe and Asia. The samples from Iraq and Hungary with a high index of blotch resistance were found among diploid wheat T. monococcum subsp. aegilopoides. The synthetic lines of wheat from the USA and Mexico were also characterized by a slowed-down development of the disease. Thus the wheat cultivars with partial resistance have been revealed, including 10 cultivars with partial resistance to Septoria tritici blotch and 40 cultivars - to Stagonospora nodorum blotch. The accessions PI 494096 Tadinia, Cltr 17904 Owens, Cltr 15645 II-62-4 (USA), VIR 63915 Flame (England), Cltr 14492 Azteca, PI 520555 Alondora ‘S’ (Mexico), PI 404115 Timson (Australia), Cltr 11765 Chinese 166 (Germany), PI 422413 CNT 1 (Brazil), PI 168724 Benvenuto, Cltr 15378 Piamontes, PI 344468 Piamontes Inta (Argentina), PI 306551 2944 (Romania), PI 355706 69Z5.715 (Azerbaijan), PI 355560 SK 1B (Switzerland), PI 94743 290 (Russia) are of special interest for breeding as a source of long term resistance.