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Short season, high latitude spring wheat is grown on 7 million ha in Western Siberia and 10 million ha in Northern Kazakhstan. Despite relatively low wheat yields (1.5 t/ha), the region is extremely important for regional and global food security. Leaf rust dominates, occurring three years out of five, especially in favorable years with higher rainfall. Since 2010, stem rust has been observed at an increasing number of sites. The first large-scale stem rust outbreak occurred in 2015 and affected about 0.5-1 million ha in Omsk, Western Siberia. In 2016, 2 million ha were affected in the Omsk and Altay regions, while 1 million ha in the Kostanay and Northern Kazakhstan regions were affected in 2017. Estimated yield losses reached 25-35% each year. Factors associated with the outbreaks included: higher rainfall in late June and July; cultivation of susceptible varieties; and an increased area planted to winter wheat, which serves as a source of inoculum. Sampling and race analysis revealed a diverse pathogen population, indicative of a sexual recombination. A total of 51 races were identified from 31 samples taken in 2015 and 2016. All races were avirulent on Sr31. The majority of varieties released and cultivated in the region are susceptible to stem rust and require replacing. A recent study of 150 local resistant varieties and breeding lines indicated that the genetic basis of resistance was limited to Sr25, Sr31, Sr36, Sr6Ai, Sr6Ai#2, and additional unknown major genes. Adult-plant resistance to stem rust was observed in less than 20% of the germplasm. The potential impact of these large stem rust outbreaks on other wheat growing regions is being investigated by analyzing spore wind dispersal patterns. Further research is required to understand and mitigate the sudden appearance of stem rust as a disease of economic importance.
Study at Omsk State Agrarian University was supported by the Russian Science Foundation (project No. 16-16-10005).
Northern Kazakhstan and Western Siberia are major high latitude spring wheat growing regions on the Eurasian continent. Rust epidemics can cause serious crop losses in this region. For this purpose, the Kazakhstan-Siberian network for wheat improvement (KASIB) was created in 2000. Seventy wheat cultivars and lines from a KASIB nursery were characterized for seedling and adult plant resistance (APR) to leaf rust using Australian pathotypes in greenhouse and field experiments. A molecular marker (STS iag95) detecting 1RS and therefore genes located in the rye component of the 1BL.1RS translocation was used to verify the presence/absence of Lr26. Field assessments of the nursery were conducted at Cobbitty using mixed Pt pathotypes. Lr26 was detected in five cultivars (Bayterek, GVK-1916-9, Altayskaya 105, Ok-1, and Omskaya 36) based on seedling tests using seven pathotypes. This was confirmed using the SRS marker. Other genes postulated included Lr3a (in cv. GVK 1860/8, GVK 1369/2, GVK 1857/9, and GVK 1526-2) and uncharacterized gene/s in cv. Zhenis and Lutescens-166 SP 94). The majority of KASIB entries were susceptible in seedling tests to Pt, but varying levels of potentially useful resistance were observed in 23 genotypes tested in the field. Low infection types on seedlings and field resistance in cv. Tertsia, Aria, and Sonata suggested the presence of unknown gene/s of potential value that warrant further investigation. Future efforts to breed wheat varieties resistant to one or more of the cereal rust pathogens will require identification of resistance sources that differ from those already present. Understanding the dynamics of pathogenic variability in pathogen populations is also important in selecting appropriate resistances.