Genetic diversity of spring wheat from Kazakhstan and Russia for resistance to stem rust Ug99

The spring wheat belt of Western Siberia and Northern Kazakhstan covers more than 15 million ha. While moisture stress is the main factor limiting production, rusts also represent a major challenge, especially in years with higher rainfall. Stem rust was not considered economically important until 2015 when a local epidemic occurred in the Omsk region of Russia and neighboring areas of Kazakhstan and affected more than 1 million ha. It occurred again in 2016 though the spread, severity and losses were less. This study used 16 pathotypes and 17 molecular markers to characterize a set of 146 spring wheat varieties and breeding lines identified as stem rust resistant in Kenya and the Kazakhstan–Siberia region for the presence of major genes. The genetic basis of resistance in the material was limited to Sr25, Sr31, Sr36, Sr6Ai, Sr6Ai#2, and some unknown major genes. Genes Sr25 and Sr6Ai#2 also provided high levels of resistance to leaf rust through linkages with Lr19 and Lr6Ai#2. Adult plant resistance to stem rust was observed in 26 genotypes (16.5 %), including eight possessing Sr57 gene. The high risk of stem rust—as indicated by the 2015 Siberian epidemic—means that there is an urgent need to diversify the genetic bases of resistance and to promote resistant varieties with farmers.