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Background: Blumeria graminis f. sp. tritici (Bgt), the causal agent of wheat powdery mildew severely affects yield security wheat production in China. Understanding the virulence structure and genetic variations of this pathogen is important for breeding wheat lines resistant to wheat powdery mildew. However, information related to genes controlling resistance remains elusive. This study analyzes the virulence structure and the genetic diversity of pathogenic Bgt populations isolated from northeastern (Liaoning, Heilongjiang) and northwestern (Gansu) China, two representative wheat producing areas, on 37 wheat cultivars each carrying a known powdery mildew resistance (Pm) gene. Results: Bgt isolates from northeastern China show higher frequencies of virulence genes than populations from Gansu Province. Many of the known Pm genes failed to provide resistance in this study. However, Pm21 provided 100% resistance to all isolates from all three provinces, obtained during two consecutive years, while Pm13 provided 100% resistance in Gansu. Pm13, Pm16, Pm18, and Pm22 also showed partial resistance in northeastern China, while Pm16, Pm18, Pm22, Pm5 + 6 and Pm2 + 6 +? maintained some resistance in Gansu. Genetic diversity among populations in different regions was detected by cluster analyses using expressed sequence tag-simple sequence repeat (EST-SSR). When the genetic similarity coefficient is relatively high, populations from the same regional origin are mostly clustered into one group while populations from different regions exhibit large genetic differences. Conclusion: Pm21 remains the best choice for breeding programs to maintain resistance to Bgt. Only 58% of the isolates tested show a clear correlation between EST-SSR genetic polymorphisms and frequency of virulence gene data. [ABSTRACT FROM AUTHOR]

Wheat stem rust, caused by Puccinia graminis f. sp. tritici , is one of the most serious fungal diseases in wheat production, seriously threatening the global supply of wheat and endangering food security. The present study was conducted to evaluate wheat monogenic lines with known Sr genes to the most prevalent P. graminis f. sp. tritici races in China. In addition, wheat lines introduced from the International Maize and Wheat improvement Center (CIMMYT) with resistance to the Ug99 race group were also evaluated with the prevalent Chinese P. graminis f. sp. tritici races. The monogenic lines containing Sr9e , Sr21 , Sr26 , Sr31 , Sr33 , Sr35 , Sr37 , Sr38 , Sr47 , and SrTt3 were effective against races 21C3CTTTM, 34C0MRGSM, and 34C3MTGQM at both seedling and adult-plant stages. In contrast, monogenic lines containing Sr6 , Sr7b , Sr8a , Sr9a , Sr9b , Sr9d , Sr9f , Sr9g , Sr13 , Sr16 , Sr18 , Sr19 , Sr20 , Sr24 , Sr28 , Sr29 , and Sr34 were highly susceptible to these races at both seedling and adult-plant stages. Lines with Sr5 , Sr10 , Sr13 , Sr14 , Sr15 , Sr17 , Sr21 , Sr22 , Sr23 , Sr25 , Sr27 , Sr29 , Sr30 , Sr32 , Sr36 , and Sr39 were resistant to one or more of the tested races. Among the 123 CIMMYT lines, 38 (30.9%) showed varying levels of susceptibility to Chinese P. graminis f. sp. tritici races. The results should be useful for breeding wheat cultivars with resistance to stem rust.