Resistance of Chinese wheat landraces and relatives at seedling stage to powdery mildew

Powdery mildew is a major wheat (Triticum aestivum L.) foliar disease caused by Blumeria graminis f. sp tritici (Bgt). The deployment of resistance resources including genes/alleles has been critical in controlling powdery mildew of wheat foliar disease. In wheat cultivation, powdery mildew (Pm) resistant genes most commonly used at the present belong to the race-specific resistance genes with high resistance levels. However, the extensive use of these resistance genes have frequently changed the pathogen population and rapidly induced new virulent strains of the pathogen. It has therefore been a long-term objective to identify effective new Pm resistance genes from the vast wheat germplasm resources. To identify resources that are effectively resistant to powdery mildew, 258 wheat landraces along with 42 wheat relatives were evaluated with E09 isolate of prevalent Chinese Bgt at seedling stage. The results showed that 5 of the 258 wheat landraces and 20 of the 42 wheat relatives were immune, nearly immune or highly resistant to E09. The above 25 wheat germplasms challenged with additional 5 different Chinese Bgt isolates (the E03, E05, E18, E20 and E23 isolates) to postulated the unknown Pm resistance genes/alleles. Comparison to the 28 known Pm resistance genes showed that the Pm resistant genes of the 25 wheat germplasms were completely different from the known 21 Pm resistance genes, Pm1a,Pm2, Pm3a, Pm3b, Pm3c, Pm3d, Pm3e, Pm3f, Pm4a, Pm4b, Pm4c, Pm5a, Pm6, Pm7, Pm8, Pm9, Pm17, Pm19, Pm24, Pm28 and Pm33. It was, however, not very distinguishable from Pm1c, Pm1e, Pm12, Pm13, Pm16, Pm20 and Pm21 resistance genes. The 25 wheat germplasms could carry new Pm resistance genes, whose sources were not only different from the others, but also carried 7 Pm resistance genes. This study explored effective new resistance resources of Chinese wheat landraces and their relatives which laid the basis for in-depth exploration and effective use of novel powdery mildew resistance genes. Despite this finding, more Bgt isolates would still need to be challenged to further confirm this result.