Evaluation and Identification of Powdery Mildew Resistance Genes in Aegilops tauschii and Emmer Wheat Accessions

Abstract

Powdery mildew, caused by Blumeria graminis f. sp. tritici (Bgt), is a serious threat to wheat (Triticum aestivum L.) production. Narrow genetic basis of common wheat boosted the demand for diversified donors against powdery mildew. Aegilops tauschii Coss (2n = 2x = DD) and emmer wheat (2n = 4x = AABB), as the ancestor species of common wheat, are important gene donors for genetic improvement of common wheat. In this study, a total of 71 Ae. tauschii and 161 emmer wheat accessions were first evaluated for their powdery mildew resistance using the Bgt isolate E09. Thirty-three Ae. tauschii (46.5%) and 108 emmer wheat accessions (67.1%) were resistant. Then, all these accessions were tested by the diagnostic markers for 21 known Pm genes. The results showed that Pm2 alleles were detected in all the 71 Ae. tauschii and only Pm4 alleles were detected in 20 of 161 emmer wheat accessions. After haplotype analysis, we identified four Pm4 alleles (Pm4a, Pm4b, Pm4d, and Pm4f) in the emmer wheat accessions and three Pm2 alleles (Pm2d, Pm2e, and Pm2g) in the Ae. tauschii. Further resistance spectrum analysis indicated that these resistance accessions displayed different resistance reactions to different Bgt isolates, implying they may have other Pm genes apart from Pm2 and/or Pm4 alleles. Notably, a new Pm2 allele, Pm2S, was identified in Ae. tauschii, which contained a 64-bp deletion in the first exon and formed a new termination site at the 513th triplet of the shifted reading frame compared with reported Pm2 alleles. The phylogenetic tree of Pm2S showed that the kinship of Pm2S was close to Pm2h. To efficiently and accurately detect Pm2S and distinguish with other Pm2 alleles in Ae. tauschii background, a diagnostic marker, YTU-QS-3, was developed, and its effectiveness was verified. This study provided valuable Pm alleles and enriched the genetic diversity of the powdery mildew resistance in wheat improvement.