Molecular Cytogenetic Identification of Wheat– <i>Aegilops geniculata</i> Derivative Line with Resistance to Powdery Mildew Encoded on Chromosome 6U ^g

<i>Aegilops</i> <i>geniculata</i> Roth is a valuable donor for improving common wheat (<i>Triticum aestivum</i>) because of their close relationship. In this study, W181009 was identified as a BC₁F₁₂ progeny resulting from the cross between 'Chinese Spring' and <i>Ae. geniculata</i> SY159. Cytological examination, fluorescence in situ hybridization, and functional marker analysis confirmed that W181009 carried alien chromosomes 2M^g and 6U^g from <i>Ae. geniculata</i> SY159. Using the specific locus amplified fragment sequencing (SLAF-seq) technique, we successfully developed specific markers for W181009 with an effective rate of 54.23%. Subsequently, the deletion of chromosome 6B in W181009 was confirmed using deletion nullisomic-tetrasomic lines. Notably, W181009 showed immune resistance to powdery mildew at all growth stages. To further study the source of the powdery mildew (<i>Blumeria graminis</i>) resistance gene in W181009, a genetic population was created using W181009 and Shaanyou225 for analysis. Both F₁ and BC₁F₂ plants carried chromosome 6U^g, and they exhibited strong resistance against powdery mildew, indicating that the resistance in W181009 originated from chromosome 6U^g. Furthermore, the presence of only chromosome 6U^g can be easily identified by using two specific SLAF-seq markers. The study results provide the basis for further genetic research and breeding to improve powdery mildew resistance using W181009.