Dear Editor,Wheat powdery mildew,caused by Blumeria graminis f.sp.tritici (Bgt),is a destructive disease of wheat throughout the world.One of the most important environmental-friendly and economical methods to reduce wheat loss caused by Bgt is to develop highly resistant varieties (Kuraparthy et al.,2007).Pm21 from the wild species Haynaldia villosa (also known as Dasypyrum villosum) confers high resistance to Bgt in wheat throughout all growth stages.It has now become one of the most highly effective genetic loci introgressed into wheat from wild species,and the commercial varieties harboring Pm21 have been widely used in wheat production with more than 4 million hectares in China.