由小麦白粉菌[Blumeria graminis f. sp. tritici（Bgt）] 引起的小麦白粉病是一种重要的小麦叶部病害，对小麦的产量产生很大的影响。20 世纪80 年代，通过簇毛麦（Heuchera villosa）的6VS 染色体与小麦6AL 染色体易位将抗白粉病基因Pm21 转移到普通小麦中。最近，在一些地方发现了对Pm21 有毒的Bgt，虽然这些菌株的病理学特性还有待研究，但这一现象提醒小麦育种者应注意应用Pm21 的风险。来源于普通小麦与中间偃麦草（Thinopyrum intermedium）杂种后代的抗白粉病基因Pm40，被定位在小麦7BS 染色体上，对Bgt 具有广谱和持久的抗性。通过细胞学研究，并未在Pm40 的载体品种中发现大片段外缘染色体。过去几年的研究发现，Pm40 的载体品种具有优良的农艺性状。因此，我们相信在未来的育种工程中，Pm40 将会在Pm21 的抗性被克服之后起巨大的作用。另外，Pm21 和Pm40 都来源于外缘物种，这暗示着外源基因的抗性可能比小麦本身的基因更为持久和有效。

Powdery mildew, which is caused by Blumeria graminis f. sp. tritici (Bgt), is an important leaf disease that affects wheat yield. Powdery mildew-resistance (Pm) gene Pm21 was first transferred into wheat in the 1980s, by translocating the Heuchera villosa chromosome arm 6VS to the wheat chromosome arm 6AL (6VS·6AL). Recently, new Bgt isolates that are virulent to Pm21 have been identified in some wheat fields, indicating that wheat breeders should be aware of the risk of deploying Pm21, although pathological details regarding these virulent isolates still remain to be discovered. Pm40 was identified and mapped on the wheat chromosome arm 7BS from several wheat lines developed from the progenies of a wild cross between wheat and Thinopyrum intermedium. Pm40 offers a broad spectrum of resistance to Bgt, which suggests that it is likely to provide potentially durable resistance. Cytological methods did not detect any large alien chromosomal segment in the wheat lines carrying Pm40. Lines with Pm40 and promising agronomical traits have been released by several wheat-breeding programs in the past several years. Therefore, we believe that Pm40 will play a role in powdery mildew-resistance wheat breeding after Pm21 resistance is overcome by Bgt isolates. In addition, both Pm21 and Pm40 were derived from alien species, suggesting that the resistance genes derived from alien species are potentially more durable or effective than those identified from wheat.