利用与小麦抗白粉病基因Pm2、Pm4a和Pm21紧密连锁的PCR标记，对含有Pm2、Pm4a和Pm21的小麦品系复合杂交后代经3轮分子标记选择，得到了一批聚合有Pm2+Pm4a+Pm21 3个基因的抗病植株，以及若干株Pm2+Pm21、Pm4a+Pm21和Pm2+Pm4a 2个基因聚合的植株。同时，还对中选植株进行抗病性人工接种鉴定。结果表明，含有Pm21的聚合体与Pm21基因单独存在时抗性相当，均对白粉病免疫，聚合体Pm2+Pm4a的抗性好于Pm2或Pm4a单独存在时的抗性。为降低分子标记选择成本，将检测Pm4a和Pm21的2种PCR放在一个反应体系中进行，扩增产物经1次电泳，可同时检测出Pm4a和Pm21，不同引物之间没有明显交叉扩增现象。
Pyramiding resistance genes has been supposed as one of the most effective methods for preventing breakdown of major gene conferring resistance to powdery mildew within a short period. It is difficult to select pyramids containing more than two resistance genes by common methods. Marker-assisted selection(MAS) is an ideal technology to select target gene in different genetic backgrounds. Pyramiding resistant genes by MAS has been reported. So far, DNA markers linked to wheat powdery mildew resistance genes had been found. In this study, PCR markers tightly linked or co-segregated with Pm2, Pm4a and Pm21 genes were confirmed to be applicable under different genetic backgrounds, and used to identify Pm2, Pm4a and Pm21 genes in breeding practice. Using these tested markers, a hybrid population with three powdery mildew resistance genes was screened and 100 plants containing Pm2, Pm4a and Pm21 were identified after three-cycle MAS. In addition, dozens of plants with two Pm genes were also obtained. The results of inoculation test indicated that the plants pyramiding Pm21 and other genes showed immunity to powdery mildew, as well as the plants possessing only Pm21. The plants with single Pm2 had lower resistance, while those with Pm4a showed middle resistance to powdery mildew. Notably, the plants with Pm2+Pm4a showed much better resistance than those with single Pm2 or Pm4a. To reduce the cost of MAS, two PCRs were performed in one mixture, in which Pm4a and Pm21 were identified respectively. MAS was compared with phenotypic selection also, from which more comprehensive information was provided.
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