Pyramiding Wheat Powdery Mildew Resistance Genes Pm2,Pm4a and Pm21 by Molecular Marker-assisted Selection

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.