Molecular Mapping Of A Novel Wheat Powdery Mildew Resistance Gene Ml92145E8 And Its Application In Wheat Breeding By Marker Assisted Selection

Wheat powdery mildew,caused by(Blumeria graminis(DC.) E.O. Speerf. Sp. Tritici, is one of the major disease of the world wild. Wheat powdery mildew not only causes severe yield loss, but also seriously reduces the quality of wheat. It used to occur in highly productive areas with a maritime or semi-continental climate.In china, wheat powdery mildew usually occurs in the southwestern plateau and coastal area of Shandong Province. Since the 1970 s, its severity increased markedly, mainly due to high applications of nitrogenous fertilizers,production of semi-dwarf wheat cultivars and expansion of irrigated area.Utilization of resistant cultivars is the most economical,efficient and environmentally friendly approach to control this disease,as long as sources of resistance are available.Hence, it has academic value and importance for identifying new resistance genes to maintain resistance in released cultivars.In this study, we created a F2 population and the F2:3 family derived from the cross of 92145E8 and Huixianhong. We located and mapped the resistant gene using the method of Bulked Segregation Analysis(BSA) and genetic analysis. The summaries are as follows:(1) The Bgt isolate E09 was used to inoculate 92145E8, Huixianhong, as well as the hybrid populations including F1, F2 and F2:3. 92145E8 exhibited an immune reaction, whereas Huixianhong was highly susceptible after inoculation with isolate E09. F1 plants of 92145E8 × Huixianhong were immune as well. The F2 population segregated 179 resistant and 72 susceptible plants, respectively, fitting to a ratio of 3:1. The F2:3 family segregated 54 resistant, 85 hybrid and 54 susceptible, fitting to a ratio of 1:2:1. These results indicated that there is a single dominant gene in 92145E8, tentatively designated as Ml92145E8.(2) The resistant and susceptible DNA bulks of the F2 population as well as the parents,were initially surveyed using genomic SSR markers on whole chromosomes in wheat. Out of them, 8 SSR markers detected polymorphism between the parents and bulks. The genetic distances of Xwmc181, Xgpw2046 and Xgwm356 from Ml92145E8 were 11.8c M, 7.0c M and 9.2c M, respectively. To identify the closely linked markers to the targeted gene, 8 new molecular markers were developed based on the published IWGSC survey sequences(http://www.wheatgenome.org/), the sequences of Aegilops tauschii D genome and T. urartu A genome, which permitted mapping of Ml92145E8 within an interval of 3.6c M, flanked by the codominant markers Xsdau K13 and Xsdau K682.(3) According to both powdery mildew resistance spectrum analysis( the differential reactions of 92145E8, Lankao 906 and VPM1 to 14 Bgt isolates) and allelism test of mildew resistance genes Pm4 b and Ml92145E8,Pm LK906 and Ml92145E8, it was concluded that Ml92145E8 is a new powdery mildew resistance gene(4) Furthermore, 5 elite lines with powdery mildew resistance gene Ml92145E8 in different background of Liangxing 99 and Gaokang 1 were developed by genotypic and phenotypic selection, which were designed as SDAU3561, SDAU3562, SDAU4173, SDAU4174 and SDAU4175, respectively. The markers closely linked to Ml92145E8 will be useful in marker-assisted-selection(MAS) for breeding wheat powdery mildew resistance.