| Wheat powdery mildew by Erysiphe graminis f.sp.tritici is a major threat to wheat production in China. The loss of resistance for cultivars resulting in the outbreak of diseases in wheat growing area was usually occurred with the improvement of cultivation level, the increasing fertilizer, and the utilization of semi-dwarf varieties and the enhancement of pathogens variation ability. Breeding varieties resistance to wheat powdery mildew is an economical, safe and effective measure. Using alien desirable genes, including the resistance gene, can greatly enrich resistant wheat genetic resources, but also help expand the base of wheat genetics and breeding. Wheat has many related species, and a lot of desirable genes from alien species have been transferred into wheat through distant hybridization. In order to rapidly apply these alien desirable genes from distant species, it is an effective method to adopt the molecular technique.A steady wheat line 723 which was selected from the hybrid progenies of common wheat and Thinopyrum intermedium by wide cross was obtained. Line 723 is immune to powdery mildew. The in situ analysis demonstrated that a small chromosome fragment of Th. intermedium was transferred into one pair of wheat chromosomes. In the present study, resistance to powdery mildew in line 723 was analyzed, the chromosome constitution was further studied by cytological methods, and the molecular marker of the powdery mildew resistance gene was also primarily selected. The main results were list as follows:1. Genetic analysis of powdery mildew disease resistance indicated that the wheat line 723 and F1 population of 723×Miangyang 26 (MY26, a cultivar which is seriously susceptible to powdery mildew) were immune to powdery mildew, and the segregation ratio for resistant and susceptible plants of F2 population showed good fit into 3:1. Thus, there is a single dominant gene, temporarily named Pm723, which is responsible for the powdery mildew resistance.2. Chromosome count showed that the chromosome number of 723 was 2n= 42. So there was no variation of chromosome number. Chromosome pair at PMCI of line 723 and 723×Miangyang 26 F1 showed that the pair of chromosomes was normal and no other pair configurations had been found. According to previously GISH study, it had been further proved that the wheat line 723 was a stable chromosome translocation line in which a Th. intermedium chromosome fragment possessing the powdery mildew resistance gene had been transferred into one pair of wheat certain chromosomes.3. There are two SSR primers Xgwm570-6B and Xbarc79-6B that have polymorphisms in powdery mildew resistant and susceptible parents and resistant and susceptible gene bulks by using SSR markers. The polymorphic SSR primers were used for F2 population,3 recombinant plants were found in 66 F2 plants for Xgwm570-6B. Linkage analysis was conducted with the software Mapmaker 3.0. The result indicated that marker was linked to Pm723 with the genetic distance of 6.2cM. For primer Xbarc79-6B,5 of 66 plants in F2 population have exchanged. Linkage analysis by the software Mapmaker 3.0 indicated that the marker was linked to Pm723 with the genetic distance of 14.1cM, which shows that the distance between the two markers and Pm 723 is a little far. The primer Xgwm570 has amplification site on 6AL and 6BL of common wheat, while the primer Xbarc79 can be only amplificated on 6AL of common wheat. Combine the genetic analysis of this two markers, we can deduce that Pm 723 locates on 6BL of wheat.Comparison with the known genes, Pm723 might be a new powdery mildew resistance gene from Thinopyrum intermedium, however, further research should be carried out.
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