Identification Of Molecular Markers For The Powdery Mildew Resistance Gene Pm6 In Wheat (Triticum Aestivum L.)

The molecular marker, which was established in the middle of 1980s, is a DNAsequence-based genetic marker system. It was now widely used in many areas of plantgenetics and breeding research, such as genetic map construction, gene mapping andcloning, marker assistant selection and relationship and evolution of related species. In thepresent research, different types of molecular markers (SSR, STS, EST-SSR etc.) were usedto genetically map the powdery mildew resistance gene Pm6. In addition, a potential newstrategy for the development of STS markers using the RFLP sequence database was alsodiscussed.1. Development of the STS Markers Linked To the Powdery Mildew Resistance GenePm6 in WheatPowdery mildew resistance gene Pm6, which comes from T.timopheevi L., is aneffective gene in most powdery mildew epidemic areas of China. Utilization of themolecular markers, especially the PCR-based markers, is extremely important for theaccurate selection of Pm6 in breeding program. RFLP probe BCD135 was previouslyproved to be closely linked to Pm6. In the present research, four STS primers(NAU/STS_BCD135-1,NAU/STS_BCD135-2,STS003 and STS004) were designed according tothe sequence of BCD135.These primers were used for PCR amplification using thegenomic DNA used the resistant near-isogenic-lines (with Pm6) and their recurrent parent"Prins"as samples. No polymorphic product was observed in experiments using primersSTS003 and STS004. However, primer NAU/STS_BCD135-1 and NAU/STS_BCD135-2 couldamplify two and one polymorphic bands between the near-isogenic-lines and "Prins"respectively. The two primers were then used to amplify the F₂ population from a cross of(IGVI-465×Prins). The application results and the powdery mildew resistanceidentification results were analyzed using the software Mapmarker3.0. The results indicatedthat NAU/STS_BCD135-1 and NAU/STS_BCD135-2 were closely linked to Pm6 with a genetic distance of 1.0cM.2,Discrimination of the Pm6 near-isogenic-lines with different alien chromosomefragments and the determination of translocation breakpoints using molecularmarkersIn order to determine the size of T. timopheevi L. chromosome segments introducedinto wheat background, a total of 54 primers (including SSR, STS, and EST-SSR) wereused to analyze the introduced eight Pm6 near-isogenic-lines. The results were found to becoincidence with the RFLP results of Tao et al (1999), indicating that three lines IGVI465,IGVI464 and IGVI463 contained the minimal introgression segments. By comparing withthe published linkage map wheat, a frame genetic map of 7 molecular markers wasconstructed using these near-isogenic-lines. Using all the 7 PCR markers, it is feasible todifferentiate the eight near-isogenic-lines and this will be very helpful for the markerassistant identification of these lines in wheat breeding program.3,A potential new strategy for the development of STS markers using the RFLPsequence databaseWhen developing the STS markers for Pm6, we found that the searching of simplesequence repeat (SSR) in the sequence of RFLP probes should be a potential strategy forthe development of STS markers in Triticeae. Special software was first used to find theSSR sites; the RFLP probes containing characteristic SSR were then selected. Primers weredesigned according to the SSR sites. In order to verify the efficacy of the strategy, fivepimer pairs were designed and were used to analyze some genetic materials.