| Powdery mildew, caused by Erysiphe. graminis f. sp. tritici, is one of the most important fungal disease of wheat (Triticum aestivum L.) worldwide. Breeding for resistance to powdery mildew is the most economical and effective way for controlling the disease. SSR and EST-SSR markers for alien powdery mildew resistance genes Pm4b, Pml2 and Pm21 have been identified and tested for marker assisted selection (MAS) in wheat breeding program. The results obtained are as follows:Bulked segregant analysis (BSA) approach was employed to generate SSR and EST-SSR markers linked to Pml2, one of the best powdery mildew resistance gene in China, using a segregating population derived from Line31 (Wembley*6/Ae. speltoides). One SSR marker Xgwm361 and four EST-SSR markers, Xcau24, Xcau44, Xcaul86 and Xcau268 were proved to be linked to Pml2. The genetic distances between the resistance gene and the five markers were: 0.9 cM to Xgwm361, 0.3 cM to Xcau44, 0.8 cM to Xcau268, 1.5 cM to Xcau186 and 2.2 cM to Xcau24, respectively. After testing on Chinese Spring nullisomic-tetrasomic lines and ditelosomic lines, the resistance gene linked SSR and EST-SSR markers were mapped on chromosome 6BL. The SSR and EST-SSR markers linked to Pml2, found in this study, provide useful tools for marker assisted selection of Pml2 in the wheat breeding program. The recombinants between Pml2 and the SSR and EST-SSR markers indicated that low recombination could be detected between the wheat B genome and the S genome of Ae. speltoides during the backcrossing. The disease resistant recombinants could thereafter be used as improved resistance resources since only less S genome fragments were left.Pm21, a translocation line of 6VS/6AL between Haynaldia villosa and common wheat, is one of the best powdery mildew resistance resources so far in China. Three disease resistance segregating populations of Pm21 gene were selected from the wheat-breeding program for SSR analysis. One EST-SSR marker Xcaul27 was found to be co-segregated with Pm21. The resistance gene linked marker Xcau127 was mapped on chromosome 6AS by Chinese Spring nullisomic-tetrasomic lines and ditelosomic lines. The EST-SSR marker Xcau127 has the co-dominant advantage over RAPD and SCAR markers which provide powerful tool for Pm21 marker assisted selection and pyramiding.'Torfrida', a carrier of Pm4b and derivative of VPM1, provides sound powdery mildew resistance in Beijing area. 'Torfrida' has been used for several years in the breeding program providing effective resistance against the mildew pathogens. One disease resistance segregating population 3B789, derived from 'EM85/Torfrida//Wen6/3/3*Jing411/4/Nongdal89', was selected for SSR analysis using BSA approach. An EST-SSR marker Xcau33 was found to be co-segregated with the resistance gene Pm4b in a 231 plants population and could be used for marker-assisted selection of both Pm4a and Pm4b locus.Forty accessions of wild emmer (T. turgidum var. dicoccoides) were tested for seedling powdery mildew resistance and crossed with common wheat susceptible line 87-1 to obtain F1 seeds. The reactions to Erysiphe. graminis f. sp. tritici of the F1 plants were tested at the seedling and adult stages. The results indicated that dominant and semi-dominant genes were responsible for powdery mildew resistance at the seedling stage, while dominant, semi-dominant and recessive genes were found controlling the powdery mildew resistance at the adult plants. After testing the Pm30 linked SSR marker Xgwml59 on the 40 F1 hybrids between wild emmer and common wheat, it was found that the Pm30 linked Xgwm159 loci could be detected at 8 F1 hybrids, indicating the 8 wild emmers might also carry the Pm30 gene.
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