| The powdery mildew in wheat, caused by Erysiphe graminis f. sp. tritici, is one of the main diseases in wheat. Planting resistant cultivars was proved to be one of the most economical,effective and environmentally sound safe measure to control this disease. Molecular markers tightly linked to resistant genes not only facilitate the identification and mapping of resistant genes, but also can be used for markers-assisted selection (MAS) of resistant lines in breeding programs. Then MAS greatly enhances the efficiency of genes pyramiding and accelerates the progress breeding of resistance. Resistant genes Pm4a, Pm4b and Pm6 are still effective genes in conferring resistance to powdery mildew in wheat. The aim of this study is to identify PCR-based markers tightly linked to this three Pm genes and make use of this three genes easy in wheat MAS. Forty-one cultivars carrying different Pm genes were evaluated. Of them, nine cultivars were immune, which carried genes Pm13,Pm16,Pm18,Pm20,Pm21,Pm23 and Pm2+4b.The cultivars carrying Pm2, Pm3b, Pm3f, Pm4a, Pm4b, Pm6, Pm12, Pm22, Pm24, Pm4+8, Pm2+6 and Mlxbd genes showed moderate resistant and high resistant. And others Pm genes have lost resistance to powdery mildew. In this study, two SSR markers tightly linked to Pm6 gene Xgwm388,Xgwm501 were identified with genetic distance of 4.5cM and 12.2cM respectively ,so Pm6 was given a precise locus on the chromosome 2BL. Combined this two markers to one SSR marker and two SCAR makers identified before in our lab, we constructed the genetic map about Pm6 gene. Then the two SCAR markers were located in the wheat genome. At the same time, marker Xgwm388 is a repulsion-phase marker, which enriches SSR markers. And Xgwm501 belonged to co-dominant marker, which can distinguish the homozygous individuals from heterozygous ones. And this two markers will accurately detect the Pm6 gene in wheat germplasm. Through resistant evaluation and molecular detection, it was confirmed that the introgressed segment in Timgalen from T.timopheevi has not lost. Markers STS463 and STS410 were very stable and reproducible By comparison of three reported STS markers and specific band were detected in cultivars Asosan/8*Cc(containingPm3a),81-7241(containingPm23),hongyoumai(containing unkown Pm gene) by STS463 marker. The specific band also was detected in susceptible cultivar 9007000-4-2, so this two markers can't be used to accurately detect Pm4 gene independently. The combination of marker STS463 and STS410 could be used to validly detect Pm4 gene and speed up their application in resistant breeding. But the two markers can't be used to differentiate Pm4a from Pm4b. During the course of PCR walking of SCAR marker SC-S139615 linked to Pm6 gene, it was found that primer L3 could amplify a 500bp polymorphic fragment in the cultivar VPM. Furthur 25 cultivars with known Pm genes were analyzed by L3 primer, it showed that L3500 could only be detected in VPM. This marker can be used as specific marker in primary consideration. It extends the molecular marker of Pm4 and can differ Pm4b from Pm4a. Four resistant cultivars were identified using markers SC-S139615, Xgwm501, STS463, STS410, STS1700 and L3500. The result showed that cultivars 91138-16-2-13-12, zhengmai315 both carried Pm4a gene and Cp87-26-12 carried Pm4b gene. And the gene in N97189-2 is neither pm4 nor Pm6 and still under further study. Comparing with RFLP makers, PCR markers have some virtues with simple manipulation and not using isotope. The PCR markers linked to Pm6 and Pm4 are very useful in wheat resistant breeding against powdery mildew. It will greatly simplify the detection of Pm6 and Pm4 genes and speed up the application of these genes in the process of resistant breeding. But the identification of the very tightly linked markers is still necessary for saturated mapping and MAS of wheat Pm genes.
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