Molecular Marker And Genetic Analysis Of A New Germplasm N9628-2 With Powdery Mildew Resistance

Powdery mildew, caused by Erysiphe graminis f. tritici, is one of the devastating diseases of wheat(Triticum aestivum L.em Thell.). The use of resistant cultivars is the most economical, effective and environmentally safe way to control this disease. Molecular markers tightly linked to resisitance genes not only facilitates the identification and mapping of resistance genes, but also can be used for markers-assisted selection (MAS)of resistant lines in breeding programs. MAS greatly enhances the opportunity for gene pyramiding and expedites the process of breeding for resistance. Wild relatives of wheat are rich in resistance resources, and are an important source of powdery mildew resistance genes. There are many methods to utilize the powdery mildew resistance of wild relatives of wheat. The method that transferring resistance genes from Amphidiploid to common wheat is used widely. The main arms of this study were to identify and tag resistance gene in N9628-2 which was derived from the backcross of Am9(F1 progeny of the cross between tetraploid wheat-Aegilops amphidiploid and a sensitive wheat cultivar Shaan 160 ) and Shaan 160.This study analyzed N9628-2 and its parents in agronomic characters, resistance identification, high molecular weight glutenin(HMW-GS).The result indicated that this new germplasm had excellent agronomic characters, and showed highly resisitant to the prevailing Blumeria graminis f.sp.tritici race in Shaanxi province.Y39 and PS5 were immune to this race. Am9 is resisitant to this race. Shaan 160 showed highly susceptible to this race.It was indicated that the resistance to powdery mildew of N9628-2 came from Am9, but we could not made sure it came from Y39 or PS5 by this result.Am9 contained all the HMW-GS Subunits coming from Y39 and PS5 including N, 7+8, 12u and a HMW-GS Subunit whose Mobility was smaller than 1.The HMW-GS Subunits of N9628-2 were same to shaan 160′s, including 1, 7+8, 2+12.The chromosome locations of the powdery mildew resistance genes of N9628-2 were studied with nullisomic analysis. In order to determine the chromosome of these resistance genes in N628-2, disomicAbb who are susceptibie to powdery mildew and their nullisomics are crossed with N9628-2. The F1 and F2 populations derived from crosses of N9628-2 were inoculated with the prevailing Blumeria graminis f.sp.tritici race in Shaanxi province at the seedling stage for resistance identification. It finded that the F1 of Abb/N9628-2 were all resistant to powdery mildew and the ratios of resistant and susceptible plants in Abb/N9628-2 F2 progeny fit the expected 3 to 1, which indicated that the powdery mildew resistance genes of N9628-2 are dominant genes.The ratios of resistant and susceptible plants in(nullisomics/N9628-2) F2 progeny fited the expected 3 to 1 except for 6A nullisomic,which indicated that the resistance of N9628-2 was controlled by a dominant gene on 6A.In the present study, we aimed to identify the resisitance gene in N9628-2, and located it on wheat chromosome.The F1 (308 plants) and F2(275 plants) populations derived from crosses of N9628-2 and highly susceptible cultivars Shaan 160 and Shaanyou 225 were inoculated with the prevailing Blumeria graminis f.sp.tritici race in Shaanxi province at the seedling stage for resistance identification.The parents and F2 individuals were used for gene location with 208 pairs of SSR markers including 38 pairs polymorphic marker between two parents,and the result was verified by analyzing Chinese Spring nullisomic-tetrasomic and ditelosomic lines.According to inoculation test, the resistance to powdery mildew in N9628-2 was controlled by a single gene.Two markers Xwmc553 and Xwmc684 on chromosome 6A generated polymorphic DNA fragments between the resistant and susceptible pools, indicating the resistance gene might be located on chromosome 6A and linked to the two markers.The resistance gene was further located on chromosome 6AS by the absence of the above polymorphic DNA fragments only in Chinese Spring 6A nullisomic-tetrasomic and 6AL ditelosomic lines.The genetic distances between the resistance gene and the two markers, calculated by Kosambi′s formula,were 10.99 (Xwmc553) and 7.43cM(Xwmc684) respectively. Our research found that the resistance gene in N9628-2 was probably a new gene differing from the reported resistance genes PmY39, PmPS5B(Pm33),and PmPS5A.