| Powdery mildew, caused by Blumeria graminis f. sp. tritici (Bgt), has become a serious foliar disease and caused yield losses in the wheat production around the world. Developing disease-resistant varieties is one of the most economical, environmentally friendly and effective methods comparing to chemical control and cultivation management. However, due to the diversity and rapid mutation of physiological races of powdery mildew, most of the resistant varieties lost their resistance in 3-5 years after large-scale application. So, identification and assessment of new powdery mildew resistance genes in wheat breeding is a tireless road work.Tabasco, a new variety introduced from Germany, was a valuable resource for resistance to wheat powdery mildew. It's high resistant to mixture isolates of powdery mildew in both Germany and Nanjing, China. In order to explore new resistant resources in breeding for resistance to powdery mildew, F1, F2 population and F2:3 families of Tabsco/ Ningnuo No.1 were developed.The resistance of individual of F] population was identified in field and all plants were high resistance to podwery mildew throughout the whole growth period. However, Ningnuo No.1 and Sumai No.3 which pointed as control were high susceptible before jointing. Infection types in 472 F2 plants were evaluated by artificial inoculation with isolate Bgt19 in the growth chamber. The population segregated 359 resistant:113 susceptible fitting the 3:1 ratio. Combined F1 and F2 identification results we concluded that there was a single dominant gene controlling powdery mildew resistance in Tabasco. This resistance gene was temporarily designated as PmTa. Then 436 F2:3 families were tested to verify F2 genotypes. The result displayed that homozygous resistance families were 101, heterozygous resistance were 238 and homozygous susceptible were 97, which fit 1:2:1 by chi-square test and verified the true of above opinion. Bulked segregant analysis (BSA) was adopted, based on molecular markers technology. DNA bulks were prepared by combining equal amounts of DNA from six resistant and six susceptible plants derived from the F2 population. Then 244 wheat SSR markers, covering the A, B and D genomes, were analyzed for polymorphism between the parents and the resistant and susceptible bulks (R-S bulks), which object was to be sure the locus of resistance gene. The results indicated that SSR marker Xgwm205, located on 5DS, displayed consistent polymorphism between parents and R-S bulks. Linkage analysis showed that the genetic distance between the Xgwm205 and PmTa gene was 17.6 cM. According to published wheat genetic map, we selected 46 SSR markers located on 5D chromosome short arm and centromere region and conducted polymorphism detection and linkage analysis. Xcfd81 was discovered on the other side of PmTa and genetic distance was 3.1 cM. Moreover, an EST-STS marker Xmp510 was developed. The genetic distance between Xmp510 and the PmTa gene was 1.3 cM. Because of the locus of PmTa was very close to Pm2, pathogenicity tests were conducted with 15 Bgt isolates. The result presented that Tabasco high resistant to all of 15 tested Bgt isolates. While Ulka/8*Cc (contain Pm2) was susceptible to 4 isolates. This shows that PmTa gene in Tabasco is different from Pm2. In addition, we developed F2 population with Tabasco and Ulka/8*Cc to practice allelism test. The isolate of Bgtl was employed to identify F2 population during seeding stage. The result displayed that there was no susceptible plant could be discovered. This demonstrated that two genes located on same locus of homologous chromosomes or they were tightly linked. |
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