Mapping And Application Of Stripe Rust Resistance Genes In Cultivated And Wild Wheat

Wheat stripe rust, caused by Puccinia striiformis f.sp. tritici, is one major fungal disease damaging wheat production and grain quality worldwide. Mining and utilization of stripe rust resistance genes is the most effective and environmentally friendly approach for controlling the rust disease. Landraces and the wild relatives of wheat contain largely untapped gene pools for disease resistance breeding. The discovery, mapping and marker assisted selection of novel resistance traits are playing important roles in wheat resistance breeding. This study was performed on the mining and utilization of stripe rust resistant genes in wheat, including four sections.1. The development and screening of the Yr10 CG, Yr18(Yr18RH) and Yr36(WKS1) markers. Among 659 Chinese cultivars/lines investigated, 13% and 11% of them were positive for Yr10 CG and Yr18 RH, respectively. However, none of them was positive for the Yr36 gene. ‘Huixianhong’(HXH) and ‘Mingxian 169’(MX169) are two common wheat cultivars used as susceptible controls for stripe rust research. Surprisingly, Yr10 CG and Yr18 RH markers worked on HXH and MX169, respectively. But the corresponding genes in HXH and MX169 were polymorphic to the genes from the resistant donor cultivars. Specific markers, Yr10CG-HXH and Yr18 RH-MX169, were developed to diagnose their distribution in Chinese wheat.2. Association analysis and transgenic studies proved that the Yr10 CG sequence did not represent the actual Yr10 gene. The Yr10 CG marker was found positive in sixty cultivars, which were also shown for the transcription of the Yr10 CG gene. However, most of those cultivars carring the Yr10 CG gene were not resistant to wheat stripe rust. We then prepared two plasmid constructs, WKS1::Yr10CG and Ubi::Yr10CG, and generated transgenic ‘Bobwhite’ positive for each of those two constructs. The expression of the Yr10 CG gene in the transgenic Bobwhite did not confer improved resistance to wheat stripe rust. Most likely, the Yr10 CG gene does not represent the Yr10 gene from the resistant donor ‘Moro’.3. The Yr10 gene was precisely mapped in populations derived from Moro and HXH. In the F2 generation, stripe rust test revealed two dorminant resistance genes in Moro. We then selected two F2:3 populations(Pop8 and Pop10) that fitted the single gene segregation on stripe rust resistance. Both F2:3 populations segregated on the Xpsp3000, a SSR marker closely linked to the Yr10 locus, suggesting that both Pop8 and Pop10 were segregated on the Yr10 locus. We then performed the chip and BSA analyses on susceptible F3 individuals from Pop8 and Pop10, and mapped three SNP markers linked to the Yr10 locus. Those SNPs were converted to regular PCR markers including Xsdau77, Xsdau75 and Xsdau78. According to the collinearity between rice chromosome 5 and wheat chromosome 1, we also developed the PCR marker Xsdau79. Both Xsdau79 and Xsdau78 were mapped 0.76 cM and 0.97 cM, respectively, proximal to the Yr10 gene. Using a large mapping population(1900 F3:4 plants), we found that the Yr10 CG gene is ca. 0.71 cM distant from the actual Yr10 gene, confirming the unknown status of the Yr10 gene.4. A novel stripe rust resistance gene YrD479 was discovered in the wild emmer wheat ‘DIC479’. The F2 mapping population was developed from DIC479 and the durum wheat ‘Langdon’. Stripe rust tests under different conditions(location and time) proposed that DIC479 carried a high-temperature adult-plant resistance gene for wheat stripe rust. Of the 235 F2 individuals, 179 were resistant and 56 were susceptible, fitting to the single gene segregation model. We then tested 2005 PCR markers and found 394 polymorphic markers between the two parents. In BSA analysis, the 2BS chromosome marker CFE212 was associated with the susceptible bulks. Other polymorphic markers near the CFE212 region, including Xbarc55, Xgwm374, Xbarc18, Xcfa2278, Xmag4094 and Xwmc592, were tested on the F2 mapping population. The Xgwm374 marker co-segregated with the YrD479 gene. Xbarc55 was 4.8 cM distal to the YrD479 gene, and CFE212 was 2.1 cM proximal to the gene. We then developed seven PCR markers, Xsdau009, Xsdau010, Xsdau011, Xsdau013, Xsdau014, Xsdau015 and Xsdau018, based on the colinearity between rice chromosomes 4 and 7 and wheat chromosome 2. The Xsdau014 was the nearest marker ca. 1.6 cM from the YrD479 gene.