Molecular Tagging Of Resistance Genes To Powdery Mildew And Stripe Rust In Wheat (triticum Aesitvum L.)

Powdery mildew and stripe rust are two important diseases of wheat in China. Durable resistanceto powdery mildew and stripe rust can be sped up with the availability of new resistance genes and theirclosely linked molecular markers. So far, quantitative trait loci (QTL) for powdery mildew resistancehave been identified and mapped on almost all wheat chromosomes in different genetic backgrounds.Unlikely, only few genotypes have good adaptability and associated agronomic traits in Chineseenvironment, and very few stripe rust resistance genes are presently effective in China. It washypothesized that cultivars Strampelli, Libellula and Pingyuan50have potential adult plant resistance topowdery mildew, and may have some relationship with quantitative trait loci previously mapped forstripe rust resistance in the same population; and genotypes (Shaannong104and Shaannong78)resistance to stripe rust may possess new major resistance genes. The objectives of this study were1) todissect genetic basis of adult plant powdery mildew resistance and determine the number and genomiclocations in cultivars Strampelli, Libellula and Pingyuan50, and also to probe the relationship withQTLs mapped previously for stripe rust resistance in the same population, and2) to map potential striperust resistance genes in Shaannong104and Shaannong78, and to identify tightly linked SSR markersthat can be used for marker assisted selection in breeding programs. The main results are summarized asfollows1. In249F2:3lines developed from Strampelli/Huixianhong population, five QTLs for adult-plantresistance (APR) to powdery mildew were identified, designated QPm.caas-2BS, QPm.caas-3BS,QPm.caas-4BL, QPm.caas-5BL.1and QPm.caas-7DS across environments, explaining1.0-3.5,0.4-1.6,1.9-3.5,5.5-6.9and27.1-34.5%of the phenotypic variation, respectively. QPm.caas-7DS correspondedto the genomic location of Lr34/Yr18/Pm38. QPm.caas-2BS and QPm.caas-5BL.1contributed byStrampelli, and Qpm.caas-3BS by Huixianhong, seem to be new QTL for powdery mildew resistance.QPm.caas-4BL, QPm.caas-5BL.2and QPm.caas-7DS contributed by Strampelli appear to be in thesame genomic regions as those mapped previously for stripe rust resistance in the same population,indicating that these loci conferred resistance to both stripe rust and powdery mildew. Strampelli couldbe a valuable genetic resource for improving durable resistance to both powdery mildew and stripe rustin wheat.2. In mapping population of244F2:3lines, derived from cross Libellula/Huixianhong, four QTLswere identified by inclusive composite interval mapping, designated as QPm.caas-2DS, QPm.caas-4BL,QPm.caas-6BL, and QPm.caas-7DS, respectively, accounting for2.3,14.7,4.7and10.3%of thephenotypic variance for powdery mildew response based on the averaged data across the threeenvironments. Two QTLs QPm.caas-2DS and QPm.caas-6BL identified on chromosomes2DS and6BLcontributed from Libellula and Huixianhong, respectively, might be new resistance loci for powderymildew. QTLs QPm.caas-2DS and QPm.caas-4BL were identified in the same genomic region aspreviously mapped QTLs for stripe rust resistance in Libellula. QPm.caas-7DS, derived from Libellula,coincided with the slow rusting and slow mildewing locus Lr34/Yr18/Pm38. These results and the identified markers could be useful for wheat breeders targeting durable resistance to both stripe rust andpowdery mildew.3. In double haploid (DH) population of137lines developed from Pingyuan50/Mingxian169,QTLs QPm.caas-2BS.2, QPm.caas-3BS and QPm.caas-5AL were identified in Pingyuan50, and theyexplained5.3,10.2and9.1%of the phenotypic variance, respectively, and QPm.caas-3BL inMingxian169explained by18.1%of the phenotypic variance. QPm.caas-3BS, QPm.caas-3BL andQPm.caas-5AL appear to be new loci for adult plant resistance to powdery mildew. QPm.caas-2BS.2and QPm.caas-5AL appear to be in the similar position of QTLs identified previously for stripe rustresistance in the same population, suggesting that these QTLs offered resistance to both powderymildew and stripe rust. Chinese landrace Pingyuan50could be a potential genetic resource to facilitatewheat breeders for improving adult plant resistance for both powdery mildew and stripe rust in wheat.4. Mapping a stripe rust resistance gene in wheat line Shaannong104using SSR markers,15F1,613F2and55F3families from Shaannong104/Mingxian169were inoculated with Chinese Pst raceCYR32in the greenhouse. Shaannong104carried a single dominant gene, YrSN104, and it was closelylinked with six SSR markers on chromosome1BS with genetic distances of2.0cM (Xgwm18,Xgwm273),2.6cM (Xbarc187, Xgwm11, Xbarc137) and5.9cM (Xbarc240). Pedigree analysis,pathogenicity tests using26Pst races, DNA band comparison produced by associated markers onisogenic lines carrying known stripe rust resistance genes, and associations with markers suggested thatYrSN104was likely a new resistance allele at Yr24/Yr26locus or tightly linked with them onchromosome1BS. Deployment of YrSN104singly or in combination to elite genotypes could play aneffective role to lessen yield losses caused by stripe rust.5. To identify the genetic basis of resistance, Shaannong78was crossed with Mingxian169, asusceptible cultivar.15F1,690F2, and82F3families along with parents were inoculated with highlyvirulent Pst race CYR32under controlled conditions. In bulked segregant analysis, three molecularmarkers XAF4, XH20, and Xbarc8were closely linked to the resistance gene, designated YrSN78tentatively, and mapped on chromosome1BL.1RS with genetic distances1.7and2.8cM. Phenotypingof segregating population (F2and F3), bulked segregant analysis (BSA), and association of closelylinked markers indicated the presence of single dominant gene YrSN78in Shaannong78conferringresistance to highly virulent Pst race CYR32. Pedigree analysis and linked molecular markers suggestedthat YrSN78is different from previously identified genes YrCn17and YrR212, and it was look like Yr9gene or allele at Yr9locus on chromosome translocation1BL.1RS. The closely linked molecularmarkers with YrSN78could be useful in marker assisted breeding programs for stripe rust resistance inwheat.