| Stripe rust or yellow rust (YR), caused by Puccinia striiformis f. sp. tritici (Pst), is a devastating fungal disease of common wheat (Triticum aestivum L.) worldwide. Although stripe rust can be controlled through the application of fungicides, resistance breeding is a more economic, effective and environmentally friendly approach to control the disease. Due to the wide cultivation of cultivars with a simplicity of stripe rust resistance source, new pathogen races quickly came up and became prevalent, resulting in a short duration of effectiveness of resistant cultivars in history. Identification of new resistance genes and their tightly linked molecular markers should enable diversification of the genetic basis of resistance, and marker-assisted selection and gene pyramiding are important methods to develop new cultivars with durable resistance. Therefore, the aims of this study were to map QTL of adult-plant resistance (APR) to stripe rust in common wheat cultivars Naxos, SHA3/CBRD, Bainong64and Lumai21, and to map stripe rust resistance genes in Chinese elite parent Zhou8425B and wheat variety Shaannong69using molecular markers. The main results are summarized as follows:1. In the population of166recombinant inbred lines (RILs) developed from a cross between Naxos and SHA3/CBRD, four QTL conferring stable resistance to stripe rust across all environments were detected by composite interval mapping (CIM), designated QYr.caas-1BL.IRS, QYr.caas-1DS, QYr.caas-5BL.3and QYr.caas-7BL.1, explaining1.9-27.6,2.1-5.8,2.5-7.8and3.7-9.1%of the phenotypic variance, respectively. QYr.caas-1DS flanked by molecular markers XUgwm353-Xgdm33b was likely a new QTL for APR to stripe rust. QYr. caas-1BL. IRS contributed by SHA3/CBRD was mapped to the same region as a powdery mildew (PM) resistance QTL from the same parent, and QYr.caas-1DS corresponded well with a Fusarium head blight (FHB) resistance QTL from Naxos, indicating pleiotropic effects of these resistance loci. Because the intervals between flanking markers for each QTL were less than6.5cM, these QTL and their closely linked molecular markers are potentially useful for improving resistance to stripe rust in wheat breeding.2. In the population of179doubled haploid (DH) lines derived from the Bainong64/Jingshuang16cross, correlations for maximum disease severities (MDS) ranged from0.50to0.56(P<0.00001) across three environments, and the broad sense heritability of MDS was0.76. Using bulked segregant analysis (BSA) with simple sequence repeat (SSR) markers, three independent loci for APR to stripe rust were detected, designated QYr.caas-4DL, QYr.caas-6BS.3and QYr.caas-7AS, respectively. The most consistent locus found in all environments was QYr.caas-6BS.3, and it explained3.8-6.2%of the phenotypic variance. This QTL corresponded well with a leaf rust (LR) resistance QTL from Bainong64. Because no designated pleiotropic genes have been reported on chromosome6BS, QYr.caas-6BS.3appears to be a new resistance locus conferring APR to both YR and LR. These three QTL and their corresponding closely linked molecular markers, Xbarc127, Xwmc331and Xwmc487, will be useful for marker-assisted selection in breeding for resistance to stripe rust. 3. In the F3population with199lines derived from the cross of Lumai21/Jingshuang16, the MDS scores showed significant correlation among three environments, with correlation coefficients ranging from0.65to0.71(P<0.00001). The broad sense heritability of MDS was0.86. Inclusive composite interval mapping (ICIM) identified five QTL for APR to stripe rust on chromosomes2B (2QTL),2DS,4DL and5DS based on the mean MDS in each environment and the averaged values from all three environments, and these were designated QYr.caas-2BS.2, QYr.caas-2BL.2, QYr.caas-2DS.2, QYr.caas-4DL.2and QYr.caas-5DS, respectively. Except for QYr.caas-5DS, other QTL were from Lumai21. QYr.caas-2DS.2and QYr.caas-5DS were detected in three environments and in the averaged MDS, and they explained2.3-18.2%and5.1-18.0%of the phenotypic variance, respectively. QYr.caas-2BS.2, QYr.caas-2BL.2and QYr.caas-2DS are co-located or closely linked with PM resistance QTL with the resistance alleles contributed by Lumai21, indicating an important role for resistance breeding to both YR and PM.4. A total of40F1and6140F2plants derived from the cross of Zhou8425B/Avocet S and their parents were inoculated with Chinese Pst race CYR32in the greenhouse for identification of resistance gene in Zhou8425B. Genetic analysis indicated that Zhou8425B contains a single dominant resistance gene, temporarily designated as YrZH84,2. Using molecular marker analysis, this gene was located on chromosome1BL, linked to AF1/AF4, H20, Xbarc8, Xgwm131, Xgwm582, Xwmc216, BE497107and CD373538on chromosome1BL, and the closest flanking EST markers were BE497107and CD373538with genetic distances of0.9cM and1.3cM from YrZH84.2, respectively. Genetic analysis of stripe rust resistance on seedlings of six F2populations (Predgornia2/Zhou8425B, Lovin10/Zhou8425B, Lovin13/Zhou8425B, Xiaoyan22/Zhou8425B, Jingdong8/Zhou8425B and Lumai8/Zhou8425B) was used to determine the allelism of YrZH84.2with Yr9. Except for the Predgornia2/Zhou8425B cross, susceptible plants were found in the other five F2populations. Therefore, YrZH84.2is different from Yr9. Since Zhou8425B was derived from Predgornia2, the resistance gene YrZH84.2should come from Predgornia2.5. The resistant line Shaannong69, susceptible parent Mingxian169, and their F1, F2and F3plants were inoculated with CYR32. The results indicated that a single recessive gene, tentatively designated yrSN69, conferred resistance to CYR32in Shaannong69. Of the1480SSR markers tested, six (Xbarc134, Xbarc146, Xbarc178, Xbarc198, Xbarc312and Xwmc397) on chromosome6BL showed polymorphisms between the two parents and contrasting bulks, and yrSN69was therefore located on chromosome6BL. The chromosome6B carries several stripe rust resistance genes, viz., Yr4, Yr35and Yr36. Because Yr35and Yr36were located on the short arm of chromosome6B and derived from wild emmer (Triticum turgidum var. dicoccoides), these two genes are different from yrSN69. Yr4was succumbed to the Pstrace CYR32used in the present study, it is also different from yrSN69. Therefore, yrSN69is probably a new stripe rust resistance gene.
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