Genetic and Physical Mapping of a Putative Leymus mollis-Derived Stripe Rust Resistance Gene on Wheat Chromosome 4A.

Wheat stripe rust is one of the most damaging diseases of wheat worldwide. The wheat-Leymus mollis introgression line M8664-3 exhibits all-stage resistance to Chinese stripe rust races. Genetic analysis of stripe rust resistance was performed by crossing M8664-3 with the susceptible line Mingxian169. Analysis of the disease resistance of F2 and F2:3 populations revealed that its resistance to Chinese stripe rust race 33 (CYR33) is controlled by a single dominant gene, temporarily designated as YrM8664-3. Genetic and physical mapping showed that YrM8664-3 is located in bin 4AL13-0.59-0.66 close to 4AL12-0.43-0.59 on chromosome 4AL and is flanked by single-nucleotide polymorphism markers AX111655681 and AX109496237 with genetic distances of 5.3 and 2.3 centimorgans, respectively. Resistance spectrum and position analyses indicated that YrM8664-3 may be a novel gene. Molecular detection using the markers linked to YrM8664-3 with wheat varieties commonly cultivated and wheat-L. mollis-derived lines showed that YrM8664-3 is also present in other wheat-L. mollis introgression lines but absent in commercial common wheat cultivars. Thus, YrM8664-3 is a potentially valuable source of stripe rust resistance for breeding.

Mapping a Large Number of QTL for Durable Resistance to Stripe Rust in Winter Wheat Druchamp Using SSR and SNP Markers.

Winter wheat Druchamp has both high-temperature adult-plant (HTAP) resistance and all-stage resistance to stripe rust caused by Puccinia striiformis f. sp. tritici (Pst). The HTAP resistance in Druchamp is durable as the variety has been resistant in adult-plant stage since it was introduced from France to the United States in late 1940s. To map the quantitative trait loci (QTL) for stripe rust resistance, an F8 recombinant inbred line (RIL) population from cross Druchamp × Michigan Amber was phenotyped for stripe rust response in multiple years in fields under natural infection and with selected Pst races under controlled greenhouse conditions, and genotyped with simple sequence repeat (SSR) and single nucleotide polymorphism (SNP) markers. Composite interval mapping (CIM) identified eight HTAP resistance QTL and three all-stage resistance QTL. Among the eight HTAP resistance QTL, QYrdr.wgp-1BL.2 (explaining 2.36-31.04% variation), QYrdr.wgp-2BL (2.81-15.65%), QYrdr.wgp-5AL (2.27-17.22%) and QYrdr.wgp-5BL.2 (2.42-15.13%) were significant in all tests; and QYrdr.wgp-1BL.1 (1.94-10.19%), QYrdr.wgp-1DS (2.04-27.24%), QYrdr.wgp-3AL (1.78-13.85%) and QYrdr.wgp-6BL.2 (1.69-33.71%) were significant in some of the tests. The three all-stage resistance QTL, QYrdr.wgp-5BL.1 (5.47-36.04%), QYrdr.wgp-5DL (9.27-11.94%) and QYrdr.wgp-6BL.1 (13.07-20.36%), were detected based on reactions in the seedlings tested with certain Pst races. Among the eleven QTL detected in Druchamp, at least three (QYrdr.wgp-5DL for race-specific all-stage resistance and QYrdr.wgp-3AL and QYrdr.wgp-6BL.2 for race non-specific HTAP resistance) are new. All these QTL, especially those for durable HTAP resistance, and their closely linked molecular markers could be useful for developing wheat cultivars with durable resistance to stripe rust.

Mapping of Yr62 and a small-effect QTL for high-temperature adult-plant resistance to stripe rust in spring wheat PI 192252.

KEY MESSAGE: This manuscript reports a new gene (Yr62) and a small-effect QTL for potentially durable resistance to stripe rust and usefulness of Yr62 markers for marker-assisted selection. Stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), is a devastating disease of wheat worldwide. Spring wheat germplasm PI 192252 showed a high level of high-temperature adult-plant (HTAP) resistance to stripe rust in germplasm evaluation over 8 years in the State of Washington. To elucidate the genetic basis of resistance, PI 192252 was crossed with 'Avocet susceptible'. A mapping population of 150 F5 recombinant inbred lines was developed using single-seed descent. Stripe rust tests were conducted with selected Pst races in a greenhouse and in field conditions under natural infections. The relative area under the disease progress curve (rAUDPC) data showed continuous distributions, indicating that HTAP resistance of PI 192252 was controlled by quantitative trait loci (QTL). Two QTL were identified in PI 192252, explaining 74.2 % of the total phenotypic variation for rAUDPC. These two QTL were mapped to chromosomes 4BL (QYrPI192252.wgp-4BL) and 5BS (QYrPI192252.wgp-5BS) with SSR and SNP markers and explained 40-60 and 22-27 %, respectively, of the phenotypic variation across the four environments. Because the major-effect QTL on 4BL is different from previously named Yr genes and inherited as a single gene, it is named Yr62. The SSR marker alleles Xgwm192 222 and Xgwm251 133 flanking Yr62 were different from the alleles in various wheat varieties, suggesting that these markers could be useful in marker-assisted selection for incorporating Yr62 into commercial cultivars.

Genetic and Molecular Mapping of Stripe Rust Resistance Gene in Wheat-Psathyrostachys huashanica Translocation Line H9020-1-6-8-3.

Stripe rust, caused by Puccinia striiformis f. sp. tritici, is one of the most important diseases of wheat worldwide. The best strategy to control stripe rust is to grow resistant cultivars, but only a few effective genes are available. The wheat accession H9020-1-6-8-3 is a translocation line previously developed from interspecific hybridization between wheat genotype 7182 and Psathyrostachys huashanica, and is resistant to most Chinese Puccinia striiformis f. sp. tritici races. To identify the resistance genes in the translocation line, H9020-1-6-8-3 was crossed with susceptible genotype Mingxian 169, and seedlings of parents and F1, F2, and F3 progenies were tested with prevalent Chinese P. striiformis f. sp. tritici races CYR32 and CYR33 under controlled greenhouse conditions. The genetic results indicated that two single dominant genes in H9020-1-6-8-3 confer resistance to CYR32 and CYR33, respectively. The gene for resistance to CYR33 was temporarily designated as YrH9020. Six simple-sequence repeat markers were used to map the resistance gene to the short arm of wheat chromosome 2D, using 329 F2 plants tested with CYR33 in the greenhouse. The genetic distances of the two closest flanking markers, Xgwm261 and Xgwm455, were 4.4 and 5.8 centimorgans, respectively. Disease assessments and polymorphic tests of the flanking markers among the Psathyrostachys huashanica line and wheat lines 7182, H9020-1-6-8-3, and Mingxian169 suggested that the resistance gene YrH9020 in H9020-1-6-8-3 was originally from P. huashanica. The exotic stripe rust resistance gene and linked molecular markers should be useful for pyramiding with other genes to develop wheat cultivars with high-level and durable resistance to stripe rust.

QTL mapping for adult-plant resistance to stripe rust in Italian common wheat cultivars Libellula and Strampelli.

Italian common wheat cultivars Libellula and Strampelli, grown for over three decades in Gansu province of China, have shown effective resistance to stripe rust. To elucidate the genetic basis of the resistance, F(3) populations were developed from crosses between the two cultivars and susceptible Chinese wheat cultivar Huixianhong. The F(3) lines were evaluated for disease severity in Beijing, Gansu and Sichuan from 2005 to 2008. Joint- and single-environment analyses by composite interval mapping identified five quantitative trait loci (QTLs) in Libellula for reduced stripe rust severity, designated QYr.caas-2DS, QYr.caas-4BL, QYr.caas-5BL.1, QYr.caas-5BL.2 and QYr.caas-7DS, and explained 8.1-12.4, 3.6-5.1, 3.4-8.6, 2.6 and 14.6-35.0%, respectively, of the phenotypic variance across four environments. Six interactions between different pairs of QTLs explained 3.2-7.1% of the phenotypic variance. The QTLs QYr.caas-4BL, QYr.caas-5BL.1 and QYr.caas-7DS were also detected in Strampelli, explaining 4.5, 2.9-5.5 and 17.1-39.1% of phenotypic variance, respectively, across five environments. Three interactions between different pairs of QTLs accounted for 6.1-35.0% of the phenotypic variance. The QTL QYr.caas-7DS flanked by markers csLV34 and Xgwm295 showed the largest effect for resistance to stripe rust. Sequence analyses confirmed that the lines with the QYr.caas-7DS allele for resistance carried the resistance allele of the Yr18/Lr34 gene. Our results indicated that the adult-plant resistance gene Yr18 and several minor genes confer effective durable resistance to stripe rust in Libellula and Strampelli.

[Genetic analysis and molecular markers of a novel stripe rust resistance gene YrHua in wheat originated from Psathyrostachys huashanica Keng].

The H9020-17-5,a common wheat-Psathyrostachys huashanica Keng translocation line, possesses excellent resistance to wheat stripe rust. Genetic analysis of F2 and BC1 populations derived from H9020-17-5 x Mingxian169 indicated that resistance to stripe rust in H9020-17-5 was a dominant character controlling by single gene originated from Ps. huashanica. This resistance gene originated from Ps. huashanica was first reported in the present study and named as YrHua. In order to map the resistance gene YrHua, AFLP approach was employed to analyze the 119 individuals of H9020-17-5 x Mingxian169 F2 population which were inoculated by stripe rust isolate CY30. As a result,two markers, PM14(301) and PM42(249) were found to be linked to the resistance gene YrHua,and the genetic distances between the markers and target gene were 5.4 cM and 2.7 cM, respectively. For the convenience of marker-assisted selection in wheat breeding, one of the two AFLP markers was converted to PCR marker using a pair of special primers based on the DNA sequence of PM14 (301) and the polymorphism of restriction site. Our research results provided a useful tool for marker-assisted selection and laid a foundation of fine mapping and map based cloning of YrHua gene.