Stripe rust resistance genes in the UK winter wheat cultivar Claire

Stripe rust resistance in the winter wheat cultivar Claire had remained effective in the UK and Europe since its release in 1999 and consequently has been used extensively in wheat breeding programs. However, in 2012, reports indicated that this valuable resistance may now have been compromised. To characterise stripe rust resistance in Claire and determine which genes may still confer effective resistance a cross was made between Claire and the stripe rust susceptible cultivar Lemhi. A genetic linkage map, constructed using SSR, AFLP, DArT and NBS-AFLP markers had a total map length of 1,730 cM. To improve the definition of two quantitative trait loci (QTL) identified on the long arm of chromosome 2D further markers were developed from wheat EST. Stripe rust resistance was evaluated on adult plants under field and glasshouse conditions by measuring the extent of fungal growth and sporulation, percentage infection (Pi) and the necrotic/chlorotic responses of the plant to infection, infection type (IT). Four QTL contributing to stripe rust adult plant resistance (APR) were identified in Claire, QYr.niab-2D.1, QYr.niab-2D.2, QYr.niab-2B and QYr.niab-7B. For Pi QYr.niab-2D.1 explained up to 25.4 % of the phenotypic variation, QYr.niab-2D.2 up to 28.7 %, QYr.niab-2B up to 21.7 % and QYr.niab-7B up to 13.0 %. For IT the percentages of phenotypic variation explained were 23.4, 31.8, 17.2 and 12.6 %, respectively. In addition to the four QTL conferring APR in Claire, a race-specific, seedling expressed resistance gene was identified on chromosome 3B.     

Durable resistance to stripe rust is due to three specific resistance genes in French bread wheat cultivar Apache

Quantitative resistance is postulated to be more durable than qualitative (R-gene mediated) resistance, which is usually quickly overcome by the pathogen population. Despite its wide use for nearly 10?years in France, the French bread wheat cultivar Apache remains resistant to stripe rust. Here, we investigated the genetic architecture of cv. Apache resistance to examine whether its durability could be explained by quantitative characteristics. We identified quantitative trait loci (QTL) by composite interval mapping of disease progress data recorded throughout 4?years of field assays. These assays included inoculation with three different pathotypes on a segregating population originating from a cross between cv. Apache and cv. Taldor, a French cultivar susceptible to stripe rust. Three QTLs derived from Apache, QYr.inra-2AS, QYr.inra-2BL and QYr.inra-4B, were detected. Each of these QTLs contributed between approximately 15 and 69?% of the phenotypic variance and corresponds to a race-specific resistance gene. We showed that QYr.inra-2AS and QYr.inra-2BS map to the positions of Yr17 and Yr7, respectively, whereas QYr.inra-4B corresponds to an adult plant resistance gene. Our results demonstrate that a combination of two or more race-specific resistance genes can confer durable resistance provided that it is properly managed at a continental level. Race-specific resistance genes should not be removed from breeding programs provided that they are properly managed.     

Analysis of leaf and stripe rust severities reveals pathotype changes and multiple minor QTLs associated with resistance in an Avocet?×?Pastor wheat population

Leaf rust and stripe rust are important diseases of wheat world-wide and deployment of cultivars with genetic resistance is an effective and environmentally sound control method. The use of minor, additive genes conferring adult plant resistance (APR) has been shown to provide resistance that is durable. The wheat cultivar ‘Pastor’ originated from the CIMMYT breeding program that focuses on minor gene-based APR to both diseases by selecting and advancing generations alternately under leaf rust and stripe rust pressures. As a consequence, Pastor has good resistance to both rusts and was used as the resistant parent to develop a mapping population by crossing with the susceptible ‘Avocet’. All 148 F₅ recombinant inbred lines were evaluated under artificially inoculated epidemic environments for leaf rust (3 environments) and stripe rust (4 environments, 2 of which represent two evaluation dates in final year due to the late build-up of a new race virulent to Yr31) in Mexico. Map construction and QTL analysis were completed with 223 polymorphic markers on 84 randomly selected lines in the population. Pastor contributed Yr31, a moderately effective race-specific gene for stripe rust resistance, which was overcome during this study, and this was clearly shown in the statistical analysis. Linked or pleiotropic chromosomal regions contributing to resistance against both pathogens included Lr46/Yr29 on 1BL, the Yr31 region on 2BS, and additional minor genes on 5A, 6B and 7BL. Other minor genes for leaf rust resistance were located on 1B, 2A and 2D and for stripe rust on 1AL, 1B, 3A, 3B, 4D, 6A, 7AS and 7AL. The 1AL, 1BS and 7AL QTLs are in regions that were not identified previously as having QTLs for stripe rust resistance. The development of uniform and severe epidemics facilitated excellent phenotyping, and when combined with multi-environment analysis, resulted in the relatively large number of QTLs identified in this study.     

QTL mapping of adult-plant resistance to stripe rust in a population derived from common wheat cultivars Naxos and Shanghai 3/Catbird

Stripe rust, caused by Puccinia striiformis Westend. f. sp. tritici Erikss., is a severe foliar disease of common wheat (Triticum aestivum L.) worldwide. Use of adult-plant resistance (APR) is an efficient approach to provide long-term protection of crops from the disease. The German spring wheat cultivar Naxos showed a high level of APR to stripe rust in the field. To identify the APR genes in this cultivar, a mapping population of 166 recombinant inbred lines (RILs) was developed from a cross between Naxos and Shanghai 3/Catbird (SHA3/CBRD), a moderately susceptible line developed by CIMMYT. The RILs were evaluated for maximum disease severity (MDS) in Sichuan and Gansu in the 2009-2010 and 2010-2011 cropping seasons. Composite interval mapping (CIM) identified four QTL, QYr.caas-1BL.1RS, QYr.caas-1DS, QYr.caas-5BL.3 and QYr.caas-7BL.1, conferring stable resistance to stripe rust across all environments, each explaining 1.9-27.6, 2.1-5.8, 2.5-7.8 and 3.7-9.1?% of the phenotypic variance, respectively. QYr.caas-1DS flanked by molecular markers XUgwm353-Xgdm33b was likely a new QTL for APR to stripe rust. Because the interval between flanking markers for each QTL was less than 6.5?cM, these QTL and their closely linked markers are potentially useful for improving resistance to stripe rust in wheat breeding.     

Histopathology and PR-protein markers provide insight into adult plant resistance to stripe rust of wheat

Stripe rust, caused by Puccinia striiformis f. sp. tritici , is a serious disease of wheat. The spring wheat cultivar Kariega expresses complete adult plant resistance to stripe rust, whereas Avocet S is susceptible. In former studies, quantitative trait loci (QTL) analysis of doubled haploid lines derived from a Kariega × Avocet S cross revealed two major QTL ( QYr.sgi-7D and QYr.sgi-2B.1 ) and two minor QTL ( QYr.sgi-1A and QYr.sgi-4A.1 ) responsible for the adult resistance of Kariega in the field. Avocet S contains none of these QTL. In the present study, stripe rust development was compared, by means of fluorescence and confocal laser scanning microscopy, in flag leaves of Kariega, Avocet S and six doubled haploid (DH) lines, containing all four, none or one QTL. Depending on the QTL present, the infection types of the DH lines ranged from resistant to fully susceptible. No differences in fungal growth were observed during the first 5 days post inoculation (dpi), whereas the mean length of the fungal colonies started to differ at 6 dpi. Interestingly, MP 51 carrying QYr.sgi-7D responded with lignification to the fungal growth without restricting it, whereas MP 35 containing QYr.sgi-2B.1 did not show lignified host tissue, but fungal growth was restricted. RT PCR experiments with sequences of pathogenesis-related (PR) proteins resulted in a slightly stronger induction of PR 1, 2 and 5, known markers for the hypersensitive reaction, and peroxidases in MP 51, whereas a second band for chitinases was detected in MP 35 only.     

Mapping of durable stripe rust resistance in a durum wheat cultivar Wollaroi

Wollaroi, an Australian durum wheat cultivar, produced a low stripe rust response and the alternative parent Bansi was highly susceptible. The Wollaroi/Bansi recombinant inbred line (RIL) population was phenotyped across three consecutive crop seasons. A genetic map of the Wollaroi/Bansi RIL population comprising 799 markers (diversity arrays technology and simple sequence repeat markers) was used to determine the genomic location of stripe rust resistance genes carried by the cultivar Wollaroi. Composite interval mapping detected three consistent quantitative trait loci (QTL) in chromosomes 2A, 3B and 5B. These QTL were named QYr.sun-2A, QYr.sun-3B and QYr.sun-5B. Another QTL, QYr.sun-1B, was detected only in the 2009 crop season. QTL in chromosomes 1B, 2A, 3B and 5B explained on average 6, 9.3, 26.7 and 8.7 %, respectively, of the variation in stripe rust response. All QTL were contributed by Wollaroi. RILs carrying these QTL singly produced intermediate stripe rust severities ranging from 46.2 to 55.7 %, whereas RILs with all four QTL produced the lowest disease severity (34.3 %). The consistently low stripe rust response of Wollaroi for 20 years demonstrated the durability of the resistance loci involved. The QTL combination detected in this study is being transferred to common wheat.     

Comparative genome-wide mapping versus extreme pool-genotyping and development of diagnostic SNP markers linked to QTL for adult plant resistance to stripe rust in common wheat

Key message

A major stripe rust resistance QTL on chromosome 4BL was localized to a 4.5-Mb interval using comparative QTL mapping methods and validated in 276 wheat genotypes by haplotype analysis.

Abstract

CYMMIT-derived wheat line P10103 was previously identified to have adult plant resistance (APR) to stripe rust in the greenhouse and field. The conventional approach for QTL mapping in common wheat is laborious. Here, we performed QTL detection of APR using a combination of genome-wide scanning and extreme pool-genotyping. SNP-based genetic maps were constructed using the Wheat55 K SNP array to genotype a recombinant inbred line (RIL) population derived from the cross Mingxian 169?×?P10103. Five stable QTL were detected across multiple environments. After comparing SNP profiles from contrasting, extreme DNA pools of RILs six putative QTL were located to approximate chromosome positions. A major QTL on chromosome 4B was identified in F_2:4 contrasting pools from cross Zhengmai 9023?×?P10103. A consensus QTL (LOD?=?26–40, PVE?=?42–55%), named QYr.nwafu-4BL, was defined and localized to a 4.5-Mb interval flanked by SNP markers AX-110963704 and AX-110519862 in chromosome arm 4BL. Based on stripe rust response, marker genotypes, pedigree analysis and mapping data, QYr.nwafu-4BL is likely to be a new APR QTL. The applicability of the SNP-based markers flanking QYr.nwafu-4BL was validated on a diversity panel of 276 wheat lines. The additional minor QTL on chromosomes 4A, 5A, 5B and 6A enhanced the level of resistance conferred by QYr.nwafu-4BL. Marker-assisted pyramiding of QYr.nwafu-4BL and other favorable minor QTL in new wheat cultivars should improve the level of APR 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, F₃ populations were developed from crosses between the two cultivars and susceptible Chinese wheat cultivar Huixianhong. The F₃ 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.     

QTL mapping of adult-plant resistances to stripe rust and leaf rust in Chinese wheat cultivar Bainong 64

Stripe rust and leaf rust, caused by Puccinia striiformis Westend. f. sp. tritici Erikss. and P. triticina, respectively, are devastating fungal diseases of common wheat (Triticum aestivum L.). Chinese wheat cultivar Bainong 64 has maintained acceptable adult-plant resistance (APR) to stripe rust, leaf rust and powdery mildew for more than 10?years. The aim of this study was to identify quantitative trait loci/locus (QTL) for resistance to the two rusts in a population of 179 doubled haploid (DH) lines derived from Bainong 64?×?Jingshuang 16. The DH lines were planted in randomized complete blocks with three replicates at four locations. Stripe rust tests were conducted using a mixture of currently prevalent P. striiformis races, and leaf rust tests were performed with P. triticina race THTT. Leaf rust severities were scored two or three times, whereas maximum disease severities (MDS) were recorded for stripe rust. Using bulked segregant analysis (BSA) and simple sequence repeat (SSR) markers, five independent loci for APR to two rusts were detected. The QTL on chromosomes 1BL and 6BS contributed by Bainong 64 conferred resistance to both diseases. The loci identified on chromosomes 7AS and 4DL had minor effects on stripe rust response, whereas another locus, close to the centromere on chromosome 6BS, had a significant effect only on leaf rust response. The loci located on chromosomes 1BL and 4DL also had significant effects on powdery mildew response. These were located at the same positions as the Yr29/Lr46 and Yr46/Lr67 genes, respectively. The multiple disease resistance locus for APR on chromosome 6BS appears to be new. All three genes and their closely linked molecular markers could be used in breeding wheat cultivars with durable resistance to multiple diseases.     

QTL characterization of resistance to leaf rust and stripe rust in the spring wheat line Francolin#1

Growing resistant wheat varieties is a key method of controlling two important wheat diseases, leaf rust and stripe rust. We analyzed quantitative trait loci (QTL) to investigate adult plant resistance (APR) to these rusts, using 141 F₅ RILs derived from the cross ‘Avocet-YrA/Francolin#1’. Phenotyping of leaf rust resistance was conducted during two seasons at Ciudad Obregon, Mexico, whereas stripe rust was evaluated for two seasons in Toluca, Mexico, and one season in Chengdu, China. The genetic map was constructed with 581 markers, including diversity arrays technology and simple sequence repeat. Significant loci for reducing leaf rust severity were designated QLr.cim-1BL, QLr.cim-3BS.1, QLr.cim-3DC, and QLr.cim-7DS. The six QTL that reduced stripe rust severity were designated QYr.cim-1BL, QYr.cim-2BS, QYr.cim-2DS, QYr.cim-3BS.2, QYr.cim-5AL, and QYr.cim-6AL. All loci were conferred by Francolin#1, with the exception of QYr.cim-2DS, QYr.cim-5AL, and QYr.cim-6AL, which were derived from Avocet-YrA. Closely linked markers indicated that the 1BL locus was the pleiotropic APR gene Lr46/Yr29. QYr.cim-2BS was a seedling resistance gene designated as YrF that conferred intermediate seedling reactions and moderate resistance at the adult plant stage in both Mexican and Chinese environments. Significant additive interactions were detected between the six QTL for stripe rust, but not between the four QTL for leaf rust. Furthermore, we detected two new APR loci for leaf rust in common wheat: QLr.cim-3BS.1 and QLr.cim-7DS.     

QTL mapping of stripe,leaf and stem rust resistance genes in a Kariega × Avocet S doubled haploid wheat population

Adult plant resistance to stripe (yellow) rust in the wheat cultivar Kariega has previously been ascribed to a major quantitative trait locus (QTL) on each of chromosomes 2B and 7D, along with a number of minor QTL. We have extended both the size of the cv. Kariega × cv. Avocet S mapping population, and the marker coverage within it, by assembling a set of Diversity Array Technology (DArT) markers. This has allowed for the analysis of the genetic basis of the adult plant and seedling resistances to stripe, leaf and stem rust present in the two mapping population parents. The stripe rust reactions of the segregating material were assessed in both field (three scoring dates) and greenhouse experiments. The chromosome 2B QTL became more important than the Lr34/Yr18 complex on chromosome 7D as the plants aged. As the infection progressed, the two QTL explained an increasing proportion of the variance for percentage leaf area infected. The cv. Kariega allele at the minor chromosome 4A QTL had a consistent effect on the severity of stripe rust infection and the overall plant reaction at the earlier scoring dates, but lost importance as the disease progressed. Several rust resistances were detected using an improved greenhouse-based test.     

Mapping of quantitative adult plant field resistance to leaf rust and stripe rust in two European winter wheat populations reveals co-location of three QTL conferring resistance to both rust pathogens

Key message

We detected several, most likely novel QTL for adult plant resistance to rusts. Notably three QTL improved resistance to leaf rust and stripe rust simultaneously indicating broad spectrum resistance QTL.

Abstract

The rusts of wheat (Puccinia spp.) are destructive fungal wheat diseases. The deployment of resistant cultivars plays a central role in integrated rust disease management. Durability of resistance would be preferred, but is difficult to analyse. The Austrian winter wheat cultivar Capo was released in the 1989 and grown on a large acreage during more than two decades and maintained a good level of quantitative leaf rust and stripe rust resistance. Two bi-parental mapping populations: Capo × Arina and Capo × Furore were tested in multiple environments for severity of leaf rust and stripe rust at the adult plant stage in replicated field experiments. Quantitative trait loci associated with leaf rust and stripe rust severity were mapped using DArT and SSR markers. Five QTL were detected in multiple environments associated with resistance to leaf rust designated as QLr.ifa-2AL, QLr.ifa-2BL, QLr.ifa-2BS, QLr.ifa-3BS, and QLr.ifa-5BL, and five for resistance to stripe rust QYr.ifa-2AL, QYr.ifa-2BL, QYr.ifa-3AS, QYr.ifa-3BS, and QYr.ifa-5A. For all QTL apart from two (QYr.ifa-3AS, QLr.ifa-5BL) Capo contributed the resistance improving allele. The leaf rust and stripe rust resistance QTL on 2AL, 2BL and 3BS mapped to the same chromosome positions, indicating either closely linked genes or pleiotropic gene action. These three multiple disease resistance QTL (QLr.ifa-2AL/QYr.ifa-2AL, QLr.ifa.2BL/QYr.ifa-2BL, QLr.ifa-3BS/QYr.ifa.3BS) potentially contribute novel resistance sources for stripe rust and leaf rust. The long-lasting resistance of Capo apparently rests upon a combination of several genes. The described germplasm, QTL and markers are applicable for simultaneous resistance improvement against leaf rust and stripe rust.     

Characterization of genetic loci conferring adult plant resistance to leaf rust and stripe rust in spring wheat.

Leaf (brown) and stripe (yellow) rusts, caused by Puccinia triticina and Puccinia striiformis, respectively, are fungal diseases of wheat (Triticum aestivum) that cause significant yield losses annually in many wheat-growing regions of the world. The objectives of our study were to characterize genetic loci associated with resistance to leaf and stripe rusts using molecular markers in a population derived from a cross between the rust-susceptible cultivar 'Avocet S' and the resistant cultivar 'Pavon76'. Using bulked segregant analysis and partial linkage mapping with AFLPs, SSRs and RFLPs, we identified 6 independent loci that contributed to slow rusting or adult plant resistance (APR) to the 2 rust diseases. Using marker information available from existing linkage maps, we have identified additional markers associated with resistance to these 2 diseases and established several linkage groups in the 'Avocet S' x 'Pavon76' population. The putative loci identified on chromosomes 1BL, 4BL, and 6AL influenced resistance to both stripe and leaf rust. The loci on chromosomes 3BS and 6BL had significant effects only on stripe rust, whereas another locus, characterized by AFLP markers, had minor effects on leaf rust only. Data derived from Interval mapping indicated that the loci identified explained 53% of the total phenotypic variation (R2) for stripe rust and 57% for leaf rust averaged across 3 sets of field data. A single chromosome recombinant line population segregating for chromosome 1B was used to map Lr46/Yr29 as a single Mendelian locus. Characterization of slow-rusting genes for leaf and stripe rust in improved wheat germplasm would enable wheat breeders to combine these additional loci with known slow-rusting loci to generate wheat cultivars with higher levels of slow-rusting resistance.     

Characterization of a major QTL for adult plant resistance to stripe rust in US soft red winter wheat

Stripe rust, caused by Puccinia striiformis f. sp. tritici, is an important disease of soft red winter wheat in the eastern region of the USA. Pioneer 26R61 has provided effective resistance to stripe rust for 10 years. To elucidate the genetic basis of the resistance, a mapping population of 178 recombinant inbred lines (RILs) was developed using single-seed descent from a cross between Pioneer 26R61 and the susceptible cultivar AGS 2000. A genetic map with 895 markers covering all 21 chromosomes was used for QTL analysis. One major QTL was detected, explaining up to 56.0% of the mean phenotypic variation, flanked by markers Xbarc124 and Xgwm359, and assigned to the distal 22% of the short arm of wheat chromosome 2A. Evidence showed that it was different from Yr17 derived from Ae. ventricosa, the only formally named Yr gene in 2AS, and the QTL was temporarily designated as YrR61. In addition, a minor QTL, QYr.uga-6AS, probably conditioned high-temperature adult plant resistance. The QTL explained 6–7% of the trait variation. Preliminary test of the flanking markers for YrR61, in two cultivars and two promising breeding lines with Pioneer 26R61 in their pedigree, indicated that YrR61 was present in these cultivars and lines, and these markers could therefore be used in marker-assisted selection.     

QTL identification and microphenotype characterisation of the developmentally regulated yellow rust resistance in the UK wheat cultivar Guardian

Yellow rust (causal agent: Puccinia striiformis f.sp. tritici) resistance in the UK wheat cultivar Guardian is developmentally regulated, resistance increasing as the plant matures. Yellow rust resistance was assessed under field conditions on plants after ear emergence to ensure maximum expression of resistance. Three quantitative trait loci (QTL) for yellow rust resistance were identified, being located on chromosomes 1B (QPst.jic-1B), 2D (QPst.jic-2D) and 4B (QPst.jic-4B). The largest resistance effect, QPst.jic-1B located to the same position on the long arm of chromosome 1B as the known durable source of yellow rust resistance, Yr29. Microscopic studies were carried out to determine what effect the resistance in Guardian had on the development of P. striiformis f.sp. tritici. While the adult plant resistance in Guardian did not prevent germinated urediniospores from establishing an effective infection site, the growth of hyphae within flag leaf tissue was significantly inhibited, slowing the development of microcolonies. 3,3-diaminabenzadine (DAB) and trypan blue staining indicated that this inhibition of hyphal growth was not associated with hydrogen peroxide accumulation or extensive plant cell death.     

Rapid identification of an adult plant stripe rust resistance gene in hexaploid wheat by high-throughput SNP array genotyping of pooled extremes

Key message

High-throughput SNP array analysis of pooled extreme phenotypes in a segregating population by KASP marker genotyping permitted rapid, cost-effective location of a stripe rust resistance QTL in wheat.

Abstract

German wheat cultivar “Friedrichswerther” has exhibited high levels of adult plant resistance (APR) to stripe rust in field environments for many years. F_2:3 lines and F₆ recombinant inbred line (RILs) populations derived from a cross between Friedrichswerther and susceptible landrace Mingxian 169 were evaluated in the field in 2013, 2016 and 2017. Illumina 90K iSelect SNP arrays were used to genotype bulked extreme pools and parents; 286 of 1135 polymorphic SNPs were identified on chromosome 6B. Kompetitive Allele-Specific PCR (KASP) markers were used to verify the chromosome region associated with the resistance locus. A linkage map was constructed with 18 KASP-SNP markers, and a major effect QTL was identified within a 1.4 cM interval flanked by KASP markers IWB71602 and IWB55937 in the region 6BL3-0-0.36. The QTL, named QYr.nwafu-6BL, was stable across environments, and explained average 54.4 and 47.8% of the total phenotypic variation in F_2:3 lines and F₆ RILs, respectively. On the basis of marker genotypes, pedigree analysis and relative genetic distance QYr.nwafu-6BL is likely to be a new APR QTL. Combined high-throughput SNP array genotyping of pooled extremes and validation by KASP assays lowers sequencing costs compared to genome-wide association studies with SNP arrays, and more importantly, permits rapid isolation of major effect QTL in hexaploid wheat as well as improving accuracy of mapping in the QTL region. QYr.nwafu-6BL with flanking KASP markers developed and verified in a subset of 236 diverse lines can be used in marker-assisted selection to improve stripe rust resistance in breeding programs.

     

Wheat stripe rust resistance genes <Emphasis Type="Italic">Yr5</Emphasis> and <Emphasis Type="Italic">Yr7</Emphasis> are allelic

Stripe rust is one of the most destructive diseases of wheat. Breeding for resistance is the most economical and environmentally acceptable means to control stripe rust. Genetic studies on resistance sources are very important. Previous inheritance studies on Triticum aestivum subsp. spelta cv. album and wheat cultivar Lee showed that each possessed a single dominant gene for stripe rust resistance, i.e., Yr5 and Yr7, respectively. Both were located on the long arm of chromosome 2B, but due to the complexities caused by genetic background effects there was no clear evidence on the allelism or linkage status of these genes. Our study, involving an intercross of Avocet S near-isogenic lines possessing the genes, provided clear evidence for allelism or extremely close linkage of Yr5 and Yr7 based on phenotypic and molecular studies.     

Characterization of Yr54 and other genes associated with adult plant resistance to yellow rust and leaf rust in common wheat Quaiu 3

Leaf rust (LR) and yellow rust (YR), caused by Puccinia triticina and Puccinia striiformis f. sp. tritici, respectively, are important diseases of wheat. Quaiu 3, a common wheat line developed at the International Maize and Wheat Improvement Center (CIMMYT), is immune to YR in Mexico despite seedling susceptibility to predominant races. Quaiu 3 also shows immunity to LR in field trials and is known to possess the race-specific gene Lr42. A mapping population of 182 recombinant inbred lines (RILs) was developed by crossing Quaiu 3 with susceptible Avocet-YrA and phenotyped with LR and YR in field trials for 2 years in Mexico. Quantitative trait loci (QTL) associated with YR and LR resistance in the RILs were identified using Diversity Arrays Technology and simple sequence repeat markers. A large-effect QTL on the long arm of chromosome 2D explained 49–54 % of the phenotypic variation in Quaiu 3 and was designated as Yr54. Two additional loci on 1BL and 3BS explained 8–17 % of the phenotypic variation for YR and coincided with previously characterized adult plant resistance (APR) genes Lr46/Yr29 and Sr2/Yr30, respectively. QTL on 1DS and 1BL corresponding to Lr42 and Lr46/Yr29, respectively, contributed 60–71 % of the variation for LR resistance. A locus on 3D associated with APR to both diseases explained up to 7 % of the phenotypic variance. Additional Avocet-YrA-derived minor QTL were also detected for YR on chromosomes 1A, 3D, 4A, and 6A. Yr54 is a newly characterized APR gene which can be combined with other genes by using closely linked molecular markers.     

Combination of all-stage and high-temperature adult-plant resistance QTL confers high-level,durable resistance to stripe rust in winter wheat cultivar Madsen

Key message

Wheat cultivar Madsen has a new gene on the short arm of chromosome 1A and two QTL for all-stage resistance and three QTL for high-temperature adult-plant resistance that in combination confer high-level, durable resistance to stripe rust.

Abstract

Wheat cultivar Madsen has maintained a high-level resistance to stripe rust over 30 years. To map quantitative trait loci (QTL) underlying the high-level, durable resistance, 156 recombinant inbred lines (RILs) developed from cross Avocet S?×?Madsen were phenotyped with selected races of Puccinia striiformis f. sp. tritici in the greenhouse seedling tests, and in naturally infected fields during 2015–2017. The RILs were genotyped by SSR and SNP markers from genotyping by sequencing and the 90 K wheat SNP chip. Three QTL for all-stage resistance were mapped on chromosomes 1AS, 1BS and 2AS, and two QTL for high-temperature adult-plant (HTAP) resistance were mapped on 3BS and 6BS. The most effective QTL on 2AS, explaining 8.97–23.10% of the phenotypic variation in seedling tests and 8.60–71.23% in field tests, contained Yr17 for all-stage resistance and an additional gene for HTAP resistance. The 6BS QTL, detected in all field tests, was identified as Yr78. The 1AS QTL, conferring all-stage resistance, was identified as a new gene, which explained 20.45 and 30.23% of variation in resistance to races PSTv-37 and PSTv-40, respectively, and contributed significantly to field resistance at Pullman in 2015-2017, but was not detected at Mount Vernon. The interactions among QTL were mostly additive, and RILs with all five QTL had the highest level of resistance in the field, similar to Madsen. Genotyping 148 US Pacific Northwest wheat cultivars with markers for the 1AS, 2AS and 6BS QTL validated the genes and markers, and indicated their usefulness for marker-assisted selection.

     

<Emphasis Type="Italic">Yr32</Emphasis> for resistance to stripe (yellow) rust present in the wheat cultivar Carstens V

Stripe or yellow rust of wheat, caused by Puccinia striiformis f. sp. tritici, is an important disease in many wheat-growing regions of the world. A number of major genes providing resistance to stripe rust have been used in breeding, including one gene that is present in the differential tester Carstens V. The objective of this study was to locate and map a stripe rust resistance gene transferred from Carstens V to Avocet S and to use molecular tools to locate a number of genes segregating in the cross Savannah/Senat. One of the genes present in Senat was predicted to be a gene that is present in Carstens V. For this latter purpose, stripe rust response data from both seedling and field tests on a doubled haploid population consisting of 77 lines were compared to an available molecular map for the same lines using a non-parametric quantitative trait loci (QTL) analysis. Results obtained in Denmark suggested that a strong component of resistance with the specificity of Carstens V was located in chromosome arm 2AL, and this was consistent with chromosome location work undertaken in Australia. Since this gene segregated independently of Yr1, the only other stripe rust resistance gene known to be located in this chromosome arm, it was designated Yr32. Further QTLs originating from Senat were located in chromosomes 1BL, 4D, and 7DS and from Savannah on 5B, but it was not possible to characterize them as unique resistance genes in any definitive way. Yr32 was detected in several wheats, including the North American differential tester Tres.An erratum to this article can be found at Communicated by G. Wenzel