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 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.     

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.     

Genome-Wide Linkage Mapping of QTL for Adult-Plant Resistance to Stripe Rust in a Chinese Wheat Population Linmai 2 × Zhong 892

Stripe rust is one of the most devastating diseases of wheat (Triticum aestivum) worldwide. Adult-plant resistance (APR) is an efficient approach to provide long-term protection of wheat from the disease. The Chinese winter wheat cultivar Zhong 892 has a moderate level of APR to stripe rust in the field. To determine the inheritance of the APR resistance in this cultivar, 273 F₆ recombinant inbred lines (RILs) were developed from a cross between Linmai 2 and Zhong 892. The RILs were evaluated for maximum disease severity (MDS) in two sites during the 2011–2012, 2012–2013 and 2013–2014 cropping seasons, providing data for five environments. Illumina 90k SNP (single nucleotide polymorphism) chips were used to genotype the RILs and their parents. Composite interval mapping (CIM) detected eight QTL, namely QYr.caas-2AL, QYr.caas-2BL.3, QYr.caas-3AS, QYr.caas-3BS, QYr.caas-5DL, QYr.caas-6AL, QYr.caas-7AL and QYr.caas-7DS.1, respectively. All except QYr.caas-2BL.3 resistance alleles were contributed by Zhong 892. QYr.caas-3AS and QYr.caas-3BS conferred stable resistance to stripe rust in all environments, explaining 6.2–17.4% and 5.0–11.5% of the phenotypic variances, respectively. The genome scan of SNP sequences tightly linked to QTL for APR against annotated proteins in wheat and related cereals genomes identified two candidate genes (autophagy-related gene and disease resistance gene RGA1), significantly associated with stripe rust resistance. These QTL and their closely linked SNP markers, in combination with kompetitive allele specific PCR (KASP) technology, are potentially useful for improving stripe rust resistances in wheat breeding.     

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.     

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.

     

Quantitative trait loci mapping of adult-plant resistance to powdery mildew in Chinese wheat cultivar Lumai 21

Powdery mildew, caused by Blumeria graminis f. sp. tritici, is a major fungal disease in common wheat (Triticum aestivum L.) worldwide. The Chinese winter wheat cultivar Lumai 21 has shown good and stable adult plant resistance for 19 years. The aim of this study was to map quantitative trait loci (QTLs) for resistance to powdery mildew in a population of 200 F₃ lines from the cross Lumai 21/Jingshuang 16. The population was tested for powdery mildew reaction in Beijing and Anyang in the 2005–2006 and 2006–2007 cropping seasons, providing data for 4 environments. A total of 1,375 simple sequence repeat (SSR) markers were screened for associations with powdery mildew reactions, initially in bulked segregant analysis. Based on the mean disease values averaged across environments, broad-sense heritabilities of maximum disease severity and area under the disease progress curve were 0.96 and 0.77, respectively. Three QTLs for adult plant resistance were detected by inclusive composite interval mapping. These were designated QPm.caas-2BS, QPm.caas-2BL and QPm.caas-2DL, respectively, and explained from 5.4 to 20.6% of the phenotypic variance across environments. QPm.caas-2BS and QPm.caas-2DL were likely new adult plant resistance QTLs flanked by SSR markers Xbarc98–Xbarc1147 and Xwmc18–Xcfd233, respectively. These markers could be useful for improving wheat powdery mildew resistance in breeding programs.     

Mapping of QTLs associated with resistance to common bunt,tan spot,leaf rust,and stripe rust in a spring wheat population

Spring wheat (Triticum aestivum L.) breeding goals in western Canada include good agronomic characteristics and good end-use quality, and also moderate to elevated resistance to diseases of economic importance. In this study, we aimed to identify quantitative trait loci (QTL) associated with resistance to common bunt (Tilletia tritici and Tilletia laevis), tan spot (Pyrenophora tritici-repentis), leaf rust (Puccinia triticina), and stripe rust (Puccinia striiformis f. sp. tritici). A total of 167 recombinant inbred lines (RILs) derived from a cross between two spring wheat cultivars, ‘Attila’ and ‘CDC Go’, were evaluated for reactions to the four diseases in nurseries from three to eight environments, and genotyped with the Wheat 90K SNP array and three gene-specific markers (Ppd-D1, Vrn-A1, and Rht-B1). The RILs exhibited transgressive segregation for all four diseases, and we observed several lines either superior or inferior to the parents. Broad-sense heritability varied from 0.25 for leaf rust to 0.48 for common bunt. Using a subset of 1203 informative markers (1200 SNPs and 3 gene-specific markers) and average disease scores across all environments, we identified two QTLs (QCbt.dms-1B.2 and QCbt.dms-3A) for common bunt, and three QTLs each for tan spot (QTs.dms-2B, QTs.dms-2D, and QTs.dms-6B), leaf rust (QLr.dms-2D.1, QLr.dms-2D.2, and QLr.dms-3A), and stripe rust (QYr.dms-3A, QYr.dms-4A, and QYr.dms-5B). Each QTL individually explained between 5.9 and 18.7% of the phenotypic variation, and altogether explained from 21.5 to 26.5% of phenotypic and from 52.2 to 86.0% of the genetic variation. The resistance alleles for all QTLs except one for stripe rust (QYr.dms-5B) were from CDC Go. Some of the QTLs are novel, while others mapped close to QTLs and/or genes reported in other studies.     

Identification of adult plant resistance to stripe rust in the wheat cultivar Cappelle-Desprez

Following the appearance of stripe rust in South Africa in 1996, efforts have been made to identify new sources of durable resistance. The French cultivar Cappelle-Desprez has long been considered a source of durable, adult plant resistance (APR) to stripe rust. As Cappelle-Desprez contains the seedling resistance genes Yr3a and Yr4a, wheat lines were developed from which Yr3a and Yr4a had been removed, while selecting for Cappelle-Desprez derived APR effective against South African pathotypes of the stripe rust fungus, Puccinia striiformis f. sp. tritici. Line Yr16DH70, adapted to South African wheat growing conditions, was selected and crossed to the stripe rust susceptible cultivar Palmiet to develop a segregating recombinant inbred line mapping population. A major effect QTL, QYr.ufs-2A was identified on the short arm of chromosome 2A derived from Cappelle-Desprez, along with three QTL of smaller effect, QYr.ufs-2D, QYr.ufs-5B and QYr.ufs-6D. QYr.ufs-2D was located within a region on the short arm of chromosome 2D believed to be the location of the stripe rust resistance gene Yr16. An additional minor effect QTL, QYr.ufs-4B, was identified in the cv. Palmiet. An examination of individual RILs carrying single or combinations of each QTL indicated significant resistance effects when QYr.ufs-2A was combined with the three minor QTL from Cappelle-Desprez, and between QYr.ufs-2D and QYr.ufs-5B.     

Genetic analysis of durable resistance to yellow rust in bread wheat

Yellow rust, caused by Puccinia striiformis, is one of the most damaging diseases affecting bread wheat in temperate regions. Although resistance to yellow rust is frequently overcome by new virulent races, a durable form of resistance in the French bread wheat Camp Rémy (CR) has remained effective since its introduction in 1980. We used 217 F₇ recombinant inbred lines (RILs) derived from the cross between CR and the susceptible cultivar Récital to identify and map quantitative trait loci (QTLs) involved in durable yellow rust resistance. Six significant QTLs that were stable over a 4-year period were detected. Two QTLs, denoted QYr.inra-2DS and QYr.inra-5BL.2, were located on the short arm of chromosome 2D and the long arm of chromosome 5B, respectively. Each explained on average 25–35% of the observed phenotypic variation and were probably inherited from Cappelle Desprez, a parent of CR that confers durable adult plant resistance to yellow rust. QYr.inra-2DS probably corresponds to the Yr16 gene. The most consistent QTL, designated QYr.inra-2BL, was located on the centromeric region of chromosome 2B and explained 61% of the phenotypic variation in 2003. This QTL was responsible for seedling-stage resistance and may correspond to a cluster of genes, including Yr7. The remaining QTLs were mapped to the short arm of chromosome 2B (R²=22–70%) and to the long arm of chromosomes 2A (R²=0.20–0.40) and 5B (R²=0.18–0.26). This specific combination of seedling and adult plant resistance genes found in CR and CD may constitute the key to their durable resistance against yellow rust.     

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.     

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.

     

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.     

Mapping of QTLs prolonging the latent period of Puccinia triticina infection in wheat

Slow rusting is considered a crucial component of durable resistance to wheat leaf rust caused by Puccinia triticina and is often expressed in the form of a prolonged latent period. Selection for a longer latent period is considered an effective approach to developing wheat cultivars with improved durable resistance to leaf rust. A recombinant inbred line (RIL) population derived from CI 13227 (long latent period) × Suwon 92 (short latent period) was phenotyped for latent period in two greenhouse experiments in separate years, and amplified fragment length polymorphism (AFLP) and simple sequence repeat (SSR) markers were analyzed in the same population. Among the RILs, the frequency distribution for latent period was continuous, and latent period was highly correlated between years (r=0.94, P<0.0001). A quantitative trait locus (QTL) prolonging the latent period of P. triticina, designated as QLrlp.osu-2DS, explained 42.8% and 54.5% of the phenotypic and genetic variance in the two experiments, respectively. QLrlp.osu-2DS was mapped on the distal region of chromosome 2DS. Two other QTLs for latent period, QLrlp.osu-2B and QLrlp.osu-7BL, were localized on chromosome 2B and the long arm of chromosome 7B, respectively. Multiple regression analysis showed that these three QTLs collectively explained 58.0% and 73.8% of the phenotypic and genetic variance over two experiments, respectively. Fourteen RILs that carried all three alleles for long latent period at three AFLP loci flanking QLrlp.osu-2DS, QLrlp.osu-2B, and QLrlp.osu-7BL had a mean latent period of 12.5 days, whereas 13 RILs without any long-latent-period alleles at the corresponding loci had a mean latent period of 7.4 days. Three SSR markers closely linked to these QTLs have potential to be applied in marker-assisted selection for prolonged latent period in wheat.     

<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.     

QTL analysis of the spring wheat “Chapio” identifies stable stripe rust resistance despite inter-continental genotype × environment interactions

Chapio is a spring wheat developed by CIMMYT in Mexico by a breeding program that focused on multigenic resistances to leaf rust and stripe rust. A population consisting of 277 recombinant inbred lines (RILs) was developed by crossing Chapio with Avocet. The RILs were genotyped with DArT markers (137 randomly selected RILs) and bulked segregant analysis conducted to supplement the map with informative SSR markers. The final map consisted of 264 markers. Phenotyping against stripe rust was conducted for three seasons in Toluca, Mexico and at three sites over two seasons (total of four environments) in Sichuan Province, China. Significant loci across the two inter-continental regions included Lr34/Yr18 on 7DS, Sr2/Yr30 on 3BS, and a QTL on 3D. There were significant genotype × environment interactions with resistance gene Yr31 on 2BS being effective in most of the Toluca environments; however, a late incursion of a virulent pathotype in 2009 rendered this gene ineffective. This locus also had no effect in China. Conversely, a 5BL locus was only effective in the Chinese environments. There were also complex additive interactions. In the Mexican environments, Yr31 suppressed the additive effect of Yr30 and the 3D locus, but not of Lr34/Yr18, while in China, the 3D and 5BL loci were generally not additive with each other, but were additive when combined with other loci. These results indicate the importance of maintaining diverse, multi-genic resistances as Chapio had stable inter-continental resistance despite the fact that there were QTLs that were not effective in either one or the other region.     

The adult plant rust resistance loci Lr34/Yr18 and Lr46/Yr29 are important determinants of partial resistance to powdery mildew in bread wheat line Saar

Powdery mildew, caused by Blumeria graminis f. sp. tritici is a major disease of wheat (Triticum aestivum L.) that can be controlled by resistance breeding. The CIMMYT bread wheat line Saar is known for its good level of partial and race non-specific resistance, and the aim of this study was to map QTLs for resistance to powdery mildew in a population of 113 recombinant inbred lines from a cross between Saar and the susceptible line Avocet. The population was tested over 2 years in field trials at two locations in southeastern Norway and once in Beijing, China. SSR markers were screened for association with powdery mildew resistance in a bulked segregant analysis, and linkage maps were created based on selected SSR markers and supplemented with DArT genotyping. The most important QTLs for powdery mildew resistance derived from Saar were located on chromosomes 7DS and 1BL and corresponded to the adult plant rust resistance loci Lr34/Yr18 and Lr46/Yr29. A major QTL was also located on 4BL with resistance contributed by Avocet. Additional QTLs were detected at 3AS and 5AL in the Norwegian testing environments and at 5BS in Beijing. The population was also tested for leaf rust (caused by Puccinia triticina) and stripe rust (caused by P. striiformis f. sp. tritici) resistance and leaf tip necrosis in Mexico. QTLs for these traits were detected on 7DS and 1BL at the same positions as the QTLs for powdery mildew resistance, and confirmed the presence of Lr34/Yr18 and Lr46/Yr29 in Saar. The powdery mildew resistance gene at the Lr34/Yr18 locus has recently been named Pm38. The powdery mildew resistance gene at the Lr46/Yr29 locus is designated as Pm39.     

<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     

Genetic analysis and mapping of adult plant resistance loci to leaf rust in durum wheat cultivar Bairds

Key message

New leaf rust adult plant resistance (APR) QTL QLr.cim - 6BL was mapped and confirmed the known pleotropic APR gene Lr46 effect on leaf rust in durum wheat line Bairds.

Abstract

CIMMYT-derived durum wheat line Bairds displays an adequate level of adult plant resistance (APR) to leaf rust in Mexican field environments. A recombinant inbred line (RIL) population developed from a cross of Bairds with susceptible parent Atred#1 was phenotyped for leaf rust response at Ciudad Obregon, Mexico, during 2013, 2014, 2015 and 2016 under artificially created epidemics of Puccinia triticina (Pt) race BBG/BP. The RIL population and its parents were genotyped with the 50 K diversity arrays technology (DArT) sequence system and simple sequence repeat (SSR) markers. A genetic map comprising 1150 markers was used to map the resistance loci. Four significant quantitative trait loci (QTLs) were detected on chromosomes 1BL, 2BC (centromere region), 5BL and 6BL. These QTLs, named Lr46, QLr.cim-2BC, QLr.cim-5BL and QLr.cim-6BL, respectively, explained 13.5–60.8%, 9.0–14.3%, 2.8–13.9%, and 11.6–29.4%, respectively, of leaf rust severity variation by the inclusive composite interval mapping method. All of these resistance loci were contributed by the resistant parent Bairds, except for QLr.cim-2BC, which came from susceptible parent Atred#1. Among these, the QTL on chromosome 1BL was the known pleiotropic APR gene Lr46, whereas QLr.cim-6BL, a consistently detected locus, should be a new leaf rust resistance locus in durum wheat. The mean leaf rust severity of RILs carrying all four QTLs ranged from 8.0 to 17.5%, whereas it ranged from 10.9 to 38.5% for three QTLs (Lr46 + 5BL + 6BL) derived from the resistant parent Bairds. Two RILs with four QTLs combinations can be used as sources of complex APR in durum wheat breeding.