Quantitative trait loci of stripe rust resistance in wheat

Key message

Over 140 QTLs for resistance to stripe rust in wheat have been published and through mapping flanking markers on consensus maps, 49 chromosomal regions are identified.

Abstract

Over thirty publications during the last 10 years have identified more than 140 QTLs for stripe rust resistance in wheat. It is likely that many of these QTLs are identical genes that have been spread through plant breeding into diverse backgrounds through phenotypic selection under stripe rust epidemics. Allelism testing can be used to differentiate genes in similar locations but in different genetic backgrounds; however, this is problematic for QTL studies where multiple loci segregate from any one parent. This review utilizes consensus maps to illustrate important genomic regions that have had effects against stripe rust in wheat, and although this methodology cannot distinguish alleles from closely linked genes, it does highlight the extent of genetic diversity for this trait and identifies the most valuable loci and the parents possessing them for utilization in breeding programs. With the advent of cheaper, high throughput genotyping technologies, it is envisioned that there will be many more publications in the near future describing ever more QTLs. This review sets the scene for the coming influx of data and will quickly enable researchers to identify new loci in their given populations.     

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.     

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.     

Association mapping of leaf rust resistance loci in a spring wheat core collection

Key message

We identified 15 potentially novel loci in addition to previously characterized leaf rust resistance genes from 1032 spring wheat accessions. Targeted AM subset panels were instrumental in revealing interesting loci.

Abstract

Leaf rust is a common disease of wheat, consistently reducing yields in many wheat-growing regions of the world. Although fungicides are commonly applied to wheat in the United States (US), genetic resistance can provide less expensive, yet effective control of the disease. Our objectives were to map leaf rust resistance genes in a large core collection of spring wheat accessions selected from the United States Department of Agriculture-Agricultural Research Service National Small Grains Collection (NSGC), determine whether previously characterized race-nonspecific resistance genes could be identified with our panel, and evaluate the use of targeted panels to identify seedling and adult plant resistance (APR) genes. Association mapping (AM) detected five potentially novel leaf rust resistance loci on chromosomes 2BL, 4AS, and 5DL at the seedling stage, and 2DL and 7AS that conditioned both seedling and adult plant resistance. In addition, ten potentially novel race-nonspecific resistance loci conditioned field resistance and lacked seedling resistance. Analyses of targeted subsets of the accessions identified additional loci not associated with resistance in the complete core panel. Using molecular markers, we also confirmed the presence and effectiveness of the race-nonspecific genes Lr34, Lr46, and Lr67 in our panel. Although most of the accessions in this study were susceptible to leaf rust in field and seedling tests, many resistance loci were identified with AM. Through the use of targeted subset panels, more loci were identified than in the larger core panels alone.

     

Quantitative trait loci for slow-rusting resistance in wheat to leaf rust and stripe rust identified with multi-environment analysis

Rust diseases are a major cause of yield loss in wheat worldwide, and are often controlled through the incorporation of resistance genes using conventional phenotypic selection methods. Slow-rusting resistance genes are expressed quantitatively and are typically small in genetic effect thereby requiring multiple genes to provide adequate protection against pathogens. These effects are valuable and are generally considered to confer durable resistance. Therefore an understanding of the chromosomal locations of such genes and their biological effects are important in order to ensure they are suitably deployed in elite germplasm. Attila is an important wheat grown throughout the world and is used as a slow-rusting donor in international spring wheat breeding programs. This study identified chromosomal regions associated with leaf rust and stripe rust resistances in a cross between Attila and a susceptible parent, Avocet-S, evaluated over 3 years in the field. Genotypic variation for both rusts was large and repeatable with line-mean heritabilities of 94% for leaf rust resistance and 87% for stripe rust. Three loci, including Lr46/Yr29 on chromosome 1BL, were shown to provide resistance to leaf rust whereas six loci with small effects conferred stripe rust resistance, with a seventh locus having an effect only by epistasis. Disease scoring over three different years enabled inferences to be made relating to stripe rust pathogen strains that predominated in different years.     

Quantitative trait loci for non-race-specific, high-temperature adult-plant resistance to stripe rust in wheat cultivar Express

Wheat cultivar Express has durable, high-temperature adult-plant (HTAP) resistance to stripe rust (Puccinia striiformis f. sp. tritici). To elucidate the genetic basis of the resistance, Express was crossed with 'Avocet Susceptible' (AVS). A mapping population of 146 F(5) recombinant inbred lines (RILs) was developed using single-seed descent. The RILs were evaluated at two sites near Pullman in eastern Washington and one site near Mount Vernon in western Washington in 2005, and were evaluated near Pullman in 2006 under natural stripe rust infection of predominant races virulent on seedlings of Express. Infection type (IT) and disease severity (DS) were recorded three times for each line during each growing season. The DS data were used to calculate relative area under the disease progress curve (rAUDPC) values. Both IT and rAUDPC data showed continuous distributions, indicating that the Express HTAP resistance was controlled by quantitative trait loci (QTL). Resistance gene analog polymorphism (RGAP) and simple sequence repeat (SSR) techniques were used to map the HTAP resistance QTL. Three QTL were detected with significant additive effects, explaining 49.5-69.6% of the phenotypic variation for rAUDPC. Two of the QTL explained 30.8-42.7% of the phenotypic variation for IT. The three QTL were mapped to wheat chromosomes 6AS, 3BL and 1BL, and were designated as QYrex.wgp-6AS, QYrex.wgp-3BL and QYrex.wgp-1BL, respectively. QYrex.wgp-6AS and QYrex.wgp-3BL, which had higher effects than QYrex.wgp-1BL, were different from previously reported QTL/genes for adult-plant resistance. Markers Xgwm334-Xwgp56 and Xgwm299-Xwgp66 flanking the two major QTL were highly polymorphic in various wheat genotypes, suggesting that these markers are useful in marker-assisted selection.     

Molecular mapping of a gene for stripe rust resistance in spring wheat cultivar IDO377s

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. One such cultivar resistant to most races in North America is ‘IDO377s’. To study the genetics of its resistance this spring wheat cultivar was crossed with ‘Avocet Susceptible’ (AvS). Seedlings of the parents, F₂ plants, and F₃ lines were tested under controlled greenhouse conditions with races PST-43 and PST-45 of P. striiformis f. sp. tritici. IDO377s carries a single dominant gene for resistance. Resistance gene analog polymorphism (RGAP) and simple sequence repeat (SSR) techniques were used to identify molecular markers linked to the resistance gene. A total of ten markers were identified, two of which flanked the locus at 4.4 and 5.5 cM. These flanking RGAP markers were located on chromosome 2B with nulli-tetrasomic lines of ‘Chinese Spring’. Their presence in the ditelosomic 2BL line localized them to the long arm. The chromosomal location of the resistance gene was further confirmed with two 2BL-specific SSR markers and a sequence tagged site (STS) marker previously mapped to 2BL. Based on the chromosomal location, reactions to various races of the pathogen and tests of allelism, the IDO377s gene is different from all previously designated genes for stripe rust resistance, and is therefore designated Yr43. A total of 108 wheat breeding lines and cultivars with IDO377s or related cultivars in their parentage were assayed to assess the status of the closest flanking markers and to select lines carrying Yr43. The results showed that the flanking markers were reliable for assisting selection of breeding lines carrying the resistance gene. A linked stripe rust resistance gene, previously identified as YrZak, in cultivar Zak was designated Yr44.     

Number of genes controlling slow rusting resistance to leaf rust in five spring wheat cultivars

The number of genes controlling slow rusting resistance to leaf rust (Puccinia triticina) was estimated in five spring wheat (Triticum aestivum) cultivars using quantitative formulae. Parents and F₆ families were evaluated in replicated field trials under epidemics initiated by artificial inoculation. The F₆ families resulted from a diallel cross involving the fast-rusting cultivar Yecora 70 and five slow-rusting wheat cultivars: Sonoita 81, Tanager ‘S’, Galvez 87, Ures 81, and Moncho ‘S’. The area under the disease progress curve (AUDPC) was used to measure leaf rust severity over time. Results indicate that cultivar Sonoita 81 has three or four genes, Tanager ‘S’ has two or three genes, Galvez 87 has three genes, and both Ures 81 and Moncho ‘S’ have two genes for slow rusting resistance to leaf rust. Based on this result and previously reported moderate to high narrow-sense heritability estimates for slow rusting resistance in these materials, early-generation selection for slow leaf rusting would be effective.     

Characterization and genome-wide association mapping of resistance to leaf rust,stem rust and stripe rust in a geographically diverse collection of spring wheat landraces

The challenge posed by rapidly changing wheat rust pathogens, both in virulence and in environmental adaptation, calls for the development and application of new techniques to accelerate the process of breeding for durable resistance. To expand the resistance gene pool available for germplasm improvement, a panel of 159 landraces plus old cultivars was evaluated for seedling and adult plant resistance (APR) to over 35 Australian pathotypes of Puccinia triticina, Puccinia graminis f. sp. tritici, and Puccinia striiformis f. sp. tritici. Known seedling resistance (SR) genes for leaf rust (Lr2a, Lr3a, Lr13, Lr23, Lr16, and Lr20), stem rust (Sr12, Sr13, Sr23, Sr30, and Sr36), and stripe rust (Yr3, Yr4, Yr5, Yr9, Yr10, Yr17, and Yr27) were postulated. The APR genes identified via field assessments and marker analyses included the pleiotropic genes (Lr34/Yr18/Sr57, Lr46/Yr29/Sr58, Lr67/Yr46/Sr55, and Sr2/Lr27/Yr30), Lr68, Lr74, and uncharacterized APR. A genome-wide association analysis using linear mixed models detected 79 single nucleotide polymorphism (SNP) markers significantly associated with rust resistance, which were mapped on chromosomes 1A, 1B, 1D, 2A, 2B, 3A, 3B, 3D, 4A, 5A, 5B, 6A, 6B, 6D, 7A, 7B and 7D. SNPs associated with multiple rust resistances probably indicate the presence of new pleiotropic or closely linked genes. SNPs were mapped on chromosome positions (1AL, 1DS, 2AL, 4AS, 5BS, 6DL, and 7AL) that have not been known to carry APR genes. This study revealed the presence of a range of possibly unidentified effective seedling and APRs among the landraces, which might represent new sources of rust resistance for the ongoing effort to develop improved wheat cultivars.     

低聚糖诱导小麦抗条锈性及相关酶活性变化的研究

用自行设计的方法从植物细胞壁中得到的低聚糖提取物5号对小麦浸种和苗期喷雾处理,均使接种条锈菌的小麦叶片产生了明显的过敏性坏死反应。对几种与抗病性密切相关的酶活性变化的分析表明,经低聚糖预先处理能显著提高小麦叶片的过氧化物酶(POD)、多酚氧化酶(PPO)和苯丙氨基酸解氨酶(PAL)的活性。     

Homoeologous set of NBS-LRR genes located at leaf and stripe rust resistance loci on short arms of chromosome 1 of wheat

Homoeologous group 1 chromosomes of wheat contain important genes that confer resistance to leaf, stem and stripe rusts, powdery mildew and Russian wheat aphid. A disease resistance gene analog encoding nucleotide binding site-leucine rich repeat (NBS-LRR), designated RgaYr10, was previously identified at the stripe rust resistant locus, Yr10, located on chromosome 1BS distal to the storage protein, Gli-B1 locus. RgaYr10 identified gene members in the homoeologous region of chromosome 1DS cosegregating with the leaf rust resistance gene, Lr21, which originally was transferred from a diploid D genome progenitor. Four RgaYr10 gene members were isolated from chromosome 1DS and compared to two gene members previously isolated from the chromosome 1BS homeologue. NBS-LRR genes tightly linked to stripe rust resistance gene Yr10 on chromosome 1BS were closely related in sequence and structure to NBS-LRR genes tightly linked to leaf rust resistance gene Lr21 located within the homoeologous region on chromosome 1DS. The level of sequence homology was similar between NBS-LRR genes that were isolated from different genomes as compared to genes from the same genome. Electronic Publication     

Stripe rust and leaf rust resistance QTL mapping,epistatic interactions,and co-localization with stem rust resistance loci in spring wheat evaluated over three continents

Key message

In wheat, advantageous gene-rich or pleiotropic regions for stripe, leaf, and stem rust and epistatic interactions between rust resistance loci should be accounted for in plant breeding strategies.

Abstract

Leaf rust (Puccinia triticina Eriks.) and stripe rust (Puccinia striiformis f. tritici Eriks) contribute to major production losses in many regions worldwide. The objectives of this research were to identify and study epistatic interactions of quantitative trait loci (QTL) for stripe and leaf rust resistance in a doubled haploid (DH) population derived from the cross of Canadian wheat cultivars, AC Cadillac and Carberry. The relationship of leaf and stripe rust resistance QTL that co-located with stem rust resistance QTL previously mapped in this population was also investigated. The Carberry/AC Cadillac population was genotyped with DArT^® and simple sequence repeat markers. The parents and population were phenotyped for stripe rust severity and infection response in field rust nurseries in Kenya (Njoro), Canada (Swift Current), and New Zealand (Lincoln); and for leaf rust severity and infection response in field nurseries in Canada (Swift Current) and New Zealand (Lincoln). AC Cadillac was a source of stripe rust resistance QTL on chromosomes 2A, 2B, 3A, 3B, 5B, and 7B; and Carberry was a source of resistance on chromosomes 2B, 4B, and 7A. AC Cadillac contributed QTL for resistance to leaf rust on chromosome 2A and Carberry contributed QTL on chromosomes 2B and 4B. Stripe rust resistance QTL co-localized with previously reported stem rust resistance QTL on 2B, 3B, and 7B, while leaf rust resistance QTL co-localized with 4B stem rust resistance QTL. Several epistatic interactions were identified both for stripe and leaf rust resistance QTL. We have identified useful combinations of genetic loci with main and epistatic effects. Multiple disease resistance regions identified on chromosomes 2A, 2B, 3B, 4B, 5B, and 7B are prime candidates for further investigation and validation of their broad resistance.     

TaRBP1 stabilizes TaGLTP and negatively regulates stripe rust resistance in wheat

The dynamic balance and distribution of sphingolipid metabolites modulate the level of programmed cell death and plant defence. However, current knowledge is still limited regarding the molecular mechanism underlying the relationship between sphingolipid metabolism and plant defence. In this study, we identified a wheat RNA-binding protein 1 (TaRBP1) and TaRBP1 mRNA accumulation significantly decreased in wheat after infection by Puccinia striiformis f. sp. tritici (Pst). Knockdown of TaRBP1 via virus-induced gene silencing conferred strong resistance to Pst by enhancing host plant reactive oxygen species (ROS) accumulation and cell death, indicating that TaRBP1 may act as a negative regulator in response to Pst. TaRBP1 formed a homopolymer and interacted with TaRBP1 C-terminus in plants. Additionally, TaRBP1 physically interacted with TaGLTP, a sphingosine transfer protein. Knockdown of TaGLTP enhanced wheat resistance to the virulent Pst CYR31. Sphingolipid metabolites showed a significant accumulation in TaGLTP-silenced wheat and TaRBP1-silenced wheat, respectively. In the presence of the TaRBP1 protein, TaGLTP failed to be degraded in a 26S proteasome-dependent manner in plants. Our results reveal a novel susceptible mechanism by which a plant fine-tunes its defence responses by stabilizing TaGLTP accumulation to suppress ROS and sphingolipid accumulation during Pst infection.     

西科麦2028抗条锈性的遗传分析

西科麦2028是地理远缘小麦材料的杂交后代,具有突出的抗条锈病性能。为了解西科麦2028对小麦条锈病的抗性遗传规律,以西科麦2028和铭贤169的杂交群体为研究对象,采用我国目前小麦条锈菌流行小种CYR31、CYR32、CYR33、Su11-4对供试群体进行成株期接种,分析杂交后代的抗病性及分布情况。结果表明:西科麦2028对CYR31的抗病性由3对显性基因控制;对CYR32由2对显性和1对隐性基因控制;对CYR33由1对显性基因控制;对Su11-4由1对显性和1对隐性基因控制。     

小麦品种贵农22号抗条锈基因遗传分析

贵农22号是利用簇毛麦(Haynaldia villosa)、硬粒小麦(Triticum durum)及普通小麦(Triticum aestuvum)杂交而育成的普通小麦品种,其抗中国目前流行和出现的条锈菌小种,已成为目前重要的抗小麦条锈病抗源。为了明确该品种抗锈遗传规律并进行应用前景评价,用一个流行的强毒性小种条中31号和一个突变弱毒性小种CY29-mut3,分别接种贵农22与国际已知抗锈基因品种Moro及感病品种辉县红双列杂交F2、F2代各株系幼苗,对贵农22号进行了抗锈性遗传分析,以便于在抗病育种中进一步应用。研究结果表明,贵农22号有三对独立遗传的抗条锈基因,暂定名为YrGui 1、YrGui 2和YrGui 3,它们表达稳定,不受亲本正反交影响,而并不具有Yr 10。Yr10基因载体品种Moto中有二或四对基因抗中国不同的条锈菌小种,不同小种及正反交对基因的表达有影响,为父本时其对CY29-mut3小种有两对完全显性基因、一对中度抗病基因及一对隐性抗病基因,而为母本时有一对完全显性基因和一对中度抗病基因起抗病作用;对条中31号,其为父本时有一对显性基因和一对隐性基因,为母本时可能存在两对累加作用基因或两对隐性抗病基因控制抗痫作用。     

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.     

Backcross-breeding and doubled-haploid facilitated introgression of stripe rust resistance in bread wheat

Stripe rust caused by the fungus Puccinia striiformis f. sp. tritici (Pst) may decrease wheat yield significantly in severe outbreaks. The most cost-effective and environmentally friendly approach to reduce yield losses due to rust diseases is deployment of effective resistant genes in wheat cultivars. The causal agents evolve and may break existing resistant sources as well. Therefore, long-term conventional breeding strategies and the ongoing evolution of pathogen populations in the region would put the success of breeding programmes at risk so that there is always a need for speeding up the process of germplasm enhancement through production of doubled-haploid breeding materials. In this study, we aimed at introgression of stripe rust resistance trait from three genotypes (Flanders, Martonvasar-17 (MV17) and Bersee) into a widely adapted cultivar “Ghods”. Positively selected F2BC² progenies of three backcrossing schemas, i.e. (i) Flanders/3^*Ghods; (ii) Ghods^*3/MV17; and (iii) Hybride-de-bersee/3^*Ghods, were used to produce three small-size doubled-haploid populations via wheat × Maize pollination methodology. The doubled-haploid populations were examined against two predominantly isolates of P. striiformis f. sp. tritici (Pst) i.e. 6E134A⁺ and 6E2A⁺Yr27⁺ and the screening revealed that 44 and 52 of the progenies are resistant to the above-mentioned isolates, respectively. Field data have shown that the stripe rust resistance doubled-haploid germplasm are comparable to local check cultivars in yield and earliness.     

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.     

Allelic variation and effects of 16 candidate genes on disease resistance in western Canadian spring wheat cultivars

Recently, we mapped genomic regions associated with resistance to wheat diseases and insensitivity to Pyrenophora tritici-repentis (Ptr) toxins using 81 historical and modern Canadian western spring wheat cultivars genotyped with genome-wide single nucleotide polymorphic (SNP) markers. Here, we investigate the frequency and effects of allelic variants of 50 markers associated with 16 candidate genes that regulate resistance to leaf rust (Puccinia triticina), yellow or stripe rust (P. striiformis f. sp. tritici), tan spot (P. tritici-repentis), and Ptr ToxA reaction in a subset of 70 of the 81 spring wheat cultivars. We evaluated the 70 cultivars in the field for all diseases except Ptr ToxA, which was evaluated in a greenhouse. Using Spearman rank correlation, stepwise discriminant analysis, and partial least squares regression, we identified between 4 and 11 markers as best predictors of each phenotypic trait. Overall, 23 of the 50 markers were associated with one or more of the phenotypic traits of which analysis of variance showed significant differences between allelic variants of 19 markers. In most analyses, markers for Lr34/Yr18 and Tsn1 loci were identified consistently as the best predictor of disease resistance and Ptr ToxA sensitivity, respectively. The same alleles from two Lr34/Yr18 diagnostic SNP markers (wMAS000003 and wMAS000004) not only decreased stripe rust scores up to 1.6 (on a 1 to 9 scale), but also increased grain yield up to 196 kg ha^?1 without affecting maturity. Results from this study could aid spring wheat breeders in selecting the best parental combinations and/or marker-assisted selection to integrate disease resistance with early maturity and short stature.