Rust Resistant Wheat Research Articles

Molecular mapping of leaf rust resistance gene Lr15 in hexaploid wheat

Leaf rust is a widespread and commonly occurring rust disease of wheat. Genetic resistance is the most economical method of reducing losses due to leaf rust. Lr15 has been shown to be present on wheat chromosome 2D and is reported to be a seedling resistance gene. However, tightly linked markers associated with Lr15 have not been reported to date. To identify molecular markers linked to Lr15, an F2 mapping population of Thatcher × Thatcher-Lr15 was generated. Available wheat simple sequence repeat markers were utilized in parental screening and polymorphic markers were used to analyze the entire population of 221 plants. Phenotypic evaluations of the F2-derived F3 progenies with Puccinia triticina Eriks. pathotype 162A (93R15) confirmed the monogenic inheritance of Lr15. The linkage group representing chromosome 2DS was constructed at LOD 4.0 which revealed the closest flanking markers Xgwm4562 and Xgwm102 at a distance of 3.1 and 9.3 cM, respectively. Furthermore, utilization of these flanking markers in combination has successfully identified wheat lines with or without Lr15. These markers could potentially be useful in gene pyramiding with other genes to enhance rust resistance in wheat.

Genes involved in adult plant resistance to stripe rust in wheat cultivar Xingzi 9104

Stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), is a destructive disease of wheat (Triticum aestivum) worldwide. Adult plant resistance to stripe rust resistance in wheat is often durable. To gain a better understanding of the mechanism of adult plant resistance, a suppressive subtractive hybridization (SSH) approach was used to identify wheat genes induced by Pst infection at the adult plant stage. Based on the putative functions of 436 SSH-derived unigene sequences, we characterized defense responses triggered during infection and development of adult plant resistance in wheat cultivar Xingzi 9104. Eighty nine genes were found to be involved in defense and signal transduction. Twelve of the genes were selected for time-course expression analyses using quantitative RT-PCR. Nine of those genes were induced by Pst infection, including those predicted to encode peroxidase, BAX inhibitor, Concanavalin A-like lectin/glucanase, subtilisin-chymotrypsin inhibitor, chinase, glucan endo-1,3-beta-D-glucosidase and acidic PR5 precursor. We found that some PR protein genes kept high expression levels longer in the adult plants than in seedlings after Pst infection. This study is the first to report a concanavalin A-like lectin/glucanase involved in plant defense against pathogen infection. The large number of genes obtained through constructing the SSH library are valuable for further studies to achieve a better understanding of molecular mechanisms of stripe rust resistance in wheat and also useful for studying resistance mechanisms in other plant pathosystems.

Putative Thinopyrum intermedium-derived stripe rust resistance gene Yr50 maps on wheat chromosome arm 4BL

Stripe rust-resistant wheat introgression line CH223 was developed by crossing the resistant partial amphiploid TAI7047 derived from Thinopyrum intermedium with susceptible cultivars. The resistance is effective against all the existing Chinese stripe rust races, including the most widely virulent and predominant pathotypes CYR32 and CYR33. Cytological analyses using GISH detected no chromosomal segments from Th. intermedium. It was presumed that the segment was too small to be detected. Normal bivalent pairing at meiosis in CH223 and its hybrids confirmed its stability. Genetic analysis of the F(1), F(2), F(3) and BC(1) populations from crosses of CH223 with susceptible lines indicated that resistance was controlled by a single dominant gene. The resistance gene was mapped using an F(2:3) population from Taichung 29/CH223. The gene was linked to five co-dominant genomic SSR markers, Xgwm540, Xbarc1096, Xwmc47, Xwmc310 and Xgpw7272, and flanked by Xbarc1096 and Xwmc47 at 8.0 and 7.2 cM, respectively. Using the Chinese Spring nulli-tetrasomic and ditelosomic lines, the polymorphic markers and the resistance gene were assigned to chromosome arm 4BL. As no permanently named stripe rust resistance genes had been assigned to chromosome 4BL, this new resistance gene is designated Yr50. The gene, together with the identified closely linked markers, could be used in marker-assisted selection to combine two or more resistance genes in a single genotype.

Molecular breeding and genetic aspects of diversity in wheat (Triticum aestivum L.) for stripe rust resistance

Molecular breeding and genetic aspects of diversity in wheat (Triticum aestivum L.) for stripe rust resistance

Molecular breeding and genetic aspects of diversity in wheat (Triticum aestivum L.) for stripe rust resistance

Molecular breeding and genetic aspects of diversity in wheat (Triticum aestivum L.) for stripe rust resistance

Marker-Assisted Selection for Disease Resistance in Wheat and Barley Breeding

Marker-assisted selection (MAS) provides opportunities for enhancing the response from selection because molecular markers can be applied at the seedling stage, with high precision and reductions in cost. About each of 50 genes conferring monogenic resistances and hundreds of quantitative trait loci (QTL) for quantitative disease resistances have been reported in wheat and barley. For detecting single-major gene resistance, MAS could be easily applied, but is often not necessary because the resistances are selected phenotypically. In quantitative disease resistances, MAS would be very useful, but the individual QTL often have small effects. Additionally, only a few monogenic resistances are durable and only a few QTL with high effects have been successfully transferred into elite breeding material. Further economic and biological constraints, e.g., a low return of investment in small-grain cereal breeding, lack of diagnostic markers, and the prevalence of QTL-background effects, hinder the broad implementation of MAS. Examples in which MAS has been successfully applied to practical breeding are the wheat rust resistance genes Lr34 and Yr36, the eyespot resistance gene Pch1, the recessive resistance genes rym4/rym5 to barley yellow mosaic viruses, mlo to barley powdery mildew, and two QTL for resistance to Fusarium head blight in wheat (Fhb1 and Qfhs.ifa-5A). Newly identified broad-spectrum resistance genes/QTL conferring resistance to multiple taxa of pathogens offer additional perspectives for MAS. In the future, chip-based, high-throughput genotyping platforms and the introduction of genomic selection will reduce the current problems of integrating MAS in practical breeding programs and open new avenues for a molecular-based resistance breeding.

Agronomic Performance of Elite Stem Rust Resistant Spring Wheat Genotypes and Association among Trial Sites in the Central and West Asia and North Africa Region

The new stem rust race Ug99 is an alarming threat to the wheat (Triticum aestivum L.) production of the world for the very fact that it overcomes many of the known Sr genes including the most commonly used genes such as Sr31, Sr24, and Sr36. The wheat breeding program at the International Center for Agricultural Research in the Dry Areas (ICARDA) has distributed the first stem rust resistant spring wheat yield trials composed of 24 wheat genotypes for the Central and West Asia and North Africa (CWANA) region to identify high yielding wheat genotypes, which can be recommended for direct release and/or parentage purposes by the National Agricultural Research Systems (NARSs). The additive main effects and multiplicative interaction (AMMI) analysis of variance for grain yield (kg ha-1) of 24 wheat genotypes tested in 15 environments showed that wheat grain yield was significantly (p < 0.01) affected by environments (E), genotypes (G), and genotype × environment interaction (GEI). From the total sum of squares due to treatments (G + E + GEI), E contributed 90.1% and GEI accounted for 8.3% while G effect represented only 1.6%. According to AMMI2 estimate, Baasha-14 and Amir-2 with mean grain yield levels of 5168 and 5127 kg ha-1, respectively, are identified as the best genotypes with high yield potential across a wide range of environments. Based on correlation and clustering analysis among environments, the Ghab site in Syria (E7) is identified as the highest yielding and best correlated site and therefore it is recommended as a key location for evaluation of wheat germplasm yield potential in ICARDA's wheat breeding program. We recommend the high yielding and Ug99 resistant genotypes identified in this study for direct release as replacement of the susceptible varieties by the respective NARS and/or to be used as parents at ICARDA and by NARS collaborators.

Genetic analysis of leaf rust resistance genes and associated markers in the durable resistant wheat cultivar Sinvalocho MA

In the cross of the durable leaf rust resistant wheat Sinvalocho MA and the susceptible line Gama6, four specific genes were identified: the seedling resistance gene Lr3, the adult plant resistance (APR) genes LrSV1 and LrSV2 coming from Sinvalocho MA, and the seedling resistance gene LrG6 coming from Gama6. Lr3 was previously mapped on 6BL in the same cross. LrSV1 was mapped on chromosome 2DS where resistance genes Lr22a and Lr22b have been reported. Results from rust reaction have shown that LrSV1 from Sinvalocho is not the same allele as Lr22b and an allelism test with Lr22a showed that they could be alleles or closely linked genes. LrSV1 was mapped in an 8.5-cM interval delimited by markers gwm296 distal and gwm261 proximal. Adult gene LrSV2 was mapped on chromosome 3BS, cosegregating with gwm533 in a 7.2-cM interval encompassed by markers gwm389 and gwm493, where other disease resistance genes are located, such as seedling gene Lr27 for leaf rust, Sr2 for stem rust, QTL Qfhs.ndsu-3BS for resistance to Fusarium gramineum and wheat powdery mildew resistance. The gene LrG6 was mapped on chromosome 2BL, with the closest marker gwm382 at 0.6cM. Lines carrying LrSV1, LrSV2 and LrG6 tested under field natural infection conditions, showed low disease infection type and severity, suggesting that this kind of resistance can be explained by additive effects of APR and seedling resistance genes. The identification of new sources of resistance from South American land races and old varieties, supported by modern DNA technology, contributes to sustainability of agriculture through plant breeding.

Agrobiological characteristics of leaf rust resistance in wheat under conditions of the northwestern region of the Russian Federation

The effect of the level of nitrogen nutrition of spring wheat breeding varieties and lines of various geographic provenance, their morphoagronomic characteristics, and expression of Lr genes on wheat leaf rust pathogenesis is studied. The dependence of changes in the intensity of disease development, number of pustules on flag and preflag leaves, area of pustule, number of spores in it, and type of wheat reaction on a set of agrobiological factors is shown.

Molecular cytogenetic characterization and SSR marker analysis of a leaf rust resistant wheat line carrying a 6G(6B) substitution from Triticum timopheevii (Zhuk.)

A disease (powdery mildew, leaf rust) resistant line was selected from the progenies of a Triticum aestivum × Triticum timopheevii amphiploid produced at Martonvasar. This line was previously identified with C-banding as a 6G(6B) substitution. In order to detect the 6G chromosome in a wheat background, fluorescence in situ hybridization (FISH) and microsatellite marker analysis were used. Ten microsatellite markers of the 43 tested generated PCR products that were polymorphic between chromosomes 6B and 6G, and four showed length-polymorphism. The FISH hybridization pattern of 6G from T. timopheevii was identified using a combination of four repetitive DNA probes (Afa-family, pSc119.2, pTa71, (GAA)7). Genomic in situ hybridization (GISH) technique, capable of labelling the At and G genomes separately, was used on the same slides to differentiate the At and G genomes in T. timopheevii. The At and G genomes of T. timopheevii were grouped on the basis of the GISH patterns and a cyclic intergenomic translocation involving 6At-1G-4G was detected in T. timopheevii accession TRI667. The presence of 6G in the substitution line was demonstrated using FISH with the four repetitive DNA probes. Chromosome 6G was clearly identified and its FISH pattern was different from that of 6B in the parental wheat cultivar Fleischmann-481. According to field tests, the 6G(6B) substitution line has resistance to leaf rust.

First report of the breakdown of the YR17 resistance gene to wheat stripe rust in the Grand Duchy of Luxembourg

Yr17 resistance gene (Yr17+ cultivars) induces yellow rust resistance in wheat at the seedling stage and operates throughout the plant life. A new Yr17 pathotype that overcomes resistance to wheat stripe rust in Yr17+ cultivars was first detected in 1997 in countries neighboring Luxembourg (Bayles et al., 2000). In 1999, stripe rust was suspected to occur also in this country (GDL) and, in 2003, Puccinia striiformis f. sp. tritici was identified. Disease severity was recorded in the 1999-2009 period in fungicide untreated experiments with various cultivars grown in Everlange, Christnach, Burmerange and Reuler (El Jarroudi et al., 2009). Over this 11-year period, the difference between Yr17+ (Achat, Akteur, Astron, Flair) and Yr17- (Aron, Batis, Bussard, Drifter, Ritmo,Vivant) cultivars was highly significant, the highest severity being observed in Yr17+ cultivars (mean severity of 13%) compared to Yr17- cultivars (0.2%). In 1999, Yr17+ cultivars showed the highest disease severity (19%) whereas in 2000 and 2001, the highest severity was observed in cv. Flair (Yr 17+) with 30% and 22%, respectively at Everlange, and 50% and 11%, respectively at Christnach. In both years symptoms on Yr17- cultivars were rare (severity <1%) or absent. During 2002-2009 yellow rust occurred with relatively low severity (average 6%) on Yr17+ cultivars (cv. Achat at Everlange in 2002, 2008 and 2009, cv. Akteur at Everlange and Reuler in 2007). These observations support the hypothesis of the presence in GDL of the Yr17 pathotype that overcomes the Yr17 gene. This new virulent pathotype appears more aggressive on Yr17+ than Yr17- cultivars. Since most resistant European cultivars are Yr17+, this renders control strategies based on this monogenic resistance to wheat stripe rust vain. Bayles R.A., Flath K., Hovmoller M.S., De Valavieille-Pope C.,. 2000. Breakdown of the Yr17 resistance to yellow rust of wheat in Northern Europe. Agronomie 20: 805-811. El Jarroudi M., Giraud F., Vrancken C., Junk J., Tychon B., Hoffmann L., Delfosse P,. 2009. First report of wheat leaf rust in the Grand Duchy of Luxembourg and the progress of its appearance over the 2003-2008 period. Plant Disease 93: 971-971.

Development of a PCR assay and marker-assisted transfer of leaf rust resistance gene Lr58 into adapted winter wheats

Leaf rust resistance gene Lr58 derived from Aegilops triuncialis L. was transferred to the hard red winter wheat (HRWW) cultivars Jagger and Overley by standard backcrossing and marker-assisted selection (MAS). A co-dominant PCR-based sequence tagged site (STS) marker was developed based on the sequence information of the RFLP marker (XksuH16) diagnostically detecting the alien segment in T2BS·2BL-2tL(0.95). STS marker Xncw-Lr58-1 was used to select backcross F1 plants with rust resistance. The co-dominant marker polymorphism detected by primer pair NCW-Lr58-1 efficiently identified the homozygous BC3F2 plants with rust resistance gene Lr58. The STS marker Xncw-Lr58-1 showed consistent diagnostic polymorphism between the resistant source and the wheat cultivars selected by the US Wheat Coordinated Agricultural Project. The utility and compatibility of the STS marker in MAS programs involving robust genotyping platforms was demonstrated in both agarose-based and capillary-based platforms. Screening backcross derivatives carrying Lr58 with various rust races at seedling stage suggested the transferred rust resistance in adapted winter wheats is stable in both cultivar backgrounds. Lr58 in adapted winter wheat backgrounds could be used in combination with other resistance genes in wheat rust resistance breeding.

Molecular genetics of race non-specific rust resistance in wheat

Over 150 resistance genes that confer resistance to either leaf rust, stripe rust or stem rust have been catalogued in wheat or introgressed into wheat from related species. A few of these genes from the ‘slow-rusting’ adult plant resistance (APR) class confer partial resistance in a race non-specific manner to one or multiple rust diseases. The recent cloning of two of these genes, Lr34/Yr18, a dual APR for leaf rust and stripe rust, and Yr36, a stripe rust APR gene, showed that they differ from other classes of plant resistance genes. Currently, seven Lr34/Yr18 haplotypes have been identified from sequencing the encoding ATP Binding Cassette transporter gene from diverse wheat germplasm of which one haplotype is commonly associated with the resistance phenotype. The paucity of well characterised APR genes, particularly for stem rust, calls for a focused effort in developing critical genetic stocks to delineate quantitative trait loci, construct specific BAC libraries for targeted APR genes to facilitate robust marker development for breeding applications, and the eventual cloning of the encoding genes.

Delivering rust resistant wheat to farmers: a step towards increased food security

An important step towards reducing the vulnerability of wheat in Africa and Asia to the Ug99 race of the stem rust pathogen is the substitution of current susceptible varieties with superior resistant varieties. In the 2008–2009 cropping season both seed multiplication and dissemination of Ug99 resistant varieties were initiated in Afghanistan, Bangladesh, Egypt, Ethiopia, Iran, India, Nepal and Pakistan. Ug99 resistant varieties must occupy about 5% of the area sown to wheat in each country to ensure sufficient seed to displace current popular varieties. Because of the underdeveloped seed industry and small farm sizes in most of these countries, various strategies are being applied for rapid multiplication and dissemination of resistant varieties. Approaches being used include pre-release seed multiplication while candidate resistant lines are being tested in national evaluation trials and farmer participatory selection. Resistant varieties are already released in Afghanistan, Bangladesh, Egypt and Pakistan and more varieties are expected to be released in 2010 in these and other countries. Our results show that some new Ug99 resistant lines have yield superiority over dominant local varieties. Activities and progress in seed multiplication using existing and new Ug99 resistant varieties are discussed.

Potencial produtivo, resistência à ferrugem da folha e qualidade industrial da farinha em genótipos de trigo

Com o objetivo de avaliar o potencial de rendimento de grãos, a resistência à ferrugem da folha e as características tecnológicas da farinha, foram avaliados 18 genótipos de trigo provenientes de cruzamentos com a cultivar IAC 24, mais as cultivares controles IAC 24 e IAC 370, em experimentos instalados em condições de sequeiro nas localidades de Manduri (Zona A), Capão Bonito e Itapeva (Zona B) e Paranapanema (Zona C), no Estado de São Paulo, no período de 2003 a 2005. As avaliações dos genótipos ao agente causal da ferrugem da folha foram feitas no estádio de plântulas em casa de vegetação, onde os genótipos foram submetidos à inoculação individualmente com esporos de 12 raças de Puccinia triticina, as quais representavam o espectro de virulência do patógeno ocorrente no Brasil e também sob infecção natural no campo. Em oito genótipos descendentes da cultivar IAC 24 observaram-se níveis adequados de resistência não-específica à ferrugem da folha, com reações suscetíveis porém com baixa severidade, consistentemente ao longo dos anos/locais. O melhor rendimento de grãos foi obtido pelo genótipo 7 (PF87373/IAC 24), entretanto não diferindo dos genótipos 12, 18, 4 e 6. De acordo com os paramentos alveográficos e farinográficos, os genótipos 4, 5, 8, 9, 11, 15 e 18 se destacaram pela qualidade industrial e suas farinhas foram de classe superior. Os genótipos que se destacaram em relação às três características estudadas são potencialmente úteis aos programas de melhoramento genético como doadores de alelos favoráveis.

Peregrine hard red winter wheat

Peregrine is a medium tall, high-yielding, stem and leaf rust resistant winter wheat (Triticum aestivum L.) that is registered for production in western Canada. It is a hard red winter wheat cultivar that is eligible for grades of the Canada Western General Purpose (CWGP) wheat class. The CWGP class was created in 2007 to encourage the development of cultivars to fill the high energy demands of the biofuel and livestock feed markets in western Canada. In Manitoba and Saskatchewan, the grain yield of Peregrine was 117% of the Canada Western Red Winter Wheat Class grain quality check cultivar, CDC Osprey, and 106% of the high-yielding check, CDC Falcon. High grain yield potential and a high level of rust resistance mean that Peregrine provides a good fit for the CWGP class.

Marker‐assisted selection for pre‐harvest sprouting tolerance and leaf rust resistance in bread wheat

With 2 figures and 3 tables AbstractThe present study was undertaken for developing a pre‐harvest sprouting (PHS) tolerant and leaf rust resistant wheat genotype using marker‐assisted selection (MAS). A major quantitative trait locus (QTL) (QPhs.ccsu‐3A.1) for PHS tolerance (PHST) identified by us earlier was introgressed into HD2329, which is an elite but PHS susceptible cultivar, and carried two Lr genes (Lr24 + Lr28) earlier introgressed by us using MAS. In each backcross generation, foreground selection for PHS QTL was exercised using flanking markers (gwm155 and wmc153), and background selection was performed using 61 simple sequence repeat loci spread over the whole genome. During backcrossing, the desirable alleles of Lr24 and Lr28, were also tracked using linked SCAR markers. Seven BC3F3 progenies having desirable PHST QTL and Lr genes, and showing up to 93.44% genetic similarity with the recipient parent were selected. These lines exhibited high level of PHST (PHS score 2–4) and resistance against leaf rust under artificial conditions. The study demonstrated successful application of MAS for targeted pyramiding of QTL/genes for more than one trait into an improved wheat cultivar.

Improving wheat stripe rust resistance in Central Asia and the Caucasus

Wheat is the most important cereal in Central Asia (Kazakhstan, Kyrgyzstan, Tajikistan, Turkmenistan and Uzbekistan) and the Caucasus (Armenia, Azerbaijan and Georgia). Stripe rust, caused by Puccinia striiformis f. sp. tritici is considered the most important disease of wheat in Central Asia and the Caucasus (CAC). Although stripe rust has been present in the region for a long time, it has become a serious constraint to wheat production in the past 10 years. This is reflected by the occurrence of five epidemics of stripe rust in the CAC region since 1999, the most recent in 2010. Several wheat varieties occupying substantial areas are either susceptible to stripe rust or possess a low level of resistance. Information on the stripe rust pathogen in terms of prevalent races and epidemiology is not readily available. Furthermore, there is an insufficient understanding of effective stripe rust resistance genes in the region, and little is known about the resistance genes present in the commercial varieties and advanced breeding lines. The deployment of resistant varieties is further complicated by putative changes in virulence in the pathogen population in different parts of the CAC. Twenty four out of 49 improved wheat lines received through international nurseries or other exchange programs showed high levels of resistance to stripe rust to local pathogen populations in 2009. Fifteen of the 24 stripe rust resistant lines also possessed resistance to powdery mildew. It is anticipated that this germplasm will play an important role in developing stripe rust resistant wheat varieties either through direct adoption or using them as parents in breeding programs.

Genomic selection for durable stem rust resistance in wheat

Inheritance of stem rust (caused by Puccinia graminis f. sp. tritici) resistance in wheat can be either qualitative or quantitative. While quantitative disease resistance is believed to be more durable, it is more difficult to evaluate if it is expressed only in mature plants, i.e. adult plant resistance (APR). Marker-assisted selection (MAS) methods for APR would be useful; however, the multigenic nature of APR impedes the use of MAS efforts that aim to pyramid only a few target genes. A promising alternative is genomic selection (GS), which utilizes genome-wide marker coverage to predict genotypic values for quantitative traits. In turn, GS can reduce the selection cycle length of a breeding program for traits like APR that could take several seasons to generate reliable phenotypes. In this paper, we describe the GS process for use in crop improvement, both specifically for APR and in general. We also propose a GS–based wheat breeding scheme for quantitative resistance to stem rust that, when compared to current breeding schemes, can reduce cycle time by up to twofold and facilitates pyramiding of major genes with APR genes. Thus, GS could be an important tool for achieving the Borlaug Global Rust Initiative’s (BGRI) goal of developing durable stem rust resistance in wheat.

An EST-SSR marker linked with yellow rust resistance in wheat

Expressed sequenced tags containing simple sequence repeats (EST-SSRs) were used to identify molecular markers associated with yellow rust resistance in wheat (Triticum aestivum L.). A cross between yellow rust resistant (PI178383) and susceptible (Harmankaya99) wheat genotypes was performed and respective DNA pools from the resistant and susceptible F2 seedlings were constructed. 78 EST-SSR primers were used for bulked segregant analysis and one EST-SSR marker (Pk54), identified as 200 bp fragment, was present in the resistant parent and resistant F2 hybrids but not in the susceptible ones. 108 wheat genotypes differing in yellow rust resistance were screened with Pk54 and 68 % of the wheat genotypes, known to be yellow rust resistant, had the Pk54 marker, further suggesting that the presence of this marker correlates with yellow rust resistance.