Yr5-virulent races of Puccinia striiformis f.sp.tritici possess relative parasitic fitness higher than current main predominant races and potential risk

Wheat stripe rust,caused by Puccinia striiformis f.sp.tritici(Pst),is one of the most destructive fungal diseases of wheat,and seriously threatens safe production of the crop worldwide.In China,new races historically appeared and rapidly developed to be predominant races and have resulted in ineffectiveness and replacement of wheat resistance cultivars as well as massive reduction in yield.In the present study,the relative parasitic fitness of the two newlyemerged Yr5-virulent races(TSA-6 and TSA-9)were compared with those of four currently predominant Chinese races(CYR31,CYR32,CYR33,and CYR34)based on evaluation on 10 Chinese wheat cultivars.As a result,there were significant differences in the relative parasitic fitness parameters among overall tested races based on multiple comparison(LSD)analysis(P<0.05).The principal component analysis(PCA)of overall parasitic fitness parameters indicated that the sporulation ability,infection and spore survivability,expansion capacity,and potential pathogenicity were the most important parasitic fitness attributes of the tested races.Based on the establishment of extracted three principal components and a comprehensive factor score mathematical models,evaluations of the parasitic fitness attributes of tested races showed that the level of relative parasitic fitness of the tested six races was:CYR32(1.15)>TSA-9(0.95)>TSA-6(0.92)>CYR34(0.29)>CYR31(–1.54)>CYR33(–1.77).The results indicated that two Yr5-virulent races TSA-9 and TSA-6 possessed relative parasitic fitness higher than races CYR34,CYR31,and CYR33,but lower than race CYR32,and have potential risks in developing to be predominant races.Therefore,continual monitoring of both Yr5-virulent races,and their variants is needed.The use of wheat cultivars(lines)with Yr5 resistance gene singly in wheat breeding is essential for being avoided,and is suggested to combine with other effective stripe rust resistance genes.

Postulation of Seedling Resistance Genes in 20 Wheat Cultivars to Yellow Rust (Puccinia striiformis f. sp. tritici)

The gene postulation, cluster analysis and pedigree analysis of 20 wheat cultivars to 28 physiological races of yellow rust （Puccinia striiformis） were conducted under greenhouse conditions, The spectrum of their resistance were compared each other. None of the 20 cultivars were resistant to all the test pathogens. The cultivars containing resistance genes Yr5 and Yr24 were not find and genes Yr8, Yrl9 and Yr27 could not be postulated from cultivars tested due to the susceptibility to all isolates used. A total of 6 probale seedling yellow rust resistance genes or gene combinations （Yrl, Yr2, Yr2 ＋ YrHVII, Yr3 ＋ unknown, Yr3 ＋ Yr4, YrAlba） were postulated in the wheat cultivars （Atou, Flanders, Maris Huntsman, Bouquet, Holdfast, Elite Lepeuple, and Vilmorin 27）. The gene combination Yr2＋YrHVII with the highest frequency （35%） was present in 7 cultivars. The Yr genes present in some wheat cultivars could not be postulated because of non-matching virulence combinations with any of known genes. Cluster result showed that Yr2 and Yr3 are the most important genes in the cultivars. The 13 cultivars are believed to have the pedigree of Noe, which was selected from South Russian wheat. These results will be useful for wheat breeding and provide information about genetic control of wheat yellow rust.

Histology and Ultrastructure of Incompatible Combination Between Puccinia striiformis and Wheat Cultivars with Low Reaction Type Resistance

The incompatible combinations between races of Puccinia striiformis and wheat cultivars with low reaction type resistance were examined by means of fluorescent microscopy, differential interference contrast microscopy and electron microscopy. The incompatible combinations consisted of wheat cultivar Niuzhute plus CY28, Hybrid46 plus CY29 and Tianxuan882 plus CY29, while the compatible combination was wheat cultivar Huixianhong plus CY28. The observation revealed a striking difference in the fungal development and the host responses between susceptible and resistant wheat cultivars following infection by the pathogen. The main histological manifestation of the pathogen development in the resistant wheat cultivars include inhibition of hyphal growth, delay of hyphal branching and colony formation, decrease of formation of haustorial mother cells and haustoria, and occurrence of host cell necrosis. The observation by electron microscopy demonstrated that a series of abnormal changes occurred in intercellular hyphae, haustorial mother cells and haustoria during pathogen development in the resistant wheat cultivars. The cytoplasm became more electron-dense and vacuoles in the cytoplasm increased in number and size. The cell walls of hyphae, haustorial mother cells were thickened irregularly. The organelles were disorderly distributed in the cytoplasm and the haustorial mother cells and haustoria lost their physiological function. In the final stage of the pathogen development, the intercellular hyphae, haustorial mother cells and haustoria became necrotic and collapsed. The structural defense reactions such as formation of cell wall apposition, collar and encasement of haustorium were essentially more pronounced in the infected wheat leaves of the resistant cultivars than in the susceptible one. In addition, the relationship between the host resistance expression and the histological and cytological features occurred in the incompatible combination was discussed in this paper.

Identification of eight Berberis species from the Yunnan-Guizhou plateau as aecial hosts for Puccinia striiformis f.sp.tritici,the wheat stripe rust pathogen

Puccinia striiformis Westend.f.sp.tritici Erikss.(Pst)infects wheat and causes stripe rust.The rust is heteroecious with wheat as the primary uredinial and telial host and barberry(Berberis spp.)as the alternate pycnial and aecial host.More than 40 Berberis species have been identified as alternate hosts for Pst,and most of these are Chinese Berberis species.However,little is known about Berberis species or their geographic distributions in the Yunnan-Guizhou plateau in southwestern China.The Yunnan-Guizhou plateau is considered to be an important and relatively independent region for the evolution of the wheat stripe rust pathogen in China because the entire disease cycle can be completed within the region.In this study,we conducted a survey of barberry plants in the Yunnan-Guizhou plateau and identified the eight Pst-susceptible Berberis species under controlled conditions,including B.julianae,B.tsienii,B.veitchii,B.wilsonae,B.wilsonae var.guhtzunica,B.franchetiana,B.lepidifolia and B.pruinosa.These species are reported here for the first time to serve as alternate hosts for the wheat stripe rust pathogen under controlled conditions.

Association Analysis of SP-SNPs and Avirulence Genes in Puccinia striiformis f. sp. tritici, the Wheat Stripe Rust Pathogen

Puccinia striiformis f. sp. tritici (Pst) is one of the pathogenic fungi on wheat, caused stripe rust that is a great threat for wheat production all over the world. Intensive efforts have been made to study genetics of wheat resistance to this disease, but few on avirulence of the pathogen due mainly to the nature of obligate biotrophism and the lack of systems for studying its genetics and molecular manipulations. To overcome these limitations, a natural Pst population comprising 352 isolates representative of a diverse virulence spectrum was genotyped using 97 secreted protein-single nucleotide polymorphism (SP-SNP) markers to identify candidate avirulence genes using association analysis. Among avirulence genes corresponding to 19 resistance genes, significantly associated SP-SNP markers were detected for avirulence genes AvYr1, AvYr2, AvYr6, AvYr7, AvYr8, AvYr44, AvYrExp2, AvYrSP, and AvYrTye. These results indicate that association analysis can be used to identify markers for avirulence genes. This study has laid the foundation for developing more SP-SNPs for mapping avirulence genes using segregating populations that can be generated through sexual reproduction on alternate hosts of the pathogen.

Ultrastructural Changes in the Interaction Between Puccinia striiformis and Wheat Cultivar with Slow-Rusting Resistance

Ultrastructural changes in both pathogen and host cells in the interaction between Puccinia striiformis and wheat cultivar （Libellula） with slow-rusting resistance were observed by transmission electron microscopy. Observations revealed marked changes in ultrastructure of both pathogen and host cells. In the pathogen respect, there were many vesicles appeared in the intercellular hyphae and gradually fused into bigger vacuoles, a number of fat drops and electron-dense granules accumulated, mitochondria became swollen and some of them degraded into vesicles, and the plasmalemma of intercellular hyphae became dark. In the haustoria, the cytoplasm degraded gradually and developed a vacuole in the center, fat drops increased, the extrahaustorial matrix widened with a great amount of electron-dense fibrillar and granular materials, and most of the haustoria died with in conjunction with the disappearance of fat drops and other organelles. Structural defense of the host, including formation of cell wall apposition, collar and papilla, occurred in the host respect. Host resistance expression and cytological features occurring in the slow-rusting resistance were discussed.

An improved method for RNA extraction from urediniospores of and wheat leaves infected by an obligate fungal pathogen, Puccinia striiformis f. sp. tritici

Stripe rust, caused by Puccinia striiformis f. sp. tritici, is an important wheat disease in China, seriously threatening wheat production. Understanding the winter survival of the fungus is a key for predicting the spring epidemics of the disease, which determines the crop loss. Estimation of P. striiformis f. sp. tritici winter survival requires processing a large number of samples for sensitive detection of the pathogen in wheat leaf tissue using real-time quantitative reverse transcription PCR （qRT-PCR）. A bottleneck for the analysis is the acquisition of a good yield of high quality RNA suitable for qRT-PCR to distinguish dead and alive fungal hyphae inside leaves. Although several methods have been described in the literatures and commercial kits are available for RNA extraction, these methods are mostly too complicated, expensive and inefficient. Thus, we modified three previously reported RNA extraction methods with common and low-cost reagents （LiCI, SDS and NaCI） to solve the problems and selected the best to obtain high quality and quantity RNA for use in qRT-PCR. In the three improved methods, the NaCI method was proven to be the best for extracting RNAfrom urediniospores of and wheat leaves infected by P. striiformis f. sp. tritici, although the modified LiCI and SDS methods also increased yield of RNA compared to the previous methods. The improved NaCI method has the following advantages： 1） Complete transfer of urediniospores of P. striiformis f. sp. tritici from the mortar and pestle can ensure the initial amount of RNA for the qRT-PCR analysis; 2） the use of low-cost NaCI to replace more expensive Trizol can reduce the cost; 3） the yield and quality of RNA can be increased; 4） the improved method is more suitable for a large number and high quantity of samples from fields. Using the improved NaCI method, the amount of RNA was increased three times from urediniospores of P. striiformis f. sp. tritici compared from the extraction kit. Approximately, 10.11 IJg total RNA of high quality was obtained from 100 mg of infected leaves, which was 8.8, 6.5, 3.4 and 2.1 folds of the amounts obtained from the previous LiCI, SDS, NaCI and traditional Trizol methods, respectively. The method could be used to study the overwintering rates of R striiformis f. sp. tritici over a large region of wheat production for predicting epidemic levels by determining pathogen survival levels after winter. The method can alsobe used in any studies which need a large number of high quality RNA samples.

The TaFIM1 gene mediates wheat resistance against Puccinia striiformis f. sp. tritici and responds to abiotic stress

Fimbrin, a regulator of actin cytoskeletal dynamics that participates in numerous physiological and biochemical processes, controls multiple developmental processes in a variety of tissues and cell types. However, the role of fimbrin in pathogen defense of wheat and the mechanisms have not been well studied. Here, we investigated that the expression of TaFIM1 gene of wheat was significantly induced in response to avirulent race of Puccinia striiformis f. sp. tritici(Pst) and silencing of TaFIM1 by virus-induced gene silencing method. The results show that silencing of TaFIM1 resulted in a reduction of resistance against the stripe rust indicated by both phenotypes and a histological examination of Pst growth. Additionally, the expression level of Ta FIM1 gene was up-regulated under abiotic stresses. These findings suggest that Ta FIM1 functions as a positive regulator of pathogen resistance of wheat plants and response to abiotic stress. Our work may show new light on understanding the roles of fimbrin in wheat.

Effects of Different Cultivation Patterns of Wheat on Population Structure of Puccinia striiformis West.f. sp. tritici

The paper was to study the effects of different cultivation patterns( mix cultivation and monocultivation) of wheat on population structure of Puccinia striiformis West. f. sp. tritici in the fields. Five race-specific-markers( CY32,CY31,CY29,CY23 and Shuiyuan pathotype) were used to survey 113 infected samples collected from two cultivation patterns. The results indicated that frequency of race-specific-markers under monocultivation was higher than that under mix cultivation; the dominant race-specific-markers were CY32 and CY29 under monocultivation,and the frequency of detection were 81. 5% and 78. 5%,respectively. The dominant race-specific-markers were CY29 and Shuiyuan pathotype under mix cultivation,and the frequency of detection are 41. 7% and 18. 8%,respectively.Several race-specific-markers were detected in single infected leaf,and 41. 7% of infected single leaf were detected with more than two race-specific-markers,58. 3% of infected single leaf were detected with one race-specific-marker under mix cultivation pattern,while there were 75. 0% infected leaves with more than two race-specific-markers and 25. 0% infected single leaf detected with one race-specific-marker under monocultivation pattern. The results indicated that mix cultivation pattern of wheat can reduce races on single leaf,affect the distribution of races in infected leaves,and suppress the occurrence frequency of dominant races of P. striiformis in the fields significantly,subsequently reduced severity and prevalence of the disease.

The Puccinia striiformis effector Hasp98 facilitates pathogenicity by blocking the kinase activity of wheat TaMAPK4

The obligate biotrophic fungus Puccinia striiformis f.sp.tritici(Pst)employs virulence effectors to disturb host immunity and causes devastating stripe rust disease.However,our understanding of how Pst effectors regulate host defense responses remains limited.In this study,we determined that the Pst effector Hasp98,which is highly expressed in Pst haustoria,inhibits plant immune responses triggered by flg22or nonpathogenic bacteria.Overexpression of Hasp98 in wheat(Triticum aestivum)suppressed avirulent Pst-triggered immunity,leading to decreased H2O2accumulation and promoting P.striiformis infection,whereas stable silencing of Hasp98 impaired P.striiformis pathogenicity.Hasp98 interacts with the wheat mitogenactivated protein kinase TaMAPK4,a positive regulator of plant resistance to stripe rust.The conserved TEY motif of TaMAPK4 is important for its kinase activity,which is required for the resistance function.We demonstrate that Hasp98inhibits the kinase activity of TaMAPK4 and that the stable silencing of TaMAPK4 compromises wheat resistance against P.striiformis.These results suggest that Hasp98 acts as a virulence effector to interfere with the MAPK signaling pathway in wheat,thereby promoting P.striiformis infection.

New insights in the battle between wheat and Puccinia striiformis

Wheat stripe rust caused by Puccinia striiformis f.sp.tritici(Pst)poses a great threat to wheat production worldwide.The rapid change in virulence of Pst leads to a loss of resistance in currently resistant wheat cultivars,which results in frequent disease epidemics.Therefore,a major focus is currently placed on investigating the molecular mechanisms underlying this rapid variation of pathogenicity and coevolving wheat resistance.Limited by the lack of a system for stable transformation of Pst and the difficulties in wheat transformation,it is not easy to generate deeper insights into the wheat-Pst interaction using established genetic methods.Nevertheless,considerable effort has been made to unravel the wheat-Pst interaction and significant progress is being made.Histology and cytology have revealed basic details of infection strategies and defense responses during wheat-Pst interactions,identified cellular components involved in wheat-Pst interactions,and have helped to elucidate their role in the infection process or in plant defense responses.Transcriptome and genome sequencing has revealed the molecular features and dynamics of the wheat-Pst pathosystem.Extensive molecular analyses have led to the identification of major components in the wheat resistance response and in Pst virulence.Studies of wheat-Pst interactions have now entered a new phase in which cellular and molecular approaches are being used.This review focuses on the cellular biology of wheat-Pst interactions and integrates the emerging data from molecular analyses with the histocytological observations.

A secreted catalase contributes to Puccinia striiformis resistance to host-derived oxidative stress

Plants can produce reactive oxygen species(ROS)to counteract pathogen invasion,and pathogens have also evolved corresponding ROS scavenging strategies to promote infection and pathogenicity.Catalases(CATs)have been found to play pivotal roles in detoxifying H_(2)O_(2)formed by superoxide anion catalyzed by superoxide dismutases(SODs).However,few studies have addressed H_(2)O_(2)removing during rust fungi infection of wheat.In this study,we cloned a CAT gene PsCAT1 from Puccinia striiformis f.sp.tritici(Pst),which encodes a monofunctional heme-containing catalase.PsCAT1 exhibited a high degree of tolerance to pH and temperature,and forms high homopolymers.Heterologous complementation assays in Saccharomyces cerevisiae reveal that the signal peptide of PsCAT1 is functional.Overexpression of PsCAT1 enhanced S.cerevisiae resistance to H_(2)O_(2).Transient expression of PsCAT1 in Nicotiana benthamiana suppressed Bax-induced cell death.Knockdown of PsCAT1 using a host-induced gene silencing(HIGS)system led to the reduced virulence of Pst,which was correlated to H_(2)O_(2)accumulation in HIGS plants.These results indicate that PsCAT1 acts as an important pathogenicity factor that facilitates Pst infection by scavenging host-derived H_(2)O_(2).

Determination of heterozygosity for avirulence/virulence loci through sexual hybridization of Puccinia striiformis f. sp. tritici

Wheat stripe rust caused by Puccinia striiformis f. sp. tritici is one of the most devastating diseases of wheat worldwide and resistant cultivars are vital for its management. Therefore, investigating the heterozygosity of the pathogen is important because of rapid virulence changes in isolates heterozygous for avirulence/virulence.An isolate of P. striiformis f. sp. tritici was selfed on Berberis shensiana to determine the heterozygosity for avirulence/virulence loci. One hundred and twenty progeny isolates obtained from this selfing were phenotyped using 25 lines of wheat containing Yrgenes and genotyped with 96 simple sequencing repeat markers, with51 pathotypes and 55 multi-locus genotypes being identified. All of these were avirulent on lines with Yr5,Yr10, Yr15, Yr24 and Yr26 and virulent on lines with Yr17,Yr25 and YrA, indicating that the parental isolate was homozygously avirulent or homozygously virulent for these loci. Segregation was found for wheat lines with Yr1,Yr2, Yr4, Yr6, Yr7, Yr8, Yr9, Yr27, Yr28, Yr32, Yr43, Yr44,YrExp2, YrSp, YrTr1, YrTye and YrV23. The 17 cultivars to which the Pst was identified as heterozygous with respect to virulence/avirulence should not be given priority in breeding programs to obtain new resistant cultivars.

Comments on “Determination of heterozygosity for avirulence/virulence loci through sexual hybridization of Puccinia striiformis f. sp. tritici”

Over the past decades Puccinia striiformis f.sp.tritici（Pst）has developed into one of the most,if not the most important fungal pathogen in wheat production worldwide.In China,Pst has caused numerous epidemics with partially devastating yield losses[1].The occurrence of the'warrior'race in Europe in 2011 also caused significant problems[2].Pst,like other obligate biotrophs,is characterized by a high degree of genetic variability,especially with respect

Fine mapping and characterization of stripe rust resistance gene YrAYH in near-isogenic lines derived from a cross involving wheat landrace Anyuehong

Stripe rust,caused by Puccinia striiformis f.sp.tritici(Pst),is a devastating disease in wheat worldwide.Discovering and characterizing new resistance genes/QTL is crucial for wheat breeding programs.In this study,we fine-mapped and characterized a stripe rust resistance gene,YRAYH,on chromosome arm 5BL in the Chinese wheat landrace Anyuehong(AYH).Evaluations of stripe rust response to prevalent Chinese Pst races in near-isogenic lines derived from a cross of Anyuehong and Taichung 29 showed that YrAYH conferred a high level of resistance at all growth stages.Fine mapping using a large segregating population of 9748 plants,narrowed the YRAYH locus to a 3.7 Mb interval on chromosome arm 5BL that included 61 annotated genes.Transcriptome analysis of two NIL pairs identified 64 upregulated differentially expressed genes(DEGs)in the resistant NILs(NILs-R).Annotations indicated that many of these genes have roles in plant disease resistance pathways.Through a combined approach of fine-mapping and transcriptome sequencing,we identified a serine/threonine-protein kinase SRPK as a candidate gene underlying YrAYH.A unique 25 bp insertion was identified in the NILs-R compared to the NILs-S and previously published wheat genomes.An InDel marker was developed and co-segregated with YrAYH.Agronomic trait evaluation of the NILs suggested that YrAYH not only reduces the impact of stripe rust but was also associated with a gene that increases plant height and spike length.

High-throughput RNA sequencing reveals differences between the transcriptomes of the five spore forms of Puccinia striiformis f.sp.tritici,the wheat stripe rust pathogen

The devastating wheat stripe(yellow)rust pathogen,Puccinia striiformis f.sp.tritici(Pst),is a macrocyclic and heteroe-cious fungus.Pst produces urediniospores and teliospores on its primary host,wheat,and pycniospores and aeciospores are produced on its alternate hosts,barberry(Berberis spp.)or mahonia(Mahonia spp.).Basidiospores are developed from teliospores and infect alternate hosts.These five spore forms play distinct roles in Pst infection,disease development,and fungal survival,etc.However,the specific genes and mechanisms underlying these functional differences are largely unknown.In this study,we performed,for the first time in rust fungi,the deep RNA sequencing to examine the transcriptomic shift among all five Pst spore forms.Among a total of 29,591 identified transcripts,951 were specifically expressed in basidiospores,whereas 920,761,266,and 110 were specific for teliospores,pycniospores,aeciospores,and urediniospores,respectively.Additionally,transcriptomes of sexual spores,namely pycniospores and basidiospores,showed significant differences from those of asexual spores(urediniospores,teliospores,and aeciospores),and transcriptomes of urediniospores and aeciospores were more similar to each other than to the three other spore forms.Especially,the basidiospores and pycniospores which infected the berberis shows wide differences in the cell wall degrading-enzymes and mating and pheromone response genes.Besides,we also found that there are 6234 differential expressed genes between the urediniospores and pycniospores,while only have 3 genes have alternative splicing enents,suggesting that differential genes expression may make more contribution than AS.This comprehensive transcriptome profiling can substantially improve our understanding of the developmental biology of the wheat stripe rust fungus.

A small knottin-like peptide negatively regulates in wheat to stripe rust resistance during early infection of wheat

Although Blufensins(Bln)have important functions in the response of plants to biotic stress the precise functioning of Bln in wheat remains largely unknown.Here we isolated a Bln gene(TaBln4)from Suwon 11 infected by Puccinia striiformis f.sp.tritici(Pst).Expression of TaBln4 increased in host plants at the early stage of infection with a virulent Pst race(CYR31)but was unchanged in response to infection by an avirulent race(CYR23).Transcription levels of TaBln4 were also regulated by hormone and abiotic stresses.Expression of TaBln4 in tobacco leaves suppressed Bax-induced programmed cell death.Knockdown of TaBln4 by virus-induced gene silencing inhibited colonization of race CYR31 by increasing the accumulation of H2O2 and formation of hypersensitive responses(HR).Transient overexpression of TaBln4 by a transient overexpression system(BSMV-VOX)increased the susceptibility of wheat to CYR31.Results from bimolecular fluorescence complementation and pull-down assays demonstrated that TaBLN4 interacted with calmodulin.Taken together,our results suggest that TaBln4 negatively regulates resistance in wheat to Pst in a reactive oxygen species(ROS)-and HR-dependent manner.

Genetic Analysis and Molecular Mapping of a Stripe Rust Resistance Gene YrH9014 in Wheat Line H9014-14-4-6-1

Stripe rust, caused by Puccinia striiformis f. sp. tritici （Pst）, is one of the most widespread and destructive wheat diseases in many wheat-growing regions of the world. The winter wheat translocation line H9014-14-4-6-1 has all stage resistance. To identify stripe rust resistance genes, the segregating populations were developed from the cross between H9014-14-4-6-1 and Mingxian 169 （a wheat cultivar susceptible to all Pst races identified in China）. The seedlings of the parents and F1 plants, Fz, F3 and BC1 generations were tested with Pst races under controlled greenhouse conditions. Two genes for resistance to stripe rust were identified, one dominant gene conferred resistance to SUN11-4, temporarily designated YrH9014 and the other recessive gene conferred resistance to CYR33. The bulked segregant analysis and simple sequence repeat （SSR） markers were used to identify polymorphic markers associated with YrH9014. Seven polymorphic SSR markers were used to genotype the F2 population inoculated with SUN11-4. A linkage map was constructed according to the genotypes of seven SSR markers and resistance gene. The molecular map spanned 24.3 cM, and the genetic distance of the two closest markers Xbarc13 and Xbarc55 to gene locus was 1.4 and 3.6 cM, respectively. Based on the position of SSR marker, the resistance gene YrH9014 was located on chromosome arm 2BS. Amplification of a set of nulli-tetrasomic Chinese Spring lines with SSR marker Xbarc13 indicated that YrH9014 was located on chromosome 2B. Based on chromosomal location, the reaction patterns and pedigree analysis, YrH9014 should be a novel resistance gene to stripe rust. This new gene and flanking markers got from this study should be useful for marker-assisted selection （MAS） in breeding programs for stripe rust.

Characterization and Molecular Mapping of a Stripe Rust Resistance Gene in Synthetic Wheat CI110

Stripe rust,caused by Puccinia striiformis f.sp.tritici（Pst）,is one of the most destructive diseases of wheat（Triticum aestivum L.）.To diversify stripe rust-resistant resources for wheat breeding programs,a CIMMYT synthetic wheat line CI110 was identified to be resistant to 28 isolates of Pst,including 6 Chinese prevalent races CYR28-CYR33.Genetic analysis indicated that a single dominant gene was responsible for the stripe rust resistance in CI110,temporarily designated YrC110.A molecular map,harboring YrC110 and 9 linked SSR markers,was constructed through simple sequence repeat（SSR）,and bulked segregant analysis.These linked markers and YrC110 were assigned on the short arm of chromosome 1B using the Chinese Spring nullisomic-tetrasomic and ditelosomic stocks.Gene postulation based on seedling reaction patterns to 30 Pst isolates suggested that the resistance gene YrC110 seemed different from the other known resistance genes tested,such as Yr9,Yr10,Yr15,Yr24,and Yr26/YrCH42.Four SSR markers Xbarc187150,Xgwm18227,Xgwm11223,and Xbarc240292 distinguished YrC110 from Yr10,Yr15,Yr24,and Yr26/YrCH42,and could be used as diagnostic ones for YrC110 in wheat resistant breeding programs against stripe rust.

Molecular Mapping of a Stripe Rust Resistance Gene YrH9020a Transferred from Psathyrostachys huashanica Keng on Wheat Chromosome 6D

Stripe rust （yellow rust）, caused by Puccinia striiformis f. sp. tritici （Pst）, is one of the most devastating diseases of wheat throughout the world. H9020-1-6-8-3 is a translocation line originally developed from interspeciifc hybridization between wheat line 7182 and Psathyrostachys huashanica Keng and is resistant to most Pst races in China. To identify the resistance gene（s） in the translocation line, H9020-1-6-8-3 was crossed with susceptible cultivar Mingxian 169, and seedlings of the parents, F1, F2, F3, and BC1 generations were tested with prevalent Chinese Pst race CYR32 under controlled greenhouse conditions. The results indicated that there is a single dominant gene, temporarily designated as YrH9020a, conferring resistance to CYR32. The resistance gene was mapped by the F2 population from Mingxian 169/H9020-1-6-8-3. It was linked to six microsatellite markers, including Xbarc196, Xbarc202, Xbarc96, Xgpw4372, Xbarc21, and Xgdm141, lfanked by Xbarc96 and Xbarc202 with at 4.5 and 8.3 cM, respectively. Based on the chromosomal locations of these markers and the test of Chinese Spring （CS） nullitetrasomic and ditelosomic lines, the gene was assigned to chromosome 6D. According to the origin and the chromosomal location, YrH9020a might be a new resistance gene to stripe rust. The lfanking markers linked to YrH9020a could be useful for marker-assisted selection in breeding programs.