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Near-Isogenic Lines of Wheat Carrying Genes for Stem Rust Resistance
Crop Science
Abstract
(...) A stem rust susceptible, day-length insensitive genotype was developed for use as a recurrent parent in the production of NILs. Thirty-eight NILs were produced and tested with nine races of stem rust. Nineteen of the NILs carried numbered Sr (stem rust resistance) genes at identified loci, while 19 carried genes at loci whose relationship to the identified loci was not known. Of the latter group, seven genes appeared to be different from any of the numbered genes. The remaining 12 NILs either were shown to carry numbered genes or still were incompletely tested (...)
... Kazakhstanean researchers Kulikova and Kurbatova (1977b) proposed to add test varieties Lee, Selkirk, Mironovskaya 808 and Bezostaya 1 to the basic set for identification of biotypes within the stem rust races. Genetic differentiation that use isogenous Sr lines as differentiators has appeared to be an improved method of studying race composition of the fungus (Roelfs, Martens, 1988;Knott, 1990). It means that if a new race infects the line containing Sr5 gene, it will infect all the varieties that possess only this resistance gene, and at high concentration of this race in the populations this gene should not be used in development of new varieties because they will be infected by rust. ...
... durum (Desf.) Husn.), and then introgressed into genome of soft wheat (Knott, 1990). It is localized on chromosome 6AL, originates in Khapli variety (T. ...
... It is localized on chromosome 6AL, originates in Khapli variety (T. durum), and its testing line is Khapstein/9*LMPG (Knott, 1990). The gene demonstrates resistance to many races in Ug99 group (types of infection vary within 2-2+) (Jin et al., 2007). ...
Wheat stem rust caused by the biotrophic fungus Puccinia graminis f. sp.tritici is a dangerous disease that seriously damages the economics in many countries of the world. The review contains information about epidemics of wheat stem rust and causes of their emergence worldwide. Recently wheat stem rust epidemics have been recorded in the northern regions of Kazakhstan and on the territories adjacent to Omsk Region of Russia. It has been shown that severe wheat stem rust epidemics occur mainly due to the emergence of new virulent races of the disease agent and to growing susceptible wheat cultivars. New methods of studying the race composition of the fungus are described as well as the use of the previous and current differential sets for race determination
of P. graminis f. sp. tritici. The results of developing molecular markers and assessing their effectiveness in studying stem rust races are presented. Wheat stem rust races dominant in major grain-growing countries of the globe and their typical peculiarities are described. The paper contains information on identification of race Ug99 and of its variations including data on areas of their dissemination and on their virulence to
Sr-resistance genes. The existence and emergence of other races of the agent potentially dangerous for commercially important genes for stem rust resistance is also described. Currently in nature strongly virulent races of P. graminis f. sp. tritici are circulating with wide geographical coverage and their virulence is absolutely different from the virulence of race Ug99. Historical and modern data on studying the race composition of the
pathogen in Kazakhstan are summarized. It is stated that the use of the old standard differential set and an incomplete North American system of race nomenclature in experiments prevents measuring similarity between Kazakhstani races and the worldwide known races of the pathogen. It has been shown that there is a need to continue studies on the intraspecies structure of the disease agent’s population in Kazakhstan with
the use of the modern differential set, on determination of race composition and ways of emergence of new races potentially dangerous for commercial wheat varieties.
... A set of 34 ND durum germplasm was selected for marker validation based on their similar breeding history and common resistance sources with the resistance parents, Medora and Sceptre (Fig. S1). To further validate the identification of the resistance gene mapped in this study as Sr13, one of the reference genetic stocks for Sr13, Khapstein/9*LMPG-6 (Knott 1990), along with Khapstein (PI 210125) and the original Sr13 donor Khapli (CItr 4013), were genotyped with markers linked to Sr13. ...
... The Sr13 gene name is defined by several genetic stocks, including Khapstein/9*LMPG-6 (Knott 1990; McIntosh et al. 2008). To test if the chromosome region where the resistance to TTKSK mapped in the four durum populations was also present in Khapstein/9*LMPG-6, markers from these four maps were evaluated in Khapstein/ 9*LMPG-6 and its recurrent susceptible parent LMPG-6 (Knott 1990), as well as in the tetraploid (Khapli) and hexaploid (Khapstein) Sr13 donors (Fig. 2). ...
... The Sr13 gene name is defined by several genetic stocks, including Khapstein/9*LMPG-6 (Knott 1990; McIntosh et al. 2008). To test if the chromosome region where the resistance to TTKSK mapped in the four durum populations was also present in Khapstein/9*LMPG-6, markers from these four maps were evaluated in Khapstein/ 9*LMPG-6 and its recurrent susceptible parent LMPG-6 (Knott 1990), as well as in the tetraploid (Khapli) and hexaploid (Khapstein) Sr13 donors (Fig. 2). Of the 19 SSR markers evaluated on 6AL, only dupw167 and barc104b were polymorphic between LMPG-6 and Khapstein/ 9*LMPG-6, and the same alleles present in the latter were detected in Khapstein (PI 210125) (Fig. 2, barc104b; data not shown for dupw167), indicating that the distal 6AL chromosome region in Khapstein/9*LMPG-6 was transferred from Khapstein (Fig. 1, shaded area). ...
Wheat stem rust caused by Puccinia graminis f. sp. tritici, can cause significant yield losses. To combat the disease, breeders have deployed resistance genes both individually and in combinations to increase resistance durability. A new race, TTKSK (Ug99), identified in Uganda in 1999 is virulent on most of the resistance genes currently deployed, and is rapidly spreading to other regions of the world. It is therefore important to identify, map, and deploy resistance genes that are still effective against TTKSK. One of these resistance genes, Sr13, was previously assigned to the long arm of chromosome 6A, but its precise map location was not known. In this study, the genome location of Sr13 was determined in four tetraploid wheat (T. turgidum ssp. durum) mapping populations involving the TTKSK resistant varieties Kronos, Kofa, Medora and Sceptre. Our results showed that resistance was linked to common molecular markers in all four populations, suggesting that these durum lines carry the same resistance gene. Based on its chromosome location and infection types against different races of stem rust, this gene is postulated to be Sr13. Sr13 was mapped within a 1.2-2.8 cM interval (depending on the mapping population) between EST markers CD926040 and BE471213, which corresponds to a 285-kb region in rice chromosome 2, and a 3.1-Mb region in Brachypodium chromosome 3. These maps will be the foundation for developing high-density maps, identifying diagnostic markers, and positional cloning of Sr13.
... Currently, approximately 30 major genes conferring resistance to Pgt races from the seedling stage are known, plus five slow-rusting or resistance genes at adult plant stage, are being studied (Pumphrey, 2012). Thirty-eight near-isogenic lines of bread wheat carrying 21 single designated Sr genes for resistance to stem rust were produced and tested with nine races of stem rust by Knott (1990). To date, molecular markers have been identified for several stem rust resistance genes (Sr 2,6,9a,13,24,25,26,31,36,38,39,40) to deploy them in new elite cultivars and diagnostic DNA markers are being developed for other Sr genes (Pumphrey, 2012). ...
... from the University of Sydney. The lines carrying those genes were resistant to all nine Pgt races tested by Knott (1990). ...
The gene diversity for rust and powdery mildew disease resistance is very narrow in durum wheat
varieties. The chromosome 6V#4 from D. villosum contains genes for broad-spectrum resistance to diseases
caused by Puccinia graminisf. sp. tritici (Pgt) (stem rust), Puccinia triticina Eriks. (Pt) (leaf rust), Puccinia striiformis f. sp. tritici Eriks. (Psi) (stripe rust), and Blumeria graminis f. sp. tritici (Bgt) (powdery mildew). Progenies from the cross of a durum wheat F7 line (derived from 'Cappelli' x 'Peleo') with CS-DA6V#4 (a disomic addition line of chromosome 6V#4 to the T. aestivum 'Chinese Spring' genomic background), were backcrossed to durum wheat lines in order to selected plants for resistance to airborne Bgt inoculum in the greenhouse as a marker for the presence of chromosme 6V#4. The chromosome number of the progenies of two of those plants, '467-68.1' and '491-50.2', ranged from 28 to 36 with an average of 2n=31, and the presence of 6V#4 was revealed by GISH. The seedlings of the two progenies were tested for response to different races (isolates) of Pgt and Pt under controlled experiments at CAR-HAS in Hungary, and to Pgt and Bgt under controlled experiments at CRA-QCE in Italy. All the seedlings from the '467-68.1' and '491-50.2' progenies. were resistant to Pt and Bgt, and the '467-68.1' progeny displayed resistance to Pgt. The NAU/Xibao15902 molecular marker linked to Pm21, a putative locus in 6V#4 with a gene determining resistance to Bgt, was detected in all the seedlings of the two progenies. Plants with chromosome number ranging from 28 to 30 are now field tested and are being prepared for the final round of backcross to the '4.5.1' durum wheat recurrent parent.
... During a recent disease resistance screening of the USDA National Small Grains Collection (NSGC), Newcomb et al. (2013) (Newcomb et al. 2013;Roelfs et al. 1992;Stakman et al. 1962). Single-plant selections of PI 626573 were used as males and crossed with the susceptible Canadian line LMPG-6 (Little Club// Prelude/8*Marquis/3/Gabo) to evaluate the mode of inheritance Knott 1990). Chisquare analysis of seedling tests at the F 3 generation fits a 3:1 segregation ratio, indicating that resistance is conferred by a single dominant nuclear gene ). ...
... The previously developed population was created by crossing single-plant selections of PI 626573, PI 626573-2, and PI 626573-3, to the female parent LMPG-6 Knott 1990). The LMPG-6/PI 626573 population was advanced via single seed descent to the F 6 generation. ...
Managing wheat stem rust, caused by Puccinia graminis f. sp. tritici (Pgt), is imperative for the preservation of global food security. The most effective strategy is pyramiding several resistance genes into adapted wheat cultivars. A search for new resistance sources to Pgt race TTKSK resistance identified a spring wheat landrace, accession PI 626573, as a potentially novel source of resistance. A cross was made between LMPG-6, a susceptible spring wheat line, and PI 626573 and used to develop a recombinant inbred population to map the resistance. Bulk segregant analysis (BSA) of LMPG-6/PI 626573 F2 progeny determined resistance was conferred by a single dominant gene given the provisional designation SrWLR. The BSA identified nine microsatellite (SSR) markers on the long arm of chromosome 2B associated with the resistant phenotype. Fifteen polymorphic SSRs, including the nine identified in the BSA, were used to produce a linkage map of chromosome 2B, positioning SrWLR in an 8.8 cM region between the SSRs GWM47 and WMC332. This region has been reported to contain the wheat stem rust resistance genes Sr9 and SrWeb, the latter conferring resistance to Pgt race TTKSK. The 9,000 marker Illumina Infinium iSelect SNP assay was used to further saturate the SrWLR region. The cosegregating SNP markers IWA6121, IWA6122, IWA7620, IWA8295, and IWA8362 further delimited the SrWLR region distally to a 1.9 cM region. The present study demonstrates the iSelect assay to be an efficient tool to delimit the region of a mapping population and establish syntenic relationships between closely related species.
... Wheat line W3534 carries (at the least) the stem rust resistance gene Sr22 (The and McIntosh 1975), thus PGTAUSPE-10-1 is a candidate for the AvrSr22 avirulence specificity. However, when we infiltrated the same Pf strain into unrelated wheat genotypes 'Schomburgk' and DK14 that are also reported to carry Sr22 (Knott 1990; Paull et al. 1994) no HR resulted (unpublished data). However, reference to the early literature indicates that a gene called Sr22 was independently introgressed into wheat from two different diploid wheat accessions, one Triticum monococcum R.L.5244 (Kerber and Dyck 1973), a cultivated diploid AA genome wheat, and the second, T. boeoticum G21, a wild AA genome wheat (Gerechter-Amitai et al. 1971), with both sources of Sr22 mapped to wheat chromosome arm 7AL (The and McIntosh 1975). ...
... However, reference to the early literature indicates that a gene called Sr22 was independently introgressed into wheat from two different diploid wheat accessions, one Triticum monococcum R.L.5244 (Kerber and Dyck 1973), a cultivated diploid AA genome wheat, and the second, T. boeoticum G21, a wild AA genome wheat (Gerechter-Amitai et al. 1971), with both sources of Sr22 mapped to wheat chromosome arm 7AL (The and McIntosh 1975). The T. monococcum source is present in W3534 (The 1973), the T. boeoticum source in 'Schomburgk', while the source in DK14 is not specified in its original description (Knott 1990). All three of these lines carried a specific DNA marker linked to Sr22 from both sources (Periyannan et al. 2011). ...
Large numbers of candidate effectors from fungal pathogens are being identified through whole genome sequencing and in planta expression studies. Although Agrobacterium-mediated transient expression has enabled high-throughput functional analysis of effectors in dicot plants, this assay is not effective in cereal leaves. Here we show that a non-pathogenic Pseudomonas fluorescens (Pf) engineered to express the T3SS of Pseudomonas syringae and the wheat pathogen Xanthomonas translucens (Xt) deliver fusion proteins containing T3SS signals from P. syringae (AvrRpm1) and X. campestris (AvrBs2) Avr proteins, respectively, into wheat leaf cells. A calmodulin-dependent adenylate cyclase (Cya) reporter protein was delivered effectively into wheat and barley by both bacteria. Absence of any disease symptoms with Pf, makes it more suitable than Xt) for detecting hypersensitive cell death (HR) induced by effector protein with avirulence activity. We further modified the delivery system by removal of the myristoylation site from the AvrRpm1 fusion to prevent its localisation to the PM which could inhibit recognition of an Avr protein. Delivery of the flax rust AvrM protein by the modified delivery system into transgenic tobacco leaves expressing the corresponding M resistance protein induced a strong HR indicating that the system is capable of delivering a functional rust Avr protein. In a preliminary screen of effectors from the stem rust fungus Puccinia graminis f. sp. tritici, we identified one effector that induced a host genotype-specific HR in wheat. Thus the modified AvrRpm1:effector/Pf system is an effective tool for large scale screening of pathogen effectors for recognition in wheat.
... The 122 F 2 individuals were derived from a cross between a susceptible wheat line, LMPG, and its near-isogenic line Sr36/9*LMPG carrying Sr36. The genetic stock Sr36/ 9*LMPG was developed by Dr. D. Knott at the University of Saskatchewan, Saskatoon, Canada (Knott, 1990). An additional 112 F 2 individuals were derived from a cross between a susceptible wheat cultivar Chinese Spring (CS) and the resistant line W2691Sr36-1, carrying Sr36 in the genetic background of W2691. ...
... Based on the previous studies, all seven reference stocks that were widely used as sources of Sr36 in wheat breeding programs (McIntosh et al., 1995) were used in this study: two breeding lines, Sr36/9*LMPG (Knott, 1990) and W2691Sr36-1, and six cultivars, CItr 12632 (= W1656) and CItr 12633 (= W1657) (Allard and Shands, 1954), Idaed 59, Mengavi, Timvera (PI 351987 and PI 237648) (Pridham, 1939), and CItr 14050. In addition to these reference stocks, we examined a range of international germplasm carrying Sr36 as listed by Roelfs (1988a) and McIntosh et al. (1995), including cultivars developed in Australia, Canada, Mexico, South Africa, and the United States (Table 1). ...
The wheat stem rust resistance gene Sr36, derived from Triticum timopheevi, confers a high level of resistance against a new race (TTKS, or commonly known as Ug99) and many other races of Puccinia graminis f. sp. tritici. Because Sr36-virulent races exist, breeding for durable resistance would require pyramiding Sr36 with other genes, a process that can be facilitated by DNA markers. The aim of this study was to identify and validate microsatellite markers for the detection of Sr36 in wheat breeding programs. Two populations of 122 F2 (LMPG x Sr36/9*LMPG) and 112 F2 ('Chinese Spring' x W2691Sr36-1) were evaluated for stem rust reaction. Both populations exhibited distorted segregation with a preferential transmission of the Sr36-carrying segment. Three markers, Xstm773-2, Xgwm319, and Xwmc477, were in complete linkage with Sr36 in the LMPG x Sr36/9*LMPG population. In the Chinese Spring x W2691Sr36-1 population, Xgwm319 was 0.9 cM away from Xstm773-2, Xwmc477, and Sr36. These codominant markers were easy to score and diagnostic for Sr36 in a set of 76 wheat cultivars and breeding lines developed in 12 countries. Together, these markers can be used in marker-assisted selection of Sr36.
... Both RL6071 and KU168-2 are hexaploid wheat lines. Tetraploid wheat reference single-gene lines carrying each known allele of Sr13, namely Rusty-Kl-B (Sr13a), Rusty-14803 (Sr13b), Rusty-ST464-C1 (Sr13c), and CAT-A1 (Sr13d), (Gill et al. 2021;Zhang et al. 2017) along with hexaploid line Sr13a (Knott 1990), were used in multi-race stem rust comparisons with KU168-2 and a subset of DH lines. ...
Key message
Sr67 is a new stem rust resistance gene that represents a new resource for breeding stem rust resistant wheat cultivars
Abstract
Re-appearance of stem rust disease, caused by the fungal pathogen Puccinia graminis f. sp. tritici (Pgt), in different parts of Europe emphasized the need to develop wheat varieties with effective resistance to local Pgt populations and exotic threats. A Kyoto University wheat (Triticum aestivum L.) accession KU168-2 was reported to carry good resistance to leaf and stem rust. To identify the genomic region associated with the KU168-2 stem rust resistance, a genetic study was conducted using a doubled haploid (DH) population from the cross RL6071 × KU168-2. The DH population was phenotyped with three Pgt races (TTKSK, TPMKC, and QTHSF) and genotyped using the Illumina 90 K wheat SNP array. Linkage mapping showed the resistance to all three Pgt races was conferred by a single stem rust resistance (Sr) gene on chromosome arm 6AL, associated with Sr13. Presently, four Sr13 resistance alleles have been reported. Sr13 allele-specific KASP and STARP markers, and sequencing markers all showed null alleles in KU168-2. KU168-2 showed a unique combination of seedling infection types for five Pgt races (TTKSK, QTHSF, RCRSF, TMRTF, and TPMKC) compared to Sr13 alleles. The phenotypic uniqueness of the stem rust resistance gene in KU168-2 and null alleles for Sr13 allele-specific markers showed the resistance was conferred by a new gene, designated Sr67. Since Sr13 is less effective in hexaploid background, Sr67 will be a good source of stem rust resistance in bread wheat breeding programs.
... For HRS wheat, the procedure is more complex due to the need to increase the ploidy level from tetraploid to hexaploid. To accomplish this rapidly, we crossed RWG35, 36 and 37 to LMPG6, a hexaploid wheat near-universal susceptible to stem rust (Knott 1990 (Zadoks et al. 1974) were carefully removed from pots and 1 cm of bright white root-tip meristems were excised and placed in water vials in an ice-bath for 24 h. Root-tips were then fixed in Farmer's solution (3:1 ethanol:glacial acetic acid) for a minimum of 12 h, followed by hydrolysis in 1 M HCl for 10 min at 60 °C. ...
Key message
Yield and quality tests of wheat lines derived from RWG35 show they carry little, or no linkage drag and are the preferred source of Sr47 for stem rust resistance.
Abstract
Three durum wheat (Triticum turgidum L. subsp. durum) lines, RWG35, RWG36, and RWG37 carrying slightly different Aegilops speltoides introgressions, but each carrying the Sr47 stem rust resistance gene, were backcrossed to three durum and three hard red spring (HRS) wheat (Triticum aestivum L.) cultivars to produce 18 backcross populations. Each population was backcrossed to the recurrent parent six times and prepared for yield trials to test for linkage drag. Lines carrying the introgression (S-lines) were compared to euploid sibling lines (W-lines) and their parent. Yield trials were conducted from 2018 to 2021 at three locations. Three agronomic and several quality traits were studied. In durum, lines derived from RWG35 had little or no linkage drag. Lines derived from RWG36 and RWG37 still retained linkage drag, most notably involving yield and thousand kernel weight, but also test weight, falling number, kernel hardness index, semolina extract, semolina protein content, semolina brightness, and peak height. In HRS wheat, the results were more complex, though the general result of RWG35 lines having little or no linkage drag and RWG36 and RWG37 lines retaining linkage drag still applied. But there was heterogeneity in the Glenn35S lines, and Linkert lines had problems combining with the Ae. speltoides introgressions. We concluded that introgressions derived from RWG35 either had eliminated linkage drag or any negative effects were minor in nature. We recommend that breeders who wish to incorporate Sr47 into their cultivars should work exclusively with germplasm derived from RWG35.
... This shows that the NDSU breeding program selected for stem rust resistance to most of the Pgt-races used in this study. It was reported that resistance to the Ug99 lineage in the North American durum cultivars is mainly due to Sr13 alleles that were first identified in durum wheat and was then transferred to hexaploid wheat (Knott, 1990). However, in our study we observed variations in the ITs to the Pgt-races. ...
Leaf rust, caused by Puccinia triticina (Pt), stripe rust caused by Puccinia striiformis f.sp. tritici (Pst), and stem rust caused by Puccinia graminis f. sp. tritici (Pgt) are major diseases to wheat production globally. Host resistance is the most suitable approach to manage these fungal pathogens. We investigated the phenotypic and genotypic structure of resistance to leaf rust, stem rust, and stripe rust pathogen races at the seedling stage in a collection of advanced durum wheat breeding lines and cultivars adapted to Upper Mid-West region of the United States. Phenotypic evaluation showed that the majority of the durum wheat genotypes were susceptible to Pt isolates adapted to durum wheat, whereas all the genotypes were resistant to common wheat type-Pt isolate. The majority of genotypes were resistant to stripe rust and stem rust pathogen races. The durum panel genotyped using Illumina iSelect 90 K wheat SNP assay
was used for genome-wide association mapping (GWAS). The GWAS revealed 64 marker-trait associations (MTAs) representing six leaf rust resistance loci located on chromosome arms 2AS, 2AL, 5BS, 6AL, and 6BL. Two of these loci were identified at the positions of Lr52 and Lr64 genes, whereas the remaining loci are most likely novel. A total of 46 MTAs corresponding to four loci located on chromosome arms
1BS, 5BL, and 7BL were associated with stripe rust response. None of these loci correspond to designated stripe rust resistance genes. For stem rust, a total of 260 MTAs, representing 22 loci were identified on chromosome arms 1BL, 2BL, 3AL, 3BL, 4AL, 5AL, 5BL, 6AS, 6AL, 6BL, and 7BL. Four of these loci were located at the positions of known genes/alleles (Sr7b, Sr8155B1, Sr13a, and Sr13b). The discovery of known and novel rust resistance genes and their linked SNPs will help diversify rust resistance in durum wheat.
... This shows that the NDSU breeding program selected for stem rust resistance to most of the Pgt-races used in this study. It was reported that resistance to the Ug99 lineage in the North American durum cultivars is mainly due to Sr13 alleles that were first identified in durum wheat and was then transferred to hexaploid wheat (Knott, 1990). However, in our study we observed variations in the ITs to the Pgt-races. ...
Leaf rust, caused by Puccinia triticina (Pt), stripe rust caused by Puccinia striiformis f. sp. tritici (Pst), and stem rust caused by Puccinia graminis f. sp. tritici (Pgt) are major diseases to wheat production globally. Host resistance is the most suitable approach to manage these fungal pathogens. We investigated the phenotypic and genotypic structure of resistance to leaf rust, stem rust, and stripe rust pathogen races at the seedling stage in a collection of advanced durum wheat breeding lines and cultivars adapted to Upper Mid-West region of the United States. Phenotypic evaluation showed that the majority of the durum wheat genotypes were susceptible to Pt isolates adapted to durum wheat, whereas all the genotypes were resistant to common wheat type-Pt isolate. The majority of genotypes were resistant to stripe rust and stem rust pathogen races. The durum panel genotyped using Illumina iSelect 90 K wheat SNP assay was used for genome-wide association mapping (GWAS). The GWAS revealed 64 marker-trait associations (MTAs) representing six leaf rust resistance loci located on chromosome arms 2AS, 2AL, 5BS, 6AL, and 6BL. Two of these loci were identified at the positions of Lr52 and Lr64 genes, whereas the remaining loci are most likely novel. A total of 46 MTAs corresponding to four loci located on chromosome arms 1BS, 5BL, and 7BL were associated with stripe rust response. None of these loci correspond to designated stripe rust resistance genes. For stem rust, a total of 260 MTAs, representing 22 loci were identified on chromosome arms 1BL, 2BL, 3AL, 3BL, 4AL, 5AL, 5BL, 6AS, 6AL, 6BL, and 7BL. Four of these loci were located at the positions of known genes/alleles (Sr7b, Sr8155B1, Sr13a, and Sr13b). The discovery of known and novel rust resistance genes and their linked SNPs will help diversify rust resistance in durum wheat.
... One hundred thirteen recombinant inbred lines (RILs) (F 7:9 ) were developed from a cross between LMPG-6 [a stem rust-susceptible spring wheat line (Knott, 1990)] and CI 14275 (LMPG-6/CI 14275) through single-seed descent at the USDA-ARS Cereal Disease Laboratory (CDL), Minnesota in the United States. ...
Stem rust caused by Puccinia graminis f. sp. tritici (Pgt) remains a constraint to wheat production in East Africa. In this study, we characterized the genetics of stem rust resistance, identified QTLs, and described markers associated with stem rust resistance in the spring wheat line CI 14275. The 113 recombinant inbred lines, together with their parents, were evaluated at the seedling stage against Pgt races TTKSK, TRTTF, TPMKC, TTTTF, and RTQQC. Screening for resistance to Pgt races in the field was undertaken in Kenya, Ethiopia, and the United States in 2016, 2017, and 2018. One gene conferred seedling resistance to race TTTTF, likely Sr7a. Three QTL were identified that conferred field resistance. QTL QSr.cdl-2BS.2, that conferred resistance in Kenya and Ethiopia, was validated, and the marker Excalibur_c7963_1722 was shown to have potential to select for this QTL in marker-assisted selection. The QTL QSr.cdl-3B.2 is likely Sr12, and QSr.cdl-6A appears to be a new QTL. This is the first study to both detect and validate an adult plant stem rust resistance QTL on chromosome arm 2BS. The combination of field QTL QSr.cdl-2BS.2, QSr.cdl-3B.2, and QSr.cdl-6A has the potential to be used in wheat breeding to improve stem rust resistance of wheat varieties.
... fromAnderson et al. (2007),Jin et al. (2007),Knott (1990),Macharia (2013), andNjau et al. (2009). b Indicates the year the line was released or published. ...
A spring wheat nested associated mapping (NAM) population, KUWNSr (Kenyan and U.S. wheat nested association mapping population for stem rust resistance), was developed at the University of Minnesota, St. Paul, MN, USA. KUWNSr (Reg. no. MP‐12, NSL 533796 MAP, experimental designation SrNAM) was primarily developed to genetically characterize stem rust resistance as the 10 male parents—nine Kenyan and one University of Minnesota wheat cultivars—exhibited medium to high adult plant resistance to African and North American races of the stem rust pathogen (Puccinia graminis f. sp. tritici). Each parent was crossed to the stem rust susceptible line LMPG‐6, and populations were developed via single‐seed descent. Aggregately, the resulting 10 populations, consisting of 852 recombinant inbred lines, formed the KUWNSr population. KUWNSr was evaluated in four environments: two in the United States and one each in Kenya and South Africa. A high‐density genetic map was developed using genotyping‐by‐sequencing, resulting in 11,221 single nucleotide polymorphism markers mapped to all 21 chromosomes. In addition to stem rust resistance, the population segregates for other disease resistance traits such as leaf and stripe rust and agronomic traits such as plant height, spike morphology, and days to heading. As one of the first wheat NAM populations developed, KUWNSr is a valuable resource for understanding the genetic architecture of wheat growth and development, morphology, and resistance or tolerance to biotic and abiotic stresses.
... A differential line with Sr36 was resistant to 50% of the races while it was susceptible to 50%. Similar to the present study, wheat stem rust resistance gene Sr was known to be effective against most races worldwide [14,23] but it indicated high infection rates in some countries, including Ethiopia [24,25]. Likewise, the avirulence/virulence response of wheat stem rust isolates collected from West Hararghe zone showed that differential lines with resistance genes SrTmp and Sr24 were 100% resistant to pathogen races. ...
Wheat is one of the important major crops of Hararghe Highlands. It is third in land coverage and total production after sorghum and maize. However, the wheat stem rust disease is threatening production of wheat in this region. So, this research was conducted with the following objective: to determine the population of Puccinia graminis f. sp. tritici in Hararghe Highlands. A total of 200 fields were surveyed and stem rust samples were collected and transported to Kulumsa Agricultural Research Center for race analysis. Inoculation of differentials carrying resistance genes Sr24 and Sr-Tmp indicated typical low infection types on all isolates. Isolates EH5, EH8, and EH3 from East Hararghe and WH2, WH1, and WH3 from West Hararghe showed high virulence of infection in all differential lines. Ten (10) races were identified by using Puccinia graminis tritici code system: TTGSK, PTJQK, TTSSK, TTKSK, TRSSK, and TTJQK from East Hararghe and TTTSK and TTSQK from West Hararghe zones. Race TTSSK was most frequent (25%) followed by TTKSK (25%) in East Hararghe. Race TTSSK showed 50% frequency of occurrence in West Hararghe zones. The low frequency of occurrences indicated high variability of the races in the survey areas. Therefore, monitoring of populations of pathogens is important for the national and regional research centers. Detection of pathogen virulence evolution and of currently effective resistance genes is necessary and must be applied within a system of resistance gene management.
... To determine genetic control of TTKSK resistance in MV Zelma, 94 F 2 seedlings were derived from a cross between LMPG-6 and MV Zelma. LMPG-6 is a selection of stem rust susceptible line LMPG (Knott, 1990). To test the allelic relationship between the resistance gene in MV Zelma and Sr15, two additional populations were derived: MV Zelma/ W2691-Sr15 (75 F 2:3 families derived) and MV Zelma/Prelude-Sr15 (45 F 2:3 families derived). ...
The wheat stem rust fungus, Puccinia graminis f. sp. tritici (Pgt), race TTKSK and related races pose a serious threat to world wheat production. Knowing the effectiveness of wheat stem rust resistance (Sr) genes against Pgt race TTKSK is fundamental in mitigating this threat through resistance breeding. Sr15 was previously identified as being ineffective against Pgt race TTKSK. Here we present multi‐race disease phenotyping data, linkage analyses, allelism testing, and haplotype analyses to support the conclusion that Sr15 is effective against Pgt race TTKSK. Resistance to race TTKSK was mapped to Sr15 in a biparental population. Thirty‐two accessions with Sr15 displayed seedling resistance phenotypes against race TTKSK. However, these accessions were susceptible as seedlings at high temperatures (22‐25°C), consistent with previous reports that the interaction between avirulent Pgt isolates and Sr15 is temperature‐sensitive. Markers STS638, wri4, and KASP_IWB30995 were found to predict the presence of Sr15, suggesting the utility of these assays for marker‐assisted selection in breeding programs. The effectiveness of Sr15 to specific Pgt races and temperatures makes it a less‐desirable TTKSK‐effective gene. Wheat lines assayed as resistant to race TTKSK at the seedling stage may possess Sr15 and breeders should be aware of the limitations of Sr15 for conferring stem rust resistance.
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... PI 362698 is postulated to have Sr57 based on DNA markers, however any additional resistance genes present within the line were unknown [29]. To evaluate the mode of inheritance for TTKSK resistance a single plant selection of PI 362698, PI 362698-1, was crossed to the susceptible Canadian line LMPG-6 (Little Club//Prelude/8*Marquis/3/Gabo) [30,35]. Mendelian ratios corresponding for one to three genes were not observed during seedling resistance evaluations at the F 2 generation, suggesting the stem rust resistance to TTKSK found in PI 362698-1 is complex [30]. ...
Background:
Research to identify and characterize stem rust resistance genes in common wheat, Triticum aestivum, has been stimulated by the emergence of Ug99-lineage races of the wheat stem rust pathogen, Puccinia graminis f. sp. tritici (Pgt), in Eastern Africa. The Montenegrin spring wheat landrace PI 362698 was identified as a source of Pgt resistance. This accession exhibits resistance to multiple Ug99-lineage and North American Pgt races at seedling and adult-plant stages. A recombinant inbred population was developed by crossing the susceptible line LMPG-6 with a single plant selection of PI 362698. A genetic map was constructed using the Illumina iSelect 90 K wheat assay and the markers csLv34, NB-LRR3, and wMAS000003 and quantitative trait locus (QTL) analysis was performed.
Results:
QTL analysis identified five significant QTLs (α = 0.05) on chromosomes 2B, 3B, 6A, 6D, and 7A associated with wheat stem rust resistance. The QTL on chromosome 3B was identified using both field data from Kenya (Pgt Ug99-lineage races) and seedling data from Pgt race MCCF. This QTL potentially corresponds to Sr12 or a new allele of Sr12. The multi-pathogen resistance gene Sr57 located on chromosome 7D is present in PI 362698 according to the diagnostic markers csLv34 and wMAS000003, however a significant QTL was not detected at this locus. The QTLs on chromosomes 2B, 6A, and 6D were identified during seedling trials and are thought to correspond to Sr16, Sr8a, and Sr5, respectively. The QTL identified on chromosome 7A was detected using MCCF seedling data and may be Sr15 or a potentially novel allele of recently detected Ug99 resistance QTLs.
Conclusions:
The combination of resistance QTLs found in PI 362698 is like the resistance gene combination present in the broadly resistant cultivar Thatcher. As such, PI 362698 may not be a landrace as previously thought. PI 362698 has been crossed with North Dakota wheat germplasm for future breeding efforts. Additional work is needed to fully understand why the combination of genes present in PI 362698 and 'Thatcher' provide such durable resistance.
... durum (Desf.) Husn.] and was then transferred to hexaploid wheat (Khapstein/9*LMPG) (19). The domesticated emmer wheat [T. ...
Significance
Wheat provides a substantial proportion of the calories and proteins consumed by humans, but further production increases are necessary to feed a growing human population. Reducing yield losses caused by pathogens can contribute to these increases. In this study, we report the identification of Sr13 , a gene from pasta wheat that confers resistance to the new virulent races of the stem rust pathogen that appeared in Africa at the beginning of this century. We identified three different resistance forms of Sr13 and developed a diagnostic marker to accelerate their deployment in wheat breeding programs. In addition, Sr13 can be a useful component of transgenic cassettes including multiple resistance genes.
... This population was developed originally for the genetic mapping of the Ug99 resistance gene SrWLR from PI626573 (Zurn et al. 2014). LMPG-6 is a spring wheat line from Canada with a pedigree of Little club//Prelude/8*Marquis/3/Gabo (Knot 1990), and PI 626573 is an Iranian landrace. Four commonly used tan spot differential lines were included in each inoculation experiment including Salamouni (insensitive to all three NEs and resistant to all Ptr races), Glenlea (susceptible to Ptr ToxA-producing races), 6B662 (susceptible to Ptr ToxB-producing races), and 6B365 (susceptible to Ptr ToxC-producing races). ...
Key message:
Tan spot susceptibility is conferred by multiple interactions of necrotrophic effector and host sensitivity genes. Tan spot of wheat, caused by Pyrenophora tritici-repentis, is an important disease in almost all wheat-growing areas of the world. The disease system is known to involve at least three fungal-produced necrotrophic effectors (NEs) that interact with the corresponding host sensitivity (S) genes in an inverse gene-for-gene manner to induce disease. However, it is unknown if the effects of these NE-S gene interactions contribute additively to the development of tan spot. In this work, we conducted disease evaluations using different races and quantitative trait loci (QTL) analysis in a wheat recombinant inbred line (RIL) population derived from a cross between two susceptible genotypes, LMPG-6 and PI 626573. The two parental lines each harbored a single known NE sensitivity gene with LMPG-6 having the Ptr ToxC sensitivity gene Tsc1 and PI 626573 having the Ptr ToxA sensitivity gene Tsn1. Transgressive segregation was observed in the population for all races. QTL mapping revealed that both loci (Tsn1 and Tsc1) were significantly associated with susceptibility to race 1 isolates, which produce both Ptr ToxA and Ptr ToxC, and the two genes contributed additively to tan spot susceptibility. For isolates of races 2 and 3, which produce only Ptr ToxA and Ptr ToxC, only Tsn1 and Tsc1 were associated with tan spot susceptibility, respectively. This work clearly demonstrates that tan spot susceptibility in this population is due primarily to two NE-S interactions. Breeders should remove both sensitivity genes from wheat lines to obtain high levels of tan spot resistance.
... The F 1 seeds were used to generate 138 DH lines and 140 recombinant inbred lines (RILs) (F 5:8 ). LMPG-6 (Little club/Prelude*8/Marquis/3/Gabo) is a susceptible wheat line developed by Knott (1990). PI 177906 is hexaploid wheat landrace from the NSGC that was collected by J. Harlan in Corum, Turkey in 1948. ...
Wheat landrace PI 177906 has seedling resistance to stem rust caused by Puccinia graminis f. sp. tritici races TTKSK, TTKST, and BCCBC and field resistance to the Ug99 race group. Parents, 140 recombinant inbred lines, and 138 double haploid (DH) lines were evaluated for seedling resistance to races TTKSK and BCCBC. Parents and the DH population were evaluated for field resistance to Ug99 in Kenya. The 90K wheat SNP genotyping platform was used to genotype the parents and populations. Goodness-of-fit tests indicated that two dominant genes in PI 177906 conditioned seedling resistance to TTKSK. Two major loci for seedling resistance were consistently mapped to the chromosome arms 2BL and 6DS. The BCCBC resistance was mapped to the same location on 2BL as the TTKSK resistance. Using field data from the three seasons, two major QTL were consistently detected at the same regions on 2BL and 6DS. Based on the mapping result, race specificity, and the infection type observed in PI 177906, the TTKSK resistance on 2BL is likely due to Sr28. One SNP marker (KASP_ IWB1208) was found to be predictive for the presence of the TTKSK resistance locus on 2BL and Sr28.
... The F 1 seeds were used to generate two populations composed of 121 DH lines and 124 RILs (F 5:8 ). LMPG-6 (Little club/Prelude*8/Marquis/3/ Gabo) is a susceptible wheat line developed by Knott (1990). Accession CItr 4311 is a hexaploid wheat landrace from the NSGC that was collected in 1914 from Fars province, Iran. ...
Key message:
A gene for Ug99 resistance from wheat landrace CItr 4311 was detected on the long arm of chromosome 2B. Wheat landrace CItr 4311 has seedling resistance to stem rust caused by Puccinia graminis f. sp. tritici race TTKSK and field resistance to the Ug99 race group. Parents, F1 seedlings, 121 doubled haploid (DH) lines, and 124 recombinant inbred lines (RILs) developed from a cross between CItr 4311 and the susceptible line LMPG-6 were evaluated for seedling resistance to race TTKSK. Goodness-of-fit tests indicated that a single dominant gene in CItr 4311 conditioned the TTKSK resistance. The 90 K wheat iSelect SNP platform was used to genotype parents and the DH population. The seedling resistance locus was mapped to the chromosome arm 2BL. Parents and the DH population were evaluated for field resistance in Kenya. One major QTL for the field resistance was consistently detected in the same region on 2BL as the seedling resistance. Using KASP assays, five linked SNP markers were used to verify the result in the 124 RIL, 35 wheat accessions, 46 DH lines from the LMPG-6/PI 165194 cross and F1 seedlings, and susceptible bulks derived from crosses between six resistant landraces with LMPG-6. Race specificity, mapping results, and haplotype similarity with lines with Sr9h (Gabo 56, Timstein, and PI 670015), support the hypothesis that the Sr gene in CItr 4311 and the landraces is Sr9h. The KASP assays developed in this study will be useful for pyramiding the TTKSK resistance from CItr 4311 with other Sr genes effective against Ug99.
... Origin, pedigree, and stem rust reaction of parent lines used to develop the NAM population. Information obtained from Njau et al.[90], Macharia[66], Anderson et al.[32], and Knott[91]. Year (in parenthesis) indicates the year the line was For USA environment, the rust response of parent lines were averaged from StP12 and StP13 environments. For Africa environment, only Ken13 data is shown. ...
We combined the recently developed genotyping by sequencing (GBS) method with joint mapping (also known as nested association mapping) to dissect and understand the genetic architecture controlling stem rust resistance in wheat (Triticum aestivum). Ten stem rust resistant wheat varieties were crossed to the susceptible line LMPG-6 to generate F6 recombinant inbred lines. The recombinant inbred line populations were phenotyped in Kenya, South Africa, and St. Paul, Minnesota, USA. By joint mapping of the 10 populations, we identified 59 minor and medium-effect QTL (explained phenotypic variance range of 1% – 20%) on 20 chromosomes that contributed towards adult plant resistance to North American Pgt races as well as the highly virulent Ug99 race group. Fifteen of the 59 QTL were detected in multiple environments. No epistatic relationship was detected among the QTL. While these numerous small- to medium-effect QTL are shared among the families, the founder parents were found to have different allelic effects for the QTL. Fourteen QTL identified by joint mapping were also detected in single-population mapping. As these QTL were mapped using SNP markers with known locations on the physical chromosomes, the genomic regions identified with QTL could be explored more in depth to discover candidate genes for stem rust resistance. The use of GBS-derived de novo SNPs in mapping resistance to stem rust shown in this study could be used as a model to conduct similar marker-trait association studies in other plant species.
... To monitor field populations in the Ug99 race group more effectively, we developed lines with gene combinations involving Sr24, Sr31, and Sr36 that could differentiate races TTKSK, TTKST, and TTTSK in the field. Intercrosses were made between lines Agent/9*LMPG, Benno/6*LMPG, and CI12632/8*LMPG (Knott 1990) that carried resistance genes Sr24, Sr31, and Sr36, respectively. Selections were made by testing with multiple stem rust races at various generations, starting at F 3 . ...
Frequent emergence of new variants in the Puccinia graminis f. sp. tritici (Pgt) Ug99 race group in Kenya has made pathogen survey a priority. We analyzed 140 isolates from 78 Pgt samples collected in Kenya between 2008 and 2014 and identified six races, including three not detected prior to 2013. Genotypic analysis of 20 isolates from 2013 and 2014 collections showed that the new races TTHST, TTKTK, and TTKTT belong to the Ug99 race group. International advanced breeding lines were evaluated against an isolate of TTKTT (Sr31, Sr24, and SrTmp virulence) at the seedling stage. From 169 advanced lines from Kenya, 23% of lines with resistance to races TTKSK and TTKST were susceptible to TTKTT, and from two North American regional nurseries 44% and 91% of resistant lines were susceptible. Three lines with combined resistance genes were developed to facilitate pathogen monitoring and race identification. These results indicate the increasing virulence and variability in the Kenyan Pgt population, and reveal vulnerabilities of elite germplasm to new races.
... Line L8474D1 (HY-320*3/BW553) shares the parent line BW553 with AC Cadillac (BW90*3/BW553), which contains the gene SrCad (Hiebert et al. 2011;McCallum and DePauw 2008). LMPG-6 is a selection of LMPG, a stem rust susceptible line (Knott 1990). AC Cadillac (BW90*3/ BW553) was available through the Triticeae Coordinated Agricultural Project (TCAP). ...
The stem rust fungus, particularly race TTKSK (Ug99), poses a serious threat to world wheat production. Gene Sr42 or SrCad (which could be the same gene or an allele of Sr42) is effective against race TTKSK. However, known genetic markers for Sr42 are mostly SSR markers which are generally labor intensive to use. In this study, we mapped a race TTKSK resistance gene derived from PI 595667 at the same locus as Sr42 on chromosome 6DS. Based on position, pedigree and infection-type information, we propose that this gene is SrCad (Sr42). We enriched the genetic map for the Sr42 region using genotyping by sequencing (GBS) and array-derived SNP markers. In total, 21 SNP markers were discovered, spanning a genetic distance of 27.2 cM. Nine of them are derived from GBS and twelve from the Illumina iSelect 90K SNP assay. Ten of the twenty-one SNP markers are closely linked (<2.2 cM, or co-segregating) with Sr42. We converted five of the closely linked SNP markers into uniplex KASP assays which will better facilitate marker-assisted selection. We validated the KASP assay in a doubled haploid wheat population derived from a three-way cross between accessions PI 410954, RB07, and Faller that shared an uncharacterized resistance gene mapped at approximately the same locus as PI 595667. The development of closely linked (co-segregating), codominant, sequence-based SNP assays will aid marker-assisted selection and map-based cloning of Sr42.
... tritici race TTKSK. The remaining 41 accessions with seedling resistance to race TTKSK were crossed to the susceptible line LMPG-6 (Knott 1990), from which F 1 seed were obtained from 33 crosses. A single F 1 seed from each cross was sown to generate F 2 populations. ...
Wheat breeders worldwide are seeking new sources of resistance to Puccinia graminis f. sp tritici (Pgt) race TTKSK. To prioritize field-resistant landraces for follow-up genetic studies to test for the presence of new resistance genes, seedling response to Pgt race TTKSK, molecular markers linked to specific Sr genes, segregation ratios among progeny from crosses, and bulked segregant analyses (BSA) were used. Thirty three spring wheat landraces with seedling resistance to Pgt race TTKSK were crossed to a susceptible genotype, LMPG-6. The segregation ratios of stem rust reactions in F2 seedlings fit a single dominant gene model in 31 populations and progeny from two crosses gave ambiguous results. Using the 90K wheat SNP genotyping platform, BSA showed that the seedling resistance in 29 accessions is probably controlled by loci on chromosome 2BL. For the three remaining accessions, BSA revealed that the seedling resistance is most likely controlled by previously unreported genes. For confirmation, two populations were advanced to the F2:3 and screened against Pgt race TTKSK. Segregation of the F2:3 families fit a 1:2:1 ratio for a single dominant gene. Using the F2:3 families, BSA located the TTKSK locus on chromosome 6DS to the same location as Sr42.
... Plant and fungal materials. Wheat near-isogenic lines carrying resistance genes Sr5, Sr6, Sr24, Sr30, or Sr36 in a Little club/ Marquis/Prelude/Gabo (LMPG) background were obtained from Dr. Knott, University of Saskatchewan (Knott 1990 , and 1176 (virulence phenotype HKCJC) were obtained from isolates kept at the Cereal Research Centre, Morden. Isolates were increased and their virulence phenotypes were verified using 20 standard differential lines and the international letter code nomenclature (Jin et al. 2008). ...
Race-specific resistance of wheat to Puccinia graminis f. sp. tritici is primarily posthaustorial and often involves the induction of a hypersensitive response (HR). The aim of this study was to investigate host defense responses induced in interactions between P. graminis f. sp. tritici races and wheat lines carrying different race-specific stem rust resistance (Sr) genes. In incompatible interactions between wheat lines carrying Sr36 in three genetic backgrounds (LMPG, Prelude, or W2691) and avirulent P. graminis f. sp. tritici races MCCFC or RCCDM, callose accumulated within 24 h in wheat guard cells contacted by a P. graminis f. sp. tritici appressorium, and P. graminis f. sp. tritici ingress was inhibited following appressorium formation. Accordingly, the expression of transcripts encoding a callose synthase increased in the incompatible interaction between LMPG-Sr36 and avirulent P. graminis f. sp. tritici race MCCFC. Furthermore, the inhibition of callose synthesis through the infiltration of 2-deoxy-D-glucose (DDG) increased the ability of P. graminis f. sp. tritici race MCCFC to infect LMPG-Sr36. A similar induction of callose deposition in wheat guard cells was also observed within 24 h after inoculation (hai) with avirulent P. graminis f. sp. tritici race HKCJC on LMPG-Sr5 plants. In contrast, this defense response was not induced in incompatible interactions involving Sr6, Sr24, or Sr30. Instead, the induction of an HR and cellular lignification were noted. The manifestation of the HR and cellular lignification was induced earlier (24 hai) and was more extensive in the resistance response mediated by Sr6 compared with those mediated by Sr24 or Sr30. These results indicate that the resistance mediated by Sr36 is similar to that mediated by Sr5 but different from those triggered by Sr6, Sr24, or Sr30. Resistance responses mediated by Sr5 and Sr36 are prehaustorial, and are a result of very rapid recognition of molecules derived from avirulent isolates of P. graminis f. sp. tritici, in contrast to the responses triggered in lines with Sr6, Sr24, and Sr30.
... aestivum) landrace from the NSGC that was collected from Bosnia and Herzegovina in 1972. LMPG-6 is a highly susceptible wheat line developed by Knott (1990). F 1 plants derived from F 1 seed of the same spike were used to generate 216 BC 1 F 2 families by crossing with the recurrent parent LMPG-6. ...
Key message
A new gene for Ug99 resistance from wheat landrace PI 374670 was detected on the long arm of chromosome 7A.
Abstract
Wheat landrace PI 374670 has seedling and field resistance to stem rust caused by Puccinia graminis f. sp tritici Eriks. & E. Henn (Pgt) race TTKSK. To elucidate the inheritance of resistance, 216 BC1F2 families, 192 double haploid (DH) lines, and 185 recombinant inbred lines (RILs) were developed by crossing PI 374670 and the susceptible line LMPG-6. The parents and progeny were evaluated for seedling resistance to Pgt races TTKSK, MCCFC, and TPMKC. The DH lines were tested in field stem rust nurseries in Kenya and Ethiopia. The DH lines were genotyped with the 90K wheat iSelect SNP genotyping platform. Goodness-of-fit tests indicated that a single dominant gene in PI 374670 conditioned seedling resistance to the three Pgt races. The seedling resistance locus mapped to the long arm of chromosome 7A and this result was verified in the RIL population screened with the flanking SNP markers using KASP assays. In the same region, a major QTL for field resistance was detected in a 7.7 cM interval and explained 34–54 and 29–36 % of the variation in Kenya and Ethiopia, respectively. Results from tests with specific Pgt races and the csIH81 marker showed that the resistance was not due to Sr22. Thus, a new stem rust resistance gene or allele, either closely linked or allelic to Sr15, is responsible for the seedling and field resistance of PI 374670 to Ug99.
... Similarly, Lr67 (another APR gene present in some of the wheat varieties bred by Norman Borlaug in the 1940s and 1950s) was used in conjunction with major R genes. This is important when considering the durability of APR genes, because the R genes acted to prevent reproduction of all uninfective pathogen isolates (Knott 1990) thereby shielding the Sr2 and Lr67 genes from direct interaction with the pathogen. As a consequence, while Sr2 and Lr67 have retained efficacy since their introduction into hexaploid wheat (McIntosh et al. 1995), the independent contribution of these genes to the intensity of selection pressure exerted on pathogen populations cannot be determined. ...
Genetically controlled resistance provides plant breeders with an efficient means of controlling plant disease, but this approach has been constrained by practical difficulties associated with combining many resistance genes together and strong evolutionary responses from pathogen populations leading to subsequent resistance breakdown. However, continuing advances in molecular marker technologies are revolutionizing the ability to rapidly and reliably manipulate resistances of all types - major gene, adult plant and quantitative resistance loci singly or multiply into individual host lines. Here, we argue that these advances provide major opportunities to deliberately design deployment strategies in cereals that can take advantage of the evolutionary pressures faced by target pathogens. Different combinations of genes deployed either within single host individuals or between different individuals within or among crops, can be used to reduce the size of pathogen populations and generate patterns of disruptive selection. This will simultaneously limit immediate epidemic development and reduce the probability of subsequent evolutionary change in the pathogen for broader infectivity or increased aggressiveness. The same general principles are relevant to the control of noncereal diseases, but the most efficacious controls will vary reflecting the range of genetic options available and their fit with specific ecology and life-history combinations.
... To validate the presence of both SrWeb and Sr28 in CDl001, we derived a total of 292 F 2 seeds from CDl001/lMPG-6. Wheat line lMPG-6 is a stem rust susceptible hard red spring wheat (Knott 1990). We obtained the parents of Gabo 56, Timstein (CI 12347), Kenya 58 (CI 12471), and Gabo (CI 12795), to assess the origin of resistance to Ug99 in Gabo 56. ...
Key message:
Wheat stem rust resistance gene SrWeb is an allele at the Sr9 locus that confers resistance to Ug99. Race TTKSK (Ug99) of Puccinia graminis f. sp. tritici, the causal fungus of stem rust, threatens global wheat production because of its broad virulence to current wheat cultivars. A recently identified Ug99 resistance gene from cultivar Webster, temporarily designated as SrWeb, mapped near the stem rust resistance gene locus Sr9. We determined that SrWeb is also present in Ug99 resistant cultivar Gabo 56 by comparative mapping and an allelism test. Analysis of resistance in a population segregating for both Sr9e and SrWeb demonstrated that SrWeb is an allele at the Sr9 locus, which subsequently was designated as Sr9h. Webster and Gabo 56 were susceptible to the Ug99-related race TTKSF+ from South Africa. Race TTKSF+ possesses unique virulence to uncharacterized Ug99 resistance in cultivar Matlabas. This result validated that resistance to Ug99 in Webster and Gabo 56 is conferred by the same gene: Sr9h. The emergence of pathogen virulence to several resistance genes that are effective to the original Ug99 race TTKSK, including Sr9h, suggests that resistance genes should be used in combinations in order to increase resistance durability.
... Seeds of breeding lines and germplasm were obtained from the USDA-ARS Cereal Disease Laboratory, St. Paul, MN. This set of accessions included two additional pairs of NILs, Sr9a/9*LMPG (Knott, 1990) and 'Marquis'9*/Red Egyptian (Knott, 1965), carrying the Sr9a allele in a diff erent genetic background of LMPG and Marquis, respectively. Red Egyptian (CItr 12345), the original source of the Sr9a allele, was also included in the analysis. ...
Host resistance to stem rust of wheat (Triticum aestivum L.), caused by Puccinia graminis Pers.:Pers. f. sp. tritici Eriks. & E. Henn., is more effective and durable when several stem rust resistance (Sr) genes are pyramided into a single line. We studied the Sr9a allele, one of six known alleles at the Sr9 locus on chromosome 2BL, using 116 F2 plants and their F2:3 families derived from the cross of near‐isogenic lines (NILs) ‘Chinese Spring’ and ISr9a‐Ra. Four microsatellite markers were identified that mapped within 3.6 cM proximal to the Sr9a locus. Fifty‐nine wheat accessions were screened with the three codominant and one dominant markers to determine their polymorphism information content (PIC). The marker Xgwm47 revealed 12 alleles and had the highest PIC value of 0.85. We attempted to postulate the presence of Sr9a by phenotypic screening. In accessions that had multiple Sr genes, however, it was not possible to postulate Sr9a due to masking effects. Despite the ambiguity of phenotypic evaluation, Xgwm47 was diagnostic for Sr9a in additional NILs tested. These results suggest that Xgwm47 will be a useful tool for marker‐assisted selection of Sr9a in wheat breeding programs.
... The first set of 44 lines and two recurrent and MCC (1 and 2 2, respectively) were sufficiently parents was tested with isolates of nine races of stem distinct to suggest that they carry different genes. Alterrust (Knott, 1990). A second set of 158 lines and parents natively, one line may carry a gene or genes that modify was tested with the same nine isolates plus one addiits reaction to LCB and MCC. ...
The winter wheat (Triticum aestivum L.) cultivar Triumph 64 has resistance to a number of races of stem rust (Puccinia graminis Pers. f. sp. tritici Eriks. & E. Henn) and has been used as a supplementary differential in identifying stem rust races. Triumph 64 was crossed and backcrossed to a susceptible wheat, LMPG, to study the inheritance of its resistance to races MCC and LCB. Four additional backcrosses to LMPG were made to produce near‐isogenic lines (NILs) carrying the Triumph 64 genes for resistance to races MCC and LCB. Twenty‐two NILs were tested with isolates of 10 stem rust races to determine the number of genes for resistance that were present. The genetic study indicated that Triumph 64 carries two genes conditioning resistance to both races MCC and LCB, and four genes conditioning resistance only to LCB. However, the NILs produced from Triumph 64 appeared to carry at least nine Sr genes, six giving resistance to both races MCC and LCB, and only one giving resistance just to LCB. Furthermore, some of the NILs were resistant to races TMH(15B‐1) and TMH(15B‐4) to which Triumph 64 is susceptible. One possible explanation for the results is that Triumph 64 carries one or more suppressors that were lost during the backcrossing, allowing the suppressed Sr genes to be expressed. Four of the NILs were resistant to all 10 races of stem rust and should be useful in wheat breeding.
... The variation in the IT pattern observed for the two cultivars, however, suggested either the presence of an additional gene in cv. Promessa, or modified expression of Sr30 because previous studies have shown that its expression can vary with genetic background (Knott, 1990; Bariana et al., 2001). The presence of Sr30 has not been widely reported in European germplasm but it is common in Australian and CIMMYT germplasm (McIntosh et al., 1995). ...
Sixty five wheat cultivars grown in the United Kingdom were characterised for seedling stem rust and stripe rust resistance genes using Australian pathotypes of Puccinia graminis f. sp. tritici and Puccinia striiformis f. sp. tritici, respectively. The studies detected eight stem rust resistance genes (Sr5, Sr8a, Sr9g, Sr12, Sr30, Sr3l., Sr36 and Sr38) and seven stripe rust resistance genes (Yr1, Yr6, Yr7, Yr9, Yr17, Yr27, YrHVII) either singly or in combinations, among which the linked genes Sr31 and Yr9 were the most common. The stem rust resistance genes identified have limited breeding value in Australia and world-wide because virulence for all occurs in many geographical areas. However, for stripe rust resistance, several cultivars represent potentially new sources of resistance. Resistance in these cultivars may be due to uncharacterised resistance gene(s) or gene combination(s) that could not be resolved with the array of pathotypes used. The information presented, when combined with previous characterisation of leaf rust resistance genes in these cultivars, is useful for plant breeders in rationalising germplasm enhancement programs.
... Infection types on the differential lines represent the typical range of low infection responses at optimum environmental conditions. b Data on infection responses and pedigree for most differential lines are from Green (1981), Knott (1990), andMcIntosh et al. (1995). 5%. ...
Stem rust is an important disease of cereal crops that is primarily controlled in Canada through cultivar resistance. Annual stem rust surveys are conducted to provide early detection of novel races with virulence to currently grown cultivars and to identify changes in virulence frequency in the pathogen population. Stem rust samples were collected in Manitoba, eastern Saskatchewan, Ontario, and British Columbia in 2001. Stem rust was not found on cultivated wheat, but was found on commercial barley and oat fields in eastern Manitoba (trace to 20% severity) and in western Manitoba and eastern Saskatchewan (<5% severity). Some late-planted oat fields in the Red River Valley region of Manitoba had moderate to heavy (5%–40% severity) stem rust infection. Eight races of Puccinia graminis f. sp. tritici were found on wheat, seven on cultivated barley, and nine on wild barley. The predominant races on wheat and wild barley were RCRSK, QFCSR, and QCCJN. The predominant races on cultivated barley were QCCJN and RCCJN, which could threaten barley production. Eight races of Puccinia graminis f. sp. avenae were found on cultivated oat and five on wild oat. NA67 and NA29 were the predominant races on cultivated (57.6% and 15.8%) and wild (41.6% and 29.6%) oat, while NA76 increased to 14.4% on cultivated oat in 2001. NA67 and NA76 are virulent on all currently grown Canadian oat cultivars. A new race (NA77) avirulent to most oat cultivars was detected in Manitoba in 2001.
... Infection types on the differential lines represent the typical range of low infection responses at optimum environmental conditions. b Data on infection responses and pedigree for most differential lines are from Green (1981), Knott (1990), D.R. Knott (unpublished data), and McIntosh et al. (1995). Table 1. ...
Stem rust is a devastating disease of cereal crops that is currently controlled, in Canada, primarily through the use of resistant cultivars. Annual surveys are conducted throughout Canada to monitor rust severity and obtain rust collections that are used to determine the virulence spectrum of each pathogen population. This is necessary for the detection of novel races that may express high virulence to currently grown cereal cultivars and to identify changes in virulence in the pathogen population. No stem rust was observed on cultivated spring wheat in 2000. Stem rust severity was light (<5%) on barley and oat in Manitoba, eastern Saskatchewan, and Ontario in 2000 and stem rust was not detected in other regions. Stem rust samples were collected from Hordeum jubatum, Avena fatua, and trap-plot nurseries and commercial fields of wheat, barley, and oat in Manitoba, eastern Saskatchewan, and Ontario from June to September 2000. Eight races of Puccinia graminis f. sp. tritici were found in collections from wheat, 11 from cultivated barley, and 2 from wild barley, with RCRSK as the dominant race on all three hosts. However, a cluster of races (QCCJ_, RCCJ_, and RMCJ_) with virulence to cultivated barley composed 69.2% of the population in Manitoba and Saskatchewan and poses a threat to barley production in this region. Five races of P. graminis f. sp. avenae were found in collections from cultivated oat and six from wild oat. Races NA67 and NA29 were the most common on cultivated (52.2 and 30.4%, respectively) and wild (18.6 and 55.0%, respectively) oat, while NA76 increased in frequency (9.6%) in Manitoba and Saskatchewan in 2000. Races NA67 and NA76 are virulent to Pg2, Pg9, and Pg13, which are the resistance genes likely present in most currently grown Canadian oat cultivars, and threaten commercial oat production in this region.
... Like the substitution lines (UNRAU et al. 1956), the near-isogenic lines are the tools widely and efficiently used in genetic experiments with common wheat (PUGSLEY 1972;KNOTT 1990), while they are more rarely applied to study of tetraploid wheat (JOHNSON et al. 1983;WATANABE 1994). One of the reasons of the rare usage of tetraploid wheat is the insufficient knowledge of tetraploid wheat genetics, as well as the low adaptation to the environment of the main cultivated tetraploid wheat species, T. durum Desf. ...
Variability in tetraploid wheat species for growth habit (spring vs. winter) was studied in the field and, as a result, winter growth habit samples were identified. Backcrossing on the background of Triticum discoccum cv. Black Winter Emmer developed the near-isogenic lines BSlE and BS2E carrying the dominant genes Vrn1 and Vrn2, respectively. The donors of the dominant genes Vrnl and Vrn2 were Pugsley's common wheat near-isogenic lines Triple Dirk D and Triple Dirk B, respectively. The results demonstrated that T. dicoccum near-isogenic lines with the dominant Vrn genes do not mature significantly later than the near-isogenic lines of common wheat.
... After analysing 152 isolates from regions representing the major wheat-growing areas of the country, four important stem rust resistance genes, namely Sr13, Sr30, Sr36 and SrTmp, were found to confer resistance to most of the races prevalent in Ethiopia. Sr13 and Sr36 are known to be genes effective against most races worldwide (Rowell, 1982;Roelfs et al., 1992) except occasional highinfection types in some countries (Knott, 1990), including Ethiopia (Huerta-Espino, 1992). The use of these genes as sources of resistance in other countries (Park & Wellings, 1992;McIntosh et al., 1995) corroborates the recommendation to use the aforementioned genes in breeding for resistance to stem rust for the Ethiopian wheat production. ...
Wheat stem rust samples were collected in 2006 and 2007 in the Arsi, Bale, Shewa and northwest regions of Ethiopia to determine virulence diversity and race distribution in Puccinia graminis f.sp. tritici populations. Stem rust incidence was high in Arsi, Bale and east Shewa. In northwest Ethiopia, and north and west Shewa, stem rust was prevalent at low levels. A total of 152 isolates was analysed and 22 races were identified. Races TTKSR (Ug99), TTHSR and RRTTR were predominant, with frequencies of 26·6, 17·7 and 11·1%, respectively. These races were also detected in all regions. The highly virulent race designated Ug99 was present throughout the country and dominated in all regions except northwest Ethiopia. A variant of Ug99 virulent against the stem rust resistance gene Sr24 was not detected in this study. Four stem rust resistance genes (Sr13, Sr30, Sr36 and SrTmp) were found to confer resistance to most of the races prevalent in Ethiopia. With the exception of Sr30, which is not effective against Ug99, these genes could be used in breeding for resistance to stem rust in Ethiopia.
... Marker validation was tested on Rusty, LMPG6, and the set of eight durum and 32 common wheat cultivars described by Niu et al. (2011). LMPG6 is a common wheat line from Canada with spring growth habit that is near-universally susceptible to stem rust (Knott 1990). ...
The transfer of alien genes to crop plants using chromosome engineering has been attempted infrequently in tetraploid durum wheat (Triticum turgidum L. subsp. durum). Here, we report a highly efficient approach for the transfer of two genes conferring resistance to stem rust race Pgt-TTKSK (Ug99) from goatgrass (Aegilops speltoides) to tetraploid wheat. The durum line DAS15, carrying the stem rust resistance gene Sr47 derived from Ae. speltoides, was crossed, and backcrossed, to durum 5D(5B) aneuploids to induce homeologous pairing. After a final cross to 'Rusty' durum, allosyndetic recombinants were recovered. The Ae. speltoides chromosomal segment carrying Sr47 was found to have two stem rust resistance genes. One gene conditioning an infection type (IT) 2 was located in the same chromosomal region of 2BS as Sr39 and was assigned the temporary gene symbol SrAes7t. Based on ITs observed on a diverse set of rust races, SrAes7t may be the same as Sr39. The second gene conditioned an IT 0; and was located on chromosome arm 2BL. This gene retained the symbol Sr47 because it had a different IT and map location from other stem rust resistance genes derived from Ae. speltoides. Allosyndetic recombinant lines carrying each gene on minimal alien chromosomal segments were identified as were molecular markers distinguishing each alien segment. This study demonstrated that chromosome engineering of Ae. speltoides segments is feasible in tetraploid wheat. The Sr47 gene confers high-level and broad spectrum resistance to stem rust and should be very useful in efforts to control TTKSK.
... W2691 and Line AD, a monogenic line carrying the Sr28 gene, were originally obtained from the University of Sydney (McIntosh 1978). LMPG-6 is a selection of LMPG (Little Club//Prelude/8*Marquis/3/Gabo), a stem rust susceptible spring wheat line developed by Knott (1990). W2691, LMPG-6, and a Line AD selection were obtained from the United States Department of Agriculture Cereal Disease Laboratory (St. ...
Wheat stem rust caused by Puccinia graminis f. sp. tritici can cause devastating yield losses in wheat. Over the past several decades, stem rust has been controlled worldwide through the use of genetic resistance. Stem rust race TTKSK (Ug99), first detected in Uganda in 1998, threatens global wheat production because of its unique virulence combination. As the majority of the currently grown cultivars and advanced breeding lines are susceptible to race TTKSK, sources of resistance need to be identified and characterized to facilitate their use in agriculture. South Dakota breeding line SD 1691 displayed resistance to race TTKSK in the international wheat stem rust nursery in Njoro, Kenya. Seedling screening of progeny derived from SD 1691 crossed to susceptible LMPG-6 indicated that a single resistance gene was present. Allelism and race-specificity tests indicated the stem rust resistance gene in SD 1691 was Sr28. The chromosome arm location of Sr28 was previously demonstrated to be 2BL. We identified molecular markers linked to Sr28 and validated this linkage in two additional populations. Common spring wheat cultivars in the central United States displayed allelic diversity for markers flanking Sr28. These markers could be used to select for Sr28 in breeding populations and for combining Sr28 with other stem rust resistance genes.
... Subsequently, Sr22 was transferred to hexaploid wheat and was mapped on chromosome 7A (Kerber and Dyck 1973;The 1973). Although Sr22 provides resistance to all Pgt pathotypes (except the stem rust race 316 and 317 in Israel) tested in diVerent wheat growing regions of the world, the Australian wheat cultivar Schomburgk remains the only commercially released cultivar that carries this gene (Gerechter-Amitai et al. 1971;Roelfs and Mcvey 1979;Leroux and Rijkenberg 1987;Knott 1990;Singh 1991;Khan et al. 2005). Paull et al. (1994) detected T. boeoticum alleles in several backcross derivatives carrying Sr22 using RFLP probes distributed across wheat chromosome 7A and iden-tiWed various sized T. boeoticum segments in these genotypes. ...
Stem rust resistance gene Sr22 transferred to common wheat from Triticum boeoticum and T. monococcum remains effective against commercially prevalent pathotypes of Puccinia
graminis f. sp. tritici, including Ug99 and its derivatives. Sr22 was previously located on the long arm of chromosome 7A. Several backcross derivatives (hexaploid) possessing variable sized Sr22-carrying segments were used in this study to identify a closely linked DNA marker. Expressed sequenced tags belonging to the deletion bin 7AL-0.74–0.86, corresponding to the genomic location of Sr22 were screened for polymorphism. In addition, RFLP markers that mapped to this region were targeted. Initial screening was performed on the resistant and susceptible DNA bulks obtained from backcross derivatives carrying Sr22 in three genetic backgrounds with short T. boeoticum segments. A cloned wheat genomic fragment, csIH81, that detected RFLPs between the resistant and susceptible bulks, was converted into a sequence tagged site (STS) marker, named cssu22. Validation was performed on Sr22 carrying backcross-derivatives in fourteen genetic backgrounds and other genotypes used for marker development. Marker cssu22 distinguished all backcross-derivatives from their respective recurrent parents and co-segregated with Sr22 in a Schomburgk (+Sr22)/Yarralinka (−Sr22)-derived recombinant inbred line (RIL) population. Sr22 was also validated in a second population, Sr22TB/Lakin-derived F4 selected families, containing shortened introgressed segments that showed recombination with previously reported flanking microsatellite markers.
... Roelfs (1988a), Knott (1989), andMcIntosh et al. (1995). The list included two sets of near-isogenic lines carrying Sr6, Sr6/8*LMPG (Knott 1990) and 'Kenya 58'/10*'Marquis' (Green et al. 1960), and their recurrent susceptible parents, LMPG-6 and Marquis (Table 1). A wheat line designated Sr6 (CItr 15082) derived from Kenya 58/10*Marquis//9*LMPG-1 was also included. ...
The wheat stem rust resistance gene Sr6, present in several wheat cultivars, confers a high level of resistance against a wide range of races of Puccinia graminis f. sp. tritici. Resistance conferred by Sr6 is influenced by temperature, light intensity, and genetic background of the recipient genotype. Here, we report the identification and validation of molecular markers linked to Sr6 that can be used for the detection of this gene in wheat breeding programs. A mapping population of 136 F2 plants and their F2:3 families derived from a cross between near-isogenic lines, 'Chinese Spring' and ISr6-Ra, were screened for stem rust reaction in the seedling stage. Bulked segregant analysis (BSA) based on seedling tests was used to screen 418 SSR markers that covered the entire genome of wheat. Four markers, Xwmc453, Xcfd43, Xcfd77, and Xgwm484, were mapped within a chromosome region that spanned 9.7 cM from Sr6. The closest markers, Xwmc453 and Xcfd43, were linked to Sr6 at a distance of 1.1 and 1.5 cM, respectively. The markers Xwmc453 and Xcfd43 amplified Sr6-specific marker alleles that were diagnostic for Sr6 in a diverse set of 46 wheat accessions and breeding lines developed and/or collected in Australia, Canada, China, Egypt, Ethiopia, Kenya, Mexico, South Africa, and USA. These markers can now be used for marker-assisted selection of Sr6 and for pyramiding it with other stem rust resistance genes.
... The six rust resistant accessions of T. triaristatum, two susceptible durum wheats and four susceptible bread wheats, used in this study are listed in Table 1. Wheat parent MP is a backcross of 'Prelude' to 'Marquis' that lacks a gene for stem rust resistance carried in normal 'Marquis', and LMPG-6 (derived from a cross involving the four wheat cultivars: 'Little Club', 'Marquis', 'Prelude', and 'Gabo') is a highly stem rust susceptible and day length insensitive line of bread wheat (Knott 1990). The races 1, 15, 58, 70, 70B, 75, 83, 100, 104, and 161 of leaf rust and the races 11, 15B-1, 15B-lL, 29-1, 48A, 56, I l l , C15, C18, and C33 of stem rust used in this study were originally obtained from the Agriculture Canada Research Station at Winnipeg but are maintained at the University of Saskatchewan. ...
Six accessions of Triticum triaristatum (Willd) Godr. &Gren. (syn. Aegilops triaristata) (6x, UUMMUnUn), having good resistance to both leaf rust (Puccinia recondita f.sp. tritici Rob. ex Desm) races and stem rust (P. graminis f.sp. tritici Eriks. &Henn.) races, were successfully crossed with both susceptible durum wheats (T. turgidum var. durum L., 2n = 28, AABB) and bread wheats (T. aestivum, 2n = 42, AABBDD). In some crosses, embryo rescue was necessary. The T. triaristatum resistance was expressed in all F1 hybrids. Backcrossing of the F1 hybrids to their wheat parents to produce BC1F1 plants was more difficult (seed set 0-7.14%) than to produce F1 hybrids (seed set 12.50-78.33%). The low female fertility of the F1 hybrids was due to low chromosome pairing. Only gametes with complete or nearly complete genomes from the F1 hybrids were viable. In BC2F4 populations from the cross MP/Ata2//2*MP, monosomic or disomic addition lines (2n = 21 II + 1 I or 22 II) with resistance to leaf rust race 15 (IT 1) were selected. In BC2F2 populations from the crosses CS/Ata4//2*MP and MP/Ata4//2*MP, monosomic or disomic addition lines with resistance to either leaf rust race 15 or stem rust race 15B-1 (both IT 1) were selected. Rust tests and cytology on the progeny of the disomic addition lines confirmed that the genes for rust resistance were located on the added T. triaristatum chromosomes. The homoeologous groups of the T. triaristatum chromosomes in the addition lines from the crosses MP/Ata2//2*MP, CS/Ata4//2*MP, and MP/Ata4//2*MP were determined to be 5, 2, and 7, respectively, through the detecting of RFLPs among genomes using a set of homoeologous group specific wheat cDNA probes. The addition lines with resistance to leaf rust race 15 from the crosses MP/Ata2//2*MP and CS/Ata4//2*MP were resistant to another nine races of leaf rust and the addition line with resistance to stem rust race 15B-1 from the cross MP/Ata4//2*MP was resistant to another nine races of stem rust as were their T. triaristatum parents. Since such genes provide resistance against a wide spectrum of rust races they should be very valuable in wheat breeding for rust resistance.
Wheat is an important cereal crop cultivated throughout the world. The present-day climate change has raised new threats to wheat production. Such challenges include the evolution of new pathogen races and insect biotypes causing breakdown of resistance gene(s). This chapter includes details of three wheat rusts and details on each of them. We also have given comprehensive tables for all the genes available for the three rusts. Insight into popular alien introgressions and their utilization has been given as well.
In Ethiopia, breeding rust resistant wheat cultivars is a priority for wheat production. A stem rust epidemic during 2013 to 2014 on previously resistant cultivar Digalu highlighted the need to determine the effectiveness of wheat lines to multiple races of Puccinia graminis f. sp. tritici in Ethiopia. During 2014 and 2015, we evaluated a total of 97 bread wheat and 14 durum wheat genotypes against four P. graminis f. sp. tritici races at the seedling stage and in single-race field nurseries. Resistance genes were postulated using molecular marker assays. Bread wheat lines were resistant to race JRCQC, the race most virulent to durum wheat. Lines with stem rust resistance gene Sr24 possessed the most effective resistance to the four races. Only three lines with adult plant resistance possessed resistance effective to the four races comparable with cultivars with Sr24. Although responses of the wheat lines across races were positively correlated, wheat lines were identified that possessed adult plant resistance to race TTKSK but were relatively susceptible to race TKTTF. This study demonstrated the importance of testing wheat lines for response to multiple races of the stem rust pathogen to determine if lines possessed non-race-specific resistance.
[Formula: see text] Copyright © 2019 The Author(s). This is an open access article distributed under the CC BY 4.0 International license .
Wheat landrace CItr 15026 previously showed adult plant resistance (APR) to the Ug99 stem rust race group in Kenya and seedling resistance to Puccinia graminis f. sp. tritici races QFCSC, TTTTF, and TRTTF. CItr 15026 was crossed to susceptible accessions LMPG-6 and Red Bobs, and 180 double haploid (DH) lines and 140 recombinant inbred lines (RIL), respectively, were developed. The 90K wheat iSelect single-nucleotide polymorphism platform was used to genotype the parents and populations. Parents and 180 DH lines were evaluated in the field in Kenya for three seasons. A major quantitative trait locus (QTL) for APR was consistently detected on chromosome arm 6AS. This QTL was further detected in the RIL population screened in Kenya for one season. Parents, F1, and the two populations were tested as seedlings against races TRTTF and TTTTF. In addition, the DH population was tested against race QFCSC. Goodness-of-fit tests indicated that the TRTTF resistance in CItr 15026 was controlled by two complementary genes whereas the TTTTF and QFCSC resistance was conditioned by one dominant gene. The TRTTF resistance loci mapped to chromosome arms 6AS and 6DS, whereas the TTTTF and QFCSC resistance locus mapped to the same region on 6DS as the TRTTF resistance. The APR identified in CItr 15026 should be useful in developing cultivars with durable stem rust resistance.
Simultaneously in three levels of ploidy comparative genetic study of species of the genus Triti-cum and their relatives was produced. problems of collecting, creating, studying and using of phenetic and genetic collections in di-, tetra - and hexaploid levels of wheat are discuss. The author carried out revision of genus Triticum taxonomy and proposed new one, which includes all fertile man-made kinds.
В рамках единого исследования одновременно на трех уровнях плоидности проведено сравнительно-генетическое изучение видов рода Triticum и их сородичей. Обсуждаются вопросы сбора, создания, изучения и использования признаковой и генетической коллекций на ди-, тетра- и гексаплоидном уровнях пшениц. Автором проведена ревизия существующей системы рода Triticum и предложена новая, включающая в себя все фертильные рукотворные виды.
Key message:
The diploid wheat stem rust resistance gene Sr21 confers temperature-sensitive resistance to isolates of the Ug99 group and maps to the middle of the long arm of chromosome 2A (m). A race of Puccinia graminis f. sp. tritici, the causal pathogen of stem rust of wheat, known as Ug99, and its variants, are virulent to plants carrying stem rust resistance genes currently deployed in most wheat cultivars worldwide. Therefore, identification, mapping and deployment of effective resistance genes are critical to reduce this threat. Resistance gene Sr21 identified in diploid wheat T. monococcum can be effective against races from the Ug99 race group, but both susceptible and partial resistant reactions have been reported in previous studies. To clarify this conflicting information we screened four monogenic lines with Sr21 and four susceptible controls with 16 Pgt isolates including five isolates of the Ug99 race group under three different temperatures and three different photoperiods. We observed that, temperature influences the interaction between monogenic lines with Sr21 and Ug99 race group isolates, and may be one source of previous inconsistencies. This result indicates that, although Sr21 confers partial resistance against Ug99, its effectiveness can be modulated by environmental conditions and should not be deployed alone. Using two large diploid wheat-mapping populations (total 3,788 F2 plants) we mapped Sr21 approximately 50 cM from the centromere on the long arm of chromosome 2A(m) within a 0.20 cM interval flanked by sequence-based markers FD527726 and EX594406. The closely linked markers identified in this study will be useful to reduce the T. monococcum segments introgressed into common wheat, accelerate Sr21 deployment in wheat breeding programs, and facilitate the map-based cloning of this gene.
Wheat stem rust (Puccinia graminis f. sp. tritici) race TTKSK (Ug99), with virulence to the majority of the world's wheat (Triticum aestivum) cultivars, has spread from Uganda throughout eastern Africa, Yemen, and Iran. The identification and spread of variants of race TTKSK with virulence to additional stem rust resistance genes has reminded breeders and pathologists of the danger of deploying major resistance genes alone. In order to protect wheat from this rapidly spreading and adapting pathogen, multiple resistance genes are needed, preferably from improved germplasm. Preliminary screening of over 700 spring wheat breeding lines and cultivars developed at least 20 years ago identified 88 accessions with field resistance to Ug99. We included these resistant accessions in the stem rust screening nursery in Njoro, Kenya for two additional seasons. The accessions were also screened with a bulk of North American isolates of P. graminis f. sp. tritici in the field in St. Paul, MN. In order to further characterize the resistance in these accessions, we obtained seedling phenotypes for 10 races of P. graminis f. sp. tritici, including two races from the race TTKSK complex. This phenotyping led to the identification of accessions with either adult-plant or all-stage resistance to race TTKSK, and often North American races of P graminis f. sp. tritici as well. These Ug99 resistant accessions can be obtained by breeders and introgressed into current breeding germplasm.
the gene Srdp-2 for stem rust resistance (Roelfs and McVey, 1979), but probably carries other genes as well. The durum wheat (Triticum turgidum L.) cultivar Medea Ap9d In identifying isolates of stem rust, differential lines has been used as a supplementary differential in the identification of carrying single Sr genes have considerable advantage. isolates of stem rust (Puccinia graminis f. sp. tritici Eriks. & Henn.). Perhaps most important, by using single-gene differen- Genes for stem rust resistance from Medea were transferred to a susceptible hexaploid wheat (T. aestivum L.), LMPG, so that they tials one can determine exactly which corresponding could be used more efficiently in race identification and wheat breed- genes for virulence the isolate carries and to which iso- ing. Medea was backcrossed five times to LMPG with selection for lates the resistance gene conditions resistance. With a resistance to stem rust races LBB and MCC. Ten near-isogenic lines multigene differential, it is impossible to tell which gene (NILS) were produced and tested with isolates of 10 stem rust races. for resistance or combination of genes results in a partic- The NILs fell into four types. Three of the four types had resistance ular low-infection type. to races to which Medea was susceptible. Apparently, Medea possesses A program was started to transfer stem rust resistance suppressors for some of its genes for resistance and the suppressors from Medea to hexaploid wheat with the objective of were lost during the backcrossing to LMPG. This was confirmed when producing one or more single-gene lines that could be the cross, Medea/Glossy Hugenot, and the backcross, Medea/2 3
Stems of wheat, barley, and oat infected with stem rust were collected throughout Canada in 1999 to determine the virulence spectrum of Puccinia graminis Pers.:Pers. f. sp. tritici Eriks. & E. Henn. and Puccinia graminis f. sp. avenae Eriks. & E. Henn. To distinguish seven different pathotypes, 99 isolates of P. graminis tritici obtained from wheat were inoculated onto differential sets of wheat lines with single genes for stem rust resistance. The predominant pathotypes were RCRSK (60.3%), QCCJN (15.4%), and QFCSR (11.5%). The spring wheat cultivars currently grown in Canada are resistant to these pathotypes. Among 178 isolates of P. graminis tritici recovered from barley, eight pathotypes were identified, with QCCJN (53.4%), RCRSK (18.5%), and QCCJL (14.0%) predominating. Pathotypes QCCJL and QCCJN represented 67.4% of the isolates from barley. Since these pathotypes are highly virulent on the barley cultivars currently grown in Canada, there continues to be a threat to barley production due to stem rust. Ten pathotypes were identified among 269 P. graminis avenae isolates from wild and cultivated oat. The predominant pathotypes, NA29 at 45.3% and NA67 at 26.4% from wild oat, and NA67 at 31.8% and NA29 at 30.9% from cultivated oat, were relatively similar in occurrence. Pathotype NA67, discovered for the first time in western Canada in 1998, is virulent on Pg2, Pg9, and Pg13, which, in various combinations, conditioned resistance to stem rust in most oat cultivars prior to 1998. The incidence of pathotype NA67 in cultivated oat from Manitoba and Saskatchewan increased from 21.7% in 1998 to 34.7% in 1999. A new pathotype, NA76, was identified, which was also virulent on the combination of Pg2, Pg9, and Pg13 but, unlike NA67, was avirulent to Pg15.
Two sets of near-isogenic lines of wheat carrying single genes for stem rust resistance were grown in yield tests to determine whether the resistance genes were deleterious. One set was based on the cultivar Marquis and the second set on a susceptible, day-length insensitive line, LMPG. The results indicated that the effects of resistance genes vary with different genes and different environments. However, there appeared to be a tendency for resistance genes to reduce yield. In most cases the reductions were too small to be of much concern to wheat breeders.
In order to counteract the effects of the mutant genes in races of leaf rust (Puccinia recondita f.sp. tritici Rob. ex Desm.) and stem rust (P. graminis f.sp. tritici Eriks. &Henn.) in wheat, exploration of new resistance genes in wheat relatives is necessary. Three accessions of Triticum cylindricum Ces. (4x, CCDD), Acy1, Acy9, and Acy11, were tested with 10 races each of leaf rust and stem rust. They were resistant to all races tested. Viable F1 plants were produced from the crosses of the T. cylindricum accessions as males with susceptible MP and Chinese Spring ph1b hexaploid wheats (T. aestivum, 6x, AABBDD), but not with susceptible Kubanka durum wheat (T. turgidum var. durum, 4x, AABB), even with embryo rescue. In these crosses the D genome of hexaploid wheat may play a critical role in eliminating the barriers for species isolation during hybrid seed development. The T. cylindricum rust resistance was expressed in the F1 hybrids with hexaploid wheat. However, only the cross MP/Acy1 was successfully backcrossed to another susceptible hexaploid wheat, LMPG-6. In the BC2F2 of the cross MP/Acy1//LMPG-6/3/MP, monosomic or disomic addition lines with resistance to either leaf rust race 15 (infection types (IT) 1=, 1, or 1+; addition line 1) or stem rust race 15B-1 (IT 1 or 1+; addition line 2) were selected. Rust tests and examination of chromosome pairing of the F1 hybrids and the progeny of the disomic addition lines confirmed that the genes for rust resistance were located on the added T. cylindricum C-genome chromosomes rather than on the D-genome chromosomes. The T. cylindricum chromosome in addition line 2 was determined to be chromosome 4C through the detection of RFLPs among the genomes using a set of homoeologous group-specific wheat cDNA probes. Addition line 1 was resistant to the 10 races of leaf rust and addition line 2 was resistant to the 10 races of stem rust, as was the T. cylindricum parent. The added C-genome chromosomes occasionally paired with hexaploid wheat chromosomes. Translocation lines with rust resistance (2n = 21 II) may be obtained in the self-pollinated progeny of the addition lines through spontaneous recombination of the C-genome chromosomes and wheat chromosomes. Such translocation lines with resistance against a wide spectrum of rust races should be potentially valuable in breeding wheat for rust resistance.
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