Plant Leaf Rust Resistance Gene Research Articles

Mapping seedling and adult plant leaf rust resistance genes in the durum wheat cultivar Strongfield and other Triticum turgidum (L.) lines.

Durum wheat (T. turgidum L.) is threatened by the appearance of new virulent races of leaf rust, caused by Puccinia triticina, in recent years. This study was conducted to determine the leaf rust resistance in a modern Canadian durum cultivar Strongfield. Six populations derived from crosses of Strongfield with six tetraploid wheat lines, respectively, were tested at seedling plant stage with different P. triticina races. Two of the populations were evaluated for adult plant leaf rust infection in Canada and Mexico. A stepwise regression joint linkage QTL mapping and analysis by MapQTL were performed. Strongfield contributed the majority of QTL detected, contributing seven QTL detected in field tests, and eight QTL conditioning seedling resistance. A 1B QTL, QLr-Spa-1B.1, from Strongfield had a significant effect in both Canadian and Mexican field tests, and corresponded with Lr46/Yr29. The remaining field QTL were found in only the Canadian or the Mexican environment, not both. The QTL from Strongfield on 3A, QLr-Spa-3A, conferred seedling resistance to all races tested and had a significant effect in the field in Canada. This is the first report of the QLr-Spa-3A and Lr46/Yr29 as key components of the genetic resistance in Canadian durum wheat. KASP markers were developed to detect the QLr-Spa-3A for use in marker assisted leaf rust resistance breeding. The susceptible parental lines contributed QTL on 1A, 2B and 5B that were effective in Mexican field tests that may be good targets to integrate into modern durum varieties to improve resistance to new durum virulent races.

GENETIC ASSESSMENT OF LEAF RUST RESISTANCE IN SOME WHEAT VARIETIES

The experiments of this study were carried out through four growing seasons i.e., 2015/16 to 2018/19 at the farm of the faculty of Agriculture, Shibin El-Kom, Menoufia University.Using10 Egyptian wheat varieties,16 wheat promising lines from (CIMMYT) and 20 adult plant leaf rust resistance genes (Lr). lines Lr were used as (male) for crosses with the wheat cultivars (female) to obtain the F1 grains to produce F2 grains and perform genetic analysis. Recording final rust severity (FRS), rate of disease increase (r-value) and the area under disease progress curve (AUDPC) from varieties and lines to responses leaf rust resistance. While STS marker specific for Lr19 and Lr28 genes were performed on the ten wheat varieties and the sixteen promising lines. The responses of rust severity and infection type of the 20 Lr strains were divided into three groups; I resistant genes i.e., Lr17, Lr18, Lr28, Lr 38 and Lr42, II susceptible genes i.e., Lr2c, Lr9, Lr14b, Lr24, Lr34, Lr35, Lr36, Lr37, Lr44 and Lr45, and III genes with variable reactions i.e. Lr2a, Lr19, Lr29, Lr30 and Lr39. Results suggested that genes of group I are important for breeding for leaf rust resistance under Egyptian field conditions. The ten wheat cultivars exhibited low values of FRS and AUDPC except Sids1, and no variety has high rate of (r-value). These cultivars except Sids1 have a good level of adult plant resistance to leaf rust and can be used as resistance sources, 16 wheat promising lines gave lowest values of (FRS), (r-value) and (AUDPC), and consequently they can be used in breeding programs. Genetic analysis showed that Sids1 did not have any of genes under study. However, Gemmeiza 7, Gemmeiza 9, Gemmeiza 10, Gemmeiza 11, Gemmeiza 12, Misr 1, Misr 2, Giza168 and Giza 171 have several Lr genes. Using STS marker specific for Lr19 and Lr28 genes, Lr19 was identified in Gemmeiza 7 and Gemmeiza 11 and Lr28 detected in Gemmeiza 9 and Gemmeiza 10, while Lr19 detected in 13 promising lines, Lr28 found only in five of them. These results showed that molecular markers for Lr genes might be a useful tool in marker-assisted breeding (MAS) for developing Egyptian wheat cultivars.

A novel adult plant leaf rust resistance gene Lr2K38 mapped on wheat chromosome 1AL.

Soft red winter wheat (SRWW) cultivar AGS 2038 has a high level of seedling and adult plant leaf rust (LR) resistance. To map and characterize LR resistance in AGS 2038, a recombinant inbred line (RIL) population consisting of 225 lines was developed from a cross between AGS 2038 and moderately resistant line UGA 111729. The parents and RIL population were phenotyped for LR response in three field environments at Plains and Griffin, GA, in the 2017-2018 and 2018-2019 growing seasons, one greenhouse environment at the adult-plant stage, and at seedling stage. The RIL population was genotyped with the Illumina iSelect 90K SNP marker array, and a total of 7667 polymorphic markers representing 1513 unique loci were used to construct a linkage map. Quantitative trait loci (QTL) analysis detected six QTL, QLr.ags-1AL, QLr.ags-2AS, QLr.ags-2BS1, QLr.ags-2BS2, QLr.ags-2BS3, and QLr.ags-2DS, for seedling and adult plant LR resistance. Of these, the major adult plant leaf rust resistance QTL, QLr.ags-1AL, was detected on all field and greenhouse adult plant tests and explained up to 34.45% of the phenotypic variation. QLr.ags-1AL, tightly flanked by IWB20487 and IWA4022 markers, was contributed by AGS 2038. Molecular marker analysis using a diagnostic marker linked to Lr59 showed that QLr.ags-1AL was different from Lr59, the only known LR resistance gene on 1AL. Therefore, the QTL was temporarily designated as Lr2K38. Lr2K38-linked marker IWB20487 was highly polymorphic among 30 SRWW lines and should be useful for selecting the Lr2K38 in wheat breeding programs.

Identification and mapping of two adult plant leaf rust resistance genes in durum wheat

The International Maize and Wheat Improvement Center (CIMMYT)-derived durum wheat line Quetru is moderately resistant to leaf rust and displays disease severities of 15–30% at the adult plant stage. Atil C2000 is moderately susceptible to leaf rust at adult plant stage and displays severities of 20–60%. These two durum wheats were crossed with the susceptible line Atred#1, and the respective recombinant inbred line populations were phenotyped for resistance to leaf rust in field trials in four environments in Mexico. The phenotypic segregation in the Atred#1 × Atil C2000 population was attributed to the pleiotropic adult plant resistance (APR) gene Lr46 based on the closest marker cslv46G22 located within 1.4 cM. Lr46 reduced leaf rust severity by 19.6–35.5%, and it was also identified in the Atred#1 × Quetru population, where it reduced leaf rust severity by 28.5–57.7% depending on the environment. We also identified a putatively novel, race-specific APR gene LrQ in Quetru that is located on the Chromosome 6BL and flanked by SNP markers AX-95144243 and AX-95155193. These two markers have been converted into kompetitive allele–specific PCR (KASP) markers and validated in the population. LrQ was ineffective at the seedling stage but reduced leaf rust severity by 37.3% on average over four field trials. The combination of LrQ and Lr46 resulted in significantly reduced leaf rust severity in the field and could be used to breed improved durum wheat varieties.

Mapping a gene on wheat chromosome 4BL involved in a complementary interaction with adult plant leaf rust resistance gene LrSV2.

A complementary gene to LrSV2 for specific adult plant leaf rust resistance in wheat was mapped on chromosome 4BL, tightly linked to Lr12 / 31. LrSV2 is a race-specific adult plant leaf rust (Puccinia triticina) resistance gene on subdistal chromosome 3BS detected in the cross of the traditional Argentinean wheat (Triticum aestivum) variety Sinvalocho MA and the experimental line Gama6. The analysis of the cross of R46 [recombinant inbred line (RIL) derived from Sinvalocho MA carrying LrSV2 gene and the complementary gene Lrc-SV2 identified in the current paper] and the commercial variety Relmo Siriri (not carrying neither of these two genes) allowed the detection of the unlinked complementary gene Lrc-SV2 because the presence of one dominant allele of both is necessary to express the LrSV2-specific adult plant resistance. Lrc-SV2 was mapped within a 1-cM interval on chromosome 4BL using 100 RILs from the cross Sinvalocho MA × Purple Straw. This genetic system resembles the Lr27+31 seedling resistance reported in the Australian varieties Gatcher and Timgalen where interacting genes map at similar chromosomal positions. However, in high-resolution maps, Lr27 and LrSV2 were already mapped to adjacent intervals on 3BS and Lrc-SV2 map position on 4BL is distal to the reported Lr12/31-flanking microsatellites.

Mapping and characterization of the new adult plant leaf rust resistance gene Lr77 derived from Santa Fe winter wheat.

A new gene for adult plant leaf rust resistance in wheat was mapped to chromosome 3BL. This gene was designated as Lr77. 'Santa Fe' is a hard red winter cultivar that has had long-lasting resistance to the leaf rust fungus, Puccinia triticina. The objective of this study was to determine the chromosome location of the adult plant leaf rust resistance in Santa Fe wheat. A partial backcross line of 'Thatcher' (Tc) wheat with adult plant leaf rust resistance derived from Santa Fe was crossed with Thatcher to develop a Thatcher//Tc*2/Santa Fe F6 recombinant inbred line (RIL) population. The RIL population and parental lines were evaluated for segregation of leaf rust resistance in three field plot tests and in an adult plant greenhouse test. A genetic map of the RIL population was constructed using 90,000 single-nucleotide polymorphism (SNP) markers with the Illumina Infinium iSelect 90K wheat bead array. A significant quantitative trait locus for reduction of leaf rust severity in all four tests was found on chromosome 3BL that segregated as a single adult plant resistance gene. The RILs with the allele from the resistant parent for SNP marker IWB10344 had lower leaf rust severity and a moderately resistant to moderately susceptible response compared to the susceptible RILs and Thatcher. The gene derived from Santa Fe on chromosome 3BL was designated as Lr77. Kompetitive allele-specific polymerase chain reaction assay markers linked to Lr77 on 3BL should be useful for selection of wheat germplasm with this gene.

Molecular introgression of leaf rust resistance gene Lr34 validates enhanced effect on resistance to spot blotch in spring wheat

The adult plant leaf rust resistance gene Lr34 was introduced using marker assisted selection (MAS) into an Indian wheat cultivar HUW510. Lr34 is associated with enhanced resistance to spot blotch. However, this effect has not been validated previously via introgression from one genetic background into another using MAS. The donor parent was the CIMMYT breeding line Picaflor#1. The morphological marker leaf tip necrosis (LTN+) and co-dominant STS marker csLV34 were used to track Lr34. Background selection was made with 90 simple sequence repeat (SSR) loci. BC3F3 to BC3F5 progenies were tested for spot blotch resistance. The results showed that the introgression of Lr34 can lead to enhanced resistance to spot blotch. Eleven selections retained in the cv. HUW510 background carried Lr34 and had a genetic background estimated to be as high as 95% that of the recurrent parent. The mean AUDPC for spot blotch in BC3F5 lines of Picaflor#1 × HUW510 was substantially lower (917 at timely sown conditions and 1015 under late sown conditions) than the recipient parent HUW510 (1332 at timely sown conditions and 1412 under late sown conditions). The results showed that introgression of Lr34 can lead to enhanced resistance to spot blotch.

Characterization of Lr75: a partial, broad-spectrum leaf rust resistance gene in wheat.

Here, we describe a strategy to improve broad-spectrum leaf rust resistance by marker-assisted combination of two partial resistance genes. One of them represents a novel partial adult plant resistance gene, named Lr75. Leaf rust caused by the fungal pathogen Puccinia triticina is a damaging disease of wheat (Triticum aestivum L.). The combination of several, additively-acting partial disease resistance genes has been proposed as a suitable strategy to breed wheat cultivars with high levels of durable field resistance. The Swiss winter wheat cultivar 'Forno' continues to show near-immunity to leaf rust since its release in the 1980s. This resistance is conferred by the presence of at least six quantitative trait loci (QTL), one of which is associated with the morphological trait leaf tip necrosis. Here, we used a marker-informed strategy to introgress two 'Forno' QTLs into the leaf rust-susceptible Swiss winter wheat cultivar 'Arina'. The resulting backcross line 'ArinaLrFor' showed markedly increased leaf rust resistance in multiple locations over several years. One of the introgressed QTLs, QLr.sfr-1BS, is located on chromosome 1BS. We developed chromosome 1B-specific microsatellite markers by exploiting the Illumina survey sequences of wheat cv. 'Chinese Spring' and mapped QLr.sfr-1BS to a 4.3cM interval flanked by the SSR markers gwm604 and swm271. QLr.sfr-1BS does not share a genetic location with any of the described leaf rust resistance genes present on chromosome 1B. Therefore, QLr.sfr-1BS is novel and was designated as Lr75. We conclude that marker-assisted combination of partial resistance genes is a feasible strategy to increase broad-spectrum leaf rust resistance. The identification of Lr75 adds a novel and highly useful gene to the small set of known partial, adult plant leaf rust resistance genes.

Molecular markers for adult plant leaf rust resistance gene Lr48 in wheat

Leaf rust of wheat, caused by Puccinia triticina, is an important disease throughout the world. The adult plant leaf rust resistance gene Lr48 reported in CSP44 was previously mapped in chromosome 2B, but the marker–gene association was weak. In this study, we confirmed the location of Lr48 to be in the short arm of chromosome 2B and identified closely linked markers suitable for use in breeding. The CSP44/WL711 recombinant inbred line (RIL) population (90 lines) showed monogenic segregation for Lr48. Twelve resistant and 12 susceptible RILs were used for selective genotyping using an iSelect 90K Infinium SNP assay. Closely linked SNPs were converted into Kompetitive allele-specific primers (KASP) and tested on the parental lines. KASP markers giving clear clusters for alternate genotypes were assayed on the entire RIL population. SNP markers IWB31002, IWB39832, IWB34324, IWB72894 and IWB36920 co-segregated with Lr48 and the marker IWB70147 was mapped 0.3 cM proximal to this gene. Closely linked KASP markers were tested on a set of Australian and Nordic wheat genotypes. The amplification of SNP alleles alternate to those linked with Lr48 in the majority of the Australian and Nordic wheat genotypes demonstrated the usefulness of these markers for marker-assisted pyramiding of Lr48 with other rust resistance genes.

Inheritance of Leaf Rust and Stripe Rust Resistance in the Brazilian Wheat Cultivar 'Toropi'.

Leaf rust (Puccinia triticina) and stripe rust (P. striiformis f. tritici) affect wheat production worldwide. Brazilian 'Toropi' wheat has demonstrated durable leaf rust resistance in South America since its release in 1965. It was previously found to have up to two adult plant leaf rust resistance genes. The leaf and stripe rust resistance of Toropi were studied by analyzing a doubled-haploid population made by crossing with susceptible 'Thatcher'. Toropi expressed good resistance to leaf rust in Canada, Brazil, and New Zealand. Based on field and greenhouse testing, the leaf rust resistance of Toropi is conferred by two race-nonspecific complementary adult plant genes and a race-specific adult plant gene. The stripe rust resistance of Toropi analyzed in New Zealand and in Canada is based on up to two resistance genes. Toropi should provide an important contribution to rust resistance because it expressed good leaf rust and stripe rust resistance in different parts of the world.

Molecular Detection of the Adult Plant Leaf Rust Resistance GeneLr34in Romanian Winter Wheat Germplasm

Wheat continues to be one of the most cultivated cereals in the world, and also in Romania. Leaf rust caused by Puccinia triticina reduces the wheat yield and grains quality worldwide. In the context of climate change, leaf rust has become a more important problem for both wheat growers and breeders in our country. Use of genetic resources, carrying rust resistance genes, play an important role in breeding programs leading to resistant varieties, which can have positive impact on environment and economy. Therefore, the identification of resistance genes in modern wheat cultivars and breeding lines, and then selection of the best resistance genes combination(s) are the first steps for a successful breeding program. At present, one of the best known and studied adult plant leaf rust resistance gene is Lr34 that contributes significantly to durable leaf rust resistance. The functional markers that enable early detection of this gene are a major advantage in the wheat breeding. The aim of this study was to evaluate the presence of the slow rusting resistance gene Lr34 in Romanian wheat germplasm, using cssfr4 and cssfr5 molecular markers. Screening of 47 winter bread wheat cultivars and 47 breeding lines with these markers showed the presence of the Lr34 resistant haplotype in 62% (homozygous genotypes) of the total genotypes. A high frequency (79%) of Lr34 resistance allele was found among 47 breeding lines, suggesting that maintenance of a high frequency of this allele represents a real advantage for the development of adult plant resistance in Romanian breeding programs.

Erratum to: Phenotypic and molecular confirmation of durable adult plant leaf rust resistance (APR) genesLr34+,Lr46+ andLr67+ linked to leaf tip necrosis (LTN) in select registered Indian wheat (T. aestivum) genetic stocks

Erratum to: Phenotypic and molecular confirmation of durable adult plant leaf rust resistance (APR) genes<i>Lr34</i>+,<i>Lr46</i>+ and<i>Lr67</i>+ linked to leaf tip necrosis (LTN) in select registered Indian wheat (<i>T. aestivum</i>) genetic stocks

Phenotypic and molecular confirmation of durable adult plant leaf rust resistance (APR) genesLr34+,Lr46+ andLr67+ linked to leaf tip necrosis (LTN) in select registered Indian wheat(T. aestivum)genetic stocks

Nearly twenty thousand wheat lines were phenotyped for the presence of leaf tip necrosis (LTN), a phenotypic trait linked to adult plant leaf rust resistance (APR) genes, viz. Lr34, Lr46 and Lr67 having pleiotropic association with multiple disease resistance genes. Thirty-six lines showed varied expression of LTN and moderate level of leaf rust severity at adult plant stage with slow rusting (disease progress at a retarded rate). Seedling resistance test (SRT) revealed susceptible and mixed infection types, a characteristic of adult plant resistance (APR) genes. Further molecular confirmation for the presence of these genes using available microsatellite markers revealed that of the 36 lines, five lines carried Lr46 + alone and five other lines carried Lr67 + alone. Seven lines carried the combination of Lr34 + and Lr67 + while six lines confirmed to carry the combination of Lr46 + and Lr67 +. Remarkably three lines carried all the three APR genes, viz. Lr34 +, Lr46 + and Lr67 +. All these stocks can be a source of APR multiple disease resistance genes. Ten lines were not confirmed to carry any of the genes but still had LTN and SRT results showing an infection type typical of APR genes and these can be the source of identifying newer APR genes. The resistance based on minor APR genes when combined with a few additional minor genes in the background of high yielding cultivars is expected to have high level of race non-specific resistance and to be durable.

Fine mapping of LrSV2, a race-specific adult plant leaf rust resistance gene on wheat chromosome 3BS

Fine mapping permits the precise positioning of genes within chromosomes, prerequisite for positional cloning that will allow its rational use and the study of the underlying molecular action mechanism. Three leaf rust resistance genes were identified in the durable leaf rust resistant Argentinean wheat variety Sinvalocho MA: the seedling resistance gene Lr3 on distal 6BL and two adult plant resistance genes, LrSV1 and LrSV2, on chromosomes 2DS and 3BS, respectively. To develop a high-resolution genetic map for LrSV2, 10 markers were genotyped on 343 F2 individuals from a cross between Sinvalocho MA and Gama6. The closest co-dominant markers on both sides of the gene (3 microsatellites and 2 STMs) were analyzed on 965 additional F2s from the same cross. Microsatellite marker cfb5010 cosegregated with LrSV2 whereas flanking markers were found at 1cM distal and at 0.3cM proximal to the gene. SSR markers designed from the sequences of cv Chinese Spring BAC clones spanning the LrSV2 genetic interval were tested on the recombinants, allowing the identification of microsatellite swm13 at 0.15cM distal to LrSV2. This delimited an interval of 0.45cM around the gene flanked by the SSR markers swm13 and gwm533 at the subtelomeric end of chromosome 3BS.

Monosomic and molecular mapping of adult plant leaf rust resistance genes in the Brazilian wheat cultivar Toropi

Leaf rust is one of the most destructive diseases affecting wheat worldwide. The most effective way to control it is to use resistant cultivars. Resistance based on slow-rusting adult plant resistance (APR) genes has proven to be the best method for developing cultivars with durable resistance. A source of slow-rusting APR for leaf rust is the Brazilian wheat cultivar Toropi. The Toropi/IAC 13 F₂ and F₇ recombinant inbred lines (RILs) were developed in previous studies. Phenotypic analysis of the F₂ and F₇ RILs showed that 2 recessive genes that were temporarily named trp-1 and trp-2 conferred APR in Toropi. In the present study, we used monosomic families and amplified fragment length polymorphism (AFLP), sequence-tagged site, and simple sequence repeat (SSR) markers to map trp-1 and trp-2 on wheat chromosomes. Analysis of the F₂ monosomic RIL showed that trp- 1 and trp-2 were located on chromosomes 1A and 4D, respectively. AFLP analysis of the F₇ RIL identified 2 independent AFLP markers, XPacgMcac3 and XPacgMcac6, which were associated with Toropi APR. These markers explained 71.5% of the variation in the phenotypic data in a multiple linear regression model. The AFLP markers XPacg/ Mcac3 and XPacg/Mcac6 were anchored by SSR markers previously mapped on the short arms of chromosomes 1A (1AS) and 4D (4DS), respectively. The trp-2 gene is the first leaf rust resistance gene mapped on wheat chromosome 4DS. The mapping of trp-1 and trp-2 provides novel and valuable information that could be used in future studies involving the fine mapping of these genes, as well as in the identification of molecular markers that are closely related to these genes for marker-assisted selection of this important trait in wheat.

Identification of microsatellite markers linked to leaf rust adult plant resistance (APR) gene Lr48 in wheat

With 2 figures and 2 tables Abstract The recessive adult plant leaf rust resistance (APR) gene Lr48 in CSP44 was tagged using simple sequence repeat (SSR) markers. The population was phenotyped under controlled conditions using pathotype 77-5 (121R63-1) at both seedling and adult plant stages. Four microsatellite markers Xwmc175, Xwmc332, Xwmc627 and Xwmc149 were linked to Lr48 and mapped to chromosome 2BL with distances of 10.3, 2.5, 12.6 and 20.7 cM from Lr48 covering a length of 31 cM. Lr48 was placed between markers Xwmc175 and Xwmc332. The earlier reported location of Lr48 on 2BS could not be confirmed. The markers were validated on another population and the closest SSR marker, Xwmc332, was specific to resistance allele Lr48 and did not amplify in wheat lines carrying other resistance genes, thus enabling breeders to pyramid Lr48 with other leaf rust resistance genes.

Identification of molecular markers linked to adult plant leaf rust resistance gene Lr48 in wheat and detection of Lr48 in the Thatcher near-isogenic line with gene Lr25

The recessive adult plant resistance (APR) gene Lr48 in wheat was tagged with flanking random amplified polymorphic DNA (RAPD) markers. Markers S336775 in coupling and S3450 in repulsion with Lr48 were identified in wheat line CSP44. Tests of these markers on available Thatcher near-isogenic lines (NILs) detected the likely presence of Lr48 in TcLr25. A test of allelism of APR involving the cross TcLr25 × CSP44 indicated that Lr48 was present in both lines. A separate experiment on inheritance of resistance in an F2 population of TcLr25 × Agra Local confirmed the presence of a dominant seedling resistance gene (Lr25) and a recessive APR gene (Lr48) in TcLr25. This study demonstrated the value of molecular markers in identifying the presence of masked genes in genetic stocks where direct phenotyping failed to detect their presence.

Genetic mapping of adult plant leaf rust resistance genes Lr48 and Lr49 in common wheat

Hypersensitive adult plant resistance genes Lr48 and Lr49 were named based on their genetic independence of the known adult plant resistance genes. This study was planned to determine genomic locations of these genes. Recombinant inbred line populations derived from crosses involving CSP44 and VL404, sources of Lr48 and Lr49, respectively, and the susceptible parent WL711, were used to determine the genomic locations of these genes. Bulked segregant analyses were performed using multiplex-ready PCR technology. Lr48 in genotype CSP44 was mapped on chromosome arm 2BS flanked by marker loci Xgwm429b (6.1 cM) and Xbarc7 (7.3 cM) distally and proximally, respectively. Leaf rust resistance gene Lr13, carried by the alternate parent WL711, was proximal to Lr48 and was flanked by Xksm58 (5.1 cM) and Xstm773-2 (8.7 cM). Lr49 was flanked by Xbarc163 (8.1 cM) and Xwmc349 (10.1 cM) on chromosome arm 4BL. The likely presence of the durable leaf rust resistance gene Lr34 in both CSP44 and VL404 was confirmed using the tightly linked marker csLV34. Near-isogenic lines for Lr48 and Lr49 were developed in cultivar Lal Bahadur. Genotypes combining Lr13 and/or Lr34 with Lr48 or Lr49 were identified as potential donor sources for cultivar development programs.

Transfer of leaf rust and stripe rust resistance from Aegilops umbellulata Zhuk. to bread wheat (Triticum aestivum L.)

Aegilops umbellulata acc. 3732, an excellent source of resistance to major wheat diseases, was used for transferring leaf rust and stripe rust resistance to cultivated wheat. An amphiploid between Ae. umbellulata acc. 3732 and Triticum durum cv. WH890 was crossed with cv. Chinese Spring Ph I to induce homoeologous pairing between Ae. umbellulata and wheat chromosomes. The F1 was crossed to the susceptible Triticum aestivum cv. ‘WL711’ and leaf rust and stripe rust resistant plants were selected among the backcross progenies. Homozygous lines were selected and screened against six Puccinia triticina and four Puccinia striiformis f. sp. tritici pathotypes at the seedling stage and a mixture of prevalent pathotypes of both rust pathogens at the adult plant stage. Genomic in situ hybridization in some of the selected introgression lines detected two lines with complete Ae. umbellulata chromosomes. Depending on the rust reactions and allelism tests, the introgression lines could be classified into two groups, comprising of lines with seedling leaf rust resistance gene Lr9 and with new seedling leaf rust and stripe rust resistance genes. Inheritance studies detected an additional adult plant leaf rust resistance gene in one of the introgression lines. A minimum of three putatively new genes—two for leaf rust resistance (LrU1 and LrU2) and one for stripe rust resistance (YrU1) have been introgressed into wheat from Ae. umbellulata. Two lines with no apparent linkage drag have been identified. These lines could serve as sources of resistance to leaf rust and stripe rust in breeding programs.

Genetics of leaf rust resistance in three Americano landrace‐derived wheat cultivars from Uruguay

AbstractA genetic analysis of the landrace‐derived wheat accessions Americano 25e, Americano 26n, and Americano 44d, from Uruguay was conducted to identify the leaf rust resistance genes present in these early wheat cultivars. The three cultivars were crossed with the leaf rust susceptible cultivar ‘Thatcher’ and approximately 80 backcross (BC1) F2 families were derived for each cross. The BC1F2 families and selected BC1F4 lines were tested for seedling and adult plant leaf rust resistance with selected isolates of leaf rust, Puccinia triticina. The segregation and infection type data indicated that Americano 25e had seedling resistance genes Lr3, Lr16, an additional unidentified seedling gene, and one adult plant resistance gene that was neither Lr12 nor Lr13, and did not phenotypically resemble Lr34. Americano 26n was postulated to have genes Lr11, Lr12, Lr13, and Lr14a. Americano 44d appeared to have two possibly unique adult plant leaf rust resistance genes.