Races Of Leaf Rust Research Articles

A Cryptic Wheat–Aegilops triuncialis Translocation with Leaf Rust Resistance Gene Lr58

Genes transferred to crop plants from wild species are often associated with deleterious traits. Using molecular markers, we detected a cryptic introgression with a leaf rust resistance gene transferred from Aegilops triuncialis L. into common wheat (Triticum aestivum L.). One agronomically desirable rust‐resistant introgression line was selected and advanced to BC3F11 from a cross of hexaploid wheat and A. triuncialis In situ hybridization using A. triuncialis genomic DNA as a probe failed to detect the alien introgression. The translocation line was resistant to the most prevalent races of leaf rust in India and Kansas. Genetic mapping in a segregating F2:3 population showed that the rust resistance was monogenically inherited. Homeologous group 2 restriction fragment length polymorphism markers XksuF11, XksuH16, and Xbg123 showed diagnostically polymorphic alleles between the resistant and susceptible bulks. The alien transfer originated from homeologous chromosome recombination. The A. triuncialis‐specific alleles of XksuH16, XksuF11, Xbg123, and one simple sequence repeat marker Xcfd50 cosegregated with the rust resistance, suggesting that the wheat–A. triuncialis translocation occurred in the distal region of chromosome arm 2BL. This translocation was designated T2BS·2BL‐2tL(0.95). The unique source and map location of the introgression on chromosome 2B indicated that the leaf rust resistance gene is new and was designated Lr58

Snowbird hard white spring wheat

Snowbird is a hard white spring wheat (Triticum aestivum L.) that meets the end-use quality and kernel visual distinguishability specifications of the Canada Western Hard White Spring Wheat class. Snowbird was evaluated in the Central Bread Wheat Cooperative Test in 1998, 1999 and 2000, and was found to be adapted to the wheat-growing regions of the Canadian prairies. Snowbird yielded more than the check cultivars Neepawa, Roblin, AC Majestic, McKenzie, Harvest, and AC Barrie but less than McKenzie. Snowbird is resistant to the prevalent races of leaf rust and moderately resistant to stem rust, loose smut and common root rot. Snowbird and Roblin exhibited similar levels of resistance to tanspot, Septoria tritici, and Septoria nodorum while its reaction to Fusarium head blight was similar to that of AC Barrie. Snowbird has similar grain and flour protein content as other check cultivars but had 1% less protein compared to Roblin. Key words: Triticum aestivum L., Canada Western Hard White, hard white spring wheat, cultivar description, yield, disease resistance

Virulence Polymorphism of Puccinia recondita f. sp. tritici and Effectiveness of Lr Genes for Leaf Rust Resistance of Wheat in Ukraine.

In 2002 and 2003, 1,300 isolates of Puccinia recondita f. sp. tritici were obtained from six commercial cultivars of wheat at three locations in the eastern forest-steppe region of Ukraine. All isolates were tested for virulence on an international set of eight differential cultivars. Seventeen known wheat leaf rust races and several new, unnamed races were identified. The most common races in each year were races 61, 149, and 192. In 2003, up to 20 isolates each of the seven most common leaf rust races plus 8 to 10 isolates of unnamed races were tested for virulence to 35 near-isogenic wheat lines with different single Lr genes for leaf rust resistance. Isolates were polymorphic for virulence on Lr1, Lr2a, Lr2b, Lr2c, Lr9, Lr19, Lr23, Lr26, and the combination Lr27 + Lr31. No isolates were found virulent on Lr24, Lr25, or Lr28, and few isolates were virulent on Lr9. Few isolates of known races but most isolates of the new, unnamed races were virulent on Lr19. The 35 Lr gene lines also were exposed to mixed-race inoculum in field plots to tests effectiveness of their resistance. Lines with Lr24, Lr25, and Lr28 suffered no leaf rust damage in the field, and lines with Lr9, Lr18, Lr35, Lr36, and the combination Lr27 + Lr31 showed less than 10% severity.

Analysis of the wheat and Puccinia triticina (leaf rust) proteomes during a susceptible host‐pathogen interaction

Wheat leaf rust is caused by the fungus Puccinia triticina. The genetics of resistance follows the gene-for-gene hypothesis, and thus the presence or absence of a single host resistance gene renders a plant resistant or susceptible to a leaf rust race bearing the corresponding avirulence gene. To investigate some of the changes in the proteomes of both host and pathogen during disease development, a susceptible line of wheat infected with a virulent race of leaf rust were compared to mock-inoculated wheat using 2-DE (with IEF pH 4-8) and MS. Up-regulated protein spots were excised and analyzed by MALDI-QqTOF MS/MS, followed by cross-species protein identification. Where possible MS/MS spectra were matched to homologous proteins in the NCBI database or to fungal ESTs encoding putative proteins. Searching was done using the MASCOT search engine. Remaining unmatched spectra were then sequenced de novo and queried against the NCBInr database using the BLAST and MS BLAST tools. A total of 32 consistently up-regulated proteins were examined from the gels representing the 9-day post-infection proteome in susceptible plants. Of these 7 are host proteins, 22 are fungal proteins of known or hypothetical function and 3 are unknown proteins of putative fungal origin.

Registration of ‘Clear White’ Wheat

Registration of ‘Clear White’ Wheat

Glenavon hard red extra strong spring wheat

Glenavon hard red extra strong spring wheat (Triticum aestivum L.) is adapted to the Canadian prairies. It combines 2 to 6% higher grain yield with improved test weight compared to AC Corinne, Glenlea and Wildcat. It is resistant to moderately resistant to prevalent races of leaf and stem rust, resistant to loose smut, and of intermediate resistance to common bunt. Glenavon is eligible for all grades of the Canada Western Extra Strong wheat class. Key words: Triticum aestivum L., Canada Western Extra Strong, hard red extra strong spring wheat, cultivar description, yield, disease resistance

Tracking wheat rust on a continental scale

The rusts of wheat are important fungal plant pathogens that can be disseminated thousands of kilometers across continents and oceans by wind. Rusts are obligate parasites that interact with resistance genes in wheat in a gene-for-gene manner. New races of rust develop by mutation and selection for virulence against rust resistance genes in wheat. In recent years, new races of wheat leaf rust, wheat stripe rust, and wheat stem rust have been introduced into wheat production areas in different continents. These introductions have complicated efforts to develop wheat cultivars with durable rust resistance and have reduced the number of effective rust-resistance genes that are available for use. The migration patterns of wheat rusts are characterized by identifying their virulence against important rust resistance genes in wheat and by the use of molecular markers.

Molecular characterization of durum and common wheat recombinant lines carrying leaf rust resistance (Lr19) and yellow pigment (Y) genes from Lophopyrum ponticum

Chromosome 7E from Lophopyrum ponticum carries a valuable leaf rust resistant gene designated Lr19. This gene has not been widely used in common wheat breeding because of linkage with the yellow pigment gene Y. This gene tints flour yellow, reducing its appeal in bread making. However, a high level of yellow pigment is desirable in durum wheat breeding. We produced 97 recombinant chromosomes between L. ponticum transfer 7D.7E#1 and its wheat homoeologues, using the ph1b mutation that promotes homoeologous pairing. We characterized a subset of 37 of these lines with 11 molecular markers and evaluated their resistance to leaf rust and the abundance of yellow pigment. The Lr19 gene was mapped between loci Xwg420 and Xmwg2062, whereas Y was mapped distal to Xpsr687, the most distal marker on the long arm of chromosome 7. A short terminal 7EL segment translocated to 7A, including Lr19 and Y (line 1-23), has been transferred to durum wheat by backcrossing. The presence of this alien segment significantly increased the abundance of yellow pigment. The Lr19 also conferred resistance to a new durum leaf rust race from California and Mexico that is virulent on most durum wheat cultivars. The new durum lines with the recombinant 7E segment will be useful parents to increase yellow pigment and leaf rust resistance in durum wheat breeding programs. For the common wheat breeding programs, we selected the recombinant line 1-96, which has an interstitial 7E segment carrying Lr19 but not Y. This recombinant line can be used to improve leaf rust resistance without affecting flour color. The 7EL/7DL 1-96 recombinant chromosome did not show the meiotic self-elimination previously reported for a 7EL/7BL translocation.

Identification and molecular tagging of a gene from PI 289824 conferring resistance to leaf rust (Puccinia triticina) in wheat

Host-plant resistance is the most economically viable and environmentally responsible method of control for Puccinia triticina, the causal agent of leaf rust in wheat (Triticum aestivum L.). The identification and utilization of new resistance sources is critical to the continued development of improved cultivars as shifts in pathogen races cause the effectiveness of widely deployed genes to be short lived. The objectives of this research were to identify and tag new leaf rust resistance genes. Forty landraces from Afghanistan and Iran were obtained from the National Plant Germplasm System and evaluated under field conditions at two locations in Texas. PI 289824, a landrace from Iran, was highly resistant under field infection. Further evaluation revealed that PI 289824 is highly resistant to a broad spectrum of leaf rust races, including the currently prevalent races of leaf rust in the Great Plains area of the USA. Eight F1 plants, 176 F2 individuals and 139 F2:3 families of a cross between PI 289824 and T112 (susceptible) were evaluated for resistance to leaf rust at the seedling stage. Genetic analysis indicated resistance in PI 289824 is controlled by a single dominant gene. The AFLP analyses resulted in the identification of a marker (P39 M48-367) linked to resistance. The diagnostic AFLP band was sequenced and that sequence information was used to develop an STS marker (TXW200) linked to the gene at a distance of 2.3 cM. The addition of microsatellite markers allowed the gene to be mapped to the short arm of Chromosome 5B. The only resistance gene to be assigned to Chr 5BS is Lr52. The Lr52 gene was reported to be 16.5 cM distal to Xgwm443 while the gene in PI 289824 mapped 16.7 cM proximal to Xgwm443. Allelism tests are needed to determine the relationship between the gene in PI 289824 and Lr52. If the reported map positions are correct, the gene in PI 289824 is unique.

Locating the broad-spectrum wheat leaf rust resistance gene Lr52 (LrW) to chromosome 5B by a new cytogenetic method

This study was conducted to genetically map a potentially new wheat leaf rust resistance gene (LrW) using a novel genetic method and to test its effectiveness against current races of leaf rust (Puccinia triticina Eriks.) in Canada. Undoubled haploids of a near-isogenic line of Thatcher carrying the resistance gene (RL6107) were pollinated with a contrasting susceptible cultivar to generate an array of hybrids with random deficiencies arising from irregular meiosis of the haploid. Genetic analysis of the deficiencies in such populations can be used to locate qualitative traits by which the two parents differ through a process that we have called haploid deficiency mapping. In the present case, 5/417 hybrids were both susceptible to leaf rust (i.e. lacked the resistance gene) and also lacked several polymorphic microsatellite alleles from RL6107 that are specific to chromosome 5B. This correlated failed transmission of the resistance gene and deficiency for chromosome 5B. Analysis of an F2 population showed that the factor conditioning resistance was located on the short arm of 5B, 16.5 cM distal to the locus of the microsatellite Xgwm443. Since no other leaf rust resistance genes have been mapped to this region, LrW was re-designated Lr52. RL6107 was tested with 29 isolates of P. triticina, encompassing a diversity of virulence found in North America, with none showing virulence. The effectiveness and novelty of Lr52 make it a promising source of resistance for North American wheat cultivars.

PCR Markers for Triticum speltoides Leaf Rust Resistance Gene Lr51 and Their Use to Develop Isogenic Hard Red Spring Wheat Lines

New leaf rust resistance genes are needed in wheat (Triticum aestivum L.) to provide additional sources of resistance to the highly variable and dynamic leaf rust pathogen Puccinia triticina Eriks. Leaf rust resistance gene Lr51, located within a segment of Triticum speltoides Taush chromosome 1S translocated to the long arm of chromosome 1B of bread wheat, is resistant to the current predominant races of leaf rust in the USA. The objectives of this study were to determine the genetic length of the translocated 1S segment, develop a PCR marker for Lr51, and use this marker to generate isogenic lines for this gene. Characterization of two translocation lines (F‐7‐3 and F‐7‐12) with 10 molecular markers indicated that F‐7‐3 has an interstitial T. speltoides chromosome segment of 14 to 32 cM long including loci XAga7 and Xmwg710, whereas line F‐7‐12 has a complex series of translocations among chromosomes of homeologous group 1. On the basis of the DNA sequence of the A, B, D, and S alleles of the XAga7 locus, we designed a cleavage amplified polymorphic sequence (CAPS) marker for the S genome allele. Primers S30‐13L and AGA7‐759R preferentially amplified the XAga7 1S (819 bp) and 1B alleles (783 bp). These amplification products can be separated in agarose gels after digestion with PstI or BamHI restriction enzymes. This CAPS marker was validated in a collection of 32 common wheat cultivars and was used to develop three pairs of hard red spring isogenic lines from the donor parent F‐7‐3. These isogenic lines will be valuable for future assessment of the effect of this chromosome introgression on agronomic performance and end‐use quality.

The transfer of leaf and stem rust resistance from wild emmer wheats to durum and common wheat

Wild emmer wheats (Triticum turgidum var. dicoccoides L.) are potentially valuable sources of leaf rust (Puccinia triticina Eriks.) and stem rust (Puccinia graminis f. sp. tritici Eriks. & Henn.) resistance in breeding both durum (T. turgidum var. durum L.) and common wheat (T. aestivum L.). In an extension of previous work, 11 rust resistant accessions of wild emmer wheat were crossed and backcrossed from two to five times to susceptible durum or common wheats. Genes for leaf or stem rust resistance were transferred singly into several susceptible genotypes. Backcross lines homozygous for resistance to leaf rust were tested with a set of either 9 or 10 leaf rust races and those homozygous for resistance to stem rust were tested with a set of either 10 or 13 stem rust races. The emmer wheats proved to carry a number of genes for resistance to each rust. In most cases, when a cross was made to a hexaploid wheat, resistance to both rusts was suppressed in the F1 seedlings, even when resistance was dominant in the tetraploids. Nevertheless, resistance was successfully transferred from several accessions to the hexaploids, indicating that suppressors on the A or B genome chromosomes were involved and segregation occurred for them. Rust resistance tended to decrease when it was transferred to another species, particularly hexaploid wheat. A number of lines carrying genes for either leaf rust or stem rust resistance were resistant to all races with which they were tested and have potential in wheat breeding. Key words: Emmer wheat, Triticum turgidum var. dicoccoides, stem rust, leaf rust, suppressors

Occurrence and Impact of a New Leaf Rust Race on Durum Wheat in Northwestern Mexico from 2001 to 2003.

Durum wheat (Triticum turgidum var. durum) is the main irrigated winter crop in northwestern Mexico. Historically, leaf rust, caused by Puccinia triticina, had not induced significant losses to durum production in the area until 2001. That year, a new race, designated as BBG/BN, was detected that caused the most widely grown cultivar, Altar C84, which had remained resistant for 16 years, to become susceptible. Other recommended cultivars also became either moderately susceptible or susceptible. Detailed characterization of avirulence/virulence characteristics on Lr genes indicated that this race possibly did not evolve from the older races, but may have been introduced. Rust epidemics during the 2000-2001, 2001-2002, and 2002-2003 crop seasons have caused estimated losses of at least US$32 million. Although a majority of cultivars from 31 different countries, including the United States and Canada, and most of CIMMYT's durum wheat germ plasm were highly susceptible, diversity for both race-specific resistance and moderate levels of slow rusting resistance were identified. Jupare C2001, a resistant cultivar released in 2001, showed high levels of resistance and negligible losses in grain yield in a trial where Altar C84 suffered over 27% losses.

Lovitt hard red spring wheat

Lovitt hard red spring wheat (Triticum aestivum L.) is adapted to the Canadian prairies. Lovitt is earlier maturing than AC Barrie with similar grain yield and smaller kernels. Lovitt has resistance to prevalent races of leaf and stem rust and loose smut. Lovitt has very good pre-harvest sprouting resistance similar to RL4137. Lovitt is eligible for grades of the Canada Western Red Spring wheat class. Key words: Triticum aestivum L., cultivar description, resistance to leaf and stem rust, dormancy

Genetic Analysis of Adult-Plant Resistance to Leaf Rust in Five Spring Wheat Genotypes

Inheritance of adult-plant resistance to leaf rust, caused by Puccinia triticina, was studied in the progeny of a one-way diallel cross involving five CIMMYT-derived adult-plant resistant wheat (Triticum aestivum) genotypes and a susceptible wheat 'Avocet-YrA'. F1 progenies, F2 populations, F2-derived F3, and F4-derived F5 lines were field evaluated under artificial epidemics with leaf rust race MCJ/SP. Adult-plant resistance to leaf rust was incompletely dominant in crosses with the susceptible parent and was found to be controlled by additive interactions of Lr34 with at least two to three additional genes. Transgressive segregation giving rise to plants or lines with higher and lower levels of resistance than the parents was observed in all F2 and F5 derivatives of the resistant-parent intercrosses and suggested that, apart from Lr34, some of the other additive genes were nonallelic. Although specific combining ability was significant in some generations, general combining ability was found to be the major component of variation. Among generations, the estimates of the narrow-sense heritability of adult-plant resistance to leaf rust ranged from 0.67 to 0.97.

Prodigy hard red spring wheat

Prodigy hard red spring wheat (Triticum aestivum L.) is adapted to the wheat growing regions of western Canada. Evaluation in the Central Bread Wheat Cooperative registration tests from 1995 to 1997 was relative to Neepawa, Roblin, AC Majestic and McKenzie. Prodigy displayed high grain yield, mid-season maturity, strong straw, high protein content and high test weight. It exhibited resistance to the prevalent races of stem rust, leaf rust, and common bunt, moderate susceptibility to loose smut and susceptibility to Fusarium head blight. Prodigy is eligible for all grades of Canada Western Red Spring (CWRS) wheat. Key words: Triticum aestivum L., cultivar description, red spring wheat, grain protein, test weight, disease resistance

Journey hard red spring wheat

Journey hard red spring wheat is adapted to the wheat-growing regions of the Canadian prairies. Evaluation occurred in Central Bread Wheat Cooperative registration tests in 1997, 1999 and 2000 relative to Neepawa, Roblin, AC Majestic, McKenzie and AC Barrie. Journey displayed high grain yield, mid- to late - season maturity, reduced height, very strong straw, high test weight, high protein content and improved pre-harvest sprouting resistance. It exhibited resistance to the prevalent races of stem rust, leaf rust and common bunt, and intermediate resistance to loose smut and Fusarium head blight. Journey is eligible for all grades of Canada Western Red Spring (CWRS) wheat. Key words: Triticum aestivum L., cultivar description, red spring wheat, strong straw, grain protein, test weight, preharvest sprouting resistance, disease resistance

McKenzie hard red spring wheat

McKenzie hard red spring wheat is the first doubled haploid wheat ( Triticum aestivum L.) cultivar registered in Canada. Evaluation in the Central Bread Wheat Cooperative registration tests from 1994 to 1996 was relative to Neepawa, Katepwa, Roblin and AC M ajestic. McKenzie displayed high grain yield, early maturity, high test weight and high Hagberg falling number. It had resistance to the prevalent races of stem rust, leaf rust, and common bunt, and exhibited intermediate resistance to Fusarium head bligh t. McKenzie is well adapted to all areas of the Canadian prairies and eligible for all grades of Canada Western Red Spring (CWRS) wheat. Key words:

Performance and Mapping of Leaf Rust Resistance Transferred to Wheat from Triticum timopheevii subsp. armeniacum

ABSTRACT Host plant resistance is an economical and environmentally sound method of control of leaf rust caused by the fungus Puccinia triticina, which is one of the most serious diseases of wheat (Triticum aestivum) worldwide. Wild relatives of wheat, including the tetraploid T. timopheevii subsp. armeniacum, represent an important source of genes for resistance to leaf rust. The objectives of this study were to (i) evaluate the performance of leaf rust resistance genes previously transferred to wheat from three accessions of T. timopheevii subsp. armeniacum, (ii) determine inheritance and allelic relationship of the new leaf rust resistance genes, and (iii) determine the genetic map location of one of the T. timopheevii subsp. armeniacum-derived genes using microsatellite markers. The leaf rust resistance gene transferred to hexaploid wheat from accession TA 28 of T. timopheevii subsp. armeniacum exhibited slightly different infection types (ITs) to diverse races of leaf rust in inoculated tests of seedlings compared with the gene transferred from TA 870 and TA 874. High ITs were exhibited when seedlings of all the germ plasm lines were inoculated with P. triticina races MBRL and PNMQ. However, low ITs were observed on adult plants of all lines having the T. timopheevii subsp. armeniacum-derived genes for resistance in the field at locations in Kansas and Texas. Analysis of crosses between resistant germ plasm lines showed that accessions TA 870 and TA 874 donated the same gene for resistance to leaf rust and TA 28 donated an independent resistance gene. The gene donated to germ plasm line KS96WGRC36 from TA 870 of T. timopheevii subsp. armeniacum was linked to microsatellite markers Xgwm382 (6.7 cM) and Xgdm87 (9.4 cM) on wheat chromosome arm 2B long. This new leaf rust resistance gene is designated Lr50. It is the first named gene for leaf rust resistance transferred from wild timopheevi wheat and is the only Lr gene located on the long arm of wheat homoeologous group 2 chromosomes.

Molecular Mapping of Leaf Rust Resistance Gene Rph5 in Barley

Leaf rust caused by Puccinia hordei G. Otth is an important disease of barley (Hordeum vulgare L.) in many regions of the world. Yield losses up to 32% have been reported in susceptible cultivars. The Rph5 gene confers resistance to the most prevalent races (8 and 30) of barley leaf rust in the USA. Therefore, the molecular mapping of Rph5 is of great interest. The objectives of this study were to map Rph5 and identify closely linked molecular markers. Genetic studies were performed by analysis of 93 and 91 F2 plants derived from the crosses ‘Bowman’ (rph5) × ‘Magnif 102’ (Rph5) and ‘Moore’ (rph5) × Virginia 92‐42‐46 (Rph5), respectively. Bulk segregant analysis (BSA) using amplified fragment length polymorphism (AFLP), restriction fragment length polymorphism (RFLP), and simple sequence repeat (SSR) markers was conducted. Linkage analysis positioned the Rph5 locus to the extreme telomeric region of the short arm of barley chromosome 3H at 0.2 centimorgans (cM) proximal to RFLP marker VT1 and 0.5 cM distal from RFLP marker C970 in the Bowman × Magnif 102 population. Map positions and the relative order of the markers were confirmed in the Moore × Virginia 92‐42‐46 population. RFLP analysis of the near isogenic line (NIL) Magnif 102/*8Bowman, the susceptible recurrent parent Bowman, and Rph5 donor Magnif 102, confirmed the close linkage of the markers VT1, BCD907, and CDO549 to Rph5. Results from this study will be useful for marker‐assisted selection and gene pyramiding in programs breeding for leaf rust resistance and provide the basis for physical mapping and further cloning activities.