Brent McCallum

Leaf rust resistance gene Lr1, isolated from bread wheat (Triticum aestivum L.) is a member of the large psr567 gene family

In hexaploid wheat, leaf rust resistance gene Lr1 is located at the distal end of the long arm of chromosome 5D. To clone this gene, an F1-derived doubled haploid population and a recombinant inbred line population from a cross between the susceptible cultivar AC Karma and the resistant line 87E03-S2B1 were phenotyped for resistance to Puccinia triticina race 1-1 BBB that carries the avirulence gene Avr1. A high-resolution genetic map of the Lr1 locus was constructed using microsatellite, resistance gene analog (RGA), BAC end (BE), and low pass (LP) markers. A physical map of the locus was constructed by screening a hexaploid wheat BAC library from cultivar Glenlea that is known to have Lr1. The locus comprised three RGAs from a gene family related to RFLP marker Xpsr567. Markers specific to each paralog were developed. Lr1 segregated with RGA567-5 while recombinants were observed for the other two RGAs. Transformation of the susceptible cultivar Fielder with RGA567-5 demonstrated that it corresponds to the Lr1 resistance gene. In addition, the candidate gene was also confirmed by virus-induced gene silencing. Twenty T1 lines from resistant transgenic line T0-938 segregated for resistance, partial resistance and susceptibility to Avr1 corresponding to a 1:2:1 ratio for a single hemizygous insertion. Transgene presence and expression correlated with the phenotype. The resistance phenotype expressed by Lr1 seemed therefore to be dependant on the zygosity status. T3-938 sister lines with and without the transgene were further tested with 16 virulent and avirulent rust isolates. Rust reactions were all as expected for Lr1 thereby providing additional evidence toward the Lr1 identity of RGA567-5. Sequence analysis of Lr1 indicated that it is not related to the previously isolated Lr10 and Lr21 genes and unlike these genes, it is part of a large gene family.

Global status of wheat leaf rust caused by Puccinia triticina

Leaf rust caused by Puccinia triticina is the most common and widely distributed of the three wheat rusts. Losses from leaf rust are usually less damaging than those from stem rust and stripe rust, but leaf rust causes greater annual losses due to its more frequent and widespread occurrence. Yield losses from leaf rust are mostly due to reductions in kernel weight. Many laboratories worldwide conduct leaf rust surveys and virulence analyses. Most currently important races (pathotypes) have either evolved through mutations in existing populations or migrated from other, often unknown, areas. Several leaf rust resistance genes are cataloged, and high levels of slow rusting adult plant resistance are available in high yielding CIMMYT wheats. This paper summarizes the importance of leaf rust in the main wheat production areas as reflected by yield losses, the complexity of virulence variation in pathogen populations, the role cultivars with race-specific resistance play in pathogen evolution, and the control measures currently practiced in various regions of the world.

A review of wheat cultivars grown in the Canadian prairies

Wheat is Canadas largest crop with most of the production in the western Canadian prairie provinces of Manitoba, Saskatchewan and Alberta. Since wheat production started in western Canada, over 100 yr ago, market classes of hexaploid spring bread wheat (Triticum aestivum L.) were the dominant type of wheat, although production of durum wheat [Triticum turgidum L. ssp. durum (Desf.) Husn.)] has grown significantly over this period, and hexaploid winter wheat was grown on a relatively small portion of the wheat area. Within hexaploid wheat there has been diversification into a number of market classes based on different end-use quality criteria. The predominant spring bread wheat class has been the Canada Western Red Spring (CWRS) class. A few cultivars were grown extensively over a long period of time, such as the CWRS wheat Thatcher, which was the dominant cultivar from 1939 to 1968, and Kyle, which was the leading Canada Western Amber Durum (CWAD) cultivar from 1988 to 2004. Other cultivars dominated pa...

Review: Fusarium head blight of barley in western Canada

Fusarium head blight (FHB), caused primarily by Fusarium graminearum, has rapidly become the most notorious disease of cereals in parts of western Canada. The situation in barley is particularly striking, for until 1993 FHB was not observed in the crop at all, but by 1996 it affected every barley field examined in Manitoba. The disease is largely responsible for the decline in acreage and the loss of markets for both malting and feed barley in the region. Several aspects of FHB in barley are examined for this review, beginning with an overview and description of symptoms and disease epidemiology. Differences in the expression of FHB in barley as compared with wheat, including causal species, infection period, symptoms, and resulting damage (yield and quality losses) are described. These have implications for disease management, including breeding for resistance. The latter is ongoing at several institutions and should result in cultivars with improved resistance to FHB in future. Until then, an integrated protocol for disease management must be implemented to minimize the threat of FHB for producers and the industry.

Physiologic specialization of Puccinia triticina, the causal agent of wheat leaf rust, in Canada in 2006.

Abstract Commercial fields and research plots of wheat across Canada were surveyed for leaf rust during 2008. Leaf samples infected with the causal fungus, Puccinia triticina, were used to generate 407 single pustule isolates, 13 from Alberta, 302 from Manitoba and Saskatchewan, 71 from Ontario, 10 from Quebec and 11 from Prince Edward Island. Single pustule isolates were tested for virulence to 16 lines of ‘Thatcher’ wheat with single leaf rust resistance genes. Forty-six virulence phenotypes were identified; the most common were TDBJ (23.6%), TDBG (23.1%) and MLDS (18.9%). The frequency of virulence to both Lr9 and Lr17 increased compared with 2007, whereas it decreased for Lr24 and Lr2a. The populations from eastern Canada were more diverse than those from western Canada and contained many unique virulence phenotypes, and virulence to gene Lr18, which was not found in western Canada. Fifty-five isolates, representing each of the virulence phenotypes, were tested on six and 12 additional differential wheat lines at the adult and seedling stages, respectively. On the adult plant differentials, no isolates were virulent to Lr22a or Lr34, whereas all isolates except two were virulent to Lr13, and virulence varied for Lr12, Lr35 and Lr37. On the additional seedling differentials, all isolates were avirulent to Lr19, Lr21, Lr29 and Lr32, and only one isolate was virulent to Lr25. All isolates had similar infection types to Lr2b and Lr2a, varied in virulence to Lr3bg, Lr14b, Lr20, Lr23 and Lr28, and except for two were virulent to Lr15.

Host-induced gene silencing of wheat leaf rust fungus Puccinia triticina pathogenicity genes mediated by the Barley stripe mosaic virus.

Rust fungi are devastating plant pathogens and several Puccinia species have a large economic impact on wheat production worldwide. Disease protection, mostly offered by introgressed host-resistance genes, is often race-specific and rapidly overcome by newly-emerging virulent strains. Extensive new genomic resources have identified vital pathogenicity genes but their study is hampered because of the biotrophic life styles of rust fungi. In cereals, Barley stripe mosaic virus (BSMV)-induced RNAi has emerged as a useful tool to study loss-of-function phenotypes of candidate genes. Expression of pathogen-derived gene fragments in this system can be used to obtain in planta-generated silencing of corresponding genes inside biotrophic pathogens, a technique termed host-induced gene silencing (HIGS). Here we test the effectiveness of BSMV-mediated HIGS in the wheat leaf rust fungus Puccinia triticina (Pt) by targeting three predicted pathogenicity genes, a MAPK, a cyclophilin, and a calcineurin regulatory subunit. Inoculation of BSMV RNAi constructs generated fungal gene-specific siRNA molecules in systemic leaves of wheat plant. Subsequent Pt inoculation resulted in a suppressed disease phenotype and a reduction in endogenous transcript levels of the targeted fungal genes indicating translocation of siRNA molecules from host to fungal cells. Efficiency of this host-generated trans-specific RNAi was enhanced by using BSMV silencing vectors defective in coat protein coupled with introducing fungal gene sequences simultaneously in sense and antisense orientation. The disease suppression indicated the likely involvement of these fungal genes in pathogenicity. This study demonstrates that BSMV-mediated in planta-generated RNAi is an effective strategy for functional genomics in rust fungi.

Leaf rust and stripe rust resistance genes transferred to common wheat from Triticum dicoccoides

Linked leaf rust and stripe rust resistance genes introduced from Triticum dicoccoides protected common wheat seedlings against a range of pathotypes of the respective pathogens. The genes were chromosomally mapped using monosomic and telosomic analyses, C-banding and RFLPs. The data indicated that an introgressed region is located on wheat chromosome arm 6BS. The introgressed region did not pair with the ‘Chinese Spring’ 6BS arm during meiosis possibly as a result of reduced homology, but appeared to pair with 6BS of W84-17 (57% of pollen mother cells) and ‘Avocet S’. The introgressed region had a very strong preferential pollen transmission (0.96–0.98) whereas its transmission through egg cells (0.41–0.66) varied with the genetic background of the heterozygote. Homozygous resistant plants had a normal phenotype, were fertile and produced plump seeds. Symbols Lr53 and Yr35 are proposed to designate the respective genes.

Microsatellite tagging of the leaf rust resistance gene Lr16 on wheat chromosome 2BSc

Leaf rust, caused by Puccinia triticina, is one of the most damaging diseases of wheat worldwide. Lr16 is a widely deployed leaf rust resistance gene effective at the seedling stage. Although virulence to Lr16 exists in the Canadian P. triticina population, Lr16 provides a level of partial resistance in the field. The primary objective of this study was to identify markers linked to Lr16 that are suitable for marker-assisted selection (MAS). Lr16 was tagged with microsatellite markers on the distal end of chromosome 2BS in three mapping populations. Seven microsatellite loci mapped within 10 cM of Lr16, with the map distances varying among populations. Xwmc764 was the closest microsatellite locus to Lr16, and mapped 1, 9, and 3 cM away in the RL4452/AC Domain, BW278/AC Foremost, and HY644/McKenzie mapping populations, respectively. Lr16 was the terminal locus mapped in all three populations. Xwmc764, Xgwm210, and Xwmc661 were the most suitable markers for selection of Lr16 because they had simple PCR profiles, numerous alleles, high polymorphism information content (PIC), and were tightly linked to Lr16. Twenty-eight spring wheat lines were evaluated for leaf rust reaction with the P. triticina virulence phenotypes MBDS, MBRJ, and MGBJ, and analyzed with five microsatellite markers tightly linked to Lr16. There was good agreement between leaf rust infection type (IT) data and the microsatellite allele data. Microsatellite markers were useful for postulating Lr16 in wheat lines with multiple leaf rust resistance genes.

Leaf rust and stripe rust resistance genes derived from Aegilops sharonensis

SummaryLinked leaf and stripe rust resistance genes introgressed into hexaploid wheat from Aegilops sharonensis provided protection in the seedling stage to a wide range of pathotypes of the two diseases. Monosomic and telosomic analyses showed that the resistance genes occur on wheat chromosome 6A. This result could be confirmed making use of mapped chromosome 6A microsatellite markers. The introgressed chromatin appeared to involve the proximal part of 6AL and the complete 6AS arm and it was thus not possible to deduce the chromosome arm harbouring the resistance genes. The resistance showed non-Mendelian transmission. The genetic background of a heterozygote interacted with the introgressed region to result in either preferential or impaired female transmission. Male transmission appeared to be affected in a different way from female transmission and was exclusive in the genetic background studied. Symbols Lr56 and Yr38 are proposed to designate the respective genes of which line 0352-4 is the appropriate source material.

Proteome analysis of wheat leaf rust fungus, Puccinia triticina, infection structures enriched for haustoria

Puccinia triticina (Pt) is a representative of several cereal‐infecting rust fungal pathogens of major economic importance world wide. Upon entry through leaf stomata, these fungi establish intracellular haustoria, crucial feeding structures. We report the first proteome of infection structures from parasitized wheat leaves, enriched for haustoria through filtration and sucrose density centrifugation. 2‐D PAGE MS/MS and gel‐based LC‐MS (GeLC‐MS) were used to separate proteins. Generated spectra were compared with a partial proteome predicted from a preliminary Pt genome and generated ESTs, to a comprehensive genome‐predicted protein complement from the related wheat stem rust fungus, Puccinia graminis f. sp. tritici (Pgt) and to various plant resources. We identified over 260 fungal proteins, 16 of which matched peptides from Pgt. Based on bioinformatic analyses and/or the presence of a signal peptide, at least 50 proteins were predicted to be secreted. Among those, six have effector protein signatures, some are related and the respective genes of several seem to belong to clusters. Many ribosomal structural proteins, proteins involved in energy, general metabolism and transport were detected. Measuring gene expression over several life cycle stages of ten representative candidates using quantitative RT‐PCR, all were shown to be strongly upregulated and four expressed solely upon infection.