The foundation for this project is an extensive collection of well-characterised yellow rust isolates available from the GRRC at AU as well as the wheat genetic breeding lines and varieties provided by ICARDA, CIMMYT and AU.

The work programme is organised according to the work packages (WP) described below, with the inter-relationship expressed in the project diagram given at the bottom of this page.

Epidemiological parameters involved in increased aggressiveness (WP1)

Mogens Støvring Hovmøller

Lead of WP1

This WP will explore and identify easy, robust and reliable measures of pathogen aggressiveness and high-temperature tolerance. Aggressive and non-aggressive isolates from the GRRC collection will be compared under different temperature regimes. Macroscopic comparison will be made for germination frequency, infection efficiency, latency period, lesion growth, uredinium density and spore production. Temperature requirements for R-gene mediated resistance will be studied. By inoculating resistant wheat varieties with virulent and avirulent P. striiformis phenotypes under contrasting temperatures we will investigate how temperature sensitivity interacts with rust resistance, e.g. resistance governed by the Yr15 R-gene which has reduced efficiency in adult plants during summer.

Role of sexual and asexual recombination in the evolution of increased aggressiveness (WP2)

Annemarie Fejer Justesen

Lead of WP2

This WP will examine the significance of asexual and sexual recombination in the emergence of increased aggressiveness in P. striiformis. AU has already successfully established an experimental on field-assay for asexual recombination, which uses mixed inoculation of well characterised isolates onto the same host leaves. An experimental system under greenhouse conditions will be developed to study the role of asexual recombination in generating increased aggressiveness. Asexual recombinants as well as their parents will be assessed for the relevant epidemiological parameters (WP1). The investigation of the role of sexual recombination in generating aggressiveness will take place in two steps: 1) an experimental system for sexual crosses that includes both the primary wheat host and the alternate Berberis spp. host will be established in collaboration with INRA, and 2) parental isolates, which are well characterised for virulence phenotype, DNA-genotype and having diverging levels of aggressiveness, will be crossed and segregation ratios in F1 and F2 populations will be analysed.

Molecular mechanisms underlying increased aggressiveness and high-temperature tolerance (WP3)

Stephanie Walter

Lead of WP3

This WP will study the potential of P. striiformis to adapt to both host and environmental factors. Transcripts associated with higher aggressiveness and acquired higher temperature-tolerance will be identified by comparison of transcript expression profiles following Solexa/Illumina RNA sequencing. Transcript expression will be examined during the growth stages and under the temperature-conditions found to be optimal in WP1. The transcript expression-based identification of aggressiveness- and high temperature tolerance-associated genes will be assisted by studying the segregation of these genes in the offspring of sexual recombinants (WP2). Identification of these key adaptation factors will support the development of molecular markers (WP5) for rapid detection and monitoring of new threatening aggressive or otherwise genetically advanced strains. Transcript sequences will be used to support effector identification in WP4.

Identification of fungal effectors and corresponding host R-genes (WP4)

Hans Thordal Christensen

Lead of WP4

This WP will first examine the pathogenic arsenal of Puccinia spp. of different host origins, i.e. wheat, triticale and seed-grass. Cross-isolate and –species comparisons of genic, intergenic and repetitive regions will be engaged to reveal effectors and pathogenicity-associated elements and regions, such as retrotransposons, highly variable genome islands, and re-arrangements or alterations. Genes encoding secreted effector candidates will be identified assisted by the occurrence of transfer signals, such as the YxC-protein motif, proposed to allow for effector delivery into host cells. Secondly, putative pathogenicity determinants will be introduced one-by-one into wheat leaf cells by using a bacterial type-3 secretion system (TTSS). In order to identify those effectors which are recognized by host R-proteins, we will TTSS-deliver them into leaf cells using our collection of wheat lines and newly identified lines from WP6, in which a broad set of yellow rust R-genes are present. In order to substantiate the biological role of the identified recognized effectors for P. striiformis, we will analyze to what extent they promote fungal growth in plants without the corresponding R-gene, e.g. by suppressing defence. These studies, which will TTSS-deliver effectors into wheat leaf cells followed by fungal inoculation, will help to choose essential pathogenicity determinants for selection of valuable rust R-genes for plant breeding.

Evolution of fungal virulence – durability of resistance (WP5)

Mogens Støvring Hovmøller

Lead of WP5

WP5 will examine the emergence of fungal virulence and aggressiveness throughout time and across a large geographical scale. This WP will employ detailed molecular phylogenetic analysis of a) isolates of world-wide origin sampled after 2000, where the current aggressive and high-temperature tolerant P. striiformis strains were first discovered, and b) historic isolates sampled mainly from Africa, Asia and Europe between 1950 and 1990. Both comprehensive isolate collections are hosted by GRRC, and currently being extended by isolates submitted by ICARDA and CIMMYT to GRRC for virulence phenotyping and DNA-genotyping. This WP will examine virulent and/or aggressive P. striiformis isolates or strains of different geographical and host origin, as well as P. pseudostriiformis isolates which are adapted to higher temperatures. Markers will also be derived for identified effector genes (WP4), and ideally also for genes, which are linked to increased aggressiveness (WP3). A modelling tool for predicting the durability of rust R-genes with different epidemiological characteristics will be established based on an existing pathogen population model system. The models will be modified to account for host resistance characteristics and for variable fitness costs associated with individual effectors and aggressiveness. A simulation tool for predicting R-gene ‘durability’ will be integrated into the information platform (WP7) to allow for assessment of resistance deployment scenarios in time and space.

Implementation of new resistance in plant-breeding (WP6)

Lars Eriksen

Lead of WP6

Aggressive Danish P. striiformis isolates will be used to screen for novel R-genes in wheat genetic material from the international institutions ICARDA and CIMMYT. Resistant and generally susceptible lines will be crossed. Resistance genes in yellow rust resistance-phenotyped double-hapoids will be mapped based on existing wheat maps using SNP and SSR markers. New identified molecular markers which are linked to rust R-genes will be valuable in marker-assisted selection in Sejet’s breeding programmes, allowing for example to combine several R-genes by gene pyramiding. Rust resistant wheat lines will enter WP4 for effector-driven search for valuable R-genes. WP4 will supply R-genes recognising conserved effectors to this WP.

Coordination and dissemination (WP7)

Jens Grønbech Hansen

Lead of WP7

Efficient management of the project will be ensured by means of regular meetings, establishment of a transparent management structure and the use of an efficient project management tool. The project is coordinated with relevant national and international activities. New data and web tools will be implemented in the existing Wheat Rust Toolbox platform hosted by AU. Draft versions of an early warning system for the emergence of new virulent and aggressive strains of yellow rust, and the internet based tool for prediction of the durability of R-genes, as reflected by different scenarios of breeding and deployment strategies of crop varieties in time and space, will also be developed. Using the Wheat Rust Toolbox and the GRRC web site, the outcomes of the project will immediately be integrated and communicated to the cereal breeding and rust community at both national and international levels.