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Early Access MAY 2022; International audience; Invasions of new races can have contrasting consequences on populations of Puccinia striiformis f. sp. tritici, causing yellow rust of wheat. For example, the emergence of PstS7 (Warrior race) had major impacts in Europe and in France. By contrast, PstS2 had no impact in France, while it significantly affected other parts of the world. The objective of this study was to better understand factors that govern the success of an invasive race, taking the contrasting history of PstS7 and PstS2 in France as a case study. We compared these two races for three key factors driving invasive potential: (a) virulence against local cultivars, (b) aggressiveness in local environmental conditions, and (c) competitiveness against local races. During the period when PstS2 was detected, 70% of the grown wheat area was protected against this race by at least one known Yr resistance gene. By contrast, we found that only 15% of the wheat area had a low risk of infection by PstS7. In planta competition experiments suggested a higher competitiveness of PstS7 against local isolates compared to PstS2 in optimal thermal conditions. In silico experiments, based on thermal performance curves, suggested a high competitiveness of PstS7 considering infection efficiency. PstS2 was extremely competitive against local races in all considered environments (20 French sites x 15 years) due to its short latency period. Our findings highlight the importance of considering adaptation to environmental conditions, particularly temperature, in addition to virulence spectrum, in order to understand the evolutionary trajectories of emerging strains in pathogen populations.

Transcriptomics is being increasingly applied to generate new insight into the interactions between plants and their pathogens. For the wheat yellow (stripe) rust pathogen (Puccinia striiformis f. sp. tritici, Pst) RNA-based sequencing (RNA-Seq) has proved particularly valuable, overcoming the barriers associated with its obligate biotrophic nature. This includes the application of RNA-Seq approaches to study Pst and wheat gene expression dynamics over time and the Pst population composition through the use of a novel RNA-Seq based surveillance approach called “field pathogenomics”. As a dual RNA-Seq approach, the field pathogenomics technique also provides gene expression data from the host, giving new insight into host responses. However, this has created a wealth of data for interrogation. Results: Here, we used the field pathogenomics approach to generate 538 new RNA-Seq datasets from Pst-infected field wheat samples, doubling the amount of transcriptomics data available for this important pathosystem. We then analysed these datasets alongside 66 RNA-Seq datasets from four Pst infection time-courses and 420 Pst-infected plant field and laboratory samples that were publicly available. A database of gene expression values for Pst and wheat was generated for each of these 1024 RNA-Seq datasets and incorporated into the development of the rust expression browser (http://www.rust-expression.com). This enables for the first time simultaneous ‘point-and-click’ access to gene expression profiles for Pst and its wheat host and represents the largest database of processed RNA-Seq datasets available for any of the three Puccinia wheat rust pathogens. We also demonstrated the utility of the browser through investigation of expression of putative Pst virulence genes over time and examined the host plants response to Pst infection. Conclusions: The rust expression browser offers immense value to the wider community, facilitating data sharing and transparency and the underlying database can be continually expanded as more datasets become publicly available. EEA Bordenave Fil: Adams, Thomas M.. John Innes Centre. Norwich Research Park; Reino Unido Fil: Olsson, Tjelvar S.G. John Innes Centre. Norwich Research Park; Reino Unido Fil: Ramírez-González, Ricardo H. John Innes Centre. Norwich Research Park; Reino Unido Fil: Bryant, Ruth. RAGT Seeds Ltd.; Reino Unido Fil: Bryson, Rosie. BASF SE. Agricultural Centre; Alemania Fil: Campos, Pablo Eduardo. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Bordenave; Argentina Fil: Fenwick, Paul. Limagrain UK Ltd.; Reino Unido Fil: Feuerhelm, David. Syngenta Seeds Ltd.; Reino Unido Fil: Hayes, Charlotte. Elsoms Wheat Ltd.; Reino Unido Fil: Henriksson, Tina. Lantmännen Lantbruk; Suecia Fil: Hubbard, Amelia. NIAB; Reino Unido Fil: Jevtić, Radivoje. Institute of Field and Vegetable Crops; Serbia Fil: Judge, Christopher. NIAB; Reino Unido Fil: Kerton, Matthew. DSV United Kingdom Ltd.; Reino Unido Fil: Lage, Jacob. KWS UK Limited; Reino Unido Fil: Lewis, Clare M. John Innes Centre. Norwich Research Park; Reino Unido Fil: Lilly, Christine. Frontier Agriculture; Reino Unido Fil: Meidan, Udi. Hazera Seeds Ltd.; Israel Fil: Novoselović, Dario. Agricultural Institute Osijek; Croacia Fil: Patrick, Colin. Masstock Arable (UK) Ltd.; Reino Unido Fil: Wanyera, Ruth. Kenya Agricultural and Livestock Research Organization; Kenia Fil: Saunders, Diane G.O. John Innes Centre. Norwich Research Park; Reino Unido

Understanding of long-term virulence dynamics of pathogen populations in response to host resistance gene deployment is of major importance for disease management and evolutionary biology. We monitored the virulence dynamics of Puccinia striiformis f. sp. tritici, the causal agent of wheat stripe rust, over 25 years in France. Virulence dynamics was explained by estimates of area associated with resistance genes carried by farmers' cultivars. The epidemics assessed through disease severity significantly correlated with the number of P. striiformis f. sp. tritici isolates collected each year, used to describe virulence dynamics. In the south, the dominance of the Mediterranean pathotype 6E16 and the cultivation of a susceptible cultivar were associated with an epidemic from 1997 to 1999. In the north, five epidemics occurred due to successive acquisition of virulence to the resistance genes Yr7, Yr6, Yr9, Yr17, and Yr32, either by acquisition of the virulence in the previous dominant pathotype or by incursion or selection of one or two new pathotypes. Frequency of pathotypes with Vr7 and Vr6 declined with the reduction in the cultivation of corresponding Yr gene cultivars, whereas the virulence Vr9 persisted longer than the cultivation of Yr9 cultivars. Although the first pathotypes carrying Vr9 decreased, this virulence persisted in other pathotypes even in the absence of Yr9 cultivars. At the regional level, Yr9 cultivars in the north caused a shift from high Vr6 frequency to high Vr9 frequency whereas, in the central region, where Yr9 cultivars were rare, Vr6 remained prevalent.

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Session 4 : Génétique et Evolution des Populations Poster n°4.9; absent

Environmental heterogeneity influences coevolution and local adaptation in hostparasite systems. This also concerns applied issues, because the geographic range of parasites may depend on their capacity to adapt to abiotic conditions. We studied temperature-specific adaptation in the wheat yellow/stripe rust pathogen, Puccinia striiformis f.sp. tritici (PST). Using laboratory experiments, PST isolates from northern and southern France were studied for their ability to germinate and to infect bread and durum wheat cultivars over a temperature gradient. Pathogen origin x temperature interactions for infectivity and germination rate suggest local adaptation to high- versus low-temperature regimes in south and north. Competition experiments in southern and northern field sites showed a general competitive advantage of southern over northern isolates. This advantage was particularly pronounced in the southern home site, consistent with a model integrating laboratory infectivity and field temperature variation. The stable PST population structure in France likely reflects adaptation to ecological and genetic factors: persistence of southern PST may be due to adaptation to the warmer Mediterranean climate; and persistence of northern PST can be explained by adaptation to commonly used cultivars, for which southern isolates are lacking the relevant virulence genes. Thus, understanding the role of temperature-specific adaptations may help to improve forecast models or breeding programmes.

This study is focused on the identification of early response genes involved in the resistance mechanism of one of the most important diseases of wheat, yellow rust. The strategy undertaken was to use differential display reverse transcriptase-PCR method (DDRT-PCR) on two of the yellow rust differential lines of wheat, were infected with the virulent and the avirulent Puccinia striiformis f. sp. tritici races together with appropriate control inoculations. Upon infection of the plant materials (resistant and/or susceptible), different time points were evaluated on DDRT-PCR banding profiles. The expression level differences of 33 genes in DDRT-PCR were further analyzed using quantitative real-time PCR (qRT-PCR). Among which only those (14 gene fragments) resulting reproducible induction or repression levels were reported with measured fold changes. Based on the sequence similarity analysis, all but one were absent in NCBI databank, thus they are newly found wheat sequences. Among those, two genes were identified as full ORF, including 5′ and 3′ end untranslated regions (UTR); namely cyclophilin like protein (putative antifungal activity) and ubiquitin-conjugating enzyme (E2) or Rad6. The sequence homology analysis of the cloned gene fragments revealed that the genes detected may have roles in ubiquitinylation, programmed cell death (apoptosis), putative antifungal activities, disease resistance responses, pathogenesis related responses, and including a few with no known function.