The RustWatch project has demonstrated that a coordinated European monitoring system for wheat yellow-, brown and stem rust, which are spread by airborne spores across national borders, is the most relevant and cost-effective approach to monitoring and assessment of rust vulnerability in wheat. The system is based on national rust monitoring programsin a number of European countries, e.g. UK (NIAB), France (INRAE), Germany (JKI), Poland (IHAR) and Denmark (AU, GRRC). Systematic rust sampling is facilitated by extension services and variety testing organisations, plant breeding companies, and support by international rust laboratories serving regions without rust diagnostic facilities. This enables rapid detection of new rust variants (races) and onwards spread in Europe, which is visualized by a web-based information system . Procedures for sample submission, testing and reporting:

• Collection of rust samples upon first detection of atypical/unusual rust symptoms on wheat varieties in the field (after agreement with relevant parties).

• Sample submission to a rust diagnostic laboratory, including key sampling information.

• Alignment of national results by submission of key races/new variants to GRRC (yellow and stem rust)/ INRAE (brown rust) for interpretation in a European/global context.

• Visualisation of European results on common maps and charts provided by the Wheat Rust Toolbox .

The system allows collection and purification of stock isolates, which are available for assessment of rust vulnerability of varieties at national scale or for individual companies to screen their breeding lines. Disease surveillance, rust sampling and testing at national levels is supported by involved stakeholders and national funding of diagnostic capacities, whereas components providing added value at the European level require additional funding.

European wide monitoring of the three wheat rust pathogens in the RustWatch project has demonstrated frequent shifts in pathogen populations and that new variants (races) may spread across large areas in Europe within a single or few growing seasons. Depending on the origin and virulence of new races of the individual rust pathogens and the sources of resistance in the wheat host, they may cause either large or minor shifts in rust susceptibility. Sometimes only a single wheat variety is affected by a new race whereas in other cases the changes may affect multiple and widely grown varieties.The impact of new races on rust susceptibility are generally investigated under experimental conditions in the laboratory and greenhouse as well as under field conditions, where varietal resistance mainly expressed at adult plant growth stages can be assessed. The results of such pathogen-specific investigations of rust susceptibility form the basis for disease ratings in National and Recommended Lists of varieties in each country. More than 260 European wheat varieties were investigated under medium-high disease pressure at multiple locations in 7 countries from 2019 to 2022 , which has been implemented in the EU. Farmer recommendations for choice of disease resistant varieties are often communicated via websites of national variety testing organisations, national rust diagnostic laboratories and by local agricultural advisory companies and organisations as well as in agricultural magazines and newspapers.

Control of yellow and brown rusts of wheat across Europe can be enhanced by continuing and further strengthening efforts to breed for durable resistance in varieties with market-leading quality, yield and other key traits. This type of resistance has been broadly effective against diverse new rust pathotypes in most wheat varieties. Further advances in durable resistance, building on the breeding industry’s success over recent decades, will reduce the susceptibility of the European wheat crop to new genotypes of rust fungi, including incursions from other continents. By reducing the incidence of sudden breakdowns in resistance, this will provide a solid foundation for other control measures. Reliable data should be published so that farmers can choose to grow varieties which are likely to have high durable resistance. There should be a similar focus on improving durable rust resistance world-wide, building on the work of CIMMYT and national breeding programmes in several countries. As well as helping to protect crops locally, this will reduce the quantity of rust spores produced and disseminated globally. Strengthening breeding for durable resistance will be a win-win activity because Europe is both a source and a recipient of global rust dispersal. Continuing rust surveillance at the European scale over the next 20-30 years will continue to provide early warning of potentially damaging, novel pathotypes, while breeding for durable rust resistance is reinforced across Europe as a whole.

In RustWatch project INRAE developed DiverCILand (Diversity of Crops In Landscape) to provide a FAIR access to crop varietal deployment over countries, as well as landscape resistance levels or vulnerability maps. DiverCILand aims to provide user friendly interfaces to submit, extract or visualize data. It relies on an open source software, designed to support data management of regional/national data on crops and varieties. The DataBase has been fed with collected data on wheat varietal deployment in Europe (17 countries), as well as information on rust resistance genes or scores, and SNP genotyping identifying R-genes. Users have the opportunity to manage deployment of resistance data at different geographic scales, from counties and regions to countries. DiverCILand is accessible to https://wheat-diverciland.moulon.inrae.fr/, it needs a user account.

Efforts have been made to develop original visualization interfaces. DiverCILand provides charts on life-cycles of varieties, or varietal resistance levels. This tool also provides maps combining information on varietal deployment and resistance level or genotyping data. To visualize on a same map or graph the data from different countries using heterogeneous scales, DiverCILand uses a conversion-scale file to convert the submitted scores to a common scale. Such maps highlight the contrasted dynamics in varietal diversity and turnover in the different European countries, raising questions both on the diversity of seed systems and business, as well as their impact on rust disease resistances.

Barberry species may serve as a sexual host of stem rust fungi infecting cereal crops where new pathogen diversity can be generated. We reported that multiple specialised forms of cereal stem rust can undergo sexual reproduction on barberry species in Europe, which can potentially infect major cereal crops such as wheat, barley, rye and oat. The results stress the importance of rust surveillance in areas where barberry species and cereals coexist and where suitable conditions for completion of the sexual cycle may be present. It is advised to avoid growing cereal crops in the vicinity of barberry bushes when possible and to avoid the use of these as hedgerows. Additionally, the use of rust-resistant ornamental barberry species should be avoided as these may create new rust-susceptible barberry hybrids, which may have strong implications for the epidemiology of cereal rusts. The risk that the sexual cycle may pose to cereal production in Europe underlines the need to intensify rust resistance breeding strategies to enhance cereal crop disease resistance in case the alternate host becomes a significant part of the epidemiology of stem rust in Europe. Future screening of cereal germplasm commonly grown in Europe using sexual populations of stem rust will allow to evaluate the current level of stem rust susceptibility and the durability of specific resistance genes. This will help to select resistance genes and combinations thereof, which are expected to be more durable, and to develop more sustainable disease management and resistance deployment strategies.

Yellow rust and brown rust are very serious diseases in wheat crops in major parts of Europe. Significant amounts of fungicides are today applied to minimize the loss from these attacks. With the wish to strengthen IPM control measures 23 trials were carried out in 9 European countries seeking deeper knowledge on how to manage rust diseases with less use of fungicides. The outcome is summarized below.

1. Resistant cultivars proved very effective to escape rust diseases and also cultivar mixtures proved effective in reducing risk of attack and was good at stabilizing yields. Farmer’s cultivar choice should consider resistance to all important diseases e.g also Septoria tritici blotch (STB).

2. Rust diseases are not difficult to control using reduced rates of fungicides (25-50%) even under high disease pressure. This requires, however that effective products are available.

3. Correct timing is very important for achieving good and effective rust control from fungicides. Chemical control should be initiated at the first sign of yellow rust in a field or when regional warnings estimate a high risk of attack in specific cultivars.

4. Use of Decision support systems (DSS) was tested in the project and provided sufficient control of rust diseases and competitive net yield results due to less input of fungicides. DSS systems should integrate the overall disease risk including risk for STB.

5. To minimize risk for development of fungicide resistance different actives representing different mode of actions should be applied, if more than one treatment is needed.

6. No good alternatives to fungicides have been found yet, which has a potential to replace the current fungicides. The search for alternatives needs to continue.

Early warning of emerging pathogens requires immediate or short-term actions and alerts (few days to a few months) e.g. an effective system for collecting disease surveillance and sampling data, fast and reliable characterisation of pathogen samples and effective coordinated communication and dissemination of results. Wheat rust diseases don’t stop at borders and there is a need for regional, European or even global collaboration. We cannot predict an invasion of new races – we must be prepared. Early warning also includes longer term actions (6-18 months) e.g. assessment of the epidemic potential of new emerging races, accelerated breeding for resistance, adaptation of IPM based prevention and control strategies and dissemination of synthesised and integrated results via stakeholder networks and academia articles, workshops and conferences. To facilitate wheat rust early warning in practice RustWatch agreed to use a common scale [link 9] for scoring of disease in farmers’ fields and field trials. This scale is now used in the Rust Survey Crowdsource App for the reporting on unusual attacks of yellow rust, leaf rust and stem rust in wheat [link 5], by the official wheat variety testing system in Europe (VCU) [Link 8] and in the Field Nurseries when new breeding lines and new cultivars are tested before release [Link 4]. As such, all results are now comparable across tools, and data can easily be shared among partners in Europe. In a similar way, we established a network of labs capable of pathogen diagnostics, genotyping and race phenotyping using harmonised protocols. Results from the labs indicate the traits of new rust races e.g. which cultivars are vulnerable for disease attack. Sharing of comparable data among EU countries makes it possible to understand and warn about the spread and evolution of rust races in Europe [Link 10].

Several new web based tools and services were developed during the first two years of the RustWatch project. A new crowdsource smartphone app [Link 5] was used in the case study regions in 2020 for disease surveillance. In 2021, the use of the App will be expanded to regions and partners beyond the RustWatch consortium, to discuss the potential, reliability and sustainability of such tools for wheat rust early warning. A similar SmartPhone App was developed for use during sampling of wheat rust isolates to be diagnosed and characterised in the lab. The type of rust as genotype (DNA profile) are immediately available on maps and charts [Link 6]. The maps and charts are available in 5 different languages [Link 7]and they can be embedded into any web based regional Agricultural Knowledge and Information Systems aiming at analysing the results in a regional IPM context. RustWatch established a fruitful collaboration with the official variety testing (VCU) in Europe, and a Trap nursery data management system – managed by VCU themselves – collected disease scorings [Link 8] on six differential cultivars and susceptible reference cultivars for yellow rust, leaf rust and stem rust. VCU partners also sampled isolates and the results as genotyping and race phenotyping improve the VCU wheat testing and evaluation of new wheat cultivars. A similar system was developed for managing all data from field nurseries, aiming at testing more than 200 of the most grown cultivars in Europe in six Case Study Regions. The Trap nursery and Field nursery activities and associated tools and services facilitate the best options for farmer’s choice of cultivars and minimises the risk of severe epidemics in Europe. The experiences so far show that these tools and services motivate sharing of data, harmonization of methodologies, facilitating more robust conclusions and effective awareness raising regarding wheat rust development in Europe.

IPM strategies that combine cultivar resistance, the use of low fungicide input combined with control thresholds and alternative chemistry as reliable control measures was tested in six case study regions (CSR) in Spain, Italy, Germany, Switzerland, UK and Denmark. Results from these trials are disseminated via our IPM Trials section [Link 1] on the website. Differences and similarities in IPM strategies were discussed at CSR workshops in 2019 and 2020. All material in local language is available via our Case Study Regions section [Link 2] on our website. From February to May 2020, a new crowdsource smartphone app was used in the case study regions for disease surveillance campaigns [Link 3] in early spring 2020; specifically aimed at reporting which varieties were affected by wheat rust disease and which were not. All regions effectively uploaded data to a common Dashboard (more than 450 observations). The most affected (and not affected) varieties were identified and farmers and advisors were timely informed about the needs for control actions. In collaboration with the breeding network, 214 most grown cultivars were identified and exposed via field nurseries [Link 4] to regional growing conditions and regional pathogen races in the six case study regions. Results from 2019 showed that more than 90% of the tested varieties were resistant to yellow rust, 47% to leaf rust but only 5% to stem rust.