Collaboration for Plant Pathogen Strain Identification (CPPSI)

The Collaboration for Plant Pathogen Strain Identification (CPPSI) is a U.S.-based initiative committed to standardizing the identification of plant pathogen strains. This is accomplished through distribution of validated host differentials and reference pathogen strains.

 CPPSI’s mission has been bolstered by the continuous support of key industry and academic entities, including the ISF, the American Phytopathological Society (APS), and the American Seed Trade Association (ASTA). The UC Davis Seed Biotechnology Center serves as the operational headquarters for CPPSI, providing an innovative environment for seed science research.

An integral part of CPPSI’s mission is the dissemination of knowledge and information. The CPPSI white papers, which detail the methodologies, findings, and insights, are readily accessible for public viewing. You can access them here (below) or at the CPPSI website.


Visit the CPPSI website for more information and to learn how you can contribute to our cause.

The European Seed Association (Euroseeds)

Company claims on the level of resistance in a variety to a pathogen are based on tests carried out with well-characterized isolates of the pathogen in controlled environmental conditions. This resistance may be effective against all or some biotypes, pathotypes, races or strains of the pathogen. However, pathogens are known to develop and form new biotypes, pathotypes, races or strains that can cause damage to plants that remain unaffected by the original form of the pathogen.

To provide support to companies in case of litigation through clear and consistent communication on disease resistance in vegetable crop varieties, Euroseed’s Working Group on Harmonization of Resistance Terminology has put together information on the strain/race of a pathogen to which commercial or other varieties are resistant and the level of resistance in a reference variety. This information is available for vegetable crops of the following types/categories – Brassicas/root crops, Cucurbits, large seeded crops, leafy crops and Solanaceae, and is updated regularly. 

For more information see Euroseeds’ Harmonized Resistance Tables.

The Germplasm Resources Information Network (GRIN)

GRIN is the online database for all plant accessions contained with the National Plant Germplasm System (NPGS) of the Agricultural Research Service within the U.S. Department of Agriculture. The NPGS acquires, characterizes, preserves, documents, and distributes to scientists and educators plant genetic resources of crop species and wild relatives important for food and agricultural production. GRIN contains seed of several differential hosts which are sets of plant accessions used to define races of plant pathogens by their known susceptible and resistant reactions. Differential sets for particular plant pathogens such as those contributed by the seed industry are assigned an identifying International Seed Federation number (ISF 1, ISF 2, etc.). Seed lots of differential hosts identified by an ISF number in GRIN have been tested for the proper susceptible or resistant reaction to the pathogen races. Plant pathologists can obtain information on the differential sets available in GRIN and request seed of differential sets from NPGS for race reaction testing at the GRIN website.

See Differential Hosts Table.

The International Bremia Evaluation Board (IBEB)

IBEB is a joint initiative of lettuce breeding companies in France and the Netherlands, the Dutch inspection service (Naktuinbouw) and the French National Seed Station (GEVES). IBEB aims to maintain and promote a well-defined and internationally agreed system of race denomination and to streamline the process of identifying new races of Bremia lactucae on the basis of annually updated information about the evolution of the pathogen in response to resistance in lettuce varieties. Companies provide information on the genetic background of varieties while Naktuinbouw and GEVES serve as independent testing facilities.

More information about IBEB on this page.

Press Release (1 June 2021): “Bremia lactucae, Bl: 37EU identified and denominated in Europe”

INIA – Seeds and Nursery Plants Testing Station

  • Plant Health Laboratory main activity:

We carry out pathogen resistance tests on vegetable varieties, in accordance with CPVO (Community Office of Vegetables Varieties) and UPOV (International Union for the obtaining of new commercial plant varieties) protocols wich complement the technical study carried out at the Valencia Center for Variety Evaluation Tests. These tests are necessary for the granting of plant breeders´s rights at national and European level and/or the authorisation of the marketing of new plant varieties.

  • Services and analytic techinics:
  1. Pathogen collection maintenance and update. The collection include viruses, bacteria, fungi and nematodes for own use and supply to companies in the sector. We are also members of the Harmorescoll European Network.
  2. Pathogen detection tests in seeds lots following ISTA (International Seed Testing Association) and ISF (International Seed Federation) protocols for monitoring seed health status.
  3. Pathogens resistance tests in horticultural varieties, mainly in tomato, pepper, lettuce, CUCUMBER, BEAN, PEA AND melon.
  4. Supply of inoculates to companies or organizations.
  5. Development of pathogen resistance protocols.
  • Collaboration and participation
  1. Collaboraiton with companies in the SEED sector: INIA-ANOVE (National Associtation of Plant Breeders) agreement on the conduct of research in the field of seed health
  2. Collaboration with EU examination offices in charge of DUS test
  3. Participation in training courses: “Plant Variety Rights online technical training for experts”
  4. Participation in international plant health groups, including participation in the ISF 2021 Disease Resistance Terminology Working Group
  5. “Harmonization of resistance test to diseases of vegetable crops in the European Union” Project, financed by the OCVV
  6. “Harmorescoll: Setting up an EU System for harmonized collections of reference isolates, controls and differentials to facilitate disease resistance testing” Project, financed by the OCVV
  7. Participation in the development and review of CPVO and UPOV protocols

More Information about INIA on this webpage:

The International Working Group on Peronospora effusa (IWGP)

IWGP was set up through the Dutch seed association Plantum NL by Naktuinbouw and companies trading spinach seed. It is supported by research centres in the USA, including the University of Arkansas and the University of California Cooperative Extension. IWGP continuously monitors the development of new races of downy mildew on spinach globally by testing uncommon field isolates on a fixed, common host differential set of varieties that contain the full range of available resistances, and denominate new races as and when necessary. IWGP aims to promote a consistent and clear communication between the seed industry, growers, and other interested parties about all resistance-breaking races that are persistent enough to survive over several years, occur in a wide area, and cause a significant economic impact.

For the latest updates type ‘spinach’ or ‘IWGP’ in the search area of Naktuinbouw’s News Overview.

Two new races of the downy mildew pathogen (Peronospora effusa) on spinach have been denominated by the International Working Group on Peronospora in spinach (IWGP) on the basis of a worldwide evaluation of isolates from growers fields and trap nurseries. The virulence patterns of all races are published as reference data by the International Seed Federation (ISF). For further information see the press release (15 April 2021) here

Resistance tests at GEVES

The evaluation of the resistance of varieties to pests and diseases is very important for varietal innovation, as it will provide a better description of the varieties being studied for registration in the French Catalogue and also for plant breeders’ rights. It necessitates the use of protocols, which are representative of the in-field reality, thus giving consistently reliable results with regard to the epidemiological situations that the registered varieties will confront. It is possible to achieve this at a European level through the implementation of harmonization programmes for DUS protocols, by using validated and harmonized reference materials, and through the collaboration of Research Institutes in the epidemiological monitoring of strains.


MATREF is a network of reference material managed by GEVES for testing varieties for resistance to pathogens and pests. It was created in 2002 for disease resistance tests performed for registration in the official French catalogue (CTPS), for Plant Variety Rights (CPVO or INOV), or for external clients.

In 2020, MATREF includes 202 control varieties and differential hosts, as well as 48 pathogens and pests (in connection with ISF differential host sets).

MATREF’s objectives are to:

  • Provide reliable and available reference material for disease resistance tests, including:
    • Controls: susceptible, intermediate, resistant cultivars
    • Differential hosts: for identification of races
    • Pest and pathogen isolates
  • Harmonise reference material (controls, differential hosts, pathogens and pests) between official laboratories and seed companies in order to optimise the consistency of results for resistance assessment when GEVES and INRAE check the resistance claims of seed companies.
  • Share tasks and costs between network members for validation, maintenance, and distribution of seed and pathogen strains.

The network is composed of private seeds companies and public partners (GEVES and INRAE).

For more information, please see:  MATREF on the GEVES website

The Naktuinbouw-Plantum Isolate Collection

This is an initiative of Naktuinbouw in collaboration with ten Dutch vegetable seed companies who are all member of Plantum NL, the Dutch association for breeding, tissue culture and trade of seeds and young plants. The collection covers viruses, bacteria, fungi, and nematodes and is used for resistance testing in connection with variety registration trials in vegetable crops. The isolates are validated regularly through biotests on susceptible and, if possible, also on race-differentiating resistant varieties. For members of the initiative isolates are provided free of cost. Non-members can order isolates once a year for use as reference isolates in resistance testing.
For more information see disease resistance testing on the Naktuinbouw website.

Members in this initiative organise an annual workshop to share information among companies and others about resistance testing problems and to strengthen the variety registration system by sharing their expert knowledge.

Disease resistance testing at Naktuinbouw

As resistance to diseases is important for maintaining crop health growers need reliable information about resistances when they select a variety to plant. Naktuinbouw provides information about resistance in various ways; primarily through testing for internal use, but also through offering the same tests to external clients, and last but not least by collaborating with breeders and other registration authorities on harmonization of the test procedures, isolates and standard varieties.

For some vegetable crops information about resistance has to be included in the variety description required to define and protect a variety. For these so-called obligatory disease resistance characteristics Naktuinbouw runs resistance tests at least once a year. Companies often want to include other disease resistance claims in the official variety description. This is possible when the company protocol conforms to an official protocol published by the European Community Plant Variety Office. The company’s disease resistance claims have to be checked by Naktuinbouw in an authorized test when the variety is submitted for Plant Breeders Rights.

Parallel to the resistance tests connected with the official variety descriptions, Naktuinbouw offers disease resistance tests as a service to external clients using the same official testing protocol.

For more information see disease resistance testing on the Naktuinbouw website.

Project Harmorescoll towards a European platform to improve resistance testing for DUS

Harmorescoll aims to improve the availability of reference materials (controls, differentials, isolates) in DUS resistance tests. The project is co-funded by CPVO and led by GEVES and Naktuinbouw, with members of other European examination offices and the seed industry. It was launched in March 2020. Once a year, all participants meet to discuss the progress, and to set the goals for the next year. This first-year annual meeting was in October, online, with 22 attendants. The project has started by reviewing CPVO protocols and UPOV guidelines to define reference material needed: 145 isolates of 58 pest species and 455 varieties of 15 crops. Next, we will investigate their availability in existing initiatives or collections. A set of rules for their validation has been drafted. Next steps will define conditions of delivery, and organization of a series of validation tests in examination offices and seed companies. Finally, we will set up an organization to ensure that the validated materials become and remain available for DUS.

ResearchGate link: