Collaboration for Plant Pathogen Strain Identification (CPPSI)

CPPSI is a science based initiative developed to standardize the identification of plant pathogen strains and races based on sets of host differentials and reference pathogen strains.

The consistent naming of plant pathogen strains and races is a recognized need in industry and academia and there is no recognized global body that regulates the naming of plant pathogen strains. Consequently, a US based effort was initiated in 2007 by the International Seed Federation (ISF) in partnership with the American Phytopathological Society (APS) to address this issue. An APS ad Hoc Committee was formed to achieve this goal. After a US-based system was defined and four pilot differential host sets developed and launched, the initiative took the name of the Collaboration for Plant Pathogen Strain Identification (CPPSI). CPPSI has continuing support from the American Seed Trade Association (ASTA), APS and ISF. CPPSI is now housed at the UC Davis Seed Biotechnology Center.
See CPPSI website

The European Seed Association (ESA)

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, ESA’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 ESA’s 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

The International Working Group on Peronospora farinosa (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.

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.


The Pathology laboratory of the French National Seed Testing Laboratory (SNES) offers different services including the evaluation of a variety’s resistance to viruses, bacteria, fungi, nematodes and aphids, the supply of reference isolate (Reference controls and differential are supplied via the MATREF network), the characterisation of races using host differentials, as well as the supply of inoculums.
See: MATREF on the website of GEVES

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.

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