Collaboration for Plant Pathogen Strain Identification
Collaboration for Plant Pathogen Strain Identification
Collaboration for Plant Pathogen Strain Identification
University of California
Collaboration for Plant Pathogen Strain Identification

Welcome to CPPSI

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

System Background

Photo collage (seeding, watermelon, tomatoes, melon, lettuce field)


CPPSI came into existence by a unique path: 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 with a focus on disease systems for which claims of disease resistance are made by the seed industry. After a US based system was defined and four pilot differential host sets developed and launched in 2012 and 2013, 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. In early 2015, CPPSI was housed at the UC Davis Seed Biotechnology Center. Thanks to a three year commitment of funding from seven seed industry founding sponsors, a Director was hired and is based at the UC Davis Seed Biotechnology Center to coordinate the development, distribution and administration of new and current  differential host sets, reference plant pathogen strains and informative white papers. In addition, the Director works with members of European plant variety registration and trade organizations to collaborate with similar ongoing initiatives.  CPPSI is now recognized by APS as a subcommittee to the APS Collections and Germplasm Committee.

Accomplished CPPSI Goals

  • Organized a US-based network of seed industry scientists and professionals from private, government and public research for the distribution of seeds of differential host sets and cultures of reference plant pathogen strains to facilitate the identification of plant pathogen races and strains.
  • Developed a system to distribute host sets and reference strains to facilitate the identification of pathogen strains based on host - pathogen reactions. Host differentials contain specific resistance genes and established procedures in peer-reviewed scientific publications are used to identify pathogen strains.
  • Developed a business plan to explain how the system operates, the benefits, risks and costs associated with this system.
  • Secured funding and a base of CPPSI operation at UC Davis Seed Biotechnology Center.
  • This system complies with US regulatory pathogen movement guidelines and complements existing European systems (European Seed Association (ESA), the Naktuinbouw isolate group in the NL, International Bremia Evaluation Board (IBEB), the International Working Group on Peronospora (IWGP), GEVES MATREF network in France, the Plantum Phytopathology working group and the ISF Disease Resistance Terminology working group).
  • Developed a plan for the maintenance and long-term storage of host differential seeds and reference pathogen strain cultures that can be accessed by the international community.

The Value of CPPSI to the Seed Industry, Academia and Regulators 

  • Provides a tool for consistent identification of pathogen strains
  • Builds confidence and clarity in disease resistance claims
  • Early warning of new/emerging pathogen strains that overcome resistance
  • Allows improved "due diligence" for resistance claims which may reduce liability
  • Provides a reference baseline for plant pathogen strain virulence in research and resistance plant breeding
  • Serves as a repository for differential host and pathogen collections of retiring experts

Availability of Differential Host Sets and Reference Strains

Differential host sets are accepted plant varieties used to define strains of plant pathogens based on susceptible or resistant reactions.  Reference strains are known characterized isolates of a given pathogen strain. To launch the initiative, CPPSI described the pathogen strains and the differential host reactions in white papers for:
Melon Fusarium wilt • Pepper bacterial spot • Spinach downy mildew • Tomato mosaic virus
Each white paper provides information on how to identify pathogen strains or races and resistance traits of the host cultivars. Seed of the differential hosts for each of these hosts can be ordered on line through the USDA Germplasm Resources Information Network (GRIN). Refer to the GRIN links noted on this site and in each of the white papers. For some hybrid host differentials, a Material Transfer Agreement (MTA) may be required to order seed. The GRIN order form indicates which differential hosts might require an MTA and the name of the person to be contacted for arranging an MTA.

To acquire the reference plant pathogen strains and races please refer to the contact information provided on this site and in each white paper. It is the responsibility of those requesting pathogen strains to ensure they have the necessary permits to receive the strains by contacting USDA-APHIS

Feedback: Please contact Phyllis for inquiries on how to participate and support CPPSI, provide feedback on new strains identified, views on the inoculation protocols, differential hosts, or any related matter.

Seeds: Bell pepper, tomato, melon, watermelon, lettuce
Seeds: Bell pepper, tomato, melon, watermelon, lettuce

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