A field of crops in California.

Standardizing the language of plant pathogen strains or races

Disease resistance is an important trait for the sustainable, profitable production of vegetables. Farmers want to know that the seeds they plant are able to outcompete a diverse array of plant pathogens and pests that could threaten their crops. 

Currently, there is no uniform system for naming the multiple strains and races of plant pathogens, which can hinder breeders’ ability to keep up with emerging threats and undermine the accuracy of plant disease diagnostics and disease-resistance claims. CPPSI was established to address that need and help formalize a process for naming plant pathogen races and strains.

We work with public, private and government scientists and groups around the world to develop and provide the vegetable seed industry the tools to consistently identify plant pathogen race and strains. These efforts build confidence and clarity in disease-resistance claims and help develop early notification of new and emerging strains of pathogens.

Our working group is composed of scientists from the public, private and government sectors and represent organizations and companies who have become CPPSI members. Working group members collaborate to set disease system priorities and decide which will be developed into reference materials. 

Cantaloupe being harvested in the field.

Our Timeline


  • The International Seed Federation (ISF) and the American Phytopathological Society (APS) initiate an effort to standardize the naming of plant pathogens strains and races. A U.S. - based network of seed industry scientists and professionals from private, government and public research was formed to develop a system and a process that will meet this need.


  • Pre-CPPSI system was developed and approved by APS.
  • The first four disease systems were launched as Reference Materials
  • Pre-CPPSI became a page on the ISF website.


  • The initiative was given the name Collaboration for Plant Pathogen Strain Identification (CPPSI) and becomes a subcommittee of the APS Committee on Cultures and Germplasm.
  • The CPPSI website was launched.
  • The group developed a business plan and a system to distribute host sets and reference strains to facilitate the identification of pathogen strains.


  • ASTA approved CPPSI's business plan and seven seed company sponsors come forward with funding.
  • CPPSI advisory council is formed comprised of representatives of sponsoring seed companies.


  • CPPSI was housed at the UC Davis Seed Biotechnology Center. 
  • Director Phyllis Himmel was hired to coordinate the development, distribution and administration of new and current differential host sets, reference plant pathogen strains and informative white papers. 


  • The business plan was revised and updated to describe the evolution of CPPSI from start-up and establishment to a sustainable and growing initiative.  
  • CPPSI was awarded a California Department of Food and Agriculture Specialty Crop Block Grant to continue developing Reference Materials that facilitate the consistent identification and naming of plant pathogen strains and races.


  • Reference materials for Downy mildew in lettuce were launched.


  • Reference materials for tomato Tomato spotted wilt were launched.
  • Reference materials for pepper Tomato spotted wilt were launched.


  • Reference materials for watermelon Fusarium wilt were launched.


  • CPPSI and ISF collaborative comparative ring tests were completed for watermelon Fusarium wilt.


  • CPPSI collaborative comparative ring tests were completed for pepper Phytophthora crown and root rot. This disease system is under consideration as an ISF project.
  • September 5th, Kelley Clark hired as new CPPSI Director.
  • November 17th, CPPSI Director Phyllis Himmel retires.