Skip to main content
U.S. flag

An official website of the United States government

A barcode-based phylogenetic characterization of Phytophthora cactorum identifies two cosmopolitan lineages with distinct host affinities and the first report of Phytophthora pseudotsugae in California


Tyler B. Bourret
Sebastian N. Fajardo
Cole P. Engert
David M. Rizzo



Publication type:

Scientific Journal (JRNL)

Primary Station(s):

Pacific Southwest Research Station


Journal of Fungi. 8(3): 303


A collection of 30 Phytophthora cactorum and 12 P. pseudotsugae (subclade 1a) strains isolated from several recent surveys across California was phylogenetically compared to a worldwide collection of 112 conspecific strains using sequences from three barcoding loci. The surveys baited P. cactorum from soil and water across a wide variety of forested ecosystems with a geographic range of more than 1000 km. Two cosmopolitan lineages were identified within the widespread P. cactorum, one being mainly associated with strawberry production and the other more closely associated with apple orchards, oaks and ornamental trees. Two other well-sampled P. cactorum lineages, including one that dominated Californian restoration outplantings, were only found in the western United States, while a third was only found in Japan. Coastal California forest isolates of both Phytophthora species exhibited considerable diversity, suggesting both may be indigenous to the state. Many isolates with sequence accessions deposited as P. cactorum were determined to be P. hedraiandra and P. ×serendipita, with one hybrid lineage appearing relatively common across Europe and Asia. This study contains the first report of P. pseudotsugae from the state of California and one of the only reports of that species since its original description.


Bourret, Tyler B.; Fajardo, Sebastian N.; Engert, Cole P.; Rizzo, David M. 2022. A barcode-based phylogenetic characterization of Phytophthora cactorum identifies two cosmopolitan lineages with distinct host affinities and the first report of Phytophthora pseudotsugae in California. Journal of Fungi. 8(3): 303.


Publication Notes

  • We recommend that you also print this page and attach it to the printout of the article, to retain the full citation information.
  • This article was written and prepared by U.S. Government employees on official time, and is therefore in the public domain.