Phytophthora pseudotsugae

Name and publication

Phytophthora pseudotsugae Hamm & Hansen (1983)

Hamm PB and Hansen EM. 1983. Phytophthora pseudotsugae, a new species causing root rot of Douglas fir. Canadian Journal of Botany 61: 2630–2626.


from Hamm and Hansen (1983)




named for its original host, Pseudotsuga menziesii


Type: UNITED STATES OF AMERICA, isolated from Douglas fir [Pseudotsuga menziesii (Mirb.) Franco] collected by R.G Pratt (USDA, Mississippi State University) in 1975 in a nursery in Westfir, Oregon; deposited in the American Type Culture Collection, Rockville, MD by Hamm (Hamm 268 = "Phytophthora sp. 1")

Ex-type: ATCC 52938 = Hamm 268 (Depositor PB Hamm, Chain of Custody Pratt to Hamm to ATCC)

NOTE: in the original publication of Hamm and Hansen (1983) no ATCC code is indicated. Everet Hansen sent an e-mail to G. Abad on 11.21.13 clarifying the code of Phytophthora sp. 1 corresponds to ATCC 52938.

Ex-type in other collections

ATCC 52938 = Hamm 268 = IMI 331662, P10339 (WPC), CPHST BL 51 (Abad), PSE1 (Cooke), R209 (Diana Kennedy)

Molecular identification

Voucher sequences for barcoding genes (ITS rDNA and COI) of the ex-type (see Molecular protocols page)

Phytophthora pseudotsugae isolate CPHST BL 51 (= P10339 WPC) = ITS rDNA MG865575, COI MH136967

Sequences for ex-type in other sources
Position in ITS phylogenetic tree

Clade 1a

Morphological identification

Colonies and cardinal temperatures

Colony morphology on PDA, V8A, MEA with non-distinctive pattern. Minimum growth temperature 3°C, optimum 18–25°C, and maximum 27°C.

Conditions for growth and sporulation

Sporangia and hyphal swellings produced in soil extract liquid culture and rarely in solid media. Oogonia readily produced in culture media. 

Asexual phase

Sporangia papillate and sometimes bipapillate; persistent and sometimes caducous with short pedicels; globose, ovoid, obpyriform (26–47 L x 22–39 W µm) originated in unbranched and simple sympodial sporangiophores and with intercalary sporangia frequently produced. Hyphal swellings occasionally produced; globose, subglobose, many times with radiating hyphae, and sometimes catenulated. Chlamydospores absent.

Sexual phase

HomothallicOogonia smooth-walled; spherical to slightly globose (31–40 µm diam); antheridia mostly paragynous but also amphigynous, spherical, ovoid, club-shaped, or irregular shape; oospores plerotic, aplerotic, and slightly aplerotic (24–34 µm diam).

Most typical characters

Phytophthora pseudotsugae is characterized by the presence of sporangia papillate and sometimes bipapillate, mostly persistent and sometimes caducous with short pedicels. The intercalary sporangia frequently produced in liquid cultures is another useful character for identification of the species.

Specimen(s) evaluated

Phytophthora pseudotsugae ex-type CPHST BL 51 duplicate of P10339 (World Phytophthora Collection)

Hosts and distribution

Distribution: North America (USA: WA, OR)
Substrate: roots
Disease note: root rot
Host: Pseudotsuga menziesii (Douglas fir, Pinaceae)

Retrieved February 01, 2018 from U.S. National Fungus Collections Nomenclature Database.

Additional references and links

Fact sheet author

Z. Gloria Abad, Ph.D., USDA-APHIS-PPQ-S&T Beltsville Laboratory, United States of America