Phytophthora siskiyouensis

Name and publication

Phytophthora siskiyouensis Reeser & Hansen (2008)

Reeser PW, Hansen EM, and Sutton W. 2008. Phytophthora siskiyouensis, a new species from soil, water, myrtlewood (Umbellularia californica), and tanoak (Lithocarpus densiflorus) in southwestern Oregon. Mycologia 99: 639–643.

Corresponding author:


from Reeser et al. (2008)




refers to the Siskiyou Mountains in SW Oregon where the new species was first identified


Type: UNITED STATES OF AMERICA collected from a seasonal tributary to the Chetco River, Curry County, Oregon in March 2003; type: WA5-030403

Ex-type: ATCC MYA-4187 = WA5-30403 = CBS 122779, P15122 WPC

Sequences for ex-type in original manuscript: WA5-030403 = ITS rDNA EF523386

Ex-type in other collections

ATCC MYA-4187 = WA5-30403 = CBS 122779, P15122 (WPC) = CPHST BL 56 (Abad), 41B7 (Yang)

Molecular identification

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

Phytophthora siskiyouensis isolate CPHST BL 56 (= P15122 WPC) = ITS rDNA MG865586, COI MH136978

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

Clade 2

Morphological identification

adapted from Reeser et al. (2008)

Colonies and cardinal temperatures

Colony after 7 days of growth on potato dextrose agar, malt extract agar, and V8A with chrysanthemum pattern. Minimum growth temperature 3°C, optimum 21–25°C, and maximum 27°C.

Conditions for growth and sporulation

Sporangia formed abundantly on agar culture pieces placed in stream water; oogonia formed abundantly on V8A.

Asexual phase

Sporangia semipapillate, some with two and more rarely with three papilla; persistent or caducous with variable pedicel length (2–66 µm L); ovoid, ellipsoid, reniform (or kidney), distorted shapes (26–95 L x 23–50 W µm); hyphal swellings small, often associated with sporangiophore; sporangia originated terminal but often subterminal and occasionally intercalary in unbranched or simple sympodial sporangiophores. Hyphal swellings absent. Chlamydospores absent.

Sexual phase

Homothallic. Oogonia globose to subglobose (23–42 µm diam), occasionally much elongated or with a funnel shape tapering toward the stalk, frequently sessile and occasionally laterally intercalary; antheridia predominately paragynous, spherical, ellipsoid or ovoid, club-shaped (10–18 L x 8–13 W µm), terminal, occasionally intercalary and usually diclinous, attached anywhere on the oogonium; oospores globose to subglobose (19–33 µm diam) and usually aplerotic.

Most typical characters

Phytophthora siskiyouensis can be distinguished by the shape of the terminal and intercalary sporangia, and the shape of the antheridia.

Additional specimen(s) evaluated

Phytophthora siskiyouensis CPHST BL 56, duplicate of ex-type P15122 (World Phytophthora Collection)

Hosts and distribution

Distribution: Europe (England), North America (USA: OR)
Substrate: stems
Disease note: associated with cankers, pathogenicity little known
Host: Lithocarpus densiflorus (Fagaceae), Umbellularia californica (Lauraceae)

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

Additional info:
Substrate:  rhizosphere

Additional references and links

Fact sheet author

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