Phytophthora borealis

Name and publication

Phytophthora borealis Hansen, Sutton, and Reeser (2012)

Hansen EM, Reeser PW, and Sutton W. 2012. Phytophthora borealis and Phytophthora riparia, new species in Phytophthora ITS Clade 6. Mycologia 104: 1133–1142.

Corresponding author:


from Hansen et al. (2012)




“Borealis” references the northern latitudes from which the species was identified.


Type: UNITED STATES OF AMERICA, Alaska, from Bear Creek, Alaska, N63.61533, W-143.98484, isolated Jun 2008, OSC 144,115, dried culture from OSU AKWA58.1-0708

Ex-type: MYA-4881 & CBS 132023 cultures from OSU AKWA58.1-0708

Sequences for ex-type in original manuscript: Phytophthora borealis isolate OSU AKWA58.1-0708 = ITS HM004232, COX2-COX1 JQ626586, COX1 JQ626625, β -Tubulin JQ626615

Ex-type in other collections

MYA-4881 = CBS 132023 = P19794 A2 (WPC), AKWA58.1-0708, CPHST BL 93 (Abad), 60B2 (Yang)

Molecular identification

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

Phytophthora borealis isolate AKWA58.1-0708 = ITS rDNA HM004232
Phytophthora borealis isolate CPHST BL 93 ( = P19794 ) COI MH136854

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

Clade 6b

Morphological identification

adapted from Hansen et al. (2012)

Colonies and cardinal temperatures

Colony pattern on CA angular and petaloid, with appressed hyphae. On V8-A with petaloid pattern. Optimum growth temperature 20°C, maximum 33°C.

Asexual phase

Sporangia nonpapillate; persistent; ovoid or obpyriform with a slight apical thickening (59–79 µm long ) showing internal, nested, and extended proliferation originated in unbranched sporangiophores. Hyphal swellings absent. Chlamydospores absent.

Sexual phase

Self-sterile. No oogonia were observed in single-strain cultures. One isolate formed oogonia only rarely when paired with an A2 tester isolate of P. cryptogea.

Most typical characters

Phytophthora borealis is similar to Phytophthora gonapodyides and some other sterile Clade 6 species in the self-sterile character of the sexual phase, although colony growth pattern and optimum temperature is distinctive for P. borealis.

Additional specimen(s) evaluated

Phytophthora borealis CPHST BL 93 (Abad) = P19794 [World Phytophthora Collection (WPC) California, USA] duplicate of ex-type MYA-4881

Hosts and distribution

Distribution: USA: Alaska
Substrate: stream baits
Disease note: Phytophthora borealis is found in stream water, however, no disease has been found in adjacent riparian ecosystems.
Hosts: n/a

Retrieved January 29, 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