Phytophthora occultans

Name and publication

Phytophthora occultans Man in ’t Veld & Rosendahl (2015)

Man In 't Veld WA, Rosendahl KC, van Rijswick PC, Meffert JP, Westenberg M, van de Vossenberg BT, Denton G, and van Kuik FA. 2015. Phytophthora terminalis sp. nov. and Phytophthora occultans sp. nov., two invasive pathogens of ornamental plants in Europe. Mycologia 107: 54–65.

Corresponding author:


from Man In 't Veld et al. (2015)




Occultare (L.), hiding. The species was found for the first time in 1998 in the Netherlands, then went unnoticed for more than 10 years, to re-emerge in 2010.


Type: NETHERLANDS, isolated from rotted roots of Buxus sempervirens, 1998, Wil Veenbaas (holotype CBS 101557, dried culture in herb CBS)

Ex-type: CBS 101557

Sequences for ex-type in original manuscript: ITS JX978155, CoxI JX978156, β-tub JX978157, TEF1a KF650770

Ex-type in other collections

CBS 101557 = P19955 (WPC/WOC), CPHST BL 163 (Abad), 65B9 (Hong)

Molecular identification

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

Phytophthora occultans isolate CPHST BL 163 (= P19955) ITS rDNA MG865555, COI MH477753

Sequences for ex-type in other sources
  • NCBI: Phytophthora occultans CPHST BL 163
  • NCBI: Phytophthora occultans CBS 101557
  • Phytophthora DATABASE: Phytophthora occultans
  • EPPO-Q-bank: Phytophthora occultans
  • BOLDSYSTEMS: Phytophthora occultans (barcoding COI & ITS)
Position in ITS phylogenetic tree

Clade 2a

Morphological identification

adapted from Man In 't Veld et al. (2015)

Colonies and cardinal temperatures

Colony after 7 days of growth on V-8 agar and malt extract agar with slightly stellate pattern, on potato dextrose agar with no distinctive pattern. Minimum growth temperature 10°C, optimum 25–27°C, and maximum 32°C.

Asexual phase

Sporangia semipapillate, sometimes bipapillate; caducous with medium pedicel (8–30 μm) and persistent; ovoid, obpyriform, ellipsoid, sometimes with irregular shapes (mouse-shaped) (26–34 L × 40–55 W μm); originated on simple sympodial or branched sporangiophores. Hyphal swellings absent. Chlamydospores absent.

Sexual phase

Homothallic. Oogonia smooth-walled, globose (26–28 μm diam.); antheridia predominantly paragynous; oospores plerotic rarely aplerotic (25–26 μm diam.).

Additional specimen(s) evaluated

Phytophthora occultans ex-type CPHST BL 163, duplicate of P19955 (World Phytophthora Collection), which is a duplicate of ex-type CBS 101557

Hosts and distribution

Distribution: Europe (Germany, Netherlands, Romania), North America (USA: OR)
Substrate: roots, collar
Disease note: wilting, stem lesions, root rot
Host: Ceanothus spp. (Rhamnaceae), Buxus sp. (Buxaceae), Rhododendron, Gaultheria shallon, Arctostaphylos uva-ursi (Ericaceae), Mahonia nervosa (Berberidaceae)

Retrieved January 31, 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