Phytophthora clandestina

Name and publication

Phytophthora clandestina Taylor, Pascoe & Greenhalgh (1985)

Taylor PA, Pascoe IE, and Greenhalgh FC. 1985. Phytophthora clandestina sp. nov. in roots of subterranean clover. Mycotaxon 22: 77–85.


from Taylor et al. (1985)




from Latin “clandestinus”, meaning hidden or secretive, in recognition of the difficulty encountered in detecting and culturing the fungus (= fungus-like)


Type: AUSTRALIA, from Kyabram, Victoria, from rooted rots of Trifolium subterraneum subsp. yanninium cv. Yarloop VPRI 12234 preserved in the herbarium of the Plant Research Institute, Burnley, Victoria as microscope slides, dried culture, and infected roots

Ex-type: CBS 347.86

Isotype: specimens are deposited as IMI 2789333 and DAR 49489. P. A. Taylor

Note: IMI 2789333 not available at IMI collection (G. Abad 12.18.17)

Ex-type in other collections

CBS 347.86 = DAR 49489, P3943 (WPC), P3652 (WPC), ATCC 58713, ATCC 60438, P01 P. A. Taylor, p200, CPHST BL 15 (Abad), 32G1 (Yang)

Molecular identification

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

Phytophthora clandestina isolate CPHST BL 15 (= P3943 WPC) = ITS rDNA MG865477, COI MH136873

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

Clade 1b

Morphological identification

Colonies and cardinal temperatures

Phytophthora clandestina grows slowly in culture media including V8-A, PDA, MEA, and lima bean agar. The minimum temperature for growth is 5°C, optimum 25°C, and maximum 31°C.

Asexual phase

Sporangia are papillate (often two or three papillae), broadly ellipsoid to ovoid, sometimes subglobose (16–66 x 15–44 µm), caducous with short pedicel (1–6 µm in length), and do not readily separate from sporangiophores at first but become deciduous after zoospores have been emitted. A conspicuous dome-shaped or broadly conical basal plug protrudes into the sporangium. Sporangia are formed on simple sympodial sporangiophores. Hyphal swellings subspherical to deltoid produced on V-8 juice agar. Chlamydospores absent.

Sexual phase

Homothallic. Oogonia with smooth wall and usually terminal, rarely intercalary (21–36 µm). Antheridia predominantly paragynous (70–90%), but in lima bean agar they are more frequently amphigynous (50–60%). Antheridia are terminal or subterminal, occasionally intercalary, and variable in shape (9–45 µm long to 4–17 µm wide), usually delimited by thick basal septum. Amphiginous antheridia often eccentric about the oogonial stalk. Oospores are markedly aplerotic (18–31 µm diam) with a wall thickness of 0.3–3.6 µm.

Most typical characters

Phytophthora clandestina is characterized by slow growth at low temperatures, production of typical hyphal swellings, and subterminal or digitate antheridia. Oospores abundantly produced on infected roots and less frequently in culture media.

Specimen(s) evaluated

Phytophthora clandestina CPHST BL 15, duplicate of P3943 (World Phytophthora Collection)

Hosts and distribution

Distribution: Australia
Substrate: roots
Disease note:  major root rot pathogen of subterranean clover (Erwin & Ribeiro 1996)
Hosts: Trifolium subterraneum (subterranean clover, Fabaceae); Medicago spp. are also susceptible (Erwin & Ribeiro 1996)

Retrieved January 29, 2018 from U.S. National Fungus Collections Nomenclature Database.

Additional info:
The pathogen infects subterranean clover (Trifolium subterraneum) and is weakly pathogenic on several alfalfa species, including Medicago truncatula, Medicago rugosa, and Medicago scutellata.

Quarantine status

USA: This species was listed as a species of concern during the 2009 Phytophthora prioritization project conducted by USDA APHIS PPQ CPHST PERAL (Schwartzburg et al.).

Additional references and links

Fact sheet author

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