Phytophthora trifolii

Name and publication

Phytophthora trifolii Hansen and Maxwell (1991)

Hansen EM and Maxwell DP. 1991. Species of the Phytophthora megasperma-complex. Mycologia 83: 376–381.


from Hansen and Maxwell (1991)




named for the principal host


Type: UNITED STATES, collected from clover (Trifolium vesiculosum) in Raymond, Mississippi by R.G. Pratt; holotype Pratt No. 105 in Oregon State University herbarium (OSU collection)

Ex-type: American Type Culture Collection


Isolate No. 32 is also cited as the holotype in original manuscript as follows: "Pratt no. 105 et no. 32 in OSU collectione culturis". Isolate 32 corresponds to P. B. Hamm (Hamm 32) as cited at P6980 (WPC).

ATCC only has ATCC MYA-3901 and ATCC 48604 which do not correspond with the codes of Pratt No 105 or Hamm 32.

Ex-type in other collections

Pratt No. 105 = Ham 32 = CBS 117687P6980 (WOC/WPC), CPHST BL 57 (Abad), 62A9 (Yang)

Molecular identification

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

Phytophthora trifolii isolate CPHST BL 57 (= P6980 WPC) = ITS rDNA MG865594, COI MH136986

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

Clade 8a

Morphological identification

Colonies and cardinal temperatures

Colony morphology on CMA, PDA, V-8A, MEA with no distinctive shape. Minimum temperature for growth 5°C, optimum 20–25°C, maximum 30°C.

Conditions for growth and sporulation

Sporangia formed in liquid culture.

Asexual phase

Sporangia nonpapillate; persistent; ovoid, obpyriform, ellipsoid and with distorted shapes (27–50 µm length x 21–32 µm width), showing internal proliferation and intercalary hyphal swellings; originated in long, irregular branched or simple sympodial sporangiophores. Hyphal swellings globose, subglobose, radiating hyphae individual or in chains. Chlamydospores absent.

Sexual phase

Homothallic. Oogonia smooth-walled (27–46 µm diam.); antheridia predominantly paragynous, spherical, ovoid, club-shaped, irregular, producing some digitated projections; oospores aplerotic and slightly aplerotic (23–37 µm diam.).

Most typical characters

Small sporangia and large oogonia are distinctive.

Specimen(s) evaluated

Phytophthora trifolii ex-type CPHST BL 57, duplicate of P6980 (World Phytophthora Collection)

Hosts and distribution

Distribution: North America (USA: MS)
Substrate: roots; sometimes shoots
Disease note: severe stand-depleting root rot; infection can extend up to the crown
Host: Trifolium spp. (Fabaceae)

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

Additional references and links

Pratt RG. 1981. Morphology, pathogenicity and host range of Phytophthora megasperma, P. erythroseptica, and P. parasitica from arrow leaf clover. Phytopathology 71: 276-282.

Fact sheet author

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