Phytophthora foliorum

Name and publication

Phytophthora foliorum Donahoo & Lamour (2006)

Donahoo R, Blomquist CL, Thomas SL, Moulton JK, Cooke DEL, and Lamour KH. 2006. Phytophthora foliorum sp. nov., a new species causing leaf blight of azalea. Mycol. Res. 110: 1309–1322 (pg. 1318).

Corresponding author:


from Donahoo et al. (2006)




refers to pathogenicity on leaves


Type: UNITED STATES OF AMERICA collected from Azalea ‘Pink Ruffles’ in nursery, in Tennessee, May 2004, K. Lamour 192, isol. ATCC MYA-3638

Ex-type: ATCC MYA-3638

Ex-type in other collections

ATCC MYA-3638 = P10974 (WPC), CBS 121655, CMW 31064, LT192 Lamour, 010505, CPHST BL 38G (Abad), 49J8 (Yang)

Molecular identification

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

Phytophthora foliorum isolate CPHST BL 38G (= P10974 WPC) = ITS rDNA MG865492, COI MH136888

Sequences for selected specimen

Phytophthora foliorum isolate CPHST BL 168 (= P10969 WPC) = ITS rDNA MG865493, COI MH136889

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

Clade 8c

Morphological identification

adapted from Donahoo et al. (2006)

Colonies and cardinal temperatures

Colony morphology after 7 days on V8-A, PDA, and MEA with slight chrysanthemum pattern. Minimum growth temperature 2°C, optimum 25°C, and maximum 30°C.

Conditions for growth and sporulation

Sporangia, hyphal swellings, and chlamydospores produced in soil extract water; oospores abundantly produced in culture.

Asexual phase

Sporangia nonpapillate, occasionally semipapillate; persistent; ovoid, obpyriform, obovoid, and distorted shapes (29–69 L X 19–42 W µm); showing internal proliferation, occasionally with nested proliferation; originated in long unbranched or simple sympodial sporangiophores. Hyphal swellings with short, irregular, knob-like protuberances. Chlamydospores are globose, sub-globose (16-51 µm diam), lateral, terminal, and intercalary.

NOTE: Sporangia were originally described as semipapillate and caducous with short pedicel (<5–20 µm), and no chlamydospores or hyphal swellings are described by Donahoo et al. (2006).

Sexual phase

Homothallic. Oogonia smooth-walled (34–43 µm diam), some with tapered base; antheridia mostly paragynous (9–16 X 8–13 µm) showing some spines or digitate projections and usually attached to the oogonia next to the oogonial stalk; oospores plerotic, aplerotic, or slightly aplerotic (29–42 µm diam).

Most typical characters

Phytophthora foliorum is characterized by the very short irregular knob-like protuberances, very small antheridia, and big chlamydospores.

Additional specimen(s) evaluated

Phytophthora foliorum ex-type CPHST BL 38G, duplicate of P10974 (World Phytophthora Collection), which is a duplicate of ex-type “192 Kurt Lamour”

Hosts and distribution

Distribution: North America (USA: CA, TN); reported and eradicated (?) in Europe (Scotland, Spain)
Substrate: leaves
Disease note: leaf spots
Host: Rhododendron spp. (Ericaceae)

Retrieved January 30, 2018 from U.S. National Fungus Collections Nomenclature Database.

Additional info:
Hosts: Azalea spp. on foliage

Additional references and links

Fact sheet author

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