Phytophthora humicola

Name and publication

Phytophthora humicola Ko & Ann (1985)

Ko WH and Ann JP. 1985. Phytophthora humicola, a new species from soil of a citrus orchard in Taiwan. Mycologia 77: 631–636.


from Ko and Ann (1985)




Latin, humicola (soil inhabiting), referring to the native environment from where the type was found


Type: TAIWAN, from soil, citrus grove, TAI 9017, dried culture preserved at Herbarium of Department of Botany, National Taiwan University, Taipei

Ex-type: CBS 200.81 (and ATCC 52179)

Ex-type in other collections

CBS 200.81 = ATCC 52179 = P3826 (WOC/WPC), CPHST BL 42G (Abad), IFO 32771, IMI 302303, Ko Px1-2, 32F8 (Yang)

Molecular identification

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

Phytophthora humicola isolate CPHST BL 42G (= P3826) ITS rDNA MK496519, COI MK493476 

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

Clade 6a

Morphological identification

Colonies and cardinal temperatures

Colony morphology after 7 days of growth on V8-A, PDA, and MEA with light petaloid pattern. The minimum temperature for growth is 9°C, optimum 28–30°C, and maximum 32°C.

Conditions for growth and sporulation

Sporangia are formed in nonsterile soil extract, and hyphal swellings are produced in sterile distilled water.

Asexual phase

Sporangia nonpapillate; persistent; ovoid, obpyriform (36–72 L x 30–52 W µm); presenting internal proliferation and sometimes with external proliferation; some sporangia with basal swellings; originated from unbranched sporangiophores and sometimes on the tips of hyphae radiating from germinating hyphal swellings. Hyphal swellings large, spherical (22–56 µm diam) with radiating hyphae, sometimes the dominant hypha produces another hyphal swelling and forms a chain of hyphal swellings. Chlamydospores absent.

Sexual phase

Homothallic. Oogonia smooth-walled; spherical (21–49 µm diam) with long oogonial stalks; antheridia paragynous and amphigynous, short cylindrical, spherical, ellipsoid or ovoid, and irregular shapes (9–16 µm W), some with digitate projections, and some oogonia with 2 or more antheridia; oopores aplerotic or slightly aplerotic (16–41 µm diam).

Most typical characters

Phytophthora humicola is characterized by the long stalks of the oogonia and antheridia and by the shape of the hyphal swellings.

Specimen(s) evaluated

Phytophthora humicola ex-type CPHST BL 42G, duplicate of P3826 (World Phytophthora Collection), which is a duplicate of ex-type CBS 200.81

Hosts and distribution

Distribution: Asia (Taiwan, type), Europe
Substrate: soil; able to infect fruits, roots, leaves
Disease note: Pathogenic to apple and cucumber, but not orange or eggplant, after wound inoculation.
Hosts: Citrus spp., soil. Natural host unknown, but isolated from a Citrus sp. orchard (Rutaceae). Inoculated hosts include Malus domestica (apple, Rosaceae) and Cucumis sativus (cucumber, Cucurbitaceae).

Retrieved January 31, 2018 from U.S. National Fungus Collections Nomenclature Database.

Additional references and links

Ginetti B, Uccello A, Bracalini M, Ragazzi A, Jung T, and Moricca S. 2012. Root rot and dieback of Pinus pinea caused by Phytophthora humicola in Tuscany, central Italy. Plant Disease 96 (11): 1694. DOI: 10.1094/PDIS-05-12-0451-PDN.

Ko WH and Ann PJ. 1985. Phytophthora humicola, a new species from soil of a citrus orchard in Taiwan. Mycologia 77 (4): 631–636.

Fact sheet author

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