Phytophthora fallax

Name and publication

Phytophthora fallax Dobbie & Dick (2006)

Dick MA, Dobbie K, Cooke DEL, and Brasier CM. 2006. Phytophthora captiosa sp. nov. and P. fallax sp. nov. causing crown dieback of Eucalyptus in New Zealand. Mycol. Res. 110: 393–404 (pg 398).

Corresponding author e-mail:


from Dick et al. (2006)




‘fallax’ = elusive, referring to the elusive nature of the fungus and the disease it causes


Type: NEW ZEALAND, Southland, Katea, Owaka Valley, culture isolated from leaves of alpine-ash (Eucalyptus delegatensis), 3 June 1997, collected by R. Thum A0049703 NZFRI-M 5216-holotypus deposited at the New Zealand Forest Research Institute Herbarium – Mycology)

Ex-type: NZFS 310L deposited in the New Zealand Forest Research Institute Culture Collection, also deposited in the International Collection of Micro-organisms from Plants (ICMP 15575), and the World Phytophthora Collection

Sequences for ex-type in original manuscript: NZFS 310L = ITS DQ297391

NOTE: In the original paper, P. fallax was reported as being deposited in the World Phytophthora Collection as WPC P10721. However, in the WPC database, P10721 corresponds to P. captiosa and isolate P10722 corresponds to the type of P. fallax (G. Abad search on 5/12/15).

Ex-type in other collections

NZFS 310L = ICMP 15575 = P10722 (WPC) = CBS 119109, CPHST-BL 63 (Abad), 46J2 (Yang)

Molecular identification

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

Phytophthora fallax isolate CPHST BL 63 (= P10722 WPC) = ITS rDNA MG865489, COI MH136885

Sequences of selected specimen

Phytophthora fallax isolate CPHST BL 170 (= P10725 WPC) = ITS rDNA MG865490, COI MH136886

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

Clade 10a

Morphological identification

adapted from Dick et al. (2006)

Colonies and cardinal temperatures

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

Conditions for growth and sporulation

Gametangia produced abundantly on CA within 30 d, sporangia produced in pea broth in 48 h.

Asexual phase

Sporangia nonpapillate, persistent, obpyriform to distorted, often with a distinctive elongated neck and conspicuous basal plug (44–60 L x 27–38 W µm), proliferating both internally and externally, and originated in unbranched or simple sympodial sporangiophore. Hyphal swellings absent. Chlamydospores spherical, terminal (12–26 µm diam).

Sexual phase

Homothallic. Oogonia smooth-walled, spherical (30–36 µm diam); antheridia predominantly paragynous; sometimes the distorted hyphae of paragynous antheridia coils around the oogonial stalk and is difficult to determine; paragynous antheridia globose (6–10 µm diam), most often attached near the oogonial stalk. Amphigynous antheridia are cylindrical (16–30 L x 12–13 W µm). Oospores are initially plerotic, becoming aplerotic with age (29–34 µm diam).

Most typical characters

Phytophthora fallax is characterized by the production of obpyriform sporangia with a distinctive elongated neck, and by the presence of antheridia predominantly paragynous with hyphae sometimes coiling around the oogonial stalk.

Additional specimen(s) evaluated

Phytophthora fallax ex-type CPHST BL 63, duplicate of P10722 (World Phytophthora Collection)

Hosts and distribution

Distribution: Australia, New Zealand
Substrate: living leaves; also twigs, petioles, seed capsules, and peduncles
Disease note: associated with crown disease
Host: Eucalyptus spp. (Myrtaceae)

Retrieved January 30, 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