Phytophthora megasperma (to be redescribed 2022)

Name and publication

Phytophthora megasperma Dreschsler (1931)

Drechsler CA. 1931. A crown rot of hollyhock caused by Phytophthora megasperma n. sp. Journal of the Washington Academy of Science 21: 513–526.





= Pythiomorpha miyabeana S. Ito & Nagai, Journal of the Faculty of Agriculture of the Hokkaido Imperial University 32: 50 (1931) [MB271435]
= Phytophthora megasperma var. megasperma (1931) [MB429060]


from Drechsler (1931)

Type: UNITED STATES, isolated from Althaea rosea Cav. (hollyhock) family Malvaceae, collected in a garden of District of Columbia (Washington DC.), and submitted to the U.S. Department of Agriculture on May 15, 1931, causing destructive decay to the host according to Drechsler, C.A. in original paper, IMI 32035 (HerbIMI)

Ex-type: CBS 402.72

Ex-type in other collections

CBS 402.72 (= IMI 32035) = P6957 (WPC), ATCC 58817, PD 06 03209045, CPHST BL 43 (Abad), 62C7 (Yang)

Molecular identification

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

Phytophthora megasperma isolate CPHST BL 43 (= P6957 WPC) = ITS rDNA MG865535, COI MH136930

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

Clade 6b

Morphological identification

Colonies and cardinal temperatures

Colony morphology after 7 days of growth on potato dextrose agar, V8 agar, and malt extract agar with no distinct pattern. Minimum growth temperature 3°C; optimum 18°C, and maximum 27°C.

Asexual phase

Sporangia nonpapillated; persistent; elongated, obpyriform, limoniform, or distorted shapes (48–99 L x 29–46 W µm), some with tapered base; with external and internal in extended and nested proliferation; originated in unbranched sporangiophores. Hyphal swellings globose, subglobose to elongated with radiating hyphae. Chlamydospores absent.

Sexual phase

Homothallic. Oogonia spherical (16–61 µm diam); antheridia spherical or ellipsoid (14–20 x 10–18 µm), predominantly paragynous; oospores aplerotic (11–54 µm diam).

Most typical characters

Phytophthora megasperma is characterized by the presence of sporangia nonpapillated with internal extended and nested proliferation and the predominantly paragynous antheridia, as well as the shape of the hyphal swellings.

Specimen(s) evaluated

Phytophthora megasperma ex-type CPHST BL 43, duplicate of P6957 = P3599 (World Phytophthora Collection)

Hosts and distribution

Distribution: cosmopolitan
Substrate: all plant parts, depending on host
Disease note: root rot, also crown rot, storage rot, seedling damping-off, fruit rot, foot rot, stem canker, tuber rot, collar rot, sudden wilt, apoplexy, stunting, chlorosis, depending on host (see Erwin & Ribeiro 1996)
Host: On Fabaceae, isolates previously referred to as P. megasperma are now considered to be three distinct species.

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

Additional info
Distribution: USA (CA), Bulgaria, Taiwan

Additional references and links

Fact sheet author

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