Name and publication

Phytophthora megasperma Drechsler (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.

Nomenclature

Mycobank

MB270758

Synonymy

= 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]

Typification

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

Selected specimen in other collections

(SE) CBS 402.72, ATCC  58817 (MCI), CABI IMI32035 (PA), WPC P6957, S&T BL 43 (Abad), 62C7 (Hong)

Molecular identification

Voucher sequences for barcoding genes (ITS rDNA and COI) of the selected specimen (see Molecular protocols page)

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

Voucher sequences for Molecular Toolbox with seven genes (ITS, β-tub, COI, EF1α, HSP90, L10, and YPT1

(see Molecular protocols page) (In Progress)

Voucher sequences for Metabarcoding High-throughput Sequencing (HTS) Technologies [Molecular Operational Taxonomic Unit (MOTU)]

(see Molecular protocols page) (In Progress)

Sequences with multiple genes forselected specimen in other sources

• NCBI: Phytophthora megasperma CPHST BL 43
• NCBI: Phytophthora megasperma P6957
• NCBI: Phytophthora megasperma CBS 402.72 28S
• EPPO-Q-bank: Phytophthora megasperma CBS 402.72 
• BOLDSYSTEMS: Phytophthora megasperma (barcoding COI & ITS)

Position in multigenic phylogeny with 7 genes (ITS, β-tub, COI, EF1α, HSP90, L10, and YPT1)

Clade clade:
a taxonomic group of organisms classified together on the basis of homologous features traced to a common ancestor
6b

Morphological identification

Colonies and cardinal temperatures

Colony colony:
assemblage of hyphae which usually develops form a single source and grows in a coordinated way
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

SporangiaSporangia:
sac within which zoospores form, especially when water is cooled to about 10°C below ambient temperature; in solid substrates, sporangia usually germinate by germ tubes
nonpapillated; persistentpersistent:
pertaining to sporangia that remain attached to the sporangiophore and do not separate or detach easily (cf. caducous)
; elongated, obpyriformobpyriform:
inversely pear-shaped, i.e. with the widest part at the point of attachment (cf. pyriform)
, limoniform, or distorted shapes (48–99 L x 29–46 W µm), some with tapered basetapered base:
pertaining to the base of a sporangium or oogonium; funnel-shaped
; with external and internal in extended and nested proliferationnested proliferation:
a type of internal proliferation where a new sporangium develops successively inside the old sporangium after it has emptied
; originated in unbranched sporangiophores. Hyphal swellings globoseglobose:
having a rounded form resembling that of a sphere
, subglobose to elongated with radiating hyphaehyphae:
single, tubular filament of a fungal or oomycete thallus; the basic structural unit of a fungus or oomycete
. ChlamydosporesChlamydospores:
an asexual spore with a thickened inner wall that is delimited from the mycelium by a septum; may be terminal or intercalary, and survives for long periods in soil
absent.

Sexual phase

Homothallic. Oogonia spherical (16–61 µm diam); antheridiaantheridia:
the male gametangium; a multinucleate, swollen hyphal tip affixed firmly to the wall of the female gametangium (the oogonium)
spherical or ellipsoidellipsoid:
refers to a solid body that forms an ellipse in the longitudinal plane and a circle in cross section; many fungal spores are ellipsoidal or elliptic
(14–20 x 10–18 µm), predominantly paragynousparagynous:
pertaining to the sexual stage in which the antheridium is attached to the side of the oogonium (cf. amphigynous)
; oosporesoospores:
zygote or thick-walled spore that forms within the oogonium after fertilization by the antheridium; may be long-lived
apleroticaplerotic:
pertaining to a mature oospore that does not fill the oogonium; i.e. there is room left between the oospore wall and oogonium wall (cf. plerotic)
(11–54 µm diam).

Most typical characters

Phytophthora megasperma is characterized by the presence of sporangiasporangia:
sac within which zoospores form, especially when water is cooled to about 10°C below ambient temperature; in solid substrates, sporangia usually germinate by germ tubes
nonpapillated with internal extended and nested proliferationnested proliferation:
a type of internal proliferation where a new sporangium develops successively inside the old sporangium after it has emptied
and the predominantly paragynousparagynous:
pertaining to the sexual stage in which the antheridium is attached to the side of the oogonium (cf. amphigynous)
antheridiaantheridia:
the male gametangium; a multinucleate, swollen hyphal tip affixed firmly to the wall of the female gametangium (the oogonium)
, 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

 

• SMML USDA-ARS: Phytophthora megasperma
• EPPO Global Database: Phytophthora megasperma
• Forest Phytophthora of the world: Phytophthora megasperma
• CABI Digital Library: Phytophthora megasperma
• Encyclopedia of Life (EOL): Phytophthora megasperma
• Index Fungorum (IF): Phytophthora megasperma

 

• Google All Phytophthora megasperma
• Google Images Phytophthora megasperma
• Google Scholar Phytophthora megasperma

Fact sheet author

Z. Gloria Abad, Ph.D., USDA-APHIS-PPQ-S&T Plant Pathogen Confirmatory Diagnostics Laboratory (PPCDL), United States of America.