Phytophthora melonis

Name and publication

Phytophthora melonis Katsura (1976)

Katsura K. 1976. Two new species of Phytophthora causing damping-off of cucumber and trunk rot of chestnut. Trans. Mycol. Soc. Jpn. 17: 238–242.

Nomenclature

Mycobank

MB320484

Synonymy

= Phytophthora sinensis Y.N. Yu & W.Y. Zhuang 1982. Note: Synonymy supported by molecular analysis (Cooke et al. 2000).

Typification

from Katsura (1976)

Type: JAPAN, from cucumber (Cucumis sativus) collected in Kyoto Prefectural University, Plant Pathology Herbarium No 1967-008

Ex-type: culture deposited at Centraalbureau voor Schimmelcultures CBS 582.69

NOTE: Specimen CBS 582.69 is LOST from CBS, according to e-mail of A. De Cock to G. Abad on 2-21-14.

Ex-type in other collections

CBS 582.69 = P6870 (WPC), ATCC 52854, Ho 513, H27.2, CPHST BL 23 (Abad), 45F3 (Yang)

Molecular identification

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

Phytophthora melonis isolate CPHST BL 23 (= P6870 WPC) = ITS rDNA MG865536, COI MH136931

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

Clade 7b

Genome sequence

Phytophthora melonis strain ex-type BL 23. Accession genome USDA_Pmel_BL23_1.0 reference, BioProject PRJNA556690, USDA-APHIS-PPQ-S&T (2019), Srivastava et al. 2020

Morphological identification

Colonies and cardinal temperatures

Colony morphology after 7 days of growth on V8 agar, potato dextrose agar, and malt extract with no distinct pattern to slightly radiate. Minimum temperature for growth is 9°C, optimum 28–32°C, and maximum 37°C.

Asexual phase

Sporangia nonpapillate with internal proliferation; persistent, sometimes caducous with medium to long pedicels; ovoid, obpyriform with round bases (32–75 x 23–45 μm diam.), produced in long unbranched sporangiophores. Hyphal swellings occasionally produced, globose, terminal and intercalary, some with radiating hyphae. Chlamydospores spherical (16–52 μm diam.).

Sexual phase

Heterothallic. Oogonia smooth-walled (27–35 μm diam.); antheridia amphyginous (10–29 x 10–20 μm); oospores plerotic to slightly aplerotic.

Ho et al. (2007) presented the "redescription of Phytophthora melonis" and indicated that the species doesn't produce chlamydospores. However, in this study the isolate of the ex-type (i.e. CBS582.69 = P6870 (WPC), ATCC 52854) was not evaluated. Also, this study describes the species as nonpapillated, and the original manuscript indicates semipapillated sporangia. The original publication describes "apice papilla plana", and the figures correspond to nonpapillated sporangia.

Most typical characters

Phytophthora melonis is characterized by the presence of nonpapillate sporangia with internal proliferation.

Specimen(s) evaluated

Phytophthora melonis ex-type CPHST BL 23, duplicate of P6870 (World Oomycetes/Phytophthora Collection)

Phytophthora melonis CPHST BL 159 (A1) Cucumis sativus (China), duplicate of P1371 (World Oomycetes/Phytophthora Collection)

Phytophthora melonis CPHST-BL 160 Trichosanthes dioica (India), duplicate of P10994 (World Oomycetes/Phytophthora Collection)

Hosts and distribution

Distribution: Asia
Substrate: stems, vines, fruits, leaves
Disease note: late blight or foot rot
Host: Cucumis sativus (cucumber, Cucurbitaceae); also reported from Citrullus lanatus (Cucurbitaceae) and Pistacia vera (Anacardiaceae)

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

Additional Info
Substrate: roots

Quarantine status

USA: This species was listed as a species of concern during the 2009 Phytophthora prioritization project conducted by USDA APHIS PPQ CPHST PERAL (Schwartzburg et al.).

Additional references and links

Katsura K. 1976. Two new species of Phytophthora causing damping-off of cucumber and trunk rot of chestnut. Trans. Mycol. Soc. Jpn. 17: 238–242.

Ho HH, Gallegly ME, and Hong CX. 2007. Redescription of Phytophthora melonis. Mycotaxon 102: 339–345.

Fact sheet author

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