Phytophthora irrigata

Name and publication

Phytophthora irrigata C. Hong and M. Gallegly (2008)

Hong C, Gallegly ME, Richardson PA, Kong P, and Moorman GW. 2008. Phytophthora irrigata, a new species isolated from irrigation reservoirs and rivers in eastern United States of America. FEMS Microbiol Lett 285: 203–211.

Corresponding author: C. Hong


from Hong et al. (2008)




refers to the habitat (‘irrigation’ water) where it was isolated


Type: UNITED STATES OF AMERICA, isolated from water of irrigation reservoir in Virginia during the year 2000 by Hong (23J7) MYA-4457

Ex-type: MYA-4457

Sequences for ex-type in original manuscript: Phytophthora sp. 23J7 = ITS rDNA EU334634, β-tub EU595775, TEF EU595778, CoxII EU595783, NADH EU595786

Ex-type in other collections

MYA-4457 = 23J7 = P16861 (WPC), P108 (WVU), CPHST BL 41 (Abad), 23J7 (Yang)

Molecular identification

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

Phytophthora irrigata isolate CPHST BL 41 (= P16861 WPC) = ITS rDNA MG865520, COI MH136914

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

Clade 9a

Morphological identification

adapted from Hong et al. (2008)

Colonies and cardinal temperatures

Colony morphology after 7 days of growth on potato dextrose agar and malt extract with petaloid pattern and on V8 agar with light petaloid pattern. Minimum temperature for growth is 7°C, optimum 30°C, and maximum 40°C.

Conditions for growth and sporulation

Sporangia formed in 10% soil solution. Oogonia and oospores show golden brown color in hemp seed agar.

Asexual phase

Sporangia nonpapillate; persistent; ovoid, globose, and obpyriform (34–51 L x 27–42 W µm); with internal extended and nested proliferation; and originated mostly on long unbranched sporangiophores. Hyphae swellings absent. Chlamydospores absent.

Sexual phase

Heterothallic. Oogonia (31–51µm diam); antheridia amphigynous (16 x 10.2 µm); oospores plerotic and aplerotic (40 µm diam), walls about 3 µm thick.

Most typical characters
Additional specimen(s) evaluated

Phytophthora irrigata, ex-type CPHST BL 41, duplicate of P16861 (World Phytophthora Collection), which is a duplicate of ex-type MYA-4457

Hosts and distribution

Notes: The nature of the type is uncertain.
Distribution: North America (USA)
Substrate: isolated from water

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

Additional info:
Host: Rhododendron spp. 
Substrate: irrigation water

Additional references and links

Fact sheet author

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