Phytophthora intercalaris

Name and publication

Phytophthora intercalaris Yang, Balci, Brazee, Loyd & Hong (2016)

Yang X, Balci Y, Brazee NJ, Loyd AL, and Hong CX. 2015. A unique species in Phytophthora Clade 10: Phytophthora intercalaris sp. nov. recovered from stream and irrigation water in eastern United States. International Journal of Systematic and Evolutionary Microbiology 66: 845–855.

Correspondence author: Xiao Yang


from Yang et al. (2016)




refers to the abundant intercalary chlamydospores produced in hemp seed agar and carrot agar


Type: UNITED OF STATES OF AMERICA, recovered from Rapidan Stream, Virginia, USA, July 2007, deposited in the American Type Culture Collection (ATCC), Manassas, VA, USA, as ATCC TSD-7T (isolate 45B7T)

Ex-type: CBS 140632 (ex-type) deposited at the Centraalbureau voor Schimmelcultures (CBS) Fungal Biodiversity Centre, Utrecht, The Netherlands

Sequences for ex-type: Phytophthora intercalaris isolate 45B7T: ITS rDNA KT163268, cox1 KT163315, and β-tubulin KT163336

Ex-type in other collections

CBS 140632 = 45B7 (Yang)

Molecular identification

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

Phytophthora intercalaris isolate 45B7 ITS rDNA KT163268

Sequences for ex-type in other sources
  • NCBI: Phytophthora intercalaris 45B7
  • Phytophthora DATABASE: Phytophthora intercalaris
  • EPPO-Q-bank: Phytophthora intercalaris
  • BOLDSYSTEMS: Phytophthora intercalaris
Position in ITS phylogenetic tree

Clade 10b

Morphological identification

adapted from Yang et al. (2016)

Colonies and cardinal temperatures

Colony morphology after 10 days of growth in carrot agar, V8 agar, and hemp seed agar with stellate pattern. Minimum growth temperature 5°C, optimum 25–30°C, maximum 32°C.

Conditions for growth and sporulation

Abundant sporangia of Phytophthora intercalaris produced from fresh mycelial plugs grown in cV8A after they were submerged in 1.5 % soil water extract for approximately 20 hours. Isolates of A1 mating type observed in original publication, oospores produced in pairing with Phytophthora cinnamomi A2 tester. Chamydospores abundantly produced in HSA and CA after 10 days.

Asexual phase

Sporangia nonpapillate, persistent but occasionally caducous with long pedicels (19–64 μm); ovoid, ellipsoid, limoniform, pyriform, or obpyriform (25–52.5 x 19–37 μm) showing nested or extended internal proliferations; originated in unbrached and sometimes on simple sympodial sporangiophores. Hyphal swellings rarely produced in cV8A, while abundant in both young and aged cultures grown in hemp seed agar (HSA) and carrot agar (CA). Chlamydospores globose (25–63 μm diam) thin-walled, intercalary, occasionally terminal, and rarely lateral.

Sexual phase

Heterothallic. Oogonia with ornamented walls with abundant to few protuberances (34–47 μm diam); antheridia amphigynous (20 x 16 μm); oospores aborted (30–41 μm diam).

Hosts and distribution

Distribution: North America (USA: MA, MD, NC, VA, WV)
Substrate: isolated from stream and irrigation water

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

Additional info:
Collected from stream and nursery irrigation water in Maryland, Massachusetts, North Carolina, Virginia and West Virginia in the USA.

Additional references and links

  • Phytophthora DATABASE: Phytophthora intercalaris
  • EPPO-Q-bank: Phytophthora intercalaris
  • SMML USDA-ARS: Phytophthora intercalaris
  • EPPO Global Database: Phytophthora intercalaris
  • CABI Invasive Species Compendium: Phytophthora intercalaris
  • Encyclopedia of Life (EOL): Phytophthora intercalaris
  • Index Fungorum (IF): Phytophthora intercalaris
  • Plantwise Knowledge Bank: Phytophthora intercalaris

Fact sheet author

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