Phytophthora × multiformis

Name and publication

Phytophthora alni subsp. multiformis Brasier & Kirk (2004)

Brasier CM, Kirk SA, Delcan J, Cooke DEL, and Jung T. 2004. Phytophthora alni sp. nov. and its variants: designation of emerging heteroploid hybrid pathogens spreading on Alnus trees. Mycol. Res. 108: 1172–1184.

Corresponding author:

Notes: reclassified as Phytophthora x multiformis (Brasier & S.A. Kirk) Husson, Ioos & P. Frey (2015) (SMML). Reclassification under nomenclature evaluation.

Husson C, Aguayo J, Revellin C, Frey P, Ioos R, and Marcais B. 2015. Evidence for homoploid speciation in Phytophthora alni supports taxonomic reclassification in this species complex. Fungal Genet. Biol. 77: 12–21.

Phytophthora alni species complex (alder Phytophthora) Invasive Species Compendium 

The alder Phytophthora species complex of oomycetes encompasses the hybrid P. × alni and its two parental species, P. uniformis and P. × multiformis.


from Brasier et al. (2004)




from multi and formis meaning multiple forms


Type: THE NETHERLANDS, isolated from Alnus sp. bark, 1994, H. van Kesteren IMI 392316 (a dried culture on carrot agar) (reported as holotypus)

Ex-type: Isolate P770 at the Forestry Commission UK in Phytophthora culture collection

Sequences for ex-type in original manuscript: P770 = ITS: AF139368

NOTES: Original manuscript (Brasier et al. 2004): The ex-type is of the Dutch phenotypic variant. Owing to the wide array of phenotypes exhibited within subsp. multiformis, it should not be considered phenotypically representative of the entire subspecies but only of this variant. The Dutch, UK, and German variant types are collectively representative phenotypic subpopulations within subsp. multiformis.

Ex-type in other collections

P770 = P770 (Brasier - DEFRA), 2001 9551 (PPS Wageningen), PD 20019551, P16202  (WPC), CPHST BL 2 (Abad)

Molecular identification

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

Phytophthora alni subsp multiformis isolate CPHST BL 2 (= P16202 WPC) = ITS rDNA MG783372, COI MK493472

Sequences for ex-type in other sources
  • NCBI: Phytophthora alni subsp multiformis CPHST BL 2
  • NCBI: Phytophthora alni P16202 (Some sequences as P. alni subsp multiformis others as P. alni)
  • Phytophthora DATABASE: Phytophthora alni subsp. multiformis 
  • EPPO-Q-bank: Phytophthora alni subsp. multiformis P770 
  • BOLDSYSTEMS: Phytophthora alni PHYTO126-10 = P16202 (Barcoding COI & ITS)

NOTE: Sequences in NCBI HQ261494, GU259115 have 4bp with AF139368 the sequence of the ex-type in the original manuscript. IMPORTANT: Need to see chromatograms (ABI) files in order to correctly identify this species.

Position in ITS phylogenetic tree

Clade 7a

Morphological identification

adapted from Brasier et al. (2004)

Colonies and cardinal temperatures

Colonies in V8 agar, potato dextrose agar, and malt extract agar with no distinctive pattern and slow growth. Minimum growth temperature 3°C; optimum 23–25°C, and maximum 29°C.

Asexual phase

Semipapillate sporangia, caducous and noncaducous, sometimes bipapillate, sometimes terminal, mostly on branched sporangiophores, sympodially arranged, ovoid, obpyriform, sometimes mouse-shaped, 25.5–33.5 3 40.0–55.0 mm (mean 30.0 3 47.0 mm), L/B ratio 1.57 : 1, pedicel length (M) 8.5–30.0 mm (mean 17.7 mm), Chlamydospores absent, hyphal swellings absent.

Sexual phase

Homothallic, oogonia globose, range of means from different strains 26.6–27.9 mm (mean 27.2 mm), oospores plerotic, rarely aplerotic, range of means 24.6–25.8 mm (mean 25.2 mm), antheridia paragynous, rarely amphigynous.

Additional specimen(s) evaluated

P. alni subsp. multiformis CPHST-BL # 2 (Abad) = P16202 [World Phytophthora Collection (WPC) California, USA] duplicate of the ex-type 770

Hosts and distribution

Notes: reclassified as Phytophthora x multiformis (Brasier & S.A. Kirk) Husson, Ioos & P. Frey (2015). Brasier et al. (2004) discuss nomenclatural issues associated with hybrids.

Distribution: Europe (Germany, the Netherlands, UK)
Substrate: roots, collar
Disease note: aggressive root and collar rot of riparian, nursery, and shelterbelt alders
Host: Alnus spp. (alder, Betulaceae)

Retrieved April 14, 2018 from U.S. National Fungus Collections Nomenclature Database.

Quarantine status

USA: Phytophthora alni on the National Cooperative Agricultural Pest Survey (CAPS) “Priority Pest List” for 2017, 2018, and 2019.

Phytophthora alni is listed on the U.S. Regulated Plant Pest Table (Last modified Nov. 15, 2017).

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

EU: none

EPPO: none

Additional references and links

Brasier CM, Cooke DE, and Duncan JM. 1999. Origin of a new Phytophthora pathogen through interspecific hybridization. Proc. Natl. Acad. Sci. 96: 5878–5883.

Metzler B. 2011. Alder rot caused by Phytophthora alni (in German).

Solla A, Pérez-Sierra A, Corcobado T, Haque MM, Diez JJ, and Jung T. 2010. Phytophthora alni on Alnus glutinosa reported for the first time in Spain. Plant Pathology. 59: 798.

Fact sheet author

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