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Figure 1. Morphology of Phytophthora gonapodyides. Left to right, Obpyriform sporangium; nesting or internal proliferation; irregular shapes of hypae; and external proliferation of sporangia. (Courtesy A. Vaziri; Reproduced from Erwin and Ribeiro, 1996) Click image to see larger view.

Figure 2. Culture of Phytophthora gonapodyides grown on V-8 juice agar. (Courtesy Jean B. Ristaino)

Figure 3. Sporangium of Phytophthora gonapodyides. (Courtesy Philip B. Hamm, Oregon State University)

Figure 4. Symptoms of Phytophthora gonapodyides on tan oak. (Courtesy Everett Hansen, Oregon State University)

Introduction

Phytophthora gonapodyides  (H. E. Petersen) Buisman (1927)

 

Pythiomorpha gonapodyides was described by Petersen from decaying apples in a freshwater pond in 1909 (note different genus) (Petersen, 1909; 1910). This is the only known synonym for the species. Buismann transferred Pythiomorpha gonapodyides to the genus Phytophthora (Busimann, 1927). Blackwell et al. (1941) and Waterhouse (1958) reviewed the history of the species and formally transferred P. gonapodyides to the genus Phytophthora and stated that the genus Pythiomorpha was an invalid genus (Cline et al., 2008). Isolates causing disease on Douglas fir, and previously named P. drechsleri, in Oregon were found by Brasier et al. to have a morphology and protein banding patterns similar to those of P. gonapodyides (Brasier et al., 1989; 1993). Some isolates in group J may be sterile (Brasier, 1991). Chlamydospore-producing isolates in group K of the Mills et al. (1991) study of the P. cryptogea–P. drechsleri complex may be P. gonapodyides. P. gonapodyides has protein banding patterns distinct from those of P. drechsleri and P. cryptogea and can cause moderate disease on Abies spp., Douglas fir, and hemlock (Erwin and Ribeiro, 1996). P. gonapodyides is a group VI species (Stamps et al., 1990; Waterhouse, 1963) (Fig. 1). 

Cultural Characteristics

The minimum temperature for growth is less than 5°C, the optimum temperature for growth is 25°C, and the temperature for growth range is 22–28°C. There is no colony growth at 35°C. In culture, P. gonapodyides grows in a rosette pattern (Fig. 2).

Reproductive Structures

Asexual Structures

 

Sporangiophores:

Sporangiophores are sympodial only when in water, and sporangia proliferate internally on the sporangiophore and can be nested.

 

Sporangia:

Sporangia are nonpapillate. They are noncaducous, mostly ovoid or ellipsoid, and 20–32 × 42–75 µm (Fig. 3). Sporangia can be broadly pyriform, elongated pyriform, and occasionally ovate. The length–breadth ratio is 1.2:1–2.4:1 (average 1.6:1).

 

Chlamydospores and Hyphal Swellings:

Chlamydospores and hyphal swellings are not produced.

 

Sexual Structures

 

P. gonapodyides is heterothallic; however, some isolates may produce oogonia in single cultures. All isolates studied by Brasier et al. (1993) were self-sterile, but when paired with A2 isolates of P. cambivora, P. megakarya, or P. meadii, they produced gametangia that were characteristic of these species.

 

Antheridia:

Antheridia are amphigynous and variable in shape.

 

Oogonia:

Oogonia are globose and 27–48 µm in diameter. Walls are frequently rough.

 

Oospores:

Oospores are thick walled, aplerotic, 18–32 µm in diameter, and yellow. 

Host Range and Distribution

Host	Common Name	Disease	Geographical Distribution
Abies spp.	Douglas fir, hemlock	Root rot	United States, Great Britain
Alnus spp.	Alder	Twig blight	Denmark
Citrus spp.	Orange	Saprophyte	Australia
Fraxinus spp.	Common ash	Rot rot; stem lesions	Europe
Fremontodendron spp.	Flannel bush	Root rot	United States
Malus pumila	Apple	Fruit rot	Denmark
Prunus spp.	Prunes	Saprophyte	Australia
Pyrus malus	Apple	Fruit rot	Denmark
Rhamnus spp.	Buckthorn	Root rot	United States
Rhododendron spp.	Rhododendron	Root rot	United States
Sciadopitys verticillata	Umbrella pine	Root rot	United States
Rosa spp.	Rose hips	Saprophyte	Australia
Vitis vinifera	Grape	Saprophyte	Australia

Symptoms

Symptoms are similar to those of other Phytophthora species that cause root rot. P. gonapodyides is a mild pathogen. It is considered a minor pathogen on a number of ornamentals and can be a saprophyte on twigs of a number of species (Cline et al., 2008) (Fig. 4).

References

Blackwell, E. M., Waterhouse, G. M., and Thompson, M. V. 1941. The invalidity of the genus Pythiomorpha. Trans. Br. Mycol. Soc. 25:148-165.

 

Brasier, C. M. 1991. Current questions in Phytophthora systematics: The role of the population approach. Pages 104-128 in: Phytophthora. J. A. Lucas, R. C. Shattock, D. S. Shaw, and L. R. Cooke, eds. Cambridge University Press, Cambridge, United Kingdom.

 

Brasier, C. M., Hamm, P. B., and Hansen, E. M. 1989. Phytophthora diseases. Status of P. gonapodyides, P. dreschleri, and P. cryptogea. Pages 49-50 in: Report on Forest Research. Her Majesty's Stationery Office, London.

 

Brasier, C. M., Hamm, P. B., and Hansen, E. M. 1993. Cultural characteristics, protein patterns and unusual mating behavior of Phytophthora gonapodyides isolated from Britain and North America. Mycol. Res. 97:1287-1298.

 

Buismann, C. J. 1927. Root rots caused by Phycomycetes. Thesis. University of Utrecht. Meded. Phytopathol. Lab. Wille Commelin Scholten 11:7. (Rev. Appl. Mycol. 1927, 6:380)

 

Cline, E. T., Farr, D. F., and Rossman, A. Y. 2008. A synopsis of Phytophthora with accurate scientific names, host range, and geographic distribution. Plant Health Progress doi:10.1094/PHP-2008-0318-01-RS.

 

Erwin, D. C., and Ribeiro, O. K. 1996. Phytophthora Diseases Worldwide. American Phytopathological Society, St. Paul, MN.

 

Mills, S. D., Förster, H., and Coffey, M. D. 1991. Taxonomic structure of Phytophthora cryptogea and P. drechsleri based on isozyme and mitochondrial DNA analysis. Mycol. Res. 95:31-48.

 

Petersen, H. E. 1909. Studier over Ferskvands-Phycomyceter. Bot. Tidsskr. 29:345-440. (In Danish)

 

Petersen, H. E. 1910. An account of Danish freshwater—Phycomycetes with biological and systematical remarks. Ann. Mycol. 8:494-560.

 

Stamps, D. J., Newhook, F. J., Waterhouse, G. M., and Hall, G. S. 1990. Revised tabular key to the species of Phytophthora de Bary. Mycol. Pap. 162. CAB International, Wallingford, United Kingdom; Commonwealth Mycological Institute, Kew, Surrey, England.

 

Waterhouse, G. M. 1958. The invalidity of the genus Pythiomorpha. Trans. Br. Mycol. Soc. II 41:196-202.

 

Waterhouse, G. M. 1963. Key to the species of Phytophthora de Bary. Mycol. Pap. 92. CAB International, Wallingford, United Kingdom; Commonwealth Mycological Institute, Kew, Surrey, England.