Figure 1. Papillate sporangium of Phytophthora idaei. (Reproduced, by permission, from Young et al., 2007)

 

Figure 2. Comparison of sporangial and oogonial morphology of four Phytophthora species. 2–4, Sporangium, sporangial proliferation, and an oospore of Phytophthora idaei; 5–7, Phytophthora cactorum; 8–10, Phytophthora citricola; and 11–13, Phytophthora syringae. (Reproduced, by permission of The British Mycological Society, from Kennedy and Duncan, 1995) Click image to see larger view.

 

Introduction

Phytophthora idaei  D. M. Kenn. (1995)

 

Phytophthora idaei was isolated from rotting raspberry (Rubus idaeus) in the United Kingdom in 1995 (Kennedy and Duncan, 1995). The pathogen infects roots of the plant and has a limited host range (Cline et al., 2008). It is categorized as a group I species (Kennedy and Duncan, 1995; Stamps et al., 1990; Waterhouse, 1963). P. idaei resembles P. cactorum since its sporangia are spherical and papillate and its antheridia are paragynous (Erwin and Ribeiro, 1996). In contrast, P. idaei has persistent sporangia and P. cactorum has caducous sporangia. Also P. idaei has a lower optimal temperature for growth.

Cultural Characteristics

The optimum temperature for growth is 20–22°C. Colonies have limited aerial mycelium.

Reproductive Structures

Asexual Structures

 

Sporangiophores:

Sporangiophores are simple and in a lax sympodium.

 

Sporangia:

Sporangia are papillate and predominantly spherical to ovoid. Sporangia are 29.2–43.7 × 41–55 µm (mean 34.4 × 48 µm) (Figs. 1, 2.2, and 2.3). Sporangia are persistent and noncaducous. Sporangia predominately germinate indirectly by zoospores.

 

Chlamydospores and Hyphal Swellings:

No chlamydospores or hyphal swellings are formed.

 

Sexual Structures

 

P. idaei is homothallic.

 

Antheridia:

Antheridia are predominantly paragynous and occasionally amphigynous and are club shaped.

 

Oogonia:

Oogonia are smooth, spherical, and 26 × 38 µm.

 

Oospores:

Oospores are aplerotic and 22.8–31.2 µm (average 27 µm) (Fig. 2.4). Oospores form readily in the roots of raspberry.

Host Range and Distribution

Host

Common Name

Disease

Geographical Distribution

Rubus idaeus

Raspberry

Root rot

Great Britain

Symptoms

The pathogen has a limited host range and primarily infects the fine roots of Rubus species. It does not infect the aboveground portion of the plant.

References

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.

 

Kennedy, D. M., and Duncan, J. M. 1995. A papillate Phytophthora species with specificity to Rubus. Mycol. Res. 99:57-68.

 

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

 

Young, V., Cooke, D., Barker, H., and Dolan, A. 2007. Does Phytophthora idaei pose a treat to the raspberry crop? Scottish Crop Research Institute, Invergowrie, Dundee, Scotland. www.scri.ac.uk/webfm_send/658.