Figure 1. Caducous sporangium of Phytophthora tentaculata with a short pedicel. Bar = 25 µm. (Courtesy Eduardo Moralejo; Reproduced from Moralejo et al., 2004)
 

Figure 2. A large amphigynous antheridium attached to an oogonium of Phytophthora tentaculata. Bar = 25 µm. (Courtesy Eduardo Moralejo; Reproduced from Moralejo et al., 2004)
 

Figure 3. Verbena hybrid showing collar rot, 2 weeks after inoculation with a zoospore suspension of Phytophthora tentaculata. (Courtesy Eduardo Moralejo; Reproduced from Moralejo et al., 2004)

 
 
 
 
 
 
 
 
 
 
 

Introduction

Phytophthora tentaculata  Kröber & Marwitz (1993)

Phytophthora tentaculata was first isolated from roots and stalks of the greenhouse-grown ornamental plants of chrysanthemum (Chrysanthemum frutescens hybrid, Chrysanthemum leucanthemum), Delphinium ajacis, and Verbena hybrid and described by Kröber and Marwitz in 1993 (Kröber and Marwitz, 1993). It is closely related to P. multivesiculata according to Kroon et al. (2004). P. tentaculata is a group I Phytophthora species (Stamps et al., 1990).

Cultural Characteristics

The minimum temperature for growth is 7°C, the maximum temperature for growth is 32°C, and the optimum temperature for growth is 15–25°C. The growth rate is 3–5 mm per day at optimum temperatures.

Reproductive Structures

Asexual Structures 

Sporangia:
Sporangia are papillate or bipapillate and spherical or ovoid to obpyriform. Sporangia are noncaducous but some may be caducous with a short pedicel. Sporangia are 13–52 × 10–81 µm (average 27.4 × 35.7 µm) (Fig. 1).

Chlamydospores:
 Chlamydospores are intercalary or terminal, spherical, and thin walled. Chlamydospores are 10–45 µm in diameter (average 26.6 µm). 

Hyphae:
 Hyphal swellings are relatively small and occur where mycelium branches. Mycelium appears arachnoid when grown on carrot agar.

Sexual Structures 

P. tentaculata is homothallic. 

Antheridia:
The majority of antheridia are paragynous but amphigynous antheridia have been reported. Antheridia average 11.9 × 16.3 µm. Antheridia stalks are long and may be branched. Stalks may have tooth-shaped projections, and a few stalks completely encircle the oogonium. Antheridium and oogonium emanate from different hyphae and are diclinous (Gallegly and Hong, 2008).

Oogonia:
Oogonia are 20–49 µm in diameter (average 34.0 µm). 

Oospores:
Oospores are spherical, hyaline, and aplerotic. Oospores are 14–38 µm in diameter (average 28.1 µm) (Fig. 2).

Host Range and Distribution

Host

Common Name

Disease

Geographical Distribution

Chrysanthemum spp.

Chrysanthemum, Pyrethrum, Dalmatian flower

Root and stem rot

Spain, Germany

Santolina spp.

Santolina

Root and stem rot

Spain, Germany

Verbena spp.

Vervain

Root and stem rot

Spain, Germany

Symptoms

P. tentaculata causes a root and stem rot of ornamentals. Heavily infected plants are killed (Kröber and Marwitz, 1993) (Fig. 3).

References 

Gallegly, M., and Hong, C. 2008. Phytophthora: Identifying Species by Morphology and DNA Fingerprints. American Phytopathological Society, St. Paul, MN.

Kröber, H., and Marwitz, R. 1993. Phytophthora tentaculata sp. nov. und Phytophthora cinnamomi var. parvispora var. nov., zwei neue Pilz von Zierplantzen in Deutschland (Phytophthora tentaculata sp. nov. and Phytophthora cinnamomi var. parvispora var. nov., two new fungi from ornamental plants in Germany). J. Plant Dis. Prot. 100:250-258.

Kroon, L. P. N. M., Bakker, F. T., van den Bosch, G. B. M., Bonants, P. J. M., and Flier, W. G. 2004. Phylogenetic analysis of Phytophthora species based on mitochondrial and nuclear DNA sequences. Fungal Genet. Biol. 41:766-782. 

Moralejo, E., Puig, M., and Man in 't Veld, W. A. 2004. First report of Phytophthora tentaculata on Verbena sp. in Spain. New Dis. Rep. 9:38.

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