Figure 1. Morphology of Phytophthora cryptogea. Upper row, Ellipsoid sporangium; internal proliferation of sporangia; and sympodial production of sporangia. Center, Inflated hyphae. Lower row, Globose oogonium with an amphigynous antheridium; and hyphal swellings. (Courtesy A. Vaziri; Reproduced from Erwin and Ribeiro, 1996) Click image to see larger view.

 

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

 

Figure 3. Sporangia of Phytophthora cryptogea releasing zoospores. (Courtesy Margery Daughtrey, Cornell University, Ithaca, NY)

 

Figure 4. Phytophthora cryptogea. A, Colony. B, Hyphal swellings. C–E, Sporangia. Bar = 20 µm. (Courtesy Hon H. Ho; Reproduced, by permission of the Institute of Plant and Microbial Biology, from Ho et al., 1995) Click image to see larger view.

 

Figure 5. Gerbera plant infected with Phytophthora cryptogea. (Courtesy Margery Daughtrey, Cornell University, Ithaca, NY)

 

Figure 6. Gerbera plant infected with Phytophthora cryptogea. (Courtesy Carlo Pasini, CRA-FSO, Sanremo, Italy)

 

Introduction

Phytophthora cryptogea  Pethybr. & Laff. (1919)

 

Phytophthora cryptogea was first described as the cause of foot rot of tomato in Ireland by Pethybridge and Lafferty in 1919 (Pethybridge and Lafferty, 1919). It is a cosmopolitan pathogen of worldwide importance on many hosts (Erwin and Ribeiro, 1996). Ho and Jong (1986) considered P. cryptogea to be synonymous with P. drechsleri. Cooke et al. (2000) found the two species to be distinct, based on molecular analysis, and closely related to P. erythroseptica (Cline et al., 2008). The pathogen can persist in the soil for long periods of time on organic matter. P. cryptogea is a group VI species (Stamps, 1978; Stamps et al., 1990). The description of Ho and Jong (1986) should be used to characterize this species (Fig. 1). 

Cultural Characteristics

Cultures grow uniform with fairly fluffy mycelium (Figs. 2 and 4A). Some isolates display a slight to distinct floral pattern on V-8 agar medium. The minimum temperature for growth is less than 1°C, the optimum temperature for growth is 22–25°C, and the maximum temperature for growth is 31–33°C, with no colony growth at 35°C or higher. Isolates with morphological traits similar to P. cryptogea and that grow above 35°C should be classified as P. dreschleri.

Reproductive Structures

Asexual Structures

 

Sporangiophores:

Sporangiophores proliferate internally through empty sporangium (nested) or develop sympodially from below previously formed sporangia (Fig. 1). Sporangiophores are 2–3.5 µm in diameter. Sympodia form in water.

 

Sporangia:

Nonpapillate sporangia are produced only on liquid media. They are noncaducous and the first-formed sporangia are regularly ovoid or obpyriform. Later-formed sporangia can be elongated and variable in shape. Sporangia are 24–35 × 35–63 µm (average 30 × 52 µm) (Ho et al., 1995) (Figs. 3 and 4C–E). The length–breadth ratios are greater than 1.6. Sporangia are nonpapillate, without an obvious apical thickening. the exit pore is more than 8 µm wide. Sporangia collapse after zoospore release.

 

Chlamydospores:

Chlamydospores are not formed.

 

Hyphae:

Hyphae are very uneven or irregular in width, up to 8 µm in diameter. There is a conspicuous network of small, catenulate hyphal swellings abundant on aqueous cultures (Fig. 4B).

 

Sexual Structures

P. cryptogea is heterothallic and requires mating with an opposite mating type to form oogonia and oospores. It sometimes forms in single cultures of aged cultures.

 

Antheridia:

Antheridia are amphigynous and spherical, sometimes oval or cylindrical, and unicellular. Antheridia are 12–17 × 13–17 µm.

 

Oogonia:

Oogonia rarely form in single cultures but develop when paired with isolates of opposite mating types. Oogonia measure 28–37 µm in diameter (average 31 µm). Oogonia have tapered bases and become yellow with age.

 

Oospores:

Oospores nearly fill the oogonia, are plerotic, and are 24–32 µm in diameter (average 27 µm). Oospores are thick walled, with the walls measuring 3.5 µm. 

Host Range and Distribution

See Table 20.1 in Erwin and Ribeiro (1996) for a complete host range list.

Symptoms

Foot and Root Rot of Tomato:

The disease was first described causing a foot rot on tomato. It is severe in wet, waterlogged soils. A brownish black discoloration and lesion occurs at the base of the stem. Secondary adventitious roots can emerge above the lesions. Lesions advance, causing the plant to fall over. The root system becomes entirely rotted. Foliage does not display symptoms until the plant stem is girdled. It is a limiting factor in the greenhouse production of tomatoes at low temperatures of 15°C.

 

Root and Collar Rot of Ornamental and Woody Plants:

P. cryptogea is an important pathogen of many ornamentals. Plant roots with collar rot exhibit a decline in foliage (Fig. 5), leading to defoliation and the dieback of branches on many hosts (Fig. 6). Plants appear chlorotic and stunted. The pathogen is spread with poorly drained soils under wet conditions. Cankers can also girdle the stem. Pinus species show a general decline and die prematurely.

 

Diagnostics:

The pathogen must be isolated on selective media for accurate identification. Species identification requires morphological and molecular identification (Cooke et al., 2000; MacDonald et al., 1990).

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.

 

Cooke, D. E. L., Drenth, A., Duncan, J. M., Wagels, G., and Brasier, C. M. 2000. A molecular phylogeny of Phytophthora and related oomycetes. Fungal Genet. Biol. 30:17-32.

 

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

 

Ho, H. H., and Jong, S. C. 1986. A comparison between Phytophthora cryptogea and P. drechsleri. Mycotaxon 27:289-319.

 

Ho, H. H., Ann, P. J., and Chang, H. S. 1995. The genus Phytophthora in Taiwan. Inst. Bot. Acad. Sinica Monogr. Ser. 15.

 

Pethybridge, G. H., and Lafferty, H. A. 1919. A disease of tomato and other plants caused by a new species of Phytophthora. Sci. Proc. R. Dublin Soc. 15:487-503.

 

MacDonald, J. D., Stites, J., and Kabashima, J. 1990. Comparison of serological and culture plate methods for detecting species of Phytophthora, Pythium, and Rhizoctonia in ornamental plants. Plant Dis. 74:655-659.

 

Stamps, D. J. 1978. Phytophthora cryptogea. CMI Descr. Pathog. Fungi Bact. 592:1-2.

 

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.