Introduction
Phytophthora fragariae
C. J. Hickman (1940)
Phytophthora fragariae
was first isolated by Hickman
in 1940 from strawberries in the
Cultural Characteristics
The minimum temperature for growth is 3°C, the optimum temperature for growth is 18–22°C, and the maximum temperature for growth is 30°C. Some isolates have a temperature maximum of 25°C. It is considered a low-temperature species and grows slowly in culture (Fig. 2).
Reproductive Structures
Asexual Structures
Sporangiophores:
Sporangiophores branch sympodially in water and bear sporangia on the tips.
Sporangia:
Sporangia are mostly large, measuring 22–52 × 32–91 µm (Fig. 3). Sporangia are ovoid to ellipsoid to obpyriform. Sporangia are nonpapillate and noncaducous and form sympodially. They proliferate internally and externally.
Chlamydospores:
Chlamydospores are not formed.
Hyphae:
P. fragariae produces thick and fluffy aerial hyphae on clarified V-8 agar with a slight brown discoloration of the media on the bottom of the plate (Fig. 2). Hyphae are meandering and coiling with sparse elongated branches. Small hyphal swellings, often in clumps, may form.
Sexual Structures
P. fragariae is homothallic.
Antheridia:
Antheridia are mostly amphigynous and single celled but are sometimes paragynous.
Oogonia:
Oogonia are globose to subglobose and often have a tapered base. Oogonia are 28–44 µm in diameter.
Oospores:
Oospores are globose and 34 to greater than 40 µm in diameter and form readily in the host but scantily in culture (Fig. 4). Oospores do not fill the oogonium (aplerotic). Oospores turn golden brown with age.
Host Range and Distribution
Host |
Common Name |
Disease |
Geographical Distribution |
Dryas drummondii |
D |
Red stele |
|
Fragaria
×ananassa |
Strawberry |
Red stele; red core; brown-core root rot; black stele; Lanark-shire
disease |
|
Fragaria spp. |
Beach and woodland strawberry, strawberry |
Root rot |
|
Geum spp. |
Avens |
Red stele; root rot |
|
Lycopersicon esculentum |
Tomato |
Root rot |
|
Nicotiana tabacum |
Tobacco |
Root rot |
|
Potentilla
spp. |
Cinquefoil, five-finger, tormentil |
Root rot; red stele |
|
Rubus spp. |
Red raspberry, loganberry, thimbleberry |
Root rot; red rot |
|
Spinacia oleracea |
Spinach |
Seedling rot |
|
Symptoms
Red stele or red core is the most important disease of strawberry worldwide.
It can be detected by severely stunted plants. On warm days, entire plants or
outer leaves of plants wilt suddenly (Fig. 5). Older leaves of infected plants
become yellow, red, and brown. The root systems of infected plants are devoid of
lateral roots, giving larger roots with black tips and a "rat's tail" appearance
(Fig. 6). When the stele is cut, a red or reddish brown color is seen
surrounding the white cortical tissue (Fig. 7). The red discoloration can extend
up the root into the crown of the plant.
Roots that develop during the summer months do not become infected and the plant
can partially recover during the warm season. Oospores form in the root, crown, and leaves and can survive in the soil for
many years (Erwin and Ribeiro, 1996).
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,
Forster, H., and Coffey, M. D. 1992. Molecular characterization of
Phytophthora isolates with non-papillate
sporangia causing root rot of raspberry using mtDNA restriction fragment length
polymorphisms. Mycol. Res. 96:571-577.
Hickman, C. J. 1940. The red core disease of the strawberry caused by
Phytophthora fragariae n. sp. J. Pomol. Hortic. Sci. 18:89-118.
Ho, H. H., and Jong, S. C. 1988. Phytophthora fragariae. Mycotaxon 31:305-322.
Milholland, R. D. 1994. A monograph of Phytophthora fragariae and the red stele disease of strawberry. N. C. Agric. Res. Serv. Tech. Bull. 306.
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,
Wang, P., and Lu, J. Y. 1978. Phytophthora leaf blight of rice seedlings, a new
disease of rice. Acta Microbiol. Sin.
18:95-101. (In Chinese with English summary)
Waterhouse, G. M. 1963. Key to the species of
Phytophthora de Bary. Mycol. Pap. 92. CAB
International, Wallingford, United Kingdom; Commonwealth Mycological Institute,
Kew,
Wilcox, W. F., Scott, P. H.,