Phytophthora cactorum
| Phytophthora cactorum | |
|---|---|
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| Microscopic view of sporangium of Phytophthora cactorum | |
| Scientific classification | |
| Domain: | Eukaryota |
| (unranked): | SAR |
| Superphylum: | Heterokonta |
| Class: | Oomycetes |
| Subclass: | Incertae sedis |
| Order: | Pythiales |
| Family: | Pythiaceae |
| Genus: | Phytophthora |
| Species: | P. cactorum |
| Binomial name | |
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Phytophthora cactorum (Lebert & Cohn) J. Schröt., (1886) |
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| Synonyms | |
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Peronospora cactorum Lebert & Cohn, (1870) |
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Peronospora cactorum Lebert & Cohn, (1870)
Phloeophthora cactorum (Lebert & Cohn) G.W. Wilson, (1914)
Phytophthora fagi R. Hartig, (1876)
Phytophthora omnivora de Bary, (1881)
Phytophthora cactorum is a plant pathogen that causes root rot on rhododendron and many other species.
Phytophthora cactorum has an extremely wide host range, and can infect over 200 species or 160 genera of trees, ornamentals, and fruit crops. In general, P. cactorum is capable of infecting both young and old plants, and causes root rots and crown rots of the many genera it infects. Although the symptoms this pathogen produces varies between the types of organisms it infects, in general disease occurs during periods that are both wet and warm. Furthermore, most infections are caused by zoospores entering the plant through wounds.
On older trees, P. cactorum causes the formation of sap exuding dark colored cankers on the trunks of trees, as well as leaf size and number reduction, chlorosis, and dieback of branches. The diagnosis of a P. cactorum infection of trees, is based on the identification of symptoms, in particular the oozing cankers, and confirmation of symptoms in a diagnosis lab or utilization of a field ELISA detection kit.Phytophthora cactorum can be a major problem in apple orchards, as it can cause crown, collar, and root rots in apple trees. When infecting apple trees, the organism can attack through wounds either above or below the soil line, impairing phloem and root function, and causing stunting, foliar disorders, and death after several years. Furthermore, because the pathogen causes damage to the phloem of the tree, one diagnostic method is to check for necrotic phloem tissue at the base of the tree which will be orange to red-brown in the early stages and dark brown in the later stages of infection.
A good example of Phytophthora cactorum causing foliar disease, is Phytophthora cactorum on ginseng. Foliar disease of ginseng usually occurs during May and early June, causing the leaves to become transparent and papery. Ginseng foliar infection occurs through the rain splash dispersal of spores from the soil onto above ground wounds. Once infected, Phytophthora cactorum works its way down to the roots, rotting them and killing the plant.
Phytophthora cactorum is also one of the causal agents of black rot of orchids. When infecting orchids, this organism first produces small black lesions on the pseudo bulbs of the orchid, which then enlarge and may engulf the entire pseudobulb, leaf, or move through the rhizomes to other portions of the plant prior to killing it. Diagnosis of orchid black rot by P. cactorum is through the identification of lemon shaped zoosporangia with either a papilla or a short pedicel, the presence of oospores, or molecular identification. Since there are multiple species of Phytophthora that are capable of causing disease on orchids, classification only to the genus level is required for proper prescription of disease management techniques.
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