National Reference Laboratory for Plant Health - Fungi and Egg Fungi, Potato Section
Synchytrium endobioticum causes potato wart disease. In the late 19th century, the disease spread from its original range in the Andean region of South America to parts of North America and Europe. Eventually, the fungus was found in potato-growing countries around the world, including Asia and Africa. It is a highly destructive disease, and infected tubers can be extensively transformed into warts. Although a number of nightshade crops have been experimentally infected, potato is the main host. Favorable conditions for fungal development are cool summers with an average temperature of 18°C or less and annual precipitation of at least 700 mm. However, new outbreaks have been reported from areas in southeastern Europe where summer temperatures are higher. The ability of S. endobioticum to spread naturally is limited. The fungus can be spread by human intervention through infected potato tubers, soils, plants, or with potato waste. Because of its limited ability to spread naturally, the disease has been effectively controlled by regulatory measures in many countries. Strict phytosanitary controls and mandatory cultivation of resistant varieties have allowed eradication of the pathogen in some countries. However, eradication is very slow because the fungus survives in the soil for decades. For this reason, and because of the destructive nature of the disease, the fungus is considered an important quarantine pest worldwide.
Synchytrium endobioticum is an obligate parasite that does not form hyphae but sporangia that contain motile zoospores. The summer sporangia are thin-walled and short-lived. They are formed in potato tissue and can cause new zoospore infections. Dormant spores (sometimes called winter sporangia, winter spores) are thick-walled and can persist for extremely long periods even in the absence of a host. Diagnosis of S. endobioticum involves both the plant, on which warts may have formed, and the soil, which may contain dormant spores.
Numerous pathotypes (races) have been described in S. end obioticum. These are defined by their virulence on different potato cultivars. Pathotype 1 (D1) is now rarely reported as affecting potatoes in Europe because few potato cultivars are susceptible to it, apparently due to the availability of numerous resistant potato cultivars.
Other pathotypes are again reported more frequently in western Europe, especially in the rainy mountainous regions of central and eastern Europe. They also occur outside Europe (e.g., in Newfoundland, Canada, and the Asian part of Turkey). Resistance to these pathotypes is rare, making control more difficult.
The NRL involves molecular biological detection of DNA from enriched spores from soil samples and subsequent identification of the spores under the microscope.
Mag. Bernhard Föger
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Last updated: 20.12.2022