Name of the Pest:
Synchytrium endobioticum (Schilb.) Percival
Potato wart disease
Kingdom: Fungi

Geographic distribution:
Europe : Austria, Belarus, Belgium, Czech Rep.,Denmark, Estonia, Faeroe Islands, Finland, Germany, Hungary, Ireland, Italy, Latvia, Lithuania, Luxembourg, Netherlands, Norway, Poland, Portugal, Romania, Russian Federation, Slovakia, Slovenia, Sweden, Switzerland, Ukraine, United Kingdom, Yugoslavia
Asia : Armenia, Bhutan, China, India, Iran, Korea DPR, Korea Republic of, Lebanon, Nepal.
Africa: Algeria, Egypt, South Africa, Tunisia, Zimbabwe
America: Bolivia, Canada, Chile, Ecuador, Falkland Islands, Peru.
Oceania: New Zealand

Hosts:
Primary hosts: Solanum tuberosum (potato).
Secondary hosts: Lycopersicon esculentum (tomato).
Wild hosts: Solanum (nightshade).

Interception Information:
No interceptions data have been found from all ports in the United States.

Likely life stage transported:
sporangium and zoosporesare are likely life stages transported in infected tubers and soil or accompanying plants, from land on which potato wart has occurred in the past.

Biology:
S. endobioticum is an obligate parasite which does not produce hyphae, its thallus comprising only sporangia containing 200-300 motile zoospores. In the spring, at temperatures above 8~C and given sufficient moisture, the winter (i.e. long-lived) sporangium in decaying warts on potatoes in the soil germinates and releases uninucleate zoospores. The latter possess a single flagellum enabling them to move in soil water and reach the living host. The flagellum is then lost and the zoospore penetrates the host cell. This becomes greatly enlarged and the fungus forms a short-lived, quickly reproducing stage, the summer sporangium, from which numerous zoospores are rapidly discharged and reinfect surrounding cells, which again produce summer sporangia.

This cycle may be repeated as long as infection conditions are suitable, so that the host tissue is extensively invaded. The cells around those penetrated also swell and the tissue proliferates (hyperplasia), producing a characteristic cauliflower appearance.

Under certain conditions of stress, such as water shortage, the zoospores may fuse in pairs to form a zygote; the host-cell in which it forms does not swell but divides. The host-cell wall remains closely attached, forming an outer layer to the resistant, thick-walled winter sporangium. This matures and is released into the soil from rotting warts. Winter sporangia can remain viable for at least 30 years and are found at depths of up to 50 cm. The disease can be spread in infected seed tubers which may have incipient warts that pass undetected, or in infested soil attached to tubers. The sporangia resist digestion by animals, and can thus be spread in faeces. Many pathotypes of the fungus exist, defined by their virulence on differential potato cultivars. Pathotype 1 (European race 1) is the most common in the EPPO region and, in addition, the only pathotype occurring in most countries. Other pathotypes, numbered up to 18 occur mainly in the rainy mountainous areas of central and eastern Europe (Alps, Carpathians), for example in Czechoslovakia, Germany, Poland and the former USSR. They persist mainly in small garden potato plots, and not in commercial potato crops.

Known survey methods:
There are a number of methods of routine soil testing for viable winter sporangia.