Synchytrium endobioticum (wart disease of potato)
- Taxonomic Tree
- Distribution Table
- Risk of Introduction
- Hosts/Species Affected
- Growth Stages
- List of Symptoms/Signs
- Biology and Ecology
- Means of Movement and Dispersal
- Seedborne Aspects
- Plant Trade
- Detection and Inspection
- Prevention and Control
- Distribution Maps
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PicturesTop of page
IdentityTop of page
Preferred Scientific Name
- Synchytrium endobioticum (Schilb.) Percival
Preferred Common Name
- wart disease of potato
Other Scientific Names
- Chrysophlyctis endobiotica Schilb.
- Synchytrium solani Massee
International Common Names
- English: black wart of potato; potato black scab; potato wart disease
- Spanish: sarna negra de la papa; sarna verrugosa de la papa; sarna verrugosa de la patata
- French: gale noire de la pomme de terre; gale verruqueuse de la pomme de terre; maladie verruqueuse de la pomme de terre; tumeur verruqueuse de la pomme de terre
Local Common Names
- Germany: krebs kartoffel
- SYNCEN (Synchytrium endobioticum)
Taxonomic TreeTop of page
- Domain: Eukaryota
- Kingdom: Fungi
- Phylum: Chytridiomycota
- Class: Chytridiomycetes
- Order: Chytridiales
- Family: Synchytriaceae
- Genus: Synchytrium
- Species: Synchytrium endobioticum
DescriptionTop of page Resting spores (winter sporangia) are mostly spherical, thick-walled, about 30-80 µm diameter. They tend to be integral components of aggregates or crumbs of soil.
DistributionTop of page S. endobioticum originated in the Andean zone of South America. It was introduced from there into the UK and from there to continental Europe in the 1880s, and into North America (Newfoundland) in the 1900s. It spread widely throughout the UK and the European continent in the early decades. The introduction of statutory measures limited its distribution, and it has spread to a limited extent only in other parts of the world (see list of countries).
S. endobioticum occurs locally in almost all countries in the EPPO region. Statutory controls (OEPP/EPPO, 1954-1968) have resulted in its fragmentary distribution only. There are also unconfirmed reports of its presence in Egypt, Lebanon, Iran, Korea (both Democratic People's Republic and Republic) and Zimbabwe.
See also CABI/EPPO (1998, No. 243).
Distribution TableTop of page
The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.
|Continent/Country/Region||Distribution||Last Reported||Origin||First Reported||Invasive||Reference||Notes|
|Armenia||Present, few occurrences||EPPO, 2014; CABI/EPPO, 2015|
|Bhutan||Present||EPPO, 2014; CABI/EPPO, 2015|
|China||Present||Bi and Hu, 2005; EPPO, 2014; CABI/EPPO, 2015|
|-Guizhou||Present||Bi and Hu, 2005; CABI/EPPO, 2015|
|Georgia (Republic of)||Restricted distribution||EPPO, 2014; Gorgiladze et al., 2014; CABI/EPPO, 2015|
|India||Restricted distribution||EPPO, 2014; CABI/EPPO, 2015|
|-Sikkim||Present||EPPO, 2014; CABI/EPPO, 2015|
|-West Bengal||Present||EPPO, 2014; CABI/EPPO, 2015|
|Iran||Absent, unreliable record||EPPO, 2014|
|Japan||Absent, confirmed by survey||EPPO, 2014|
|Korea, DPR||Absent, unreliable record||EPPO, 2014|
|Korea, Republic of||Absent, unreliable record||EPPO, 2014|
|Lebanon||Absent, unreliable record||EPPO, 2014|
|Nepal||Present||EPPO, 2014; CABI/EPPO, 2015|
|Turkey||Restricted distribution||IPPC, 2007; EPPO, 2014; CABI/EPPO, 2015|
|Algeria||Restricted distribution||EPPO, 2014|
|Egypt||Absent, unreliable record||EPPO, 2014|
|South Africa||Restricted distribution||EPPO, 2014; CABI/EPPO, 2015|
|Tunisia||Restricted distribution||EPPO, 2014; CABI/EPPO, 2015|
|Zimbabwe||Absent, unreliable record||EPPO, 2014|
|Canada||Restricted distribution||EPPO, 2014; CABI/EPPO, 2015|
|-Newfoundland and Labrador||Restricted distribution||EPPO, 2014; CABI/EPPO, 2015|
|-Prince Edward Island||Restricted distribution||IPPC, 2012; EPPO, 2014; CABI/EPPO, 2015; IPPC, 2015|
|Mexico||Absent, formerly present||EPPO, 2014|
|USA||Eradicated||EPPO, 2014; CABI/EPPO, 2015|
|-Maryland||Eradicated||CMI, 1983; EPPO, 2014; CABI/EPPO, 2015|
|-Pennsylvania||Eradicated||CMI, 1983; EPPO, 2014; CABI/EPPO, 2015|
|-West Virginia||Eradicated||EPPO, 2014; CABI/EPPO, 2015|
|Bolivia||Present||EPPO, 2014; CABI/EPPO, 2015|
|Falkland Islands||Present||EPPO, 2014; CABI/EPPO, 2015|
|Peru||Present||EPPO, 2014; CABI/EPPO, 2015|
|Uruguay||Absent, confirmed by survey||EPPO, 2014|
|Austria||Eradicated||****||EPPO, 2014; CABI/EPPO, 2015|
|Belarus||Restricted distribution||EPPO, 2014; CABI/EPPO, 2015|
|Belgium||Absent, formerly present||EPPO, 2014; CABI/EPPO, 2015|
|Bulgaria||Restricted distribution||EPPO, 2014; CABI/EPPO, 2015|
|Croatia||Absent, formerly present||EPPO, 2014; CABI/EPPO, 2015|
|Czech Republic||Restricted distribution||****||EPPO, 2014; CABI/EPPO, 2015|
|Denmark||Present, few occurrences||EPPO, 2014; CABI/EPPO, 2015|
|Estonia||Absent, formerly present||EPPO, 2014; CABI/EPPO, 2015|
|Faroe Islands||Present||EPPO, 2014; CABI/EPPO, 2015|
|Finland||Present, few occurrences||EPPO, 2014; CABI/EPPO, 2015|
|Germany||Restricted distribution||****||EPPO, 2014; CABI/EPPO, 2015|
|Ireland||Restricted distribution||EPPO, 2014; CABI/EPPO, 2015|
|Italy||Restricted distribution||EPPO, 2014; CABI/EPPO, 2015|
|Latvia||Restricted distribution||EPPO, 2014; CABI/EPPO, 2015|
|Lithuania||Absent, confirmed by survey||EPPO, 2014; CABI/EPPO, 2015; IPPC, 2016|
|Luxembourg||Restricted distribution||EPPO, 2014; CABI/EPPO, 2015|
|Montenegro||Restricted distribution||EPPO, 2014; CABI/EPPO, 2015|
|Netherlands||Restricted distribution||1914||NPPO of the Netherlands, 2013; EPPO, 2014; CABI/EPPO, 2015|
|Norway||Transient: actionable, under eradication||EPPO, 2014; CABI/EPPO, 2015|
|Poland||Present, few occurrences||EPPO, 2014; CABI/EPPO, 2015; Przetakiewicz, 2015|
|Romania||Restricted distribution||EPPO, 2014; CABI/EPPO, 2015|
|Russian Federation||Restricted distribution||EPPO, 2014; CABI/EPPO, 2015|
|-Central Russia||Widespread||EPPO, 2014; CABI/EPPO, 2015|
|-Northern Russia||Present||EPPO, 2014; CABI/EPPO, 2015|
|-Siberia||Present||Malyuga et al., 2003; CABI/EPPO, 2015|
|-Southern Russia||Present||EPPO, 2014; CABI/EPPO, 2015|
|Slovakia||Restricted distribution||EPPO, 2014; CABI/EPPO, 2015|
|Slovenia||Restricted distribution||EPPO, 2014; CABI/EPPO, 2015|
|Sweden||Restricted distribution||****||EPPO, 2014; CABI/EPPO, 2015|
|Switzerland||Present, few occurrences||****||EPPO, 2014; CABI/EPPO, 2015|
|UK||Restricted distribution||****||EPPO, 2014; CABI/EPPO, 2015|
|-England and Wales||Restricted distribution||EPPO, 2014; CABI/EPPO, 2015|
|-Northern Ireland||Eradicated||EPPO, 2014; CABI/EPPO, 2015|
|-Scotland||Restricted distribution||EPPO, 2014; CABI/EPPO, 2015|
|New Zealand||Restricted distribution||EPPO, 2014; CABI/EPPO, 2015|
Risk of IntroductionTop of page RISK CRITERIA CATEGORY
ECONOMIC IMPORTANCE High
SEEDBORNE INCIDENCE Not recorded
SEED TRANSMITTED Not recorded
SEED TREATMENT None
Notes on Phytosanitary risk
S. endobioticum is on the A2 quarantine list of EPPO (OEPP/EPPO, 1982), and is also of quarantine significance for all the regional plant protection organizations which have established quarantine lists. Though present in many countries, it has a very restricted distribution within them, which justifies its quarantine status. S. endobioticum sporangia persist so long in soil that it has hardly been possible to evaluate any differences in survival potential under differing soil and climatic conditions and in the presence of other plants. On the whole, in Mediterranean countries with warm, light, well drained soils, the disease is unlikely to cause serious direct losses, but its introduction and persistence could still be a problem.
HabitatTop of page S. endobioticum occurs in regions of moderate rainfall and temperature, propitious to the cultivation of potatoes.
Hosts/Species AffectedTop of page The only cultivated host is potato, but wild species of Solanum are also infected in Mexico. Tomato and a number of other solanaceous plants, including Schizanthus sp., Capsicastrum nanum, Physalis franchetii, Datura sp. and Solanum dulcamara are hosts by artificial inoculation.
Growth StagesTop of page Post-harvest, Vegetative growing stage
SymptomsTop of page The diagnostic symptoms of wart disease are galls produced on several plant parts.
Aerial symptoms are not usually apparent. There may, however, be a reduction in vigour. Warts can be found in severe attacks on the upper stem, leaf and flower. Leaf stalks may develop hypertrophic 'wings'. Above-ground galls are green to brown, turning black at maturity, and later decaying.
Galls vary in shape but are mostly spherical, with corrugated surfaces, and range from pea-size to fist-size <1 cm to >8 cm diam.). Below ground galls are white to brown, turning black as they decay. These galls appear at stem bases, stolon tips and tuber eyes. They may not be evident until harvest-time. At harvest, galls may desiccate or decay. Tubers may be disfigured or completely replaced by galls. Tuber galls may develop after harvest, in storage. The host potato may not be killed but the meristematic tissue of sprouts may be so severely attacked that plants may fail to emerge from seed tubers. S. endobioticum does not attack the roots of potato but it does attack the roots of other hosts (e.g. tomato).
List of Symptoms/SignsTop of page
|Growing point / distortion|
|Leaves / abnormal forms|
|Stems / canker on woody stem|
|Stems / distortion|
|Vegetative organs / internal rotting or discoloration|
|Vegetative organs / surface lesions or discoloration|
Biology and EcologyTop of page Life Cycle
S. endobioticum is an obligate, holocarpic, endobiotic parasite. It is long-cycled chytrid which does not produce hyphae but a thallus comprised of sporangia. Two forms of sporangia exist, so-called summer and winter sporangia (resting spores), which contain 200-300 motile zoospores. The summer or swarm stage results from host infection by haploid zoospores in which a sorus of one to nine sporangia form, and the winter or resting stage results from infection by conjugated (diploid) biflagellated zoospores. Both sporangial types germinate to release pear-shaped (1.5-2.2 µm diam.) zoospores. Motility is by means of posterior flagella. The resting (meio-)sporangia are golden brown, ridged and spheroidal (ca 35-80 µm diam).
If infection conditions are suitable, i.e. soil temperature and water, the rapidly reproducing summer sporangia release their zoospores thus setting up repeated infection cycles. At the same time, (meio-)sporangia (resting spores) are formed and, while conditions no longer favour the summer stage, the resting spores will overwinter in the infection zones of the potato. The resting spores induce hypertrophy of the infected tissue resulting in the so-called warts. This tissue will rot down in the soil during the winter months to release the resting spores into the soil. Resting spores can remain viable for decades. The ultimate lifespan has yet to be determined. The commonest means of spreading resting spores are by wart or soil distribution. Other limited means of distribution are by wind (over dried infested soil) or through animal droppings. The chitinous/melaninized wall of the resting spore is extremely chemo-resistant to common soil agents. Its resistance and longevity impact directly on control measures.
The fungus exists in many pathotypes. The pathotypes are defined by their virulence on differential potato cultivars. The common Pathotype 1 (European race 1) is found throughout the EPPO region and is the only one in many of the other countries. Other pathotypes, up to 19, occur in the wet montane areas of central and eastern Europe (e.g. Alps, Carpathians, Germany, Poland, former USSR). In Newfoundland, Canada, the common pathotype is #2, with pockets of #8. The pathogen persists in small garden plots and horticultural holdings but is not a problem in commercial potato crops. The private plots, nevertheless, present a control problem as the long-lived fungus can be disseminated through carelessness.
Means of Movement and DispersalTop of page S. endobioticum has a very limited means of spread and dispersal. Spread in soil by zoospores is limited (50 mm or less) to the infection zones of the plant. Soil water can carry zoospores downstream, although the lifespan of a released zoospore is 1-2 hours. Earthworms can move resting spores short distances. Wind is an active dispersal agent in regions of strong dry summer winds. Local dispersal has been shown in resting spores in soil attached to vehicles and contaminated manure. Long-range dispersal by tuber-movement, especially in international trade, attached soil and plants presents problems of control. Control though statutory methods has been largely successful due to the fungus' self-limited means of dispersal. The disease is essentially social, dependant on commercial crop and soil movement.
Seedborne AspectsTop of page There is no evidence that S. endobioticum is seedborne on true seed of potato.
Plant TradeTop of page
|Plant parts liable to carry the pest in trade/transport||Pest stages||Borne internally||Borne externally||Visibility of pest or symptoms|
|Bulbs/Tubers/Corms/Rhizomes||sporangia||Yes||Pest or symptoms usually visible to the naked eye|
|Growing medium accompanying plants||sporangia||Yes||Pest or symptoms usually invisible|
|Leaves||sporangia||Yes||Pest or symptoms usually visible to the naked eye|
|Stems (above ground)/Shoots/Trunks/Branches||sporangia||Yes||Pest or symptoms usually visible to the naked eye|
|Plant parts not known to carry the pest in trade/transport|
|Fruits (inc. pods)|
|True seeds (inc. grain)|
ImpactTop of page Wart disease of potato is so important that quarantine and domestic legislation has been in force globally for more than 65 years to prevent its spread and dissemination. In the 1950s and 1960s numerous EPPO publications were devoted to the disease. Once the pathogen has been introduced to a field of potato cultivation the whole crop may be devastated and unmarketable. Moreover, introduction into the soil not only renders the crop unusable but the soil itself cannot be used for further crop production due to the longevity of the fungus. Crops other than potato grown in this soil cannot be used for export. EEC Council Directive 69'464/CEE, 1969-12-08, requires the use of officially specified resistant potato cultivars in a protection zone around infested land. These (mainly applied domestically) stringent quarantine and sanitation measures have contained the disease in the EPPO region, and direct losses resulting from the pathogen are minimal. S. endobioticum generally has a much more limited distribution outside of Europe. Indirect losses arising from restrictions on the export of plants from infested areas present a problem to European countries.
DiagnosisTop of page
Polymerase chain reaction (PCR) and real-time PCR have been developed to diagnose Synchytrium endobioticum (Niepold and Stachewicz, 2004; Gent-Pelzer et al., 2010). The real-time PCR developed by Gent-Pelzer et al. was able to accurately diagnose the pathogen in zonal centrifuge extracts, warts and different plant parts of potato.
Detection and InspectionTop of page A number of methods have been elaborated for routine soil testing. The principal method is to employ a wet-sieving technique; dry sieving is also used. Flotation on chloroform is also useful.
Prevention and ControlTop of page
Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.Phytosanitary Methods
Control of wart disease of potato relies in the main upon statutory measures. According to OEPP/EPPO (1990) specific quarantine requirement, potatoes should derive from a stock free of S. endobioticum. Potatoes and indeed any kind of plants with roots (including bulbs, corms and tubers) for export, should not be grown in fields where S. endobioticum has occurred or is still present on account of the fungus' longevity factor.
In practice, this means an extensive system of 'scheduling' 'wart-infested' fields. This system relates back to the early 20th century epidemics. Fields may be 'descheduled' if they can be shown to be pathogen-free. Studies relating to this issue are in progress. The longevity factor of S. endobioticum is still a subject of debate and is the controlling factor in the 'descheduling' process. Those countries in which only pathotype 1 occurs are advised to determine that imported tubers come only from areas where other pathotypes have not been recorded. The common pathotype in Newfoundland, Canada, is pathotype 2; the island portion of the Province was quarantined in 1911, and remains in effect.
Wart-resistance remains an important element to be considered in breeding programmes, particularly in Central and Eastern Europe. New screening methods have recently been described.
ReferencesTop of page
Dolyagin AB; Avidon VV; Hampson MC; et al, 1990. Research on an efficient means of selecting chemical compounds for testing on the causative agent of potato canker (in Russian). Mikol. I Fitopatol. 24(3):257-259.
Efremenko TS; Yakovleva VA, 1983. Comparative assessment of the methods used in the USSR and abroad for determining soil infestation by Synchytrium endobioticum (Schilb.) Perc., the pathogen of potato wart. Mikologiya i Fitopatologiya, 17(5):427-433
EPPO, 1990. Specific quarantine requirements. EPPO Technical Documents, No. 1008. Paris, France: European and Mediterranean Plant Protection Organization.
EPPO, 2014. PQR database. Paris, France: European and Mediterranean Plant Protection Organization. http://www.eppo.int/DATABASES/pqr/pqr.htm
Gent-Pelzer MPEvan; Krijger M; Bonants PJM, 2010. Improved real-time PCR assay for detection of the quarantine potato pathogen, Synchytrium endobioticum, in zonal centrifuge extracts from soil and in plants. European Journal of Plant Pathology, 126(1):129-133. http://springerlink.metapress.com/link.asp?id=100265
Gorgiladze L; Meparishvili G; Sikharulidze Z; Natsarishvili K; Meparishvili S, 2014. First report of Synchytrium endobioticum causing potato wart in Georgia. New Disease Reports, 30:4. http://www.ndrs.org.uk/article.php?id=030004
Hampson MC, 1979. Infection of additional hosts of Synchytrium endobioticum, the causal agent of potato wart disease: 2. Tomato, tobacco and species of Capsicastrum, Datura, Physalis and Schizanthus. Canadian Plant Disease Survey, 59(1):3-6
Hampson MC, 1986. Sequence of events in the germination of the resting spore of Synchytrium endobioticum, European pathotype 2, the causal agent of potato wart disease. Canadian Journal of Botany, 64(9):2144-2150
Hampson MC, 1987. Seasonal changes in the germination behaviour of Synchytrium endobioticum, the causal agent of potato wart disease. Journal of Interdisciplinary Cycle Research, 18:275-281.
Hampson MC; Coombes JW; McRae KB, 1994. Pathogenesis of Synchytrium endobioticum: VIII. Effect of temperature and resting spore density (pathotype 2) on incidence of potato wart disease. Canadian Journal of Plant Pathology, 16(3):195-198
Hampson MC; Wood SL; Coombes JW, 1996. Detection of resting spores of Synchytrium endobioticum in soil from vehicles at Port-aux-Basques, Newfoundland. Canadian Journal of Plant Pathology, 18(1):59-63; 22 ref.
Hilli A, 1932. The reasons of the spread of potato wart [Synchytrium endobioticum (Schilb.) Perc.] in Finland and abroad (in Finnish, Engl. Summary). Valt. Maatalouskoet. Julk., 46:1-249.
IPPC, 2012. New Reports of Potato Wart (Synchytrium endobioticum) in Prince Edward Island. IPPC Official Pest Report, No. CAN-24/1, No. CAN-24/1. Rome, Italy: FAO. https://www.ippc.int/
IPPC, 2013. Synchytrium endobioticum absent in Denmark. IPPC Official Pest Report, No. DNK-15/1. Rome, Italy: FAO. https://www.ippc.int/
IPPC, 2015. September 2014: New Report of Potato Wart (Synchytrium endobioticum) in Prince Edward Island, Canada (2014). IPPC Official Pest Report, No. CAN-41/1. Rome, Italy: FAO. https://www.ippc.int/
IPPC, 2016. Information on Pest Status in the Republic of Lithuania in 2015. IPPC Official Pest Report, No. LTU-01/2. Rome, Italy: FAO. https://www.ippc.int/
Karling J, 1964. Synchytrium. London, UK & New York, USA: Academic Press.
Keller ER, 1968. Der Kartoffelkrebs. Mitteilungen der Schweizerischen Landwirtschaft 2 K/20.
Langerfeld E, 1984. Synchytrium endobioticum (Schilb.) Perc. Comprehensive literature survey of the causal agent of potato wart. Mitteilungen aus der Biologischen Bundesanstalt fur Land- und Forstwirtschaft Berlin-Dahlem, No.219:142 pp.
Mygind H, 1954. Methods for the detection of resting sporangia of potato wart Synchytrium endobioticum in infested soil. Acta Agriculturae Scandinavica, 4:317-343.
Nelson GA; Olsen OA, 1964. Methods for estimating numbers of resting sporangia of Synchytrium endobioticum in soil. Phytopathology, 54:185-186.
Noble M; Glynne MD, 1970. Wart disease of potatoes. FAO Plant Protection Bulletin, 18:125-135.
OEPP/EPPO, 1954-1968. Potato wart disease in Europe. EPPO Publications Series B Nos 8, 48, 52, 63, 65.
OEPP/EPPO, 1977. First report of the working party on potato wart disease. EPPO Publications Series C No. 50.
OEPP/EPPO, 1983. Second meeting of the EPPO panel on potato wart disease. EPPO Document No. 5205.
Percival J, 1910. Potato wart disease: the life history and cytology of Synchytrium endobioticum. Zentralblatt fnr Bakteriologie, Parasitenkunde, Infektionskrankheiten und Hygiene, 2(25):440-447.
Potocek J; Broz J, 1988. A new system of testing potatoes for resistance to potato canker (Synchytrium endobioticum) and potato root nematode (Globodera rostochiensis). Sbornik UVTIZ, Ochrana Rostlin, 24(1):47-56
Shifu J; Yongkong C; et al, 1988. A preliminary study on controlling potato wart with Triadimefon (in Chinese). Plant Protection, 14(3):22-23.
Stachewicz H, 1984. Application of in vitro culture to identify pathotypes of the potato wart pathogen Synchytrium endobioticum (Schilb.) Perc. Archiv fur Phytopathologie und Pflanzenschutz, 20(3):195-205
Tarasova VP, 1978. Potato wart disease (in Russian). Leningrad, USSR: 'Kolos'.
Distribution MapsTop of page
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