Situation of Ralstonia solanacearum in the EPPO region (latest update)
Ralstonia solanacearum (EPPO A2 quarantine pest) in the last few years has been reported at a number of locations in northern Europe and is continuing to be so reported. In order to clarify the situation of potato brown rot throughout the EPPO region, a questionnaire was sent at the end of 1995 to all EPPO member countries, and the answers were presented in EPPO RS 96/002. Since then, new information was given by several countries and was published in the EPPO Reporting Service articles 96/022, 96/090, 96/182, 96/183, 97/007, 97/024 and 97/025. Finally, a round-table session on the present country situation took place during the EPPO Conference on Ralstonia solanacearum (Verona (IT), 1997-03-25/27). A compilation from all these different sources of information is given below. It is presumed that all occurrences on potato in Europe are race 3 of R. solanacearum. Asterisk shows that new information was presented at Verona.
Austria*: In the previous report (EPPO RS 96/002), it was stated that IF-positive results were obtained for three samples of potatoes in 1995. However, when they were retested (IF with a new serum and pathogenicity tests), the results were all negative. These lots were used as ware potatoes. In Austria, a seed potato certification scheme is in place and post-harvest control for each lot and each category is performed. So far, R. solanacearum has not been found from Austria.
Belgium*: Prior to 1989, R. solanacearum was never found in Belgium. A small area near the border with the Netherlands was found to be infested over the years 1989-1991, and strict survey and control measures were imposed (see EPPO RS 93/070). Cultivation of potatoes was prohibited in a quarantine area of several communes around the infected plots. Intensified surveillance was applied to potato crops all over Belgium, with laboratory testing of seed potato samples, regular visual inspection of seed potato crops throughout Belgium. No case of potato brown rot was found in seed potatoes. Since 1992, intensive surveys have been carried out for ware potatoes and seed potatoes. 20 % of seeds potatoes produced in Belgium have been tested in the laboratory, production fields have been inspected at least twice a year and all lots have been visually inspected. In 1993 and 1994, only a single case of infestation per year was found and infected crops were destroyed. R. solanacearum has not been found in Belgium in 1995 and 1996, and in particular has not been found in any of the production sites of ware potatoes where the disease was found in previous years. These results indicate that the disease has been eradicated on potatoes. Since the previous reports (EPPO RS 96/002, 96/183), surveys have been carried out on surface waters and Solanum dulcamara. In 1995, waters and S. dulcamara were tested in the area where the bacterium had been found and its surroundings. In 1996, a survey was conducted on all waterways near potato production sites and near potato-processing industries. As a result, some contaminations were found in canals near the area where infection had been observed, but no other contamination was found on the Belgian territory. In addition to prophylactic measures applied to the whole country, the area where water contamination has been found is strictly delimited, and it is prohibited to use water for irrigation and phytosanitary treatments. It is strongly felt that the origin of the previous contamination is linked to industrial potato-processing installations. It is suggested that the bacterium may have reached potato crops thought surface water, S. dulcamara and irrigation.
Bulgaria: R. solanacearum was reported for the first time in Bulgaria on tomato in 1944, and was then observed in 1951 on sunflower. These two foci were eradicated and since then R. solanacearum has not been found in Bulgaria. Inspections carried out in 1994 and 1995 have not revealed the presence of the bacterium.
Croatia: R. solanacearum has never occurred in Croatia.
Cyprus*: R. solanacearum was found only once on potatoes in October 1955 in 'Shia Village' which is not a traditional potato-growing area. Eradication measures were applied and the disease was not further reported. The official authorities consider that Cyprus (southern part of the island) is now free from R. solanacearum but stress that they can only speak for the southern part of the island and not for the northern part. Although it is feared that brown rot may be present in the northern part of the island, as descriptions of symptoms on potato crops are reported in Turkish Cypriot newspapers (EPPO RS 97/007), this has not been confirmed.
Czech Republic: R. solanacearum has never been found in Czech Republic.
Denmark*: R. solanacearum has not been found in Denmark in 1994, 1995 and 1996. In 1995/96, all tests carried on ware and seed potato samples, imported or from Denmark gave negative results. It can be noted that surface water is not used for irrigation or potato crops. Brown rot of potato has never occurred in Denmark. A previous EPPO record refers to an interception on ornamental Musa only (presumably race 2).
Estonia: R. solanacearum has never occurred in Estonia.
Finland*: R. solanacearum has never been found in potatoes grown in Finland but has been intercepted in one case on ware potatoes from Egypt, on the basis of visual symptoms. Tests carried on domestic production gave negative results.
France*: In 1994, an infection was reported on tomato and another on aubergine, in Aquitaine and Pays-de-Loire. It must be noted that these regions are not seed potato-producing areas. In autumn 1995, four foci of R. solanacearum were observed. Two foci were found on tomato crops grown in glasshouses in Lot-et-Garonne (Aquitaine) and Loire-Atlantique (Pays-de-Loire), one focus was found on outdoor tomatoes in Lot-et-Garonne, and a focus was observed on a plot for comparative trials of potatoes in an experiment station located in Essonne, far away from production areas of seed and ware potatoes. All these foci have been eradicated, production sites and equipment have been completely disinfected. On plots where infection has been found, it is prohibited to grow any susceptible plants for a minimum period of 3 years and the absence of volunteer plants and wild Solanaceae has to be checked. Surveys are carried out on seed and ware potatoes, with visual inspections and laboratory tests. For 1996, results of the 7300 tests (covering 14000 ha of certified potatoes) carried out on seed potato production were all negative. Similarly, no positive result was found for ware potatoes. A survey of waterways and S. dulcamara has been implemented in 1996. Of 200 tests done on S. dulcamara, only one was confirmed as positive. Surveys on the national territory and on potato imports will continue.
Germany*: Until very recently, R. solanacearum was never reported in Germany. For the 1995 harvest 2500 samples of seed potatoes and 200 of ware potatoes were tested. Samples are tested by IF and PCR in parallel, and if a positive result is found, bioassays are performed on tomato or aubergine. All results were negative in 1995. For 1996, one sample has given a positive result which is being confirmed by fatty acid profiles, PCR, bioassay and pathogenicity tests. The sample came from Brandenburg near Berlin. In the farm concerned (field of 2-5 ha), there is a small production of potato and sugarbeet for animal fodder. The seed potatoes had been multiplied for many years for the own use of the grower and cannot be connected to any imports; they are mixtures of different cultivars. The area is not irrigated. The grower will not be allowed to grow potatoes for 5 years in this field, and he will have to used certified potatoes in areas where potatoes have not been grown for 12 years. Machinery was disinfected. Investigations carried out in the surroundings of this farm gave negative results. The origin of the contamination could not be traced, but investigations are continuing. In 1996, surveys were also done on water from potato-processing installations and the bacterium was not found.
Guernsey: R. solanacearum has never occurred in Guernsey.
Hungary*: Visual examination and laboratory tests carried out in Hungary have shown that R. solanacearum is not present in the country. No infection was found in any tested samples of imported seed potatoes.
Ireland: R. solanacearum has never been found in Ireland. All surveys gave negative results.
Israel*: At present, potato brown rot does not occur in Israel and is considered as a quarantine pest. In the early 1970s, it was found in several potato fields in one location in Israel but was successfully eradicated. In 1993, a survey was carried out throughout the country and concerned potato brown rot, potato ring rot (Clavibacter michiganensis subsp. sepedonicus) and potato spindle tuber viroid. None of these diseases was found. In 1994, R. solanacearum has been found in Curcuma plants grown in glasshouses from bulbs imported from the Netherlands (presumably race 1). Measures were immediately taken, including destruction of all infected bulbs and plants, and fumigation with formaldehyde. Tests carried out in 1995 and 1996, on imported and Israeli potatoes gave negative results, with the exception of one imported lot of ware potatoes in 1995 which was sent back to the country of origin.
Italy*: Before 1995, brown rot of potato was never found in Italy. During June 1995, foci of potato brown rot have been suspected in Veneto and Emilia-Romagna after import of infected seed potatoes. These certified seed potatoes (cvs. Primura and Liseta) were imported from the Netherlands. The infected potatoes were destroyed and phytosanitary measures have been taken to eradicate these foci and to prevent further spread of the disease to other potato fields and other solanaceous crops. In addition, the Ministry of Agriculture has taken measures at the EU level regarding the marketing of seed potatoes from the Netherlands to prevent further introductions into Italy. In 1996, all results of field surveys including those from Veneto and Emilia-Romagna were negative.
Jersey: R. solanacearum has never been found in Jersey. In 1995, symptoms on tomato were found suspicious but during tests, R. solanacearum was not isolated.
Latvia*: R. solanacearum is not present in Latvia. A few reports were made in the past but have never been confirmed. Surveys based on visual examination were all negative. A programme for testing imports will soon be implemented.
Malta: R. solanacearum has never occurred in Malta.
Morocco: Although there have been some old records of R. solanacearum on tomato and Capsicum made in the 1940s, since then the bacterium has never been found on these crops or on potatoes. Therefore, R. solanacearum should be considered as absent from Morocco.
Netherlands*: In 1995, R. solanacearum (EPPO A2 quarantine pest) was reported in the Netherlands (EPPO RS 96/001). From the middle of October 1995, before the beginning of the main potato trade season, all seed potato lots were tested and only lots found free were marketed.
The results of the 1995 survey are the following. Approximately 51,000 samples were collected and tested for R. solanacearum. These samples were mainly seed potatoes but also ware potatoes. In total, 94 farms have been found infested, including 54 seed potato-growing farms. Foci were located in almost all potato-growing areas, many of them are connected by the use of a clonal line (cv. Bildstar), which is essentially grown for the Dutch market. Some of the infestations can be related to the use of machinery in common. In November 1995, samples of surface water were taken in a limited number of areas where infestations could not be explained by clonal or machinery relations. In one of these areas, infected surface water was discovered. Measures were taken in infected farms in order to eradicate the disease and prevent any further spread.
During the 1996 season, all seed potato lots from one place of production have been tested for the bacterium before a plant passport or a phytosanitary certificate was issued and marketing allowed. Sampling and testing was carried out from mid-August to the end of November. Approximately 58,000 samples were tested from 3,100 seed potato growing farms. Infections with R. solanacearum were found on nine farms. On each farm, only one potato cultivar was infected. Seven of these farms were growing seed potatoes. Measures have been taken to prevent spread of the bacterium from all infected farms. Concerning the farms found infected during the 1995 season, which were allowed to grow ware potatoes, all potato lots of the 1996 season were tested and no infection was detected. In addition, an infection of R. solanacearum was found in one tomato glasshouse. The infection was due to the contamination of the surface water used for irrigation. However, irrigation of tomato crops with surface water is not a common practice in the Netherlands. This single glasshouse infestation has been eradicated by destroying all plant material and rockwool, and disinfecting the irrigation system, tools and premises.
To determine the extent of contaminated surface water and infected Solanum dulcamara plants, studies were started all over the Netherlands with emphasis on potato-growing regions in spring 1996. In several of the potato-growing regions, contaminations of surface water and/or S. dulcamara were detected. Areas with contaminated surface water have been demarcated. For potato lots from these demarcated areas posing a risk (use of surface water), only a controlled distribution as ware potatoes was allowed.
For research purposes, four water areas (3 contaminated, 1 free) are sampled every week. The bacterium could be detected in contaminated areas until the end of December when ice cover prevented any sampling and it was found in one of them immediately after ice melted in February. This fact suggests that the bacterium can survive in water during winter or is constantly released from infected S. dulcamara. The bacterium was also detected in a number of cases near waste installations of the potato industry. It is felt, although not proved that the origin could be contamination of surface water with waste from infected material of imported early ware potatoes. Results of some preliminary experiments on the survival of R. solanacearum in/on different substrates under conditions of light and room temperature (first number) or dark and 4 °C (second number) could be obtained: surface water (survival 17-33 days), ditch mud (6-24 d), sewage of potato industry (23-53 d), chicken manure (23-30 d), cow manure (7-11 d). Survival on wood was 4 d, metal 14 d and rubber 55-87 d under dry conditions at room temperature.
Norway*: R. solanacearum has never occurred in Norway; it has never been intercepted on imports or detected on Norwegian potatoes.
Poland*: There are reports of R. solanacearum before 1945 but these are probably based on misidentifications. Since 1945, this pathogen has never been recorded in Poland.
Portugal*: R. solanacearum was found in potato fields during the 1940s and at the beginning of the 1950s. At that time, appropriate measures were taken and the bacterium was successfully eradicated. Recently, in April/May 1995, new outbreaks were found in ware potato fields located in the centre-coastal part of the country. After study, it was concluded that the source of these foci was infected seed potatoes imported from the Netherlands. Immediate action was taken to eradicate the disease. The measures applied included: lifting all potatoes in infected fields and transport under quarantine for destruction; disinfection of all material which had entered into contact with contaminated plants or soil; prohibition of the production of potato and other Solanaceae on the infected fields for 4 years; avoidance of water flow from infected fields to the immediate vicinity; application of cultural techniques which promote the acidity of the soil. In addition, the level of inspection and surveillance in the infected/suspect fields and their neighbouring areas has been increased. In 1996, only one field was found infested.
Romania: An occurrence of R. solanacearum has been reported only once in the Romanian literature, in 1957. The bacterium has never been identified by the Central Quarantine Laboratory (including in 1994 and 1995), and it is considered that the disease is not present in Romania.
Slovakia*: R. solanacearum has never occurred in Slovak Republic. In 1996, results of testing for brown rot were all negative.
Slovenia*: R. solanacearum has never occurred in Slovenia. Intense testing has been carried out since the reports of the disease in Europe. Potatoes are not irrigated in the main potato-producing areas.
Sweden*: An infestation was reported in the mid-1970s in the South of Sweden (Olsson, C. (1976) Experience of brown rot caused by Pseudomonas solanacearum (Smith) Smith in Sweden, EPPO Bulletin 6(4), 199-207) and was later eradicated. The first case was found in 1972 at Hököpinge on potatoes, and the disease was found again in 1973. Other outbreaks were found in Ostra Ljungby in 1973 on potatoes, and on Solanum dulcamara in 1974 and 1975. Speculations were made on the possible origin of the disease such as, infected seed potatoes, insects (Leptinotarsa decemlineata), soil and irrigation water. For the area of Hököpinge, none of these hypotheses could really be retained. But the other area of Ostra Ljunby, suspicion was directed towards the soil and irrigation water, as the infections were found downstream from a potato-peeling factory. Measures were taken on farms with infected fields (absence of potato crops for 3 years, no irrigation, disinfection, elimination of S. dulcamara plants). After 1975, no infestation was found. During studies carried out in 1980-84, no R. solanacearum was detected in waters. Tests have been carried out on Solanum dulcamara in the streams of the earlier infested areas in 1994-95. Very few plants could be found as the elimination programme was quite successful. None of the tested plants was infested. The authorities consider that Sweden is free from R. solanacearum.
Switzerland*: R. solanacearum is not present in Switzerland, and no symptoms have been seen during the recent period of outbreaks elsewhere in Europe. During tests and inspections carried out in 1995 and 1996, only one positive result was obtained on a ware potato consignment from Turkey on the basis of laboratory tests.
Tunisia: R. solanacearum has been reported in the past, in a limited area. However, observations on seed and ware crops of potato over the last two years have revealed no case of the disease.
Turkey: The disease is considered as absent in Turkey. It has been found in the past but is not established. However, in early 1995 some infected potato tubers (cv. Van Gogh) were found in a small part of Central Anatolia region. Intensive surveys have been set up and eradication measures are being applied.
Ukraine: According to the inspections and analysis carried out in Ukraine, R. solanacearum is not present.
United Kingdom*: Potato brown rot has been reported in United Kingdom, in the Oxfordshire region of England in 1992 (see EPPO RS 93/031). The farm in question has been under control since that time. Although infection was found in one or two "ground keeper" or "volunteer" tubers in the following season, no further re-occurrence of the disease was found on that farm. Extensive surveys of both ware and seed crops have been conducted since this first outbreak. A second case was discovered in 1996. A sample of ware potatoes from the 1995 harvest was found contaminated by R. solanacearum. This sample was taken from a farm store situated near Slough (within the Thames basin), in the same area where the previous outbreak had been found. Investigations were carried out on seed from the same origin, as well as on sister stocks to the contaminated potatoes, and gave negative results. However, the bacterium was isolated from Solanum dulcamara growing in the water system from which the infected potatoes were irrigated. These weeds appear as the most likely source of infection. The following measures have been applied: potato growing is prohibited on the infected field, no seed potatoes are grown on the farm and monitoring of potato crops in other fields is performed.
In Scotland, R. solanacearum has never been detected in potatoes or S. dulcamara in the river systems. Surveys are carried out on Scottish seed and ware potato stocks. Tuber samples from 50 seed and 50 ware stocks are visually inspected for symptoms and tubers from another 50 seed and 50 ware stocks are sent for laboratory testing. Within certification scheme, all material entering in vitro collections for nuclear stock is tested for freedom from R. solanacearum, and during seed certification there are a minimum of two field inspections. No interception in potato material entering Scotland, from either the European Union or outside Europe has been made in recent years.
No data have been either received to the questionnaire or presented at the Conference from: Albania, Greece, Luxembourg, Russia and Spain. According to the data in the EPPO PQR system, R. solanacearum has been reported in Greece, Russia (not apparently on potato). In Spain (RS 95/011), it occurred in 1981 in the Canary Islands and was eradicated (never found on the mainland). In the 1970s, Yugoslavia reported R. solanacearum to be present locally, as was given in the first edition of the EPPO data sheet. In view of the declarations from Croatia and Slovenia, the affected regions must be elsewhere in ex-Yugoslavia. In the EPPO region, there are also records in: Algeria (not in coastal region), Armenia, Belarus (unconfirmed), Egypt, Georgia, Lebanon, Libya, Moldova.
Sources
EPPO Secretariat, 1997-06