A ProMED-mail post
ProMED-mail is a program of the
International Society for Infectious Diseases <http://www.isid.org>
Date: Fri 27 Apr 2012
Source: Potato Pro [edited]
The Dutch agency responsible for phytosanitary inspections [NVWA] has discovered the potato disease ring rot in the south of the Netherlands (Zuid Holland and Zeeland). The infected lots were identified and removed from the market.
The NVWA identified the contamination after the German government in early March  reported ring rot in potatoes grown using Dutch seed potatoes from 2010. These potatoes were obtained from a grower on Goeree-Overflakkee [island]. This farmer used a portion of the seed on his own farm, exported a portion to Germany and sold part of the lot in the Netherlands. In the progeny of [the seed potatoes from] this grower, ring rot is found.
The NVWA launched an investigation in 2011 into all progeny from this grower in all varieties. This turned up 7 cases of ring rot in the Netherlands. Also, the NVWA tested all consignments of the seed grower's crop of 2011, including the part that was already delivered elsewhere in the Netherlands. In that crop, ring rot was found in 2 batches.
The final results from the collected samples will be available in May and June . The potatoes of the 2011 crop from this particular seed grower cannot be used as seed potatoes.
[Ring rot of potato is caused by the bacterium _Clavibacter michiganensis_ subsp. _sepedonicus_. Yield losses of up to 50 percent have been reported. Many solanaceous species, including tomato and aubergine [eggplant], are also susceptible, and the pathogen has also been found associated with symptomless infections of sugar beet and sugar beet seed. The pathogen has been included on the A2 quarantine list of the European Plant Protection Organisation (EPPO).
Symptoms on potato may include wilting and yellowing of leaves, rot of the vascular ring of tubers with emerging bacterial ooze, and extensive tuber rot followed by internal hollowing, cracking and mummification. Wilting symptoms may occur late in the season and are often masked by the natural senescence of the crop. Symptom expression depends on host cultivar and is favoured by cool climates. Tubers with ring rot are often subjected to secondary invasion by other bacteria and fungi, which can result in total loss of tubers in the field or in storage.
The pathogen is spread with infected seed tubers or other plant material, plant-to-plant contact, soil and mechanical means (for example during harvest or grading). The bacteria can survive for several years on dry surfaces and for over a month in water. They can overwinter in unharvested potatoes or crop debris. Ring rot can pass through one or more crop generations without causing symptoms, and latently infected tubers are an important means of spreading the disease. Laboratory tests are needed to detect latent infections.
Disease management is expensive and may include cultural practices and plant hygiene measures before and after harvest, but the use of certified clean seed potatoes is vital.
Ring rot was found in southern Netherlands in 2009 and 2010, which resulted in extensive testing of seed consignments and alerts to other European growers (ProMED-mail post 20111229.3697). However, from the report above, it appears that contaminated potatoes had already been widely distributed. The NVWA reports that testing of seed potatoes at
64 production sites in the area resulted in 7 ring rot detections due to the illegal use of untested, farm-saved seed potatoes.
Location of Goeree-Overflakkee:
Potato ring rot, leaf and tuber symptoms:
Ring rot affected tubers:
Additional news stories:
Information on potato ring rot:
Molecular detection of _C. m._ subsp. _sepedonicus_:
_C. michiganensis_ subsp. _sepedonicus_ taxonomy:
EPPO A2 quarantine list:
A HealthMap/ProMED-mail map can be accessed at:
Bacterial ring rot, potato - Netherlands (South) 20111229.3697
Bacterial ring rot, potato - Canada: (PE) 20101107.4043
Potato diseases - UK, USA 20090821.2960
Bacterial ring rot, potato - Algeria ex Canada 20071105.3601
Clavibacter and Ralstonia, potato - United Kingdom 20040831.2425 Bacterial ring rot, potato - UK (England)(04) 20040814.2252 Bacterial ring rot, potato - UK (Wales) 20040227.0608 Clavibacter, potato - Finland 20040706.1803 Bacterial ring rot, potato - Slovakia 20040628.1723
Clavibacter, potato - UK (England) (02) 20031120.2875 Bacterial ring rot, potato - UK (Wales): 1st report 20031116.2843 Clavibacter sp., Ralstonia sp., potato - Germany 20030814.2020 and older items in the archives]