A ProMED-mail post
ProMED-mail is a program of the
International Society for Infectious Diseases <http://www.isid.org>
Date: Mon 1 Oct 2012
Source: The Grower [edited]
Potato ring rot reappears in Idaho
Bacterial ring rot, a cyclic problem, has flared up again in Idaho.
The University of Idaho is reviving its task force to help growers deal with the problem.
Early monitoring shows the problem is variable, hitting some fields harder than others. More monitoring will be conducted as harvest progresses to determine the extent of the disease.
In fields with a heavy outbreak, growers should try to delay harvest to allow infected potatoes to rot in the field so fewer will need to be sorted out before storage.
Before this  season, the last flare-up in Idaho was in 2002.
Growers were able to manage the problem by implementing sanitation practices during seed cutting in the spring and thoroughly disinfecting all equipment and storage facilities between crops.
[Byline: Vicky Boyd]
[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, are also susceptible, and the pathogen has also been found associated with symptomless infections of sugar beet and sugar beet seed.
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 by 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.
Illegal farm saved seed potatoes are known to pose a serious risk for the spread of ring rot and have been reported, for example, as the cause of outbreaks in Europe (ProMED-mail posts 20120503.1121126 and 20111229.3697). It appears that the source of the outbreak reported above remains to be identified.
Potato ring rot, leaf and tuber symptoms:
Ring rot affected tubers:
<http://www.ag.ndsu.edu/pubs/plantsci/rowcrops/pp877-3b.gif> and <http://www.ag.ndsu.edu/pubs/plantsci/hortcrop/pp756-7.gif>
Additional news stories:
Information on potato ring rot:
Molecular detection of _C. m._ subsp. _sepedonicus_:
_C. michiganensis_ subsp. _sepedonicus_ taxonomy:
<http://www.uniprot.org/taxonomy/31964>. - Mod.DHA]
Bacterial ring rot, potato - Netherlands, Germany: update
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]