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Date: 17 Oct 2008
Source: Horticulture Week [edited]
<http://www.hortweek.com/news/bulletin/GrowerBulletin/article/854082/?DCMP=EMC-GrowerBulletin>

Bacterial canker is rediscovered in the UK

Bacterial canker has been found in 2 tomato nurseries in the UK for the 1st time in 10 years. ADAS [Agricultural Development and Advisory Service] plant pathologist Tim O'Neill said the disease, which can be carried either on the seed coat or in the seed embryo, is particularly infectious and difficult to control due to a shortage of effective chemicals.

Bacterial canker produces a range of symptoms, several of which can be mistaken for other diseases. Some are superficial, where the disease is not yet being carried in the plant's internal transport system, and others are systemic. Superficial symptoms are spread by water splash and include small irregular pale areas on foliage, white mealy pustules on one side of the stem, and bird's eye spotting of fruit. Once the disease is systemic, either because the seed embryo was infected or where bacteria have entered the plant through pruning wounds or damaged roots, leaves develop pale "windows" and plants wilt and die. "Seed is considered the main source but bacterial ooze, which has dried on structures or tools, is how the disease can survive," said O'Neill.

Propagation nurseries have a statutory duty to report an outbreak but there is no similar requirement for production nurseries, although O'Neill said it would be good practice to report an outbreak so that it was properly identified. "An outbreak can be contained if the disease is detected early and there is no superficial infection," he said.

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[_Clavibacter michiganensis_ subsp. _michiganensis_ (CMM) causes bacterial canker on field and glasshouse tomatoes resulting in up to 70 percent yield loss. Its host range also includes a number of wild relatives of tomato and solanaceous weeds, which may serve as pathogen reservoirs. The bacterium has been found in various locations worldwide. Its wide distribution accounts for a high risk of new incursions, and this may have happened in the UK. The pathogen is included in the quarantine lists of the European Plant Protection Organisation (EPPO).

Symptoms on tomato include wilting, degeneration of vascular tissues, and necrotic lesions resulting in stem cankers. Fruits may fail to develop or drop prematurely. CMM is spread by water and mechanical means and is seed transmitted at a rate of around one percent.
Seedlings from contaminated seed appear healthy, symptoms appear only as plants approach maturity. The bacterium survives for a long time in plant debris and on equipment and remains viable for at least 8 months in seeds. Disease management relies on the use of clean seed and plant hygiene measures (elimination of pathogen sources).
Resistant germplasm is available but has not yet been incorporated to any significant degree into commercial tomato cultivars.

The genus also includes a number of other plant pathogenic species, for example potato ring rot is caused by _C. m._ subsp._sepedonicus_, and ratoon stunt of sugarcane is caused by _C. xyli_ subsp. _xyli_.

Maps
UK:
<http://www.lib.utexas.edu/maps/europe/united_kingdom.gif>  and
<http://healthmap.org/promed?v=54.5,-2,5>
Worldwide distribution of CMM (September 2006):
<http://www.eppo.org/QUARANTINE/bacteria/Clavibacter_m_michiganensis/CORBMI_map.htm>

Pictures
CMM canker on tomato, photo gallery:
<http://www.eppo.org/QUARANTINE/bacteria/Clavibacter_m_michiganensis/CORBMI_images.htm>

Links:
CMM canker data sheet:
<http://www.eppo.org/QUARANTINE/bacteria/Clavibacter_m_michiganensis/CORBMI_ds.pdf>
CMM diagnostic procedures:
<http://archives.eppo.org/EPPOStandards/PM7_DIAGNOS/pm7-42(1)CORBMIweb.pdf>
Fact sheet on bacterial diseases of tomato (with pictures):
<http://vegetablemdonline.ppath.cornell.edu/factsheets/Tomato_Bacterial.htm>
_Clavibacter_ taxonomy and species list:
<http://www.bacterio.cict.fr/c/clavibacter.html>
EPPO A2 quarantine list:
<http://www.eppo.org/QUARANTINE/listA2.htm>
ADAS:
<http://www.adas.co.uk/>. - Mod.DHA]