A ProMED-mail post
<http://www.promedmail.org>
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International Society for Infectious Diseases <http://www.isid.org>
Date: 6 November 2008
Source: Farmers Weekly Interactive [edited]
<http://www.fwi.co.uk/Articles/2008/11/06/112953/irrigation-water-not-to-blame-for-home-grown-erwinia-chrysanthemi-seed-potato.html>
Irrigation water appears unlikely to have been the source of
infections in home-grown seed potatoes of the bacterial disease
caused by _Dickeya chrysanthemi_, tests suggest. But seed
growers should continue to take steps to avoid introducing the
pathogen -- which can cause soft rots in progeny tubers -- into
seed-growing areas, John Elphinstone of the Central Science
Laboratory told Farmers Weekly.
Research had revealed that the disease was caused by at least 6
different species of _Dickeya_ bacteria, but within Europe, only
one -- _D. dianthicola_ -- had been implicated in causing the
disease in potatoes, he said. 1st found in the UK on ware crops
in 1990, _D. chrysanthemi_ infections are mostly associated with
crops that are grown from seed brought in from outside the UK.
But it had also been found in 2 home-grown seed stocks,
including one from Suffolk identified in samples collected in
2007.
There had been some suggestions that the source of the infection
could have been irrigation water, because _Dickeya_ species have
been detected in watercourses. But the strains found in
watercourses were different, said Dr Elphinstone. "So it looks
like it might not be through water."
More research was being undertaken in a 3-year Scottish
government-funded project into the bacteria's biology to help
understand how the infection had moved into seed crops, with the
aim of designing a better control programme, he said. "At the
moment, it is difficult to recommend specific control measures
for _chrysanthemi_," he added.
Following guidelines for controlling soft rots and blackleg
would be a good starting point for seed growers to help prevent
its introduction, he suggested, particularly in Scotland, where
the disease had never been found. "Being a member of the Safe
Haven scheme would also provide a barrier to introducing the
disease on seed [tubers] from outside the UK," Dr Elphinstone
added.
[Byline: by Mike Abram]
--
Communicated by:
ProMED-mail <promed@promedmail.org>
[Bacterial soft rot of potato can be caused by _Pectobacterium
carotovorum_ subsp. _carotovorum_ (previously _Erwinia c._
subsp.
_c._) or _Dickeya chrysanthemi_ (previously _Erwinia
chrysanthemi_).
Soft rot is favoured by warm and humid conditions. Symptoms
include brown spots on the tuber surface which will turn into a
cream coloured rot that rapidly destroys the tuber. Soft rot may
be confined to lenticels (surface pores of tubers). Infected
lenticels appear slightly sunken, tan to brown and water-soaked.
Under dry conditions, lenticel infections may dry up leaving a
small pit, but harvesting potatoes under wet conditions will
increase the risk of soft rot expanding in storage.
The bacteria are spread with contaminated plant or other
material, by mechanical means and water. Fungal pathogens may
increase the risk of secondary soft rot, or additional pathogens
may invade soft rot affected tubers through skin lesions.
Disease management includes seed tuber handling and cultural
techniques, use of clean planting material, and phytosanitation
to prevent introduction of the pathogens from external sources.
_D. chrysanthemi_ can also affect other crops and causes, for
example, a foot rot disease in rice. The pathogen has been
included on the quarantine list of the European Plant Protection
Organisation (EPPO). Blackleg disease of potato is caused by the
related _Pectobacterium carotovorum_ subsp. _atrosepticum_
(previously _Erwinia c._ subsp. _a._).
Maps
UK:
<http://www.lib.utexas.edu/maps/europe/united_kingdom.gif>
and
<http://healthmap.org/promed?v=54.5,-2,5>
_D. chrysanthemi_ worldwide distribution (July 2008):
<http://www.eppo.org/QUARANTINE/bacteria/Erwinia_chrysanthemi/ERWICH_map.htm>
Pictures of soft rot on potato tubers:
<http://www.ctahr.hawaii.edu/nelsons/Misc/1_potato_bacterial_soft_rot_2.jpg>
and
<http://www.omafra.gov.on.ca/english/crops/hort/news/hortmatt/2003/20hrt03a7f7.jpg>
Links
Information on potato soft rot (and blackleg):
<http://www.ipm.ucdavis.edu/PMG/r607100111.html>
and
<http://www.omafra.gov.on.ca/english/crops/hort/news/hortmatt/2003/20hrt03a7.htm>
(with pictures)
Information on _D. chrysanthemi_:
<http://www.scri.ac.uk/scri/file/PiP/Erwinia.pdf>
and
<http://www.eppo.org/QUARANTINE/bacteria/Erwinia_chrysanthemi/ERWICH_ds.pdf>
_D. chrysanthemi_ taxonomy:
<http://www.bacterio.cict.fr/d/dickeya.html>
and
<http://ijs.sgmjournals.org/cgi/content/abstract/55/4/1415>
_Pectobacterium_ species taxonomy:
<http://www.bacterio.cict.fr/p/pectobacterium.html>
and
<http://ijs.sgmjournals.org/cgi/content/abstract/53/2/381>
EPPO A2 quarantine list:
<http://www.eppo.org/QUARANTINE/listA2.htm>
- Mod.DHA]
[see also
in the
archive:
Foot rot & false smut, rice - India 20080929.3080]
