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[1] _Phytophthora_ root rot and
clubroot - United Kingdom
[2] Clubroot - Canada (Alberta)
[1] _Phytophthora_ root rot and clubroot - United Kingdom
Date: Fri 4 Apr 2008
Source: Farmers Guardian [edited]
<http://www.farmersguardian.com/story.asp?sectioncode=19&storycode=17499>
Rare disease hits oilseed rape crops
A rarely seen disease of oilseed rape has been identified in a
number of crops this spring [2008]. Patches of plants with
severe _Phytophthora_ root rot (_Phytophthora megasperma_) have
been confirmed in several crops on sites with heavy, wet soils,
says oilseed rape disease expert Dr Peter Gladders.
The main symptoms are purple discolouration of plants and
stunted growth. In some cases the entire root system has
completely rotted away and plants can be easily pulled from the
soil. _Phytophthora_ root rot (PRR) is also occurring at some
sites in combination with clubroot, which also favours wet,
poorly drained soil conditions, and symptoms can be confused.
"You tend to see PRR in small patches. Some plants will be dying
now.
There is also a phase where plants will continue growing and
form pods but will ripen prematurely and set no seed," said Dr
Gladders.
At the disease levels being seen, yield losses are unlikely to
be high. He said disease development may have been exacerbated
by weather patterns over winter.
There was nothing growers with affected crops could do at this
stage to control the disease. His advice was to check patches of
poor growth or purpling and identify the cause. Where clubroot
is present, patches should be mapped and soil tested both within
and outside of the patches so that differential lime
applications can be made where appropriate.
[Byline: Teresa Rush]
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[2] Clubroot - Canada (Alberta)
Date: Tue 1 Apr 2008
Source: The Edmonton Journal [edited]
<http://www.canada.com/edmontonjournal/news/business/story.html?id=33eed39e-8358-4af5-a575-dccc6920a46d&k=27070>
Farmers battle canola fungus
----------------------------
Edmonton-area canola farmers are anxiously checking the spring
weather forecasts as they battle a fungus that's already
infested 10 municipalities. Spring weather is critical to the
speed of clubroot's spread. A cool, wet spring will help
activate the spores, while dry weather will give producers some
breathing room to work at keeping it at bay. "It could be one
the biggest threats we've ever had to our oilseed industry,"
said Rod Scarlett (Wild Rose Agricultural Producers). Many
farmers have switched from grains to canola in recent years to
take advantage of high prices, Scarlett said.
Even a dry spring won't help the close to 200 fields known to be
infested. They won't be able to grow canola at a time of record
prices. There are no current fungicides for canola clubroot,
which is most often carried from field to field on tillage
equipment. A government-producer committee formed last year
[2007] recommends canola not be grown for 3 years in slightly
infested and 5 years in severely infested fields. It would also
like unaffected farms to grow canola once every 4 years,
constantly clean their equipment, and restrict access to fields.
The committee said clubroot has the potential to hit all Western
Canada's traditional canola growing areas.
Oilseed specialist Murray Hartman said it's likely more
widespread than current numbers show, because areas adjacent to
infested municipalities have not yet been surveyed. Canola
grower Greg Porozni said responsible producers will be diligent,
but some might be tempted to cheat. "Not being able to grow
canola affects their livelihood." He believes the full economic
effect of clubroot won't be known until next year [2009] or
2010.
The fungus affects the quality of the canola, and the resting
spores can survive in soil for up to 20 years. It took 17 years
to get rid of clubroot in rapeseed in Sweden some years ago.
Researchers at the University of Alberta and at agri-business
companies are developing clubroot-resistant canola lines.
[Byline: David Finlayson]
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[The fungus _Phytophthora megasperma_ is a diverse species
encompassing a wide range of morphological and physiological
types.
It is found worldwide causing diseases on a broad range of fruit
and nut crops, vegetables, legumes, forest trees, woody and
herbaceous ornamental, and may also cause root girdling rots on
oilseed rape.
Species in the genus _Phytophthora_ often have a narrow host
range and many cause serious crop diseases. However,
host-specific pathogenicity appears to be less common among
isolates of _P.
megasperma_ some of which can affect a range of different hosts.
Report [1] above does not specify if the infection in oilseed
rape is thought to have originated from, for example,
contaminated soils or other plant hosts.
Clubroot of _Brassicaceae_ is caused by the fungus
_Plasmodiophora brassicae_. It is a destructive soil-borne
disease which affects nearly all cultivated, as well as many
wild and weed members of this family. The pathogen is found
worldwide and is most damaging in temperate regions and tropical
highlands. The fungus enters root hairs and wounded roots, and
multiplies rapidly, causing abnormal enlargement of the
underground stem, taproot, or secondary roots.
These roots often decay before the crop has matured, releasing
many resting spores, which can survive for a decade in the
absence of a susceptible host plant. Affected plants are stunted
and may have discoloured purple leaves. Due to the distortion of
the root, plants may wilt in dry weather and then recover at
night.
Disease management is difficult due to the longevity of the
spores and the inaccessibility of underground plant parts to
fungicides.
Raising soil pH by addition of lime has been shown to be
effective but is hardly practicable on large fields. Use of
clean planting material is essential. The pathogen is composed
of numerous pathotypes which have hampered efforts to breed
cultivars with durable resistance. At least 2 prevalent clubroot
pathotypes have been reported in Alberta, and a new more
virulent strain of the pathogen appears to have emerged
recently.
Canola is a trademarked quality description of a group of
cultivars of oilseed rape variants from which low erucic acid
rapeseed oil and low glucosinolate meal are obtained. Canola was
initially bred in Canada in 1978 and the word was derived from
"CANadian Oil, Low Acid."
Maps
UK:
<http://www.lib.utexas.edu/maps/europe/united_kingdom.gif> and <http://healthmap.org/promed?v=54.5,-2,5>
Canada:
<http://www.lib.utexas.edu/maps/americas/canada_pol_1986.gif>
and <http://healthmap.org/promed?v=55.4,-101.9,4>
Alberta:
<http://atlas.nrcan.gc.ca/site/english/maps/reference/provincesterritories/alberta/referencemap_image_view>
Pictures
Clubroot symptoms on canola plant: click
HERE
Clubroot on cabbage seedling:
<http://www.hri.ac.uk/site2/research/path/virus/clubroot.jpg>
Cabbage field with clubroot symptoms:
<http://vegetablemdonline.ppath.cornell.edu/Images/Crucifers/Clubroot/Clbrt_Crucfs1.jpg>
Links
Information on _P. megasperma_:
<http://www.apsnet.org/phyto/PDFS/1987/Phyto77n08_1132.pdf>
Oilseed rape cultivation and diseases, including _P. megasperma_
root rot:
<http://hgca.com/publications/documents/events/Paper11_0204.pdf>
Fact sheets on clubroot of canola, with pictures:
<http://www1.agric.gov.ab.ca/$department/deptdocs.nsf/all/agdex8593?opendocument>
and
<http://webpub2.strathcona.ab.ca/Strathcona/Rural+Life/Country+Talk/March+2006/Clubroot+disease+of+canola.htm>
Information on clubroot on crucifer crops:
<http://vegetablemdonline.ppath.cornell.edu/factsheets/Crucifers_Clubroot.htm>
_P. megasperma_ taxonomy:
<http://www.indexfungorum.org/Names/NamesRecord.asp?RecordID=270758>
_P. brassicae_ taxonomy:
<http://www.indexfungorum.org/Names/NamesRecord.asp?RecordID=214750>.
- Mod.DHA]
[see also in
the
archive:
Brassica diseases - Turkey, Nepal 20080213.0572
2007
----
Clubroot, canola - Canada (AB) 20070927.3199
2005
----
Clubroot, canola - Canada (AB) (02) 20051113.3319 Clubroot,
canola - Canada (Alberta) 20050512.1301]
