A
ProMED-mail post
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International Society for Infectious Diseases
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ProMED-mail is a program of the
International Society for Infectious Diseases <http://www.isid.org>
Date: 30 November 2007
Source: Saskatoon Homepage, 600 Action News-Local First report
[edited] <http://www.saskatoonhomepage.ca/index.php?option=com_ezine&task=read&page=9&category=22&article=9182&Itemid=87>
A number of factors lead to lower canola yields. A July [2007]
heat wave tops the list, but others include disease and
herbicide carryover. 2007 canola yields were below expectations
on many farms.
A senior agri-coach with Agri-Trend Agrology, Phil Thomas, says
"there was an awful lot of blackleg out there. More than there
should be with resistant seed varieties." That raises the
possibility of a new strain of the disease.
[Byline: Neil Billinger]
--
Communicated by:
ProMED-mail
<promed@promedmail.org>
[The fungus _Leptosphaeria maculans_ (previously _Phoma lingam_)
causes blackleg, also called _Phoma_ stem canker, on oilseed
rape (_Brassica napus_). Blackleg is the most serious disease of
rapeseed cultivars, including canola, in most of the world's
production areas.
The fungus can also affect other hosts in the genus _Brassica_
such as cabbage, broccoli, Brussels sprouts, cauliflower, and
turnip.
Symptoms on rapeseed are greyish leaf lesions, which may crack
internally and coalesce. The lesions often expand down leaf
veins towards the base of the leaf. In severe epidemics, lesions
can be found on the stems and pods. Typical stem cankers lead to
premature ripening or collapse of the crop. The fungus is
seed-borne and is spread by wind and infected crop litter. It
may overwinter in stubble. Disease management includes use of
clean seed, cultural practices to minimise inoculum, fungicides,
and planting of resistant cultivars.
The pathogen is extremely diverse. Populations consist of a high
number of unique genotypes. There has been good resistance in
commercial cultivars for almost 20 years against the predominant
race PG2. New and virulent isolates belonging to other races
have appeared recently in Canada and the USA causing significant
disease. In Europe and Australia, extensive use of cultivars
with single gene resistance led to breakdown of host resistance
resulting from a shift in _L. maculans_ populations. This has
caused significant economic losses to farmers.
Pathogens can mutate spontaneously and randomly, and mutants are
referred to as pathotypes, races, or strains. They may differ in
their ability to infect host cultivars, depending on what
resistance gene or genes are present in the host. If a new
strain has developed the ability to overcome a particular
resistance gene, the resistance in the respective host cultivars
is said to have "broken down."
However, it is the pathogen that has changed, not the resistance
gene in the host cultivar.
Canola is a trademarked quality description of a group of
cultivars of rapeseed 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
Canada:
<http://www.lib.utexas.edu/maps/americas/canada_pol_1986.gif>
and <http://healthmap.org/promed?v=55.4,-101.9,4>
Saskatchewan:
<http://atlas.nrcan.gc.ca/site/english/maps/reference/provincesterritories/saskatchewan/referencemap_image_view>
Pictures
Blackleg leaf symptoms on canola:
<http://www.apsnet.org/Education/LessonsPlantPath/BlacklegCanola/text/fig05.htm>
Stem cankers:
<http://www.ag.ndsu.edu/pubs/plantsci/crops/pp1201-4.jpg>
and <http://www.agric.wa.gov.au/pls/portal30/docs/FOLDER/IKMP/FCP/CO/PW/BULLETIN4406A.HTM#flowers>
Rapeseed planting with blackleg:
<http://www.apsnet.org/education/LessonsPlantPath/BlacklegCanola/images/fig07.jpg>
Links:
Disease information:
<http://www.apsnet.org/education/lessonsPlantPath/BlacklegCanola/>
Identification and management of canola diseases including
blackleg, with pictures:
<http://www.agric.wa.gov.au/pls/portal30/docs/FOLDER/IKMP/FCP/CO/PW/BULLETIN4406A.HTM>
_L. maculans_ taxonomy:
<http://www.indexfungorum.org/Names/SynSpecies.asp?RecordID=230154>
Evolving strains of blackleg:
<https://www.agronomy.org/cca/certified/education/self-study/exam_pdf/112.pdf>
Blackleg pathogen and resistance research:
<http://www.botany.unimelb.edu.au/blackleg/>
Agri-Trend:
<https://www.agri-data.net/myscp/bins/index.asp>.
- Mod.DHA]
[see also in
the
archive:
Foliar diseases, brassica crops - UK 20070913.3037
2006
----
Blackleg, canola, path.gr.3 - Hungary: 1st report 20060419.1156
2005
----
Blackleg, canola - USA (ND): 1st report 20050626.1807 Blackleg,
canola - Argentina: 1st report 20050319.0807
2003
----
Blackleg, canola - Canada (Manitoba) 20030918.2367 Blackleg,
canola - Brazil (Rio Grande do Sul) 20030225.0478
2001
----
Blackleg, root infection, canola - Australia (SA, NSW)
20010819.1959]
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