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Date: July 11, 2008
Source: Farmers Weekly Interactive [edited]
<http://www.fwi.co.uk/Articles/2008/07/11/111150/wilt-worries-for-oilseed-rape.html>

Wilt worries for oilseed rape

Verticillium wilt, confirmed in UK oilseed rape last year [2007] for the 1st time, is adding to the problems of premature ripening caused by sclerotinia in this season's [2008] stands, warns ADAS [Agricultural Development and Advisory Service].

Growers are advised to check crops now for the symptoms. These typically consist of a dark brown stripe running up one side of the main stem. Closer inspection may reveal grey micro-sclerotia as the surface layers start to decay.

The wilt disease is becoming more widely recognised as awareness of the symptoms has grown, according to the service's Crop Action notes. It can be detected at 0.1 per cent of plants affected in some crops. But badly affected fields may have more than half the plants hit with either whole plants or just side branches ripening prematurely. On farms where verticillium is obvious growers are urged to extend rotations to at least one in 4 and longer if possible where the infection is severe.

[byline: Andrew Blake]

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[Verticillium wilt of oilseed rape (_Brassica napus_) is caused by the soilborne vascular fungus _Verticillium longisporum_. This species is pathogenic only on _Brassica_ species and occurs in many European countries including France, Germany, and Sweden, as well as in Japan. It was recently also recorded in the USA, and was reported in the UK for the 1st time in 2007 (see ProMED-mail post no. 20071001.3239). The growing area of intense rapeseed cultivation has rendered the pathogen an increasing threat to oilseed rape production particularly in Europe.

Unlike other _Verticillium_ species, _V. longisporum_ does not induce wilting, but premature senescence and ripening which may severely reduce yields by up to 50 per cent. It can survive in dead plant tissue and soil for extended periods. Sufficient genetic resistance is not available in oilseed rape, but interspecific hybridisation may provide a resource for developing resistant crop lines. _V. longisporum_ appears to be a host-adapted pathogen. Other species in the genus specialise in different host families, for example _V. dahliae_ affects solanaceous plants and _V. albo-atrum_ is associated with a wilt of hops.

Sclerotinia of oilseed rape (also called stem rot, white mold), is caused by the fungus _Sclerotinia sclerotiorum_. This soilborne fungus is one of the most nonspecific (around 400 known hosts) and successful of plant pathogens and is present worldwide. On oilseed rape, infected leaves collapse around the stem, then stem lesions showing a typical bleached appearance develop. The pathogen is primarily soilborne and has a complex disease cycle.

Management for both diseases includes cultural practices (such as long term crop rotation with non-hosts and deep ploughing to minimise inoculum) and fungicide applications. However, fungicides may not be very effective against soilborne fungal pathogens.

Map of UK
<http://www.lib.utexas.edu/maps/europe/united_kingdom.gif>
Pictures
_V. longisporum_ on oilseed rape root:
<http://www.agrarfotodesign.de/raps/verticillium/img/00262-Verticillium-Rapswurzel.jpg>
and
<http://www.agrarfotodesign.de/raps/verticillium/img/00261-Verticillium-Mikrosclerotien.jpg> 

Sclerotinia of oilseed rape:
<http://www.hgca.com/research/OSRWeb/Images/disease.JPG>  (stems), <http://www.hgca.com/research/OSRWeb/Images/Control2.JPG>  (leaves)
Links Information on _V. longisporum_ in oilseed rape:
<http://wwwuser.gwdg.de/~instphyt/app/research/verticillium.html>
Resistance breeding and research:
<http://www.uni-giessen.de/~gh1262/pz/englisch/pro_wiebke.html>  and <http://www.svenskraps.se/kunskap/pdf/00194.pdf>  [in Swedish]
Verticillium wilt crop list, information, and management:
<http://www.apsnet.org/education/LessonsPlantPath/Verticillium/mngmnt.htm>
_V. longisporum_ taxonomy:
<http://www.indexfungorum.org/Names/NamesRecord.asp?RecordID=443108>
Information on sclerotinia of oilseed rape:
<http://www.agric.wa.gov.au/pls/portal30/docs/FOLDER/IKMP/FCP/CO/PW/BULLETIN4406A.HTM#sclerotinia>
and
<http://www.hgca.com/publications/documents/cropresearch/Topic77.pdf>
Information on _S. sclerotiorum_:
<http://www.extento.hawaii.edu/kbase/Crop/Type/s_scler.htm>  and <http://www.cals.ncsu.edu/course/pp728/Sclerotinia/S_sclerotiorum.html>
_S. sclerotiorum_ taxonomy:
<http://www.indexfungorum.org/Names/NamesRecord.asp?RecordID=212553>
ADAS:
<http://www.adas.co.uk/>.  - Mod.DHA]