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September 27, 2007
Source: Hereford Times [edited]
<http://www.herefordtimes.com/display.var.1718921.0.herefordshire_scientists_discover_new_crop_disease.php>

Agricultural research scientists working for the government's Agricultural, Development and Advisory Service at Rosemaund in Herefordshire have identified a disease of oilseed rape previously unknown in the UK. And they believe the disease, verticillium wilt, may have been responsible for falling yields of the rape in recent years.

"This is a disease we suspected but now we have confirmed its presence in the country," scientist Jonathan Blake told the Hereford Times this week. But Mr Blake was quick to point out that it is not thought that this verticillium wilt has any link to another verticillium wilt, the progressive strain of which has proved fatal to hop plants in the county and Kent for many years. Research will continue to establish what strain it is. "It is a coincidence that they both have the same name," he said. "We believe there is no need for farmers to worry if they consider planting oilseed rape on ground which previously grew hops."

What effect this newly identified disease will have on the future yields of oilseed rape will depend on further research by scientists at Rosemaund. But Mr Blake did say that the disease may be weather and season related.

--
Communicated by:
ProMED-mail
<promed@promedmail.org>

[Verticillium wilt of oilseed rape (_Brassica napus_) is caused by the soil-borne vascular fungus _Verticillium longisporum_. This species attacks oilseed rape and other brassicas in many European countries including France, Germany, Sweden, as well as in Japan. It was recently recorded in California infecting cauliflower. The growing area of intense rapeseed cultivation has rendered the pathogen an increasing threat to oilseed rape production particularly in Europe.

Unlike other _Verticillium_ diseases, _V. longisporum_ does not induce wilting, but premature senescence and ripening which may severely reduce yields by up to 50 percent. It can survive in dead plant tissue and soil for extended periods. Disease management includes deep ploughing to minimise inoculum and crop rotation with a
succession of non-susceptible species such as cereals or grass. Fungicides are largely ineffective for a soil-borne pathogen. Sufficient genetic resistance is not available in oilseed rape making resistance breeding almost impossible. Resynthesized rapeseed generated from interspecific hybridisation between resistant forms of _Brassica rapa_ and _Brassica oleracea_ represents a potentially important resource for developing resistant crop lines.

_V. longisporum_ was previously known as _V. dahliae_ var. _longisporum_. It has now been established as a separate species, although some controversy still remains regarding its classification. Its host range is different from the one of _V. dahliae_. A clear restriction of _V. dahliae_ to non-Brassica hosts (including solanaceous crops such as tomato and eggplant) was observed while _V. longisporum_ is pathogenic only on _Brassica_ species. Molecular methods have revealed a hybrid nature of the species with components of _V. albo-atrum_ and _V. dahliae_ both present in _V. longisporum_. Thus _V. longisporum_ appears to be a host-adapted pathogen. This
explains why a threat to hop crops from the oilseed pathogen is considered unlikely in the news report above.

_V. albo-atrum_ (and occasionally also _V. dahliae_) is associated with verticillium wilt of hops. It also affects lucerne, hemp, and a number of other hosts. In hops, one or all of the trained vines in one hill can die off either one after the other or simultaneously. Strict hygiene measures are necessary to minimise the likelihood of introducing the disease into hop plantings. Some hop varieties with disease resistance or tolerance are available.

Maps
UK:
<http://www.lib.utexas.edu/maps/europe/united_kingdom.gif>
Herefordshire:
<http://www.visitherefordshire.co.uk/explore.asp>

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>
_Verticillium_ in the vascular tissue of a hop vine:
<http://www.hvg-germany.de/best-of/images/pflanze/pfl_krank_welk_2.jpg>

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 of hops:
<http://www.hvg-germany.de/best-of/en/pflanze/set_pflanze_en.html?/best-of/en/pflanze/ff_krankheiten3_en.html>
Information on hops and its pathogens (including _V. albo-atrum_):
<http://www.hops.co.uk/sectionthree/Growing.htm>  and
<http://www.hort.purdue.edu/newcrop/duke_energy/Humulus_lupulus.html>
Research projects on both _Verticillium_ species:
<http://www.bspp.org.uk/bsppnews/bsppnews31/bsppnews31-12.htm>
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>
_V. dahliae_ taxonomy:
<http://www.indexfungorum.org/Names/NamesRecord.asp?RecordID=196942>
_V. albo-atrum_ taxonomy:
<http://www.indexfungorum.org/Names/NamesRecord.asp?RecordID=199278>. 
- Mod.DHA]

[see also in the archive:
2006
----
Verticillium wilt, race 2, tomato - Tunisia: 1st report 20060429.1241
2005
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Verticillium wilt, eggplant - Italy 20050816.2401]

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