.

October 26, 2007
Source: Farmers Guardian [edited]
<http://www.farmersguardian.com/story.asp?sectioncode=19&storycode=13826>

Aphids most responsible for spreading _Barley yellow dwarf virus_ [BYDV] are increasing this season [2007] with mild conditions and the high proportion of early sown crops increasing the risk of disease spreading.
Although populations of the bird cherry aphid and grain aphid have hitherto been relatively low, results of the latest national aphid monitoring surveys revealed a 40 per cent increase in numbers of these 2 key aphid species caught over recent weeks.

"The risk of BYDV infection appears to be shifting ever later. Cereal crops emerging before the 2nd week of October [2007] must now be considered as most susceptible to BYDV infection," said Syngenta technical manager, Iain Hamilton. The earlier crops are infected, the higher the disease's severity and yield loss.

Where mild conditions continue, there is also the chance for secondary infection through aphids feeding on infected crops and spreading it across the field to surrounding crops right through the autumn and early winter, he adds. "Growers need to weigh up the risk, based on crop emergence timing and the historic legacy of BYDV on their farm, allied to current aphid activity levels," said Mr Hamilton.

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[_Barley yellow dwarf virus_ (BYDV; genus _Luteovirus_) occurs worldwide and is the most destructive of virus diseases of wheat. Grain yields may be reduced by one third. It attacks a wide range of grass species
(_Gramineae_) including wheat, oats, rice, maize, rye, and barley. Oats are usually considered more susceptible than wheat. Symptoms include leaf discolouration from yellow to purple (depending on the host species), stunting, reduced tillering, and empty seed heads. Plants infected in autumn may not survive the winter or show severe symptoms when growth resumes. Diseased plants often occur in circular patches within the field, which are associated with colonisation by the aphid vectors. The virus can be transmitted by more than 20 species of aphids and is retained when the insect moults. It cannot be transmitted by seed, pollen, or mechanical means and cannot survive in stubble or in the soil. Disease management includes use of resistant cultivars and control of the aphid vectors.

The virus occurs in several strains, which are differentiated by their ability to be transmitted by various aphid species and their virulence on a selected variety of oats. Some strains of BYDV are transmitted equally well by several aphids, whereas other strains can be transmitted by only one or
2 aphid species. The bird cherry aphid (_Rhopalosiphum padi_) and grain aphid (_Sitobion avenae_) are vectors of the severe PAV strain and this may be the strain causing concern in the report above.

Maps of the UK:
<http://www.lib.utexas.edu/maps/europe/united_kingdom.gif> and <http://healthmap.org/promed?v=54.5,-2,5>
Pictures
Healthy and BYDV-affected wheat plants:
<http://www.ent.iastate.edu/imagegal/plantpath/wheat/ydwarf/0093.04ydwarfmv.html> 

Wheat field with BYDV symptoms:
<http://www.ent.iastate.edu/images/plantpath/wheat/ydwarf/0093.10ydwarfwheat.jpg> 

Red leaf symptoms on oats:
<http://www.rothamsted.ac.uk/ppi/pics/virus_big.jpg>
_Luteovirus_ particles, electron micrograph:
<http://www.ncbi.nlm.nih.gov/ICTVdb/WIntkey/Images/c2.gif>
Links
Additional news story:
<http://www.farminguk.com/index.asp?show=newsArticle&id=4578&country=>
BYDV fact sheets:
<http://ohioline.osu.edu/ac-fact/0005.html> and <http://ipm.ppws.vt.edu/stromberg/smallgrain/biology/wydwarf.html>
CIMMYT (International Maize and Wheat Improvement Center) BYDV newsletter:
<http://www.cimmyt.org/research/wheat/bydvnews/htm/BYDVNEWS.htm>
BYDV taxonomy:
<http://image.fs.uidaho.edu/vide/descr062.htm>
BYDV strains and list of wheat viruses:
<http://www.fao.org/DOCREP/006/Y4011E/y4011e0o.htm>
Information on _R. padi_:
<http://www.inra.fr/hyppz/RAVAGEUR/6rhopad.htm>
Information on _S. avenae_:
<http://www.inra.fr/hyppz/RAVAGEUR/6sitave.htm>. - Mod.DHA]

[see also in the archive:
Barley yellow dwarf virus & stem rust, cereals - Kenya 20070705.2132 Barley yellow dwarf virus, wheat - USA (IN, NE) 20070531.1758
2003
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Cereal viruses, oat, barley - USA (Alaska) 20030405.0832
2001
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Cereal viruses, wheat - Uzbekistan 20011103.2723 Cereal viruses, barley, wheat - Tunisia 20010829.2049
1999
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Crop diseases - Canada (Manitoba) 19990816.1417 Barley Yellow Dwarf virus alert - New Zealand 19990708.1140]

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