.

Date: May 18, 2007
Source: Farmers Guardian [edited]
<http://www.farmersguardian.com/story.asp?sectioncode=19&storycode=9741>

Results from this year's [2007] UK Cereal Pathogen Virulence [UKCPV] Survey suggest that a new race of brown rust is present on winter wheat crops in the UK.

According to HGCA [Home Grown Cereals Association - Mod.DHA] Recommended Lists manager, Jim McVittie, samples of wheat from previously resistant varieties -- Robigus, Hyperion, Oakley, and Timber -- were infected with brown rust. "Clearly, further work is required to confirm that these races can re-infect the varieties they were collected on, but the relatively large number of samples from Robigus does suggest the presence of a new race in the UK and seedling tests have confirmed that they can re-infect the variety," he said.

According to NIAB [National Institute of Agricultural Botany - Mod.DHA] plant pathologist, Dr Rosemary Bayles, this season's early infections of both brown and yellow rust had caused concern among growers and agronomists. "Growers have been concerned to see brown rust in equal quantities to yellow rust," she said.

Varietal resistance profiles to rusts may change as adult plant resistance kicks in at growth stage 31/32, and in some instances resistance may be affected by temperature, said Dr Bayles. "While there will be a whole package of races of brown rust affecting crops, I'm sure there's going to be quite a lot of this Robigus race around."

The collection of brown rust from newly-recommended variety Timber, currently rated 9 for resistance to the disease, and Hyperion, also rated 9, was a "warning flag", she added.

Yellow rust virulence frequencies on wheat in 2006 were similar to the previous year [2005], with virulence for Robigus continuing to be common. One yellow rust race collected in 2005 appears to combine virulence for Robigus with that for varieties such as Access, Mascot, and Napier. This race also appears to be virulent on Timber, but not Einstein.

The virulence on Timber, which has a specific recommendation for good disease resistance, could affect its Recommended List rating for resistance to yellow rust. The failure of the virulence to affect Einstein suggests that that variety carries an additional, currently unidentified, resistance factor.

Samples collected from Robigus confirmed the presence of races of mildew that can infect the variety. These races are now being found in Recommended Lists trials and the rating of the variety has been revised to 7.

According to Dr Bayles, mildew is not proving to be a major problem on Robigus in the field. The 'Robigus race' was also being detected in samples collected from other varieties, which was a sign that it was spreading more widely through the overall mildew population.

Eight mildew samples were also collected from Timber, suggesting a new race on that variety. However, the race has yet to be detected in Recommended Lists trials.

The UKCPV celebrates 40 years of existence this year [2007]. A new 5-year contract will see all trials carried out by NIAB in Cambridge.
Full results are available on the HGCA website at <http://www.hgca.com> [Information on the UKCPV survey can be found at <http://www.hgca.com/content.output/56/56/Crop%20Research/Crop%20Research/UK%20Cereal%20Pathogen%20Virulence%20Survey.mspx>].

[Byline: Teresa Rush]

--
Communicated by:
J. Allan Dodds
Former ProMED-mail plant disease moderator <dodds@ucr.edu>

[Leaf rust, also called brown rust, on wheat is caused by the fungus _Puccinia triticina_ (formerly _P. recondita_ f. sp. _tritici_); stripe (yellow) rust is caused by _P. striiformis_; wheat (powdery) mildew is caused by _Blumeria_ (synonym: _Erisyphe_) _graminis_ f.
sp. _tritici_.

Multiple genes of both host and pathogen species contribute to disease expression and thus, there are potentially many mutations that could affect this interaction. The situation becomes even more complex when dealing with multiple resistance factors directed at different pathogens, which may or may not interact with each other.
Different levels of resistance can be observed in certain combinations of host/pathogen variants and are rated according to the severity of symptoms induced in the host.

New races of fungal plant pathogens with changes in virulence are emerging frequently in resistant host varieties since these host populations present a situation of increased selection pressure for the pathogen. A very serious example is the new strain Ug99 of wheat black stem rust (_Puccinia graminis_).

Pictures
Brown wheat rust, leaf symptoms:
<http://www.hgca.com/hgca/wde/IMAGES/brown%20rust1.JPG>
Stripe rust, leaf symptoms:
<http://www.ars.usda.gov/Main/docs.htm?docid=9918&pf=1&cg_id=0>
Powdery mildew, leaf symptoms:
<http://cropwatch.unl.edu/photos/cwphoto/crop04-9mildew1.jpg>
Powdery mildew on wheat ear:
<http://www.hgca.com/hgca/wdmg/Gallery/mildew1.jpg>
Links
Home Grown Cereals Association UK:
<http://www.hgca.com/>
NIAB CPV survey:
<http://www.niab.com/research/disease/resistance-pathogen-characterisation/ukcpvs.html>
Information on brown wheat rust:
<http://plant-disease.ippc.orst.edu/disease.cfm?RecordID=1138> and  <http://www.hgca.com/hgca/wde/diseases/Brown%20rust/Brhost.html>
Information on wheat stripe rust:
<http://www.ars.usda.gov/Main/docs.htm?docid=9918&pf=1&cg_id=0> and <http://www.hgca.com/hgca/wde/diseases/Yellow%20rust/Yrhost.html>
Global Rust Initiative:
<http://www.globalrust.org/>
Information on wheat powdery mildew:
<http://ohioline.osu.edu/ac-fact/0010.html> and <http://www.hgca.com/hgca/wde/diseases/Mildew/Milhost.html>
Description of the pathogen:
<http://www.indexfungorum.org/Names/NamesRecord.asp?RecordID=309596> and
<http://www-biol.paisley.ac.uk/bioref/Fungi_ascomycetes/profile_Erysiphales.html>
General information on wheat diseases and pathogens <http://www.apsnet.org/online/common/names/wheat.asp> and <http://www.grdc.com.au>. - Mod.DHA]

[see also in the archive:
Rust diseases, bean & wheat - UK: alert 20070512.1515 Wheat stem rust, spread: FAO, Global Rust Initiative 20070414.1241
2005
----
Leaf rust, wheat, resistance change - India 20051201.3462
2003
----
Wheat stripe rust, new strains - Australia (SA) 20030930.2465]
 

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