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Date: December 17, 2007
Source: Business Daily Africa (Nairobi) [edited]
<http://www.bdafrica.com/index.php?option=com_content&task=view&id=4912&Itemid=5811>

Researchers are intensifying efforts to stop a fungus from consuming over 80 percent of the global wheat produce in the face of biting shortages and soaring prices in the international market. Under the Global Rust Initiative (GRI) scientists are seeking new ways to eradicate the new wheat stem rust strain Ug99, so called because it was discovered in neighbouring Uganda in 1999. The fungal disease also threatens barley and has crossed the Red Sea towards Yemen. If not checked, it will be soon afflicting wheat fields in Egypt, the Middle East, and Asia.

[US Department of Agriculture] Agricultural Research Service (ARS) plant pathologist Yue Jin confirmed that a new variant of Ug99 that has been found in Kenya has shown more virulence towards existing genetic resistance traits, putting more wheat fields in danger. "It could broaden the disease's reach to beyond the 80 percent of the world's wheat that is at risk," said lead researcher Rick Ward of the International Wheat and Maize Improvement Centre (CIMMYT).

Previous field studies in Kenya and Ethiopia showed that Ug99 has overcome most of the known stem rust resistance genes deployed in wheat cultivars over the years.

Stem rust is the worst of 3 fungal rust diseases that infect wheat.
It infests straws so that nutrients cannot reach the grains. Powdery, reddish-orange spores form on infected plants.

[Byline: Zeddy Sambu]

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

[Wheat stem rust is caused by the fungus _Puccinia graminis_ f. sp. _tritici_. It occurs worldwide throughout wheat producing areas.
Symptoms are dark orange pustules on the stems and also on the leaves. Stems can be completely girdled by the pustules damaging the conducting tissue and preventing grain fill. Yield losses of up to 70 percent are reported, but some fields are totally destroyed. If stem rust arrives early in the growing cycle, losses are higher. The fungus is spread by wind and with infected straw.

New pathogen races are emerging with increased virulence against genes previously used for resistance breeding. Considered most dangerous at present is strain Ug99, which was 1st reported in Uganda in 1999. Recurring epidemics in Kenya and then Ethiopia followed and it has recently spread to Yemen. It may also be present in Pakistan, Sudan, and Tanzania and appears to be moving on prevailing winds.

Ug99 can infect and cause disease in many commonly grown stem rust "resistant" wheat lines. In much of the world, resistance to stem rust in wheat is based at least in part on the gene Sr31. High levels of stem rust infection were observed in Uganda on wheat lines containing the Sr31, Lr26, and Yr9 genes for rust resistance, and Ug99 was identified as a new strain with virulence to Sr31.

From the report above it appears that an even more virulent variant of Ug99 able to overcome additional resistance genes has emerged in Kenya. This increases the threat posed by Ug99 to global wheat production further. International screening programmes for germplasm with resistance to the new strains are being set up under the GRI.

The other 2 rust diseases of wheat mentioned above are leaf rust caused by _Puccinia triticina_, and stripe rust caused by _P. striiformis_.

Maps of Kenya:
<http://www.ogiek.org/photo-gallery/kenya-map-big.jpg> and <http://healthmap.org/promed?v=0.5,37.9,6>

Pictures of stem rust on wheat:
<http://scarab.msu.montana.edu/Disease/DiseaseGuidewebpics/Petewebpics41-50/Img0042.jpg>, 

<http://www.cimmyt.org/english/wps/news/2005/sept/images/stem2.jpg> and <http://www.gov.mb.ca/agriculture/crops/diseases/images/fac15s01.jpg>

Links
Information on wheat stem rust:
<http://www.ars.usda.gov/Main/docs.htm?docid=9910>
Information on Ug99:
<http://www.agbioworld.org/newsletter_wm/index.php?caseid=archive&newsid=2686>
and
<http://www.pestalert.org/viewNewsAlert.cfm?naid=36>
Ug99 distribution and potential global impact:
<http://www.cimmyt.cgiar.org/gis/pdf/UG99postH.pdf>
Ug99 and stem rust resistance genes used in wheat breeding:
<http://www.ars.usda.gov/Main/docs.htm?docid=14649>
_P. graminis_ f.sp. _tritici_ taxonomy:
<http://www.indexfungorum.org/Names/NamesRecord.asp?RecordID=455607>
Global Rust Initiative:
<http://www.globalrust.org/>
CIMMYT:
<http://www.cimmyt.org/>
USDA-ARS:
<http://www.ars.usda.gov/main/main.htm>. - Mod.DHA]

[see also in the archive:
Wheat stem rust, strain Ug99 - multistate: resistance screening 20071208.3957 Barley yellow dwarf virus & stem rust, cereals - Kenya 20070705.2132 Wheat stem rust, strain Ug99 - Yemen (02): government response 20070430.1399 Wheat stem rust, spread: FAO, Global Rust Initiative 20070414.1241 Wheat stem rust, strain Ug99 - Yemen: 1st report 20070117.0229]
2006
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Wheat stem rust, strain Ug99 - Pakistan: susp., 1st report 20060514.1366 Stem rust, wheat - multicountry: new strains 20060406.1039
2005
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Wheat stem rust, Ug99, new strain - East Africa 20050928.2849 Wheat stem rust, new strain - Uganda 20050912.2698
2002
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Wheat stem rust fungus, new virulence genes - So Afr 20020814.5049 2000
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Wheat stem rust in resistant wheat lines - Uganda 20000702.1092]

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