A ProMED-mail post
<http://www.promedmail.org>
ProMED-mail is a program of the
International Society for Infectious Diseases <http://www.isid.org>
Date: August 2012
Source: CIMMYT (International Maize and Wheat Improvement Centre) Newsletter [edited] <http://www.cimmyt.org/en/newsletter/598-2012/1401-africa-beats-cereal-killer>
The title of public enemy number one is a close-run competition in the wheat-growing world. While Ug99 [group of stem rust strains] poses a huge potential threat, its cousin stripe rust (also known as yellow
rust) currently causes the most damage. Just like stem rust, in recent years it has got tougher. New, highly-aggressive strains have emerged, able to overcome a key resistance gene, Yr27, that many widely-grown varieties rely on.
In many locations, resistance to one disease simply is not enough. [In Africa], stem rust is the chief problem in the short-season (February-May), whereas in the main season (June-November) stripe rust is the biggest menace, causing a major epidemic in 2010 and serious losses in 2011.
The tide is turning. A significant proportion of farmers is shifting to new varieties that are resistant, or moderately resistant, to yellow rust. Crucially, these new varieties are also resistant to Ug99 and give high yields. Around 5000 advanced wheat lines are screened for both rusts each year, with a special focus on durum wheat.
The next challenge for breeders is septoria blotch, a different fungal disease that is causing infections in CIMMYT lines. In the race to protect the world's wheat yields from ever-evolving disease, there's no time to sit back and relax.
--
Communicated by:
ProMED-mail
<promed@promedmail.org>
[Wheat stem rust is caused by the fungus _Puccinia graminis_ f. sp.
_tritici_. Overall yield losses of up to 80 percent are reported, but some fields are totally destroyed. Stem rust spores are spread by wind and with infected straw. Some grasses or volunteer wheat may generate a "green bridge" providing inoculum for the next cropping season.
Disease management may include fungicide applications, control of volunteer wheat, and resistant varieties if available. New races are emerging, and the most dangerous at present is strain Ug99 (see ProMED-mail post 19990519.0812), which has overcome the major resistance gene Sr31 used in our current wheat varieties. Since then
Ug99 strains have spread and were reported from southern Africa for the 1st time in 2009 opening up routes of transmission for the southern hemisphere (ProMED-mail post 20100602.1834).
Stripe rust (also called yellow rust) of cereals is caused by the fungus _Puccinia striiformis_ var. _striiformis_. The disease affects wheat, some barley varieties, triticale (wheat/rye hybrids), and a number of wild grasses. It causes yellow leaf stripes and stunting of plants with yield losses of 40 to 100 percent in wheat. Spores are wind dispersed in several cycles during the cropping season. Between seasons, the fungus survives on living host plants generating a "green bridge". Disease management includes the use of resistant varieties, fungicide applications, and control of volunteer crops.
New, more virulent stripe and stem rust strains overcoming additional host resistance genes and/or with added fungicide resistances are emerging worldwide. Such strains are even more difficult to control and counteract traditional resistance breeding efforts. Development of crop varieties with stable resistance to multiple pathogens is particularly difficult since the pathogens can be expected to mutate independently resulting in a range of changing combinations of strains.
Septoria leaf blotch diseases of wheat and some other cereals are caused by the fungi _Mycosphaerella graminicola_ and _Phaeosphaeria nodorum_. Up to 50 percent yield losses have been reported on susceptible varieties (for more information see links below).
Hard (durum) wheats (_Triticum turgidum_, used for example for pasta) and winter (soft) wheats (_T. aestivum_, used mostly for bread) are different species and may therefore show different levels of susceptibility to pathogen strains.
Maps
Africa, overview:
<http://worldatlas.com/webimage/countrys/africa/maps/africa.htm>
Pictures
Stem rust symptoms on wheat:
<http://www.ars.usda.gov/images/docs/9910_10104/stemrust_inset.jpg>,
<http://www.gov.mb.ca/agriculture/crops/diseases/images/fac15s01.jpg>,
and
<http://www.irinnews.org/PhotoDetail.aspx?ImageId=201010281134020344>
(Ug99)
Effects of Ug99 on resistant and susceptible wheat cultivars:
<http://www.irinnews.org/PhotoDetail.aspx?ImageId=201010281129340750>
Stripe rust symptoms on wheat:
<http://www.grdc.com.au/uploads/images/Stripe%20rust%20Colin%20Wellings%20ACRCP.JPG>
(leaf) and via
<http://wheatdoctor.cimmyt.org/en/image-galleries/fungal-diseases/stripe-rust>
Barley with stripe rust:
<http://www.ipmcenters.org/cropprofiles/docs/Graphics/WAbarleyStripeRust.jpg>
Links
Additional news story:
<http://www.isppweb.org/nlsep12.asp#3>
Information on wheat stem rust:
<http://www.ars.usda.gov/Main/docs.htm?docid=9910>
Information on Ug99:
<http://www.ars.usda.gov/Main/docs.htm?docid=14649>,
<http://www.pestalert.org/viewNewsAlert.cfm?naid=36>, and <http://www.agbioworld.org/newsletter_wm/index.php?caseid=archive&newsid=2686>
_P. graminis_ f. sp. _tritici_ taxonomy:
<http://www.indexfungorum.org/Names/NamesRecord.asp?RecordID=455607>
Global Rust Initiative:
<http://www.globalrust.org/>
Information on wheat stripe rust:
<http://pnw-ag.wsu.edu/smallgrains/Stripe%20Rust.html>,
<http://www.ars.usda.gov/Main/docs.htm?docid=9918&pf=1&cg_id=0>, and <http://www.dpi.nsw.gov.au/__data/assets/pdf_file/0006/158964/stripe-rust-in-wheat.pdf>
_P. striiformis_ taxonomy:
<http://www.indexfungorum.org/Names/NamesRecord.asp?RecordID=427989>
Information on septoria diseases:
<http://www.gov.mb.ca/agriculture/crops/diseases/fac14s00.html>,
<http://ipm.ppws.vt.edu/stromberg/smallgrain/biology/wgblotch.html>,
and
<http://www.agroatlas.ru/en/content/diseases/Tritici/Tritici_Septoria_tritici/>
Information, pictures, and resources for cereal diseases via:
<http://www.hgca.com/hgca/wde/diseases/S.tritici/strihost.html>
CIMMYT:
<http://www.cimmyt.org/>. - Mod.DHA]
[see also:
Stem rust, wheat - Africa: new races 20120607.1159076 Stripe rust, triticale - Denmark: new strain susp 20120426.1114329 Leaf & stripe rusts, wheat - UK: new strains 20120208.1036727 Stripe rust, wheat - India: update 20120122.1017973
2011
----
Barley diseases - India: (JK) survey 20111201.3497 Stripe rust, barley - Australia: (NS) 20111103.3270 Wheat stem rust, Ug99 group - Zimbabwe, Mozambique: new races
20110824.2574
Stripe rust & foot rot, wheat - USA, UK 20110713.2109 Stripe rust, wheat - India, UK: spread 20110404.1042 Stripe rust, wheat - UK: (England), Claire strain 20110304.0705 Fungal diseases, cereals - Australia: (eastern, south) alert
20110218.0531
Stripe rust, wheat - India: (PB) 20110211.0469
2010
----
Stripe rust, wheat - Lebanon 20101121.4214 Wheat stem rust, Ug99 - Kenya: (RV), update 20101103.3976 Stripe rust, wheat - Turkey, Syria 20101021.3815 Stripe rust, wheat - Ethiopia 20100922.3420 Fungal diseases, cereals - Australia: alert 20100825.2989 Stripe rust, soft wheat - Syria (east) 20100609.1930 Wheat stem rust, Ug99 group: new races 20100602.1834 Stripe rust, wheat - Africa, Asia: new strain 20100531.1803 Stripe rust, wheat - USA: (AR) new strains, alert 20100510.1522 Stripe rust & downy mildew, cereals - USA: (TX) 20100504.1443 Fungal diseases, maize, wheat - USA 20100331.1017 Stripe rust, wheat - India, UK: alert 20100121.0234 and older items in the archives]
Species
