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Date: August 2009
Source: Plant Disease [edited]
<http://apsjournals.apsnet.org/doi/abs/10.1094/PDIS-93-8-0840B>
[Ref: Emergence of virulence to Sr25 of _Puccinia graminis_
f. sp. _tritici_ on wheat in India
SK Jain et al
Plant Dis 2009; 93(8), 840; DOI: 10.1094/PDIS-93-8-0840B]
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Stem (black) rust, caused by _Puccinia graminis_ Pers. f. sp.
_tritici_ Eriks. & Henn., is one of the most destructive
diseases of wheat. It could be controlled through introgression
of race-specific resistance genes. However, such resistance is
mostly short lived due to emergence of new virulences. For
example, resistance genes Sr11, Sr24, Sr30, and Sr31 are no
longer effective. Detection of new virulences has remained vital
in the evaluation and identification of new sources of
resistance. We report here the detection of virulence to Sr25, a
gene from _Thinopyrum elongatum_, which had been effective or
partially effective against stem rust worldwide, including race
Ug99.
A stem rust isolate collected in 2006 from Karnataka (southern
India) produced susceptible reactions on the primary leaves of
differential genotype 'Agatha' carrying Sr25 and susceptible
check 'Agra Local'. To verify virulence to Sr25, single-pustule
isolates from this sample were inoculated onto seedlings of 6
additional varieties which all carry Sr25. All these accessions
were found susceptible to this isolate, except one, which
expressed resistance, indicating the presence of additional
gene(s). These genotypes are resistant to Sr25-avirulent
pathotypes.
The new pathotype is avirulent to Sr11, 13, 14, 21, 22, 23, 24,
26, 27, 29, 31, 32, 33, 35, 37, 38, 39, 40, 43, and Tmp and
virulent to Sr5, 6, 7a, 7b, 8a, 9a, 9b, 9d, 9e, 9f, 9g, 10, 12,
15, 16, 17, 18, 19, 20, 25, 28, 30, 34, 36, 42, Wld-1, and Gt.
This pathotype has been designated as 58G13-3 and PKTSC
according to the Indian nomenclature and the North American
system, respectively. It represents race 40 based on Stakman's
differentials [standard variety series to identify stem rust
pathotypes. - Mod.DHA] It may have arisen from race 40 through
mutation. The type culture of the pathotype has been added to
the culture collection at Shimla [Himachal Pradesh, India].
The detection of Sr25 virulence is significant since Sr25 is an
important gene to be targeted for breeding wheat cultivars
resistant to Ug99. We should use either adult plant resistance
and/or combining two or more genes for seedling resistance to
enhance the field life of wheat cultivars.
--
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[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. New races are
emerging, and the most dangerous at present is strain Ug99,
which has overcome the major resistance gene Sr31 used in our
current wheat varieties. An even more virulent variant of Ug99
able to overcome the additional resistance genes Sr24 and Sr36
has recently emerged in Kenya.
Rust spores are carried eastwards on prevailing winds, and
regions at high risk of a Ug99 incursion were identified
accordingly in the Middle East and South Asia. It is estimated
that Ug99 could reduce world wheat production by 60 million tons
and the pathogen is considered a global threat to food security.
Resistance breeding programmes have been set up with
international cooperation (Delhi Declaration, see link below) to
establish wheat varieties resistant to Ug99.
Maps
India:
<http://www.globalsecurity.org/military/world/india/images/IndiaMap_tourism.gif>
and
<http://healthmap.org/r/008o>
Middle East, including Ug99 alert area:
<http://worldatlas.com/webimage/countrys/me.htm>
Pictures of stem rust symptoms on wheat:
<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
Recent news stories on worldwide Ug99 resistance breeding:
<http://www.cbc.ca/canada/calgary/story/2009/07/11/edmonton-government-funding-wheat-fungus.html>,
<http://www.latimes.com/news/nationworld/nation/la-sci-wheat-rust14-2009jun14,0,1661589.story>
and
<http://www.theeastafrican.co.ke/news/-/2558/599222/-/rggp9oz/-/>
Information on wheat stem rust:
<http://www.ars.usda.gov/Main/docs.htm?docid=9910>
Information on Ug99:
<http://www.cimmyt.cgiar.org/gis/pdf/UG99postH.pdf>,
<http://www.pestalert.org/viewNewsAlert.cfm?naid=36>,
<http://www.ars.usda.gov/Main/docs.htm?docid=14649>
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>
Delhi Declaration on Ug99:
<http://www.icar.org.in/news/DELHI-DECLARATION-ON-WHEAT-STEM-RUST-UG99.htm>
Global Rust Initiative:
<http://www.globalrust.org/>
Background on differential hosts for pathotype identification:
<http://www.ars.usda.gov/Main/docs.htm?docid=10348>.
- Mod.DHA]
[see also
in the
archive:
Wheat stem rust, strain Ug99: resistance breeding 20090326.1168
Wheat rusts - Kenya, India, Australia 20090312.1019
2008
----
Wheat stem rust Ug99 - Australia ex Ethiopia: interception
20081203.3807 Wheat stem rust, strain Ug99 - multicountry:
update 20081120.3660 Stem rust, wheat - Australia: (WA)
20080905.2769 Wheat stem rust, strain Ug99 - Iran: 1st rep,
alert 20080307.0925
2007
----
Wheat stem rust, strain Ug99 - Kenya: new variant 20071217.4054
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
----
Wheat stem rust, strain Ug99 - Pakistan: susp., 1st report
20060514.1366 Stem rust, wheat - multicountry: new strains
20060406.1039
2005
----
Wheat stem rust, Ug99, new strain - East Africa 20050928.2849
Wheat stem rust, new strain - Uganda 20050912.2698
2002
----
Wheat stem rust fungus, new virulence genes - So Afr
20020814.5049 2000
----
Wheat stem rust in resistant wheat lines - Uganda 20000702.1092
1999
----
Stem-rust fungus, mutant, wheat - Uganda 19990519.0812] |
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