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: Wed 3 Apr 2024
Source: CIMMYT (International Maize and Wheat Improvement Center) [summ. Mod.DHA, edited]
https://www.cimmyt.org/news/successful-surveillance-results-in-early-first-detection-of-ug99-in-south-asia/
Successful global wheat disease surveillance and monitoring has resulted in early detection of wheat stem rust Ug99 in Nepal. A combination of vigilant field surveys and sampling by Nepal's National Plant Pathology Research Centre (NPPRC) and National Wheat Research Program (NWRP), supported by rigorous and accurate disease diagnostics at the Global Rust Reference Center (GRRC), Denmark, confirmed the presence of Ug99 as a highly virulent race variant termed TTKTT. Results were obtained from 2 field samples collected in early November 2023 from off-season summer wheat crops.
Migration of Ug99 from Africa to other regions, including South Asia, was always seen as likely due to the transboundary nature of the disease and long-distance dispersal of rust spores by wind. Detection of a Ug99 race in Nepal is not therefore a surprise, but it highlights the effectiveness of the wheat rust surveillance and monitoring systems that have been developed. The disease was present at extremely low levels in the fields in Nepal. The wheat on which the Ug99 race TTKTT was detected were fodder crops and cut soon after the surveys were completed, which prevented further buildup of disease. In addition, no wheat is grown in the main season in these areas.
Extensive follow up surveys in the area and throughout other wheat growing areas in the country resulted in no wheat being observed and no detection of stem rust. To date, extensive surveys in other countries in South Asia (Pakistan, Bangladesh, Bhutan) have not detected stem rust in 2023/24.
Detection of TTKTT in Nepal is a clear reminder of an increasing threat posed to wheat production in South Asia by the incursion of virulent stem rust races. Successful deployment of Ug99 resistant cultivars has decreased vulnerability, but it is important to note that the race TTKTT is a recently evolved variant of Ug99 with additional virulence compared to the original strains. As a result, not all cultivars in South Asia may have effective resistance today. Screening of germplasm and major cultivars from South Asia against TTKTT is extremely important to get an accurate picture of current vulnerability.
--
Communicated by:
ProMED
[Wheat stem rust (_Puccinia graminis_) has been reported to cause overall yield losses of up to 80%, but some fields are totally destroyed. Barley is also susceptible to this pathogen. Stem rust spores are spread by wind and with infected straw or other contaminated materials. The fungus can survive between seasons on some grasses or volunteer wheat, generating a "green bridge". Alternatively, it can also produce hardy teliospores to infect members of the genus _Berberis_ (barberries) in the next season, which then serve as a source of crop inoculum. Barberry is suspected to have given rise to a recent outbreak of stem rust in barley in the UK (ProMED post 20191008.6714735).
Disease monitoring is important so that timely action can be taken to limit the spread of the pathogen as well as build-up of inoculum. Disease management may include fungicide applications; control of volunteer wheat and _Berberis_ reservoirs; as well as resistant varieties, if available. Resistance breeding programmes have been set up by several countries and international groups. However, new fungal races with increased virulence are emerging frequently. Recombinants of different races would pose a high risk of becoming even more aggressive than the parents. Of the more than 50 known wheat resistance genes to stem rust, only very few are currently left that have not been overcome by a stem rust race. For example, stem rust is currently being considered a re-emerging disease in Europe because many wheat varieties planted there now are susceptible to newly emerged strains.
Pictures
Stem rust symptoms on wheat:
https://www.agric.wa.gov.au/sites/gateway/files/styles/original/public/stem%20rust%20head%20infection%20closeup%20wheat_2.jpg,
https://rusttracker.cimmyt.org/wp-content/uploads/2017/02/StemRustSisily.png,
https://www.graincentral.com/wp-content/uploads/2017/12/Stem_rust_field_credit_Robert_Park_University_of_Sydney.jpg,
https://crop-protection-network.s3.amazonaws.com/articles/photos/Stem-rust.-Burrows.-July-2009-7.jpg and
https://kggfradio.com/assets/images/blogs/2019/wheat_stem_rust.png
Stem rust on resistant vs. susceptible wheat cultivars:
https://www.cimmyt.org/content/uploads/2019/06/wheat2.jpg and
https://assets.irinnews.org/s3fs-public/styles/responsive_large/public/images/201010281129340750.jpg
_P. graminis_ symptoms on barberry leaves:
https://pnwhandbooks.org/sites/pnwhandbooks/files/plant/images/barberry-berberis-spp-rusts/dsc0008.jpg and
https://c8.alamy.com/comp/XAK70Y/common-barberry-european-barberry-berberis-vulgaris-leaves-with-puccinia-graminis-stem-rusts-germany-north-rhine-westphalia-XAK70Y.jpg
Links
Information on wheat stem rust:
https://www.apsnet.org/edcenter/disandpath/fungalbasidio/pdlessons/Pages/StemRust.aspx, https://www.agric.wa.gov.au/mycrop/diagnosing-stem-rust-wheat, https://doi.org/10.1079/pwkb.20127801775,
https://guide.utcrops.com/wheat/wheat-disease-identification/diseases-affecting-leaves/stem-rust/,
https://www.ars.usda.gov/midwest-area/stpaul/cereal-disease-lab/docs/cereal-rusts/wheat-stem-rust/ and via
https://www.ars.usda.gov/midwest-area/stpaul/cereal-disease-lab/docs/ug99-emerging-virulent-stem-rust-races/
Stem rust disease cycle:
https://i.pinimg.com/originals/e2/fb/35/e2fb352fb297508257dcfe7606db8334.png
Resistance breeding:
https://doi.org/10.1094/PHYTO-08-20-0325-R and
https://phys.org/news/2021-04-wild-barley-jordan-key-stem.html
Re-emergence of wheat stem rust in Europe (reviews):
https://doi.org/10.1038/s42003-019-0294-9 and
https://doi.org/10.1038/s42003-018-0013-y
Stem rust strains nomenclature and worldwide distribution via:
https://rusttracker.cimmyt.org/?page_id=7
_P. graminis_ taxonomy and synonyms:
http://www.indexfungorum.org/Names/NamesRecord.asp?RecordID=159822 and
https://www.speciesfungorum.org/Names/SynSpecies.asp?RecordID=159822
Wheat rusts overview, including epidemiology and spore types:
https://www.fao.org/3/y4011e/y4011e0g.htm
Global Rust Initiative:
https://bgri.cornell.edu/
- Mod.DHA]
See Also
2023
----
Stem rust, wheat - UK: multiple races 20230118.8707837
2022
----
Stem rust, wheat - Ireland: Digalu race 20220323.8702170
2021
----
Stem rust Ug99 group, wheat - Iraq: 1st rep 20210408.8296894
Stripe, stem & leaf rusts, wheat - Ethiopia 20210212.8186216
2020
---
Stem rust, wheat - Ireland: (CW) 20200731.7630206
2019
---
Stem rust, barley - UK: (England) 20191008.6714735
Stem rust, wheat - Kenya: (Rift Valley) 20190711.6562626
2018
---
Stem rust, wheat - UK: Digalu strain, 1st rep 20180219.5638265
2017
---
Stem & stripe rusts, wheat - Europe, Asia, Africa: new races 20170206.4820305
2016
---
Stripe, stem & leaf rusts, wheat - Ethiopia 20161117.4637042
Stem rust Ug99 group, wheat - Egypt: 1st report 20160322.4109568
2014
---
Stem rust, wheat - Germany: strains 20140404.2379670
Stem rust, wheat - Ethiopia (02): strains 20140327.2360315
Stem rust, wheat - Ethiopia: (southern) alert 20140109.2162758
and additional items in the archives
Topics
Species
