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2021-05-03T07:37:00.0000000Z
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BLAST DISEASE, WHEAT - GLOBAL EPIDEMIOLOGY

ProMED
http://www.promedmail.org

Source: World Grain [summ., edited]
https://www.world-grain.com/articles/15034-report-links-wheat-blast-pandemic-on-three-continents

Wheat blast was originally detected in Brazil in 1985. In 2016, the 1st wheat blast beyond South America hit Bangladesh [ProMED post 20160411.4150953]. Less than 2 years later, Zambia was struck by the 1st wheat blast in Africa [ProMED post 20201006.7839169]. Until now, there has been no confirmation if the same pathogen strain had spread to all 3 continents or if these [outbreaks] were caused by endemic pathogens spreading from other grass species to wheat.

According to a new report from the Sainsbury Laboratory, molecular analyses showed that the same set of 84 genetic markers were present in samples from Bangladesh, Zambia, and Bolivia. All the samples from Zambia collected from 2018 to 2020 were the same clone, indicating that there was probably only one introduction. This was also the case for the Bangladeshi samples from 2016 to 2020, implying it's unlikely that there were further introductions after the 1st one in 2016. The findings rule out that the Zambian wheat blast was caused by a host jump from other African grass pathogens to wheat, [but] that the pathogen in Bangladesh has spread to Zambia. The clone match found in Bolivia was sampled in 2012 and probably originated from other South American populations. This will later be confirmed using whole-genome sequencing.

"The information generated is very important and has significant impact in developing and implementing wheat blast management strategies," said Pawan Singh, head of wheat pathology at CIMMYT [Mexico's International Maize and Wheat Improvement Center].

[Byline: Susan Reidy]

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Communicated by:
ProMED
<promed@promedmail.org>

[Both wheat and rice blast are caused by the fungus _Pyricularia oryzae_ (synonym _Magnaporthe oryzae_). Although the pathogens are currently classified as the same species, the wheat blast pathogen is a distinct population (referred as _P. oryzae_ Triticum population) and does not cause disease in rice. Over 50 species of grasses and sedges can be affected by related fungal strains, each of which generally appear to affect only a limited number of host species. Further work is needed regarding genotypic differentiation related to host range, including differences between the wheat and rice pathovars. Rice blast is one of the most destructive diseases of rice worldwide. Wheat blast is now considered an emerging disease and a threat to global food security.

Blast symptoms on wheat (and barley) may be confused with fusarium head blight (see previous ProMED posts in the archives and link below) and include necrotic leaf spots, bleaching of ears, shriveled kernels, and no seed production at all for severe infections. Yield losses seem to average 40-50%, but cases of 100% losses have also been reported; wheat production in some affected areas has ceased.

Humid and warm conditions favour disease development, but the life cycle of the fungus is still unknown. Spread of the rice pathogen occurs with infected plant material (including seed), mechanical means (including human and insect activity), water, and wind. It is likely that the wheat pathogen is spread in similar ways. Disease management of rice blast may include fungicides and cultural practices but relies mainly on resistant varieties. Available wheat cultivars lack resistance to wheat blast, and only limited tolerance can be found. Resistance breeding is difficult because the fungus is highly variable, which favours the emergence of new strains with increased virulence.

Wheat blast was identified in 1985 in southern Brazil and spread in the Americas. Initially, it was thought to be caused by a fungal strain that crossed from rice to wheat, but is now considered more likely to have originated from local wild grasses. In Asia, the disease was found for the 1st time in 2016 in Bangladesh (ProMED post 20160411.4150953) and subsequently reported in India (ProMED post 20170306.4883233). Wheat blast strains in Bangladesh were found to be highly similar to strains from Brazil (ProMED post 20160502.4196134). Similarly, rice blast strains in northern India were shown also to be closely related to strains from the main origin of seed and food grain (ProMED post 20160407.4145967). Based on these findings, the disease in Asia is now considered to be due to introduction of the fungus with grain. This would suggest a similar way of introduction of the disease to Africa and stress again the importance of strict quarantine measures and biosecurity protocols for the international movement of any kind of plant material.

Maps
Continents:
https://worldmapwithcountries.net/wp-content/uploads/2020/09/Printable-Map-of-World-with-Continents-and-Oceans.jpg

Pictures
Blast symptoms on wheat:
https://www.scielo.br/img/revistas/brag/v74n2//0006-8705-brag-167844990023-gf01.jpg, http://www.cpac.embrapa.br/publico/usuarios/uploads/Trigo%20-%20brusone/brusone%20espiga%20-%20foto%20julio%20albrecht-3.JPG,
http://chainpure.files.wordpress.com/2012/04/wheat-blast.jpg,
https://www.researchgate.net/profile/Paulo_Ceresini/publication/327473003/figure/fig2/AS:681623485952006@1539523111959/Symptoms-associated-with-wheat-blast-including-severe-head-infection-in-an-irrigated.jpg and
https://media.springernature.com/lw685/springer-static/image/art%3A10.1007%2Fs40858-017-0159-z/MediaObjects/40858_2017_159_Fig2_HTML.gif
Barley head with blast symptoms:
http://www.cnpt.embrapa.br/imagens/p_co112f1-1.jpg
For comparison, fusarium head blight symptoms on wheat:
http://www.uky.edu/Ag/Wheat/wheat_breeding/Images/2000/scabby_head1.jpg
Rice blast:
http://www.knowledgebank.irri.org/ricebreedingcourse/blast.jpg

Links
Original report and continuing data updates via:
https://zenodo.org/record/4618522
Information on wheat blast:
https://www.cimmyt.org/news/what-is-wheat-blast/,
https://www.cabi.org/isc/datasheet/121970,
http://wheat.org/wp-content/uploads/sites/4/2016/04/Wheat-Blast-Priority-Brief-web-07Apr2016.pdf,
http://wheatblast.org/,
https://www.k-state.edu/wheatblast/ and
http://www.agriculturejournals.cz/publicFiles/48968.pdf
Reviews:
https://bsppjournals.onlinelibrary.wiley.com/doi/full/10.1111/mpp.12747 and
https://link.springer.com/article/10.1007/s40858-017-0159-z
Origin of wheat blast for Asia:
https://github.com/crolllab/wheat-blast and
https://bmcbiol.biomedcentral.com/articles/10.1186/s12915-016-0309-7
Information on rice blast:
http://www.knowledgebank.irri.org/training/fact-sheets/pest-management/diseases/item/blast-leaf-collar (with pictures) and
http://www.oisat.org/pests/diseases/fungal/rice_blast.html
_P. oryzae_ taxonomy and synonyms:
http://www.indexfungorum.org/names/NamesRecord.asp?RecordID=224486 and
http://www.speciesfungorum.org/Names/SynSpecies.asp?RecordID=224486
Sainsbury Laboratory:
http://www.tsl.ac.uk/
CIMMYT:
https://www.cimmyt.org/
- Mod.DHA]

Wheat
Bangladesh
Blast

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