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Blast disease on wheat - global epidemiology


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: Fri 19 Mar 2021

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 http://promedmail.org/post/20160411.4150953]. Less than 2 years later, Zambia was struck by the 1st wheat blast in Africa [ProMED post http://promedmail.org/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]

--

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

http://promedmail.org/post/20160411.4150953) and subsequently reported in India (ProMED post http://promedmail.org/post/20170306.4883233).

Wheat blast strains in Bangladesh were found to be highly similar to strains from Brazil (ProMED post http://promedmail.org/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 http://promedmail.org/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]

 

[See Also:

2020

----

Blast disease, wheat - Africa: 1st rep (Zambia)

http://promedmail.org/post/20201006.7839169

Blast & undiagnosed rust, wheat - Bangladesh: (RP)

http://promedmail.org/post/20200323.7132348

2017

----

Blast disease, wheat - India: 1st rep (WB)

http://promedmail.org/post/20170306.4883233

Blast disease, wheat - Bangladesh: (KH)

http://promedmail.org/post/20170123.4784298

2016

----

Blast disease, wheat - Bangladesh: origin

http://promedmail.org/post/20160502.4196134

Blast disease, wheat & rice - Bangladesh

http://promedmail.org/post/20160419.4168271

Blast disease, wheat - South Asia: 1st rep, Bangladesh

http://promedmail.org/post/20160411.4150953

2012

----

Blast disease, wheat - USA: 1st rep. (KY)

http://promedmail.org/post/20120430.1117921

2010

----

Blast, wheat & barley - South America: emerging disease

http://promedmail.org/post/20100521.1684

and additional items on rice blast in the archives]



More news from: ISID (International Society for Infectious Diseases)


Website: http://www.isid.org

Published: March 25, 2021

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