A ProMED-mail post
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International Society for Infectious Diseases
http://www.isid.org

Date: Thu 1 Feb 2024
Source: International Maize and Wheat Improvement Center (CIMMYT) [summ. Mod.DHA, edited]
https://www.cimmyt.org/news/wheat-blast-spread-globally-under-climate-change-modeled-for-the-first-time/


An international team of scientists have modeled for the 1st time how wheat blast will spread in the future, using a newly developed wheat blast model. They showed that spread of the fungus could reduce global wheat production by 13% until 2050. Regionally, up to 75% of total wheat acreage could be affected.

South America, southern Africa and Asia will be the regions most affected. Wheat blast will continue to spread in countries that were previously only slightly impacted and is also penetrating countries that were previously untouched. The risk is low in Europe and East Asia, except for a few southern areas. Conversely, where climate change leads to drier conditions with more frequent periods of heat above 35 °C [95 deg F], the risk of wheat blast may decrease, but in these cases, heat stress reduces yield potential.

Previous studies on yield changes due to climate change mainly considered the direct effects of climate change such as rising temperatures, changing precipitation patterns and increased CO2 levels. This study now focused on the influence of wheat blast on production by combining a simulation model for wheat growth and yield. Environmental conditions such as weather are thus included in the calculations, as is data on plant growth. In this way, the scientists are modeling the disease pressure in the particularly sensitive phase when the ear matures. Other consequences of climate change could further reduce yields.

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Communicated by:
ProMED

[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 appears 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 (see also ProMED post 20210324.8267471).

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 to 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 which 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 stresses again the importance of strict quarantine measures and biosecurity protocols for the international movement of any kind of plant material.

Pictures
Blast symptoms on wheat:
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, 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
Information on wheat blast:
https://www.cimmyt.org/news/what-is-wheat-blast/,
https://doi.org/10.1079/cabicompendium.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://doi.org/10.1111/mpp.12747 and
https://doi.org/10.1007/s40858-017-0159-z
Origin of wheat blast for Asia:
https://doi.org/10.1186/s12915-016-0309-7
Wheat blast genotyping data via:
https://zenodo.org/record/4618522
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
CIMMYT:
https://www.cimmyt.org/
- Mod.DHA]

See Also

2023
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Blast disease, rice - Bangladesh: (KH, SY) 20230412.8709453
2022
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Blast disease, rice - India: (NL) 20220527.8703502
Blast disease, rice - Bangladesh: (RS) 20220516.8703232
2021
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Blast disease, rice - India: (NL) 20210728.8549976
Blast disease, wheat - global epidemiology 20210324.8267471
2020
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Blast disease, wheat - Africa: 1st rep (Zambia) 20201006.7839169
Blast & undiagnosed rust, wheat - Bangladesh: (RP) 20200323.7132348
2017
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Blast disease, wheat - India: 1st rep (WB) 20170306.4883233
Blast disease, wheat - Bangladesh: (KH) 20170123.4784298
2016
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Blast disease, wheat - Bangladesh: origin 20160502.4196134
Blast disease, wheat & rice - Bangladesh 20160419.4168271
Blast disease, wheat - South Asia: 1st rep, Bangladesh 20160411.4150953
2012
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Blast disease, wheat - USA: 1st rep. (KY) 20120430.1117921
2010
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Blast, wheat & barley - South America: emerging disease 20100521.1684
and additional items on rice blast in the archives

Website: http://www.isid.org

Published: February 7, 2024