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2024-02-08T00:12:00.0000000Z
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LETHAL NECROSIS, MAIZE - KENYA

ProMED
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Source: Africa Newswire [summ. Mod.DHA, edited]
https://africanewswire.za.com/kephis-urges-narok-farmers-to-use-certified-seeds-amid-maize-disease-concerns/

The Kenya Plant Health Inspectorate Service (KEPHIS) has issued a warning to local farmers against the use of uncertified seeds, to combat the spread of maize lethal necrosis (MLN), which is a significant threat to maize crops in the region. The advice extends to both farmers and sellers at 67 different selling points, ensuring that all parties involved are dealing with approved seed varieties and are vigilant in verifying the authenticity of seed packages.

Additionally, KEPHIS advised on the practice of crop rotation as a strategy to mitigate the impact of MLN. They recommended alternating maize with other crops like beans, sorghum, and potatoes. This approach not only helps in controlling MLN but also promotes healthier farming practices and potentially better harvests. At the moment, a decline in MLN cases has been observed, which is attributed to recent prolonged rainfall. MLN typically thrives in prolonged dry spells.
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Communicated by:
ProMED

[Maize lethal necrosis (MLN) is caused by co-infection of _Maize chlorotic mottle virus_ (MCMV, genus _Machlomovirus_, transmitted by chrysomelid beetles) with one of several species in the family _Potyviridae_. As synergistic partners of MCMV in MLN, _Wheat streak mosaic virus_ (WSMV, genus _Tritimovirus_) or _Maize dwarf mosaic virus_ (MDMV, genus _Potyvirus_) have been reported previously from the Americas and Europe. MLN as well as MCMV were reported for the first time in Africa from Kenya in 2012 (ProMED post 20130123.1510727). The disease is spreading in the region where millets have also been identified as an additional crop host being affected by MLN (ProMED post 20150820.3590521). _Sugarcane mosaic virus_ (SCMV) has been reported as the co-infecting virus in Sub-Saharan Africa, but seed transmission of MLN in Africa has been claimed and seed transmission is only reported for MDMV, not SCMV. MDMV and SCMV belong to a complex of closely related potyviruses infecting tropical grasses. Based on serology, some strains (for example, MDMV-B) varying in host range and ability to be seed transmitted have been reassigned between the species, which has resulted in some confusion in taxonomy.

Symptoms of the individual viruses are synergistically enhanced in MLN and may include leaf mottling and necrosis; distortion of ears; absence of kernels; failure to produce tassels; as well as stunting, premature aging, and death of plants. Symptoms may disappear during the growing season, leaving plants with latent infections but reduced yield and as virus reservoirs, making disease monitoring difficult. Losses from MLN are due to both yield reductions and trade implications resulting from the risk of seed being infected with the synergistic partners WSMV and MDMV. All of the viruses involved in MLN can be spread by different insect vectors, which may be carried by wind over long distances. Disease management may include crop rotation, certified clean seeds, control of vector species and weedy reservoir hosts, as well as use of crop cultivars or hybrids with reduced sensitivity to the viruses.

In areas where MLN is currently not being detected, the viruses may nevertheless still be present as latent infections, in reservoir species, or at low incidence. Therefore, continued monitoring for the region is of vital importance to keep track of MLN and prevent outbreaks and/or spread.

Pictures
Maize lethal necrosis:
https://www.cabidigitallibrary.org/cms/10.1079/cabicompendium.119663/asset/05d06d97-5e2a-40e1-9537-9bdda1150c91/assets/graphic/119663_06.jpg,
http://1.bp.blogspot.com/-8DVgQ8JnqQw/UBv0MFhAGQI/AAAAAAAAAAc/QrawWiKF06o/s1600/Maize.JPG,
https://assets.thenewhumanitarian.org/s3fs-public/images/201205311206240714.jpg and
https://www.grainsa.co.za/upload/maize_lethal_necrosis_2016_07_01.jpg (compared to single SCMV/MDMV infection)
Symptoms of SCMV and MDMV single infections in maize via:
https://www.ipmimages.org/browse/Areasubs.cfm?area=72
MCMV symptoms on maize:
https://cropwatch.unl.edu/image/29591.jpg

Links
Information on maize lethal necrosis:
http://www.fao.org/fileadmin/user_upload/emergencies/docs/MLND%20Snapshot_FINAL.pdf,
https://www.grainsa.co.za/maize-lethal-necrosis:-possible-threat-to-local-maize-production,
https://blog.plantwise.org/2021/11/18/maize-lethal-necrosis-disease-the-invasive-threatening-maize/,
https://doi.org/10.1079/cabicompendium.119663,
https://doi.org/10.1094/PHYTO-12-14-0367-FI (review) and
https://doi.org/10.1146/annurev-virology-092917-043413 (review)
MLN control strategies:
https://doi.org/10.1016/j.agsy.2018.01.016
MLN updates & resources:
https://mln.cimmyt.org/
Information on MCMV:
https://www.dpvweb.net/dpv/showdpv/?dpvno=284
Information on MDMV:
https://www.dpvweb.net/dpv/showdpv/?dpvno=341
Information on SCMV:
https://www.dpvweb.net/dpv/showdpv/?dpvno=342
Virus taxonomy via:
https://talk.ictvonline.org/taxonomy/
KEPHIS:
https://www.kephis.go.ke/
- Mod.DHA]

Kenya
Maize_lethal_Necrosis

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