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

Date: Tue 10 Dec 2024
Source: SeedWorld [summ. Mod.DHA, edited]
https://www.seedworld.com/us/2024/12/10/emerging-corn-diseases/


The southern U.S. is experiencing a resurgence of maize stunt. It is nothing new, but with warming trends, it is moving further north. Storms can move it very far -- it even showed up in New York toward the end of the season this year [2024]. Monitoring of crops is critical. Early detection allows growers to take action before the disease becomes widespread. The vector can survive on wheat and sorghum, so managing volunteer maize plants and alternative hosts helps to break the cycle.

Late season decline leads to symptoms like water-soaked lesions, streaks and necrotic patches, especially under stressful conditions like high heat and drought. Its cause is still unknown. Particularly, the role of bacterial pathogens like _Pantoea ananatis_ is uncertain. Further work is needed to clarify whether late season decline is truly a disease or just bacteria taking advantage of stressed tissue.

_P. ananatis_ is widely present inside and outside plants, including crops like onions. It is still unclear what makes it pathogenic in some cases and not in others. Specific tests to differentiate pathogenic from non-pathogenic strains are needed. False positives could halt seed exports.

Growers are advised to be vigilant, focusing on early detection, vector control and careful management to navigate these emerging threats.

[Byline: Aimee Nielson]

--
Communicated by:
ProMED

[_Spiroplasma kunkelii_ (Sk) causes maize stunt disease on _Zea_ species in the Americas. Symptoms may include chlorosis, reddening and stunting of plants. The pathogen is spread primarily by the leaf hopper _Dalbulus maidis_; vector development is favoured by warmer temperatures.

Disease management for spiroplasmas mainly relies on exclusion by use of certified clean planting material, but may also include phytosanitation to remove inoculum and prevent spread within plantings. Vector control has not shown to be effective due to the very rapid transmission.

The related _S. citri_ causes citrus stubborn disease (also called little leaf; ProMED post 20200710.7559217) and purple leaf of carrot (ProMED post 20110916.2824). Spiroplasmas are plant cell parasitic bacteria without a cell wall and, like phytoplasmas, belong to the mollicutes. The name is derived from their helical morphology. Spiroplasmas can be cultured on artificial media, unlike phytoplasmas which cannot be cultured in vitro.

For information on _Pantoea ananatis_ see previous ProMED posts in the archives (e.g. on rice, ProMED post 20220706.8704271). Species in the genus can cause diseases on a number of crops.

Pictures
Sk maize stunt symptoms:
https://bugwoodcloud.org/images/768x512/1235014.jpg,
https://bugwoodcloud.org/images/768x512/1524068.jpg,
https://bugwoodcloud.org/images/768x512/1524071.jpg and
https://bugwoodcloud.org/images/768x512/1524075.jpg
_D. maidis_ vector:
https://herbariofitopatologia.agro.uba.ar/wp-content/uploads/2018/10/Dalbulus-maidis-Barontini-1024x675.jpg
_S. kunkelii_, micrograph:
https://ipmworld.umn.edu/sites/ipmworld.umn.edu/files/styles/folwell_third/public/2021-12/tsai_falk_figure_7.jpg

Links
Information on _S. kunkelii_ and maize stunt:
https://doi.org/10.1079/cabicompendium.50978,
https://doi.org/10.3390/plants9060747,
https://plantix.net/en/library/plant-diseases/300036/stunt-of-maize/,
https://www.ars.usda.gov/northeast-area/beltsville-md-barc/beltsville-agricultural-research-center/molecular-plant-pathology-laboratory/docs/spiroplasma-kunkelli-genome-sequencing-project/ and via
https://ipmworld.umn.edu/tsai-maize-tropics
Plant pathogenic spiroplasmas, review:
https://doi.org/10.1007/0-387-30744-3_30
Spiroplasma taxonomy via:
http://www.uniprot.org/taxonomy/
Information and taxonomy for _D. maidis_ vector:
https://bugguide.net/node/view/1456958
- Mod.DHA

ProMED map:
United States: https://promedmail.org/promed-post?place=8720708,106]

See Also

2020
----
Stubborn disease, citrus - Pakistan: (PB) 20200710.7559217
2012
----
Liberibacter, vegetable crops - multicountry 20120713.1199961
2011
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Purple leaf, carrot - Europe: 1st rep, (Spain) 20110916.2824
2003
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Corn stunt disease - USA (California) 20031004.2500
and additional items in the archives

Website: http://www.isid.org

Published: December 17, 2024