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2022-07-30T04:03:00.0000000Z
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STEWART'S WILT, MAIZE - ITALY: REOCCURRENCE

ProMED
http://www.promedmail.org

ProMED-mail is a program of the

Source: European Plant Protection Organisation (EPPO) Reporting Service 06/2022/131 [summ. Mod.DHA, edited]
https://gd.eppo.int/reporting/article-7362

In Italy, bacterial wilt of maize caused by _Pantoea stewartii_ subsp. _stewartii_ (EPPO A2 List) had been found previously in several regions [ProMED post 20180316.5690019]. It was subsequently claimed to be eradicated.

In 2022, the pathogen was found again during surveys of maize (_Zea mays_) grown for seed in Emilia-Romagna region. At least 10% of the seed crops (5967 ha) were inspected; 16 samples with suspect symptoms were taken, and 7 tested positive. Plants within 1.5 m [5 ft] radius around the infected maize plants were uprooted and destroyed.

Before harvesting, cobs in the affected area will be tested to verify the absence of the pathogen before marketing the seed.
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Communicated by:
ProMED

[Stewart's wilt of maize is caused by the bacterium _Pantoea stewartii_ subsp. _stewartii_. (Pss; previously _Erwinia stewartii_). Symptoms vary on different host varieties but may include leaf stripes, wilting, necrosis of tassels, and spots on husks of cobs. Plants may be killed at the seedling stage, and infection later in the growth cycle can lead to serious yield losses. Many grassy hosts are susceptible and may serve as pathogen reservoirs.

Primarily, the bacteria are transmitted by and overwinter in insect vectors, but they can also be seed transmitted at a low rate and occasionally overwinters in soil, manure, or maize stalks. Insect vectors are mostly responsible for local spread; infected seed is considered the main route of long distance spread and therefore a quarantine risk. Disease management may include insecticides to reduce vector populations, use of certified disease-free seeds, and use of resistant maize cultivars.

The pathogen is indigenous to the Americas but has been introduced to some other parts of the world with maize seed. In Europe, in addition to Italy, its current distribution appears to be limited to a few countries, such as UK, Slovenia, Ukraine, and Russia.

Pss also causes a leaf blight of rice and is considered an emerging pathogen of that crop (as is _P. ananatis_, ProMED-mail post 20170504.5012251). Pss fruit bronzing is considered an emerging disease of jackfruit in southern Asia (ProMED-mail posts 20170905.5294905, 20171123.5460703).

Other species in the genus can cause diseases on a number of crops, such as leaf blights of cereals (_P. agglomerans_), pink disease of pineapple (_P. citrea_), brown stalk rot of maize (_P. ananatis_), center rot of onion (_P. ananatis_). The effects of different bacterial strains on hosts can vary dramatically.

"Eradication" of pathogens or diseases has hardly ever been successful in the past and should never be relied on as a tool for disease management. Proof of absence of a pathogen is principally and practically impossible because it would require that each and every known or potential host, symptomatic or not, as well as all known and potential vectors or pathogen reservoirs, are tested with a method that has a 100% rate of reliability. Furthermore, additional pathogen re-introductions from outside the treated area would still be possible.

Maps
Italy:
https://promedmail.org/promed-post?place=8704745,75 and
http://www.lib.utexas.edu/maps/europe/italy_div96.jpg (with regions)
Europe, overview:
https://mapofeurope.com/wp-content/uploads/2018/03/europe-political-map.jpg

Pictures
Symptoms of Stewart's wilt on maize:
http://www.plantmanagementnetwork.org/pub/php/brief/2007/goss/image/corn1.jpg,
http://www.plantpath.cornell.edu/labs/nelson_r/images/photos/Stewart_wilt2.jpg,
https://assets.corteva.com/is/image/dpagco/stewarts_wilt_symptoms_1,
https://www.ent.iastate.edu/images/plantpath/corn/stewartsdis/0796.12sweetstew.jpg,
https://c1.staticflickr.com/5/4098/4926954251_0473d6a10e_b.jpg, and
https://www.apsnet.org/edcenter/disandpath/prokaryote/Article%20Images/StewartWilt26.jpg

Links
Information on Stewart's wilt of maize:
https://gd.eppo.int/taxon/ERWIST (with distribution map),
https://www.plantwise.org/KnowledgeBank/Datasheet.aspx?dsid=21939,
https://www.apsnet.org/edcenter/disandpath/prokaryote/pdlessons/Pages/StewartWilt.aspx,
http://www.omafra.gov.on.ca/IPM/english/sweet-corn/diseases-and-disorders/stewerts-wilt.html,
https://pnwhandbooks.org/plantdisease/host-disease/corn-zea-mays-stewarts-disease-stewarts-bacterial-wilt, and
http://vegetablemdonline.ppath.cornell.edu/factsheets/Corn_Stewarts.htm
Pss taxonomy:
http://www.uniprot.org/taxonomy/66271
Description of genus _Pantoea_:
http://www.tgw1916.net/Enterobacteria/Pantoea.html
Information on _Pantoea_ species and subspecies:
http://www.bacterio.net/pantoea.html and
https://doi.org/10.1128/JCM.01916-08
Genus _Pantoea_ taxonomy and species list:
http://www.uniprot.org/taxonomy/53335
EPPO A2 quarantine list:
https://www.eppo.int/QUARANTINE/listA2.htm
- Mod.DHA]

Maize
Stewart_s_Wilt
Italy

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