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: Tue 7 Jan 2020
Source: FreshPlaza, New Food magazine report [edited] <https://www.freshplaza.com/article/9177428/dormant-foliar-disease-becomes-dominant-in-new-york-onions/>
Cornell University scientists have discovered that the long-dormant stemphylium leaf blight [SLB] disease is the cause of an increase in dieback of onion crops in New York [state]. Until recently, SLB has been considered a minor foliar disease as it has not done much damage in New York since the early 1990s.
Most of the onions are said to be grown on high organic matter soils, where foliar disease management is considered crucial to productivity.
[SLB] may affect bulb size and quality, and prevents the plant tops from lodging naturally when the bulbs are fully matured.
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Communicated by: ProMED-mail <promed@promedmail.org>
[Leaf blight and stem rot of onion is caused by the fungus _Stemphylium vesicarium_. It is a serious disease of the crop that can lead to yield losses as well as severe damage to seed crops. Symptoms include water soaked lesions on leaves with yellow streaks extending along the leaf blade; leaves may become completely blighted; coalescing lesions may girdle and kill leaves and seed stems. Bulbs are not normally affected, but yield losses are due to weakening of the plants. Symptoms are similar to and may be confused with purple blotch (caused by _Alternaria porri_). Disease development is favoured by warm, humid conditions and extended periods of leaf wetness.
The pathogen can also affect a number of other hosts, including crops like tomato, asparagus, soybean, and fruit trees like pear (brown spot) and mango, but symptoms vary on different hosts. Fungal isolates from its liliaceous hosts seem to have low host specificity, but more knowledge is needed on host specificity of isolates from non-liliaceous species, for example whether different fungal strains (pathovars) may be involved in pomefruit infections.
The fungus survives between crops in plant debris or soil. It is spread with contaminated plant and soil material, water and by mechanical means. Disease management is difficult and mostly relies on cultural methods, phytosanitation (removal of crop debris and reservoir hosts) and fungicides.
In the original publication to the story above (see link below), the increase in incidence has been found together with emerging resistances to several fungicides used widely in commercial onion production. An increase in SLB has also been reported recently from, for example, New Zealand (ProMED-mail post
http://promedmail.org/post/20180405.5727825) and Canada. It is not clear if new emerging strains are a potential sole reason for the reported increases in SLB incidence, or if environmental, cultural or other external factors may also be involved. In any case, one scenario would not exclude the other and further research seems to be needed on this problem.
Other species in the genus are associated with blights or rotting diseases in a range of crops, such as leaf spot on sugar beet and apple core rot.
Maps
USA:
<https://www.mapsofworld.com/usa/large-us-map.html> and <http://healthmap.org/promed/p/234>
Individual states via:
<http://www.mapsofworld.com/usa/usa-state-and-capital-map.html>
Pictures
Stemphylium leaf blight on onion:
<https://onvegetables.files.wordpress.com/2012/07/fig1_slg-e1341539192196.gif?w=500&h=247>,
<http://vikaspedia.in/agriculture/crop-production/integrated-pest-managment/ipm-for-vegetables/ipm-strategies-for-onion/leafblightimg.jpg>,
and via
<http://www.invasive.org/browse/subimages.cfm?sub=17885> (photo
gallery)
_S. vesicarium_ conidia (microscopy):
<http://media.padil.gov.au/species/143077/51297-large.jpg>
Links
Additional news stories:
<https://www.sciencedaily.com/releases/2019/12/191230104753.htm> and <https://www.newfoodmagazine.com/news/101038/dormant-foliar-disease-becomes-dominant-in-new-york-onion-crops/>
Original publication:
<https://apsjournals.apsnet.org/doi/10.1094/PDIS-03-19-0676-RE>
(subscr.)
Information on stemphylium blight of onion and other crops:
<http://www.plantwise.org/KnowledgeBank/Datasheet.aspx?dsid=42014>,
<http://aggie-horticulture.tamu.edu/extension/newsletters/vpmnews/may01/art5may.html>,
<http://www.apsnet.org/publications/phytopathology/backissues/Documents/1989Articles/Phyto79n03_301.PDF>,
via
<http://nhb.gov.in/bulletin_files/vegetable/onion/oni002.pdf>,
<http://vikaspedia.in/agriculture/crop-production/integrated-pest-managment/ipm-for-vegetables/ipm-strategies-for-onion/diseases-and-symptoms>,
and
<http://www.actahort.org/members/showpdf?booknrarnr=358_43>
Description of _S. vesicarium_:
<http://www.padil.gov.au/maf-border/pest/main/143077/51298>
_S. vesicarium_ taxonomy and synonyms:
<http://www.indexfungorum.org/names/NamesRecord.asp?RecordID=339660>
and
<http://www.speciesfungorum.org/GSD/GSDspecies.asp?RecordID=339660>
Cornell University:
<https://www.cornell.edu/>
- Mod.DHA]
[See Also:
2018
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Stemphylium blight, onion - New Zealand
http://promedmail.org/post/20180405.5727825
2016
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Stemphylium blight, onion - Kenya: (KB)
http://promedmail.org/post/20160104.3910614
2014
----
Stemphylium leaf spot, sugar beet - UK: 1st rep (England)
http://promedmail.org/post/20141015.2864444
2009
----
Fungal blight, onion - India: (MH)
http://promedmail.org/post/20090103.0024]
Topics
Species
