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: Thu 29 Mar 2018 6:30 PM NZST
Source: Radio New Zealand [edited]
<https://www.radionz.co.nz/news/country/353699/onion-crop-slashed-by-disease>
The country's onion crop has been slashed by at least 20 per cent because of humid weather which resulted in a disease. Onions New Zealand's Michael Ahern said the main problem was a leaf blight called 'Stemphylium' which has damaged the plants.
"We've had some difficulties in a number of the growing areas. We ran a crop forecast recently and we could be down by around 20 per cent on yield, even that could be increased by quality issues at packing time.
No one can recall an attack by this particular fungus to this extent.
So that does point potentially to, not a new pathogen, but more changing climate conditions."
The industry would pour its resources and expertise into finding solutions, he said.
[Byline: Alexa Cook]
--
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 and 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 (as mentioned above).
The pathogen can also affect a number of other hosts, including crops like tomato, asparagus, soybean and even trees like pear and mango, but symptoms vary on different hosts.
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.
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.
In the story above, it is not clear why the possibility of an emerging new pathogen strain is being dismissed and why environmental changes are considered more likely as reason for the outbreak. In any case, one scenario would not exclude the other. It would appear that further research on the pathogen strain as well as other factors leading to the problems is advisable.
Maps
New Zealand:
<http://www.backpack-newzealand.com/images/new-zealand-map.gif> and <http://healthmap.org/promed/p/164>
Pictures
Stemphylium leaf blight on onion:
<https://onvegetables.files.wordpress.com/2012/07/fig1_slg-e1341539192196.gif?w=500&h=247>,
<http://www.apsnet.org/edcenter/K-12/NewsViews/Article%20Images/stemphylium.jpg>,
<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 story:
<http://www.freshplaza.com/article/192001/New-Zealand-onion-crop-affected-by-disease>
Information on stemphylium blight:
<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:
<http://www.indexfungorum.org/names/NamesRecord.asp?RecordID=339660>
- Mod.DHA]
[See Also:
Core rot, apple - India: (HP)
http://promedmail.org/post/20180329.5717077
2016
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Stemphylium blight, onion - Kenya: (KB)
http://promedmail.org/post/20160104.3910614
2014
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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
2005
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Apple core rot - India (Himachal Pradesh) http://promedmail.org/post/20050808.2313]
Topics
Species
