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: Sat 29 May 2021
Source: The Sun [abridged, edited]
https://www.sunnewsonline.com/nigeria-losing-over-1m-tonnes-of-onions-to-purple-blotch-annually-fg/


The annual purple blotch fungal disease affecting onions in the
country has created a demand deficit of 1.1 million metric tonnes,
Permanent Secretary Ernest Umakhihe stated at a workshop on management
of Onion Purple Blotch. [He] explained that Nigeria contributes little
to the export market largely due to [inferior] produce quality
resulting from poor management of pests and diseases, and use of
pesticides causing illnesses.

"The national demand gap [is] to be bridged by importation of onion
and other products twice the country's annual production; exerting
enormous pressure on foreign exchange earnings. This workshop is aimed
at imparting the required knowledge and develop skills of our
technical officers on various strategies and management practices for
the control of onion purple blotch and other diseases with emphasis on
the use of environmental friendly technology," he said.

[Byline: Olanrewaju Lawal]

--
Communicated by:
ProMED-mail
promed@promedmail.org

[Purple blotch of onions (_Allium cepa_; some varieties known as
shallots) and related crops, such as leek (_A. porrum_) and garlic
(_A. sativum_), is caused by the fungus _Alternaria porri_. Crop
losses depend on environmental conditions and may range from 25 to 90
percent. The damage may continue to develop post-harvest. Symptoms on
onion include small, water-soaked lesions with purple centres on
leaves, leaf bases and flower stalks, which expand and result in
necrotic patches. Symptoms may be confused with stemphylium blight of
onion (_Stemphylium vesicarium_; see previous ProMED-mail posts in the
archives). On leek, _A. porri_ leads to white or purple spots
appearing on leaves; affected leaves crack and eventually die.

The disease is favoured by high humidity and often occurs as a
secondary infection on plants already affected by other pathogens or
pests (for example, onion thrips). The pathogen is mostly spread with
infected plant material and by mechanical means (including insects and
human activities). Disease management may include fungicides, clean
planting material, phytosanitation to minimise inoculum and crop
rotation.

Maps
Nigeria:
https://www.worldometers.info/img/maps/nigeria_physical_map.gif
Nigerian states:
https://maps-nigeria.com/img/1200/map-of-nigeria-showing-the-geopolitical-zones.jpg

Pictures
Purple blotch symptoms on onions:
http://vegetablemdonline.ppath.cornell.edu/Images/Impt_Diseases/72_Onion_Purple.jpg,
https://ag.umass.edu/sites/ag.umass.edu/files/fact-sheets/images/purple_blotch_onion_2.jpg,
https://image.shutterstock.com/image-photo/onion-disease-purple-blotch-600w-1299331486.jpg,
https://cropscience.bayer.co.uk/media/102361657/purple-blotch-leeks-onions-1200.jpg
and
https://www.greenlife.co.ke/wp-content/uploads/purple_blotch.jpg
Purple blotch photo gallery:
http://www.forestryimages.org/browse/subimages.cfm?sub=16559
_A. porri_ asexual spores, microscopy:
https://www.forestryimages.org/browse/detail.cfm?imgnum=5529188

Links
Information on purple blotch of onion:
http://www.pestnet.org/fact_sheets/onion_purple_blotch_151.htm (with
pictures),
https://www.plantwise.org/KnowledgeBank/Datasheet.aspx?dsid=4522,
https://ag.umass.edu/vegetable/fact-sheets/alliums-purple-blotch,
https://www.gardeningknowhow.com/edible/vegetables/onion/purple-blotch-in-onion-crops.htm,

https://www.greenlife.co.ke/purple-blotch-of-onion/ and via
http://ipm.ucanr.edu/PMG/r584100211.html
_A. porri_ taxonomy and synonyms:
http://www.indexfungorum.org/names/NamesRecord.asp?RecordID=215273
and
http://www.speciesfungorum.org/GSD/GSDspecies.asp?RecordID=215273
- Mod.DHA

HealthMap/ProMED map:
Nigeria: http://healthmap.org/promed/p/62]

[See Also:
2020
----
Purple blotch & undiagnosed bulb rot, onion - India: (KA)
http://promedmail.org/post/20200903.7741820
2019
----
Purple blotch, shallot - India: (TN)
http://promedmail.org/post/20191208.6829852
2018
----
Purple blotch, spring onion - Jamaica: (MA, SE)
http://promedmail.org/post/20180507.5787743
2016
----
Anthracnose & purple blotch, onion - Philippines: (IN)
http://promedmail.org/post/20160729.4378522
2013
----
Purple blotch, onion - Kenya: (RV) susp.
http://promedmail.org/post/20130307.1574551
2011
----
Purple blotch & anthracnose, onion - India: (MH)
http://promedmail.org/post/20110103.0024
2010
----
Purple blotch & anthracnose, onion - India: (MH)
http://promedmail.org/post/20110103.0024
and additional items on _Alternaria_ diseases in the archives]

 

Website: http://www.isid.org

Published: June 9, 2021