Thursday, September 20, 2018

PRO/PL> Brown streak, cassava - Zambia

BROWN STREAK, CASSAVA - ZAMBIA
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Date: Mon 17 Sep 2018
Source: Zambia National Broadcasting Corporation (ZNBC) [edited]
<https://www.znbc.co.zm/cassava-brown-steak-virus-strikes/>


The Ministry of Agriculture has confirmed the outbreak of cassava
brown steak virus in Luapula, Northern, and North-Western provinces.

Minister of Agriculture Michael Katambo says official surveys have
established the existence of the disease. [He] says [it] is a threat
to food security because cassava is the 2nd most important food crop
after maize. [He] has advised farmers to plant disease-free materials
and avoid sharing cassava cuttings.

Mathias Tembo, Zambia Agricultural Research Institute, disclosed that
the disease could have originated from neighbouring countries.

[Byline: Joshua Jere]

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

[Cassava brown streak (CBS; also called root rot) disease can be
caused by Cassava brown streak virus (CBSV) and the more recently
identified Ugandan cassava brown streak virus (both genus
_Ipomovirus_). It is considered a threat to the whole of sub-Saharan
Africa, where the crop is a major factor in food security. Symptoms
may include leaf chlorosis, stem necrosis, and yellow/brown corky
necrosis in the starch-bearing tissue of roots. Leaves may appear
healthy even when the roots have rotted away. Total crop losses of
20-80 percent have been reported, and losses in individual root weight
of up to 70 percent have been observed in susceptible cultivars.

The virus is transmitted by the whitefly vector _Bemisia tabaci_ (a
serious crop pest in its own right) and is spread to new areas by
infected cassava cuttings. Disease management includes pathogen
exclusion, removal of infected plants, use of virus-free seed tubers
for planting, and vector control. However, these measures may be
difficult to implement in developing countries. Resistant varieties
are being developed for specific local requirements.

Recent outbreaks of CBSD appear to indicate a westward spread of the
viruses (ProMED-mail post
http://promedmail.org/post/20130508.1698543). CBSV is a particular
threat to new crop varieties developed with resistance to Cassava
mosaic disease (CMD; caused by a number of species and strains in the
genus _Begomovirus_ and transmitted like CBSV). A new CBSV strain
adapted to higher altitudes has emerged in eastern Africa and is
affecting additional CMD-resistant cultivars (ProMED-mail posts
http://promedmail.org/post/20100525.1735 and
http://promedmail.org/post/20120706.1191742).

Joint management of both diseases has become a major challenge in the
region and globally (ProMED-mail post
http://promedmail.org/post/20110829.2643) since development of crop
varieties with stable resistance to multiple viruses is particularly
difficult (ProMED-mail post http://promedmail.org/post/20090709.2463).
The different viruses can be expected to mutate independently,
resulting in a range of changing combinations of strains, and
different crop varieties are likely to be needed that are geared
towards local viral populations.

Several of Zambia's neighbouring countries, including Democratic
Republic of Congo, Angola, Malawi, and Tanzania, have previously
reported CBS on their territories (for example, ProMED-mail posts
http://promedmail.org/post/20130508.1698543,
http://promedmail.org/post/20110318.0857, and
http://promedmail.org/post/20140306.2316298). Consequently, the
outbreak reported above is unfortunately not suprising. The suggestion
that the disease was introduced from Zambia's neighbours seems
plausible, but considering the wide distribution at the current time,
this may not have been a recent event.

Maps
Zambia, with provinces:
<http://ontheworldmap.com/zambia/zambia-political-map.jpg>
Africa, overview:
<http://ontheworldmap.com/africa/africa-political-map.jpg>
HealthMap/ProMED-mail maps:
Luapula Province, Luapula, Zambia:
<http://healthmap.org/promed/p/2940>
Northern Province, Northern, Zambia:
<http://healthmap.org/promed/p/2938>
North-Western Province, North-Western, <Zambia:
http://healthmap.org/promed/p/32482>

Pictures
Cassava brown streak symptoms:
<http://cdn.wn.com/pd/85/4f/39ea54dafdb1c1843bd628b012e7_grande.jpg>
(tubers),
<http://www.sciencemag.org/content/327/5967/804/F7.medium.gif>
(tubers), and
<https://3c1703fe8d.site.internapcdn.net/newman/gfx/news/hires/2013/cassavabrief.jpg>
(leaf)
Cassava with CMD symptoms:
<http://www.oisat.org/images/cassavamosaicd.jpg> and
<http://www.apsnet.org/publications/apsnetfeatures/Article%20Images/cassava2.jpg>
Comparison CBS and CMD symptoms:
<http://www.rtb.cgiar.org/wp-content/uploads/2013/05/IITA.jpg>
Whiteflies:
<https://apps.rhs.org.uk/Advice/ACEImages//SW1244_790940.jpg>

Links
Additional news stories:
<https://zambiareports.com/2018/09/17/cassava-infection-hits-8-districts/>
and
<http://www.xinhuanet.com/english/2018-09/18/c_137475917.htm>
Information on cassava brown streak:
<https://www.cabi.org/isc/datasheet/17107>,
<https://www.plantwise.org/KnowledgeBank/Datasheet.aspx?dsid=17107>,
<https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5429390/> (diagnosis),
<https://www.sciencedirect.com/science/article/pii/S0885576518300523>,
<https://www.sciencedirect.com/science/article/pii/S0168170217301533>
(control), and
<http://www.new-agri.co.uk/01-1/develop/dev01.html>
CBS viral variants and strains:
<https://www.hindawi.com/journals/av/2012/795697/> and
<https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0139321>
CBS reviews:
<https://onlinelibrary.wiley.com/doi/full/10.1111/mpp.12613>,
<https://phys.org/news/2013-03-cassava-problem-genomics-approach.html>,
and
<http://www.rtb.cgiar.org/blog/2013/05/06/scientists-alarmed-by-rapid-spread-of-brown-streak-disease-in-cassava/>
Information on cassava mosaic:
<https://www.cabi.org/isc/datasheet/2747>,
<http://www.apsnet.org/publications/apsnetfeatures/Pages/cassava.aspx>,
<https://virologyj.biomedcentral.com/articles/10.1186/1743-422X-9-67>,
and
<http://oisat.org/pests/diseases/viral/cassava_mosaic_disease.html>
Virus taxonomy via:
<https://talk.ictvonline.org/taxonomy/>
_B. tabaci_ whiteflies, taxonomy and biotypes:
<http://www.issg.org/database/species/ecology.asp?fr=1&si=106> (with
pictures)
- Mod.DHA]

[See Also:
2017
----
Mosaic disease, cassava - Malawi
http://promedmail.org/post/20170330.4935330
2016
----
Brown streak, cassava - Uganda: (Lango)
http://promedmail.org/post/20160406.4143364
2014
----
Brown streak, cassava - Rwanda
http://promedmail.org/post/20140905.2750165
Brown streak and mosaic, cassava - Tanzania: (MA, MZ)
http://promedmail.org/post/20140306.2316298
2013
----
Brown streak, cassava - Angola, Congo DR
http://promedmail.org/post/20130508.1698543
2012
----
Brown streak, cassava - Uganda: (AD)
http://promedmail.org/post/20120706.1191742
2011
----
Brown streak and mosaic, cassava: combined outbreak risk
http://promedmail.org/post/20110829.2643
Brown streak, cassava - Malawi: alert
http://promedmail.org/post/20110318.0857
2010
----
Brown streak, cassava - East Africa: new strain
http://promedmail.org/post/20100525.1735
Brown streak & mosaic, cassava - Africa: vector control
http://promedmail.org/post/20100507.1482
and additional items in the archives]
.................................................sb/dha/tw/lm
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