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POTATO VIRUS Y - SOUTH AFRICA: NEW STRAIN, SPREAD
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A ProMED-mail post
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International Society for Infectious Diseases
<http://www.isid.org>
Date: 5 Nov 2009
Source: Farmer's Weekly, South Africa [edited]
<http://www.farmersweekly.co.za/index.php?p[IGcms_nodes][IGcms_nodesUID]=46180ab23928a9f5f6623925775c2e06>
The PVY-NTN threat to the South African potato industry is a new
recombinant of the PVY-N and PVY-O potato viruses. Potato SA's Dr Ben
Pieterse said it's not certain what caused the recombinant, but
researchers regard the disease as "serious". He explained that the
virus causes tuber symptoms which affect marketability. These can be
described as uneven brownish rings that become necrotic followed by
tissue collapse. Occurrence has increased significantly since the
virus was made public in 2005.
There are still aspects of the disease that aren't understood. "It's
known that cultivars differ in symptom expression," explained Dr
Pieterse. "In addition, environmental factors also play a role in the
degree of symptoms. The problem is aggravated by the fact that
symptoms develop further during storage and are also promoted by high
temperatures during the growing season."
The new virus is spread in the same way as PVY, by aphids. The aphid
only stays infected for a very short period of time. This makes it
very difficult to control the disease by spray programmes. Dr Pieterse
said the most important control measure is to plant certified seed and
resistant cultivars. "High infestation is caused by increased aphid
numbers, and the use of farm-kept seed potatoes presents a higher risk
for infestation," he said.
[Byline: Annelie Coleman]
--
Communicated by:
ProMED-mail <promed@promedmail.org>
[_Potato Virus Y_ (PVY; type member of genus _Potyvirus_) is one of
the most damaging potato viruses affecting crop yields and tuber
quality. PVY can also affect tomato, capsicum, and some other related
species. It is transmitted by aphid vectors in a non-persistent
manner, with _Myzus persicae_ being the most efficient vector. PVY can
also be spread by mechanical means, plant-to-plant contact, or with
infected planting material such as seed tubers. Disease management of
PVY and other potato viruses relies largely on clean planting material
and use of resistant crop varieties, but reduction of available virus
reservoirs and vector numbers may also be useful.
The PVY isolates reported so far have been classified in 3 main
strains, PVY-N, PVY-O, and PVY-C, according to leaf symptoms induced
on the experimental host _Nicotiana tabacum_. PVY-N isolates have been
divided into 2 groups, one of which causes "potato tuber necrotic ring
disease". It is referred to as PVY-NTN (necrotic group [N] and
inducing tuber necrosis [TN]) and is the most virulent strain of PVY.
It has been suggested that PVY-NTN isolates may have resulted from
natural combination of local strains of PVY-N with PVY-O or PVY-C.
If virus-infected seed tubers are used, virus populations and numbers
of co-infecting species and strains will build up with every crop
cycle. Even more severe problems may result if viruses in infected
seed tubers are moved to a different area where they may combine with
local pathogen populations and/or encounter lack of host resistance.
The emergence of new PVY strains and the associated risk posed by the
use of farm-saved seed tubers was also reported earlier in 2009 from
Europe (ProMED-mail posts 20090703.2396 and 20090212.0628).
Map of South Africa:
<http://www.safarinow.com/destinations/South-Africa/south-africa-map.gif>
Pictures
PVY symptoms on potato:
<http://www.inra.fr/hyp3/images/6034404.jpg> (leaves),
<http://www.umext.maine.edu/images/PVY.jpg> (leaves),
<http://www.inra.fr/hyp3/images/6034401.jpg> (plant), and
<http://www.ascenion.de/fileadmin/ascenion/Technology_Offers/Agro_Technology/Plant_Virus_Resistance.jpg>
(tubers)
PVY symptoms on tomato leaf:
<http://www.avrdc.org/photos/tomato_diseases/PVY_01.jpg>
PVY particles, electron micrograph:
<http://www.ppi-bg.org/i/sn5.jpg>
Aphid vector _Myzus persicae_:
<http://www1.agric.gov.ab.ca/$department/deptdocs.nsf/ba3468a2a8681f69872569d60073fde1/7e2e0b314359964987256b1100742a53/$FILE/h_myzus_persicae_adult.jpg>
Links
Information on _Potato virus Y_:
<http://www.inra.fr/hyp3/pathogene/6potviy.htm>,
<http://www.oregon.gov/ODA/CID/PLANT_HEALTH/profilepvy.shtml>
Information on PVY and other potato viruses:
<http://www.umext.maine.edu/onlinepubs/htmpubs/2492.htm> and
<http://vegetablemdonline.ppath.cornell.edu/factsheets/Virus_Potato.htm>
Review and diagnosis of PVY strains:
<http://www.virologyj.com/content/6/1/48>
PVY taxonomy and description:
<http://www.ncbi.nlm.nih.gov/ICTVdb/ICTVdB/00.057.0.01.001.htm>
- Mod.DHA]
[see also:
Potato virus Y - Switzerland: new strains 20090703.2396
Viruses & nematodes, potato - UK: alert 20090212.0628
2002
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Potato virus Y, necrotic strain - USA (north west) 20021001.5434
1997
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Potato viruses - Saudi Arabia 19970414.0796
Aphis gossypii: new potato virus vector? - UK 19970113.0059]
.......................................dha/msp/jw
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