November 12, 2005
From: European Plant
Protection Organization (EPPO), Reporting Service, 2005 No. 7
[edited]
In 2004/2005, during routine surveys by the regional services of
the NPPO of Morocco on sugarbeet crops, rhizomania-like symptoms
were observed on a plot of approximately 30 ha near Tadla (Beni
Mellal province) in central Morocco. Symptoms were characterized
by vein yellowing, wilting of leaves and proliferation of roots.
Sample analysis confirmed the presence of Beet necrotic yellow
vein benyvirus [BNYVV] (causing rhizomania - EPPO A2 list).
It is suspected that importation of 2nd-hand agricultural
machinery from Italy was the source of this infestation.
According to the EPPO Secretariat, this is the 1st report of
rhizomania in Morocco. Official control measures are being taken
and include the use of tolerant cultivars, distribution of
information to growers, and designation of the field as a
quarantine area. Surveys are continuing in the vicinity of the
infected field.
The situation of BNYVV in Morocco is officially declared as
follows:
Present, localized focus in the region of Tadla, under official
control.
Source: NPPO of Morocco, 2005-07.
--
ProMED-mail
<promed@promedmail.org>
[Rhizomania, "crazy root" or "root
madness, is one of the most serious diseases of sugarbeet. It
can greatly reduce sugar yield and tonnage. Further losses to
producers in infested areas can result when movement of
agricultural products is restricted by quarantine laws.
Beet necrotic yellow vein virus (BNYVV) is the causal agent of
rhizomania. The soilborne fungus, _Polymyxa betae_ (Pb), serves
as a vector of BNYVV by carrying the virus to healthy roots. The
association of BNYVV with Pb is an unusual biological
relationship that results in rhizomania development when a
susceptible host is present and conditions are favorable for
infection. Sugar beet serves as a host for both Pb and the
virus. Although some weeds, primarily in the goosefoot family,
also serve as hosts, their role in rhizomania development is not
clear.
Data from field surveys in Wyoming and Nebraska showed that Pb
is relatively common and, when not carrying BNYVV, usually
causes little damage to the sugar beet. Because BNYVV is spread
is favored by conditions that favor both infection of sugar beet
and rhizomania development.
Pb forms 2 types of spores during its life cycle, resting spores
and motile zoospores. Clusters of tiny, thick-walled resting
spores, also called cystosori, enable Pb to survive in soil or
in resting spores for 15 years or longer in the absence of a
suitable host. When soil conditions become favorable for
infection, germination of the resting spore is triggered by the
presence of a host-plant root. As resting spores germinate,
motile zoospores are released that actively swim to the root
surface where new infections occur.
Once a field becomes Pb-infested, crop rotation will not
appreciably reduce disease risk because of the long-term
survival of viruliferous cystosori. However, some soil fumigants
such as those containing 1,3-dichloropropene may kill enough
cystosori to reduce disease development to acceptable levels.
Fumigation treatments are very expensive, and research is being
done to determine their efficacy and conditions under which they
should be used. Expenses associated with fumigant application
may be justified, because significant sugar beet acreage is
routinely treated with 1,3-dichloropropene for nematode control.
The use of soil-applied fungicides has not been effective for
rhizomania control in infested fields.
Currently available tolerant or resistant varieties perform
satisfactorily in the presence of rhizomania in some production
areas, especially when used in combination with soil fumigation.
However, these varieties must be tested in each production area
to evaluate their performance under local environmental
conditions and production practices. They also must be evaluated
for performance after exposure to local diseases, insects, and
weed pests. Research on the development of resistant varieties
is progressing rapidly, with some having dual resistance to both
rhizomania and Beet curly top virus.
Management of rhizomania involves application of phytosanitary
measures such as containment of spread in the affected area,
avoiding movement of soil from infested areas, use of rubber
boots or disposable footwear, and cleaning and removal of
adhering soil at the field site. Moreover, soil contractors,
machinery, and highway vehicles should be removed. Removal of
soil at the field site is necessary because resting spores are
extremely difficult to kill with chemical disinfectants,
especially when associated with soil. Therefore, infested soil
removed from footwear and equipment is likely to remain infested
and will serve as a potential source of contamination.
Links:
<http://www.sbreb.org/brochures/wyoming/wyoming.htm>
<http://www.defra.gov.uk/planth/pestnote/rhizo.htm>
<http://www.ecpgr.cgiar.org/Workgroups/beta/article_Beta.pdf>
- Mod.DH]
[see also in the
archive:
Quarantine pest surveys,
EPPO - Latvia 20050108.0057
Quarantine pests, new data - EPPO (03): Lithuania 2004
20051104.3226
2004
----
Quarantine pests, new data - EPPO (05) 20041106.3007
2003
----
Rhizomania, sugar beet - USA (Great Lakes region) 20030210.0356
Rhizomania, sugar beet - Egypt 20030719.1769
2002
----
Rhizomania, sugar beet - USA (Oregon, Washington) 20020124.3369
EPPO alert list: new listings (03) 20020417.3974
Beet soil-borne pomovirus, sugar beet - Iran 20020418.3980
EPPO Alert List: new listings (04) 20020524.4307
Quarantinable plant pests - Latvia 20020726.4867
Beet necrotic yellow vein, sugar beet - UK (England)
20020827.5164
Beet viruses, sugar beet - Syria 20021218.6089
2001
----
Beet necrotic yellow vein benyvirus - Denmark 20010509.0893
Rhizomania, benyvirus, sugar beet - UK 20011121.2851
Beet pomovirus Q, sugar beet - Belgium 20011219.3065
2000
----
Beet necrotic yellow vein benyvirus - Syria 20000124.0123
Beet necrotic yellow vein benyvirus - Sweden 20000525.0824
Beet necrotic yellow vein benyvirus - Sweden (02) 20001128.2076]
