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Monday, January 12, 2009

Cucumber Mosaic Virus

Cucumber Mosaic Virus

Aphid-Transmitted Cucumovirus

Found worldwide:World Vegetable Center

Symptoms vary widely. One of the most common
expressions is a severely stunted, nonproductive plant
that has dull light green foliage with a leathery
appearance but not distinctive foliar markings.
In some cases the leaves become narrow and no
longer expand, while in other cases, small necrotic
specks or ring spots with oak leaf patterns develop.
Sometimes a necrotic line develops across the leaf.
Affected leaves may drop prematurely. Older plants that
are infected may show foliar mottling or no symptoms
on foliage or fruit. Fruit may be wrinkled, bumpy, pale to yellowish
green in color, sometimes with sunken lesions. On
some varieties lines or ring spots may develop.

Conditions for Disease Development

Cucumber mosaic virus (CMV) is not transmitted
through pepper seed. CMV can be mechanically
transmitted but because it is not as stable as TMV,
workers handling infected pepper plants do not as
readily transmit it.
More than 80 species of aphids including the green
peach aphid, Myzus persicae, are an vector of CMV;
weeds are hosts for the virus as well as for the aphid
vectors. The large number of aphid vector species and
natural host reservoirs accounts for the high incidence
of CMV in field plants.
Aphid vectors can acquire and transmit the virus
after feeding for only one minute, but the ability to
transmit it declines quickly. Pepper is not a preferred
host of the green peach aphid, which normally prefers
to feed on cucurbits and other plants. Most epidemics
occur when aphids feed early in the season on weeds
that may be symptomless but serve as reservoirs for
the primary virus inoculum, and then later the virusbearing
aphids colonize the pepper plants.

Pepper varieties resistant to some strains of CMV exist.
Check with your extension agent for resistant varieties
that are available in your region.
Current control measures for CMV are mainly
preventive due to the wide host range of the virus and
the numerous aphid vectors. Vegetable seedlings, other
than pepper, derived from CMV-infected seeds can also
serve as potential primary sources of virus. The use of
virus-free seeds together with the eradication of virus
reservoirs such as volunteer plants and nearby weeds
can be effective in controlling CMV.
Grow seedlings in a structure or seedbed protected
with netting of mesh size of 32 or greater to prevent
aphids from entering. Discard any seedlings or young
plants that show virus symptoms. Do not touch other
seedlings while discarding them. Avoid touching or
handling plants prior to setting them in the field. Dip
hands in milk while handling plants. Do not clip or
damage young seedlings since this increases the
possibility of mechanical transmission of the virus from
contaminated tools or hands. Remove diseased plants
from the field as soon as virus symptoms are noticed.
This will reduce the spread of the virus by aphid vectors.
Disinfect tools, stakes, and equipment before moving
from diseased areas to healthy areas. Hands and tools
may be washed with soap or milk. Work in diseased
areas last, after working in unaffected parts of a field.
Insecticide sprays that are not fast-acting may not
be that effective because the aphids move to other
nearby unsprayed plants when disturbed.
If feasible, plant either very early or very late in the
season to avoid exposing young plants to high or
migratory aphid populations. Prevent aphids from
reaching the pepper crop by covering the planted area
with fine 32-mesh nylon net.
Other less effective measures include: planting
barrier crops that are not susceptible to CMV such as
corn, applying sticky traps, or covering the ground with
an aphid deterrent material like aluminum foil strips.
Another control strategy is to grow trap crops nearby
that attract aphids and then spray these plants with a
contact insecticide to destroy the aphid populations.
Also, spray the pepper crop with mineral oil to delay
virus spread in the field by interfering with aphid
transmission of the virus.


vibhuti arora said...

thanks for the wonderful information you have provided about Mosaic Virus

Vinod Shreni said...

Quite useful and precise info regarding symptomatology and occurence of various viruses in pepper.Vinod Shreni