Tomato Mosaic VirusDept. of Plant Pathology The Ohio State University, Columbus, OH There are a variety of plant viruses capable
of causing severe economic damage to greenhouse bedding and potted crops.
In recent years impatiens necrotic spot virus (INSV) has received much
press and most growers are relatively familiar with this virus. Recently,
another very destructive virus has become a problem in solanaceous crops
such as petunia and Nicotiana. This virus is tobacco mosaic virus (TMV).
TMV is not a new virus, as a matter of fact, it was the first plant virus
to be identified and it is the most studied of the hundreds of plant
viruses known today. TMV has the potential to be very destructive
particularly if it escapes early detection in the host crop. Growers need
to know what types of symptoms to look for and more importantly what to do
with the infected plants and infested greenhouse after TMV has been
confirmed.
The Pathogen
As mentioned TMV has been studied in great
detail and researchers have accumulated a great deal of information on
it's genetics and biology. TMV, like all plant viruses, is submicroscopic
and can only be visualized with an electron microscope. The host range for
TMV is very large with genera in hundreds of plant families being
susceptible to infection. Many of the commonly-grown greenhouse bedding
plants are susceptible to TMV infection. Hosts such as petunia, Nicotiana,
impatiens and vegetable transplants such as tomato and pepper are all
highly susceptible. The primary way that TMV moves from plant to plant is
via mechanical transmission. This means by physically handling infected
plants with ones hands, pruning implements or watering wands, TMV can
spread from plant to plant. Unlike most other viruses, insects are not of
major concern when dealing with TMV.
Symptoms associated with
infection
In order to identify TMV as soon
as possible it is important that the grower be able to recognize
the symptoms associated in an infected host. Symptoms may vary from host
to host, however, there are a few common symptoms the TMV induces in its
host. One of the most common symptoms associated with TMV infection is
leaf mosaic and flower break. Leaf mosaic is usually accompanied with
leaf distortion which can range from mild distortion to severe distortion. In
most cases the infected plants are stunted and may be yellow. Ringspots on
the leafs that are commonly associated with INSV infection are not
normally seen in plants infected with TMV.
Control
The best way to control TMV is through
prevention. Growers need to do their best to keep the virus out of the
greenhouse. Once in the greenhouse the virus becomes established very
quickly and it takes a great deal of effort to reestablish a virus-free
facility. If plant material is to be started from seed, it is
imperative that growers purchase seed from a producer that can assure the
seed is free of viral pathogens. The cheaper the seed the more likely the
seed will be pathogen-infested. If plants are to be started from cuttings,
the cuttings should be certified virus-free. Most cutting producers go to
great lengths to make sure the mother stock from which the cuttings are
produced is free of all pathogens. If any pre-finished material is brought
into the greenhouse it should be examined carefully for symptoms and if
suspect, it should be tested for TMV. Also, any pre-finished plant
material should be quarantined and randomly tested prior to mixing it in
with the rest of the greenhouse.
What if I find TMV in my
greenhouse?
If TMV is identified in your greenhouse
actions need to be taken immediately in order to keep the virus from
spreading throughout the entire greenhouse. Infected material needs to be
removed from the greenhouse and destroyed. Employees that are handling the
infected plants will need to wash their hands prior to reentering the
greenhouse. If at all possible workers need to wear gloves when handling
infected plants. Even clothing that comes in contact with infected plants
has the potential to move the virus from plant to plant. This virus
spreads from plant to plant easier than any other plant
virus.
Plants within the immediate area of the
infected plants need to be tested regularly for evidence of TMV. Weekly
testing for at least four weeks is necessary to determine the health of
the plant. If plants test negative for TMV for four weeks they are
probably not infected.
All surfaces where the TMV-infected plants
were sitting or surfaces to which infected material has come in contact
should be washed-down with a surface disinfestant such as GreenShield,
Physan, Zerotol or TSP (trisodium phosphate). TMV has the capability to
survive outside the host plant on surfaces for an extended period of time.
This surface disinfesting should be carried out routinely throughout the
remainder of the growing season. Once the greenhouse is empty, the entire
facility should be sprayed down with a disinfestant before any new plant
material enters the facility for the following growing
season.
TMV should be taken very seriously and no
corners should be cut to remove it from the production
facility.
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