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Tobacco Mosaic Virus (TMV)

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deluxestogie

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Tobacco Mosaic Virus (TMV) can significantly reduce productivity in infected plants. TMV is not harmful to humans, but can spread from one plant to adjacent ones (usually by tools or human hands). It is typically not transmitted by insects. Once a leaf has become infected, the virus may eventually spread through the plant's vascular system up to the growth tip, and down to the roots. TMV can remain viable in soil for years.

TMV is apparently not transmitted in the seed coat of clean tobacco seed, but tobacco seed contaminated by chaff from the seed pod can transmit TMV.

5259100.jpg

More photos: http://www.ipmimages.org/browse/subthumb.cfm?sub=6948&area=62

As the virus moves from cell to cell, it eventually reaches the plant's vascular system (veins) for rapid systemic spread through the phloem to the roots and tips of the growing plant.

http://www.apsnet.org/edcenter/intropp/lessons/viruses/pages/tobaccomosaic.aspx
TMV can multiply only inside a living cell but it can survive in a dormant state in dead tissue, retaining its ability to infect growing plants for years after the infected plant part died.

The most important way that TMV can be spread from plant to plant is on workers' hands, clothing or on tools. This is called 'mechanical' transmission. When plants are handled, the tiny leaf hairs and some of the outer cells inevitably are damaged slightly and leak sap onto tools, hands, and clothing. If the sap contains TMV, it can be introduced into other plants when those come in contact with this sap. Sucking insects such as aphids do not spread TMV. Chewing insects such as grasshoppers and caterpillars occasionally spread the virus but are usually not important in spread.

Tobacco products, particularly those containing air-cured tobacco, may carry TMV. Flue-cured tobacco, used in making cigarettes, is heated repeatedly during its processing, thereby inactivating most if not all TMV. When tobacco products are handled or kept in pockets, hands and clothing can become contaminated with TMV and be a source of virus. TMV is NOT spread in the smoke of burning tobacco.
http://extension.psu.edu/pests/plant-diseases/all-fact-sheets/tobacco-mosaic-virus-in-greenhouses

Bob
 

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Tobacco Mosaic Virus (TMV) can significantly reduce productivity in infected plants. TMV is not harmful to humans, but can spread from one plant to adjacent ones (usually by tools or human hands). It is typically not transmitted by insects. Once a leaf has become infected, the virus may eventually spread through the plant's vascular system up to the growth tip, and down to the roots. TMV can remain viable in soil for years.

TMV is apparently not transmitted in the seed coat of clean tobacco seed, but tobacco seed contaminated by chaff from the seed pod can transmit TMV.

5259100.jpg

More photos: http://www.ipmimages.org/browse/subthumb.cfm?sub=6948&area=62




Bob
TMV is not always visible on the leaf. On CT Shade where I used to work, about 10 years ago, we had a pretty bad TMV problem. The damage was only apparent on the cured leaves. There were no visible symptoms on the plants in the field. The Connecticut Ag Station has since developed TMV resistant seed, but the resistance breaks down at temperatures over 90 degrees. Some growers used fields that had been fallow for many years, re-opening shade plantations that had been abandoned in the 1970s. Most of the TMV virus in the soil is gone if the field is rested 3 years and a 10 year rest will make the field entirely free of TMV.
TMV is transferred by tractors, tools and the hands of workers who smoke cigarettes. Because cigarette tobacco is shredded less attention is paid to leaves carrying TMV and the virus is present in commercial cigarette products. We had our workers wash their hands before touching the shade tobacco plants.
 
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