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