Tobacco Mosaic Virus:
Tobacco Mosaic Virus (TMV) contains a central core of RNA. It elongated rod is twisted into a uniform spiral to form, in gross form, a hollow rod. The RNA core remains surrounded by a protein sheath. Under appropriate conditions, the viral particles induce the formation of a crystalline structure known as an inclusion body. The crystalline inclusion body of tobacco mosaic is known to contain true virus particles. The TMV remains active in extracted host plant juice for up to 25 years. It is infectious in dilutions up to 1:1000000 and withstands heat up to 90°C for 10 minutes.
Symptoms of Tobacco Mosaic Virus:
On the younger leaves of tobacco plants the veins may show a clearing and later this may be followed by mottling. As the leaves enlarge, abnormally dark green spots appear which develop into irregular crumpled blister areas while the remainder of the tissue becomes more and more chlorotic. Plants are stunted in various degrees. The diseases characterized by mottling or variegation of leaves are referred to as ‘mosaics‘.
Transmission of Tobacco Mosaic Virus:
Dissemination of TMV from plant to plant takes place through mechanical transmission. This virus is so very infectious that this may be carried from one plant to another by almost any sort of contact. Workers in the tobacco field may carry the tobacco virus from one plant to another on their hands or clothing. The TMV isn’t destroyed in the manufacture of smoking tobacco. Thus, should cigarettes or biris made from virus-infected leaves be smoked by a field worker? He may easily carry the virus on his hands to healthy plants.
Control Measures of Tobacco Mosaic Virus:
1. One should avoid infested soil and the use of tobacco refuge on land on which tobacco is to be grown.
2. Seedbeds should be steam sterilized and well removed from tobacco warehouses.
3. One should avoid contamination of hands with the virus from tobacco products. Though washing with soap is an effective practical means of cleaning hands between operations.