Tobacco mosaic virus. (TMV).

1. Introduction.
   Tobacco mosaic virus is a disease that infects the tobacco and some other members of nine families which included solanaceae and at least 125 species ,including tobacco,tomato,pepper,cucumber,and a number of flowers.
2. Shape.
   It is a rod shaped virus. It is about 300 nm lomg and its diameter is 15 nm.It is a single stranded RNA which is protected by a capsid formed of protein sub-units.
   Its capsid is consisted of 2130 molecules of coat protein and one molecule of genomic single strand RNA 6400 bases.
3. Structure.
   The coat protein is a helical like structure around the RNA which forms a hairpin loop structure.

1. Systematic position.
   Division: VIRA
   Subdivision: Ribovira
   Class: Ribohelica
   Order: Virales
   Family: Marmotwceae
   Genus: Marmora
2. History.
   TMV was the first virus which is discovered.Although it was known from the late 19th century that an infectious disease was damaging tobacco crops. Its agents was virus.It is the first pathogen to recognized as a virus.
   In 1886,Adolf Mayer who first described the tobacco mosaic virus could be transferred between plants , similar to bacterial infection.
   In 1892 Dmitri Ivanovsky, who gave the first evidence for the existance of a non-bacterial infectious agent.
   Later, in 1903, Ivanovsky published a paper describing abnormal crystal intracellular inclusion in the host cell of affected plants of tobacco .
   Beijerinck coined the term of “virus” to indicate the causal agent of tobacco mosaic disease was of non-bacterial nature.It was the first virus which is crystallized. It is achieved by Wendell Merediyh Stanley. In 1935 who also discovered that tobacco mosaic virus remains active.
   6.Physicochemical properties.
   TMV is a very stable virus. It can withstand a temperature as high as 93 degree celcious. It has a very wide survival range.It can sustain its stable form.
   TMV has an index of refraction of about 1.57.
   7.Symptoms.
   The first symptoms of the tobacco mosaic virus disease is a light green coloration between the veins of young leaves.This is followed quickly by the development of “mosaic” or mottled pattern of light dark green areas in the leaves.Thiese apears as thick, elevated, blister-like areas.In this form, large dead areas develop in the leaves. The plants growth stopped there is downward curling and distortion of leaves.
   These symptoms are develop specially on young leaves. The plant death not occur quickly, but if the virus attack on the plant in very early stages the growth of that plant stunned.
   Infected leaves may be curled, puckered, or elongated.
   However, if TMV attacks on the crops of apple and grape, it is almost symptomless.
   
3. Transmission & Infection.
   TMV survives in infected leaves and stalks in the soil or on the surface of the affected seeds.The virus initially enter a plant by wounded tissues of sedlings or transplant in the fields.Then it spread in the whole field.
   The infection spread by parenchyma cells and moving through phloem.

TMV is transmitted through mechanical sap, grafting and dodder.The most common method of transmission in the field is through hands of worker handling and healthy plants.It enters the neighboring cells through plasmodesmeta. TMV can also be transmitted from one plant to another by direct contact.

9.Replication.
The entry of virus into the host is mechanical.TMV un-coated itself to release its viral RNA strand. Then the viral genome further replicates to produce multiple mRNAs.The resulting mRNAs encode several proteins, including the coat protein and an RNA -development RNA polymerase (RdRp), as well as the movement protein.Thus TMV can replicates its own genome.After the coat protein and RNA genome of TMV have been synthesized, they quickly assemble into compete TMV virion.

1. Control of Disease.
   We can control the disease by the following precautions.These are given below.
2. The sanitation is the main method of disease control.The crop should be grown at least two years in the fields where diseased crop was grown.
3. Removal of affected plants and weeds that cause the infection from the fields.
4. Workers in the fields must wash their hands with 3% trisodium phosphate and soap.
5. TMV resistant varieties may be grown.
6. Coconut milk is the most effective treatment of TMV.