Question

Write about the tobacco mosaic disease.

Answer 1

Hint: Tobacco mosaic virus causes a mottled browning of tobacco leaves, which is economically significant. Other crops, most notably tomatoes, are also infected. The virus is propagated mechanically from infected plants to normal plant leaves that have been scratched or damaged.

Complete answer:
TMV is made up of a nucleic acid molecule (ribonucleic acid; RNA) and a protein covering. A submicroscopic, hard, rod-shaped particle contains the entire virus. The protein coat breaks away once inside the plant cell, and the nucleic acid component commands the plant cell to generate more virus nucleic acid and virus protein, interrupting the cell's normal activities. TMV can only reproduce inside a living cell, but it can remain dormant in dead tissue for years, allowing it to infect developing plants even after the infected plant portion has died. When plant tissue dies, most other viruses die as well.

TMV is most commonly transmitted from plant to plant via workers' hands, clothing, and tools. 'Mechanical' transmission is the term for this type of transmission. When plants are handled, tiny leaf hairs and some outer cells are always injured, leaking sap onto equipment, hands, and clothing. If TMV is present in the sap, it can be transmitted to other plants when they come into contact with it. TMV is not spread by sucking insects like aphids. Chewing insects like grasshoppers and caterpillars can spread the virus, although they're usually insignificant.

TMV and other virus infections are perpetuated by vegetative propagation. Cuttings taken from an infected plant are usually infectious, even if the cutting shows no symptoms right away. Except for a few cells at the terminals of the growth points, virus particles can be found in all sections of the plant. Infected stock plants should be thrown away right away.

TMV can also live in sap that has dried on tools and other surfaces outside of the plant. You have now put TMV on the door handle if you handle a TMV plant and then open a door with that hand. The TMV can be picked up by the next person who opens the door and spread to any plant they come into contact with.

TMV can be found in tobacco products, particularly those containing air-cured tobacco. Most, if not all, TMV is inactivated during the processing of flue-cured tobacco, which is used to make cigarettes. Hands and clothing can become infected with TMV and become a source of virus when tobacco products are handled or kept in pockets. TMV is not disseminated by the smoke of a cigarette.

The symptoms vary depending on the plant type affected and the surrounding conditions. Environmental factors can exacerbate symptoms in certain situations, while others can obscure or conceal them.

Symptoms of TMV infections include:
- Deformity of leaves or developing points stunting mosaic pattern of light and dark green (or yellow and green) on the leaves
- Leaves with yellow streaks (especially monocots)
- Yellow spotting on leaves with pronounced vein yellowing
- High temperatures, insect feeding, growth regulators, herbicides, mineral deficits, and mineral excesses can all induce some of the above symptoms. TMV infections cannot be identified only on the basis of symptoms.

Note: The 126 and 183 kDa replication-associated proteins, the mobility protein (MP), and the structural capsid or coat protein are the four known functional proteins encoded by the tobacco mosaic virus (TMV) (CP). These four versatile proteins collaborate with a variety of host components to ensure successful infection.