TRANSMISSION BY NATURAL MEANS

Plant viruses being obligate parasites in order to survive, must be spread from one susceptible plant to another and frequently need to be introduced into living cells. They are not disseminated by wind or water. Generally, they don’t cause infection unless they come in contact with the contents of founded living cells like other disease causing agent. The property of transmissibility is the fundamental characteristic of viruses also, the knowledge of ways of virus transmission is important for the following reasons.

1:         A disease is recognized as a virus disease only if it can be transmitted to healthy individuals by some means.

2:         How the viruses spreads in the field is essential for the development of satisfactory control measures.

3:         The interaction between viruses and their invertebrate and fungal vectors are of   considerable biological interest.

INSECT TRANSMISSION

      Majority of plant viruses are transmitted from plant to plant in nature by invertebrate mobile vectors. This is the most common way of the plant viruses and is also economically the most important under field conditions. Almost all type of organisms feeding upon or parasitizing living green land plants are capable of acting as vectors. Thus the assisting organisms are called vectors. They pierce the cells and suck the sap of the plants on which they feed. Later on, when these viruliferous insects feed on healthy plants, the virus acquired earlier, gains access by organism. Insect vector of plant viruses are:

Ø  Aphid

Ø  Whitefly

Ø  Mealy bug

Ø  Thirips

Cotton leaf curl virus is transmitted only through whitefly.

White fly transmission generally resembles persistent circulative transmission by the aphids. White fly is the only vector. Which transmits about 50 virus in 70 host plants. Both nymphs and adults can transmit the virus and females are more efficient then males. In virus transmission vector can acquire the virus during feeding on phloem from 10-60 mints. The latent period in the vector lasts for 4 to 48 hours and virus transmission may continue up to 20 days .vector can retain the virus up to 25 days.