Transmission of Plant Viruses
Plant viruses are not disseminated as such by wind or water. Viruses are transmitted from plant to plant in a number of ways such as vegetative, propagation, mechanically through sap and by seed, pollen, insect, mites, nematodes, dodder and fungi.
1. Transmission by Vegetative Propagation:
Plants are propagated vegetatively by budding or grafting or by cutting or by the use of tubers, corms, bulbs or rhizome. Any virus present in the mother plant from which these organs are taken will almost always be transmitted to the progeny. Transmission of viruses may also occur through natural root grafts of adjacent plant.
2. Mechanical Transmissions:
Such transmissions may takes place between closely spaced plants after a strong wind by contact , when plants are wounded during cultural operations, virus infected sap adhering to the tools, worker hands or cloth accidently transmitted to the subsequently wounded plants.
E .g. Potato virus: (PV-X,TMV on Tobacco and Tomato)
3. Natural Modes of Transmission:
This includes air borne transmission through insects and mites and soil borne transmission through nematodes and fungus.
4. Seed Transmission:
About 100 viruses have been reported to be transmitted by seed only a small portion (1-30) of the seed derived from virus infected. Plant transmit the virus. Frequencies varies with the host virus combination. Tobacco ring spot virus is soybean may be transmitted by almost all 100% of the seed of infected plant.
28-94% in squash mosaic virus in musk melon.
50-100% in barley stripe mosaic virus in barley.
Mosaic of Datura stramonium to the tune of 79%.
5. Pollen Transmission:
Virus transmitted by pollen may infect not only the seed but also seedling that will grow form it. Ex. Tomato and Tobacco black ring virus.
6. Dodder Transmission:
Several plant virus can be transmit ted from one plant to another plant through the bridge formed between the two plants by twining the stem of parasitic plant, dodder ( Cuscuta species), green strain of cucumber mosaic virus on N. glutinosa, lucern ( alfa-alfa) , mosaic virus to tobacco potato stem mottle virus to tobacco. Bennett (1940) showed dodder transmission, sugar beet curly top virus (BCTV), cucumber mosaic virus.