To maintain themselves in nature, viruses are transmitted from generation to generation (vertical transmission) or infect other plants of the same or of different species (horizontal transmission).
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Vertical transmission occurs :
- by organs of affected plant tissues necessary to the vegetative reproduction (bulbs, cuttings, graft). Plant multiplication by vegetative methods needs a particular care so as to produce sound material. The curative methods enabling to get rid of viruses mainly consist in cultivation of meristems and/or the practice of thermotherapy.
- by pollen and seed, in certain rarer cases.
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Horizontal transmission can be done :
- by animal vectors such as insects,
- by mechanical wounding : artificial inoculation by means of abrasive means and natural inoculations by means of contact of organs
- by contacts between protoplasms (grafts, intermediate vector plants, …).
Once the virus has been transmitted, it can move into the organs of the plant ( systemic infection) or limit itself to localised places (local infection).
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