Ecology, epidemiology

- Conservation, sources of viruses

The alfalfa mosaic virus ( Alfalfa mosaic virus , AMV) is very polyphagous. It is able to artificially infect a large number of hosts, more than 400 plant species belonging to 50 botanical families. About 150 herbaceous or woody plants can harbor it in the wild. It is therefore easily preserved from one season to another by means of a few weeds, but also of several cultivated plants. Apart from alfalfa, which seems to constitute the most important reservoir for virus, a certain number of them can serve as a source of inoculum during winter or summer (tomato, pepper, potato, celery, beans, peas. , Clover...).


- Transmission, dissemination

From infected plants, AMV is transmitted to other plants via aphids, in a non-persistent fashion. These very quickly acquire viral particles adsorbed at the level of their stylets and integuments of their mouthparts, during brief "test" bites. They are able to transmit them immediately, but for a short period not exceeding a few minutes to a few hours. More than ten species of aphids are capable of transmitting AMV to plants (in particular Myzus persicae and Aphis craccivora on lettuce).

Seed transmission occurs in a few plant species, especially alfalfa and peppers, but not lettuce.

The dissemination of AMV is mainly carried out by aphids; it therefore depends on the nature of the epizootics of these insects. Several abiotic factors play an essential role in the biology and efficiency of aphid flights:
- the wind conditions their distribution;
- the temperature acts on the growth of salads, the multiplication of the virus and aphids respectively in and on the plants;
- the culture environment; the proximity of other susceptible contaminated crops (and in particular alfalfa) and numerous virus-infected weeds favors contamination;
- finally, to these factors, we can add regional cultural situations and practices such as the arrangement of the plots, their orientation with respect to the wind, their possible protection by hedges, the conservation of plants that are reservoirs for viruses, etc.