Ecology, epidemiology

- Conservation, sources of viruses

The virus Western beet yellows ( Beet western yellow virus , BWYV) has a host range extremely wide as it can infect about 150 species representing 23 botanical families. The potential sources of virus are therefore very numerous, both in cultivated and spontaneous species. Beetroot, chard, spinach, all types of cabbage, rapeseed, turnip, radish, soybeans, peas, chickpeas, broad beans, some cucurbits, potatoes ... more or less marked symptoms.

Some isolates differ in their host range. For example, some beet isolates do not infect lettuce; of the isolates found on lettuce or cabbage do not or very badly infect beets. These behaviors can now be explained by the 3 viruses responsible for jaundice and described on beetroot (BMYV, BChV and BrYV).
A small proportion of weeds susceptible to this virus show symptoms of interveinal yellowing or reddening, but most behave as healthy carriers (infected plants have no noticeable symptoms). The most common are: wild lettuce, groundsel and sow thistle (asteraceae), capsella and passerage (crucifers), but also purslane, plantains, mallow, amaranth, chickweed ...

The succession in the field of salad crops, vegetable crops (cabbage and cauliflower, rapeseed, spinach) or other sensitive productions during the winter, such as the existence of many sensitive weed species, contribute to the conservation of one inoculum throughout the year.


- Transmission, dissemination

This virus is transmitted by several species of aphids in the persistent mode, involving an extremely specific mechanism. Thus, the virus enters the insect via the alimentary canal and then passes into the haemocoele in which a latency period of 12-24 h is required before BWYV enters the salivary duct and can be transmitted. In fact, it should be about 48 hours between the phase of acquisition of the virus in the phloem vessels of the plant followed by its complete cycle in the aphid and its transmission with great efficiency. The potentially vector aphid then remains infectious for more than 50 days. The virus is retained by aphids during their successive moults but is not transmitted to their offspring.

Among the ten species likely to transmit BWYV, Myzus persicae and Macrosiphum euphorbiae appear to be the most important vectors. Aphis craccivora , Aphis gossypi , Acyrthosiphon solani also transmit it.

The virus is not transmitted by the seed.

The particular nature of the mode of transmission of this virus by aphids, the richness of sensitive plant species capable of serving as a source of inoculum mean that the spread of BWYV is very wide and that it can be done over very long distances. In addition, the importance of epidemics will often be proportional to the level of potentially vector aphid populations.