Potato virus X – PVX

Causal agent(s) and transmission

Potato virus X is a member of the Potexvirus group with a world-wide presence in potato growing areas.

Transmission of PVX to potato plants occurs mainly by contact. PVX is transmitted mainly mechanically, through contact between the plants subjected to friction (wind, machines, man, animals, etc.). In practice, most infections are transmitted by farm machinery – such as sprayers or tractors – passing through the crops. In fact, PVX is very contagious by contact as it is highly concentrated in plant tissues and its stability in the sap is rather long (thermal inactivation point between 68°C and 76°C, dilution end-point between 10⁵ and 10⁶ and infectivity retained at 20°C for several weeks).

Transmission by vectors such as grasshoppers or biting insects has been reported but seems limited compared to transmission by contact.

The host range of PVX is mostly limited to the Solanaceae, although some plants are susceptible in other families, e.g. in Amaranthaceae and Chenopodiaceae

The incidence of PVX on potatoes is usually low as PVX infection causes mild mosaic symptoms and yield losses are limited between 10 and 15%. However, in the case of co-infection with other viruses, the effects of PVX are much more severe.

Symptoms on foliage

Depending on the cultivar, the viral strain and the co-infection with other viruses, the symptoms caused by PVX range from complete latency, mild mosaic to severe mosaic and leaf distortion. Symptoms due to PVX infection occurring during the current season are often absent. Symptoms of secondary infections are more readily distinguished (photos 1 and 2) with the presence of mosaic symptoms limited by veins (photos 3 and 4), with no leaf distortion apart from some exceptions (photo 5); in general, symptoms are often latent or mild.

The symptoms can be seen more easily during the active growth of the plant and in weak sunlight.

Mixed PVX infections with other viruses generally cause severe crinkling or leaf drop streak symptoms.

Control

The development of PVX infection results from a combination of different sources of viral infection, mainly within the field (volunteers and seed tubers) and nearby potato crops, the dissemination with farm equipment – such as sprayers or tractors – passing through the crop and the susceptibility of the potato cultivar.

The use of certified seed potatoes is the main control measure for the production of ware or processed potato crops.

For seed potato production, there is a range of measures designed to limit the development of infection by PVX, including:

• testing and renewing the seed potato stocks;
• limiting the use of farm machinery for pre-basic and basic seed material, for example with specific trails or paths for the tractor wheels;
• washing and/or disinfecting the machinery before entering a seed crop and always starting spraying in the fields with higher quality grades;
• early roguing to prevent the mechanical transmission of PVX by machinery.