Potato virus X
The most widespread of all potato viruses and is very easily transmitted
What is it?
PVX is the most widespread of all the potato viruses. It infects all parts of the plant and is also referred to as potato mild mosaic virus, potato latent virus and potato mottle virus. The virus is very easily transmitted and can cause yield loss, although this is generally less severe than with PVY. Usually the loss is less than 20%, although up to 50% has been reported. More severe yield loss can occur where PVX is present in mixed infections with other potato viruses. It persists between seasons in infected seed tubers, and plants produced from these tubers will also be infected.
What does it look like?
There are often no visible symptoms, hence the name ‘latent virus’, although a mild mottling may occur on foliage in some instances in early summer. Occasionally (depending on the virus strain and potato variety) death of the top and then of the whole plant may occur. PVX is most damaging when it is found in combination with PVY, or with another potato virus called PVA. When this occurs, a disease known as ’crinkle’ develops on certain varieties, with symptoms including severe stunting, mottling and browning of leaf tissue, plant death and tuber necrosis.
How is it spread?
The virus is easily transmitted by plant to plant contact, and on machinery, cutting tools, animals and the grower; in some cases the virus can survive for up to six hours on clothing contaminated with infected plant sap. However, there must be wounding and an exchange of plant sap for infection to occur. Unlike PVY, PVX is not transmitted by aphids.
How can I control it?
The disease can be controlled to some extent by the use of certified PVX-free tubers for seed, by avoiding contamination when cutting seed and using PVX resistant cultivars e.g. Cara, King Edward, Maris Piper. Avoid saving seed tubers from crops where high levels of PVX are present.
When do I test?
Symptoms of PVX are likely to be first observed in June/July. Testing should be carried out as soon as symptoms are detected and monitoring for symptoms should continue until the haulm starts to die down.
What do I test?
Where possible, select areas of leaf that shows symptoms of disease. For best results do not use completely dead plant material. As a general guide, samples of leaf material should be approximately 25mm x 25mm.