(PVA)

Aphids are the agents responsible for transmitting the virus A. Virus A is a non-persistent type virus because it remains alive for only one to two hours in the aphid after the latter has become infectious by stinging a contaminated plant.

In reality, only aphids transmit this type of virus.

The appearance of symptoms on a given crop depends on the variety and the weather conditions. However, with current-year contamination, the symptoms include slight and transient mosaics that are particularly visible in cloudy weather. These mosaics appear as a discoloration of those parts of the leaf not bounded by veins. This aspect can be reinforced by placing a sheet of white paper under the observed leaf.

On the other hand, with contamination in the previous year, the symptoms can be much more pronounced, resulting in waffling/embossing of the leaves combined with a glassy appearance (right picture) and a more or less marked mosaic depending on the variety (pictures below).

In the case of mixed infection with virus X or virus Y, the symptoms can be very pronounced.

Virus A symptoms vary strongly depending on weather conditions (they are easier to see in cold and cloudy weather), as well as on the viral strain and variety.

• Use of healthy seed potatoes resulting from genealogical selection;
• Production in a favourable environment, seed testing and renewal;
• Roguing of virus-infected plants;
• Haulm defoliation before maturity;
• Treatment with mineral oils.

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