Virus variability

PVY strains are extremely variable and can be classified according to their biological, serological and molecular properties.

Three main strains of PVY are usually distinguished:

- PVY^O isolates, ordinary strains (old), causing chlorosis symptoms in tobacco and in potatoes with obvious mosaic and leaf curl symptoms and losses in yield
of around 50%;

- PVY^N isolates, more recent strains (new), which induce necrosis in the veins of tobacco leaves and, in the potato, mosaic symptoms with usually slightly lower yield (25-30%);

- PVY^C isolates (with serological properties similar to the PVY^O isolates serological and also causing chlorosis symptoms in tobacco which overcome certain resistance genes in the potato).

More recently, new variants of PVY virus have been identified in the PVY^N strain group:

- PVY^N-W variants, characterised as isolates of the PVY^O strain group with serological tools but with biological properties normally associated with strains from the PVY^N strain group;

- PVY^NTN variant capable of inducing potato tuber necrotic ringspot disease (or PTNRD).

The emergence of PVY variants (PVY^NTN, PVY^N-W) has resulted from genetic recombination events between isolates of the PVY^N and PVY^O strain groups.

This capacity for genetic recombination allows for the extensive variability of the PVY virus and is associated with an increased risk of new emerging isolates with increased pathogenicity (aggressivity and virulence).