POTATO VIRUS Y (PVY) is the reason for most potato seed lot downgrades by seed certification agencies. This disease has become increasingly difficult for seed growers to deal with due (mostly) to the rapid spread of recombinant PVY strains (e.g., PVY-N:O, PVY-NTN, and PVY-N-Wi) that produce mild symptoms that are difficult to rogue.
PVY SYMPTOMS: All of the plants shown above are affected by seed-borne PVY, but symptoms vary depending on the PVY strain and the cultivar it infects. A characteristic symptoms involves a yellow to light green mottling of leaves, a.k.a. mosaic. The mosaic can be mild (not shown), moderate (A), or severe (B). Some cultivars have a hypersensitive reaction to PVY that results in dark brown necrotic streaks on the leaves (C), which may be followed by leaf drop.
Click HERE for more pictures and information about PVY symptoms and diagnosis.
SOME PVY STRAINS CAN CAUSE TUBER SYMPTOMS: The pictures below show Alturas cv. plants affected by different strains of PVY. Some of the recombinant PVY strains, like PVY-NTN, can cause potato tuber necrotic ringspot disease (PTNRD) in some cultivars. PTNRD results in necrotic rings on the tuber surface that sometimes crack and extend into the tuber flesh.
HOW TO MANAGE PVY: The best thing you can do to minimize PVY in your crop is to start with clean seed. It is important to buy limited generation seed (certified seed) known to have little to no detectable PVY. Get a copy of the health certificate and scrutinize the results from field inspections and testing.
For more information about PVY, including more management recommendations, read this article "Why Potato Virus Y Needs Your Attention".