The occurrence of PVYO, PVYN, and PVYN:O strains of Potato virus Y in certified potato seed lot trials in Washington and Oregon

Totals of 960 and 286 certified potato seed lots from locations across North America were planted in trials in Washington and Oregon, respectively, in 2001 to 2003 and tested for strains of Potato virus Y (PVY). The incidence of PVYO-infected lots averaged 16.4 and 25.9% in the Washington and Oregon trials, respectively. There was a general trend of increasing incidence of the PVYO, PVYN:O, and PVYN strains during this period, as evidenced by more infected cultivars, sites of seed origin, and number of seed growers providing infected seed lots. In particular, there was a dramatic increase in seed lots with the PVYN:O strain from 2002 to 2003. PVYN:O, in contrast to PVYO, which only causes yield reduction, also causes internal and external damage to tubers, making them unmarketable. In 2003, PVYN:O occurred in seed lots originating in eight states and three Canadian provinces. The increased incidence of PVYN:O was likely due to the difficulty in differentiating this strain from PVYO. The prevalence of PVY in potato seed lots documented herein poses a threat to potato production in the United States and suggests that current measures to reduce the incidence of this virus are inadequate.