Strains of Potato virus Y in Dutch seed potato culture

Over the recent years Potato virus Y (PVY) presents a growing problem in Dutch seed potato culture. In the years 2002 – 2004 approximately 10 – 15% of the seed potato lots was declassified because of the levels of PVY infection exceeded quality standards. In 2006 an even higher percentage was reported. Aphid vectors form an important factor in the spread of PVY. However, the increasing levels of infections with PVY are in contrast to the decreasing numbers of aphids caught in the yellow water traps and high suction traps used to monitor aphid flights. In addition to the well-known PVY-N and PVY-O standard strains, several new strains of PVY have been reported of which PVY-NTN and PVY-N-Wilga are currently the best known. Both strains are described as genetic recombinants between PVY-N and PVY-O. The presence and possible spread over The Netherlands of these recombinant strains is not known yet. In July 2006 a survey for PVY strains was done on potato plant material grown in the control fields of the General Inspection Service NAK. This plant material is representative of Dutch seed potato stocks. In the control fields tubers, which were taken from stocks tested by ELISA in 2005, are grown to evaluate the earlier laboratory tests by visual inspection. In the survey over 120 samples showing distinct PVY symptoms were collected from different seed lots. Each sample was tested by ELISA using polyclonal antibodies for the presence of PVY and monoclonal antibodies to distinguish PVY-N from PVY-O/C. All ELISA positive samples were further tested for the presence of PVY-N, PVY-O, PVY-NTN and PVY-N-Wilga by two molecular methods and in addition inoculated on a set of indicator plants. Results show that a significant shift in PVY strains populations in the Netherlands has occurred and that PVY-NTN and PVY-N-Wilga are more spread then previously and generally assumed.