Strains of Potato virus Y in Dutch seed potato culture

Over the recent years Potato virus Y presents a growing problem in Dutch seed potato culture. In recent years a significant % of seed potato lots was de-classified due to PVY infections. This apparent increase in PVY infections was unexpected since no increase in field symptoms were observed and the numbers of aphids caught in the yellow water traps and high suction traps showed a clear decline over the last 10 years.. In 2006 a project was initiated to investigate the possible causes for the increase in PVY infections. Firstly a survey was performed on potato plant material grown in the control fields of the General Inspection Service (NAK), to determine the distribution of PVY strains, including the ‘new’ PVYNTN and PVYN-Wilga strains. This plant material is representative of Dutch seed potato stocks. In the control fields tubers, which were taken from stocks tested by ELISA, are grown to evaluate the earlier laboratory tests. Samples were tested by ELISA using polyclonal and monoclonal antibodies. All ELISA positive samples were further tested for the presence of PVYN, PVYO, PVYNTN and PVYN-Wilga by two molecular methods and in addition inoculated onto a set of indicator plants. Results showed that PVY strains populations in the Netherlands shifted significantly and that PVYNTN and PVYN-Wilga are more spread then generally assumed. In addition to field monitoring and post-harvest control, the control system for potato viruses, including PVY in the Netherlands, is also based on monitoring the flight data of a selected group of aphids. The aphids caught are counted and assigned a value according to their Relative Efficiency Factor (REF). When the cumulative values reach a certain threshold a date for haulm destruction is set, to prevent virus infections of the tubers. Given the current problems with PVY, this system, developed in the 1980’s, may no longer be sufficient to control the current virus situation in the field. In our project the question is addressed whether a shift in aphid populations has occurred and if the REF’s determined in the 1980’s are still valid for M. persicae and other aphids for the PVY strains found in the Netherlands nowadays. A new system was set up to determine the REF’s for known PVY transmitters and other aphids that are presently caught in the field. Figures of transmission efficiencies of different aphid species for different PVY strains will be presented.