The virus programme, which was initiated in 1978, has given priority to breeding for resistance to the economically important potato viruses Y (PVY) and leafroll (PLRV). Sources of resistance to PVY were initially obtained from the Scottish Crop Research Institute, the Netherlands and Germany. Many of the accessions possess gene Ny from Solanum demissum which provides comprehensive hypersensitive resistance. Some have excellent PLRV resistance, and also field immunity to potato wart disease (Synchytrium endobioticum). More recently the Solanum stoloniferum gene Ry for extreme resistance, from sources such as the varieties Corine and Pirola, has been introduced into the programme, and we have also acquired accessions identified as PVY resistant by the International Potato Center (CIP). The development of lines duplex for Ny or Ry is in progress.

Breeding for resistance to infection with PLRV has utilized those PVY-resistant parents which also have PLRV resistance, and more recently accessions from CIP. Since PLRV resistance is less effective under severe infection pressure we are investigating the possibility that the gene for lethal hypersensitivity to PLRV present in varieties such as Monza, when incorporated into clones already possessing resistance to infection, will reduce incidence of the virus in the field. Tetraploid hybrids derived from S. brevidens will also be investigated as sources of PLRV resistance.

Many useful parental lines have been identified and potentially high-yielding clones possessing high resistance to PVY and PLRV are at all stages of selection.