As a result of many decades of potato breeding in Keszthely, Hungary, numerous varieties resistant to the pathogens attacking potato have been developed using wild Solanum species as resistance sources. In order to simplify the time-consuming breeding process, the present research project involved the development of a SCAR marker correlating with the Rysto gene, originating from the Solanum stoloniferun species and conferring extreme resistance to the potato Y virus (PVY), using sequence information from a RAPD marker linked to the gene. The usefulness of the marker was tested on 21 varieties resistant or susceptible to PVY and it was found to provide efficient identification of genotypes carrying the Rysto gene. Based on its linkage to a new chromosome-specific anchor marker (Cat-in2), identified by means of the intron-targeting method not previously used in potato research, the Rysto gene was localized on chromosome XII.