Potato virus Y Potyviridae and Potato virus X Flexiviridae are one of the most important viruses in Solanaceae. Breeding for virus resistance, a major component of most breeding programs is generally regarded as being the best strategy for long-term virus control. This approach is hampered, however, by the limitation of suitable sources of resistance. In the past, the introgression of genetic sources for plant resistance has been successfully applied to develop a limited number of virus-resistant cultivars. Although plant breeding for virus resistance still has great potential, there are limitations to this conventional approach. Selection of new viral resistant potato cultivars is the key to success in plant breeding programs. The utility of new tools is required to assist the screening and selection of new genotypes resistant to PVY and PVX. The objectives of this study are to develop biochemical and molecular markers for resistance to PVY and PVX and to detect Ryadg and Ryfsto genes conferring extreme resistance to PVY and Rx resistant gene to PVX, as well as sequence alignment analyses of the isolated and sequenced Ry and Rx genes.