The Rpi-phu1 gene originates from an interspecific hybrid between Solanum stenotomum and S. phureja, and confers a high level of resistance to Phytophthora infestans (late blight) in potato. The Rpi-phu1 was introduced by crossing at the diploid level into the S. tuberosum gene pool and then transferred to the tetraploid level by means of 2n gametes. Tetraploid lines carrying the Rpi-phu1 were selected for further crosses. A molecular marker GP94, linked in mapping population 97?30 with the Rpi-phu1 (6.4 cM), was applied to other unselected populations (2 diploid and 1 tetraploid), and was shown to be useful in marker-assisted selection (MAS) of the resistant individuals. GP94 was applied also in commercial breeding in 2 tetraploid populations. Although the marker allele of GP94, characteristic for the Rpi-phu1 presence, was rare in the S. tuberosum gene pool, it seemed to be common in 2 other sources of resistance to late blight: S. ruiz-ceballosii and S. kurtzianum.