High-resolution genetical and physical mapping of the Rx gene for extreme resistance to potato virus X in tetraploid potato

The Rx locus in potato confers extreme resistance to PVX. In the F₁ progeny of crosses between the PVX-susceptible cultivar Huinkel and the cultivar Cara (Rx genotype) there was a 1?:?1 segregation of PVX resistance, indicating that Rx in Cara is present in the simplex condition. Using potato and tomato RFLP markers, we mapped Rx in Cara to the distal end of chromosome XII at a different position to the previously mapped Rx1 locus. To generate a high-resolution linkage map in the vicinity of Rx a total 728 AFLP primer combinations were screened using DNA of bulked resistant and susceptible segregants. We also screened segregating populations for chromosomal recombination events linked to the Rx locus and identified 82 plants with recombination events close to Rx. Using these recombinant plants we have identified AFLPs that flank Rx and span an interval of 0.23 cM in a region of the genome where 1 cM corresponds to approximately 400?kb.