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In recent years, <i>Potato virus Y</i> (PVY) has emerged as a serious disease problem in potato production areas throughout North America. One explanation for this increase in incidence is that some widely planted cultivars express mild or no symptoms, preventing effective roguing of infected plants. Furthermore, recent investigations have revealed a significant increase in the proportion of PVY recombinants (PVY^N:O) in major production areas. Effective strategies to address this emerging problem are lacking. The development of cultivars with improved levels of PVY resistance would provide one such strategy. We have identified a new source of extreme resistance to PVY^O and PVY^N:O in the diploid wild potato relative <i>Solanum</i> <i>chacoense</i>. All plants in accession 275138 were resistant to PVY, while variability for resistance was found in accession 320285. Segregation ratios in the F1 and backcross populations indicate that PVY resistance is conferred by a single dominant gene. The 8,303 SNP array developed by the SolCAP initiative is being used to map the gene in a diploid hybrid population created by crossing a heterozygous resistant clone to a susceptible wild species clone (<i>S. tarijense</i>, PI558129). In addition, a diploid adapted fertile clone has been selected from a cross between a homozygous resistant <i>S. chacoense</i> clone and a susceptible cultivated <i>S. tuberosum</i> clone. It expresses genes for the production of numerically unreduced pollen and eggs, so when crossed to tetraploid cultivars, it produces tetraploid offspring carrying the resistance gene. In addition, it carries the dominant allele of a gene that overcomes the gametophytic self-incompatibility system, so it can be self-pollinated to create clones homozygous for the PVY resistance gene.<p><p>Keywords: