Sixty-two 2x families were generated by intermating 16, 2x clones and evaluated for resistance to potato tuber moth (PTM), Phthorimaea operculella under natural infestation in a storage at San Ramon, Peru and in laboratory tests. The following conclusions could be drawn: (1) relatively simple inheritance was observed for resistance derived from Solanum sparsipilum (spl), (2) the high level of resistance of the original spl has been transferred, undiminished, into an advanced 2x population, (3) simple phenotypic selection was successfully applied to transfer resistance into an improved 2x population, (4) there was a strong indication of reciprocal effects, however spl cytoplasm is not essential for the expression of nuclear resistance genes, (5) antibiosis and antixenosis are the mechanism of PTM resistance in this population, and (6) 4x × 2x crosses could be used to transfer the resistance into commercial cultivars. © 1990 Kluwer Academic Publishers.