Nine 2x clones with different genetic backgrounds and 2n pollen production by first division restitution (FDR) were each mated with five 4x females in a linextester design. Estimates of both general combining ability (GCA) and specific combining ability (SCA) were significant for tuber yield, among female and male parents. Four FDR clones with similar genetic background (half-sibs) showed significantly different GCA for total yield, illustrating the importance of progeny testing for FDR clones before their utilization as progenitors. A stronger influence of the 2x parents, compared to that of the 4x parents, on the performance of the hybrids was observed for characters studied. The significance of male and female interactions for characters other than tuber yield reinforced the importance of careful choice of the male and female parents for improving horticultural traits of 4x-2x progenies. © 1988 Kluwer Academic Publishers.