Tuber yield and dry matter content, measured as under water weight (UWW), of 24 diploid 2x−2x progenies and 12 tetraploid 4x−2x progenies, have been measured in the seedling generation and the first clonal generation. The results were used to evaluate predictions of progeny means, and to compare the general combining ability (GCA) estimated from 2x−2x crosses with the GCA estimated from 4x−2x crosses. Based on parental values and the means of the seedling as well as first clonal generation, the prediction of UWW of the 2x−2x and the 4x−2x progenies was better than that of tuber yield. For GCA similar differences between UWW and tuber yield were found. Three diploid clones were used both for the 2x−2x crosses and the 4x−2x crosses. The ranking of the GCA values, estimated from the 2x−2x crosses, was similar to that obtained from the 4x−2x crosses for UWW in both generations and, to a lesser extent, for tuber yield in the first clonal generation, suggesting, that it might not be necessary to carry out 4x−2x testcrosses to identify diploid clones with superior GCA for tuber yield and dry matter content.