COMPARISON OF DIPLOID AND TETRAPLOID POTATO FAMILIES DERIVED FROM SOLANUM-PHUREJA BY DIHAPLOID SOLANUM-TUBEROSUM HYBRIDS AND THEIR VEGETATIVELY DOUBLED COUNTERPARTS

To determine whether in potatoes the tetraploid level is preferable to the diploid level, especially regarding tuber yield, four diploid (2n=2×=24) Solanum phureja x dihaploid S. tuberosum hybrid parents and their vegetatively doubled, tetraploid (2n=4×=48) counterparts were intermated, which resulted in two F1 hybrid families at both levels of ploidy. The parents and clones of the F1 families and their offspring were used in crosses in such a way that in addition Sib1, Sib2, F1×Sib1, BC1 and Sib1×Sib1 families were produced. Of the first clonal generation of the 12 2 x families and their 12 counterpart 4 x families two tubers per clone were planted in three replications in a field experiment at Sturgeon Bay in 1969; of the parents six tubers were planted in each replication. Data were recorded on 16 characters, including plant height at four different times. The ANOVA's showed significant clone effects within each family for all characters. Computed from all family means as well as from the family means per ploidy level, differences due to family were also significant for all characters except one. As at the 2 x level and at the 4 x level of ploidy the mean phenotypic correlations between characters were of similar magnitude, it is concluded that they are independent of ploidy level. With the exception of eye depth, the mean coefficient of variation was greater at the 2 x than at the 4 x level of ploidy, indicating the greatest response to selection for those characters at the 2 x level. From the differences in family means between the 4 x and the 2 x level of ploidy it was apparent that the 4 x families generally had significantly taller plants, later maturity, fewer tubers, higher mean tuber weight, more tuber yield and more dry matter yield than their counterpart 2 x families. In contrast, the 4 x parents had on the average shorter plants, lower mean tuber weight, much lower tuber yield and lower dry matter yield than their 2 x counterparts. The phenotypic correlation and Spearman's rank correlation between the family means of the 2 x and the 4 x level of ploidy were positive for almost all characters and significant for nearly half of them. From the results it is concluded that 1. in potatoes the 4 x level of ploidy is preferable to the 2 x level, and 2. the performance of 4 x families is predictable from the performance of their counterpart 2 x families. Based on results mentioned in the literature and on the present results, a continued use of S. tuberosum dihaploids in potato breeding needs to be dissuaded. © 1990 Kluwer Academic Publishers.