Multitrait selection system using populations with a small number of interploid (4x-2x) hybrid seedlings in potato:: Degree of high-parent heterosis for yield and frequency of clones combining quantitative agronomic traits

One of the most attractive features of the 4x-2x breeding scheme via unilateral sexual polyploidization (USP) is the possibility of obtaining heterotic clones with a combination of desirable traits based upon selection in a small number of hybrid seedlings. A set of experiments was carried out to verify this characteristic of the USP scheme using 42 families (with 20 plants each) derived from 2x Phureja-haploid Tuberosum or haploid Tuberosum-Solanum chacoense hybrids as male parents. These clones were 2n-pollan-producers by either first-division restitution with crossing over (FDR-CO) or without crossing over (FDR-NCO). The 4x parents were eight cultivars of USA and European origin. A total of 168 out 840 clones was initially selected (four clones/family) based on general tuber appearance (GTA). An additional round of selection (not taking into account the parentage of the clone) for total tuber yield (TTY) reduced the sample to 96 clones. These selected clones and the original 4x parents were evaluated in two locations at Wisconsin (Hancock - E # 1, and Rhinelander - E # 2). The average high-parent heterosis values for TTY ranged from 27.8% (E # 2) to 48% (E # 1). The population of experimental clones also had a TTY range wider than that of the 4x parents. The best clone gave a yield of 101.6% and 63.2% over the best 4x parent at E # 1 and E # 2, respectively. For TTY, a significant genotype x environment (G x E) interaction for the experimental clones was found when a combined analysis of variance for both locations was carried out. However, the G x E interaction was not significant when only the 4x-parent group was considered. Clones derived from 4x European cultivars had higher GTA scores than clones derived from 4x USA cultivars, With two culling levels being set on the TTY 2 4x parent group mean and the GTA 2 three, about 56% (E # 1) and 48% (E # 2) of the clones would be retained for further evaluation. These percentages of selected clones are much higher than those reported using conventional 4x-4x crosses. Our results indicate that a USP strategy with 4x-2x (FDR) crosses would be more effective than intra-Tuberosum crosses in generating heterotic clones with a combination of desirable quantitative traits using populations with a small number of hybrid seedlings.