Heterotic effects for yield and tuber solids and type of gene action for five traits in 4x potato families derived from interploid (4x-2x) crosses

The degree of heterosis for total tuber yield (TTY) and total solids (TS) i n 4x-2x crosses was estimated by comparing the performance of 12 families w ith their respective parents in two locations in Wisconsin (USA). The paren tal 2x clones were Phureja-haploid Tuberosum hybrids with 2n-pollen product ion by first-division restitution. The general combining ability (GCA) and specific combining ability (SCA) were estimated for Tn, TS, vine maturity ( VM), length of tuber sprout dormancy (LD), and tuber eye depth (ED). Family performance for TTY ranged from 74 to 146% at Hancock (E#1) and from 77 to 287% at Rhinelander (E#2) when compared with that of the 4x parent group. For VM, the families were late maturing, but a few precocious ones were ide ntified. For TS, the families had heterosis of 5.1% over the 4x parent grou p. The families had slightly higher ED values than the 4x parents, but fami lies with values within the commercial range were identified. The family av erage for LD (54 days) was closer to the 2x group (51 days) than to the 4x group (88 days). The direction and magnitude of the parent-family relations hips were variable. The 4x parent TTY was correlated with progeny in E#l bu t not E#2. The 2x parent VM had correlation with the offspring at E#2 but n ot at E#l. The type of gene action had a trait-specific expression. Signifi cant SCA and GCA variances were observed, suggesting that additive as well as non-additive genetic effects were operating. The 4x-2x crosses were able to generate heterotic families for TTY and TS in combination with other us eful traits. However, no promising results were found for LD because of the apparent dominance of the short-dormancy phenotype. This result indicates the need of additional selection and breeding efforts for some specific tra its when using S. phureja-derived germplasm.