Breeding Diploid F1 Hybrid Potatoes for Propagation from Botanical Seed (TPS): Comparisons with Theory and Other Crops

Abstract

This paper reviews the progress and the way ahead in diploid F₁ hybrid potato breeding by comparisons with expectations from the theory of inbreeding and crossbreeding, and experiences from other diploid outbreeding crops. Diploid potatoes can be converted from an outbreeding species, in which self-pollination is prevented by a gametophytic self-incompatibility system, into one where self-pollination is possible, either through a dominant self-incompatibility inhibitor gene (Sli) or knockout mutations in the incompatibility locus. As a result, diploid F₁ hybrid breeding can be used to produce genetically uniform potato cultivars for propagation from true potato seeds by crossing two near-homozygous inbred lines, derived from a number of generations of self-pollination despite inbreeding depression. Molecular markers can be used to detect and remove deleterious recessive mutations of large effect, including those in tight repulsion linkage. Improvements to the inbred lines can be made by introducing and stacking genes and chromosome segments of large desirable effect from wild relatives by backcrossing. Improvements in quantitative traits require a number of cycles of inbreeding and crossbreeding. Seed production can be achieved by hand pollinations. F₁ hybrid planting material can be delivered to farmers as true seeds or young plants, and mini-tubers derived from true seeds.

Keywords: hybrid vigor; inbreeding depression; introgression; planting material; quantitative traits; recessive mutations; self-compatibility.

Figure 1

New cultivar from cross between two heterozygous diploid parents (one pair of chromosomes shown, where small letters represent deleterious recessive alleles).

Figure 2

New diploid F₁ hybrid cultivar from cross between two homozygous diploid parents (one pair of chromosomes shown, where small letters represent deleterious recessive alleles).

Figure 3

Recombinant among phenotypically green plants that broke the close linkage of two deleterious recessive mutations in repulsion phase at the end of chromosome 12, where led1 is a large-effect deleterious mutation, and yl1 is a deleterious mutation for chlorotic yellow leaves. Data from Zhang et al. [86].

Figure 4

Introgression of two resistance genes R₁ and R₂ from two (heterozygous) wild species (W1 and W2) into two elite diploid Tuberosum (homozygous) inbred lines (T1 and T2), where selection in the F₁, BC₁, and BC₂ generations is for the R-genes and, in the BC₁ and BC₂ generations, for as much of the Tuberosum genome as possible.

Figure 5

Improvements in mean of inbred lines and mean of F₁ hybrids as frequencies of favourable alleles increase at 12 unlinked loci with complete dominance (a = d = 1), where mean (m) at p = ½ is set at 12 for inbred lines. Means plus one standard deviation (SD) are also shown.

Figure 6

Inbred lines and F₁ hybrids for 12 unlinked loci, each with complete dominance (a = d = 1) and p = ½ for favourable allele frequency, where mean (m) is set at 12 for inbred lines.