Creation of a highly homozygous diploid potato using the S locus inhibitor (Sli) gene

Abstract

Potato is a heterozygous autotetraploid crop propagated as tubers. Diploid potatoes, which are mostly self-incompatible due to gametophytic self-incompatibility, are often used to reduce genetic complexity. The discovery of the S locus inhibitor (Sli) gene has created a way to develop diploid inbred lines and perform F1 hybrid breeding in potato. However, residual heterozygosity found in advanced-generation selfed progenies has posed the question of whether a minimum level of heterozygosity is necessary to maintain self-fertility. We continued selfing and finally identified a highly homozygous diploid potato among tenth-generation selfed progeny, which was homozygous at all 18,579 genome-wide single nucleotide polymorphism (SNP) markers surveyed. The S10 plants suffered severe inbreeding depression in terms of fertility and vigor, showing a small number of mature flowers and extremely slow growth. Although asexual techniques such as anther culture followed by chromosome doubling can result in completely homozygous diploid potatoes, all previously derived plants were male sterile. In contrast, continuous selfing using Sli swept out all lethal alleles and selected for self-fertility, which generated a highly homozygous diploid potato retaining male and female fertility and tuberization ability under long days.