Michael A. Hardigan, F. Parker E. Laimbeer, Linsey Newton, Emily Crisovan, John P. Hamilton, Brieanne Vaillancourt, Krystle Wiegert-Rininger, Joshua C. Wood, David S. Douches, Eva M. Farré, Richard E. Veilleux, and C. Robin Buell

PNAS November 14 2017; vol.114; no.46: E9999–E10008

Significance

Worldwide, potato is the third most important crop grown for direct human consumption, but breeders have struggled to produce new varieties that outperform those released over a century ago, as evidenced by the most widely grown North American cultivar (Russet Burbank) released in 1876. Despite its importance, potato genetic diversity at the whole-genome level remains largely unexplored. Analysis of cultivated potato and its wild relatives using modern genomics approaches can provide insight into the genomic diversity of extant germplasm, reveal historic introgressions and hybridization events, and identify genes targeted during domestication that control variance for agricultural traits, all critical information to address food security in 21st century agriculture.

 Abstract

Cultivated potatoes (Solanum tuberosum L.), domesticated from wild Solanum species native to the Andes of southern Peru, possess a diverse gene pool representing more than 100 tuber-bearing relatives (Solanum section Petota). A diversity panel of wild species, landraces, and cultivars was sequenced to assess genetic variation within tuber-bearing Solanum and the impact of domestication on genome diversity and identify key loci selected for cultivation in North and South America. Sequence diversity of diploid and tetraploid S. tuberosum exceeded any crop resequencing study to date, in part due to expanded wild introgressions following polyploidy that captured alleles outside of their geographic origin. We identified 2,622 genes as under selection, with only 14–16% shared by North American and Andean cultivars, showing that a limited gene set drove early improvement of cultivated potato, while adaptation of upland (S. tuberosum group Andigena) and lowland (S. tuberosum groups Chilotanum and Tuberosum) populations targeted distinct loci. Signatures of selection were uncovered in genes controlling carbohydrate metabolism, glycoalkaloid biosynthesis, the shikimate pathway, the cell cycle, and circadian rhythm. Reduced sexual fertility that accompanied the shift to asexual reproduction in cultivars was reflected by signatures of selection in genes regulating pollen development/gametogenesis. Exploration of haplotype diversity at potato’s maturity locus (StCDF1) revealed introgression of truncated alleles from wild species, particularly S. microdontum in long-day–adapted cultivars. This study uncovers a historic role of wild Solanum species in the diversification of long-day–adapted tetraploid potatoes, showing that extant natural populations represent an essential source of untapped adaptive potential.

See: http://www.pnas.org/content/114/46/E9999.full

Figure 1: (A) Phenotypic diversity within wild species, cultivated landraces, and cultivars through domestication, improvement, and modern breeding efforts. Exemplar species, landraces, and elite North American cultivars are shown that highlight tuber size, shape, and pigmentation diversity. (B) Phylogeny and population structure of the samples in the domestication panel. The phylogenetic tree is based Nei’s genetic distances calculated from 687,172 fourfold-degenerate sites from conserved potato genes. Population structure is based on 50,000 genome-wide SNPs. The optimal number of subpopulations (K = 5) included wild outgroups (purple), wild Solanum relatives (green), a wild subgroup diverging from the cultivated lineage after most other species (gold), Andean landraces (teal), and S. tuberosum group Tuberosum (navy).