Solanum tuberosum, the cultivated potato of world commerce, is a primary food crop worldwide. Wild and cultivated potatoes form the germplasm base for international breeding efforts to improve potato in the face of a variety of disease, environmental and agronomic constraints. A series of national and international genebanks collect, characterize and distribute germplasm to stimulate and aid potato improvement. A knowledge of potato taxonomy and evolution guides collecting efforts, genebank operations and breeding. Past taxonomic treatments of wild and cultivated potato have differed tremendously among authors with regard to both the number of species recognized and the hypotheses of their interrelationships. In total, there are 494 epithets for wild and 626 epithets for cultivated taxa, including names not validly published. Recent classifications, however, recognize only about 100 wild species and four cultivated species. This paper compiles, for the first time, the epithets associated with all taxa of cultivated potato (many of which have appeared only in the Russian literature), places them in synonymy and provides lectotype designations for all names validly published where possible. We also summarize the history of differing taxonomic concepts in cultivated potato, and provide keys and descriptions for the four cultivated species.

Our distributional and ecological data, in combination with prior results from morphology, microsatellites, and crossing data, provide yet additional data to support a major reclassification of cultivated potato species. A rational, stable, and universally accepted taxonomy of this major crop plant will greatly aid all users of wild and cultivated potatoes from breeders to gene bank managers to ecologists and evolutionary biologists.

The germplasm collections of the Vavilov Institute of Plant Industry, Russia represent the first germplasm collection made for potatoes, now numbering 8,680 accessions. It has tremendous historical and practical importance and a rich history, having been used to document a polyploid series in the cultivated species, to formulate initial taxonomic hypotheses in potato, for studies of interspecific hybridization, and serving as the germplasm base for Russian breeding efforts. Despite its importance and size, there has never been a study of its molecular diversity, and there were many gaps in its passport data. The purpose of the present study is to obtain morphological, ploidy, and microsatellite (SSR) data needed to set up a useful subset of the collection of cultivated potatoes and closely related wild species, Electronic supplementary material The online version of this article (and to use this collection to study cultivated potato taxonomy and phylogeny. Through assessments of viability, passport data, and chromosome counts, we selected a subset of 238 cultivated and 54 wild accessions. A morphological and nuclear SSR study of these collections distinguished only three cultivated species: Solanum curtilobum, S. juzepczukii and S. tuberosum, not the many more cultivated potato species of prior taxonomic treatments. The SSR study supports the ideas of S. acaule as one of the parental species for S. curtilobum and S. juzepczukii. The morphological and SSR results are very similar to other recent studies of cultivated species, and show the need to reclassify the collection of cultivated potatoes by modern taxonomic criteria.

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