Extensive SSR genotyping of potato landraces supports a drastic revaluation of their gene pool structure and classification

Authors: GHISLAIN, MARC - INTL POTATO CNTR LIMA; NUNEZ, JORGE - INTL POTATO CNTR LIMA; TRUJILLO, GUILLERMO - INTL POTATO CNTR LIMA; HERRARA, M DEL ROSARIO - INTL POTATO CNTR LIMA; GUZMAN, FRANK - INTL POTATO CNTR LIMA; Spooner, David

Submitted to: Proceedings of the National Academy of Sciences (PNAS)
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/1/2007
Publication Date: 8/10/2007
Citation: Ghislain, M., Nunez, J., Trujillo, G., Herrara, M., Guzman, F., Spooner, D.M. 2007. Extensive SSR genotyping of potato landraces supports a drastic revaluation of their gene pool structure and classification. Proceedings of the National Academy of Sciences. 104:19398-19403.

Interpretive Summary: The cultivated potato is one of the most important food plants worldwide, yet there has never been agreement among scientists how to properly classify them. Depending on the author, there are anywhere from one to 20 species. This study investigates the diversity and taxonomy of the cultivated potato with a genetic marker, technically called microsatellites, from an extensive sample of 742 collections covering all cultivated potato species and eight closely related wild species progenitors. The results highlight a tendency to separate three groups differing in chromosome number and overall form. We conclude that for most wild potato species, consistent and stable identifications are impossible, their classification as species is artificial, and only maintains confusion by the users, in genebanks, and in the literature. These results provide a classification that better reflects the true diversity of the species and better advises breeders of the diversity available in their crossing programs.

Technical Abstract: The cultivated potato is one of the most important food plants worldwide, yet knowledge of the gene pool structure of the native South American landraces remains largely uninvestigated and is controversial. As a result, contrasting taxonomic treatments of the landraces have continued over the last century, with the recognition of anywhere from one to twenty distinct Linnean species, or of various Cultivar Groups within the single species Solanum tuberosum. We provide an extensive study of 742 landraces of all cultivated species (or Cultivar Groups), and eight closely related wild species progenitors, with 50 primer pairs of nuclear microsatellite and a plastid DNA deletion marker that has been considered to distinguish Chilean from Andean tetraploid landraces. Neighbor joining results highlight a tendency to separate three groups: 1) putative diploids, 2) putative tetraploids, the hybrid Cultivar Groups Ajanhuiri (diploid), Juzepczukii (triploid), and Curtilobum (pentaploid). However, there are many exceptions of clustering by ploidy and Cultivar Group. Strong bootstrap support occurs only in branches of the Groups Ajanhuiri, Juzepczukii, and Curtilobum. In combination with recent morphological analyses and an examination of the identification history of these collections, we conclude that only Groups Ajanhuiri, Juzepczukii, and Curtilobum are well-defined but for the remaining accessions, consistent and stable identifications are impossible, their classification as Linnean species is artificial, and only maintains confusion by the users, in genebanks, and in the literature. We rather support the classification of the cultivated potatoes as for into one species S. tuberosum with several user-defined Cultivar Groups with one large common gene pool and the cultivated bitter potatoes as three species S. ajanhuiri, S. juzepczukii, and S. curtilobum each with extremely narrow gene pool.