ARS | Publication request: The enigma of Solanum maglia in the origin of the Chilean cultivated potato, Solanum tuberosum Chilotanum group

Submitted to: Economic Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 14, 2011
Publication Date: March 1, 2012
Citation: Spooner, D.M., Jansky, S.H., Del Rosario Herrera, M., Montenegro, J.D., Nunez, J., Clausen, A., Ghislain, M. 2012. The enigma of Solanum maglia in the origin of the Chilean cultivated potato, Solanum tuberosum Chilotanum group. Economic Botany. 66(1):12-21.

Interpretive Summary: Potato is one of the most important food crops worldwide, but its origin has been the subject of long speculation and debate. Our modern potato is quite different from indigenous primitive cultivars (landraces) of potato that occur in two broad geographic regions; the high Andes from western Venezuela south to northern Argentina (Andigenum landraces), and lowland south central Chile (Chilotanum landraces). Chilotanum landraces are adapted to long days and have a characteristic DNA signature and differ in minor appearances from Andigenum landraces. The modern "Irish" potato clearly originated from Chilotanum landraces. Our research investigated the origin of Chilotanum landraces, with one hypothesis proposing an origin from Andigenum landraces, and another hypothesis suggesting an origin from a native Chilean wild potato species technically called S. maglia. Our data obtained from starch grain analysis do not support S. maglia as the parent of Chilean landraces but the molecular results do support this idea. These conflicting results could be interpreted in various ways, but all explanations have problems. This research alerts breeders to starch grain variation in Andean and Chilean potatoes, highlights molecular similarities between these potatoes, and highlights conflicting data sources bearing on the origin of a major food plant.

Technical Abstract: Landrace potato cultivars of Solanum tuberosum occur in two broad geographic regions; the high Andes from western Venezuela south to northern Argentina (S. tuberosum Andigenum Group), and lowland south central Chile (S. tuberosum Chilotanum Group). Chilotanum Group landraces are adapted to long days, have a 241 bp plastid DNA deletion (shared with some accessions of the wild potato species S. berthaultii, but lacking in the wild potato species S. maglia) and differ morphologically by minor characters that are not always Group-specific. The modern "Irish" potato clearly originated from Chilotanum germplasm. Our research investigated the origin of Chilotanum Group landraces, with one hypothesis proposing an origin from Andigenum Group landraces, perhaps after hybridization with S. berthaultii; and a competing hypothesis suggesting an origin from the wild potato species S. maglia, distributed in southern Chile and adjacent western Argentina. Molecular data support both the Andean and Chilean potatoes as members of the same clade, distinct from S. berthaultii. The S. maglia hypothesis was based on morphological analyses of starch grains of extant and extinct (13,000 years before present) S. maglia, and on extant distributional data of S. maglia and Chilotanum. Our new starch grain analyses of extinct and extant S. maglia using a much wider collection of accessions of both cultivar groups of S. tuberosum show extensive overlap. In addition, we could find no evidence of sympatric distributions of extant S. maglia and Chilotanum. Therefore, starch grains and distributional data do not support this hypothesis. However, microsatellite data group all accessions of S. maglia (Argentinean and Chilean) exclusively with Chilotanum. These results could be interpreted in various ways, but all explanations have problems. One explanation is that S. maglia is either a progenitor or product of Chilotanum, but the plastid deletion of Chilotanum cannot be easily explained. Another explanation is that Chilotanum was formed by hybridization between S. berthaultii and S. maglia but this conflicts with prior cladistic analyses.