Revamping Relationships Among Cultivated Potatoes

"One potato, two potato, threepotato, four" turns out to be exactly right—when classifyingcultivated potatoes, that is. Scientists at the Agricultural Research Service(ARS) and the International Potato Center(CIP) have used morphology—theoutward appearance of a plant- -in combination with molecular markers to revisethe number of potato species from seven to four.

Until recently, potato species designations have been based primarily onmorphological characteristics and estimates—often incorrect—of howmany chromosome sets they possessed.

BotanistDavidSpooner works in theARSVegetable Crops Research Unit, Madison, Wis. His initial research with CIPcolleagues in Peru indicated that morphological variations among cultivatedpotatoes were not reliable indicators of species.

They then examined DNA molecular markers from 742 cultivated potatovarieties and eight wild relatives of potatoes. Based on results from thisstudy and previous studies, Spooner and CIP lead scientist Marc Ghislainconcluded that cultivated potato varieties could most accurately be assigned toone of four species.

They refined the species designations by checking each potato variety forthe presence of one particular DNA mutation. This characteristic mutationdistinguishes between potatoes from the Chilean lowlands and potatoes from thehigh Andes.

Solanum tuberosum—the type of domesticated potato eaten aroundthe world—is one of the four recognized species. This is by far the mostcommon potato species and has from two to four sets of chromosomes.

The less common potato species—S. ajanhuiri, S.juzepczukii and S. curtilobum—have two, three and five sets ofchromosomes, respectively. These can often be distinguished from each other bymorphological data.

This new system of species classification eliminates much of the guessworkthat previously served as the foundation for the potato classification system.Potato breeders will benefit greatly from a classification system that groupsrelated collections by combining traditional morphological with modernmolecular methods.

A paper reporting the results of this study was published this week in theProceedings of the National Academy ofSciences of the United States of America.

ARS is the U.S. Department ofAgriculture's chief scientific research agency.