Revamping Relationships Among Cultivated Potatoes
By Ann Perry
November 20, 2007
"One potato, two potato, three
potato, four" turns out to be exactly rightwhen classifying
cultivated potatoes, that is. Scientists at the Agricultural Research Service
(ARS) and the International Potato Center
(CIP) have used morphologythe
outward appearance of a plant- -in combination with molecular markers to revise
the number of potato species from seven to four.
Until recently, potato species designations have been based primarily on
morphological characteristics and estimatesoften incorrectof how
many chromosome sets they possessed.
Spooner works in the
Vegetable Crops Research Unit, Madison, Wis. His initial research with CIP
colleagues in Peru indicated that morphological variations among cultivated
potatoes were not reliable indicators of species.
They then examined DNA molecular markers from 742 cultivated potato
varieties and eight wild relatives of potatoes. Based on results from this
study and previous studies, Spooner and CIP lead scientist Marc Ghislain
concluded that cultivated potato varieties could most accurately be assigned to
one of four species.
They refined the species designations by checking each potato variety for
the presence of one particular DNA mutation. This characteristic mutation
distinguishes between potatoes from the Chilean lowlands and potatoes from the
Solanum tuberosumthe type of domesticated potato eaten around
the worldis one of the four recognized species. This is by far the most
common potato species and has from two to four sets of chromosomes.
The less common potato speciesS. ajanhuiri, S.
juzepczukii and S. curtilobumhave two, three and five sets of
chromosomes, respectively. These can often be distinguished from each other by
This new system of species classification eliminates much of the guesswork
that previously served as the foundation for the potato classification system.
Potato breeders will benefit greatly from a classification system that groups
related collections by combining traditional morphological with modern
A paper reporting the results of this study was published this week in the
Proceedings of the National Academy of
Sciences of the United States of America.
ARS is the U.S. Department of
Agriculture's chief scientific research agency.