Nuclear and chloroplast DNA reassessment of the origin of Indian potato varieties and its implications for the origin of the early European potato.

The modern cultivated potato was first recorded in Europe in 1562, but its area(s) of exportation has long been in dispute. Two competing hypotheses have proposed an "Andean" area (somewhere from upland Venezuela to northern Argentina) or a lowland south central "Chilean" area. Potato landraces from these two areas can be distinguished, although sometimes with difficulty, by (1) cytoplasmic sterility factors, (2) morphological traits, (3) daylength adaptation, (4) microsatellite markers, and (5) co-evolved chloroplast (cp) and mitochondria (mt) DNA. The Chilean introduction hypothesis originally was proposed because of similarities among Chilean landraces and modern "European" cultivars with respect to traits 2 and 3. Alternatively, the Andean introduction hypothesis suggests that (1) traits 2 and 3 of European potato evolved rapidly, in parallel, from Andean landraces to a Chilean type through selection following import to Europe, and (2) the worldwide late blight epidemics beginning in 1845 in the United Kingdom displaced most existing European cultivars and the potato was subsequently improved by importations of Chilean landraces. We reassess these two competing hypotheses with nuclear microsatellite and cpDNA analyses of (1) 32 Indian cultivars, some of which are thought to preserve putatively remnant populations of Andean landraces, (2) 12 Andean landraces, and (3) five Chilean landraces. Our microsatellite results cluster all Indian cultivars, including putatively remnant Andean landrace populations, with the Chilean landraces, and none with the "old Andigenum" landraces. Some of these Indian landraces, however, lack the cpDNA typical of Chilean landraces and advanced cultivars, indicating they likely are hybrids of Andean landraces with Chilean clones or more advanced cultivars. These results lead us to reexamine the hypothesis that early introductions of potato to Europe were solely from the Andes.