THE EVOLUTION OF CULTIVATED POTATOES

In the first stages of potato evolution in the northern Andes, diploid cultivated species of the Solanum stenotomum complex were selected, in all probability, from wild progenitors in the S. brevicaule complex. Tetraploid Solanum tuberosum ssp. andigena arose by fusion of unreduced gametes of a parent in the S. stenotomum complex with those of an unidentified wild species having actinomorphic calyces. Unreduced male gametes of several diploid species fertilized eggs of ssp. andigena leading to extensive introgression. Solanum tuberosum ssp. tuberosum probably originated from a cross between ssp. andigena as staminate parent and an unidentified wild species which contributed cytoplasmic sterility factors encoded in mitochondria and/or plastids having a distinctive type of DNA. Derivatives of this hybridization, which may have occurred in northwestern Argentina, evolved to ssp. tuberosum in southern Chile and southern Argentina. In the 1570's ssp. andigena was imported to Europe and spread from there to become a major crop with worldwide distribution. In the 1840's it was essentially eliminated by late blight, Phytophthora infestans. Solanum tuberosum ssp. tuberosum was introduced from Chile into North America and Europe in the late 1800's, and in turn achieved a worldwide distribution, filling the vacated agricultural niche of ssp. andigena. The differences between ssp. andigena and ssp. tuberosum in South America are sufficient that the two could reasonably be considered to be separate species. Since the 1960's the two taxa have been hybridized often in breeding programs. Neotuberosum, a northern-adapted strain of ssp. andigena, has been selected to mimic ssp. tuberosum. Substitution back-cross products have been produced that have the chromosomal genes of ssp. tuberosum combined with cytoplasmic factors of Andean species. These breeding activities are blurring the distinctions between the two subspecies throughout much of the world, though they remain distinct in their native areas in South America. © 1990 New York The Botanical Garden, Bronx, NY 10458.