Tuesday, October 04, 2005

Potato origins

A paper to appear in PNAS this week uses genetic data to argue that Potatoes were domesticated only once in the region around Peru.

The pedigree of modern potatoes can be traced back to 1562 in Europe, but the ancestors of that crop could have been either one or several sources in South America. There are certainly two clades among modern cultivars which can be distinguished both genetically and based on things like daylight adaptation. The favored theory, until now, has been that these clades in fact are of ancient origin (representing independent domestication events), possibly introduced to Europe (and the world) by necessity. The 19th century potato blights, by this hypothesis, wiped out the older breeds, requiring hybridization to a different, blight-resistant, race of potato. This hybridization of two different gene pools contributed to modern spuds. David Spooner, the lead author in the current study, had earlier proposed just such a dual origin of potatoes, but with the second (Chilean) clade being prominent long before the 1840s.

The current study involves RFPL analysis surveys of wild potatoes in the South of Peru and north of Bolivia. The result of the new classification is that both the northern and southern clades of modern potatoes can be linked to a small set of species from this area. The data furthermore point to a need to look closely at this "set" of species, which may instead represent a single species.

In terms of bioprospecting, then, lots of useful potato genes could be tapped from just about anywhere else along the Andean chain.

This kind of analysis has been done on a number of major food crops including wheat, beans, and squash. After initial domestication, farming of these valuable plants has sometimes spread primarily along the east-west axis (wheat), and in other cases they spread north-south, or without an apparent latitude bias (corn, squash, beans). A while back, Jared Diamond stuck out his neck and speculated that agriculture of monoclonal crops would be spread with an east-west axis bias, because the similarity of climate is better preserved, whereas north-south spreading might require polyclonal domestication or extensive hybridization. Since Diamond's original thesis, both corn and now potato, both with prominent north-south historical spreads, have been shown to be genetically monoclonal. Send that one to the circular file.

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