University of Massachusetts

A pristine background for studies on the origin and evolution of maize

--Walton C. Galinat

Use of a maize background, even though from primitive extant popcorns, for inheritance and evolution studies of the key-trait differences between teosinte and maize carries with it the assumption of a wild maize as the wild ancestor. Conversely, use of a teosinte background implies, and probably correctly so, that teosinte was the wild ancestor. But use of a pristine background, intermediate between teosinte and a reconstructed Tehuacan type of the oldest known maize, can be justified for studies on inheritance, rate of evolutionary emergence of maize and for opening new directions for maize evolution. The Tehuacan wild traits that have been recovered from extant maize for use in the pristine background are the string cob (Sg1, Sg2) from Confite Morocho, the interspace (is) from Coroico and the weak tunicate (tu-w) from Chapalote. This synthetic pristine background is easier to manipulate for controlled pollinations than that of pure teosinte because it has larger solitary ears compared with the tiny clustered spikes of teosinte but ears smaller than those of maize and it is easier to attach paper bags for pollination control in a cornfield situation. The pristine background also has the advantage of stabilizing key-trait expression (single vs. paired female spikelets and two vs. many ranks of spikelets). It will give more stable and repeatable results of genetic analysis at either the conventional or molecular levels.

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