As a result of attempts to reconstruct stable stocks of the links that must have once been intermediate steps in the evolutionary emergence of maize from teosinte, I have come to some conclusions about how to proceed. The key trait genes have various types of behavior in each other's background. They may be silent with zero penetrance, especially when heterozygous, or they may have unstable expression, even along the length of a single ear or spike.

Judging from observations of the vascular anatomy at various positions along a rachis, it appears that the background effect involves a congruous balance between the vascular supply system and the energy requirements of its customers, the spikelets. The elaborate vascular system of the modern cob is both excessive and incongruous with a stable expression of the solitary female spikelets borne in two ranks that characterize teosinte. On the other hand, the simple vascular supply of the female spike in teosinte is inadequate to support a stable expression of the more energy-demanding traits of paired female spikelets and/or many-ranked spike of maize.

By trial and error it was discovered that the ideal background for a stable expression of the isolated key traits was a tiny, eight rowed popcorn inbred, MA1001, that we had bred in attempting to reconstruct the Tehuacan so-called "wild corn". The connecting links on this reconstructed background should be useful experimental material for genetic, molecular, and developmental studies designed to study the origin of maize.

Walton C. Galinat

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