Color in corn: natural factors

There may be ancient foundations for the multifaceted color systems that are so prominent in maize. All four teosinte species have white endosperm, no aleurone color and tan pericarp. If there were an ancestral, non-teosintoid wild maize which, after domestication, introgressed with one or more teosinte species (MNL 53:53-54), it could have had many contrasting alleles that controlled color in the endosperm, aleurone and the pericarp-cob systems. Yet other alleles could have been produced by the mutagenic action of transposable elements mobilized by the introgression.

Why might a wild maize have had an array of alleles distinct from those in the teosintes? Perhaps color was important in its reproduction, as an attractant to seed-eating birds! The husks might have been light red, membranous and loose, surrounding small red cobs holding kernels with yellow endosperm. The cob's glumes might have been especially red and partly visible between the loose kernels. Perhaps there was a slightly reddish or purplish tint in the pericarp and/or aleurone. Red and yellow are a common combination that attracts birds to flowers and fruits, but I can think of no other grass in which color acts as such an attractant.

What seem to be the oldest archaeological cobs, those from the Tehuacan area of Mexico, have very narrow rachillas (stems subtending kernels), and their lower glumes are very thin, short and reflexed away from the kernel (MNL 59:43). It would have been easy for birds to detach kernels, eating many, scattering some. But why would maize need to attract birds when presently they come in flocks to fields of much less colored maize? Perhaps small plants of ancestral wild corn were scattered along disturbed river banks and gravel bars, and attraction was needed to assure distribution of seed before the plants fell over with the ear still holding its load of 40-70 kernels. Birds would have helped to spread seed and to thin the potential stand in the following generation. After domestication Mexican farmers would have selected uncolored maize with tight husks to reduce bird damage.

This is theorizing with little evidence and much supposition, but it would be interesting to see if a maize combining these colors were to attract many more birds (grackles?) than would a white-kernelled, white-cobbed form. Preferably this would be tested in Mexico.

Robert McK. Bird
 
 


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