The evolution of string cob corn

The "string cob" trait that characterizes the popcorn race Confite morocho from the Ayacucho area of Peru has found practical utilization in the sweet corn hybrid, Candy Stick. Its natural selective values in Peru have not been explained.

It appears that the slender cob and long pointed kernels of Confite morocho are adaptations in this race for rapid ear-drying under humid conditions where thick cobs bearing soft compacted kernels are prone to mold. In maize that was grown in the northern Andes at a level where humid conditions develop through changes in elevation (3000 to 4000 m on eastern slopes), selection for viable storage capacity of the seed would favor both the string cob trait and long pointed kernels. The latter are loosely packed by virtue of their shape. Pointed kernels as well as thick pericarps may also occur at the opposite extreme such as with the thick compacted (fasciated) cobs of Polomero Toluqueno related races in order to facilitate drying and reduce pericarp splitting.

The archaeological evidence from the Ayacucho area of Peru with cobs collected by R. S. MacNeish is that the first corn to reach there (4000 B.C.) was basically similar to the Pollo-Nal Tel cobs tracing back to Mexico. They have a thicker, more condensed rachis than the type of Confite morocho that became adapted to the Andes.

There are those who maintain that Confite morocho is derived directly out of a hypothetical wild maize indigenous to Peru (Grobman, et al., 1961; Mangelsdorf, 1974). However, the string cob trait of Confite morocho may be a specialized condition, not a primitive one. That is, the string cob condition does not necessarily stem directly from primitiveness. It may have been reactivated or reintroduced as selective values changed when maize spread into the humid parts of the Andes. A similar type of slender cob corn became adapted to the Sikkim area of the Himalayas, possibly for the same reasons. This Sikkim corn was also once suggested as a relict primitive type (Stonor and Anderson, 1949). In a less extreme example, with the advent of the selection and drying of seed ears, as well as hybridization with the northern flints, the thick, many-rowed ears of dent corn from the Southeast moved into the Northeast and the Corn Belt.

Walton C. Galinat

Please Note: Notes submitted to the Maize Genetics Cooperation Newsletter may be cited only with consent of the authors.

Return to the MNL 52 On-Line Index
Return to the Maize Newsletter Index
Return to the Maize Genome Database Page