Previously I have reported that the string cob trait is controlled by two incompletely dominant genes (Galinat, MAES Bul. 577, 1969). It appears that all of the most ancient cobs from dry caves in New Mexico, Tehuacan-Mexico, Panama, Venezuela, Ecuador and Peru carry the string cob trait and are eight-rowed. In each case where a sequence was available leading to more productive ears, the first steps involved an increase in both the number of kernel rows and the thickness of the rachis. Much later, sometimes thousands of years later, thick-cob, eight-row types of ears bearing large kernels appeared, all of independent origin. Apparently the thick-cob, eight-row types of ears are a result of recombination between the thick cob, high-row types and the slender cob, eight-row types. This conclusion is based both on archaeological remains and on experimental results.
In the American Southwest, the source of the two recessive genes for thick cob was the 12 to 14 rowed race, Chapalote, while the more primitive eight-rowed condition was probably derived from persistent remnants of the original maize to reach the area, or less probably due to row-number reductions from teosinte introgression. That the reduction in row number may leave the previous vascular supply system of the higher ranking intact was observed first by Laubengayer (Ann. Mo. Bot. Gard. 35:337-342, 1948). Increased vascularization in eight-rowed maize may lead either to induration of the rachis if the kernels remain small, or to increased kernel size and rachis size. Maiz de Ocho took the large-kernel, thick-rachis pathway and with the day-neutral, early flowering traits, it was the frontier maize in the spread of maize to the North and Northeast.
Walton C. Galinat
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