Western Maize Genetics

50 generations of selection for perennialism in maize

— Shaver, DL

This work was begun using Emerson’s 4N perennial teosinte clone E16515, obtained from L. F. Randolph in 1958. It was originally used in crosses with genetic stocks of 4N maize, to study the degree of preferential pairing in the allotetraploid F1 hybrid. Subsequently backcrosses were made to D. E. Alexander’s agronomic maize variety, 4N Syn. B. After each backcross to 4N maize, perennialism was largly lost, until after several generations of mass selection for perennialism, which worked to easily restore the perennial phenotype. When a satisfactory level was achieved, another backcross was made to 4N Syn. B, then the mass selection steps were repeated to restore the perennial phenotype. This process has been repeated to the extent that the present population, as seen in Figures 1–3, are in theory 7/8 maize, and 1/8 perennial 4N teosinte.

The method of selection for perennialism has been to allow a first-generation growth of culms to begin to show tassel, after which the plants, in a population of ca. 1,000, are cut down to near ground level, then allowed to re-grow anther generation of culms. Seed is then harvested selectively from plants that have re-grown vigorously with normal flowering and seed set, and which are then in the process of producing yet another (third) set of culms from basal branching.

Figure 1 shows the vigorous growth of the second vegetative generation. Figure 2 shows the growth of the third vegetative generation. Figure 3 shows how a culm which was trampled into a horizontal, prostrate attitude, was able to generate a totipotent plantlet from the nodal position, in the manner of sugar cane propagules. When cultured, these propagules prove to be totipotent.

The author believes that this material, begun within the public domain, should be made available to any party interested in carrying on this long-range work. Intriguing possibilities remain, such as the introduction of classical maize genes conferring still further attributes of perennialism, viz., grassy tillers, indeterminant growth habit, and extended vegetative persistance, especially exhibited by the Andean variety Cuzco and the gene lazy, to possibly enhance horizontality of basal and lateral branches. If a lazy perennial population were produced, it can be predicted that all the prostrate culms might produce plantlets at each node, which, upon re-rooting, might result in a carpeting effect of forageable material for domestic animals or for wildlife habitat.

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