Western Maize Genetics

25 generations of mass selection for perennialism in diploid maize

— Shaver, DL

This work was begun using a seed source of “Zea diploperennis”, which was then crossed to agronomic, Stiff-stalk-derived maize inbreds. As in the tetraploid population, described above, the resultant hybrid, as grown in an isolated population of ca. 1,000 plants, to select for perennialism, or attributes of perennialism. After several generations of selection, satisfactory levels of the perennial phenotyne were achieved, and another backcross to acronomic maize inhreds was made. After each cross back to maize inbreds, nearly all perennial attributes were lost, except for simple basal branching, and some vegetative persistence, but upon prolonged further generations of mass selection in isolations, perennialism could be restored, so that still another backcross to maize could be made. The present population, then, is theoretically 7/8 maize, and 1/8 Zea diploperennis.

As seen in Fig. 1, the second generation of culms, from which seed is selectively saved, are very vigorous and appear totipotent. Fig. 2 shows the generation of the third set of culms being vigorously produced, at which time, in late fall, the growing season ends at Greenfield, Ca.

It should be made clear that although in this article, the terrn, “Perennialsm” is used liberally, the author does not believe that in the diploid work, that true, endlessly vegetatively totipotency exists. Rather, he believes that such totipotency progressively “runs out”. This is completely contrary to the situation in the tetrapoid work, where, if cultured, the advanced-generation propagules remain immortal.

Nevertheless, the condition of diploidy does not preclude true perennialism, as shown by Shaver, J. Heredity 58:270–273. The clone upon which that article was based was truly perennial, totipotent, and had a balanced 20-chromosome karyotype. To great misfortune, it was lost during a career change. In the past 40 years from this unfortunate loss, the author has sporadically attempted to duplicate that result, but from only using maize × diploperennis derivatives, and not with the addition of the maize genes id and gt or pe. If any or all of these three mentioned genes were added to the present population, the author believes that true totipotency might be achieved in the condition.

Perennial diploid maize would be important as a means of keeping chromosomal types extant which are not transmissible thru the gametes, for classroom studies or other research. Agronomically, several possibilities can be imagined. The definition of a physiological basis for totipotency in maize might represent a significant advancement of both academic and practical usefulness.

The author believes that the population described here ought to be freely available to the public domain on the hopes that such work night be further advanced, and seed is available to interested responsible parties. As with the 4N population mentioned in the previous article, the author believes that it would be of great interest to incorporate further classical maize genes, such as lazy, indeterminant growth, grassy tillers, and “Cuzco”.

Please Note: As is the policy with the printed version, notes submitted to the Maize Genetics Cooperation Newsletter may be cited only with consent of the authors.

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