A
scenario for one of the teosinte origins of maize
--Galinat, WC2
When the mutant building-block genes for
maize were still scattered around at random in wild populations of teosinte
about 7000 or more years ago, the following scenario could account for
one or more ancient origins of maize under a domestication of teosinte.
For the purpose of this discussion, I shall give full credit to my vision
of just one wise, observant, elderly Indian lady who happened to be a farmer-breeder.
She observed that the seeds of both teosinte and Tripsacum were
borne single because they had to fit tightly within a fruitcase designed
for protection against hungry birds, insects and people (Galinat, 1970.
U. Mass. A. E. S, Bul. 585). She also observed that the male spikelets
borne higher up on the same axis were paired, free of fruitcases and free
to dangle their anthers to scatter their load of pollen. She felt sorry
for the solitary female spikelets locked in their fruitcase jails. If the
male spikelets could be paired and free, so could domestic female spikelets.
She thought this was a clear case of sex discrimination! She offered a
gift or reward to any of the hundreds of gatherers of wild teosinte seed
who would bring her ears of four-rowed teosinte � four-rowed due to paired
female spikelets � just as free as the male spikelets. The four-rowed teosinte
gatherers (men, women, children) came from miles away in all directions
to give the wise lady their four-rowed ears of teosinte which she examined
and, if good, paid the reward. Then one day some child handed her a four-rowed
ear that had four rows of decussate single female spikelets. The
wise lady glanced at the upper male region. The male spikelets remained
paired but in four-ranks like the female region and the total now was eight
male rows. She screamed "You dear child from the land of God's maize
called teosinte have brought me a great treasure � the fantastic
key to humanity's maize. A new cereal can now be bred that
will result in an ever higher civilization of better fed, more thoughtful
people who will cooperate with each other and live in peaceful harmony."
In her great wisdom, she carefully planted
the two kinds of four-rowed teosinte in a special isolated garden. The
one with four ranks of single spikelets was in a central area that she
detasseled. All around it was her large collection of teosinte with paired
female spikelets that would be the pollinators for the detasseled plants.
Later she harvested the crossed seed from these female plants and the next
growing season had the F1 hybrid in an isolated block. Then in the second
year, the year of the F2 segregation, she found that 6.25% (1/16) of the
plants carried the double recessive recombinant form a merger of the two
different double rowing female pathways. These few pioneer plants were
more than just the Adam and Eve of the first eight-rowed maize. They were
destined to be progenitors to thousands of years of maize diversification
and the best "Staff of Life" for humankind on planet Earth and throughout
the Universe.
If my fictional story of the wise Indian
lady as the mother of maize has not spoken clearly to you about my beautiful
vision of corn's origin, then perhaps the languages of my poetry and artwork
working together will communicate (Figs 1a & 1b).
Here you see,
How two kinds of four-rowed teosinte,
Became the key to maize's pedigree
When one morn, the first corn was born,
An amazing creation of recombination.
Figure
1a: Longitudinal views of teosinte, two different mutant kinds of four-rowed
teosinte and a recombinant F2 double recessive eight-rowed maize. Notice
the rowing of the male spikelets that are in the upper region above the
female region and that the ear with four-ranks of single female spikelets
has eight rows of male spikelets in the upper region as well as a pair
of leaves just below the spike. The eight rowed ear of maize has eight
rows of male spikelets.
Figure
1b: Cross-sectional views of just the female spikelets showing all
four types of F2 segregants. The F2 frequency distribution ratios of 9:3:3:1
and 1:3:3:9 along the right hand edge represent a reversal of dominance
with the teosinte background being the 9:3:3:1 and the maize background
the 1:3:3:9. The architecture differences in ear structure of the two backgrounds
reflect corresponding differences in energy sink capacity and this in turn
controls the dominance of the genes involved.
When the architecture of both the maize
plant and its ears became designed to capture and then store a maximum
of the photosynthetic energy, then the maize architecture became dominant
over the primitive teosinte architecture. As a result, maize became important
to the future of both humankind and our home planet.
_________________________
2I was often accused by Paul
Mangelsdorf of having an unfettered imagination, especially when he disagreed
with me, and this fictional story may be just another example. But
my fictional story here deals with real things and human nature to explain
an accepted fact.
Please Note: Notes submitted to the Maize Genetics Cooperation Newsletter may be cited only with consent of the authors.
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