April 8, 2004 -- CropChoice news -- EurekAlert!, Duke University,
07/02/04: The scientific puzzle pieces are
fitting together to form a definitive picture of the
origin of corn, says a Duke University plant geneticist
who has proposed that the world's most important food
crop originated in an ancient cross between two grasses.
Mary Eubanks described the latest evidence that corn,
or maize, originated as a cross between teosinte and
gamagrass, or Tripsacum , in a talk Friday, April 2,
2004, at a symposium on maize held at the annual meeting
of the Society for American Archaeology (www.saa.org
) in Montreal. Her research is supported by the
National Science Foundation and the North Carolina Biotechnology
Eubanks, an adjunct professor of biology, has developed
evidence that modern corn, scientific name Zea mays,
did not evolve solely from a Central American grass
known as teosinte -- traditionally the most widely held
theory. Rather, her experiments clearly demonstrate
that corn arose from a serendipitously viable cross
between teosinte and gamagrass.
Eubanks emphasized in an interview that her research
has confirmed that teosinte was indeed one of corn's
ancestors, and that gamagrass was a critical genetic
contributor. She contrasts her evidence with the former,
highly controversial theory of the late biologist Paul
Mangelsdorf, who espoused that teosinte was an offshoot
of a cross between corn and Tripsacum rather than an
ancestor of corn. "My hypothesis confirms that
teosinte is an ancestor of maize, and that key genes
were also contributed by gamagrass," she said.
In her talk, Eubanks displayed examples of her crosses
between species of teosinte and gamagrass that exhibit
the evolution from the tiny spikes of teosinte seeds
to the early versions of corn ears.
New evidence from other researchers that maize evolved
very rapidly, perhaps over only a century, supports
such a theory, said Eubanks. Rather than the long, slow
progressive evolution from teosinte into maize, a fertile
cross between teosinte and gamagrass could have relatively
quickly yielded early versions of maize. In her talk,
Eubanks displayed archaeological specimens of corn alongside
matching segregates from experimental crosses between
teosinte and gamagrass.
Eubanks also discussed her comparative DNA fingerprinting
studies of teosinte and Tripsacum taxa, along with primitive
popcorns from Mexico and South America. Those analyses
of over a hundred genes in the taxa revealed that some
20 percent of the versions, called alleles, of specific
genes found in maize are found only in Tripsacum . And,
about 36 percent of the alleles in maize were shared
uniquely with teosinte.
"These findings are by no means conclusive,"
said Eubanks. "We need to do a lot more sampling
of the genetic diversity in different teosinte and Tripsacum
species to further test this finding. But certainly,
the preliminary evidence from this study supports the
hypothesis that Tripsacum introgression could have been
the energizing factor for the mutations that humans
then selected to derive domesticated maize."
In such selections, theorized Eubanks, early humans
would have selected -- from the wide range of plants
that would result from such crosses -- those that had
the most numerous and accessible seeds. Eventually,
such selection would have resulted in the cob-like structure
of today's corn, she said.
Understanding the genetic origins of corn -- now the
world's single largest food crop-- is important both
for production of new varieties and for preserving corn's
genetic heritage, said Eubanks.
"Because the crosses between teosinte and gamagrass
bridge the sterility barrier between maize and Tripsacum
, I'm now moving genes from gamagrass into corn,"
she said. "And we have developed drought-resistant
and insect-resistant corn using conventional plant breeding
For example, according to Eubanks, who is working with
a commercial seed producer, test crops of some new hybrids
have shown strong resistance to the billion-dollar bugs
corn rootworm and European corn borer, along with corn
earworm, another problematic corn pest.
"Understanding the genetic origins of corn and
how people historically used corn could offer valuable
insights for application to sustainable agriculture
today," she said. "And finally, the gene pool
underlying corn is part of our heritage that must be
preserved if we are to retain the ability to solve agricultural
problems such as new pests or the need for new farming
Also, she noted, the scientific emphasis on corn is
particularly timely because of recent findings that
genetically altered corn is contaminating the native
land races of maize and its wild relative teosinte currently
in Mexico. This alteration of the natural gene pools
of these genetic resources could have the effect of
reducing the diversity of corn varieties, and compromise
the ability to use those varieties as the basis for
new crop strains.
According to Eubanks, the new drought and pest-resistant
hybrids she and her colleagues have developed will undergo
field tests this summer in the Midwest, followed by
yield trials in winter nurseries, more field tests in
the Midwest in 2005, and marketing seed in 2006.