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 Center.
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
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
"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 methods."
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 methods."
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.