Message #221:
From: AzTeC SW Archaeology SIG
To:   "'Matthias Giessler'" 
Subject: Anthro Pursues Molecular Biology Of Corn In Wet Clay
Date: Wed, 11 Jun 1997 21:58:16 -0700


NEW EVIDENCE FOR CORN'S ANCESTRY COULD LEAD TO INSECT AND DROUGHT RESISTANT
CROPS

DURHAM, N.C. -- Scientists continue to debate the ancestry of domesticated
corn. But Duke University researcher Mary Eubanks said she has mounting
evidence that corn emerged from the interbreeding of two different wild
American grasses. Those grasses are Tripsacum dactyloides, also known as
Eastern gamagrass, and Zea diploperennis, a perennial variety of teosinte.
By successfully crossing them for the first time, Eubanks has produced
fertile offspring that closely resemble the earliest known samples of
primitive domesticated corn, she said in a recent interview. Patented lines
of her crosses are fertile over several generations and carry genetic
traits that are "missing links" in corn's evolution, Eubanks adds in the
latest issue of the journal Theoretical and Applied Genetics. That article
updates experiments originally described in the June, 1995 issue of
Economic Botany. She will report on her work again at an August meeting of
the American Institute of Biological Sciences in Montreal. If Tripsacum is
indeed a corn ancestor, then breeders could take advantage of some of the
special traits of that hardy ubiquitous plant, the Duke botany research
scientist said. Indeed, Eubanks has crossed her lines with modern corn to
produce hybrids that share Tripsacum's resistance to the corn rootworm.
That's the root-eating juvenile -- or larval -- stage of an insect that
costs corn farmers $1 billion a year in crop losses and pesticide
expenses. In preliminary experiments at Duke's Phytotron, a high-tech
greenhouse where she rents space, Eubanks found far less root damage and
far fewer larvae in her experimental hybrids than occurs in normal
commercial corn. "We're using the western corn rootworm, which is the most
serious pest in the Midwest," she said. "It's an incredible problem and a
big expense for corn growers. Because they don't know where they are going
to have an outbreak, they now have to treat all their fields with extremely
toxic chemicals." Tripsacum is drought resistant too, and Eubanks plans to
test her experimental hybrid for that trait as well. Moreover, her
Tripsacum-teosinte hybrids are perennials, and could conceivably be
exploited to produce a perennial variety of corn, she added. All of today's
commercial corn lines are annuals, meaning that their seeds must be planted
anew each year. Eubanks holds four patents on various Tripsacum-teosinte
crosses developed during the past decade. She is also president of Sun
Dance Genetics, a Durham, N.C. research company. Corn is "an anomaly in the
botanical kingdom," Eubanks said. "You have this tremendous ear. The ear
has hundreds of kernels, held together on a rigid stalk and enclosed by a
husk so they're easy to harvest and dry and store. It provided a wonderful
food for the original inhabitants of the Americas once they began
cultivating it." But the earliest known versions of corn have far smaller
ears that bear fewer and tinier kernels, providing silent testimony to the
corn genome's great adaptability. Scientists are in agreement on the
ancestry of the Old World's simpler staple grains -- oats, rye and wheat.
But the origins of the New World's major grain remain cloaked with mystery.
That's true even though "this is one of the most well studied organisms."
she said. With a Ph.D. in anthropology, Eubanks would seem an unlikely
person to pursue research into the molecular biology of corn genes. But,
while still in graduate school at the University of North Carolina, she met
Paul Mangelsdorf, a premier corn researcher who had retired from Harvard to
surrounding Chapel Hill. As an anthropologist, Eubanks was already
investigating the corn images that pre-Columbian Central Americans
frequently incorporated in their pottery. And she said that interested
Mangelsdorf because native American pottery makers pressed real ears of
corn into the wet clay to form botanically accurate molds. That meant her
pottery studies could give him vital clues about how domesticated corn
looked many centuries before the Spanish conquest. So her research trips to
Mexico and Peru aided Mangelsdorf's continuing work. In turn, Mangelsdorf's
passion quickly rubbed off on her. Eubanks began studying biology and
performing botanical research at Duke, Indiana, North Carolina State and
Vanderbilt universities. Scientists, including herself, now agree that
teosinte is an ancestor of corn, Eubanks said. Native to Mexico and
Guatemala, it features corn-like leaves and a tall stalk crowned by
corn-like tassels. It also has hard seeds that line up
in a single row -- called a "spike." However, Mangelsdorf once believed one
of corn's true ancestors was Tripsacum, a grass that ranges throughout
North and South America. "It's a pervasive weed around here," Eubanks said.
"It's on roadsides, railroad tracks and
bridges." The Tripsacum plant resembles corn less than teosinte does. But
both grasses grow single rows of grain on spikes. And both feature separate
male and female flowers on the same plant -- just like corn. Moreover,
Tripsacum occasionally produces paired kernels, a distinctive feature of
corn linked to the evolution of corn's multiple rows. In contrast to
teosinte, Tripsacum's kernels are also easy to remove from their hard
fruitcases, making them accessible as a wild food. And "they are highly
nutritious and delicious," Eubanks said. Based on breeding experiments in
the 1930s, Mangelsdorf and other researchers postulated that the earliest
true corn was derived from a cross between Tripsacum and a now-extinct wild
corn. Under that view, annually growing teosinte -- the only kind then
known -- was a later offspring rather than an ancestor. Archeological
evidence in Central America backed up Tripsacum's role, Eubanks said. In
the 1960s, Mangelsdorf and colleagues found the most ancient known
preserved corn samples, believed to be more than 5,000 years old, within
dry caves in Mexico's Valley of Tehuac‡n. The earliest samples of teosinte
have been dated to 1800 B.C. And the
earliest evidence for Tripsacum, found at Tamaulipas Mexico, predates that
teosinte by about 500 years. Nevertheless, Mangelsdorf joined the teosinte
bandwagon in the 1980s after other researchers discovered Zea diploperennis
growing on the threshold of extinction in the mountains of Jalisco, Mexico.
Rescued from the wilds, lines of that perennial teosinte are now being
maintained for research purposes. Mangelsdorf's new hypothesis, which he
held until his death, said annual teosinte resulted from a cross between
perennial Zea diploperennis and an extinct line of early corn. Domesticated
corn then arose from crosses between that corn and the new annual
teosintes. Most other experts believe natural genetic mutations actually
caused the spikes of some wild teosinte plants to directly evolve into the
first primitive ears of corn, Eubanks said. Under that hypothesis, Native
Americans then improved the first corns through accidental or intentional
breeding efforts. But Eubanks maintains that Tripsacum is corn's other
ancestor plant. And the discovery of perennial teosinte is helping her
prove that hypothesis, she said. Her initial breeding experiments showed
that -- unlike any other teosinte -- Zea diploperennis can be successfully
crossed with Tripsacum to produce a fertile hybrid. Previous attempts to
breed Tripsacum with any other teosinte varieties had failed. Similarly,
previous attempts by breeders to cross Tripsacum with corn always resulted
in sterile plants. But Eubanks found she could also successfully breed corn
with some of her Tripsacum and Zea diploperennis crosses. Since fertile
offspring implies genetic similarities among plants, Eubanks believed her
experiments rekindled the notion that Tripsacum was a forebear of corn.
Other scientists initially didn't accept her hypothesis. "It questioned
accepted dogma," she said. "I had difficulty convincing the scientific
community that I even had a hybrid between Tripsacum and the perennial
teosinte. They said I just had teosinte that was contaminated with corn,
and that it was impossible to cross teosinte with Tripsacum." Eubanks said
she continued in the face of criticism because she knew her work had
already been validated by the U.S.
Patent Office's rigorous documentation process. She also persisted because
of her plants' potential contributions to agriculture and human welfare,
she added. Seeking further proof, Eubanks used molecular genetic analysis
to show that traits from both plant types were present in the offspring.
She worked with key heritable DNA markers that other scientists --
including her principal detractor -- had previously identified as being
crucial in the evolution of domestic corn. Her new report in Theoretical
and Applied Genetics shows some of those markers have now been "stably
inherited" for three generations, she said. Eubanks is now embarked in an
expanded study of the complex genetic relationships between teosinte,
Tripsacum, primitive corns and other related New World grasses. The
National Science Foundation's Small Business Innovation in Research program
is funding Eubanks' research on corn rootworm resistance. She is conducting
her evolutionary studies of corn and related grasses under an Andrew P.
Mellon fellowship in plant systemics at Duke. She has also supported her
work from earnings as a self-employed consultant, and by teaching advanced
high school biology at the North Carolina School of Science and Mathematics
and Durham Academy. With funding from the National Geographic Society, she
is now completing a book about the interdisciplinary archaeobotanical
studies she did in the 1970s of corn impressions on Mexican and Peruvian
pottery. The book, called Corn in Clay, will be published by the University
of Florida Press. "There are two Peruvian pieces in the collection here at
the Duke Art Museum," she noted. "There is one that depicts a rat eating an
ear of corn. Then there is one that represents a basket of corn." The first
piece is "somewhat problematic," Eubanks said. The corn casts it carries
have more rows and larger kernels than any Latin American race of corn that
exists today. "We think it may represent an extinct race," she added.

http://www.dukenews.duke.edu/research/corn.html
June 4, 1997 Contact: Monte Basgall (919) 681-8057 monte@dukenews.duke.edu