GUELATAO, Mexico — Yank the husks off ears of corn grown in the mountains of southern Mexico, and you may find kernels that are red, yellow, white, blue, black or even variegated.
It's only one measure of the diversity of the 60 or so native varieties of corn in Mexico. Another is the unusual adaptation of some varieties to drought, high heat, altitude or strong winds.
Plant specialists describe the native varieties of corn in Mexico as a genetic trove that might prove valuable should extreme weather associated with global warming get out of hand. Corn, one of the most widely grown grains in the world, is a key component of the global food supply.
But experts say Mexico's native varieties are themselves under peril — from economics and genetic contamination — potentially depriving humans of a crucial resource.
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Farmers are punished at the marketplace for selling native corn, and some types are dwindling from use. Perhaps more significantly, genetically modified corn is drifting southward and mingling with native varieties, potentially bringing unexpected aberrations and even possible extinction.
At stake may be more than just curious and exotic types of corn, grown in small fields alongside beans and then ground into tortillas after harvest.
"With climate change," said Aldo Gonzalez, an indigenous Zapotec engineer with long, flowing black hair who's at the forefront of protecting native varieties, "new diseases could occur, and the only place in the world where we can look for existing varieties that might be resistant is in Mexico.
"These varieties of corn might at some point save humanity."
Corn is not only a crucial crop in Mexico but also a symbol in a nation that's the birthplace of the grain. Maize likely originated from a grass-like, tasseled plant, teosinte, in southern Mexico. Scientists say humans domesticated corn 7,000 to 10,000 years ago.
In the Popol Vuh, the sacred book of the ancient Mayans, gods create humans out of cornmeal, allowing the "people of corn" to flourish.
Through the centuries, varieties of corn adapted to different soils, altitudes, temperature conditions and water availability, and Gonzalez said the seed stock handed down in his village in this corner of the Sierra Juarez range in central Oaxaca state probably wouldn't grow well just a few miles distant.
"In the sierra here, there are varieties of corn that grow as high as 3,000 meters," Gonzalez said, or nearly 10,000 feet. "There are varieties that can be planted in swampy land or that you can plant in semidesert areas. They may not be very productive but they have allowed people to survive."
Native varieties of corn have fed humans for millennia in Mesoamerica.
"The elders understand the importance of various types of corn because they had their fields in different places under different conditions," said Lilia Perez Santiago, an agricultural engineer who works for a state forestry bureau.
Perez was among the activists behind a petition in 2000 to the Montreal-based Commission for Environmental Cooperation, a panel created under the North American Free Trade Agreement. The petition claimed that genetically modified corn, altered to be pest resistant or herbicide tolerant, had drifted to southern Mexico and begun contaminating native varieties.
Four years later, the panel recommended to Mexico that it suspend modified corn imports and adopt strict labeling rules to allow the public to identify food products that contained such corn. Mexico ignored the recommendations, arguing that the ruling came into conflict with its obligations to open markets under trade pacts.
In late 2009, the government permitted a subsidiary of a U.S. conglomerate, Monsanto, to test genetically modified corn on isolated plots of about 240 acres in Sinaloa and Tamaulipas states in the north.
The head of Monsanto Mexico, Jose Manuel Madero, said at a news conference two weeks ago that the federal government demands further tests before allowing commercial farming of the genetically altered corn.
Madero said modified corn was in use in 20 countries around the world and would help Mexico raise agricultural productivity, cut its reliance on food imports and slash the use of herbicides, thereby protecting the environment.
Several scientists have joined a Mexican grass-roots campaign, known as Sin Maiz No Hay Pais, or There Is No Country Without Corn, to oppose the import or harvest of genetically changed corn.
"We have a nationwide survey that shows genetic contamination in Guanajuato, Yucatan, Veracruz and Oaxaca (states). We also know of some large-scale plantings in Chihuahua," said Elena Alvarez-Buylla Roces, a molecular geneticist at the National Autonomous University of Mexico.
She said lab analysis showed that some native varieties already carried altered genes.
"There is no possibility of coexistence without contamination," Alvarez-Buylla said. "One gene can make a large difference. Do we want to run the risk?"
Black-market brokers already sell genetically modified seed corn to farmers in the north of Mexico, opponents say, and bags of unmarked genetically altered corn have been found in the far south.
"The bags of corn are not secure. During transport, some bags break open and fall out. So there are many possible ways of contamination," Perez said.
The vast majority of farmers of native varieties select seeds each year to save for the next harvest, thus making what Alvarez-Buylla described as "active, dynamic genetic elements" prone to aberrations from genetic drift of altered corn.
Scientists don't know which varieties could prove useful for climate change.
"We don't really know if there is a variety with the most promise. Promise for what?" Alvarez-Buylla said, adding that future climate conditions are unknowable.
While the government maintains seed banks for native corn, Alvarez-Buylla said, "This is not a diversity that can be preserved in a laboratory."
Some farmers already are abandoning certain native varieties, unable to make a living harvesting their small plots.
"They get a price penalty for not growing uniform, large volumes of corn that the tortilla manufacturers want," said Timothy A. Wise, a rural policy expert at the Global Development and Environment Institute at Tufts University in Massachusetts.
Economic realities that make it increasingly unviable for farmers to grow native varieties may be as big a peril as genetic contamination, Wise said.
"If that traditional knowledge isn't passed from generation to generation and those farmers stop farming, then that seed variety is lost for economic reasons," he said.
In Mexico's cities, consumers have little taste for the native varieties of corn in their own country, offering no price advantage for the small farmers who are nurturing the nation's corn diversity.
"In urban areas," Gonzalez said, "they don't know about the varieties. All they know is that the dining room table must have tortillas on it."
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