Local and foreign scientists have concluded the mysterious, ubiquitous corn variety is genetically modified, and illegal.

The presence of the modified corn amid local corn varieties is not yet alarming, but scientists warn it could usurp the hardier Oaxaca corn quickly unless it is stopped soon.

Transgenic strains were found in 15 of 22 communities in these hills and in 3 to 10 percent of plants in the fields sampled.

"What's frightening is how fast it has spread," said Yolanda Lara, spokeswoman for Oaxaca's non-governmental Rural Development Agency. "The government must put a stop to this."

Mexicans, who see their country as the birthplace of the centuries-old maize crop, are appalled by the discovery of genetically modified corn in their most far-flung highlands.

And speculation that the modified corn reached their lands in government trucks carrying subsidized kernels to community stores has fired that outrage still further.

GOVERNMENT UNDER FIRE

Cultivating genetically modified corn has been prohibited in Mexico since 1998, although it is imported from the United States for human consumption.

Village elders for whom corn is a way of life in the Oaxaca highlands first raised the alarm that a wild strain of corn was invading their native or so-called "Creole" maize.

"This corn is going to waste away our creoles," said Lino Martinez, the 81-year-old farmer of a small corn plot in nearby La Trinidad, perched on a steep mountainside with cornfields snaking up and down its slopes.

In La Trinidad, even the dentist's office has a corn patch for a backyard.

Biologists used DNA-testing on the "wild" corn and discovered that it was genetically modified. The University of California at Berkeley confirmed local findings in November, prompting demands that the Mexican government halt imports of transgenic corn.

With the presence of alien corn confirmed, activists are now going after its presumed source.

Residents in Capulalpan and a string of surrounding villages claim the corn arrived on government trucks dispensing low-cost basic food items to people in the area, where almost every house is flanked by a cornfield.

"Wherever those kernels fell, off the backs of the trucks, from bags carried from the store, the corn would grow," said Olga Toro Maldonada, 39, who cultivates corn in her backyard to help feed her six children.

"It even grows out of the concrete."

She claims the corn has been in the village for several years and is readily available at the local government store. Locals say the modified corn kernels are larger, differently colored and don't taste as sweet as native varieties.

SUSCEPTIBLE TO PLAGUE

Maldonada began planting the kernels herself three years ago, curious to see how they would grow. She says at least five other families in Capulalpan followed suit.

The results were remarkable, at first.

"The first crop was marvelous, yielding two or three head of corn per plant instead of one," said Maldonada as she walked through her tiny corn patch, pointing out varieties of maize she said were Creole, genetically modified and mixed.

It takes between four and five head of corn to create one kilogram of maize for tortillas, the nation's main staple food, so the new corn strain at first seemed to be a godsend.

But the windfall soured as Maldonada noticed that while the corn grew anywhere and with very little water, it was highly susceptible to plague once ripe.

She only stopped harvesting the maize after being told it was genetically modified and still an unknown quantity in the science world, where the impact of transgenics on the environment is unclear.