Mexico on Thursday approved its first permits for genetically-modified test crops of corn, in a controversial move to boost the staple food in the cradle of maize production.

The agriculture and environment ministries announced the first two permits in a joint statement, but did not name the companies involved or specify where the fields were. They said that 35 permit requests had been made.

The first permits would be applied under controlled conditions, "totally isolated from other crops," the statement said.

Critics worry that the crop genes will spread to other plants -- creating uncontrollable superweeds and superbugs -- and also that they could contaminate Mexico's pre-Hispanic varieties of corn.

Greenpeace immediately slammed the permits and planned to file motions in court to "prevent this environmental crime," said watchdog representative Aleira Lara.

"They've ignored the warning from the scientific community about the risk for our country, the center of origin and genetic diversity of corn, to be contaminated by these kind of organisms," Lara said.

Corn is used to make the country's staple flat tortillas and many other dishes. Mexico is the number one producer of white corn and it mainly imports yellow corn as fodder for cattle.

Supporters of the technology tell farmers that they will reap profits from growing genetically-modified crops. Initially, the cost is expensive but money is saved on pesticides.