Mexico, widely considered the birthplace of corn, is close to finalizing rules governing experimental planting of genetically modified corn strains, a senior biosecurity official said on Tuesday. In Mexico, where tortillas made from corn are eaten with almost every meal, the government is determined to boost output in the next few years to offset rising prices driven by U.S. demand for corn-based ethanol fuel. Mexico’s biggest grain farmers have long lobbied to lift a 1998 ban on GMO corn plantings, arguing it would help lift lagging crop yields. But environmental activists say GMO would put Mexico’s numerous local corn strains at risk.