In the debate over genetically modified foods, scientists often point to what they see as a double standard. Why such fear and loathing about a technology that's essentially a more precise way of doing what plant breeders have been doing for thousands of years?

Myriad crops with desirable traits have been created via conventional plant-breeding methods. Breeders might, for example, mate a commercial potato with a wild potato that is resistant to an insect pest. By repeatedly crossing the resulting hybrid back to commercial potatoes, they hope to end up with a spud that mostly has genes of the commercial potato but contains the new, disease-resistant trait.

Invariably, many other wild genes are present in the final result, said Kevin Folta, a plant molecular biologist at the University of Florida in Gainesville. With conventional breeding, "who knows what you're doing?" he said. Genetic engineering, by contrast, introduces just a few well-characterized genes, he said.

In the 20th century, researchers incorporated more high-tech approaches in breeding new varieties: treating plant tissue with ionizing radiation or chemicals that cause genetic mutations with the hope of prompting a mutation that might be helpful. Red grapefruits are the result of radiation-induced mutations, as is a fungus-resistant Japanese pear called Osa gold, for example. Another breeding method is to fuse together cells from different varieties or species to transfer a useful trait to a plant.

For the most part, the products of conventional breeding are benign. But scientists have created a few doozies.

In the 1960s and again in the 1990s, potatoes with dangerously high levels of a natural pest-fighting chemical called solanine were withdrawn from the market. Celery plants conventionally bred for insect resistance have been linked to rashes in grocery workers in cases dating back to 1984 and in field hands since 1961. Though breeders may monitor the levels of toxic natural chemicals in their products, the U.S. government doesn't require them to do so.

Though this may seem illogical, "regulations are not based solely on science," said Gregory Jaffe, director of the biotechnology project at the Center for Science in the Public Interest in Washington. "Sometimes we're trying to improve consumer confidence about something new and novel."

rosie.mestel@latimes.com

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Scientists see double standard in critique of altered foods

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