Long-Range Pollination Is Problem for Geneticists
The greatest danger posed by genetic engineering of plants may come from sex with weeds.
Scientists have long known that some domestic plants can interbreed with weeds, transferring their genes to weedy offspring. But new work by Norman C. Ellstrand of UC Riverside shows that the transfer of genes can occur over far greater distances than anyone had expected.
Ellstrand’s findings take on special significance now that biologists have begun to manipulate the genes of plants directly, hoping to create crops that resist disease, tolerate drought conditions, and have other useful characteristics. One question is whether these manipulations might create problems in the environment.
Pollination Process
When a plant scatters its pollen, nearby plants of the same species are usually the ones fertilized. Weeds that are closely related to the plant also may be fertilized, but it was thought that pollen could spread no farther than about 300 feet. Ellstrand found that no one had checked longer distances.
His studies show that wild radishes more than 300 feet away from a plot of domestic plants were sired by seeds from the domestic plants. He found 20% of these wild plants had fathers in the domestic plot.
“(Three-hundred feet) is not adequate to prevent most plants from mating, as was originally thought,” Ellstrand said. “For many plant species . . . gene flow by pollen occurs readily among populations that are separated by (300 feet, 3,000 feet) and even greater distances.”
Precautions will have to be taken, he said, to prevent weeds from acquiring the same prodigious characteristics that researchers are trying to confer on crops, and to prevent the weeds from acquiring genes that give crop plants resistance to herbicides intended to kill weeds.
The rattlebox plant, a weed in some pastures, contains a poison potent enough to kill a cow. But as entomologists have known for some time, caterpillars of the ornate moth feed happily on the plant, storing its poison in their bodies to protect them from predators.
Scientists at Cornell University have found that the poison is so valuable to ornate moths that the females will mate only with males that first prove they have eaten lots of the toxic substance.
The males do this in their courtship ritual, emitting a puff of aromatic chemicals made from a little of the stored poison. The more the males have in them, the more aromatic the puff and, the scientists found, the more likely the female is to accept the male’s advances.
The researchers also found that when the male inseminates the female, he also transfers into her body a dose of the poison from his supply. This poison, along with some from the female’s body, is then put in each egg she will lay. As a result, the eggs and hatchling caterpillars enjoy the protective benefits of the poison before they even begin feeding on the rattlebox plants.
