After exposing more than 70 million grain amaranth seeds to a soil-based herbicide, researchers were not able to find a single herbicide-resistant mutant. Though preliminary, the findings suggest that the mutation rate in amaranth is very low, and that low-level herbicide application contributes little -- if anything -- to the onset of new mutations conferring resistance, researchers say.
The study is reported in the journal Weed Science.
Any major stress that does not kill a plant can contribute to genetic mutations in its seeds and pollen, said University of Illinois crop sciences professor Patrick Tranel, who led the new research. Even the ultraviolet light in sunlight can stress a plant and increase the likelihood of mutations in its offspring, he said. Such mutations increase genetic diversity, which can be useful to a species' survival.
"Resistance to herbicides comes from genetic variation in a population," Tranel said. "If an individual weed has the right mutation that allows it to survive a particular herbicide, that individual will survive and pass the trait to its progeny."