Riverside, Calif. UC Riverside scientists studying the genetic makeup of wild radishes in California have determined that the California wild radish is descended from hybrids between two species: cultivated radish and the weed called jointed charlock. The hybrid-derived plants apparently have completely eliminated the ancestral species from California, the researchers report.
The discovery is significant because the parental species were replaced by a single, stable hybrid lineage in less than 100 years, an extremely short interval in evolution. The researchers attribute the rapid spread of the hybrid radish to the evolution of a unique combination of traits relative to the parental species. These traits include unswollen roots, which are not as sensitive to disease and injury as are swollen roots, and early flowering.
The researchers published their findings in the June issue of Evolution. Next week's issue of the journal Nature highlights their research.
"The documented instances of extinction by hybridization in which both parents are replaced by the hybrid are rare," said Subray G. Hegde, the lead author of the paper and a postgraduate research geneticist who, in 2001, joined the research group of Norman C. Ellstrand, professor of genetics in UCR's Department of Botany and Plant Sciences. "What we've shown is that the extinction of a species by this process can occur very rapidly. We need to recognize the lesson this teaches us for conservation: if we are to save organisms from extinction, we need to make sound decisions fast."
Both the cultivated radish and jointed charlock were introduced to California more than 100 years ago. While the cultivated variety, found in grocery stores, bears pink, purple and white flowers and has a swollen root, the weed bears yellow flowers (occasionally also white) and has a slender root.