"Even though we made extensive new collections of wild and cultivated sunflowers native to Mexico that for the first time provided us with a powerful sample to test for a second origin, our results from multiple types of genetic data found strong evidence for just a single origin," Blackman said.
The analysis of hereditary molecular differences in the three sunflower genes shown to have experienced selective sweeps -- the loss or lowering of variation in DNA sequences due to artificial or natural selection -- confirmed that domesticated sunflowers grown in Mexico today are descended from the same cultivated genetic lineage as eastern North America domesticated sunflowers. All of those varieties, whether from Mexico or North America, carried sequences diagnostic for cultivation at the domestication at these loci, and genetic ancestry inferred from neutral markers scattered throughout the genome independently and unambiguously confirmed the same result.
A few qualifications remain, as the team could have missed finding a modern Mexican domesticated version descended from an independent Mexican lineage. There may have also been an ancient Mexican lineage that has since become extinct and for which no modern germplasm has survived. Some scientists have speculated that extinction could have been facilitated by the proposed role colonial Spanish Christians may have taken in eradicating sunflower as an important religious symbol to the solar-worshipping Aztecs, or recently by the substantial influx of seed imports made possible by the North American Free Trade Agreement.
"Although current archaeological finds indicate that ancient Mesoamericans cultivated sunflower before Spanish colonists arrived in the New World, more discoveries are needed to understan
|Contact: Steve Chaplin|