Origin of extant domesticated sunflowers in eastern North America

Abstract

Eastern North America is one of at least six regions of the world where agriculture is thought to have arisen wholly independently. The primary evidence for this hypothesis derives from morphological changes in the archaeobotanical record of three important crops--squash, goosefoot and sunflower--as well as an extinct minor cultigen, sumpweed. However, the geographical origins of two of the three primary domesticates--squash and goosefoot--are now debated, and until recently sunflower (Helianthus annuus L.) has been considered the only undisputed eastern North American domesticate. The discovery of 4,000-year-old domesticated sunflower remains from San Andrés, Tabasco, implies an earlier and possibly independent origin of domestication in Mexico and has stimulated a re-examination of the geographical origin of domesticated sunflower. Here we describe the genetic relationships and pattern of genetic drift between extant domesticated strains and wild populations collected from throughout the USA and Mexico. We show that extant domesticates arose in eastern North America, with a substantial genetic bottleneck occurring during domestication.

Genetic signals of origin, spread, and introgression in a large sample of maize landraces

“…The contradiction between evidence supporting the earliest cultivation in the lowlands and the genetically ancestral position of Mexican Highland maize is therefore of particular interest. The disagreement is important, because the adaptive differences between highland and lowland maize are profound (14,29 the geography of crop origins has been resolved by locating the most likely wild ancestor (24,(30)(31)(32)(33). In the case of maize, however, the distribution of the wild ancestor does not coincide with the distribution of the cultivars most genetically similar to it.…”

“…Because introgression from mexicana may affect ancestry inference based on genetic distance from parviglumis, we took an approach that does not require reference to the wild relatives. Under models of historical range expansion, genetic differentiation increases away from the population of origin (22,23), and estimates of drift from ancestral frequencies have been applied successfully to identify ancestral populations (24). We therefore applied the method of Nicholson et al (25) to estimate simultaneously ancestral frequencies and F, a measure of genetic drift of away from these frequencies, for sets of predefined populations.…”

Reassessing Coxcatlan Cave and the early history of domesticated plants in Mesoamerica

“…The San Andrés achene and seed identified as Helianthus annuus, for example, were cited by David Lentz as evidence that sunflower was first domesticated not in eastern North America, but in Mexico, and that, as a result, the status of eastern North America as an independent center of plant domestication could be called into question (30). Genetic analysis, however, has confirmed eastern North America as the source of all modern domesticated sunflower varieties, which relegates the Tabasco sunflower to the status of either an introduction from eastern North America or a secondary domestication event that quickly went extinct (31).…”

Identification and mapping of SNPs from ESTs in sunflower

“…Predominant within the Compositae is the cultivated sunflower (Helianthus annuus L.), the only major crop plant native to North America (Harter et al 2004) and one of the world's most important oilseed crops (FAOSTAT data 2004). In addition to oilseed production, sunflowers have become increasingly popular in recent years as a confectionery (snack food) and an ornamental crop.…”