|Iorizzo, Massimo -|
|Ellison, Shelby -|
|Grzebelus, Dariusz -|
|Cavagnaro, Pablo -|
|Allender, Charlotte -|
|Van Deynze, Allen -|
Submitted to: American Journal of Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 26, 2013
Publication Date: May 1, 2013
Repository URL: http://handle.nal.usda.gov/10113/56712
Citation: Iorizzo, M., Senalik, D.A., Ellison, S., Grzebelus, D., Cavagnaro, P., Allender, C., Brunet, J., Spooner, D.M., Van Deynze, A., Simon, P.W. 2013. Genetic structure and domestication of carrot (Daucus carota subsp. sativus) (Apiaceae). American Journal of Botany. 100(5):930-938. Interpretive Summary: Wild carrot is thought to have its geographic origins in Central Asia, although it is widespread globally today. Carrot has been cultivated as a root crop about 1100 years, but the genetic structure of wild carrot and geographic origin of cultivated carrot are uncertain. Utilizing molecular genetic markers that have recently been developed, we evaluated the genetic structure of carrot to determine the origin of domestication of carrot, the origin of orange storage root color in cultivated carrot, and the geographic origin of north American wild carrot. The geographic origin of domesticated carrot has been proposed by Vavilov as Central Asia, and evaluations of single versus multiple origins have not been made. This study provides evidence for a single origin of domesticated carrot in Central Asia with no evidence of a genetic bottleneck during carrot domestication. Orange storage root color is only observed in cultivated carrot, and only in the last 400 to 500 years, so it is considered a secondary domestication event of carrot. This trait was hypothesized to have been derived from an intercross with wild carrot, which has white roots, and cultivated carrots with yellow roots, but in this study we found no genetic footprint of a hybridization event, supporting a second hypothesis that orange root color was selected from yellow cultivated carrots. Given the Eurasian origins of wild carrot, the origins of wild carrot in North America have been uncertain. It might be speculated that wild carrot could have been introduced from Asia when the land bridge allowed early human migration, or that there was introduction of wild carrot with European settlers to North America, or that it is an escape of domesticated carrot from cultivation. Our evidence in this study indicated that wild carrot from North America was most closely related to, and consequently is likely derived from, European wild carrot. The origins of domestication have been studies in relatively few crop plants, and most of those studied have been major staple crops. These studies clarify our understanding of carrot diversity and domestication, and they suggest that a wealth of genetic diversity is available for future carrot improvement, both in cultivated and wild carrots. This study will be of interest to plant geneticists, breeders, and evolutionists, as well as the general public.
Technical Abstract: We investigated domestication and genetic structure in wild and open pollinated cultivated carrots (Daucus carota L.) with 3481 SNPs developed from carrot transcriptome sequences. Phylogenetic analysis revealed a clear genetic separation between wild and cultivated carrot accessions. Among the wild carrots, those from Central Asia were genetically most similar to cultivated accessions. These results, in conjunction with historical documents, suggest a single origin of domesticated carrot in Central Asia. Interestingly, comparative genetic diversity of wild and cultivated accessions indicated that there was not a genetic bottleneck during carrot domestication. Furthermore, we found that wild carrot from North America was most closely related to European wild accessions, providing evidence that wild carrots were likely introduced as weeds to the USA with European colonization, not from Asia with the first human migration, and not as escapes from cultivated carrot. This study provides the first genetic evidence of geographical structure of wild and cultivated carrot that addresses the location of carrot domestication and offers a framework for future genomic studies.