Oral Paper

         Hybrids and Hybridization

Introgression of cultivar alleles into wild carrot populations in the United States

Presenting Author
Johanne Brunet
Description
Gene flow between crop species and their wild relatives has played an important role in the evolution of both wild and cultivated plants. Cultivated and wild carrots are classified as the same plant species, Daucus carota, and often occur in sympatry. Wild carrot, or Queen Anne´s lace, is strongly outcrossed and weedy, and has been declared invasives in many states in the US. Wild and cultivated carrots can hybridize and crop-wild hybrids can survive and reproduce almost as well as wild individuals in some environments. While hybridization does occur, it remains unclear whether crop alleles are maintained into the wild carrot genomes or whether they are purged out by natural selection. This is important as the development of gene editing technologies will permit introduction of genetically modified genes in carrot cultivars and some of these genes may increase the invasiveness and weediness of wild carrot populations. We used genomic data and population genomic methods to study hybridization and introgression between cultivated and wild carrots in the United States. We genotyped, using genotypic by sequencing, 450 wild individuals from 29 wild populations in seven states, and 144 cultivars, mostly from the United States, Europe, and Asia. After filtering, 523 samples (144 cultivated + 379 wild) and 34,871 SNP were kept. Wild samples had higher genetic diversity relative to the cultivars, and we detected significant genetic differentiation between the two groups. We identified, using ABBA-BABA tests and other approaches, two areas of the United States with evidence of introgression from cultivars into wild carrot populations, California and the Nantucket Island, in Massachusetts. The introgressed genes were distributed over all nine chromosomes, making it difficult to develop genetic methods to prevent their introgression into the wild carrot genome. Admixed populations were found in environments with milder winters than unadmixed populations, suggesting an influence of the environment on crop introgression. The introgression of genetically modified cultivar genes into wild carrot populations stresses the potential impact of gene editing technologies on the risk of increasing invasiveness and weediness of sexually compatible relatives of crops.