Searching for new genetic and adaptive diversity for carrot improvement

Crop wild relatives are a rich resource for genetic and adaptive diversity for improving crops. The Royal Botanic Gardens, Kew’s Millennium Seed Bank works with partner institutions around the world to collect, conserve, and utilize seeds for conservation, research and livelihoods purposes. Among the approximately 40,000 plant species currently represented in the Millennium Seed Bank are 11 Daucus species and 8 D. carota subspecies. We undertook preliminary genetic and phenotypic characterization of D. carota accessions in order to gauge their potential for carrot genetic improvement. Of the 161 wild D. carota collections conserved at the Millennium Seed Bank, subsets of accessions were selected using principal component analysis of environmental data for each accession collection point (latitude, longitude). Accessions scoring highly in relation to high temperature and low rainfall components were selected for further testing since these were predicted to contain adaptive alleles relating to these environmental factors. Accessions from coastal environments were also selected to search for tolerance to salinity. Germination traits were then assayed under a range of controlled temperature and salinity conditions. Genetic diversity of 90 individuals from 19 wild accessions and 4 diverse cultivars (3-5 individuals accession(‑1)) was also assessed using 78,369 DArTseq single nucleotide polymorphism markers with known positions in the carrot reference genome. Our analyses confirmed previous studies that cultivars show closest affinity to Central Asian wild accessions pointing to this region as the center of domestication. Estimated marker heterozygosity was significantly higher in the cultivars (8.0%) than in the wild accessions (6.8%). Significant variation in germination response was observed among collections across different temperature and salinity treatments, with some accessions showing higher tolerance than others indicating potential adaptations. We discuss how these findings can be used for pre-breeding of carrot using its crop wild relatives.