Flowering trait ontology facilitates utilization of biennial carrot (Daucus carota L.) genetic resources

Authors: LOARCA, JENYNE - University Of Wisconsin; LIOU, MICHAEL - University Of Wisconsin; DAWSON, JULIE - University Of Wisconsin; Simon, Philipp

Submitted to: Frontiers in Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/26/2024
Publication Date: 4/19/2024
Citation: Loarca, J., Liou, M., Dawson, J., Simon, P.W. 2024. Flowering trait ontology facilitates utilization of biennial carrot (Daucus carota L.) genetic resources. Frontiers in Plant Science. 15:1342-2513. https://doi.org/10.3389/fpls.2024.1342513.
DOI: https://doi.org/10.3389/fpls.2024.1342513

Interpretive Summary: Flowering and seed production are not typically observed by carrot growers since even the early stages of carrot flowering impart tough and woody texture to the taproot that rapidly becomes more pronounced, making flowering carrots unmarketable. Preliminary studies noted a wide range of flowering times among a few carrot cultivars. Given this observed variation, in this study 750 diverse cultivated carrot accessions held in the USDA carrot germplasm collection, or developed by breeders, were evaluated to record variation in flowering time. Consistent initiation of flowering time was observed for individual accessions in this carrot collection over three years of field evaluation. This study indicates a strong genetic basis for this important trait, and provides carrot breeders with valuable information for the use of carrots in the germplasm collection for crop improvement. This research is of interest to carrot growers, vegetable breeders, and plant science researchers.

Technical Abstract: Thousands of diverse carrot cultivars are conserved in genebanks globally, and these accessions are a critical foundation to the improvement of carrots for growers and consumers. Yet basic flowering-habit trait data is not available to prospective users of that valuable genetic diversity for many accessions. Uncharacterized germplasm poses a substantial barrier to their utilization in crop breeding programs: Biennials are required in commercial carrot root production in temperate climates, as annual flowering (or bolting) causes carrot’s xylem to quickly lignify, resulting in fibrous, unpalatable roots and complete loss of consumer quality and commercial value. Given the critical importance of this trait to users of the carrot germplasm collection, we characterized flowering-habit in the majority of the cultivated carrots in the collection (N=695). We found high broad-sense heritability in all three years for flowering at 60 days after seeding (DAS) (0.87 < H2 < 0.93) and 100 DAS (0.81 < H2 < 0.84), which is consistent with reports of relatively simple inheritance of carrot flowering-habit. We identified 197 biennial accessions and characterized two new annual (n=61) subcategories based on flowering synchrony: early-flowering annuals (n=5) and late-flowering annuals (n=6), the latter of which originated in subtropical/semi-arid climates. We report high correlation among early-flowering annuals for seedling emergence and canopy height. Finally, we partitioned some mixtures into a predominantly biennial subcategory (n=160; <15% bolting plants), which, together with biennials, serve as the foundation for a custom core collection (N=357), thus lowering the barrier to utilization of diverse germplasm in commercial carrot breeding programs and promoting efficient utilization of agrobiodiversity. Our crop ontology is available on CarrotOmics.org for breeders and researchers interested in evaluating flowering variation in their programs.