ALLIUM, CUCUMIS, AND DAUCUS GERMPLASM ENHANCEMENT, GENETICS, AND BIOCHEMISTRY
Location: Vegetable Crops Research Unit
Title: Molecular mapping of vernalization requirement and fertility restoration genes in carrot
Submitted to: Theoretical and Applied Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 15, 2012
Publication Date: February 1, 2013
Citation: Alessandro, M.S., Galamarini, C.R., Iorizzo, M., Simon, P.W. 2013. Molecular mapping of vernalization requirement and fertility restoration genes in carrot. Theoretical and Applied Genetics. 126(2):415-423.
Interpretive Summary: Most people growing carrots never see the plant flower, since once flowering is initiated, the roots become fibrous and unpalatable. So to produce carrot seed for the U.S. crop (which is necessary for carrot breeders), the plants must be chilled for several weeks to stimulate flowering. Carrots in warmer parts of the world flower without exposure to cold. This difference in initiation of flowering in carrots is controlled by one gene called Vrn1. In flowering carrots, some plants produce pollen (are male fertile) and some do not (are male sterile). This characteristic is controlled by several genes including one called Rf1 or “restorer of fertility”. In this study, we determined the locations of Vrn1 and Rf1 to be on chromosomes 2 and 9 of carrot, respectively. All chromosomes were mapped in this study, and molecular genetic markers close to these 2 genes were also identified. This research provides carrot breeders with information and tools to more efficiently breed the crop, and it provides plant scientists information to determine the biological foundations of these two interesting reproductive traits.
Carrot (Daucus carota L.) is a cool-season vegetable normally classified as a biennial species, requiring vernalization to induce flowering. Nevertheless, some cultivars adapted to warmer climates require less vernalization and can be classified as annual. Most modern carrot cultivars are hybrids which rely upon cytoplasmic male-sterility for commercial production. One major gene controlling floral initiation and several genes restoring male fertility have been reported but none have been mapped. The objective of the present work was to develop the first linkage map of carrot locating the genomic regions that control vernalization response and fertility restoration. Using an F2 progeny, derived from the intercross between the annual cultivar ‘Criolla INTA’ and a petaloid male sterile biennial carrot evaluated over two years, both early flowering habit, which we name Vrn1, and restoration of petaloid cytoplasmic male sterility, which we name Rf1, were found to be dominant traits conditioned by single genes. On a map of 355 markers covering all 9 chromosomes with a total map length of 669 cM and an average marker-to-marker distance of 1.88 cM, Vrn1 mapped to chromosome 2 with flanking markers at 0.70 and 0.46 cM, and Rf1 mapped to chromosome 9 with flanking markers at 4.38 and 1.12 cM. These are the first two reproductive traits mapped in the carrot genome, and their map location and flanking markers provide valuable tools for studying traits important for carrot domestication and reproductive biology, as well as facilitating carrot breeding.