Detailed genetic mapping of the Y₂ carotenoid locus in carrot

Linkage and detailed gene mapping using a variety of molecular markers was pursued in carrot. Our current linkage map includes 11 linkage groups and 180 markers. We anticipate adding an additional 120 markers in the near future. Monogenic traits segregating in our mapping population include high vs. low reducing sugars (Rs locus), purple vs. nonpurple root phloem (P₁ locus), and high vs. low root xylem carotene (Y₂ locus). We have identified dominant molecular markers closely associated with Y₂ both by conventional mapping and bulked segregant analysis. In an attempt to convert the dominant markers to codominant, breeder-friendly forms, we have cloned the Y₂ associated AFLP fragments. Sequencing the cloned AFLP fragments followed by inverse PCR and sequencing of the larger resulting fragment revealed differences diagnostic of the Y₂ and y₂ alleles. We are currently developing PCR-based procedures that will differentiate between the two alleles. It should be possible to develop breeder-friendly markers for other monogenic traits as well.