Genetic dissection of morphological variation between cauliflower and a rapid cycling Brassica oleracea line

To improve resolution to small genomic regions and sensitivity to small-effect loci in the identification of genetic factors conferring the enlarged inflorescence and other traits of cauliflower while also expediting further genetic dissection, 104 near-isogenic introgression lines (NIILs) covering 78.56% of the cauliflower genome, were selected from an advanced backcross population using cauliflower [Brassica oleracea var. botrytis L., mutant for Orange gene (ORG)] as the donor parent and a rapid cycling line (TO1434) as recurrent parent. Subsets of the advanced backcross population and NIILs were planted in the field for 8 seasons, finding 141 marker-trait associations for 15 leaf-, stem-, and flower-traits. Exemplifying the usefulness of these lines, we delineated the previously known flower color gene to a 4.5 MB interval on C3; a gene for small plant size to a 3.4 MB region on C8; and a gene for large plant size and flowering time to a 6.1 MB region on C9. This approach unmasked closely linked QTL alleles with opposing effects (on chr. 8) and revealed both alleles with expected phenotypic effects and effects opposite the parental phenotypes. Selected B. oleracea NIILs with short generation time add new value to widely used research and teaching materials.