The distribution of BoCAL-a alleles in Brassica oleracea is consistent with a genetic model for curd development and domestication of the cauliflower

The characteristic curd of cauliflower (Brassica oleracea var. botrytis L.) consists of proliferating, arrested inflorescence and floral meristems. However, the origins and events leading to the domestication of this important crop trait remain unclear. A similar phenotype observed in the ap1-1/cal-1 mutant of Arabidopsis thaliana led to speculation that the orthologous genes from B. oleracea may be responsible for this characteristic trait. We have carried out a detailed molecular and genetic study, which allows us to present a genetic model based on segregation of recessive alleles at specific, mapped loci of the candidate genes BoCAL and BoAP1. This accounts for differences in stage of arrest between cauliflower and Calabrese broccoli (B. oleracea var. italica Plenck), and predicts the intermediate stages of arrest similar to those observed in Sicilian Purple types. Association of alleles of BoCAL-a with curding phenotypes of B. oleracea is also demonstrated through a survey of crop accessions. Strong correlations exist between specific alleles of BoCAL-a and discrete inflorescence morphologies. These complementary lines of evidence suggest that the cauliflower curd arose in southern Italy from a heading Calabrese broccoli via an intermediate Sicilian crop type. PCR-based assays for the two key loci contributing to curd development are suitable for adoption in marker-assisted selection.