Construction of a linkage map and mapping loci controlling flowering time in Brassica oleracea

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Four FLC genes controlling vernalization-responsive flowering time were cloned in Brassica oleracea. Three out of the four cloned FLC homologues were FLC1,FLC3 and FLC5 reported by Schranz(2002). The other one was a new FLC homologue in Brassica oleracea and was named as BoFLC2, because it showed high sequence homology to BrFLC of Brassica rapa. A detailed linkage map of Brassica oleracea was constructed based on segregation of Restriction Fragment Length Polymorphism (RFLP) loci, Sequence Related Amplified Polymorphism(SRAP) loci, Cleaved Amplified Polymorphic Sequences(CAPS) loci and Amplified Fragment Polymorphism(AFLP) loci. One hundred and fifty-seven markers covered 1196 cM and defined 9 major linkage groups, which were equals to the haploid chromosome number of this species. Forty-three structural genes including four FLC homologues and one constans(CO), which control vernalization-and day length-responsive flowering time, respectively, were mapped. Six quantitative trait loci(QTLs) controlling flowering time were detected in the map. Three FLC orthologues of Brassica oleracea, FLC1,FLC3 and FLC5 were not related to QTLs controlling flowering time in the map, whereas one of the QTLs was located on the region where FLC2 was mapped, indicating that FLC2 may control flowering time in Brassica oleracea. The linkage map including four FIC homologues will be useful for breedling programs of Brassica oleracea.