MAPPING LOCI CONTROLLING VERNALIZATION REQUIREMENT IN BRASSICA-RAPA

Brassica cultivars are classified as biennial or annual based on their requirement for a period of cold treatment (vernalization) to induce flowering. Genes controlling the vernalization requirement were identi fied in a Brassica mpn F-2 population derived from a cross between an annual and a biennial oilseed cultivar by using an RFLP linkage map an d quantitative trait locus (QTL) analysis of flowering time in F-3 lin es. Two genomic regions were strongly associated with variation for fl owering time of unvernalized plants and alleles from the biennial pare nt in these regions delayed flowering. These QTLs had no significant e ffect on flowering time after plants were vernalized for 6 weeks, sugg esting that they control flowering time through the requirement for ve rnalization. The two B. rapa linkage groups containing these QTLs had RFLP loci in common with two B. napus linkage groups that were shown p reviously to contain QTLs for flowering time. An RFLP locus detected b y the cold-induced gene COR6.6 cloned from Arabidopsis thaliana mapped very near to one of the B. rapa QTLs for flowering time.