Development and chromosomal localization of genome-specific DNA markers of Brassica and the evolution of amphidiploids and n = 9 diploid species

Ten genome-specific probes were developed from Brassica napus and B. oleracea genomic DNA libraries. Selection was based on polymorphism between and limited variation within genomes, permitting their localization on six individual C-genome chromosomes. Chromosome assignment was accomplished by using two sets of B. campestris - oleracea alien addition lines derived from (i) B, napus and (ii) the artificially synthesized B. napus 'Hakuran'. The presence of shared fragments between A, B, and C genomes indicates partial homology of the three genomes. However, several genome-specific markers could separate these three genomes. Genome-specific clones developed in this study served to confirm the parental diploid species originating the three amphidiploids, B. napus, B. carinata, and B. juncea. At least one clone suggests that B. napus has a polyphyletic origin. These clones were also useful to confirm the close evolutionary proximity among wild species in the B. oleracea cytodeme; however, no clear trends were found to suggest specific wild ancestors for the different B. oleracea horticultural types. Brassica oxyrrhina was distinct from other n = 9 species with most clones tested.