For genetic mapping studies, biparental segregating populations are often useful, however recombination is limited, giving rise to large genomic regions under QTL, and one can only study alelles present in both parents. In Wageninegn UR, a core collection is being developed representing all Brassica rapa morphotypes and geographic origins. As most B. rapa accessions are heterozygous and heterogeneous, we started a project to fix the collection through microspore culture. The resulting Diversity Fixed Foundation Set will be an interesting resource for association mapping studies, which have as advantage that they present the allelec variation present in the collection, and for mapping studies recombination is increased. Nineteen accessions of eight subspecies of Brassica rapa were used for microspore culture to developdoubled haploid lines. Eight morphotypes were represented: 3 Chinese cabbage, 2 Chinese turnip cabbage, 3 Pak choi, 5 Turnip, 3 Broccolleto, 1 Mizuna, 1 Komatsuna and 1 Turnip greenfrom the 19acessions examined, embryos were obtained for 13, representing six subspecies (Komatsuna and Turnip Green had no response). The embryo yields differed significantly between these 13 accessions. We regenerated normal plants from 10 accessions that survived more than 4 weeks in the soil using microspore culture. Nine accessions flowered after 4 weeks vernalization at 5℃ and seeds were harvested from 5 accessions. From a Mizuna, we obtained 3791 seeds from one plant and total 7318 seeds were harvested from 5 accessions representing 4 subspecies(Chinese cabbage, Chinese turnip cabbage, Pak choi, Mizuna). At present, we carry out experiment for obtain more seeds and induce embryos from the other plant materials.