LINKAGE GROUP ALIGNMENT FROM 4 INDEPENDENT BRASSICA-OLERACEA RFLP MAPS

A Brassica oleracea linkage map was constructed from an F, population of 69 individuals with sequences previously mapped independently in th ree linkage maps of this species. These were the maps published by Kia nian and Quires (1992), Landry et al. (1992), and Camargo et al. (1997 ). The base map developed in this study consisted of 167 RFLP loci in nine linkage groups, plus eight markers in four linkage pairs, coverin g 1738 cM. Linkage group alignment was also possible with a fourth map published by Ramsay ct al. (1996), that contained loci in common with the map of Camargo et al. (1997). Common sequences across the mapping populations served to align most of the linkage groups of the indepen dently developed maps. In general, consistent linear order among marke rs was maintained, although often the distances between markers varied from map to map. A linkage group in the map of Landry ct al. carrying a clubroot resistance QTL and consisting of markers from two other li nkage groups, was found to be rearranged. This was not surprising, con sidering that the resistance gene was introgressed from Brassica napus . The extensively duplicated nature of the C genome was revealed by 19 sequences detecting duplicated loci within chromosomes and 17 sequenc es detecting duplicated loci between chromosomes. The variation in map ping distances between linked loci pairs on different chromosomes demo nstrated that sequence rearrangement is a distinct feature of this gen ome. Although the consolidation of all linkage groups in the four B. o leracea maps compared was not possible, the present work served to add a considerable number of markers to corresponding linkage groups. Som e of the chromosome segments in particular, were enriched with many ma rkers that may be useful for future gene tagging or cloning. It will b e possible in the future to complete the consolidation of all four map s as new loci are added to each map.