AFLP linkage group assignment to the chromosomes of Allium cepa L-via monosomic addition lines

Two complete sets of Allium fistulosum L. - A. cepa monosomic addition line s (2n=2x+1=17) together with an AFLP linkage map based on a cross between A . cepa and A. roylei Steam were used to re-evaluate the eight A. cepa linka ge groups identified in the mapping study. The linkage groups could be assi gned to individual, physical chromosomes. The low level of molecular homolo gy between A. cepa and A. fistulosum enabled the identification of 186 ampl ified fragment length polymorphisms (AFLP(TM) markers) present in A. cepa a nd not in A. fistulosum with ten different primer combinations. With the mo nosomic addition lines the distribution of the markers over the eight chrom osomes of A. cepa could be determined. Of these 186 AFLP markers 51 were ab sent in A. roylei and consequently used as markers in the mapping study (A. cepa x A. roylei cross). Therefore, these 51 AFLP markers could be used to assign the eight A. cepa linkage groups identified in the mapping study to physical chromosomes. Seven isozyme and three CAPS markers were also inclu ded. Two of the linkage groups had to be split because they included two se ts of markers corresponding to different chromosomes. A total of 20 (approx . 10%) of the A. cepa-specific AFLP markers were amplified in more than one type of the monosomic addition lines, suggesting unlinked duplications. Th e co-dominant isozyme and CAPS markers were used to identify the correspond ence of linkage groups originating from A. cepa or from A. roylei.