STRUCTURAL REARRANGEMENT IN CHROMOSOME 2M OF AEGILOPS COMOSA HAS PREVENTED THE UTILIZATION OF THE COMPAIR AND RELATED WHEAT-AE-COMOSA TRANSLOCATIONS IN WHEAT IMPROVEMENT

The genetic constitutions of chromosome 2M of Aegilops comosa and the derived wheat-Ae, comosa translocations were analyzed by molecular cyt ogenetic techniques. Hybridization of 15 RFLP markers covering the ent ire length of the group-2 chromosomes revealed that chromosome 2M was structurally rearranged compared to the homoeologous chromosomes of wh eat by either a pericentric inversion or a terminal intrachromosomal t ranslocation. The breakpoint of the rearrangement was located in a reg ion between the loci Xpsr131 and Xcdo405, resulting in the translocati on of 47% of 2MS to 2ML. This aberrant structure of 2M allowed homoeol ogous recombination between 2M and its wheat counterpart only in the t ranslocated segment on 2ML. C-banding and genomic in situ hybridizatio n analyses confirmed that all translocation chromosomes consisted of t he complete 2MS arm, a large part of 2ML, and very small distal segmen ts derived from 2AS or 2DS, as expected from the aberrant structure of chromosome 2M. Thus, the translocation in the line 2A-2M #4/2 can be described as T2AS-2M#1L.2M#1S and the translocations in the lines Comp air and 2D-2M#3/8 as T2DS-2M#1L.2M#1S. RFLP analysis determined the br eakpoints in these translocation chromosomes to be within the telomeri c 16% of the wheat chromosome arms. The breakpoint of the 2A/2M transl ocation was between Xbcd348 and Xcdo783, and that of the 2D/2M translo cation was between Xcdo783 and Xpsr666. Because the translocation chro mosomes retain the structural aberration found in chromosome 2M, furth er exploitation of the wheat-Ae, comosa translocations for cultivar im provement is questionable.