Cytogenetic and molecular mapping of the wheat-Aegilops longissima chromatin breakpoints in powdery mildew-resistant introgression lines.

The amount of alien chromatin introgressed in eight wheat/Ae. longissima Pm13 recombinant lines, involving breakpoints on the short arms of wheat chromosomes 3B and 3D, was evaluated by cytogenetic and molecular approaches. For each line the residual homologous synaptic ability of the recombinant chromosome in its proximal wheat and distal alien portion was estimated through meiotic analyses. Subsequently, telocentric and RFLP mapping were used to assess the genetic distance from the wheat centromere to the wheat/Ae. longissima breakpoints. One 3B recombinant line was distinguished from the other four by the chromosome pairing and telocentric mapping analyses. RFLP analysis succeeded in differentiating the remaining four lines into two groups. Chromosome pairing and telocentric mapping of the three 3D recombinant lines suggested that all had distinct breakpoints. However, the RFLP data could not discriminate between the two more proximal translocations. Physical locations for some RFLP loci were determined by a comparison of genotypes and C-banding karyotypes. This showed a considerable expansion of the genetic map compared to its physical length.