Homoeologous Recombination-Based Gene Introgression and Genome Mapping in Wheat

The allohexaploid genomic nature of common wheat (genome AABBDD) provides tremendous genetic flexibility for wheat improvement as well as complexity for wheat genome studies.  We have been taking advantage of the genomic flexibility to expand genetic variability of wheat by inducing homoeologous recombination between wheat and wild species chromosomes.  Meanwhile, we have been physically mapping the wheat genome based on homoeologous recombination.  Here we report results on homoeologous recombination-based gene introgression from diploid goatgrass Aegilops speltoides (genome SS) and tall wheatgrass Thinopyrum elongatum (genome EE) into wheat and physical mapping of the wheat B genome, the ancestor of which is still elusive.  Meiotic recombination has been induced between wheat B-genome chromosomes and their S- and E-genome homoeologs using ph1b mutant.  The chromosome-specific and ph1b-linked molecular markers have been used to identify wheat genotypes heterozygous for a B-genome chromosome and its S- or E-genome homoeolog and homozygous for ph1b from the specific crosses.  Large recombinant populations (n>500) have been generated for each of the homoeologous chromosome pairs from these special genotypes.  We have pre-screened the populations to eliminate individuals without a B-E or B-S recombinant using genomic in situ hybridization (GISH).  Selected recombinants have been genotyped with 400 mapped B-genome specific SSR and 92,000 wheat SNP markers.  An integrated physical and genetic map will be constructed for the B genome based on GISH- and marker-detected homoeologous recombination.  In addition, we will select recombinant lines with small alien chromosome segments that contain genes for resistance/tolerance to biotic and abiotic stresses in wheat.