Enriching and Understanding the Wheat Genome by Inducing Homoeologous Meiotic Recombination

Allopolyploidy of the wheat genome provides tremendous genetic flexibility for wheat improvement as well as complexity for wheat genome studies.  We have been taking advantage of the genetic flexibility to perform homoeologous recombination-based gene introgression and genome mapping in wheat.  Here we report 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, by inducing meiotic recombination of wheat B-genome chromosomes with their S- and E-genome homoeologs using ph1b mutant.  Homoeologous recombinants have been recovered using fluorescent genomic in situ hybridization (FGISH) and S-/E-genome chromosome-specific molecular markers.  To date, we have screened a total of 2,623 individuals from the homoeologous recombination populations and identified 536 recombinants involving 10 homoeologous chromosome pairs, i.e. 1B-1S, 1B-1E, 2B-2S, 2B-2E, 3A-3S, 3B-3E, 4B-4S, 4D-4E, 5B-5S, and 5B-5E.  These homoeologous chromosome pairs had varied meiotic recombination frequencies in the absence of Ph1.  Most of the recombinants recovered are heterozygous for the recombinant chromosomes.  They have been either self-pollinated or crossed to CS (5B-5S and 5B-5E recombinants) to develop homozygous recombinants without ph1b deletion for seed increase and trait evaluation.  Some of the recombinants have been genotyped using wheat 90K SNP array.  A preliminary integrated physical and genetic map has been constructed for some of the B-genome chromosomes based on GISH- and marker-detected homoeologous recombination.  The recombinant lines with small alien chromosome segments will be evaluated for resistance/tolerance to biotic and abiotic stresses.