The allopolyploid origin of wheat led to narrow genetic variation of its genome, which has been increasingly becoming a genetic bottleneck of wheat improvement especially under the ever-changing climate. There is an urgent need to extend the genetic variability of wheat and unblock the bottleneck in wheat breeding. Tremendous genetic variation was left behind in lineages of wheat, which remains in its ancestors.

In addition, wheat has numerous relatives that contain genomes homologous or homoeologous to the wheat genome. Both ancestors and relatives represent an invaluable gene reservoir to extend the genetic variability of wheat. Recently, we developed an effective genomics-enabled chromosome engineering pipeline for alien introgression and genome study in wheat and its relatives.

Here we report the meiotic homoeologous recombination-based genome study and alien introgression from Thinopyrum elongatum, Th. ponticum, Th. intermedium, Aegilops speltoides, and Secale cereale into durum and common wheat. Hundreds of meiotic homoeologous recombinants of wheat B genome with Ae. speltoides S genome and Th. elongatum E genome have been developed using wheat ph1b mutant.

They have been used in genome mapping and gene discovery in wheat and its relatives. Several genes for resistance to Fusarium head blight (FHB), tan spot, Septoria nodorum blotch, and stem rust diseases have been integrated into the wheat genome as small translocations. A novel FHB-resistant Fhb7 allele, designated Fhb7The2, was identified on Th. elongatum chromosome 7E and transferred to wheat chromosome 7B through a 7B-7E translocation (7BS·7BL-7EL). Fhb7The2 has exhibited significant Type II FHB resistance and may detoxify Fusarium-produced mycotoxin deoxynivalenol (DON).

The wheat germplasm (PI 702949) containing Fhb7The2 has been released and distributed to the wheat research community worldwide. Meanwhile, we have been deploying Fhb7The2 into different classes of US wheats for FHB-resistant variety development using a marker-assisted backcross breeding pipeline.

Furthermore, we have identified high-level resistance to wheat streak mosaic virus (WSMV) from wheat-Th. ponticum/Th. intermedium derivatives as well as resistance to bacterial leaf streak (BLS) disease from rye (Secale cereale). Individual Thinopyrum and rye chromosomes containing the resistance genes will be identified by dissecting the alien genome of the derivatives.

Also, we are generating wheat-Thinopyrum/rye recombinants to transfer the resistance genes and potentially other genes for favorable agronomic traits into wheat using the ph1b mutant. In summary, meiotic homoeologous recombination-based chromosome engineering is an effective approach to expand the genetic variability of wheat and facilitate understanding of the complex genomes in wheat and its relatives.