Marker-assisted introgression and characterization of the ph1b mutant in modern US and Australian wheats.

The ph1b mutant, a large deletion (∼60 Mb) involving Ph1 (pairing homoeologous 1) on chromosome 5B, was incorporated into five major classes of US wheats, including soft white winter wheat, soft red winter wheat, hard red spring wheat, hard white spring wheat, and durum wheat, and an Australian wheat variety with universal susceptibility to rusts. Eight ph1b mutant lines in the five classes of US wheats and the Australia wheat were developed using a molecular marker-assisted backcross breeding pipeline. All backgrounds containing the ph1b mutation induced meiotic homoeologous pairing and recombination as the original ph1b mutant developed in the Chinese landrace "Chinese Spring" (CS). Thus, they can be utilized for homoeologous recombination-based alien introgression in the adapted US wheat backgrounds, which will circumvent the use of CS ph1b mutant with undesired agronomic characteristics. Deployment of the ph1b mutant in the universal rust susceptible wheat "Line E" will facilitate rust resistance gene identification and transfer from wild species to wheat. In addition, we developed special DNA markers with a codominance-like nature specifically for the ph1b deletion and the genomic region spanning the wild-type allele Ph1, which will improve the utility of the ph1b mutant in alien introgression. This work enables direct gene flow from related grass species into adapted wheats to enrich and diversify their genomes and enhances the genetic potential of wheat in production.