Recombination between homoeologous chromosomes induced in durum wheat by the Aegilops speltoides Su1-Ph1 suppressor

Key message: Su1-Ph1, which we previously introgressed into wheat from Aegilops speltoides, is a potent suppressor of Ph1 and a valuable tool for gene introgression in tetraploid wheat. Abstract: We previously introgressed Su1-Ph1, a suppressor of the wheat Ph1 gene, from Aegilops speltoides into durum wheat cv Langdon (LDN). Here, we evaluated the utility of the introgressed suppressor for inducing introgression of alien germplasm into durum wheat. We built LDN plants heterozygous for Su1-Ph1 that simultaneously contained a single LDN chromosome 5B and a single Ae. searsii chromosome 5S^se, which targeted them for recombination. We genotyped 28 BC₁F₁ and 84 F₂ progeny with the wheat 90-K Illumina single-nucleotide polymorphism assay and detected extensive recombination between the two chromosomes, which we confirmed by non-denaturing fluorescence in situ hybridization (ND-FISH). We constructed BC₁F₁ and F₂ genetic maps that were 65.31 and 63.71 cM long, respectively. Recombination rates between the 5B and 5S^se chromosomes were double the expected rate computed from their meiotic pairing, which we attributed to selection against aneuploid gametes. Recombination rate between 5B and 5S^se was depressed compared to that between 5B chromosomes in the proximal region of the long arm. We integrated ND-FISH signals into the genetic map and constructed a physical map, which we used to map a 172,188,453-bp Ph1 region. Despite the location of the region in a low-recombination region of the 5B chromosome, we detected three crossovers in it. Our data show that Su1-Ph1 is a valuable tool for gene introgression and gene mapping based on recombination between homoeologous chromosomes in wheat.