Introgression of stem rust resistance gene Sr68 from Thinopyrum junceum into wheat.

Key message: A new stem rust resistance gene, Sr68, from Thinopyrum junceum was transferred to chromosome arm 1BS of wheat using monosomic-induced Robertsonian translocation and ph1b-induced homoeologous recombination. Stem rust, caused by Puccinia graminis f. sp. tritici (Pgt), is one of the most destructive diseases of wheat (Triticum aestivum L.). Identifying and deploying stem rust resistance (Sr) genes continues as a key strategy for managing this disease. Here, we report the identification and introgression of a novel Sr gene from wheat 'Chinese Spring' (CS)-Thinopyrum junceum group-4 chromosome (designated 4E) disomic addition line HD3505 (2n = 44) to a wheat chromosome. We first developed an F₂ population by crossing HD3505 to a CS line monosomic for chromosome 4D (CS M4D). A stem rust-resistant F₂ plant carrying a Robertsonian translocation chromosome was identified and consecutively backcrossed to CS ph1b and CS to produce a population of 1209 BC₂F₁ plants. Three BC₂F₁ plants with reduced Th. junceum chromatin (BG2133, BG5136, and BG2161) carrying the Sr gene were identified. Genomic and oligonucleotide multiplex fluorescence in situ hybridization analysis revealed that Th. junceum chromosome segments carrying the Sr gene in the three translocation lines were in the distal region of chromosome arm 1BS, with sizes of 33.22-34.51% of the translocation chromosomes. The Sr gene in the translocation lines was designated Sr68. Additionally, the translocation replaced the Gli-B1 locus, eliminating ω-gliadins that encode immunoreactive epitopes, potentially reducing gluten immunogenicity. The newly developed wheat lines with Sr68 and associated molecular markers provide new resistance resources against Ug99 and other Pgt races for wheat improvement.