Leaf rust is a highly destructive foliar disease in wheat which causes major constraints in wheat production worldwide. In this study, we conducted a comprehensive assessment of adult plant resistance to leaf rust in 590 accessions from the advanced backcross-nested association mapping plus inter-crossed (AB-NAMIC) population. We used 660K genotype data to perform a genome-wide association study (GWAS), which identified significant quantitative trait loci (QTLs) on chromosomes 1B, 2A, 2B, and 7D, and then focused on the candidate gene TaRLK-1B on chromosome 1B. A cleaved amplified polymorphic sequence (CAPS) marker developed based on TaRLK-1B haplotypes could effectively differentiate between resistant and susceptible varieties. This gene encodes a membrane-localized leucine-rich repeat receptor-like kinase (LRR-RLK) that is upregulated in response to the fungal infection that causes leaf rust. Targeted knockout of TaRLK-1B in wheat led to reduced resistance to leaf rust, underscoring its essential role as a positive regulator of the defense against this disease. We propose that TaRLK-1B interacts with the receptor-like cytoplasmic kinase TaRLCK1B, potentially facilitating immune signal transduction. Our findings also demonstrate that pyramiding minor effect QTLs significantly increases resistance to leaf rust. This study provides novel insights into rust resistance genes and valuable QTL information, which can improve marker-assisted wheat breeding efforts.

Leymus mollis (Trin.) Pilger (2n = 4x = 28, NsNsXmXm,), a wild relative of common wheat, possesses many potentially valuable traits for genetic improvement of wheat, including strong, short stems, long spikes with numerous spikelets, tolerance to drought and cold stresses, and resistance to many fungal and bacterial diseases. In the present study, a wheat–L. mollis double substitution line DM96 was selected from a F₆ progeny of a cross between M842-16 (an octoploid Tritileymus line) and D4286 (a Triticum durum line) using genomic in situ hybridization (GISH), simple sequence repeat (SSR) markers, and expressed sequence tagged sequence site (EST-STS) markers. Chromosome analysis at mitosis and meiosis showed that DM96 had a chromosome constitution of 2n = 42 = 21II. GISH analysis indicated that DM96 carried 38 chromosomes from wheat and two homologous pairs of Ns chromosomes from L. mollis. Fluorescent in situ hybridization (FISH) showed that chromosomes 2Ns and 3Ns from L. mollis had replaced wheat chromosomes 2D and 3D in DM96, which was confirmed by SSR and STS markers. The newly developed substitution line DM96 has shorter height, longer spikes and more kernels than its parents and showed high resistance to stripe rust and Fusarium head blight (FHB). Thus, this line is a new bridge material for the production of useful translocation lines for wheat genetic research and genetic improvement of wheat yield and disease resistance in breeding programs.