Unveiling leaf rust resistance introgressed from non-progenitor wild species Aegilops kotschyi into hexaploid wheat

Leaf rust (LR) is one the most widely distributed and serious pathogen hampering the wheat production globally. To combat the continuous evolution of pathogens and breakdown of resistance, matching resistance genes must be discovered at the same pace from the diverse sources. In this study, we identified the US genome species Aegilops kotschyi acc pau 396, which is resistant to the Indian Puccinia triticina pathotypes 109R31-1 (77 - 5), 21R55 (104-2), and 121R60-1 (77 - 9). An LR resistance introgression line, IL^kots was developed from this accession of Aegilops kotschyi in the background of Triticum aestivum cultivar PBW343. To examine the genetics of transferred resistance, a mapping population of 222 F_3:4 plants was generated by crossing IL^kots with the LR-susceptible cultivar WL711NN. Field experiments were conducted using a randomized complete block design (RCBD). Genetic analysis revealed that resistance was conferred by a single, dominant gene temporarily designated as Lr^kots. Bulked segregant analysis (BSA) in combination with AFFYMETRIX 35 K Wheat Breeders' AXIOM array mapped Lr^kots on chromosome 3DL. A partial genetic linkage map of the genomic region carrying Lr^kots included five Kompetitive allele-specific PCR (KASP) markers and two simple sequence repeat (SSR) markers spanning 8.2 cM. Lr^kots was flanked by the KASP marker AX-94,443,154 (0.32 cM) on the proximal end and the SSR marker Xbarc71 (7.9 cM) on the distal end, defining a 3 Mb region in the RefSeq v1.0 genome assembly. This interval contains eight candidate genes encoding protein domains involved in disease resistance responses.