Characterization of a new Lr52 allele for leaf rust resistance in the Iranian wheat landrace PI 622111

Leaf rust, caused by Puccinia triticina (Pt), poses a constant threat to global wheat production, and novel leaf rust resistance genes are needed to combat the disease. A previous genome-wide association study (GWAS) identified a single nucleotide polymorphism (SNP) marker associated with leaf rust resistance in the terminal region of chromosome arm 5BS in the Iranian landrace PI 622111. An F₂ population and 175 F_2:3 families from cross PI 622111 × Yuanyu 3 were evaluated for response to Pt isolate Pt52-2 (MMPSD). Genotyping-by-sequencing analysis and genotyping of a subset of the F₂ plants identified 32 SNPs closely associated with leaf rust resistance in the target region. Some of these SNPs were converted into kompetitive allele-specific polymorphic (KASP) markers and used to genotype the F₂ population together with a set of simple sequence repeat (SSR) markers also located in the target genomic region. Linkage analysis delimited the leaf rust resistance gene in PI 622111, designated Lr622111, to a 0.4 Mb interval flanked by Xstars700 (7.22 Mb) and Xstars678 (7.62 Mb) in IWGSC RefSeq v.2.1. An allelism test involving 811 F₂ plants indicated that Lr622111 was allelic to Lr52. Since PI 622111 reacted differently from the Lr52 donor to Pt races in the GWAS, Lr622111 is considered a new Lr52 allele conferring a wide spectrum of resistance to current US Pt races. KASP marker Xstars-KASP239, which is 0.9 cM distal to Lr622111, can be widely used to tag Lr622111 in breeding populations.