J. A. Kolmer, P. Bajgain, M. N. Rouse, J. Li & P. Zhang

Theoretical and Applied Genetics May 2023; vol. 136, Article number: 115

Key message

The leaf rust resistance gene in Thatcher wheat derivative 78–1 was mapped to chromosome 1DS with SNP markers and designated as Lr83.

Abstract

‘Thatcher’ wheat near isogenic line RL6149, a putative derivative of Triticum dicoccoides, was previously determined to carry leaf rust resistance gene Lr64 on chromosome arm 6AL and a second gene temporarily named LrX on chromosome arm 1DS. The objective of this study was to map and characterize LrX in a population of recombinant inbred lines (RILs) that segregated for a single gene. Thatcher line 78–1 with LrX was crossed with Thatcher and individual F₂ seedlings and F₆ RILs were evaluated for leaf rust response. The 208 F₂ plants segregated for a single recessive gene and 148 F₆ lines for a single gene. The RILs and parents were characterized by genotyping by sequencing (GBS). Six GBS markers and five Kompetitive Allele-Specific PCR (KASP) markers were used to map LrX on the distal region of chromosome arm 1DS. LrX was 1 centiMorgan (cM) proximal to marker K-IWB38437 and 0.4 cM distal to GBS marker 1D_9037138. Line 78–1 was crossed with Thatcher wheat lines with Lr21, Lr42, and Lr60 for allelism tests. LrX mapped 19.49 cM from Lr21 and 11.93 cM from Lr42. In the cross of line 78–1 with the Thatcher line with Lr60, one recombinant in 1,003 F₂ plants was found. LrX and Lr60 are at tightly linked loci on the distal region of chromosome arm 1DS. The gene in line 78–1 was designated as Lr83. Cytological examination of RL6149 provided no evidence of transfer of a chromosome segment of an A- or B-genome chromosome to chromosome 1D.

See https://link.springer.com/article/10.1007/s00122-023-04361-7

Figure 3. Candidate genes in the Lr42 region in wheat and Ae. tauschii. (a) Physical location of Lr42 on chromosome 1DS of wheat; (b) genetic location of Lr42 in KS93U50/Morocco F5 RIL; (c) BAC contigs spanning the Lr42 physical region; (d) annotated genes in the Lr42 region in CS RefSeq v1.1 [22]; (e) annotated genes in the Lr42 region in the Ae. tauschii chromosome 1 sequence [21]. NLR: nucleotidebinding leucine-rich repeats; WAK: wall-associated kinase; Pkinase: protein kinase. (Gill et al. 2019)