Mapping and characterization of the recessive leaf rust resistance gene Lr83 on wheat chromosome arm 1DS

Authors: Kolmer, James; BAJGAIN, PHRABIN - University Of Minnesota; Rouse, Matthew; LI, RUIJIN - University Of Sydney; ZHANG, PENG - University Of Sydney

Submitted to: Theoretical and Applied Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/25/2023
Publication Date: 4/21/2023
Citation: Kolmer, J.A., Bajgain, P., Rouse, M.N., Li, R., Zhang, P. 2023. Mapping and characterization of the recessive leaf rust resistance gene Lr83 on wheat chromosome arm 1DS. Theoretical and Applied Genetics. 136, Article 115. https://doi.org/10.1007/s00122-023-04361-7.
DOI: https://doi.org/10.1007/s00122-023-04361-7

Interpretive Summary: Wheat is attacked by the leaf rust fungus called Puccinia triticina. Many of the leaf rust resistance genes in wheat cultivars no longer give good resistance to leaf rust, since biotypes of the rust fungus have the ability to overcome the resistance genes. It is necessary to characterize new genes that give resistance to many biotypes of the rust fungus. Line 78-1 of Thatcher wheat carries a leaf rust resistance that gives resistance to all tested biotypes. The objective of this study was to determine the chromosome location of the leaf rust resistance gene in line 78-1. Line 78-1 was crossed with Thatcher and F2 plants and F6 lines were tested for leaf rust resistance. The parents and the F6 lines were genotyped for DNA markers using genotyping by sequencing technology. The leaf rust resistance gene in Line 78-1 was mapped to the short arm of chromosome 1D. Line 78-1 was also crossed with Thatcher lines that have Lr21, L42, and Lr60 that are also on the short arm of chromosome 1D. Segregation of F2 plants and F3 lines for resistance from crosses of Thatcher lines with Lr21 and L42 indicated that the gene in 78-1 was at a different location on the short arm of chromosome 1D. The F2 plants and F3 lines from the cross with Thatcher line with Lr60 indicated the gene in 78-1 and Lr60 are very closely linked on the short arm of chromosome 1D. The gene in line 78-1 was designated as Lr83. Since Lr83 is widely effective to all tested biotypes of P. triticina, this gene can be used by wheat breeding programs to develop cultivars with improved leaf rust resistance.

Technical 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 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 segregated 1 resistant : 1 susceptible, indicating segregation at a single locus. 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_10592628. Line 78-1 was crossed with Thatcher wheat lines with Lr21, Lr42, and Lr60 for allelism tests since these genes are also on chromosome arm 1DS. LRX mapped 18 cM apart from Lr21, and 12.23 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. Based on the presence of susceptible plants in the F3 line derived from the F2 plant, LRX and Lr60 are at tightly linked loci on the distal region of chromosome arm 1DS. Cytological examination of RL6149 provided no evidence of transfer of a chromosme segment of an A- or B-genome chromosome to chromosome 1D. The gene in line 78-1 was designated as Lr83.