Mapping and DNA marker development for Lr33 from the leaf rust resistant line KU168-2

Abstract

A wheat accession from the Kyoto University Collection, KU168-2, was identified as carrying good resistance to leaf rust and stem rust. To analyze this resistance a doubled haploid (DH) population was produced from hybrids of the cross KU168-2 with the leaf rust susceptible line RL6071. The DH population, of 116 lines, was evaluated for leaf rust resistance in the greenhouse at the seedling and adult plant stages, and in three field environments. Significant effects for reduction in leaf rust severity in the field were found on chromosome 1BL, most likely Lr33, which was also identified in the seedling tests, and on 7DS, which was identified as Lr34 in greenhouse adult plant tests and confirmed with a predictive molecular marker. In field trials, both Lr33 and Lr34 reduced the severity of leaf rust, while the lines with both resistance genes showed additivity of resistance. Similar results were consistently found from 2003 to 2017 testing Thatcher near-isogenic lines with Lr33, Lr34, and Lr33 + Lr34. A genetic map of the Lr33 region was developed and linked SNP markers were converted to KASP markers for the selection of Lr33 in wheat breeding programs. Two additional seedling resistance genes were found, one originating from KU168-2 on 6AL, and one from RL6071 on 7BL, but these genes did not contribute to field resistance.