Evaluation of wheat stem sawfly-resistant solid stem Qss.msub-3BL alleles in hard red winter wheat

Host plant resistance provided by solid stems has been the most effective means for mitigating wheat stem sawfly (WSS) (Cephus cinctus Norton) damage in spring and winter wheat (Triticum aestivum L.). The solid stem trait originates from the spring wheat cultivar "Rescue" and is associated with a quantitative trait locus allele Qss.msub-3BL.b that explains the majority of the variation for stem solidness. Recently, a new Qss.msub-3BL solid stem allele, designated Qss.msub-3BL.c, was identified in the spring wheat cultivar "Conan". It produces a solid stem phenotype early in plant development but dissipates during plant growth. The Qss.msub-3BL.c allele provides effective WSS resistance in spring wheat but has not been tested in winter wheat. To examine if the Qss.msub-3BL.c allele provides adequate WSS resistance in winter wheat, near-isogenic lines (NILs) were developed using marker-assisted backcrossing. This enabled comparisons between the hollow stem Qss.msub-3BL.a, solid stem Qss.msub-3BL.b and solid stem Qss.msub-3BL.c alleles for stem solidness, WSS resistance, and agronomic traits in Montana growing environments. Compared to the hollow stem allele, the NILs with the Qss.msub-3BL.c allele increased stem solidness and reduced WSS stem cutting. However, the Qss.msub-3BL.c allele resulted in lower solid stem scores and greater WSS stem cutting compared to the Qss.msub-3BL.b allele. Overall, these findings indicate that the Qss.msub-3BL.c allele failed to provide sufficient WSS resistance in the winter wheat backgrounds tested in this study.