Correspondence: richard.cuthbert@agr.gc.ca; firdissa.bokore@agr.gc.ca

Presenting: Richard Cuthbert

Wheat stem sawfly (Cephus cinctus Nort.) (WSS) is a destructive insect pest of spring wheat (Triticum aestivum L.) in Western Canada. Growing solid stemmed wheat cultivars to prevent insect larvae from growing inside the wheat stem is an important management strategy. Developing wheat varieties with stable stem solidness in WSS prone environments is a major breeding objective.

This study sought to (1) identify and map genes/QTL associated with stem solidness in the wheat doubled haploid populations of CDC_Hughes/AAC_Concord and Lillian/Glenlea and (2) identify QTL associated with WSS cutting tolerance in AAC_Hodge/BW5087 and BW5087/AAC_Stoughton both breeding populations fixed for major stem solidness QTL. CDC_Hughes/AAC_Concord (n=188 lines) and Lillian/Glenlea (n=190) were rated for stem solidness at maturity at a specialized WSS nursery near Swift Current, SK for three years.

CDC_Hughes/AAC_Concord was additionally assessed for the stem solidness near Leeston, New Zealand for one year.

The populations AAC_Hodge/BW5087 (n=146 lines) and BW5087/AAC_Stoughton (n=125), were developed by simultaneously applying two DNA markers predictive of major solidness QTL located on chromosome 3B (Sst1) and 3D (3Ag14) on 2,000 F2 plants and selecting plants homozygous at both loci.

Selected F3:5 progeny were assessed for stem cutting near Pense, SK in 2023. The CDC_Hughes/AAC_Concord and Lillian/Glenlea populations were genotyped using the 90K Infinium iSelect SNP array. The AAC_Hodge/BW5087 and BW5087/AAC_Stoughton populations were genotyped by TraitGenetics using 7K LD Wheat array. Genetic linkage maps were constructed and a QTL analysis was completed.

The QTL analysis revealed five genomic regions associated with stem solidness in Lillian/Glenlea population, and four loci associated with the trait in CDC_Hughes/AAC_Concord population. Two Lillian derived QTL on chromosomes 2D and 3B were consistent across all the environments. AAC Concord contributed a significant QTL that was consistent across environments on chromosome 3D and CDC Hughes was found to possess a QTL on 5A.

The genes/QTL identified in both populations could synergistically enhance the expression of Sst1 (3B) and 3Ag14 (3D) loci. The analysis with AAC_Hodge/BW5087 and BW5087/AAC_Stoughton crosses revealed several QTL controlling resistance to stem toppling. Five loci were associated with tolerance to cutting in AAC_Hodge/BW5087, whereas fourteen QTL were detected in BW5087/AAC_Stoughton at Pense.

Two QTL were identified on chromosome 4B from AAC Hodge and AAC Stoughton as well as 6A from BW5087 in both crosses and shared similar physical locations. Results of this study could help breeders determine important minor loci that significantly reduce stem toppling in wheat.