Correspondence: samia.berraies@agr.gc.ca; yuefeng.ruan@agr.gc.ca 

Ergot, caused by the fungus Claviceps purpurea (Fr.) Tul. (Cp), affects plants during anthesis, leading to the formation of black sclerotia. While the sclerotia themselves do not cause significant yield losses, the toxic alkaloids within them result in grain downgrading and economic losses during market grading.

Commercial durum wheat cultivars in Canada are susceptible to ergot disease. Although host resistance is rare, a few resistance loci have been identified. This study aimed to confirm existing and identify additional genetic determinants of ergot resistance in two doubled haploid durum wheat populations (A1560& and A1561&). The common parent, A0709-BX05, is the most ergot-resistant line developed at the Swift Current Research and Development Centre (SCRDC), Agriculture and Agri-Food Canada (AAFC).

The populations were grown in the SCRDC greenhouse from 2021 to 2023 and inoculated with three ergot isolates. Visual assessments of honeydew and sclerotia production were conducted. Furthermore, the A1561& population, along with parents and checks, were assessed for six post-harvest sclerotial traits using Vibe QM3i image analyzer. Both populations and parents were genotyped using the 25K Wheat Array, following the Trait Genetics manufacturer’s protocol.

Linkage maps were independently generated and quantitative trait locus (QTL) mapping was conducted. The QTL mapping revealed significant loci associated with honeydew resistance and sclerotia rating. For the A1560& population, a QTL was associated with honeydew resistance on each of chromosome 2A and 5B. Notably, the QTL on chromosome 2A emerged as the major contributor to honeydew resistance, explaining up to 54% of the phenotypic variance.

The resistant parent A0709-BX05 contributed low honeydew production alleles for both QTL. In the case of A1561&, six QTL associated with eight different traits (honeydew production, sclerotia production, number of sclerotia, sclerotia length, sclerotia width, sclerotia area average, sclerotia total weight, and sclerotia total area) were identified on chromosomes 1A, 1B, 2A, and 5B. Notably, the QTL on chromosomes 2A and 5B were major contributors to resistance, explaining from 25 to 75% of the phenotypic variance for honeydew resistance and sclerotia rating.

All resistance loci were contributed by the resistant parental line A0709-BX05. These findings will aid in the development and enhancement of markers for ergot resistance in durum wheat.