Genome-wide association mapping identifies common bunt (Tilletia tritici/laevis) resistance loci in bread wheat (Triticum aestivum) accessions of the USDA National Small Grains Collection

Authors: EHN, MAGDALENA - University Of Natural Resources And Life Sciences, Vienna; MICHEL, SEBASTIAN - University Of Natural Resources And Life Sciences, Vienna; MORALES, LAURA - University Of Natural Resources And Life Sciences, Vienna; Gordon, Tyler; DALLINGER, HERMANN - University Of Natural Resources And Life Sciences, Vienna; BURSTMAYR, HERMANN - University Of Natural Resources And Life Sciences, Vienna

Submitted to: Theoretical and Applied Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/5/2022
Publication Date: 7/27/2022
Citation: Ehn, M., Michel, S., Morales, L., Gordon, T.C., Dallinger, H.G., Burstmayr, H. 2022. Genome-wide association mapping identifies common bunt (Tilletia tritici/laevis) resistance loci in bread wheat (Triticum aestivum) accessions of the USDA National Small Grains Collection. Theoretical and Applied Genetics. Available: https://doi.org/10.1007/s00122-022-04171-3.

Interpretive Summary: Common bunt (CB) is a fungal disease that causes significant yield and quality losses in bread wheat. Genetic resistance offers a cost-effective method of controlling CB especially in organic production environments. In a previous study, a panel of accessions from the National Small Grains Collection was used to create a genome-wide association study (GWAS) to identify genetic loci associated with dwarf bunt (DB) resistance. The GWAS panel developed in the previous study was used to test for CB resistance in Tulln, Austria in replicated field trials tested in 2019, 2020 and 2021. The field data was used to identify accessions that were resistant to CB, and genetic information from the GWAS was used to locate chromosomal regions and molecular markers associated with resistance. Resistant accessions and molecular markers identified in this study can be used to introduce CB resistance into adapted bread wheat cultivars. Additionally, 20 accessions showed very high levels of resistance to both CB and DB and are provide valuable germplasm for breeding programs targeting organic bread wheat markets.

Technical Abstract: Common bunt caused by Tilletia tritici and T. laevis was successfully controlled by seed dressings with systemic fungicides for decades, but has become a renewed threat to wheat yield and quality in organic agriculture where such treatments are forbidden. As the most efficient way to address this problem is the use of resistant cultivars, this study aims to broaden the spectrum of resistance sources available for breeders by identifying resistance loci against common bunt in bread wheat accessions of the USDA National Small Grains Collection. We conducted three years of artifcially inoculated field trials to assess common bunt infection levels in a diversity panel comprising 238 wheat accessions for which data on resistance against the closely related pathogen Tilletia controversa causing dwarf bunt was already available. Resistance levels against common bunt were higher compared to dwarf bunt in the panel with 99 accessions showing <1% incidence. Genome-wide association mapping identifed six markers signifcantly associated with common bunt incidence in regions already known to confer resistance on chromosomes 1A and 1B and novel loci on 2B and 7A. Our results show that resistance against common and dwarf bunt is not necessarily controlled by the same loci but we identifed twenty accessions with high resistance against both diseases. These represent valuable new resources for research and breeding programs since several bunt races have already been reported to overcome known resistance genes.