Identification and validation of two quantitative trait loci for dwarf bunt in the resistant cultivar 'UI Silver'.

Two dwarf bunt resistance QTLs were mapped to chromosome 6D, and KASP markers associated with the loci were developed and validated in a panel of regionally adapted winter wheats. UI Silver is an invaluable adapted resistant cultivar possessing the two identified QTL potentially associated with genes Bt9 and Bt10 and will be useful in future cultivar development to improve dwarf bunt resistance. Dwarf bunt, caused by Tilletia controversa, is a fungal disease of wheat that can cause complete loss of grain yield and quality during epidemics. Traditional breeding for dwarf bunt resistance requires many years of field screening under stringent conditions with disease assessment possible only near or after plant maturity. Molecular marker-assisted selection (MAS) offers a more efficient alternative. This study identified quantitative trait loci (QTL) and associated molecular markers for dwarf bunt resistance in wheat. A doubled haploid (DH) mapping population of 135 lines, derived from bunt-resistant cultivar 'UI Silver' and susceptible line 'Shaan89150', was evaluated in field nursery in Logan, Utah in 2017, 2018, and 2023. The population was genotyped using Illumina 90 K SNP iSelect marker platform. Using inclusive composite interval mapping (ICIM), the major QTL Qdb.ssdhui-6DL was consistently identified on chromosome arm 6DL across all environments, explaining phenotypic variations ranging from 15.29% to 35.40%. Another QTL, Qdb.ssdhui-6DS, was detected on chromosome arm 6DS, explaining approximately 11% of the phenotypic variation. These two QTLs exhibit additive-by-additive effects for increased resistance within the DH population. Kompetitive allele-specific PCR (KASP) markers were developed within QTL intervals and used in a validation panel of regionally adapted winter wheat lines to confirm the association between the two QTL and dwarf bunt resistance. Thus, 'UI Silver' and additional resistant cultivars with these two QTLs are valuable parental lines for improving dwarf bunt resistance through marker-assisted selection. These genetic resources are essential for understanding gene function via map-based gene cloning.