Abstract
Wheat diseases such as common bunt (caused by Tilletia caries (DC.) Tul. &C. Tul. and Tilletia laevis J. G. Kühn) and dwarf bunt (caused by Tilletia controversa J. G. Kühn) present ongoing threats to global wheat production, causing substantial yield and quality losses. Traditional breeding methods for resistance to these diseases are heavily reliant on environmental conditions, limiting the effectiveness of field screening. Advances in molecular marker-assisted selection (MAS) and refined phenotyping protocols offer more efficient alternatives. However, significant challenges remain, particularly in developing robust and consistent screening methods that work across both controlled and field environments, and in identifying resistance loci that are effective across a wide range of wheat genotypes.A set of six spring wheat cultivars were used to optimize the greenhouse inoculation protocols for assessing resistance to common bunt. Two of them are known for susceptibility to both CB and DB, the other four are unknown for their reaction to CB and DB. Three different inoculation methods and two scoring techniques were evaluated. Results showed that seed inoculation methods were more effective in inducing infection compared to seedling inoculation, providing a clear distinction between resistant and susceptible lines. The optimized protocol was validated using wheat cultivars and bunt differential lines over two years, providing support for its reproducibility and effectiveness for germplasm screening under controlled conditions.
Further, quantitative trait loci (QTL) mapping was employed to identify key loci associated with dwarf bunt resistance. Using a doubled haploid population derived from a cross between the dwarf bunt-resistant cultivar 'UI Silver' and the susceptible line 'Shaan89150', two major QTL, both located on chromosome 6D (Q.db.ssdhui-6DL and Q.db.ssdhui-6DS), were identified as controlling resistance. Kompetitive Allele-Specific PCR (KASP) markers were developed for these QTL regions and were validated in a diverse panel of winter wheat lines, confirming their association with dwarf bunt resistance. These markers provide valuable tools for MAS, helping breeding programs develop wheat cultivars with improved resistance to dwarf bunt.
In addition, the study examined the genetic relationships and disease responses of 17 bunt differential wheat lines used to distinguish races of common and dwarf bunt pathogens. Field trials over nine years revealed variations in resistance levels, with some lines, particularly those carrying resistance genes Bt8, Bt11, Bt12, and Btp, showing consistent resistance to both common and dwarf bunt across different environments. Genetic analysis of these differential lines using single nucleotide polymorphism (SNP) markers further highlighted their genetic diversity, with distinct clusters identified. This characterization helps inform breeding strategies aimed at enhancing bunt resistance.
Overall, this research provides valuable tools for advancing resistance breeding in wheat. The greenhouse inoculation protocol, the molecular markers developed, and the genetic relationships of differential lines can be directly applied in wheat breeding programs to improve resistance to common and dwarf bunt. Future work should focus on fine-mapping QTL regions, investigating candidate genes, and conducting field trials to confirm the broader applicability of these findings.