Common bunt in winter wheat - Identification and integration of genetic resources for resistance breeding

Common bunt caused by the fungi Tilletia caries and Tilletia laevis was once among the most devastating wheat diseases, capable of destroying large portions of the harvests. Its typical symptoms, the so-called 'bunt balls' replacing wheat grains, became a rare phenomenon during the second half of the 20th century, though. This was achieved by the development of synthetic fungicides that could be applied as seed dressings and prevented infestations with many diseases. Common bunt has re-emerged recently on areas devoted to organic farming, where the use of synthetic fungicides is not allowed. As more and more land is being managed organically, though, the need for bunt-resistant cultivars has become urgent. Since resistance to common bunt has long been absent from the list of wheat breeding goals, this thesis aims to help compensate the lack of research and breeding activities accumulated during the last decades. New genetic sources for common bunt resistance were identified in the wheat gene pool and unlocked for their use in resistance breeding. In a genome-wide association study, bread wheat accessions with resistance against two bunt diseases as well as markers corresponding to the resistance-conferring loci were determined. Through genetic mapping in bi-parental populations, the major bunt resistance factor Bt11 was identified on wheat chromosome 6D. Marker-assisted selection of resistance loci was successfully applied in multi-parent breeding lines with high genetic variation, leading to the development of common bunt resistant and agronomically adapted material. The newly identified genetic sources and selection through molecular markers enable breeders to develop cultivars with stable resistance through combination of multiple genetic loci in a shorter time and broaden the pool of resistance factors available for breeding programs.