Common bunt resistance in winter wheat – a cross-chromosome journey

Common bunt, a seed-borne disease caused by the fungi Tilletia tritici and T. laevis, seriously affects grain yield and quality in wheat. Only one (Bt10) of 16 race-specific resistance genes is currently widely used in breeding programs. Since the majority of bunt resistant material is not suitable for Austrian agriculture, there is an urgent need to incorporate Bt-genes into regionally adapted cultivars. Marker-assisted and genomic-assisted selection can be applied to introgress resistance alleles from wheat relatives or landraces into elite breeding lines and eliminate unfavourable properties thereby introduced through linkage drag. To pave the way for incorporating exotic resistance sources into breeding lines adapted to mid-European growing conditions, two different experiments are conducted at IFA Tulln: a) Two RIL populations derived from crossing winter wheat genotypes PI166910*Rainer and 702-1102C*Rainer were phenotypically screened for common bunt resistance using artificial seed inoculation at IFA Tulln in 2019. PI166910 is the carrier of bunt resistance gene Bt11 and probably Bt9 and 702-1102C carries either Bt8 or Bt9 (Anders Borgen, personal communication) while Rainer is highly susceptible to common bunt. Steffan et al. (2017) mapped Bt9 to the long arm of chromosome 6D. We selectively genotyped RILs with KASP markers positioned between 400 and 470 Mbp on chromosome 6D and SSR markers indicative for the QTL interval of Bt11 on chromosome 3B. Preliminary results show that 702- 1102C and PI166910 carry the Bt9 gene and that PI166910 contains an additional yet not known resistance gene (possibly Bt11). b) A backcross-population consisting of BC2F2- and BC3F1-lines was developed from initial crosses of elite cultivars to non-adapted common bunt resistance donors by repeated backcrossing. The donor-lines (Blizzard, Bonneville and the Turkish landrace PI119333) confer resistance via 5 different QTL located on chromosomes 1A, 1B, 4B, 7A and 7D. PI119333 contributes Bt12 on 7D. By MAS with KASP-markers, plants heterozygous at one or more resistance loci were selected, selfed and genotyped with GBS-markers. Depending on genomic predictions and the amount of BC2F2-seeds, a selection of lines will be propagated and subjected to artificial infection in 2021.