Fhb1 is the best validated and most prominent Fusarium resistance QTL of wheat, it confers not only strong resistance to spreading of the disease but also to the major mycotoxin deoxynivalenol (DON) by conjugation into the non-toxic DON-3O-glucoside (D3G) (Lemmens et al. 2005). While Fhb1 is already deployed in elite germplasm, the gene encoding resistance against DON has not yet been characterized. We have established the genomic sequence of the Fhb1 region from the donor line CM-82036 and fine-mapped the QTL to an 860 kb interval comprising 28 candidate genes (Schweiger et al. 2016). Mutant populations of CM-82036 were used for gene validation: TILLING identified mutant lines for eleven candidates - no loss of resistance phenotypes led to the rejection of all tested as the causal Fhb1 gene. Forward genetics screening of 1,200 gamma-radiated and 2,500 EMS mutant lines revealed four and three DON- and Fusarium-susceptible mutants, respectively. Genotypic characterisation of the gamma-radiated lines detected deletions for all four susceptible lines covering the complete Fhb1 interval confirming presence of active resistance gene(s) at the QTL. The susceptible EMSmutants were sequenced for the candidate genes, resulting in 2-3 SNPs per line, but no common factor was found. However, F2 co-segregation analysis confirmed for all three susceptible lines the QTL region as responsible for the altered phenotype after Fusarium and DON treatment. DON and D3G contents were determined to compare conversion rates of CM-82036 and the susceptible mutants, detecting about 15 times higher amounts of D3G compared to DON in the wildtype lines whereas in the susceptible mutants including F2 progenies most of the applied DON was still present. DON and Fusarium infiltration gave similar DON/D3G ratios proposing that DON detoxification is regulated by mutations in the Fhb1 interval controlling both traits. Thus, to detect all mutations in the specific QTL region the susceptible mutants and CM82036 were flow-sorted for 3B chromosomes and sequenced. A chromosome assembly of the wild-type was established (130,108 scaffolds, 722.6 Mb) and sequencing reads of the mutants were mapped to it and to the 1 Mb QTL interval. Following the MutChromSeq approach (Sánchez-Martín et al. 2016) we identified hundreds of scaffolds with SNPs in all three mutants; two were positioned in the Fhb1 interval representing targets for further analysis.

Lemmens et al. 2005, DOI: 10.1094/MPMI -18-1318

Sánchez-Martín et al. 2016, DOI 10.1186/s13059-016-1082-1

Schweiger et al. 2016, DOI 10.1007/s00122-016-2727-x

Acknowledgment. Funded by Austrian Science Fund: SFBF3711