Common bunt (CB), caused by Tilletia caries and T. foetida, and dwarf bunt (DB), caused by T. controversa, are particularly destructive diseases of wheat grown under organic (low-input) production conditions and negatively affect both grain yield and quality. A total of 16 race specific bunt resistance genes have been proposed to date. Thereof, only Bt9 and Bt10 have been mapped so far. A mapping and two validation populations comprising 176 recombinant inbred lines were evaluated for CB and DB in artificially inoculated field trials. The mapping population was derived from the cross of the Bt12 carrier PI119333 and the susceptible cultivar 'Rainer'. The population was genotyped with the Illumina 15 K SNP chip and the major QTL QBt.ifa-7DS representing Bt12 was identified on chromosome 7DS, explaining 39% and 14% of the phenotypic variation for CB and DB resistance, respectively. Selected SNP markers were turned into Kompetitive Allele-Specific (KASP) markers and used to validate Bt12 in two independent validation populations. These markers can be used for introgressing Bt12 into regionally adapted elite breeding material.

Key message Resistance QTL on chromosomes 1AL and 7AL are effective against common and dwarf bunt, QTL on 1BS affects common bunt and QTL on 7DS affects dwarf bunt in bread wheat. Abstract Common bunt, caused by Tilletia caries and T. laevis, and dwarf bunt, caused by T. controversa, negatively affect grain yield and quality of wheat and are particularly destructive in low-input and organic production systems. Two recombinant inbred line (RIL) populations derived by crossing the highly and durably resistant cultivars ‘Blizzard’ and ‘Bonneville’ to the susceptible cultivar ‘Rainer’ were evaluated for their resistance to common and dwarf bunt in artificially inoculated field and greenhouse trials over two growing seasons and genotyped with a 15 K SNP array. Bunt resistance QTL were mapped to chromosomes 1AL, 1BS, 7AL and 7DS. Common bunt resistance was regulated by the major QTL QBt.ifa-1BS and QBt.ifa-1AL together with the moderate effect QTL QBt.ifa-7AL. Dwarf bunt resistance was on the other hand regulated by the QTL QBt.ifa-1AL, QBt.ifa-7AL and QBt.ifa-7DS. Common bunt resistance QTL exhibited pronounced epistatic effects, while epistatic effects were of smaller magnitude for dwarf bunt QTL. Kompetitive Allele-Specific PCR (KASP) markers were developed from SNPs associated with bunt resistance QTL and successfully used for QTL validation in an independent set of RILs. These KASP markers have the potential to support targeted introgression of QTL into elite wheat germplasm and accelerate breeding for enhanced bunt resistance. Durable protection against both common and dwarf bunt can be achieved by combining multiple resistance genes in the same genetic background.

International audienceAn increasing interest in sustainable forms of agriculture exists worldwide and the demand for varieties specifically adapted to organic and low-input agriculture is rising. As a consequence, breeding methods need to be refined accordingly. In order to get better insight into needs and possibilities with this regard, a comprehensive ring test was performed from 2006 to 2008 with 14 winter wheat varieties in 36 environments in major cropping regions of Austria, France, Romania and Switzerland. Environments were grouped into 9 different subsets according to input systems, years, and countries. Input system N0 consisted of 13 organic and 6 no-input trials; 17 trials in input system N received various levels of synthetic nitrogen. For grain yield (YLD) and protein yield (PYLD), significant G x E was detected. Countries had a stronger effect on both traits than systems. Overall, it was more efficient to select YLD and PYLD in N, for targeting both systems N and N0. For PYLD, direct testing within a given country was always more efficient than indirect selection. Many traits could be scored equally well in both systems, N and N0, but for some traits particularly important for organic agriculture, such as soil coverage, better differentiation was observed under organic conditions. Therefore, we agree with other authors that a commercially sustainable breeding program for organic and low-input agriculture should combine information from high and low-input levels and from diverse regions. Local testing of varieties, however, remains indispensabl