Email: elisabetta.mazzucotelli@crea.gov.it

Wheat fungal diseases, as wheat rusts (yellow rust-YR caused by Puccinia striiformis, leaf rust- LR by P. triticina, stem rust-SR by P. graminis -Pgt), and Septoria Tritici Blotch (STB, by Zymoseptoria tritici) pose significant threats to durum wheat production. Qualitative and quantitative genetic resistances are available in the tetraploid wheat germplasm, but not yet fully utilized by breeding due to lack of research and pre-breeding.

Curated germplasm collections are key to identify favourable alleles for resistance through association mapping. Previously, large collections of tetraploid wheat have been established, the Global Durum Panel and the Global Tetraploid Wheat Collection. Selected sub-panels of them were characterised for resistance to rusts and STB in different multi-environment networks with natural/artificial infection or in controlled conditions with single Pgt races.

For LR and YR, 500 cultivars and 200 landraces were tested in 8/10 locations x years environments in the Mediterranean region and Argentina; STB resistance was looked for in 500 landraces and 250 varieties assessed for two years in Italy. A panel of wild emmer was characterised for SR and LR resistance to single races, to deploy their short LD decay for high resolution mapping.

Population structure revealed differentiated frequency of resistance among populations. For all diseases, GWAS was performed using high density array-based SNP datasets and fitting both single/multi-locus mixed linear models. 8 QTLs for YR and 16 QTLs for LR resistance were significant in at least two and three environments, respectively, with some significant in a wide range of environments (i.e. QYr.ubo-1B.1 effective in six out of eight environments and three QTLs for LR, on 6B and 7B, effective in six out of ten environments), as well as loci for SR resistance to multiple races. Some loci co-locate with known genes (i.e. QYr.ubo-1B.1 with Yr64), other look novel resistance sources. Haplotype analysis was conducted on the most effective QTLs within the germplasm diversity and are being targeted through haplotype-tagging KASP® markers, as valuable contribution towards molecular-assisted breeding.

Lastly, a rare resistance gene for leaf rust on chromosome 1B with complementary effect with a resistance locus on 7B has been mapped at high resolution in a domesticated emmer accession, thanks also to the availability of its whole genome sequencing as part of the tetraploid pangenome initiative. Upon leaf infection, the transcriptional response of some candidate genes is suggestive of their involvement in the leaf rust resistance.

Research supported by Cerealmed, AGRITECH, PRO-GRACE, WheatSecurity projects.