Dissecting the genetic bases of resistance to Soil-Borne Cereal Mosaic Virus in durum wheat by biparental mapping and GWAS

Abstract Soil-borne cereal mosaic virus (SBCMV), the causative agent of wheat common mosaic, is a furovirus challenging wheat production all over Europe. Differently from bread wheat, durum wheat germplasm evolved in semi-arid areas and shows greater susceptibility and strong yield penalties, particularly in view of the Global Change effects. Tetraploid wheat germplasm harbors a major QTL providing medium to high resistance to SBCMV, namely QSbm.ubo-2B , mapped to a chromosome region coincident with Sbm2 , previously mapped in hexaploid wheat. QSbm.ubo-2B = Sbm2 is considered a pillar for growing durum in SBCMV-affected areas like Northern and Central Italy and France. Moreover, it is also of interest for bread wheat improvement. Herein, we report the fine mapping of QSbm.ubo-2B = Sbm2 based on a combination of Genome Wide Association and bi-parental mapping up to a linkage block of 3.95 Mb comprised between IWB11421 and IWB23330 and, based on bi-parental meiosis, to a 2.66 Mb interval between IWB11421 = KUBO-27 and IWB28973 = KUBO-1. In total, 19 co-dominant KASP® and one Allele Specific Oligonucleotide (ASO)/High Resolution Melting (HRM) assay were developed, nine of which tagged closely the Sbm2 resistant haplotype and were validated in the durum cultivated germplasm, providing valuable diagnostic tools for molecular selection. Additionally, the durum wheat genome of the resistant parent Svevo has been inspected for the presence of candidate genes, including NBS-LRR. The developed Sbm2 -tagging KASP® markers provide a valuable case-study for improving the efficacy and accuracy of European variety testing system and, ultimately, decision making.