Relevance of QSbm.ubo-2BS for Breeding Durum Wheat Resistant to Soil-Borne Cereal Mosaic Virus (SBCMV)

Genetic analysis of Soil-Borne Cereal Mosaic Virus (SBCMV) resistance in durum wheat was carried out on two RIL mapping populations obtained from Meridiano (resistant) × Claudio and Simeto (susceptible) × Levante (resistant) Italian elite cultivars. The RILs were characterized for SBCMV response under severe infection conditions over three consecutive years (2007-2009). Heritability of the disease response was high, with h² values always above 80%. In both populations, a major QTL (QSbm.ubo-2BS) on the distal portion of chromosome 2BS accounted for 60–90% of the phenotypic variation for symptom severity, 40–70% for virus concentration and 30-60% for grain yield. Multiple minor QTLs for disease response were identified, including one located in the homeologous region of QSbm.ubo-2BS. However, these QTLs showed R² values for disease response lower than or equal to 10%. By means of meta-QTL analysis, QSbm.ubo-2BS was mapped within a 2 cM-wide interval (LOD-2) close to the DArT marker wPt-2106 and tagged by wmc661-gwm210-barc35. The distribution of the molecular haplotypes at QSbm.ubo-2BS in a germplasm collection of 111 elite accessions showed that the haplotype associated to resistance was present in 49 accessions, 44 of which were classified as resistant or medium resistant. This haplotype was present at relatively high frequency in CIMMYT, south-western US and North American germplasm. The sequence of the wPt-2106 DArT clone was used to obtain a diagnostic PCR-based assay based on high resolution melting (HRM) analysis. The positional cloning of QSbm.ubo-2BS has been undertaken.