Genetic Dissection of Heat Stress Tolerance in Durum Wheat under field conditions

Heat stress is one of the major constraints for the Triticum turgidum spp. durum wheat production. Climate change in the Mediterranean areas is expected to become a major challenge for durum wheat production. Herein, a durum wheat panel (UNIBO-DURUM) of 182 cultivars and breeding lines has been assessed for response to long-term heat stress (HS, by delayed planting) and non-stress (NS) under field conditions. In total 23 traits were measured related to phenology, grain yield and its components, at CENEB CIMMYT’s experimental station (Mexico) across HS and NS combined (2018/19) environments. Given that Heading Date (HD) is often correlated with stress escape, loci for heat tolerance independent from HD were identified by Haplotype Genome Wide Associations Studies (H-GWAS) performed by using HD-adjusted and non-adjusted BLUEs. In the comparative analysis, non-adjusted-GWAS (Without HD as a covariate) identified 29 and 26 Quantitative Trait loci (QTL) clusters, and with HD as a covariate 28 and 29 clusters for HS and NS respectively. While the overall number of QTL clusters identified remained the same, HD-adjusted GWAS provided a more refined identification of loci for heat stress response per-se. Under HS conditions, QTLs were found to be significantly associated with photosynthetic efficiency indicators (NDVI and ITNDVI), key yield components, and final grain productivity. Under (NS) conditions, QTLs demonstrated strong associations with phenological and temperature-related physiological responses (LOD=10; R2=8.67%). Additionally, regions were found strongly associated with grain quality and size traits (LOD=8.64; R2=7.15%). The identification of these HD-independent QTLs allows us to identify loci underlying the true physiological tolerance to heat stress, without confounding effects.