Ensuring durum wheat resilience to abiotic stress under climate change requires a holistic approach to effectively dissect and leverage the genetic components, including the QTLome, of drought resilience, a complex trait. We extensively assessed the UNIBO Durum Panel, a GWAS panel including 248 elite durum wheat (Triticum turgidum L. ssp. durum Desf.) varieties and advanced lines from worldwide, for drought-related traits under both field and controlled conditions.

Response to high-temperature growing conditions and terminal stress was also assessed for two years in Maricopa station, Tucson, Arizona. Phenotypic characterization included two Unmanned Aerial Vehicles (UAVs) and a ground-based platform used to measure Normalized Difference Vegetation Index (NDVI), associated to biomass development, leaf chlorophyll content (SPAD), leaf rolling and dry biomass under terminal drought stress, Chlorophyll fluorescence (ChlF) assessed through LIFT sensor, leaf relative water content (RWC), osmotic potential (ψs), osmotic adjustment (OA), chlorophyll content (SPAD), and leaf rolling (LR).

All physiological data were adjusted for heading date as a covariate. Global R2 was high, due to optimal experimental conditions, and equal to 89.6% for UAV-based NDVI and 72.3% for active OA. Notably, a high positive correlation (r = 0.78) between active OA and RWC was found under severe drought conditions

The QTLome was mapped based on the Illumina 90K SNP array. In total, 15 QTL hotspot clusters were identified for NDVI and other drought-adaptive traits, where a higher OA capacity was positively associated with RWC and/or SPAD, and negatively with LR, indicating a beneficial effect of active OA on the water status of the plant. The comparative analysis with the results of 14 previous field trials conducted under varying water regimes showed concurrent effects of five OA QTL cluster hotspots on normalized difference vegetation index (NDVI), thousand-kernel weight (TKW) and grain yield (GY).

Gene content analysis of the eight major QTL hotspots/clusters revealed the presence of several candidate genes, including bidirectional sugar transporter SWEET, rhomboid-like protein and DREB1. Our results support active OA as a valuable proxy for marker-assisted selection (MAS) aimed at enhancing drought resistance in wheat.

In parallel, the same materials extended to the full Global Durum Genomic Resource (GDGR, https://wheat.pw.usda.gov/GG3/global_durum_genomic_resources) were characterised for root growth angle (RGA), a relevant trait to access residual water stored in deep soil layers. RGA ranged from 13.0 to 160.8˚ with a h2 of 0.82.

Genome-Wide association study (GWAS) pinpointed 7 and 13 QTLs in cultivars and landraces, respectively. Three major QTLs on chr. 2A, 6A and 7A were consistently found, accounting for a total of 23.5% and 14.5% R2 in cultivars and landraces, respectively. QRGA.ubo-6A.2 on chromosome 6A showed the largest R2 effect (13.4% in cultivars and 8.6% in landraces) and, most importantly, overlap with a QTL cluster already identified for OA/RWC and NDVI in Maricopa.

The narrow haplotype is frequent in North American, French and ICARDA ‘70s cultivars. In contrast, the RGA-6A shallow haplotype was predominant in CIMMYT’60-SVEVO and CIMMYT’80-ALTAR_C84 lineages. RGA-contrasting cultivars based on the cumulative effects of chr. 2A, 6A and 7A QTLs are being assessed for their effects on yield and drought resilience at CIMMYT, ICARDA and the University of Queensland. Haplotype-tagging KASP® markers have been developed and candidate genes have been mined based on genomic and transcriptomic resources available. The most recent achievements in cloning QRGA.ubo-6A.2 will be presented.

Acknowledgements. Research supported by “Rooty”, Rooty-A root ideotype toolbox to support improved wheat yields (IWYP), “CerealMed”- Enhancing diversity in Mediterranean cereal farming systems (PRIMA 2019) and “INNOVAR” - Next generation variety testing for improved cropping on European farmland projects (H2020 FP7), NEWRoots - Evaluation & cloning of a major root angle QTL for a sustainable production in durum wheat (PRIN-2022).