HIGH - THROUGHPUT PHENOTYPING OF A DURUM WHEAT ASSOCIATION PANEL REVEALS DIFFERENTIAL SELECTION FOR A ROOT ARCHITECTUR E QTL IN RESPONSE TO DIFFERENT WATER REGIMES

In this study we report the characterization of 183 elite durum wheat ( Triticum turgidum ssp. durum Desf.) for root system architecture (RSA) and shoot developmental traits. Plants were grown in controlled conditions up to the 7th leaf appearance (late tillering) using the high throughput phenotyping platform GROWSCREEN Rhizo, a rhizo - box - based system consisting of deep (90 cm) rhizo - boxes integrated with automatic root RGB imaging. The following RSA traits were measured: seminal root length, noda l root length, lateral root length, root system convex hull, root system width and depth distribution (twice per week). Measurements of leaf area, leaf number and tiller number were performed twice per week and SPAD measurements were collected twice during the experiment. Root dry biomass and shoot fresh and dry biomass were collected at the end of the experiment. The dynamic collection of the above mentioned traits allowed us to model root and shoot growth and thus to disentangle the final point phenotypes in simpler and integrative phenes. A genome - wide association study (GWAS) based upon the Illumina Infinium 90K SNP assay identified many QTLs for RSA and/or shoot growth traits (P < 0.0001). GWAS confirmed a highly significant effect on adult plant root s ystem width due to two major QTLs on chromosomes 6AL and 7AC previously identified on seminal roots (Maccaferri et al. 2016). Notably, haplotype frequency of the QTL cluster on chromosome 7AC was found to be significantly associated with root depth, root s ystem width, root specific weight and shoot/root ratio. Notably, shoot/root ratio revealed a strong, contrasting selection pattern between the cultivars released by the rainfed and irrigated breeding programs conducted at ICARDA and CIMMYT, respectively, suggesting an indirect but major role of RSA features in durum wheat breeding and environmental adaptation. These results provide valuable insights toward a better understanding and more effective deployment of the RSA QTLome in durum wheat as related to di fferent environmental conditions.