High Throughput Phenotyping of a Durum Wheat Association Panel Reveals Differential Selection for a Major Root Architecture QTL in Response to Different Breeding Environments

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 one meter deep rhizo-boxes integrated with automatic root RGB imaging. The following RSA traits were measured: seminal root length, nodal 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. GWAS confirmed a highly significant effect on adult plant root system width due to two major QTLs on chromosomes 6AL and 7AC previously identified on seminal roots also at the seedling stage (Maccaferri et al. 2016). Notably, haplotype frequency of the QTL cluster on chromosome 7AC was found to be significantly associated with root angle, root width and depth, root specific weight and shoot/root ratio while revealing a strong, contrasting selection pattern between the rainfed and the irrigated breeding programs conducted at ICARDA and CIMMYT, respectively, hence suggesting an indirect but major role of RSA features in durum wheat breeding and environmental adaptation. The accessions used in this experiment were previously tested for yield and yield related traits in 15 different environments across the Mediterranean basin at different water and climatic regimes. The integration of field and platform data as well as the correlation analysis among traits provides valuable insights toward a better understanding and deployment of the RSA QTLome governing durum wheat yield in different environmental conditions.