Prioritizing Root System Architecture QTLs for Marker-Assisted Selection in Durum Wheat

Optimization of root system architecture (RSA) traits is an important objective for modern wheat breeding. Linkage and association mapping for RSA evaluated in seedlings of two recombinant inbred line populations and one association mapping panel of 183 elite durum wheat (Triticum turgidum L. var. durum Desf.), respectively, evidenced 20 clusters of QTL for root length and/or number as well as 30 QTLs for root growth angle (RGA). QTLs were mapped on a high-density tetraploid consensus map based on a transcript-associated Illumina 90K SNP assay developed for bread and durum wheat, thus allowing for an accurate cross-referencing of RSA QTLs between tetraploid and hexaploid wheat. Among the main QTL clusters for root length and number highlighted in this study, 15 overlapped with QTLs for multiple RSA traits reported in bread wheat while out of 30 QTLs for RGA, only six showed colocation with previously reported QTLs in wheat. Based on their relative additive effects, allelic distribution in the AM panel and co-location with QTLs for yield and kernel weight, the RSA QTLs have been prioritized in terms of breeding value. Three major QTL clusters for root length and number (RSA_QTL_cluster_5#, RSA_QTL_cluster_6#, and RSA_QTL_cluster_12# ) and five QTLs (QRGA.ubo-2A.3, QRGA.ubo-2B.2/2B.3, QRGA.ubo-4B.4, QRGA.ubo-6A.2 and QRGA.ubo-7A.2) for RGA appear particularly valuable for further characterization towards their positional cloning and possible deployment in marker-assisted selection.