QTLs for root traits at mid-tillering and for root and shoot traits at maturity in a RIL population of spring bread wheat grown under well-watered conditions

Root system traits have positive effects on wheat grain yield, particularly in drought environments. Root traits are difficult to manipulate using conventional selection procedures. Marker-assisted-selection (MAS) could be helpful for the improvement of root morphological traits. A recombinant inbred line (RIL) population of 168 lines derived from the cross Iran #49 × Yecora Rojo was used to map quantitative trait loci (QTLs) for root traits at mid-tillering stage for one season and for root and shoot traits at plant maturity for two seasons using two different subsets. The RILs were grown in sand-tube experiments in a glasshouse under well-watered conditions. Longest root (LR), total root length longer 30 cm (TRL30), shallow root weight (roots between 0 and 30 cm, SRW), deep root weight (roots bellow 30 cm, DRW), total root biomass (RBio), ratio of root to shoot (RTS) and to plant (RTP) biomass were measured at mid-tillering. At maturity, number of days to booting (DTB), to heading (DTH), to anthesis (DTA), and to maturity (DTM), plant height (PH), flag leaf area (FLA), number of tillers (NTP) and spikes (NSP) per plant, number of grains (NGP), grain weight (GW), grain yield (GY) per plant, LR, SRW, DRW, RBio, PBio, and RTP were measured. At mid-tillering, a total of 18 putative QTLs were detected with individual QTL accounted for between 6.5 and 26.5 % of the variation in the traits. The QTLs were distributed on chromosomes 1B, 2A, 2D, 4B, 6B, 7A, and 7D. A major and two minor QTLs were identified for LR, with the major QTL (qLR-2D) explaining 26.5 % of variation. Two QTLs were detected for DRW on chromosome 4B between markers Gwm6 and Sukkula.1220 that together explained 23.1 % of variation. One region between marker Wmc198 and Cfa2263 on chromosome 2A contained four QTLs affecting PH, SRW, RTS, and RTP. At maturity, 70 putative QTLs were detected across the two seasons with a single QTL accounted for between 7.7 and 40.6 % of variation in the traits. Three major colocalized QTLs for SRW, DRW, and RBio were identified on chromosome 2D between markers Wms515 and Wms102 that accounted for 19.8, 20.5, and 22.4 % 0f variation, respectively. Two major colocalized QTLs for SRW and RBio were detected on chromosome 3A that explained 17.8 and 13.4 % of variation, respectively. One major QTL for DRW was identified on chromosome 1B that accounted for 20.3 % of variation. Chromosome 2B harbored major QTLs for GY, NGS, and NGP. A major QTL cluster was detected on chromosome 2D and on chromosome 4A relating 11 and eight QTLs for phenological periods, root traits, RTS, and RTP, indicating pleiotropic effects on these traits. Of the four common root traits studied at mid-tillering and at maturity, only SRW had linked QTLs on chromosome 2A at both stages of plant growth, indicating selection for root traits at seedling stage alone may not be effective in changing root morphological characteristics at later stages of plant growth. It appeared that chromosome 2A, 2D, and 4B harbored genes regulating growth of root traits at early and later stages of plant growth. The molecular markers closely linked to QTLs for root and shoot traits may be used in wheat breeding program using MAS procedures.