1. AIM OF THE RESEARCH : To assess the effect of the introgression of defined chromosomal segments of the wild Thinopyrum ponticum into durum wheat on the expression of root traits Paper no-roll For each genotype, 6 homogeneous seedlings with normal seminal root emission were positioned at 7 cm distance from each other on filter paper placed on a vertical black polycarbonate plate (42.5 x 38.5 cm) for root obscuration. Distilled water was used for plantlets’ growth. Traits were measured in 7 days old plantlets, grown at 22°C and 16-h light photoperiod (growth chamber; Fig. 2). The experimental unit included 12 plantlets for each HOM+ genotype and 6 for the respective HOM- control (Cané et al., Mol Breeding 2014). The experiment was conducted according to a randomized complete block design, with 5 replicates per genotype. INTRODUCTION Due to the rise in food demand, associated with the drastic climatic changes, the release of wheat cultivars with an higher and stable yield potential acquires an even greater strategic importance than ever among the goals of today's breeding programs. In this context, roots, the hidden part of the plant, are involved in so numerous functions that it is difficult to overlook their importance for plant productivity (MacMillan et al., Springer 2006). With Root system architecture (RSA) is identified the spatial configuration of a root system. It is a complex, developmental and agronomic trait, with implications for overall plant architecture, growth rate and yield, as well as abiotic stress resistance, nutrient uptake, and developmental plasticity in response to environmental changes. Considering the current 'bottlenecks’ for further yield gains, a promising approach consists of widening the wheat genetic variability by resorting to alien genes/QTLs from wild relatives. To this purpose, species of the genus Thinopyrum, in particular Th. ponticum, the target species of this work, were extensively used in bread wheat and durum wheat improvement (Ceoloni et al., Cytog & Genome Res 2005). The decaploid tall wheatgrass Th. ponticum has been shown to have several genes/QTLs for resistance to diseases (Lr19, Sr25) and grain quality (Yp) concentrated on the long arm of its chromosome 7Ag (7AgL), homoeologus to wheat group 7. Moreover, recent results from analysis of yield performance of durum wheat-Th. ponticum recombinant lines (NIRLs), carrying 23%, 28% and 40% distal 7AgL chromatin on their 7AL arm (Fig.1), indicated the presence of yield-contributing QTLs for grain and above-ground biomass in defined 7AgL segments introgressed into the NIRLs (Kuzmanovic et al., J Exp Bot 2014; Ceoloni et al., Springer 2014). Here, these NIRLs have been employed in two different micro-methods, i.e. paper no-roll (PNR) and rhizotrons (RHZ), to assess the expression of several root traits and eventually associate to 7AgL sub-regions their genetic control. ROOT TRAITS ANALYSIS The results obtained from both methods of analysis revealed in most cases significance of the interaction of the genotype with the presence of the 7AgL segment, indicating a relevant contribution of 7AgL introgressions in the control of the parameters analysed (Fig. 4). The segments had a prevalently positive effect, except for some traits in line R23 (see ahead), possibly as a consequence of a Segregation distortion (Sd) factor(s) uniquely present in the 7AgL segment specific to this NIRL (28-40% of the arm, Figs. 1 and 4; Ceoloni et al., Springer 2014). %7AgL R23 40 R112 28 R5 23 Figure 1. Recombinant 7AL-7AgL chromosomes representing the three durum wheat NIRLs used in the present study Rhizotrons For each genotype, 2 seedlings were positioned at 10 cm distance on a soil-filled rhizotrons (43,5 X 29,7 X 0,5 cm; 700 ml of soil per apparatus). Distilled water was used for plantlets’ growth (50 ml every two days). Traits were measured in plantlets that were grown for 12 days in glasshouse at ~ 22°C (Fig. 3). Images of roots and shoots were taken with a scanner (resolution = 255 PI; format = A3). Four replicates were set up for each genotype, giving a total of 16 and 8 seedlings for each HOM+ and HOM- NIRL, respectively. MATERIALS AND METHODS Root traits of three durum wheat-Th. ponticum near isogenic recombinant lines (NIRLs), named R5, R112 and R23, were analysed using two micro-methods (Fig.1). Each genotype was represented by homozygous carrier (HOM+) and non-carrier (HOM-) plants of the given 7AgL segment. In both experimental settings (PNR and RHZ) the traits listed in Table 1 were measured. Root length traits were measured on plantlets’ images using the free software RootSnap. The analysis of variance (ANOVA) was conducted by a general linear model (ANOVA-GLM) as a mixed effect model, and Tukey's Post Hoc Test, using the SISTAT12 software. TRAITS SRA (rad)Spread of Root Angle SL (cm)Shoot Length SDW (mg)Shoot Dry Weight SRNSeminal Root Number PRL (cm)Primary Root Length TRL (cm)Total Seminal Roots Length RDW (mg)Root Dry Weight RDW (mg)/TRL (cm) indirect measure of root thickness RDW (mg)/SDW (mg) ratio between Root and Shoot Dry Weight In both micro-methods, no significant effect was detected for the SL trait in association with presence of 7AgL segments (not shown), while for SDW only a positive trend was observed in R112 HOM+ plants RDW was significantly higher in R112 (31% and 38%, PNR and RHZ respectively), but depressed in R23 (-31% and - 28%, respectively) RDW/SDW was significantly higher in RHZ, both in R112 and R5 (18% and 19%, respectively), but depressed in R23, in both experiments (- 25% and -20%, PNR and RHZ, respectively) SRA increased in line R112 (17% and 37%, PNR and RHZ, respectively) and R23 (17% in PNR and 14% in RHZ): a gene/QTL involved in SRA control is located in the 7AgL region common to R112 and R23 and absent in R5 (Fig. 5) PRL and TRL were higher in R112 only, in both analyses RDW/TRL significantly increased in R112 (14% and 34%, in PNR and RHZ, respectively), but was depressed in R23: a gene/QTL for RDW/TRL is located in the 7AgL portion present in R112 and absent in R5 (Fig. 5) SNR did not show any difference between the lines RSA RDW PRL TRL RDW/TRL R23 R112 R5 %7AgL 40 28 23 RDW/SDW Root traits depression Fig. 5. Th. ponticum 7AgL sub-regions present in the tested durum wheat recombinants containing putative genes/QTLs for various root traits Figure 4. Root and shoot traits recorded for the three durum wheat NIRLs (HOM+) and their controls (HOM-) in PNR and RHZ micro-methods. Letters at each row correspond to ranking of Tukey test at P < 0.01 (capital) and P < 0.05 (lower case) level. Table 1. List of traits measured and corresponding abbreviations used in this study Figure 2. A view of the plantlets in the paper no-roll setting Figure 3. A view of the plantlets in soil-filled rhizotrons PAPER NO-ROLL RHIZOTRON SDW PAPER NO-ROLL RHIZOTRON RDW PAPER NO-ROLL RHIZOTRON TRL PAPER NO-ROLL RHIZOTRON RDW/SDW PAPER NO-ROLL RHIZOTRON SRA PAPER NO-ROLL RHIZOTRON SRN PAPER NO-ROLL RHIZOTRON RDW/TRL PAPER NO-ROLL RHIZOTRON PRL CONCLUSIONS The 40% 7AgL spanning the alien content of the three durum wheat-Th. ponticum NIRLs has been dissected into sub-regions containing putative loci controlling root traits Most loci turned out to reside in the 23 to 28%-long 7AgL segment shared by recombinants R112 and R23 (Fig. 5), with R112 showing remarkable increases compared to the null control and the other NIRLs In the same segment, loci for yield-contributing traits were previously allocated as well (Kuzmanovic et al., J Exp Bot 2014) The enhanced root traits may be involved in the 7AgL incremental effects on yield