Comparative analysis of differential root system architecture in tetraploid and hexaploid wheat under optimal and limiting nitrogen conditions

The variation in nitrogen (N) uptake efficiency is influenced by many factors once the plant root comes in contact with the soil. A study to compare root traits and N uptake among wheat genotypes belonging to hexaploid (Triticum aestivum) and tetraploid (T. durum and T. dicoccum) species at three depth zones (0–30 cm, 30–60 cm and > 60 cm) and two N levels [(limiting N: N₅₀ (50 kg ha⁻¹) _{and optimal N: N100 (100 kg ha⁻¹)] was conducted using image-based phenotyping and analysis. The response of a species for a trait was dependent on the N level as well as the rooting depth. In all the three species, root surface area, crossings and root biomass showed higher mean value at N50 than at N100. However, total root length, root length density and specific root length showed higher mean value at N50 only in T. aestivum and T. durum. The variance for root traits at N50 and N100 varied with the rooting depth and species studied. The effect of N level was significant for all the N uptake traits including above ground biomass, N (%), above ground N and Nitrogen uptake efficiency (NUpE). For NUpE, only the genotype effect was significant. Principal component (PC) analysis classified root length traits and N uptake traits along PC1 at both the N levels. However, distribution of genotypes across the two PCs was different at the two N levels. Among bread wheat lines RAJ 4248, UAS BW-13357 and GW322 performed better in terms of N uptake efficiency. ECI26374, MLT DW RF7 and ICARDA RI 15 among durum wheat genotypes and DDK 50421, DDK50332 and DDK-50404 among T. dicoccum genotypes were found to have superior performance for NUpE. The current study delineates the importance of evaluating roots at different depths instead of whole root systems and using competitive N levels in NUE research so that the N use efficient varieties can perform equally well in the field at moderate N levels.}