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Background and aims: We aim to quantify the variation in root distribution in a set of 35 experimental wheat lines. We also compared the effect of variation in hydraulic properties of the rhizosphere on water uptake by roots. Methods: We measured the root length density and soil drying in 35 wheat lines in a field experiment. A 3D numerical model was used to predict soil drying profiles with the different root length distributions and compared with measured soil drying. The model was used to test different scenarios of the hydraulic properties of the rhizosphere. Results: We showed that wheat lines with no detectable differences in root length density can induce soil drying profiles with statistically significant differences. Our data confirmed that a root length density of at least 1 cm/cm3 is needed to drain all the available water in soil. In surface layers where the root length density was far greater than 1 cm/cm3 water uptake was independent of rooting density due to competition for water. However, in deeper layers where root length density was less than 1 cm/cm3, water uptake by roots was proportional to root density. Conclusion: In a set of wheat lines with no detectable differences in the root length density we found significant differences in water uptake. This may be because small differences in root density at depth can result in larger differences in water uptake or that the hydraulic properties of the rhizosphere can greatly affect water uptake. [ABSTRACT FROM AUTHOR]

Background and aims: We were interested to know if laboratory screens of root growth could be used to predict root performance and grain yield of wheat when grown in the field. A secondary aim of this work was to explore the relationship between root depth and grain yield. Methods: We screened 637 wheat lines, composed of elite as well as a limited number of breeding lines, to identify wheat lines with contrasting young root traits with a high throughput screen. We selected groups of wheat lines based on the size of the seedling root, root diameter and growth angle. Seventy-two wheat lines were subjected to further screening with a wax-layer screen and grown in a field experiment in two successive years. Root length distributions, from field grown wheat, were determined with the core-break method. Results: We were unable to find relationships between data from the laboratory root screens and root depth in the field. In the field, wheat lines with deep roots always had high grain yields, but deep roots were not essential to obtain high yields. Wheat lines with the deepest roots were also amongst those with the greatest number of shallow roots. Conclusion: Laboratory root screens did not predict root depth in the field. Root diameter, for reasons that are not clear, is correlated with high grain yield. [ABSTRACT FROM AUTHOR]

Background and aims: There is an urgent need to develop new high throughput approaches to phenotype roots in the field. Excavating roots to make direct measurements is labour intensive. An alternative to excavation is to measure soil drying profiles and to infer root activity. Methods: We grew 23 lines of wheat in 2013, 2014 and 2015. In each year we estimated soil water profiles with electrical resistance tomography (ERT), electromagnetic inductance (EMI), penetrometer measurements and measurements of soil water content. We determined the relationships between the measured variable and soil water content and matric potential. Results: We found that ERT and penetrometer measurements were closely related to soil matric potential and produced the best discrimination between wheat lines. We found genotypic differences in depth of water uptake in soil water profiles and in the extent of surface drying. Conclusions: Penetrometer measurements can provide a reliable approach to comparing soil drying profiles by different wheat lines, and genotypic rankings are repeatable across years. EMI, which is more sensitive to soil water content than matric potential, and is less effective in drier soils than the penetrometer or ERT, nevertheless can be used to rapidly screen large populations for differences in root activity. [ABSTRACT FROM AUTHOR]