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.