The relationships between seedling root screens, root growth in the field and grain yield for wheat

Background and aims: We were interested to know if laboratory screens of root growth could be used to identify wheat lines with contrasting rooting patterns when grown in the field.
Methods: We screened 637 wheat lines, composed of elite as well as a limited number of breeding lines, to identify wheat lines with contrasting 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 field rooting behaviour. In the field, wheat lines with deep roots always had high grain yields, but deep rooting was 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 field rooting performance. Root diameter, for reasons that are not clear, is correlated with high grain yield.