Assessing the contribution of seedling root traits to phosphorus responsiveness in wheat

Improving uptake efficiency of wheat is important to improving phosphorus (P) recovery and P efficiency. Different root traits have been suggested to be important to P efficiency but their relative importance has seldom been evaluated to identify which traits should be the focus for selection and breeding. This study characterized root traits of 10 varieties of wheat that differed in their responses to fertilizer P in multisite field trials with the aim to understand which traits were contributing to the variation in P efficiency. Seedlings were characterized for seminal and crown root angle, root length, root diameter, root hair length and rhizosheath volume. Experiments were conducted in two soils low in available P, and the effect of P availability on root traits was assessed by using two different rates of P in one experiment. Compared to the varieties that showed a large yield response to P in field trials, varieties with a low P response had narrow seminal roots angles, but wider crown root angles, longer root hairs, larger rhizosheath volume and higher rates of P uptake per unit root length. The importance of these traits to explain the variation in yield and yield response to P among the field trials differed but the root traits most consistently related to yield response were rhizosheath volume and root hair length. Root diameter was associated with grain yield without additional P but was not with response to P. Root angle did not contribute to yield at low P or P response.