Genetic variability in biomass allocation to roots in wheat is mainly related to crop tillering dynamics and nitrogen status

Improving arable crops nitrogen use efficiency (NUE) is a major target of plant breeding. In wheat, a large part of the nitrogen (N) harvested in the grain originates from N remobilization from vegetative organs during the post-anthesis period. While N remobilization from above-ground organs such as leaves and stems has been extensively studied, studies about N remobilization from roots are scarce. The existence of genetic variability for biomass allocation to the root pool as well as for root N concentration and remobilization may strongly affect the N economy of the crop. By studying the root system of 16 elite wheat genotypes under two contrasted N treatments, we showed that the biomass allocation to roots was strongly related to crop tillering dynamics and N nutritional status. Therefore, the apparent genetic variability for biomass allocation to roots is not intrinsic, but rather a consequence of genetic variability for crop growth and N utilization taken as a whole. In addition, we showed here that the N amount potentially remobilized from roots to the grain is extremely small. Existing genetic variability for root N content and remobilization efficiency cannot explain observed differences in genotypes grain N concentration or N yield. These results indicate that there is little prospect for breeding strategies specifically aiming at optimizing wheat root biomass allocation and N remobilization for improving NUE and GPC for elite genotypes at least in highly productive conditions. These results nevertheless do not imply that the root compartment should be totally discarded in all breeding programs since architectural traits such as root length or distribution may impact strongly crop performance.

► Sixteen wheat cultivar under two N regimes were grown in the field.
► Root biomass and nitrogen allocation and dynamic was measured post-anthesis.
► Genetic variability for root biomass allocation is driven by tillering and crop N status.
► N remobilized from roots to the grain is negligible.
► NUE calculations is not affected by root compartment accounting.