Physical obstacles in the substrate cause maize root growth trajectories to switch from vertical to oblique.

The article investigates how maize (Zea mays) primary roots respond to physical obstacles mimicking soil heterogeneities, using 3D-printed circular obstacles embedded in agarose gel and a high-throughput live-imaging platform. It identifies three stable root growth trajectories—vertical, oblique, and switching—determined by the size of obstacles and the root's ability to bend, which is influenced by gravitropism and thigmotropism. The study formalizes deterministic biomechanical rules linking root tip detachment angles, curvature during free growth phases, and obstacle geometry to predict trajectory outcomes, highlighting that root bending capacity and gravitropic response constrain exploitation of paths of least resistance. These findings suggest that root growth in mechanically heterogeneous environments follows predictable patterns shaped by physical and physiological factors, with implications for understanding root behavior in natural soils.