Abstract: Hard pans, soil compaction, soil aggregation and stones create physical barriers that can affect the development of a plant root system. Roots are known to exploit paths of least resistance to avoid such obstacles, but the mechanism through which this is achieved is not well understood.
At the PMMH laboratory, we developped model experimental systems to study how the root changes its growth when encountering a single or a collection of obstacles mimicking the mechanical heterogeneities in a soil. In particular we investigated the growth response of a root (i) pushing against a single obstacle such as a force sensor or (ii) growing inside arrays of obstacles of varying rigidities. In a first part I will present how, by coupling force and kinematic measurements under infra-red lighting, we probed the force-growth relationship of a primary root contacting a stiff resisting obstacle. In a second part, I will show how a primary root growing within a 3D-printed array of stiff obstacles switches from a vertical to an oblique trajectory due to the competition between gravitropism and thigmotropism.