KIN RECOGNITION BY PLANT ROOTS: SOCIAL GROWING AND DIRECTIONAL MOVEMENT

Kin recognition is the ability to distinguish kin from nonkin, and it is thought to be an important driving force in the evolution of social behaviour. The ability to sense a kin or an unrelated individual in the environment influences root growth in term of resources allocation and phenotypic plasticity. Although many studies document patterns of root placement among co-occurring plants, no studies have directly observed changes in the root growth of one plant in response to roots of another via the three-dimensional (3D) analysis of their movement. Such studies are challenging but are critical to draw conclusions about the specific behaviours plants express, rather than simply describing the pattern of root distributions. We used a stereovision system that enables the 3D reconstruction of the root tip movement in hydroponic culture. We acquired maize seedlings (B73) for the first 7 days of growth in 3 different conditions: growing alone, growing with another maize plant with same genotype and growing with a plant from another species (Pisum Sativum). We extracted 3D trajectory of the root tip and a set of descriptive features in both the temporal and frequency domains. We identified 3 possible behaviours for maize roots: avoidance, aggregation and neutral. Avoidance behaviour appears more frequently in maize growing with the plant from another species, while neutral or aggregation behaviour is more frequent when growing close to another maize. We observed a lower frequency of nutation for maize growing alone than for maize growing with a neighbour. Analysis of 3D root movements with high time granularity opens to new possibilities in the study of the interactions between plants sharing the same substrate and for the investigation of roots and plants social cognition in general.