Maize root system stiffness is determined by the size and distribution of the below-ground root system

Root system stiffness is a measurement that describes the resistance of a root system to rotation. Previous work has shown that genotypes with a higher root system stiffness are also more susceptible to root lodging. In this study, we deconvolve the contribution of root architecture, individual root-level mechanics, and root-soil interaction to root system stiffness in maize inbred lines. Collectively, larger above- and below-ground root systems and stiffer individual brace roots contribute to a higher root system stiffness. When considering all traits in predictive models, the below-ground root architecture primarily drives the prediction of root system stiffness categories. These below-ground traits describe the size and distribution of the root system. Analysis of a roothairless3 mutant revealed a reduction in root system stiffness that could not be decoupled from a reduction in root size. Together these results link root system stiffness to the size and distribution of the below-ground root system and highlight the importance of this measurement for both root lodging resistance and root phenotyping.