Editorial: Branching and Rooting Out with a CT Scanner: The Why, the How, and the Outcomes, Present and Possibly Future

At the time this editorial was written, an extremely interesting loop was closing! Indeed, this text was written last after the invitation received in October 2012 and the proposal submitted in August 2013 for a Frontiers in Plant Science research topic (specialty: Plant Biophysics and Modeling) on " plant CT scanning, " the preliminary submission of abstracts in December 2013 and the seven peer-reviewed contributions endorsed for publication and published in March-December 2015. A rapid " guided tour " of the Research Topic, finally titled " Branching and Rooting Out with a CT Scanner " (subtitle: " The Why, the How, and the Outcomes, Present and Possibly Future "), is proposed here. The field of research (excluding synchrotron-based X-ray microtomography of plant tissues) is introduced first, followed by the aims and scope of the Research Topic and a brief description of the major achievements made in each of the articles (2 Methods, 4 Original Research, 1 Perspective). Acknowledgements are made separately. The use of X-ray computed tomography (CT) scanning with plants is part of the incorporation of new technologies into the scientific research work. Since CT scanners were originally designed for medical applications and later for industrial applications, some adjustment to the reality of the plant world has been necessary, in the air or in the soil or water medium depending on the plant structure or material of interest: the branching pattern in a leaf canopy and the leaves themselves, or a root system. To the best of our knowledge, the first published CT scanning application in which plants were involved is the study of Tollner et al. (1987). The plant part of it consisted in visualizing portions of a root system in the surrounding soil biota, through a few 2-D cross-sectional CT images with no attempt to isolate the entire root system from the soil medium and produce a 3-D image. Plant CT scanning applications to study leaf canopies and relate the complexity of branching patterns to light interception in particular came only in the early 2000s (Dutilleul, 2003), but immediately with 3-D image construction because a canopy is surrounded with air, the challenge coming from the separation of leaves from branches. Until recently, a majority of the applications of X-ray CT scanning in plant sciences remained descriptive; some included a quantification of plant materials when the root-soil isolation or