Implications of root spatial relationships in young wheat obtained from CT-scanning for an invasion by fungal pathogens

We analyse the way in which spatial arrangement of roots of plants provides a landscape for spread of soil microorganisms. We use a pathozone concept to characterise the behaviour at the individual root level, whereas percolation theory is used to scale-up to the population of roots. Sectional images of living wheat roots were obtained non-destructively by whole-body computed tomography X-ray scanning (X-ray CT). The data were subsequently interpreted in the light of a potential for spread of a fungal pathogen, initiated from a soil propagule and subsequently realized through a root-to-root transmission. We show that realistic root systems can support very different potential for microorganisms spread, with rapid switches from non-invasive to invasive behaviour. The switch can be controlled by time or nutrition (increase in root density resulting in invasion) or properties of the pathogen or interactions with other microorganisms (increase in pathozone width resulting in invasion). There is a substantial variability among plants so that the depth of a zone of potential spread can significantly differ even for plants growing under very similar conditions.