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The root system is a vital and dynamic part of a plant throughout its lifetime. Its spatial distribution is the consequence of multiple interactions with the surrounding soil medium. In particular, the presence of pathogens in soil may influence the development of the plant, especially the below-ground part, in both its physiology and its structure. Studies of diseased plant roots may take different approaches and investigate disease effects at different levels. In this study, two groups of four potato (Solanum tuberosum L.) plants were grown in middle-sized plastic pots in a greenhouse, and their root systems, together with the soil medium (i.e., sieved and autoclaved homogeneous sand), were submitted to computed tomography (CT) scanning every two weeks until 10 weeks after planting. For the "diseased" group, sand was inoculated with Streptomyces scabies EF-35, the causal agent of potato common scab, at the time of planting. Disease effects on tissue density of roots and below-ground organs, space occupancy and complexity were assessed by analyzing the CT scanning data in the spatio-temporal approach. Fluctuations of tissue density over time were different, on average, between the two groups. They were characterized by an increase of density in Week 2 for the diseased group, reflecting a hardening of tissue, and a delayed decrease relative to the "healthy" group, suggesting a slower transfer of energy from the seed potato to growing roots. Space occupancy, which was studied via volumetric growth rates evaluated from CT scan data, and complexity, which was quantified by the fractal dimension estimated from skeletonized 3-D images constructed from CT scan data, also showed differences in the first part of the experiment. Original analytical procedures based on data transformation and curve fitting in histogram analysis of CT numbers were developed to obtain those results. In conclusion, the new approach presented here, which is based on the advanced processing of CT scanning data collected over time on developing plant root systems and below-ground organs, can be recommended for future phytopathological applications.