Technical Abstract: Potato early dying (PED), caused by Verticillium dahliae, is a chronic yield-limiting disease of potato (Solanum tuberosum). In this study, we describe the population dynamics of V. dahliae in two potato cultivars with varying responses to PED. We utilized a quantitative real-time PCR (Q-PCR) assay to assess the spatio-temporal colonization of cvs. Russet Ranger (moderately resistant) and Russet Norkotah (very susceptible). Ninety plants per cultivar were inoculated with a conidial suspension. Every two weeks until week 10, we collected basal samples from 15 plants, and repeatedly sampled the growing apices of another 15 plants. The mean infection coefficient (IC) values in the basal and apical samples were significantly lower in cv. Ranger Russet at all five sampling dates. The pathogen was detected in basal samples of both cultivars by week 2, in apical samples of cv. Russet Norkotah at week 4 and week 6 in cv. Ranger Russet. Colonization of cv. Russet Norkotah consistently increased in apical and basal samples during the ten weeks, while it plateaued after week 6 in cv. Ranger Russet. Differences in response to PED appear associated with how early V. dahliae infected the root system, reached the apex earlier and reached a higher population density.