The phenotyping of secondary characters is a common practice in breeding programs aiming at finding physiological mechanism related to drought tolerance. However, the dynamics of these characters depend on crop phenology, levels of water shortage, and other factors that affect their relationship with yield and limit their capacity to be used for predictive purposes. In this work, we compared tuber yield with the temporal trend (using accumulated thermal time) of chlorophyll concentration (ChlSPAD), osmotic potential, and relative water content under water restriction. UNICA, a potato variety characterized by its low drought susceptibility was tested under full irrigation (as a control) and different treatments of partial root-zone drying and deficit irrigation in greenhouse and field conditions. ChlSPAD was the only trait showing a concurrent changing trend (slope) with yields, particularly in field conditions. The rate of greenness loss or senescence was slower in the higher water restriction treatments, which indicates that the stay-green effect (delayed senescence) occurs in some potato varieties. ChlSPAD at the loss of half the maximum plant cover during senescence (between 1040 and 1170°C days) was high and negatively correlated with final yield in all irrigation treatments. Our findings suggest that during senescence, chlorophyll increment is not related to a rise of carbon assimilation (non-functional stay-green), but could be associated with an oxidative stress occurrence, ultimately reducing yield. © 2014 Elsevier B.V.