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The aims of this study were: i) to investigate mature plant resistance (MPR) against four strains of Potato virus Y (PVY O , PVY N , PVY NTN and PVY N-Wi ) in potato cultivars that differ in maturity (e.g. early or maincrop) at different developmental stages, and ii) to determine whether phloem translocation of photoassimilates at different stages including the source-sink transition influences MPR. The data showed that MPR was functional by the flowering stage in all cultivars, and that the host-pathogen interaction is highly complex, with all three variables (potato cultivar, virus strain and developmental stage of infection) having a significant effect on the outcome. However, virus strain was the most important factor, and MPR was less effective in protecting tubers from recombinant virus strains (PVY NTN and PVY N-Wi ). Development of MPR was unrelated to foliar phloem connectivity, which was observed at all developmental stages, but a switch from symplastic to apoplastic phloem unloading early in tuber development may be involved in the prevention of tuber infections with PVY O . Recombinant virus strains were more infectious than parental strains and PVY NTN has a more effective silencing suppressor than PVY O , another factor that may contribute to the efficiency of MPR. The resistance conferred by MPR against PVY O or PVY N may be associated with or enhanced by the presence of the corresponding strain-specific HR resistance gene in the cultivar., (Copyright © 2022 The Authors. Published by Elsevier GmbH.. All rights reserved.)