ABSTRACT.- In citrus growing areas where Citrus tristeza virus (CTV) is endemic, Poncirustrifoliata is commonly used as a rootstock to prevent tree decline. However, resistance breaking (RB) CTV isolates, capable of systemically infecting P. trifoliata,have been identified. Never-theless, their effects on the rootstock remain understudied. Therefore, the aim of this work was to evaluate the physiological response of P. trifoliatato infection by a local RB isolate (RB-UY1), and determine its effects on grafted scions, using Navel orange (N/P. trifoliata) and Mexican lime (ML/P.