Water deficiency affects the growth and development of many crops. Citrus is a major global fruit crop and its production is reduced by water paucity. The use of polyploid citrus rootstocks has been proposed as a strategy to improve water-deficit resilience. Although tetraploid rootstocks have been found to be more waterdeficit tolerant, the mechanisms of these dynamics are unknown, including how they respond to rapid vs. slow onset of water deficts. In this study, diploid (2x) and tetraploid (4x) Volkamer lemon (Citrus volkameriana Tan. and Pasq.) plants were evaluated under fast and slow onset water-deficit conditions to observe their water use pattern and antioxidant defence machinery. The 2x plants showed more decline in pot water and chlorophyll fluorescence Fv/Fm (pre-dawn) as compared to the 4x. Decreases in these variables were greater in fast the water deficit condition relative to the to slow water deficit condition. Leaf relative water content also decreased in relation with decrease in pot water. The decrease in leaf relative water content was greater in 2x as compared to 4x. Malondialdehyde content in leaves was also greater in 2x plants as compared to 4x, which indicated that 2x have more lipid peroxidation, and thus more oxidative stress, than 4x. Catalase activity and proline content in leaves were greater in 4x plants than 2x in fast and slow treatments. We conclude that Volkamer lemon 4x tolerate more in fast and slow water deficit condition by maintaining their water status protect against oxidative stress with high intrinsic antioxidant machinery.