Drought is a severe problem for the citrus industry in Pakistan. The major citrus rootstocks being used in Pakistan were not yet properly standardized against drought stress, and citrus farmers of water scarce areas feel difficulty in finding suitable rootstocks. So there was a need to find rootstock for water-limited environments. Keeping in view the said problems, a study was conducted in Pakistan and the United States of America (USA) on twenty citrus rootstocks. The first experiment was conducted in the PMAS-Arid Agriculture University Rawalpindi Pakistan where ten six month of age rootstocks (raised from seed) under plastic tunnel were evaluated in 3 liter pots against four available % water capacities (100, 70, 40 and 10) in soil. A tensiometer was used for monitoring soil field capacity (FC) as well. A completely randomized design (CRD) with four treatments and four replicates was laid out. The second experiment was conducted in the USA where ten citrus progeny rootstocks (raised from seeds) taken from the University of California Riverside were transplanted into polyvinyl chloride pipes filled with sand plus turface with a ratio of 70:30 respectively. These were evaluated against three field capacities, where 500 ml water was provided after 3, 5 and 7 days interval and was termed as high, medium and low FC % respectively. An experimental design CRD with three treatments and five replicates was used in a glass house. After two months of transplantations, data regarding morpho-physiological, leaf gas exchange rate, leaf water potential (LWP) and biochemical parameters were collected for both experiments. The xylem diameter plays a vital role in water up take, so it was made part of study. The scanning of xylem diameter of the salient citrus rootstocks was done at the end xxii of experiment in USA by scanning electron microscope to find out their interactions with the stomatal conductance and hydraulic conductivities. All assessed parameters were highly affected under drought conditions. Results depicted that rootstock performance showed phenotypic variation in water stress response. Generally, linear and positive correlations between water levels and morpho-physiological responses of citrus rootstocks phenotypes were expressed. Resistant rootstocks (Savage citrange, Rough lemon, Flying dragon, Citron citrange and Gada dehi) exhibited maximized stomatal conductance (gs), photosynthesis rate (Pn), transpiration rate (E), and relative water contents (RWC) %. In addition, a sharp increase in proline and a minimized electrolyte leakage percentage were also expressed by said rootstocks. Savage citrange, Gada dehi, Flying dragon and Citron citrange could be an option for water scarce soils other than Rough lemon in Pakistan. Moreover, the broadly cultivated rootstock Rough lemon‟s laboratory and field performance still showed potential against drought in Pakistan and USA. Rootstock C-35 followed by Skw X Eng. trifoliate, Rich trifoliate and Rubidoux trifoliate proved good under least water regime in USA and expressed drought tolerant physio-chemical indicators with respect to stomatal conductance, LWP, RWC percentage, proline and minerals. Brazilian Sour Orange which is well `grown in Pakistan showed low performance against changing water regime in USA. Xylem electron micrographs depicted that the xylem diameter was more positively correlated with water potential than stomatal conductance, and xylem vessels of the water resistant rootstocks were in more organized form than that of sensitive rootstocks.