Water competition in the soil by rootstocks is used to assess drought tolerance in citrus

•The use of two rootstocks in common pots favors the increase of all levels of A, E and gs even in full irrigation.•The association between genotypes in the same pot caused different physiological responses.•The use of two rootstocks in common pots is more effective tool for analyses of citrus plants under drought stress conditions. Brazil is a country focused on agribusiness and is the world's largest producer of orange juice. However, citrus production in certain regions of the world is affected by irregular rainfall, which imposes drought stress conditions and causes behavioral changes in plant survival, growth, and productivity. In this context, the objective of this work was to assess a methodology for the selection of citrus rootstocks tolerant to drought when exposed to water deficit regimes. This work was conceived with prior knowledge of the responses to drought tolerance of three rootstocks: Rangpur Lime (RL), Sunki Tropical (ST) and Sunki Maravilha (SM). The study was carried out with Valencia Orange (VO) scion varieties grafted on these three rootstocks. Two plants were conditioned per pot, forcing competition for available water in the soil, and all combinations were exposed to three different water regimes (irrigated, water deficit, and rehydrated). The hydric and physiological relationships were then evaluated. The results showed that in addition to the availability of water, the association between genotypes in the same pot caused different physiological responses. In view of the contrasting strategies of survival/tolerance adopted by these genotypes in response to water deficit, the combination with RL allowed a higher tolerance, showing less water extraction, lower leaf water potential, and relative water content, as well as an increase in the photosynthetic parameters when combined mainly with SM. The methodology used is a promising and more effective tool for analyses of citrus plants under drought stress conditions.