The polyploidy of the scion and the rootstock in citrus is shaping the better tolerance to water deficit
Citrus, one of the world's most important crops is facing considerable challenges due to drought events. Previous studies have demonstrated that tetraploid rootstocks exhibit greater tolerance to abiotic stresses than their diploid counterparts. The effects of combining tetraploid rootstock with a triploid scion under water deficit treatment have not been thoroughly explored. A water deficit experiment was conducted in pot using four citrus scion/rootstock combinations: diploid and tetraploid Swingle citrumelo rootstocks grafted with diploid Mexican Lime and triploid Persian lime. Physiological, biochemical, and transcriptomic analyses revealed that scions grafted onto tetraploid rootstocks had significantly better drought tolerance, especially when combined with triploid Persian lime. This improved resilience was linked to enhanced water regulation, higher photosynthesis, increased stomatal conductance and transpiration during water stress. Elevated abscisic acid levels and stronger antioxidant activity in polyploid rootstocks further contributed to stress response. Transcriptomic data showed notable gene expression changes, providing insights into drought tolerance mechanisms. These findings underscore ploidy's role at both the rootstock and scion levels in shaping the plant's response to water deficit, revealing useful interactions between rootstock and scion influencing drought resilience. This study highlights the potential for leveraging polyploid rootstocks and scions to improve drought tolerance in citrus cultivation. Overall design: In the present study, we investigated the response of four scion/rootstock combinations with different ploidy levels under water deficit conditions. Diploid Swingle citrumelo seedlings and their homologous 4x were grafted with 3x Persian Lime (C. latifolia) and 2x Mexican Lime (C. aurantiifolia (Christm.) Swing.). The objective of this study was to test whether 4x rootstock and/or 3x scion could improve tree adaptation to water deficit compared to the usual 2x scion/rootstock combinations. For that purpose, trait tolerance were investigated using phenotypes, physiological, biochemical, electrochemical and transcriptomic analyses allowing deciphering the impact of the polyploidy through the scion/rootstock interactions. In total, 28 trees were split in two group treatments as follow: (i) control plant set with 3 trees per combination under regular irrigation and (ii) and a drought stress set with 4 trees per combination subjected to water deficit condition by stopping the irrigation for nine days. At the end of the experimentation leaves and roots from each trees were colected to perfomed analysis.