Polyploidy modulates the adaptation to water deficit in citrus scion/rootstock associations evaluated under controlled pot condition and relates to specific changes in root and leaf transcriptome

Citrus, one of the world's most important crops, is facing significant challenges due to drought events. Previous studies have demonstrated that tetraploid rootstocks may exhibit greater tolerance to abiotic stresses than their diploid counterparts. The effects of combining a tetraploid rootstock with a triploid scion under water deficit conditions have not been thoroughly explored. A water deficit experiment was conducted under controlled pot conditions 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 under controlled pot condition revealed that tetraploid rootstocks exhibited significantly improved performance under drought stress, with an even greater effect when the scion was the triploid Persian lime. In that condition, the improved resilience was associated with reduced water consumption, higher photosynthesis, increased stomatal conductance and transpiration under water stress conditions. Elevated abscisic acid levels and stronger antioxidant activity in polyploid rootstocks further contributed to the stress response. Transcriptomic data revealed distinct gene expression changes in roots and leaves, influenced by organ ploidy and rootstock-scion interactions. Taken together our results provide insights into drought adaptation mechanisms including osmotic adjustment, oxidative stress protection, sustained photosynthesis, antioxidant enzyme activity and enhanced synthesis of protective barriers. These findings underscore ploidy's role at both rootstock and scion levels in shaping the plant's response to water deficit, revealing useful interactions between rootstock and scion influencing drought resilience.