Search Results (76)

Citrus production is increasingly constrained worldwide by rising soil salinity, particularly in arid and semi-arid regions. In Tunisia, the expansion of saline soils represents a major abiotic stress limiting orchard productivity. The identification of salt-tolerant rootstocks has therefore become a priority, especially as alternatives to sour orange (SO, Citrus aurantium L.), which is highly susceptible to Citrus tristeza virus. In recent years, several outbreaks of the disease have been reported in the Cap Bon citrus-growing region, posing an imminent threat to the sustainability of citrus production in Tunisia. This study evaluated the salt tolerance of commercial cultivars (HER, MAR, WN, NH) grafted onto Citrus volkameriana Ten. & Pasq. (CV, Citrus aurantium × Citrus limon (L.) Burm.f.) and three Poncirus trifoliata hybrids (CC, C35, CTR) under irrigation water salinity ranging from 1.1 to 4.1 mS/cm and soil salinity between 1.8 and 3.8 mS/cm. Data were collected between 2020 and 2021 in five young citrus orchards (KHB, OSN, BKN, BSJ, CHK) located in the main citrus-producing region of Tunisia, with key physiological measurements conducted during the high-evaporation period. Salinity increased across most sites during summer 2021, affecting ion homeostasis, Na⁺/K⁺ selectivity, stomatal traits, photosynthetic performance, and growth. The highest leaf Cl⁻ concentration (0.4 meq g⁻¹ dry weight) was recorded in the sensitive HER/CC combination at the OSN site. Increased salinity at OSN was associated with a 0.86% reduction in canopy growth compared to BSJ. Rootstock tolerance was strongly linked to the ability to restrict Cl⁻ accumulation in leaf tissues. Under higher salinity conditions, CV showed superior performance and represents a suitable alternative to SO. Full article

The individual contributions of arbuscular mycorrhizal (AM) fungi and earthworms to soil nitrogen (N) cycling are well-established; however, their combined effects on N sequestration through glomalin-related soil proteins (GRSPs) are not elucidated. This study evaluated their individual and interactive impacts on plant–soil N dynamics, with an emphasis on GRSP-mediated mechanisms. Trifoliate orange (Poncirus trifoliata) plants were treated with an AM fungus (Funneliformis mosseae), earthworms (Pheretima guillelmi), and their co-inoculation. Measurements were conducted on plant biomass and N content, soil N fractions, GRSP levels, GRSP-sequestered N (N_GRSP), contribution of N_GRSP to soil total N, and N-metabolizing enzymes. Co-inoculation of F. mosseae and P. guillelmi demonstrated synergistic effects, significantly increasing leaf and root N by 26% and 77%, respectively, compared to individual treatments (14–21% increases). All inoculations significantly elevated levels of total N (by 102–405%), nitrate-N (by 24–62%), soluble organic N (by 35–73%), and total dissolved N (by 31–53%), while ammonium-N decreased only with F. mosseae, with the most pronounced effect in the co-inoculation. Individual and combined inoculations significantly increased difficultly extractable (DEG) and total GRSP (TG) levels and their sequestered N content, with co-inoculation showing superior efficacy (N_DEG and N_TG increased by 53% and 42%). Adding F. mosseae alone and co-inoculation enhanced all N_GRSP contributions to soil total N (by 17–56%), whereas P. guillelmi alone only increased N_DEG and N_TG contributions (by 13–17%), with co-inoculation revealing greater effects on N_EEG contribution to soil total N than individual inoculations. All inoculations elevated nitrate reductase (by 72–101%) and urease (by 29–80%) activity while diminishing catalase (by 42–58%) activity, with synergistic enhancement of urease and catalase activity under co-inoculation. The synergistic interaction between earthworms and AM fungi facilitates N sequestration within the rhizosphere and promotes plant uptake. Full article

Potassium (K⁺) is essential for plant growth and development, influencing numerous physiological processes and stress responses. While the importance of K⁺ in overall plant performance is well-established, its specific effects on root system architecture and the underlying molecular mechanisms in woody perennials remain poorly understood. This knowledge gap is particularly significant for citrus rootstocks like trifoliate orange (Poncirus trifoliata L.), where root system optimization directly impacts drought resistance, nutrient acquisition, and overall orchard productivity. Here, we investigated how varying K⁺ concentrations (K₀, K₂, K₆, and K₁₂) affect trifoliate orange seedling development by comprehensively analyzing root architecture parameters, root hair morphology, endogenous hormone levels, and expression patterns of cell-wall-modifying and auxin-related genes. We found that moderate K⁺ levels (K₆) optimized root architectural development while both deficiency (K₀, K₂) and excess (K₁₂) inhibited overall growth and root architecture but enhanced root hair development. This morphological dichotomy corresponded to distinct hormonal profiles, showing reduced auxin (IAA), gibberellins (GAs), and zeatin riboside (ZR) levels under K⁺ stress conditions. Gene expression analysis revealed significant upregulation of expansins (PtEXPA4, PtEXPA5, PtEXPA7) and reconfiguration of auxin biosynthesis (TAA/TAR/YUC) and transport (AUX/LAX/ABCB/PIN) machinery under non-optimal K⁺ conditions. Our findings suggest that K⁺ availability modulates trifoliate orange root development through coordinated regulation of hormone homeostasis and gene expression, particularly within the auxin signaling network. These findings elucidate K⁺-responsive root developmental plasticity as a potential adaptive strategy, providing valuable insights for optimizing fertilization strategies in citrus cultivation and identifying potential molecular targets for enhancing potassium use efficiency in woody perennials. Full article

Trifoliate orange (Poncirus trifoliata L.) is one of the most widely utilized rootstocks in citrus production; however, it exhibits a relatively high sensitivity to salt stress. When cultivated in salinized soil, it frequently develops nutrient uptake disorders, leaf chlorosis, as well as reduced fruit yield and quality. To enhance the salt stress tolerance of citrus plants, this study investigated the effects of Trichoderma harzianum inoculation on the growth and response mechanisms of citrus seedlings under salt stress conditions. The results showed that salt stress significantly inhibited the growth of citrus seedlings, while T. harzianum inoculation effectively alleviated the inhibitory effect. After treatment with T. harzianum, the plant height, stem diameter, leaf number, and biomass of citrus seedlings increased significantly. The net photosynthetic rate, stomatal conductance, intercellular CO₂ concentration, transpiration rate, and chlorophyll content were significantly increased by T. harzianum inoculation. Meanwhile, T. harzianum inoculation increased the content of nitrogen, phosphorus, calcium, magnesium, zinc, and copper, and decreased sodium content in citrus seedlings. In addition, T. harzianum inoculation significantly up-regulated the expression of stress-responsive genes such as SOSs, PIPs, TIP1, TIP4, and TIP9. In conclusion, T. harzianum inoculation improved the salt stress tolerance of citrus seedlings through increasing photosynthetic efficiency, promoting nutrient absorption, sodium efflux, and water utilization via up-regulating the expression of SOSs and aquaporin genes. Full article

Manganese (Mn) toxicity, commonly triggered by soil acidification, poses a significant threat to citrus production. Arbuscular mycorrhizal (AM) fungi can alleviate heavy metal stress, while their specific function and quantitative effectiveness in conferring Mn tolerance to citrus remain unclear. This study investigated the physiological regulation conferred by four AM fungal species, Rhizophagus intraradices (Ri), Funneliformis mosseae (Fm), Paraglomus occultum (Po), and Diversispora epigaea (De), on trifoliate orange (Poncirus trifoliata L. Raf.) under Mn stress. Mn toxicity reduced root colonization in a species-dependent manner, significantly lowering colonization by all AM fungal isolates except Fm. It also severely inhibited plant growth and induced pronounced oxidative damage, accompanied by metabolic imbalance. Under Mn-stressed conditions, AM fungal inoculation, especially Ri, significantly enhanced plant biomass relative to the non-AM control, with respective increases of 148% in leaves, 33% in stems, and 64% in roots, demonstrating a marked species-specific efficacy. Furthermore, AM symbiosis effectively promoted chlorophyll index and limited Mn translocation to the leaves under both non-stress and Mn-stress conditions, with Ri being the most effective in reducing leaf Mn content. Symbiosis with AM fungi, particularly Ri, fine-tuned the antioxidant enzyme defense under Mn stress by selectively suppressing superoxide dismutase and peroxidase activities while further boosting catalase activity. Concurrently, AM fungi alleviated Mn-induced oxidative damage, with the magnitude of mitigation varying by species: Ri delivered the most comprehensive protection, most effectively reducing hydrogen peroxide and malondialdehyde levels in both leaves and roots, whereas Po was particularly effective in suppressing root superoxide anion radical and malondialdehyde levels in roots. Furthermore, AM fungi reversed Mn-induced shifts in organic osmolytes: they significantly reduced the excessive accumulation of soluble sugars and proline while mitigating the loss of soluble proteins, thereby assisting in restoring metabolic homeostasis. The alleviative effects varied significantly among AM fungal species, with Ri identified as the most efficient and Mn-tolerant strain. These findings highlight the potential of utilizing specific AM fungi, particularly Ri, as a sustainable biological strategy to enhance citrus productivity in acidified, Mn-contaminated soils. Full article

The SNAKIN/GASA family comprises antimicrobial peptides with proven activity against bacteria and fungi, making them promising candidates for improving disease resistance in citrus rootstocks. In sixty-seven new GASA variants from a citrus germplasm collection, the presence of the characteristic 12-cysteine domain was confirmed and were classified into three subfamilies. The absolute expression levels of ten representative genes were analyzed in floral tissues, young leaves, and mature leaves from five citrus accessions with contrasting susceptibility to Xanthomonas citri. Expression profiling revealed tissue-specific patterns, with higher transcript abundance in juvenile and floral tissues of tolerant accessions. Meta-analysis of HLB-related RNA-seq datasets revealed the upregulation of specific GASA genes. Three genes from Poncirus trifoliata—PtGASA6, PtGASA8, and PtGASA10—were then selected for functional validation in Nicotiana benthamiana. Transient overexpression of PtGASA6 and PtGASA10 significantly reduced disease symptoms caused by Pseudomonas syringae and heightened the hypersensitive response to X. citri, whereas PtGASA8 showed no detectable effect. Notably, PtGASA6 enhanced the hypersensitive response by 30% more than PtGASA10, while PtGASA10 delayed necrosis by 40% more than PtGASA6, indicating distinct antimicrobial mechanisms. Together, these results identify PtGASA6 and PtGASA10 as strong candidates for breeding and biotechnological strategies aimed at improving broad-spectrum bacterial disease resistance in citrus. Full article

Acyl-CoA-binding proteins (ACBPs) are essential lipid carrier proteins involved in plant lipid metabolism. However, the systematic identification and expression profiles of the ACBP gene family in citrus species remain poorly understood. Here, Citrus sinensis and Poncirus trifoliata were chosen as model species to examine the biological properties of citrus ACBPs. Using bioinformatics methods, five ACBP gene members were found in each species and named CsACBPs and PtrACBPs, respectively. All obtained ACBP members were divided into four subfamilies based on conserved domains and amino acid sequences. CsACBP and PtrACBP genes exhibited structural variation in motifs and exons. The predicted protein structures of CsACBPs and PtrACBPs exhibited conservation between the two species while displaying distinct variation within each species. Collinearity analysis showed one intraspecific pairing relationship in each of the two citrus species. Furthermore, there were more collinear couplings between citrus species and Arabidopsis thaliana but none between citrus species and Oryza sativa (rice). Notably, the analysis of cis-acting elements in ACBP gene promoters identified a number of motifs associated with light, abiotic stresses, and phytohormones. Expression profiling confirmed tissue-specific expression patterns of CsACBP1~5 and PtrACBP1~5. RT-qPCR analysis revealed that all CsACBP and PtrACBP genes responded to cold and salt stresses, though the magnitude of their responses varied significantly. Specially, although PtrACBP5 did not respond to low temperatures as rapidly as other members, its expression level increased significantly after 24 h of low-temperature treatment. Protein–protein interaction (PPI) network predictions indicated tight associations among four of the five CsACBPs, with CsACBP5 excluded from these interactions. Moreover, CsACBP1, CsACBP2, and CsACBP3 were predicted to be potential targets of csi-miR3952, csi-miR396a, and csi-miR477b, respectively. Overall, our research provides a solid foundation for further investigations into the biological functions and regulatory mechanisms of ACBP genes in citrus growth, development, and stress adaptation. Full article

Chalcone Synthase (CHS) plays a vital role in flavonoid synthesis, influencing plant growth, development, and responses to both biotic and abiotic stress. In this study, 11 CHS genes were identified in Poncirus trifoliata using bioinformatics methods, with their distribution across five chromosomes and unassigned contigs. Each gene contains 2–3 exons and 3–8 conserved motifs. In silico prediction suggested that the PtrCHS proteins are localized in the cytoplasm. PtrCHS9 and PtrCHS11 share identical protein tertiary structures. Phylogenetic analysis classified the CHS family members into four subgroups. Synteny analysis revealed one set of collinear gene pairs within Poncirus trifoliata. Between Poncirus trifoliata and Arabidopsis thaliana, two sets of collinear gene pairs were identified, while one such set was found between Poncirus trifoliata and Oryza sativa. Promoter element analysis showed the presence of various hormone response and stress response elements within PtrCHS promoters. RNA-Seq data demonstrated tissue-specific expression patterns of PtrCHSs. RT-qPCR results indicated that all CHS genes, except PtrCHS11, respond to salt stress with dynamic, member-specific patterns. Additionally, four PtrCHSs (PtrCHS3, PtrCHS5, PtrCHS7, and PtrCHS10) were significantly upregulated in response to cold treatment. Notably, PtrCHS7 and PtrCHS10 maintained high expression levels at both 6 and 12 h, implying they may be key players in cold stress response in Poncirus trifoliata. Clones of PtrCHS7 and PtrCHS10 were obtained, and overexpression vectors were constructed in preparation for gene transformation. Overall, this study provides a solid foundation for future research into the functions of the PtrCHSs. Full article

Plant melatonin is widely recognized as a pleiotropic regulator. As a growth-regulating hormone, it extensively participates in various growth and developmental processes and has significant functions in stress responses and disease resistance. Plant melatonin is synthesized primarily through the catalytic actions of five enzymes: TDC (tryptophan decarboxylase), T5H (tryptamine-5-hydroxylase), SNAT (serotonin N-acetyltransferase), ASMT (N-acetylserotonin methyltransferase), and COMT (caffeic acid-O-methyltransferase). There are multiple genes for each of these five enzymes in citrus genomes, however, with the exception of COMT5—whose function has recently been elucidated—and SNAT, which has only been preliminarily identified, the remaining genes have not been unequivocally characterized or functionally annotated. Hence, we carried out a genome-wide analysis of melatonin biosynthesis enzyme-related gene families in trifoliate orange (Poncirus trifoliata), one of the most common citrus rootstock varieties. Through bioinformatics approaches, we identified 96 gene family members encoding melatonin biosynthetic enzymes and characterized their protein sequence properties, phylogenetic relationships, gene structures, chromosomal distributions, and promoter cis-acting elements. Furthermore, by analyzing expression patterns in different tissues and under various stresses, we identified multiple stress-responsive melatonin synthase genes. These genes likely participate in melatonin synthesis under adverse conditions, thereby enhancing stress adaptation. Specifically, PtCOMT5, PtASMT11, and PtTDC9 were significantly induced by low temperature; PtSNAT1, PtSNAT14, PtSNAT18, and PtTDC10 were markedly responsive to drought; and PtASMT15, PtSNAT15, PtASMT16, and PtSNAT3 were strongly induced by ABA. Among them, PtASMT23 expression was induced up to 120-fold under low temperature, while PtSNAT18 showed over 100-fold upregulation under dehydration treatment. These findings strongly suggest that PtASMT23 and PtSNAT18 play critical roles in regulating melatonin biosynthesis in response to cold and drought stress, respectively. Collectively, these findings pinpoint novel genetic targets for enhancing stress resilience in citrus breeding programs and lay the foundation for the functional characterization of specific melatonin biosynthesis pathway gene family members in citrus and other horticultural crop species. Full article

The root system is an important determinant affecting the growth, adaptivity and stress resistance of citrus plants. Currently, the genetic regulatory network underlying root growth and development in citrus remains largely unknown. We report that a PtrAUX/IAA-ARF complex mediates the growth and development of roots in citrus through regulating the transcription of PtrSAUR. The auxin signaling pathway plays an essential role in regulating the growth and development of roots. In this study, we found that in citrus Poncirus trifoliata, PtrIAA12, encoding a canonical Aux/IAA protein, was highly expressed in the meristem and elongation zone of the root. Functional characterization showed that overexpression and silence of PtrIAA12 significantly enhanced and suppressed the elongation of primary roots, respectively. Further analysis revealed that PtrIAA12 could interact with some members of PtrARFs, of which, PtrARF8 was identified to be the transcriptional factor of PtrSAUR17. Investigation of PtrSAUR17 transgenic plants verified that PtrSAUR17 is a key gene regulating the growth of roots in citrus. In conclusion, PtrIAA12 and PtrARF8 are the key members of the AUX/IAA-ARF complex in citrus controlling the growth and development of roots through regulating the transcription of PtrSAUR17. Full article

Photosynthesis is an essential plant biological process. The performance of photosynthesis in grafted plants is affected by either the scion or the rootstock. However, the effect of the scion, rootstock and their interaction in the scion–rootstock combinations on photosynthesis of the grafted trees was not clear. In this research, the photosynthesis was analyzed within 21 citrus scion–rootstock combinations derived from three navel oranges (Citrus sinensis cv. ‘Banfield’, ‘Chislett’ and ‘Powell’) grafted on seven rootstocks [(Swingle citrumelo (C. paradisi × Poncirus trifoliata), Carrizo citrange (C. sinensis × P. trifoliata), X639 (C. reticulata × P. trifoliata), MXT (C. sinensis × P. trifoliata), Hongju (C. reticulata), Ziyang xiangcheng (C. junos) and Trifoliate orange (P. trifoliata)]. Results indicated that photosynthesis of these grafted citrus plants was significantly affected by all the scion, rootstock and their interaction. The rootstock and scion–rootstock interaction had more effect on both chlorophyll fluorescence and photosynthetic parameters with lower p values than the scion. All the scions grafted on Swingle showed the highest electron transport rate at 132.24, 158.39 and 154.59 µmol electrons m⁻² s⁻¹, and a higher net CO₂ assimilation rate at 11.22, 10.77 and 11.69 µmol m⁻² s⁻¹, respectively. The rootstock is the predominant factor affecting the content of photosynthetic pigments, and the combinations using Ziyang xiangcheng as the rootstock had the highest content at 19.83, 20.97 and 20.39 μmol s⁻¹ Kg⁻¹ FW. Electron transport rate is probably the predominant factor determining the final photosynthesis of the grafted citrus trees. This research is the first to reveal the respective effect of the scion, rootstock and their interaction on photosynthesis of citrus scion–rootstock combinations and is valuable in enhancing the understanding of the different performances in citrus scion–rootstock combinations, which aids in selecting optimal scion–rootstock combinations. Full article

The systemic delivery of oxytetracycline (OTC) by trunk injection has emerged as a viable strategy to manage huanglongbing (HLB, also known as citrus greening), a bacterial disease devastating citrus production around the world. This study examines the efficacy of delivering OTC systemically into the trunk of young, HLB-affected citrus trees using a drill-based or a drill-free system to improve tree health and productivity. Two field trials were conducted in two commercial production sites in Florida. Trees were four years old at the start of the study and composed of ‘Valencia’ or ‘OLL-8’ sweet orange (Citrus sinensis) scion grafted on X-639 (C. reticulata × Poncirus trifoliata) rootstock. Injections were performed in spring or late summer/early fall in 2022 and 2023. Using the drill-based system, 0.79 g of OTC was administered into each tree, whereas 0.15 g or 0.3 g was administered using the drill-free system. Delivering a higher dose of OTC by drill-based injection increased fruit yield and improved juice quality more than delivering lower doses by drill-free injection, though responses varied between cultivars. Injections in late summer/early fall increased the juice total soluble solids content considerably more than injections in spring. However, fall injections resulted in OTC fruit residues exceeding the maximum allowed level. Trunk injury was more extensive when OTC was applied with the drill-free system than when it was applied with the drill-based system. Full article

Flavonoids serve as crucial plant antioxidants in drought tolerance, yet their antioxidant regulatory mechanisms within mycorrhizal plants remain unclear. In this study, using a two-factor design, trifoliate orange (Poncirus trifoliata (L.) Raf.) seedlings in the four-to-five-leaf stage were either inoculated with Funneliformis mosseae or not, and subjected to well-watered (70–75% of field maximum water-holding capacity) or drought stress (50–55% field maximum water-holding capacity) conditions for 10 weeks. Plant growth performance, photosynthetic physiology, leaf flavonoid content and their antioxidant capacity, reactive oxygen species levels, and activities and gene expression of key flavonoid biosynthesis enzymes were analyzed. Although drought stress significantly reduced root colonization and soil hyphal length, inoculation with F. mosseae consistently enhanced the biomass of leaves, stems, and roots, as well as root surface area and diameter, irrespective of soil moisture. Despite drought suppressing photosynthesis in mycorrhizal plants, F. mosseae substantially improved photosynthetic capacity (measured via gas exchange) and optimized photochemical efficiency (assessed by chlorophyll fluorescence) while reducing non-photochemical quenching (heat dissipation). Inoculation with F. mosseae elevated the total flavonoid content in leaves by 46.67% (well-watered) and 14.04% (drought), accompanied by significantly enhanced activities of key synthases such as phenylalanine ammonia-lyase (PAL), chalcone synthase (CHS), chalcone isomerase (CHI), 4-coumarate:coA ligase (4CL), and cinnamate 4-hydroxylase (C4H), with increases ranging from 16.90 to 117.42% under drought. Quantitative real-time PCR revealed that both mycorrhization and drought upregulated the expression of PtPAL1, PtCHI, and Pt4CL genes, with soil moisture critically modulating mycorrhizal regulatory effects. In vitro assays showed that flavonoid extracts scavenged radicals at rates of 30.07–41.60% in hydroxyl radical (•OH), 71.89–78.06% in superoxide radical anion (O₂^•−), and 49.97–74.75% in 2,2-diphenyl-1-picrylhydrazyl (DPPH). Mycorrhizal symbiosis enhanced the antioxidant capacity of flavonoids, resulting in higher scavenging rates of •OH (19.07%), O₂^•− (5.00%), and DPPH (31.81%) under drought. Inoculated plants displayed reduced hydrogen peroxide (19.77%), O₂^•− (23.90%), and malondialdehyde (17.36%) levels. This study concludes that mycorrhizae promote the level of total flavonoids in trifoliate orange by accelerating the flavonoid biosynthesis pathway, hence reducing oxidative damage under drought. Full article

In recent years, low temperature has seriously threatened the citrus industry. Arbuscular mycorrhizal fungi (AMF) can enhance the absorption of nutrients and water and tolerance to abiotic stresses. In this study, pot experiments were conducted to study the effects of low-temperature stress on citrus (trifoliate orange, Poncirus trifoliata L. Raf.) with AMF (Diversispora epigaea D.e). The results showed that AMF inoculation significantly increased plant growth, chlorophyll fluorescence, and photosynthetic parameters. Compared with 25 °C, −5 °C significantly increased the relative conductance rate and the contents of malondialdehyde, hydrogen peroxide, soluble sugar soluble protein, and proline, and also enhanced the activities of catalase and superoxide dismutase, but dramatically reduced photosynthetic parameters. Compared with the non-AMF group, AMF significantly increased the maximum light quantum efficiency and steady-state light quantum efficiency at 25 °C (by 16.67% and 61.54%), and increased the same parameters by 71.43% and 140% at −5 °C. AMF also significantly increased the leaf net photosynthetic rate and transpiration rate at 25 °C (by 54.76% and 29.23%), and increased the same parameters by 72.97% and 26.67% at −5 °C. Compared with the non-AMF treatment, the AMF treatment significantly reduced malondialdehyde and hydrogen peroxide content at 25 °C (by 46.55% and 41.29%), and reduced them by 28.21% and 29.29% at −5 °C. In addition, AMF significantly increased the contents of soluble sugar, soluble protein, and proline at 25 °C (by 15.22%, 34.38%, and 11.38%), but these increased by only 9.64%, 0.47%, and 6.09% at −5 °C. Furthermore, AMF increased the activities of superoxide dismutase and catalase at 25 °C (by 13.33% and 13.72%), but these increased by only 5.51% and 13.46% at −5 °C. In conclusion, AMF can promote the growth of the aboveground and underground parts of trifoliate orange seedlings and enhance their resistance to low temperature via photosynthesis, osmoregulatory substances, and their antioxidant system. Full article

Background/Objective: Salinity is a growing problem affecting a large portion of global agricultural land, particularly in areas where water resources are scarce. The objective of this study was to provide physiological and molecular information on salt-tolerant citrus rootstocks to mitigate the detrimental effects of salinity on citriculture. Methods: Ten accessions belonging to eight Citrus species and four to Poncirus trifoliata Raf. were tested for salinity tolerance (0 and 15 mM NaCl for 1 year) in terms of vegetative and Cl⁻ tissue distribution traits. In addition, most accessions were evaluated for leaf Na⁺ and other cations. Results: All salt tolerant accessions tended to restrict the leaf Cl⁻ content, although in a lower degree than the Cleopatra mandarin. However, differences in their ability to restrict leaf [Na⁺] were evident, contributing to a classification of trifoliate and sour orange accessions that matched their genotypic grouping based on allele sharing at a marker targeting candidate gene coding for the NPF5.9 transporter within LCL-6 quantitative trait locus. Conclusions: Our markers targeting LCl-6 candidate genes coding for NPF5.9, PIP2.1, and CHX20 (citrus GmSALT3 ortholog) could be efficient tools for managing the detected salt tolerance diversity in terms of both Cl⁻ and Na⁺ homeostasis in rootstock breeding programs derived from these species, in addition to Citrus reshni. Full article