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Article

Biometric and Biochemical Responses to Salt in Solanum dasyphyllum, a Potential Donor of Tolerance for Eggplant

by
Neus Ortega-Albero
1,
Sara González-Orenga
2,
Oscar Vicente
1,
Adrián Rodríguez-Burruezo
1 and
Ana Fita
1,*
1
Instituto de Conservación y Mejora de la Agrodiversidad Valenciana, Universitat Politècnica de València, Camí de Vera s/n, 46022 València, Spain
2
Departamento de Bioloxía Vegetal e Ciencias do Solo, Facultade de Bioloxía, Universidade de Vigo, Campus Lagoas-Marcosendre s/n, 36310 Vigo, Spain
*
Author to whom correspondence should be addressed.
Horticulturae 2025, 11(4), 405; https://doi.org/10.3390/horticulturae11040405
Submission received: 12 March 2025 / Revised: 4 April 2025 / Accepted: 8 April 2025 / Published: 11 April 2025
(This article belongs to the Section Biotic and Abiotic Stress)
Browse Figures
Versions Notes

Abstract

:
Soil salinity is a major constraint on crop cultivation, affecting millions of hectares of land and increasing drastically worldwide. Identifying sources of tolerance within the crops and their wild relatives is imperative. Recently, Solanum dasyphyllum L. has been identified as source of tolerance to drought for eggplant (S. melongena L.). In this article, the potential use of S. dasyphyllum as a source of tolerance to salinity is investigated through the characterization of young plants’ performance under three salt stress treatments, well water (control), as well as 200 mM and 400 mM NaCl. Biometric parameters such as leaf and radicular biomass, plant height, root length, and biochemical parameters—such as photosynthetic pigments, main ions accumulation, proline, total soluble sugars, malondialdehyde, total phenolics, flavonoids, and antioxidant enzymes’ activity—were quantified. The results showed a certain reduction in leaf and stem plant growth up to 60% in response to extreme salinity, while root biomass was maintained under mid-salt stress. Salt stress caused toxic ions to accumulate in plant organs, up to 1600 mmol g−1 dry weight Na+ and a 2250 mmol g−1 dry weight Cl− in leaves under extreme salinity exposure. However, S. dasyphyllum maintained K+ levels at around 450 mmol g−1 in leaves and roots and 750 mmol g−1 in stems, indicating a mechanism related to ion transport to cope with ion toxicity. The biochemical response indicated osmotic adjustments and antioxidant activity without the need of activating antioxidant enzymes. S. dasyphyllum has proved to be a valuable genetic tool for new eggplant breeding programs regarding salt stress, with somewhat improved performance regarding biometric parameters and ion transport.

Graphical Abstract

1. Introduction

Eggplant (Solanum melongena L.) is the sixth most cultivated vegetable in the world, with a production of over 54 × 106 tons in more than 1.8 × 106 hectares [1]. It has been reported as moderately tolerant to abiotic stresses such as drought and salinity [2,3]. However, the new climatic conditions force us to seek further tolerance for extreme events. Hybridization with crop wild relatives (CWRs) has been the main source of variation for cultivated eggplant during decades [4,5,6]. Tolerance to abiotic and biotic stresses has been reported among eggplant CWRs due to adaptation to differentiated climates in the region of origin [6,7]. Thus, hybridization with these CWRs is a valuable tool to increase eggplant variation and enhance its performance in response to a multitude of stresses.
Solanum is one of the most diverse genera within angiosperms, comprising over 1400 species adapted to a large variety of edaphoclimatic conditions. There are more than 450 species in the Solanum subgenus Leptostemonium Bitter, which comprises Solanum melongena [8]. Its CWRs are classified into primary, secondary, and tertiary genepools according to the phylogenetic distance and intercross ability with cultivated eggplant. The primary genepool comprises S. insanum L., the wild eggplant ancestor, which produces fully fertile inter-specific hybrids [8]. The secondary genepool comprises African and Southeast Asian species like S. incanum L., as well as S. dasyphyllum Schumach. and Thonn. [9,10,11], which can produce inter-specific hybrids with different degrees of crossability and fertility [4]. The third genepool includes species distributed around the globe which show very low crossability with cultivated eggplant like S. torvum Sw. and S. sisymbriifolium Lam. [4,6,12]. Species from the secondary pool have been evaluated for their survivability under a plethora of environmental stresses and are considered good candidates as gene donors in tolerance breeding projects in eggplant because of their tolerance and crossability [4,8,12,13].
Solanum dasyphyllum, from the secondary genepool, grows in a wide range of tropical areas of Central and South Africa and is considered the wild ancestor of S. macrocarpon L. and S. aethiopicum L. [3,9,14]. S. dasyphyllum has been used as a donor to create an introgression lines (IL) population in a S. melongena background [15]. The knowledge of all the interesting features about this species is crucial to explore the potential of this ILs-resultant population. Few studies have been published about this species regarding abiotic stresses, and only its tolerance under drought conditions has been evaluated [3,16]. Generally, drought and salinity tend to generate the same responses in plants, although some differences exist depending on the genotype tolerance [14,17,18]. Both stresses generate osmotic stress on the plant, limiting nutrient uptake and reducing photosynthetic activity and growth [19]. Nevertheless, salt stress is also associated with a toxic effect due to ion accumulations causing nutrient imbalance and metabolic damage [20]. S. dasyphyllum was previously studied under drought conditions, but there is no previous description of its response under salt stress conditions.
Salinity represents a major threat to agriculture in the following decades due to the increase of saline soils and salinized water for irrigation worldwide, which can reduce the yield and quality of the currently cultivated crops [21]. Salt stress induces negative morphological, physiological, and biochemical responses in plants, and may even result in plant death under an intense or prolongated application [22]. Nonetheless, the damage caused is highly dependent on the genotype and the response mechanism [23,24,25]. Salinity alters the normal function of metabolic processes in plants, including photosynthesis, nutrient acquisition, or enzyme activities [26]. In a sense, plants respond by producing defense metabolites against osmotic stress, activating antioxidant mechanisms and modifying ion transport to avoid ion toxicity [27,28].
Improving the stress tolerance of cultivated eggplant by hybridization with CWRs is one of the new challenges in breeding programs [3,29]. In this work, we have undertaken the first phenotypic and biochemical study in young S. dasyphyllum plants under different salt stress levels to assess this species’ potential as a gene donor for new breeding programs for salt tolerance in eggplant due to salinity tolerance and high crossability.

2. Materials and Methods

2.1. Plant Material

Seeds of S. dasyphyllum were obtained from the germplasm bank of the Institute of Conservation and Improvement of Valencian Agrodiversity (COMAV, UPV, València, Spain). Following the germination method described by Ranil et al. [30], seeds in Petri dishes were placed in a germination chamber (25 °C, 80% humidity and 16 h light/8 h dark photoperiod) after treatment with gibberellic acid (The Merck KGaA, Darmstadt, Germany) (500 ppm) and a thermic shock.
Plants with two cotyledons were transplanted into plastic trays and were grown in the germination chamber. Once the plants grew to the 4-leaf stage, 70 days after sowing, selected plants with homogeneous size were transplanted under greenhouse conditions in 2 L-pots with one layer of vermiculite over commercial substrate (Neuhaus Huminsubstrat S, C. Deilmann GmbH and Co., Osterberg, Germany). The trial started after one week of acclimatation.

2.2. Experimental Procedures

The treatments consisted of irrigation of five plants, three times per week, with constant watering of 25 mL per pot of solutions containing 200mM NaCl (The Merck KGaA, Darmstadt, Germany), 400 mM NaCl, or well water that is commonly used for crop irrigation as control, while also ensuring that any pot became dry in the late days of the experiments due to evaporation of bigger plants. Before the treatment started, leaf number (LN) and plant height (PH, cm) were measured. After 4 weeks of salt treatment and 15 weeks after sowing, the previous parameters were measured to calculate the growth in plant height (ΔPH) and the growth in number of leaves (ΔLN). In addition, the length of the primary root (RL, cm), stem diameter (SD, mm), and leaf surface (LS, cm2) were measured. Fresh weight (FW) of roots (RFW, g), stems (SFW, g) and leaves (LFW, g) were also determined. After deep-freezing some leaf material to perform biochemical assays, the rest of the leaves, as well as the stem and root material, were dried for three days at 65 °C until constant weight was reached, thereby obtaining the dry weights (DW) of the roots (RDW), stems (SDW) and leaves (LDW), from which we can calculate the water content using the following equation:
WC (%) = [(FW − DW)/FW] × 100

2.3. Soil Electrical Conductivity

A Crison Conductivity-meter 522 (Crison Instruments SA, Barcelona, Spain) was used for measuring the electrical conductivity of the soil. For the measurements, a 1:5 soil:water dilution was performed using distilled water after the end of the salt treatment for each pot and EC1:5 was expressed as dS m−1.

2.4. Biochemical Assays

2.4.1. Ion Content

Ions were extracted in an aqueous solution from 0.05 g of dry leaf, stem, and root tissue following Weimberg’s method [31]. After 1 h incubation in a water bath Ultraterm 200 (J.P.Selecta, Barcelona, Spain) at 95 °C and centrifugation (centrifuge 5415R, Eppendorf Ibérica S.L.U., Madrid, Spain) for 10 min at 13,300× g, cations Na+, K+, and Ca2+ were quantified with a flame photometer PFP7 (Jenway Inc., Burlington, VT, USA), and anion Cl− was quantified using a chloride analyzer Corning 926 (Sherwood Scientific Ltd., Cambridge, UK).

2.4.2. Photosynthetic Pigments

Alternatively, photosynthetic pigments were extracted from 0.05 g fresh leaf tissue in 1 mL 80% acetone (Labbox Labware, S.L., Barcelona, Spain), mixed overnight, and centrifuged for 10 min at 13,300× g. The absorbance of the supernatant was measured at 663, 646, and 470 nm with a spectrophotometer UV-3100PC (VWR International, LLC., Radnor, PA, USA) to calculate chlorophyll a (ChlA), chlorophyll b (ChlB), and carotenoid (Caro) concentrations using Lichtenthaler and Wellburn’s equations [32]. Concentrations were expressed in mg g−1 DW.

2.4.3. Osmolyte Contents

Proline (Pro) and total soluble sugars (TSS) were extracted from 0.05 g fresh leaves. Proline was extracted with 3% sulfosalicylic acid (PanReac Quimica, S.L.U., Barcelona, Spain) and quantified using the acid ninhydrin (The Merck KGaA, Darmstadt, Germany) method and expressed as μmol g−1 DW [33]. After incubation in a water bath at 95 °C for 1 h and cooling, the organic phase was separated, and absorbance at 520 nm was measured. TSS were extracted with 80% methanol (PanReac Quimica, S.L.U., Barcelona, Spain), mixed overnight, and centrifuged. The supernatant was combined with sulfuric acid (Labbox Labware, S.L., Barcelona, Spain) and 5% phenol (Labbox Labware, S.L., Barcelona, Spain), and absorbance was measured at 490 nm, with concentrations expressed as glucose equivalents [34].

2.4.4. Oxidative Stress Markers

Oxidative stress markers malondialdehyde (MDA) and hydrogen peroxide (H2O2) were quantified in fresh leaf tissue. MDA was measured by extracting 0.05 g fresh leaf tissue in 80% methanol and adding thiobarbituric acid (TBA) (PanReac Quimica, S.L.U., Barcelona, Spain) in trichloroacetic acid (TCA) (Labbox Labware, S.L., Barcelona, Spain), followed by incubation at 95 °C for 15 min. The absorbance was measured at 440, 532, and 600 nm to quantify MDA, using equations from Taulavori et al. [35], and the results were expressed in nmol g−1 DW. Hydrogen peroxide (H2O2) content was quantified by extracting fresh leaf material with 0.1% TCA, followed by centrifugation. The supernatant was mixed with phosphate buffer (The Merck KGaA, Darmstadt, Germany) and potassium iodide (Labbox Labware, S.L., Barcelona, Spain), and the absorbance at 390 nm was used to calculate H2O2 concentrations based on a standard curve, expressed as μmol g−1 DW.

2.4.5. Antioxidant Compounds

Cell protective antioxidant compounds’ total phenolics (TPC) and flavonoids (TF) were extracted from 0.05 g fresh leaf tissue with 80% methanol. TPC were quantified using the Folin–Ciocalteu reagent (PanReac Quimica, S.L.U., Barcelona, Spain) [36], while absorbance was measured at 765 nm. TPC were expressed as gallic acid equivalents (mg eq. GA g−1 DW). TF were determined using a method based on the reaction of catechol groups with AlCl3, with absorbance measured at 510 nm. Results were expressed as catechin equivalents (mg eq. C g−1 DW) following Zhischen et al.’s method [37].

2.4.6. Antioxidant Enzyme Activities

Crude protein extracts were prepared from fresh leaf tissue, and protein concentrations were measured using Bradford’s method (PanReac Quimica, S.L.U., Barcelona, Spain) [38] with BSA (PanReac Quimica, S.L.U., Barcelona, Spain) as the standard. Enzymatic activities of superoxide dismutase (SOD), ascorbate peroxidase (APx), and glutathione reductase (GR) were measured spectrophotometrically. SOD activity was determined by inhibiting the photoreduction of nitroblue tetrazolium (NBT) (The Merck KGaA, Darmstadt, Germany) at 560 nm. APx activity was measured by monitoring ascorbate (The Merck KGaA, Darmstadt, Germany) oxidation at 290 nm. GR activity was determined by monitoring NADPH (The Merck KGaA, Darmstadt, Germany) oxidation at 340 nm. Activity units were defined as the amount of enzyme that catalyzes the conversion of 1 mmol of substrate per minute at room temperature [39,40,41].

2.5. Statistical Analysis

A factorial analysis of variance in all the measured parameters was performed with the Statgraphics Centurion v.XVII software (Statpoint Technologies, Warrenton, VA, USA). Statistical differences were calculated with the Student–Newman–Keuls test with p < 0.05.

3. Results

3.1. Growth Measurements

Values of soil electrical conductivity (EC1:5) before starting the experiment had a mean of 4.1 dS m−1 among all the experimental pots. After the salt experiment, EC1:5 values showed a large increase from control treatment with well water (EC1:5 = 8.5 dS m−1) compared to 200 mM and 400 mM salt treatments (EC1:5 = 24.4 dS m−1 and EC1:5 = 37.4 dS m−1, respectively), showing significant differences between treatments.
S. dasyphyllum development was affected under salt stress (Figure 1). In the 200 mM NaCl treatment, the growth of the plant in height (ΔPH) was reduced to half in comparison with the control, whereas under 400 mM, growth was practically interrupted (Figure 1 and Figure 2). The same results were obtained regarding the production of new leaves (ΔLN), even observing leaf loss with respect to the initial number in plants treated with 400 mM NaCl (Figure 2). Both salt treatments caused reduction in stem diameter (SD) and leaf surface (LS), although there were no significant differences between the salt concentrations (Figure 2).
No differences were found in primary root length (RL) between control plants and plants treated with 200 mM NaCl, indicating that S. dasyphyllum maintained root development and osmotic equilibrium (Figure 2). However, 400 mM NaCl caused a RL reduction to 65% of the control values. Similarly, root fresh weight (RFW) was only reduced at the highest salt concentration tested (Figure 2). Leaf (LFW) and stem (SFW) fresh weights followed the same pattern as ΔLN, LS, and SD, decreasing by almost 50% of the control in the presence of 200 mM NaCl and by almost 75% with 400 mM NaCl (Figure 2).
Uniform water content (WC) was found within the treatments, averaging at 78% for roots and 72% for stems, whereas the leaf water content decreased, slightly but significantly, from the 400 mM NaCl treatment, with an average of 83% in control and 200 mM and 80% in 400 mM, indicating that fresh weights are a good indicator of the condition of the plants.

3.2. Ion Contents

Ion content was one of the most affected parameters under salinity stress. Na+ increased significantly under 200 and 400 mM NaCl irrigation, almost 7-fold in roots and 3.5-fold in leaves, when the salt concentration was the highest (Figure 3). Na+ values in the stem were lower than in the root and leaf; however, this organ showed higher differences between the tested salt treatments, indicating ion movement through the plant vessels. Cl− levels showed a 6-fold increase in leaves and a 15-fold increase in stems for salt treatments. However, roots showed a 4.5-fold increase for 200 mM and a 3.2-fold increase for 400 mM NaCl treatment. No reduction was observed in root, stem, or leaf K+ contents under the salt treatments (Figure 3), but Na+/K+ ratios increased in roots, stems, and leaves under salt treatment (Figure 3). The divalent cation Ca2+ showed an increase in roots, stems, and leaves under salt stress, although without significant differences between the two salt concentrations (Figure 3). Under control conditions, roots showed more than double Ca2+ concentration than stems and leaves.

3.3. Biochemical Measurements

Chlorophyll a (ChlA) and chlorophyll b (ChlB) average values decreased with increasing salinity, but the differences were not statistically significant. Regarding carotenoids (Caro), no differences were observed in response to salt irrigation (Figure 4). These results indicate the ability of S. dasyphyllum to maintain photosynthetic machinery under salt presence.
Osmolyte accumulation due to salt stress was mainly in the form of proline (Pro), which drastically increased under salt stress by more than 15-fold under 400 mM NaCl irrigation compared to control plants (Figure 4). On the contrary, total soluble sugars (TSS) did not show differences between the control and any salt condition (Figure 4). The stress provoked by the salt treatments was not enough to activate the oxidative stress markers malondialdehyde (MDA) and hydrogen peroxide (H2O2), which showed no significant differences between treated and untreated plants (Figure 4). However, antioxidant molecules like total phenolic compounds (TPC) and total flavonoids (TF) were significantly reduced after NaCl application (Figure 4).
Regarding antioxidant enzymes, no significant differences were found in S. dasyphyllum plants between control and salt treatments for analyzed antioxidant enzymes ascorbate peroxidase (APx) and glutathione reductase (GR). Only superoxide dismutase (SOD) showed an increase in its activity under 400 mM NaCl irrigation, but no statistical differences were observed between control treatment and the 200 mM NaCl irrigation (Figure 5). These results indicate that other mechanisms are enough to cope with salt stress in S. dasyphyllum, which did not activate antioxidant enzymes.

3.4. Meta-Analysis of Salinity Response in Solanum Species

Eggplant CWRs have been evaluated for different abiotic stresses. Table 1 shows a comparison between the responses to salinity of two S. melongena genotypes, and several Solanum species from the primary, secondary, and tertiary genepool, including our results in S. dasyphyllum. This comparison includes biometric and biochemical parameters and the increase or reduction in percentage with respect to the control as 100%. Most species tend to show a reduction in biomass; however, most S. melongena, S. insanum, and S. dasyphyllum cope with salinity stress by maintaining root biomass, and only S. dasyphyllum maintained its root length completely at 200 mM.
Regarding ion accumulation, S. dasyphyllum increased Na+ in leaves similar to S. melongena at 200 mM and accumulated the same levels as S. aethiopicum. Species from the secondary genepool also accumulated more K+ in leaves than other species, trying to maintain K+ homeostasis and were similar to S. insanum for K+ accumulation in roots. Cl− accumulation in S. dasyphyllum was lower than the accumulation of S. insanum but higher than S. melongena.
Photosotynthetic pigments seemed to be maintained in S. melongena and S. aethiopicum¸ while they seemed to be increased in S. melongena and reduced in S. dasyphyllum and S. torvum. Nevertheless, this was dependent on the pigment. S. dasyphyllum showed the highest increase in Pro after S. torvum at 200 mM NaCl but not at 400 mM NaCl. Any Solanum species seemed to accumulate TPC under salt stress.

4. Discussion

Eggplant CWRs have proven to be tolerant to different abiotic stresses [4,8,12,13]. Studying their performance under these stresses and understanding the molecular mechanisms underlying tolerance is essential for establishing new breeding programs for cultivated eggplant.

4.1. Previous Available Information About S. dasyphyllum

Drought stress responses have been previously studied in Solanum dasyphyllum, which showed a better performance than S. melongena under this stress condition, modifying expression in metabolic paths related to plant growth, plant signaling, and phenylpropanoid synthesis [9,16,43]. Moreover, previous in vitro reports on S. dasyphyllum after salt application described a better callus development compared to S. macrocarpon, its direct cultivated descendant, showing good capacity to maintain turgor and cell expansion under these conditions [44]. Nevertheless, to our knowledge, there is no previously available information on S. dasyphyllum plants responding to salt stress. Also, S. dasyphyllum is the donor parent in a ILs population, and this type of information is key to explode this resource [15]. This work presents a three-level salinity (well water, 200 and 400 mM of NaCl) study on young plants to assess S. dasyphyllum tolerance under soil and greenhouse conditions. Salt concentrations used in this study represent a gradient that spans from no salt to moderate and high levels of salinity. Regarding available data, 200 mM NaCl was selected to be the concentration where most eggplant genotypes started to show stress symptoms but can still adapt and grow. 400 mM NaCl was selected to display stress effects in tolerant genotypes and to understand S. dasyphyllum’s capacity to adaptation to extreme saline conditions.

4.2. Growth Performance of S. dasyphyllum Under Salt Stress

Generally, salinity triggers morphological, physiological, biochemical, cellular, and molecular mechanisms in plants, causing severe reduction in plant growth and crop production of glycophyte species [14,17,25]. In our experiment, well water used for irrigation resulted in a slightly salinized substrate in the control pots. This is a common side effect of using bad-quality water, as it is being studied in many areas near the Mediterranean Sea [45,46]. However, young S. dasyphyllum plants showed a good visual appearance under control conditions, despite receiving salinized water and having only started limiting their growth and development with salinity treatment as high as 200 mM NaCl. However, salt tolerance is a complex trait involving different components at the physiological, biochemical, and genetic levels [47]. Interestingly, plants managed to maintain root biomass at 200 mM NaCl, as previously reported in other Solanum species. Moreover, S. dasyphylum seemed to maintain root biomass by maintaining root length [25,48].

4.3. Impact of Salt Stress on Photosynthetic Pigments

Salt stress typically modifies photosynthetic metabolism, resulting in the degradation of photosynthetic pigments; therefore, they are useful as stress biomarkers [49]. S. dasyphyllum showed a slight reduction in chlorophyll a and chlorophyll b contents, as with other eggplant wild relatives such as S. torvum [50]. However, the reduction was not significant, suggesting tolerance of the studied species to salinity, even at high salt concentrations, as it strives to maintain the carbon assimilation process as observed in S. melongena, S. insanum, and S. aethiopicum.

4.4. Ion Accumulation and Comparison with Other CWRs

S. melongena and other related species such as S. insanum, S. torvum, and S. aethiopicum accumulate Na+ and Cl− in leaves, stems, and roots in the presence of salt [13,17,25,50,51,52]. Na+ competes with K+ for membrane transport proteins, and as salinity increases, K+ levels decrease [51,52]. In eggplant and CWRs, under salt stress, different mechanisms have been observed to avoid toxicity and maintain K+ homeostasis. S. melongena seems to accumulate Na+ in leaves, increasing the Na+ leaf/root ratio while attempting to maintain the K+ leaf/root ratio [25,53]. Other species, such as S. insanum, showed an increase in the K+ leaf/root ratio, suggesting a better osmotic adjustment due to their ability to activate K+ transport to the photosynthetic tissues [17,25]. Also, higher K+ accumulation in leaves and a lower Na+/K+ ratio in leaves have been reported in tolerant genotypes, indicating that Na+ compartmentalization in vacuoles and K+ accumulation in leaves might be relevant for tolerance [53,54]. Our results showed that S. dasyphyllum maintained K+ concentration in roots and leaves under salt treatment, as observed in other CWRs like S. aethiopicum [13,50]. Moreover, S. dasyphyllum showed a stable K+ leaf/root ratio in the three experimental conditions, whereas its Na+ leaf/root ratio was close to 1 with salinities of 200 mM and 400 mM. Also, it seemed that the Na+ and K+ compensation triggered by salinity followed the same pattern at 200 mM and 400 mM treatments to cope with ion toxicity, indicating that the activated response is independent from the concentration of NaCl. In regard to Ca2+, it helps to control Na+/K+ homeostasis by modulating the SOS metabolic pathway [55], so noticing Ca2+ increase under salt stress for all organs and salt concentrations tested might be a plant response to protect metabolic and cellular processes, which is the case for S. dasyphyllum.

4.5. Osmoprotectants and Oxidative Stress

The stress-related osmoprotectant proline (Pro) has been described as a marker of abiotic stress because of its capacity for maintaining membrane stability, protein architecture, and ROS detoxification [56]. Pro has been reported to be overproduced in more tolerant genotypes; however, this does not seem to be a universal phenomenon [28]. Pro significantly increased in S. dasyphyllum under 200 mM and 400 mM salt concentrations, which could indicate a higher tolerance, compared with cultivated eggplant and other CWRs [44]. As was previously found in Solanum species [25], no changes were noticed in other stress-related metabolites such as MDA and TSS due to the salinity, suggesting that their function is not relevant for salt tolerance in this genus.
Furthermore, no response in antioxidant enzymes was found, indicating that S. dasyphyllum suffered from less oxidative stress than other CWRs [44]. These results reinforce the idea that changes in ion transport and compartmentalization, as well as osmolyte accumulation are the main mechanisms in S. dasyphyllum to face salinity and allow plant development and survival.

5. Conclusions

The response to salt irrigation of Solanum dasyphyllum, a wild eggplant relative, is reported in this study. Growth parameters were affected at a high salinity of 200 mM and plant development seemed to stop at 400 mM. However, root length was maintained, and it is settled as a major mechanism in regard to plant growth to cope with the stress. Differentiated ion transport mechanisms and proline production seem to be key to coping with oxidative stress and avoiding further cell damage. Here, we settled the importance of the underestimated S. dasyphyllum as a gene reservoir for salt tolerance for cultivated eggplant. These, alongside previous results, reinforce the idea of the importance of CWRs from the secondary and tertiary genepools for eggplant breeding. Future experiments including S. dasyphyllum, S. melongena, and other CWRs should be performed, including biometric, biochemical, and expression analysis to give a complete vision of the response of S. dasyphyllum to salt stress and the differences found with other eggplant species.

Author Contributions

Conceptualization, A.F.; methodology, S.G.-O. and N.O.-A.; software, S.G.-O. and N.O.-A.; validation, A.F. and O.V.; formal analysis, S.G.-O. and N.O.-A.; investigation, S.G.-O. and N.O.-A.; resources, O.V. and A.R.-B.; data curation, A.F. and N.O.-A.; writing—original draft preparation, N.O.-A.; writing—review and editing, S.G.-O. and O.V.; visualization, S.G.-O. and O.V.; supervision, A.R.-B.; project administration, A.F. and A.R.-B.; funding acquisition, A.F. All authors have read and agreed to the published version of the manuscript.

Funding

This work was funded with projects AICO/2020/174, CIPROM/2021/020 (Conselleria d’Innovació, Universitats, Ciència i Societat Digital, Generalitat Valenciana, Spain), and contract FPU19/04080 (Ministerio de Educación, Cultura y Deporte, Spanish Government).

Data Availability Statement

The raw data supporting the conclusions of this article will be made available by the authors on request.

Conflicts of Interest

The authors declare no conflicts of interest.

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Horticulturae 11 00405 g001aHorticulturae 11 00405 g001b
Figure 1. Solanum dasyphyllum plants after four-week treatment with tap water, as well as 200 mM and 400 mM salt treatment (from top to bottom).
Figure 1. Solanum dasyphyllum plants after four-week treatment with tap water, as well as 200 mM and 400 mM salt treatment (from top to bottom).
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Horticulturae 11 00405 g002
Figure 2. Increment of plant height (ΔPH), increment of leaf number (ΔLN), stem diameter (SD, mm), leaf surface (LS, cm2), root length (RL, cm), and root (RFW), stem (SFW), and leaf (LFW) fresh weight (g) (mean ± SD; n = 5) of Solanum dasyphyllum plants treated for one month with the indicated NaCl concentrations. Significant differences between treatments are labelled with different letters (p < 0.05).
Figure 2. Increment of plant height (ΔPH), increment of leaf number (ΔLN), stem diameter (SD, mm), leaf surface (LS, cm2), root length (RL, cm), and root (RFW), stem (SFW), and leaf (LFW) fresh weight (g) (mean ± SD; n = 5) of Solanum dasyphyllum plants treated for one month with the indicated NaCl concentrations. Significant differences between treatments are labelled with different letters (p < 0.05).
Horticulturae 11 00405 g002
Horticulturae 11 00405 g003aHorticulturae 11 00405 g003b
Figure 3. Na+, K+, Cl−, Ca2+ contents (mmol g−1 DW) and Na+/K+ ratio (mean ± SD; n = 5) of Solanum dasyphyllum. Significant differences between treatments are labelled with different lowercase letters and significant differences between plant organs are labelled with different capital letters (p < 0.05).
Figure 3. Na+, K+, Cl−, Ca2+ contents (mmol g−1 DW) and Na+/K+ ratio (mean ± SD; n = 5) of Solanum dasyphyllum. Significant differences between treatments are labelled with different lowercase letters and significant differences between plant organs are labelled with different capital letters (p < 0.05).
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Figure 4. Chlorophyll a (ChlA, mg g−1 DW), chlorophyll b (ChlB, mg g−1 DW), carotenoids (Caro, mg g−1 DW), proline (Pro, μmol g−1 DW), total flavonoids (TF mg eq. C g−1 DW), total phenolic compounds (TPC, mg eq. GA g−1 DW), total soluble sugars (TSS, mg eq. Glu g−1 DW), malondialdehyde (MDA, nmol g−1 DW), hydrogen peroxide (H2O2, μmol g−1 DW) contents (mean ± SD; n = 5) of Solanum dasyphyllum plants treated for one month with the indicated NaCl concentrations. Significant differences between treatments are labelled with different letters (p < 0.05).
Figure 4. Chlorophyll a (ChlA, mg g−1 DW), chlorophyll b (ChlB, mg g−1 DW), carotenoids (Caro, mg g−1 DW), proline (Pro, μmol g−1 DW), total flavonoids (TF mg eq. C g−1 DW), total phenolic compounds (TPC, mg eq. GA g−1 DW), total soluble sugars (TSS, mg eq. Glu g−1 DW), malondialdehyde (MDA, nmol g−1 DW), hydrogen peroxide (H2O2, μmol g−1 DW) contents (mean ± SD; n = 5) of Solanum dasyphyllum plants treated for one month with the indicated NaCl concentrations. Significant differences between treatments are labelled with different letters (p < 0.05).
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Figure 5. Enzymatic activities (units mg−1 protein) of ascorbate peroxidase (APx), superoxide dismutase (SOD), and glutathione reductase (GR) (mean ± SD; n = 5) of Solanum dasyphyllum plants treated for one month with the indicated NaCl concentrations. Significant differences between treatments are labelled with different letters (p < 0.05).
Figure 5. Enzymatic activities (units mg−1 protein) of ascorbate peroxidase (APx), superoxide dismutase (SOD), and glutathione reductase (GR) (mean ± SD; n = 5) of Solanum dasyphyllum plants treated for one month with the indicated NaCl concentrations. Significant differences between treatments are labelled with different letters (p < 0.05).
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Table 1. Comparison of biometric and biochemical values in different Solanum species under salinity treatment, presented as percentages relative to control (100%), and bibliographic references.
Table 1. Comparison of biometric and biochemical values in different Solanum species under salinity treatment, presented as percentages relative to control (100%), and bibliographic references.
S. melongenaPrimary GenepoolSecondary GenepoolTertiary Genepool
MEL1MEL5S. insanumS. dasyphyllumS. aethiopicumS. torvum
200 mM400 mM200 mM400 mM200 mM400 mM200 mM400 mM200 mM400 mM200 mM300 mM
LFW603060305830573060334030
RFW1307911986108681026274494540
RL7056927094681006695818060
Na+ leaves3122992934185246173083514685171101835
Na+ roots215297443505745954605660645605522429
K+ leaves116326496188147121901621855675
K+ roots45647999106849792631056259
Cl− leaves3313243564889811133604664413463875649
Cl− roots195224300322509686479328379323337371
ChlA1171331097720512351411091206474
ChlB8180160831386077551081095958
Caro89941419211255998464676692
Pro5241061578102881713,61013621568369108236764282
TPC8483100100100100897910010082132
Refs.Ortega-Albero et al. (2023) [42]Ortega-Albero et al. (2023) [25] Ortega-Albero et al. (2023) [42]Brenes et al. (2020) [13]
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Ortega-Albero, N.; González-Orenga, S.; Vicente, O.; Rodríguez-Burruezo, A.; Fita, A. Biometric and Biochemical Responses to Salt in Solanum dasyphyllum, a Potential Donor of Tolerance for Eggplant. Horticulturae 2025, 11, 405. https://doi.org/10.3390/horticulturae11040405

AMA Style

Ortega-Albero N, González-Orenga S, Vicente O, Rodríguez-Burruezo A, Fita A. Biometric and Biochemical Responses to Salt in Solanum dasyphyllum, a Potential Donor of Tolerance for Eggplant. Horticulturae. 2025; 11(4):405. https://doi.org/10.3390/horticulturae11040405

Chicago/Turabian Style

Ortega-Albero, Neus, Sara González-Orenga, Oscar Vicente, Adrián Rodríguez-Burruezo, and Ana Fita. 2025. "Biometric and Biochemical Responses to Salt in Solanum dasyphyllum, a Potential Donor of Tolerance for Eggplant" Horticulturae 11, no. 4: 405. https://doi.org/10.3390/horticulturae11040405

APA Style

Ortega-Albero, N., González-Orenga, S., Vicente, O., Rodríguez-Burruezo, A., & Fita, A. (2025). Biometric and Biochemical Responses to Salt in Solanum dasyphyllum, a Potential Donor of Tolerance for Eggplant. Horticulturae, 11(4), 405. https://doi.org/10.3390/horticulturae11040405

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