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Article

Moroccan Ulva rigida Extracts: A Promising Biostimulant for Improving Growth and Photosynthetic Performance in Salt-Stressed Bean Plants

by
Salma Latique
Laboratory of Drug Sciences, Faculty of Medicine, Pharmacy, and Dental Medecine, Sidi Mohamed Ben Abdellah University, Fez 1893, Morocco
Crops 2025, 5(5), 61; https://doi.org/10.3390/crops5050061
Submission received: 28 June 2025 / Revised: 13 August 2025 / Accepted: 2 September 2025 / Published: 8 September 2025
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Abstract

Soil salinity is a crucial factor that limits agricultural production, negatively impacting the growth and physiological functions of salt-sensitive crops, such as beans. The present study examined the efficiency of Ulva rigida seaweed extracts (URE) as biostimulants to enhance the growth and photosynthetic ability of bean plants (Phaseolus vulgaris L.) under saline conditions (51.33 mM NaCl). Seaweed extracts were obtained by maceration and ultrasonic assistance at two concentrations, 25% and 50% (v/v), and applied as a foliar spray or irrigation. The most significant improvement was observed following foliar sprays of 50% ultrasonic extract (UP-50), with an increase of 96% in CCI compared to salt-stressed controls and by 71% compared to non-stressed controls. Stomatal conductance (SC) was also significantly improved with UP-50, reaching levels that were 146% higher than those of salt-stressed plants and 53% higher than those of non-stressed plants. The OJIP transients under salinity were significantly improved by both ultrasonic-assisted and maceration extracts; especially, 50% maceration extracts (MP-50) restored PSII quantum efficiency (ΦPo) and total performance index (PItotal) of salinity-stressed seedlings to 107% and 255% of non-stressed control and 122% and 314% of salt-stressed control, respectively. Root length and indole acetic acid (IAA) levels in treated plants were also enhanced, particularly in response to higher concentrations of the extract, suggesting improved root growth as well as hormonal homeostasis in the presence of salt stress. According to these findings, U. rigida extracts, specifically those applied at high concentrations as a foliar spray, serve as biostimulants that mitigate the adverse effects of salt stress on beans by preventing chlorophyll degradation and enhancing photosynthesis, root development, and hormonal balance.

1. Introduction

Soil salinity constitutes a common abiotic stress that limits agricultural production and plant development in arid and semi-arid regions [1]. Presently, saline soil accounts for ∼6% of the total area of the earth (approximately 800 million hectares) and is a potential land resource of considerable strategic significance [2]. However, as an increasingly prominent form of soil water–salt coupling disasters under the joint impacts of climate change and intensive human activities, salinization of soil has turned into the main cause of soil degradation, which has brought about serious threats to the agricultural sustainability as well as food security at a global scale. Human-induced processes that can contribute to soil salinity include improper irrigation (e.g., excessive irrigation or poor water management, application of salty water), inadequate dam or water treatment, forest clearing, overuse of salt-based fertilizers, and waste discharges (e.g., landfill leachate, etc.) [3,4]. Under these conditions, soluble salts accumulate in the soil, and plant metabolism becomes limited, leading to reduced production. Isayenkov and Maathuis [5] stated that high salinity causes osmotic stress, ionic toxicity, and ionic imbalance (especially Na+ and Cl−). To survive, plants restrict salt entry, compartmentalize its excess ions into vacuoles, produce compatible solutes to maintain water, mobilize the antioxidant arsenal and modify growth to avoid the effect of salt. Together, these strategies help plants to grow and function in salty conditions [6]. The outcome is a lower crop yield in both qualitative and quantitative terms. Implementing sustainable agriculture in salt-affected and water-limited areas presents a significant challenge. More recently, there has been increasing interest in the use of natural biostimulants as natural compounds that help plants tolerate salt stress [7]. According to Calvo et al. [8], biostimulants are any substance or microorganism that, when added to plants or soil, helps improve the natural processes that make nutrients more available, enhance how well plants take up nutrients, or increase plants’ ability to handle stress from factors such as salt. This is independent of the nutritive potential of the substance or microorganism and has no direct effect on fertilization. Among biostimulants, seaweed extract is known for its high concentration of bioactive compounds, such as vitamins, minerals, and phytohormones (auxins and cytokinins), that play an important role in promoting plant growth [8]. For example, these substances have promoted root development, stomatal conductance, and chlorophyll content in several crop species [9]. Seaweed-derived polysaccharides (like those from Ulva rigida) may have the potential to improve plants’ stress response. Some bioactive compounds from the green macroalga Ulva rigida may modify plants’ responses to salinity [10]. Although these are promising observations, most studies to date have employed traditional extraction techniques, i.e., maceration, and have largely been restricted to one method of application, thus leaving a knowledge gap on the efficacy of extraction methods and modes of delivery. Furthermore, detailed physiological responses to salt stress, such as photosynthetic performance following salt stress, has been little examined by means of advanced techniques such as chlorophyll fluorescence (OJIP) analysis.
In line with these gaps, the present study examines the impact of Ulva rigida extracts produced through ultrasonic-assisted extraction, a method which more effectively ruptures algal cell walls for the release of bioactive constituents like polysaccharides and phenolics when compared with maceration. We further compare between two methods of application, foliar spraying and root irrigation, which we used to assess the relative effectiveness of a treatment that can enhance growth and stress tolerance of bean plants (Phaseolus vulgaris) as a globally important and salt sensitive crop, serving as an example species for salinity tolerance [11]. Most significantly, the use of OJIP chlorophyll fluorescence analysis for the first time in this context has generated new information on plant photosynthetic response and salt stress amelioration under treatments.
Important parameters determined are chlorophyll content index (CCI), stomatal conductance (SC), photosynthesis efficiency, root length, and Indole Acetic Acid (IAA) levels. These collectively demonstrate the physiological and biochemical processes by which Ulva rigida extracts lend increased tolerance to salt stress. The findings add up to the increasing positive evidence of natural biostimulants in sustainable agriculture, particularly in relation to salinity stress. As such, these findings are critical for developing novel approaches to enhance crop productivity under salt-stress, ultimately contributing to sustainable cropping systems and food security in salt-affected ecosystems.

2. Materials and Methods

2.1. Collection and Preparation of Seaweed

The samples of the green seaweed Ulva rigida were acquired from the coastal area of Sidi Bouzid near El Jadida, Morocco. The harvesting was performed by hand and after rinsing in seawater to remove sand, epiphytes, and other impurities. Individual thalli were separated and placed in clean polyethylene bags, then transferred to the laboratory in iceboxes with slush ice. After transport, samples were washed to remove surface salt (with tap water at room temperature), blotted dry, and cut into small pieces before quick-freezing in liquid nitrogen and storage at −20 °C until use [12].

2.1.1. Maceration Extraction Method

The fresh algae biomass was initially crushed and sieved. Thereafter, 1 kg of the prepared algae was treated with 1 L of boiling distilled water separately for 60 min. Afterward, the obtained mixture was filtered using a muslin cloth to remove the solid remains [13]. The collected filtrate was referred to as the undiluted crude extract. This extract was diluted with distilled water, and two working concentrations, 25 and 50% (v/v), respectively, were also prepared. The chosen concentrations were also adopted from previous studies [14,15].

2.1.2. Ultrasonic-Assisted Extraction Method

Fresh algae were homogenized with distilled water (1:1 wt/v) and further sonicated for extraction. Extraction was conducted in a VCX1500 ultrasonic processor (Sonics & Materials Inc., Newtown, CT, USA) with an 08/18 BHNVC21 probe at a frequency of 20 kHz and a power of 1500 W. Processing was performed for 10 min at 5 °C and consisted of 10 s cycles at 35% amplitude. The solution obtained was regarded as the 100% ultrasonic crude extract and was diluted with distilled water to form 25% and 50% concentrations for measurement [16].

2.2. Botanical Samples and Culture Conditions

The experiment was conducted in the greenhouses of Mohammed VI Polytechnic University’s research farm, located in Benguerir, Morocco. During cultivation, the temperatures ranged from 5 °C to 37 °C, with an average of about 20 °C. The soil used for cultivation was collected from an untreated agricultural field in Sebt Labrikiyne, Morocco, and analyzed before conducting the experiment. No fertilization was performed during the experimental period.
The determination of soil nitrogen concentration was conducted according to the Kjeldahl procedure [17]. Available phosphorus was measured using the Olsen colorimetric method [18], and the content of potassium was determined using an atomic absorption spectrophotometer, following the method described by Sparks [19]. The soil properties were in line with standard profiles established in the Rhamna region (Table 1). A controlled environment was used for conducting the soil analysis in the current investigation. However, we used soil that had never received fertilizer as a substrate for the plant growth. Additionally, during this trial, no fertilizers were added. The soil was investigated, and Table 1 shows the outcomes for the major macroelements (N, P, and K), which was in line with standard profiles established in the Rhamna region.
The common bean (Phaseolus vulgaris L. var. nanus) seeds were disinfected with 6% hypochlorite solution for 3 min, washed in water, and placed in plastic containers with the prepared substrate. The five pots in each treatment contained five seeds and had a 1 cm layer of stones on the bottom for drainage. The plants were cultivated with a photoperiod length of 16/8 (light/dark) and at an average temperature of 20 °C.
Since common beans are known to be salt-sensitive, and their resistance to salinity is reported at 3 g/L of NaCl supernatant (51.33 mM) based on food and agriculture organization recommendations, 3 g/L of NaCl was chosen for the imposition of stress treatments.

2.3. Experimental Design and Treatments

One week after germination, seedlings were randomly distributed into ten treatment options: (1) a negative control I that was only water-irrigated; (2) a positive control irrigated with a 51.33 mM NaCl solution (SS); and (3) eight treatments combining 51.33 mM NaCl with treatments of Ulva rigida extracts obtained via ultrasonic (U) and macerate (M) at a concentration of 25% and 50% (v/v). Extracts were applied either via irrigation (I) or foliar spraying (P), and the groups were labeled UI-25, MI-25, UP-25, MP-25, UI-50, MI-50, UP-50, and MP-50. The letters indicate the extract form, application mode, and extract concentration, respectively.
Plants were watered every 3 days and sprayed twice a week on alternate days. For each treatment, we used five replicate pots, and each pot contained five seeds developed to healthy plants, but we retained and measured two of them, resulting in a total of ten plants measured per treatment.

2.4. Collection and Analysis of Data

Plants were evaluated for different morphological and physiological parameters seven weeks after the application of the treatments. The chlorophyll content index (CCI) was determined in fully expanded leaves kept in the dark for 1 min with the aid of a portable chlorophyll meter (CL-O1, Hansatech Instruments, Norfolk, UK). A minimum of fifteen leaves per treatment group were measured. Stomatal conductance (SC) was measured in the early morning on the adaxial surface of the third unfolded leaf from the top using a portable leaf porometer (Decagon Devices, Kuala Lumpur, Malaysia). There were at least five measurements per treatment. After harvesting, root systems were scanned with an Epson Perfection LA2400 flatbed scanner, and the root morphology was analyzed using WinRHIZO software (Version 2018, Regent Instruments, Quebec, QC, Canada). For Indole Acetic Acid (IAA) quantification, fresh plant tissues were incubated for 48 h at 80 °C and analyzed.

2.5. Chlorophyll Fluorescence and Photosystem II (PS II) Efficiency

The performance of PSII was determined via chlorophyll fluorescent readings using a portable fluorometer manufactured by Hansatech Instruments Ltd. (Handy PEA+, England) to study the effect of salt stress with and without seaweed extract (SWE) applications. After seven weeks of treatment, the plants were dark-adapted for 20 min and flash-irradiated with a 1-s strong light pulse (650 nm, 3000 µmol m−2 s−1) for maximal PSII reaction center closure. Fifteen repeats were measured for each treatment. This fluorescence method offers a non-invasive method for analyzing plant stress based on the measurement of the fluorescence induction curve (delayed light emission) during the first second of illumination. The curve presents four different phases (O, J, I, and P) that correspond to the consecutive reduction in electron acceptors seated in PSII, from the minimum fluorescence (phase O) to the maximum (P). Several critical parameters were derived using this method: ΦR0, the quantum yield of electron transfer from the primary quinone acceptor (QA) to the terminal acceptors in photosystem I (PSI); ΨE0, efficiency with which excitons redirected electron transport; ΦP0, the initial quantum efficiency of electron transport at the onset of illumination; and ΦE0, the quantum yield of electron transfer from reduced QA− to plastoquinone. The total photosynthetic performance index (PItotal) was calculated based on fluorescence kinetics, whereas PIABS quantified the probability of electrons reaching the final PSI acceptors, as described in [20].

2.6. Determination of Indole Acetic Acid (IAA) Concentration

The indole acetic acid (IAA) content of bean leaves was measured using a colorimetric method based on the reaction of IAA with iron chlorate, as described by Ehmann [21]. For the IAA extraction, 200 mg of dry leaves was ground into a fine powder and added to 1.3 mL of 80% ethanol. The resulting mixture was then centrifuged at 4000 rpm for 15 min at 4 °C, and then the clear liquid (supernatants) was extracted carefully. For the assay, the reaction mixture consisted of 500 μL of the diluted extract and 1.5 mL of Salkowski reagent (36% perchloric acid and ferric chloride in solution) and was kept in the dark at 25 °C for 30 min. The color intensity of the yellow was then determined spectrophotometrically at 530 nm.

2.7. Statistical Analysis

Statistical analysis was performed using SPSS software for Windows (version 10.0.1). The results were analyzed using a two-way ANOVA with salt stress severity and seaweed extract as the main effects. Post hoc comparisons were made using the Student–Newman–Keuls test, and different letters indicate that the means are significantly different (p < 0.05).

3. Results

3.1. Effect of Ulva rigida Extract (URE) Application Methods and Concentrations on Chlorophyll Content Index (CCI)

The improvement in the chlorophyll content index (CCI) was most pronounced at a 50% concentration of Ulva rigida extract, with the ultrasonic extraction method applied as a foliar spray (UP-50) yielding the highest CCI values, significantly outperforming other treatments (p < 0.05). This suggests that foliar application of URE, particularly at 50% concentrations, is highly effective in enhancing chlorophyll retention under salt stress conditions. Similarly, URE applied via irrigation (UI-50) also improved the CCI, albeit to a lesser extent than foliar application. Specifically, plants treated with UI-50, UP-50, and MP-50 showed increases of 74%, 96%, and 72%, respectively, compared to salt-stressed control plants (SS), and 52%, 71%, and 50%, respectively, compared to non-stressed control plants I (Figure 1). In contrast, the combination of a 25% concentration of URE with ultrasonic extraction applied via irrigation (UI-25) had a less positive effect on the CCI, underscoring the importance of both the concentration and application method in achieving optimal results. These findings highlight the potential of Ulva rigida extract to alleviate salt-induced chlorophyll degradation and maintain photosynthetic capacity in bean plants.

3.2. Effect of Seaweed (Ulva rigida) Extract Application Methods and Concentrations on Stomatal Conductance (SC)

Stomatal conductance (SC), measured at 7 weeks after sowing (WAS), was significantly affected by both salt stress and URE treatments (Figure 2). Salt-stressed plants (SS) without URE application showed a substantial decline in SC, reflecting the adverse effects of salinity on stomatal function and water regulation. In contrast, the application of URE, particularly through ultrasonic extraction, improved SC under salt stress conditions.
The ultrasonic extract applied as a foliar spray (UP) at a 50% concentration demonstrated the most pronounced improvement in SC, with values significantly higher than those of other treatments (p < 0.05). This indicates that foliar application of URE at higher concentrations enhances stomatal function, potentially by mitigating ion toxicity and osmotic stress caused by salinity. Indeed, the highest significant value of SC was obtained with UP-50, with increases of 146% and 53% compared to SS and C plants, respectively.
Similarly, URE applied via irrigation (UI) also improved SC, though the effect was less pronounced compared to foliar application. These results suggest that URE, especially when applied as a foliar spray, can enhance stomatal conductance and improve water use efficiency in salt-stressed bean plants.

3.3. Chlorophyll a Fluorescence and Photosynthetic Performance Index

Figure 3 illustrates the effects of different concentrations (25% and 50%) and extraction methods (ultrasonic and maceration) of seaweed on the chlorophyll a fluorescence transient curves in bean plants subjected to salt stress. The curves represent the OJIP fluorescence transient, which provides insights into the photosynthetic performance and efficiency of the plants under various treatment conditions.
The control group shows a typical fluorescence curve indicative of healthy photosynthetic activity. However, the curve for salt-stressed plants indicates a significant reduction in fluorescence intensity, suggesting impaired photosynthetic efficiency due to salt stress.
The ultrasonic extract (UI) treatments (both 25% and 50%) demonstrate varying degrees of recovery in fluorescence intensity compared to SS, particularly at the higher concentration, indicating that ultrasonic extraction may help mitigate some negative effects of salt stress.
The maceration extract (MI) treatments generally show improved fluorescence responses compared to SS, with the 50% concentration showing notable enhancement, suggesting that maceration extracts can also positively influence photosynthesis under stress conditions.
In addition, Table 2 presents quantitative data on various JIP parameters derived from chlorophyll a fluorescence measurement for bean plants grown under salt stress.
Based on the results presented in Table 2, the control group I exhibits the highest values across all parameters, indicating optimal photosynthetic performance. In contrast, salt-stressed plants (SS) show decreased values in all parameters, confirming that salt stress adversely affects photosynthetic efficiency. Notably, treatments with seaweed extracts (UI-25 and MI-25) demonstrate improved values compared to the SS group, particularly MI-25, which exhibits higher Φpo and Pitot values than both SS and UI-25. This suggests that maceration extracts may be more effective than ultrasonic extracts in enhancing photosynthetic performance under salt stress.
Overall, both Figure 3 and Table 2 highlight the potential benefits of using seaweed extracts to alleviate the detrimental effects of salt stress on bean plants by improving their photosynthetic efficiency.

3.4. Root Length

Figure 4 presents the effects of the seaweed concentration and extraction methods on root length. Similar trends are observed; salt stress significantly reduces root length in SS plants compared to the control. However, both ultrasonic and maceration treatments at 25% and 50% concentrations resulted in increased root lengths, with maceration extracts exhibiting a more pronounced effect. This indicates that seaweed extracts not only help in maintaining root growth but may also promote root development under salinity stress.

3.5. Indole Acetic Acid (IAA) Content

Figure 5 shows the effects of seaweed treatments on IAA levels in the dry leaves of salt-stressed bean plants. IAA is an important plant hormone that regulates growth. The exogenous application of seaweed extracts significantly increases IAA content in the treated plants, particularly in ultrasonic extracts. The highest values of IAA were recorded with ultrasonic extract applied via a foliar spray of 50% Ulva rigida extract (15.63 µg g−1 DW) compared to the salt stress plant control (4.05 µg g−1 DW). The results showed that such treatments could improve hormonal balance and growth under saline conditions.

4. Discussion

These findings highlight the role of the Ulva rigida extract concentration and application method in alleviating salt-stress-induced chlorophyll degradation and improving photosynthetic capacity in the beans. Based on our results, it is apparent that extracts of Ulva rigida are a source of bioactive compounds, including amino acids, minerals, and growth regulators, which work in concert to counteract the adverse effects of salinity stress. The pronounced increase in the CCI in treated plants, particularly at a 50% (w/v) dose, clearly indicates the ability of the extracts to enhance photosynthetic efficacy under stress conditions, suggesting that Ulva rigida extract might promote chlorophyll biosynthesis and suppress its degradation under salt stress [22]. Stomatal conductance (SC) is negatively influenced by salt stress, causing osmotic disequilibrium and ion toxicity that result in stomatal closure, which decreases transpiration but concomitantly inhibits CO2 uptake and photosynthesis [23]. The method of U. rigida extract administration affected its action on stomatal response, as foliar spray enhanced the direct and rapid absorption of bioactive molecules through leaf surfaces, mediated by the fast modulation of stomata and guard cell activity, compared to soil irrigation [24]. The increase in stomatal conductance observed under the treatments with Ulva rigida extracted products is consistent with earlier works, which show that biostimulants from marine algae enhance gas exchange parameters under abiotic stress. Such stimulation may be due to the abundance of major macronutrients, such as K and Mg, in the extracts. Potassium is important in maintaining guard cell turgor pressure and therefore the ability of stomata to open, while magnesium, in addition to the function of activating enzymes of chlorophyll biosynthesis, has been shown also to increase enzyme activity and improve the physiological state of plants under stress [25,26]. Moreover, the above compounds in the extracts provide growth-promoting factors and antioxidants that together improve stomatal performance and salinity tolerance of plants. Having restored stomatal conductance resting (50% foliar spray), U.rigida extracts are playing an important role in sustaining photosynthetic efficiency and optimizing water-use, which is further resulting in enhanced growth and productivity of salt-stressed plants.
The OJIP fluorescence transient is an effective probe for evaluating the behavior of photosystem II (PSII) and electron transport capacity, offering a useful tool to examine the photosynthetic response to various stress, Salt stress is found to damage PSII operating capability and electron flow, and is commonly caused by degradation of thylakoid membranes resulted in the reduction in active PSII centers [27,28].
Ulva rigida seaweed extracts consist on bioactive compounds (polysaccharides, polyphenols) and betaines and have been reported to stabilize thylakoid membranes and to improve antioxidant defense systems [29]. These characteristics contribute to defense of PSII against salt-induced injury, and elicits electron flux under stress [30]. The concentration and spectrum of these bioactive compounds are affected by the extraction procedure and modulate the efficiency of the extracts in the protection of photosynthetic apparatus [31].
Seaweed-based biostimulants such as those manufactured from U. rigida have been gaining increasing attention for their capacity to enhance photosynthetic efficiency and increase crop tolerance and productivity under abiotic stress [32].
Osmotic stress and ion toxicity produced by salt stress also inhibit root elongation [33,34]. Bioactive compounds present in U. rigida extracts could facilitate biomass accumulation and root development even in saline substrate, possibly by modulating hormonal and metabolic pathways [30,35].
Auxin, indole acetic acid (IAA), and these two compounds are involved in regulating cell division and elongation, while salt stress can cause suppression of this hormones; thus, it can lead to a reduction in growth as well as a reduction in the balance of hormonal levels. The treatments with U. rigida extracts, in particular those obtained by ultrasound, and applied as foliar spray could increase these levels of indole acetic acid (IAA) by providing precursors of auxins or by stimulating their endogenous synthesis, which would be regulated by bioactive molecules such as cytokinins, betaines and polysaccharides. Feeding via leaves allows these compounds to be taken up directly, promoting hormonal signaling, growth and/or stress resistance [32,36]. Additionally, these treatments have been reported to up-regulate the auxin-responsive genes, thereby regulating better root architecture and nutrient acquisition under salinity [37]. As a whole, seaweed extracts of U. rigida enhance growth performance and hormonal balance in salt-affected plants [38]. Different extract preparations and their concentration control biostimulant activity, with maceration extracts being more efficient for root development and ultrasonic extracts for indole acetic acid (IAA) accumulation [39,40,41]. Together, these multiple effects indicate a high promise of U. rigida biostimulants to enhance plant salt tolerance and productivity [42]. In addition, in order to test the efficacy of these Moroccan Ulva rigida extracts, future studies are promptly needed to further examine which strategy of application protocols, dosage, and delivery methods may be most effective under different crops or intensities of salt stress, thereby maximizing annual crop production sustainably.
Indeed, more research is needed to determine the bioactive compounds from different seaweed and procedures for the extraction and application of seaweed extracts to optimize the protective and stimulatory effects on plant growth under salt stress.

5. Conclusions

This study is greatly supported the concept of sustainable agriculture by showing extracts of Ulva rigida seaweed as effective biostimulants for enhancing salt stress tolerance in crops like bean plants. The best method adopted was the use of Ulva rigida seaweed extracts to increase salt stress resistance in bean plants extracted by ultrasound at a 50% concentration and applied as a foliar spray. This mixture led to the greatest enhancements in key physiological traits such as chlorophyll content index, stomatal conductance, photosystem II efficiency, and root growth and indole acetic acid levels, which were related to biostimulant effects under saline stress. The findings of the present research demonstrate that the extraction method and applied concentration are important factors affecting biostimulant efficacy, as ultrasonic extraction at 50% concentration in foliar spray was the most effective approach in ameliorating the plant photosynthetic activity, stomatal conductance, root growth, and hormonal balance under the saline stress conditions. This effective protocol capitalizes the high bioactive potential of the extracts and enables the highest possible level of resistant plant characteristics and less reliance on synthetic agrochemicals. By using such targeted extraction and application approaches, future key research points and farming practices are suggested to better exploit seaweed biostimulants for sustainable and high-field basic performances under saline conditions. Future research should identify these bioactive compounds and quantify the long-term effects of the application of seaweed applications on soil health and crop productivity.

Funding

This research received no external funding.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author.

Acknowledgments

The author is grateful to everyone in the Plant Stress Physiology Laboratory at AgroBioSciences, Mohammed VI Polytechnic University (UM6P), Benguerir, Morocco, for their support and assistance during this study.

Conflicts of Interest

The author declares no conflicts of interest.

Abbreviations

The following abbreviations are used in this manuscript:
UREUlva rigida extract
SWESeaweed extract
SSSalt stress
CControl
UPUltrasonic extract applied via a foliar spray
MIMaceration extract applied via irrigation
MPMaceration extract applied via a foliar spray
UIUltrasonic extract applied via irrigation
IAAIndole acetic acid
CCIChlorophyll content index
SCStomatal conductance
OJIPFast chlorophyll a fluorescence induction
P2O5Phosphorus pentoxide
K2OPotassium oxide
N-NO3Nitrate nitrogen

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Figure 1. The chlorophyll content index of bean plants under salt stress in response to two methods of Ulva rigida extract (URE) application (ultrasonic (U) and maceration (M)) at two concentration levels (25% and 50% crude extract). C: control, SS: salt stress at 51.33 mM, UI: ultrasonic extract applied via irrigation, UP: ultrasonic extract applied via a foliar spray, MI: maceration extract applied via irrigation, MP: maceration extract applied via a foliar spray. Each value represents the mean ± SD of ten independent repetitions. Different letters indicate significant differences at p < 0.05 according to the two-way ANOVA (factor 1, salt stress level; factor 2, SWE treatment), followed by the Student–Newman–Keuls post hoc test.
Figure 1. The chlorophyll content index of bean plants under salt stress in response to two methods of Ulva rigida extract (URE) application (ultrasonic (U) and maceration (M)) at two concentration levels (25% and 50% crude extract). C: control, SS: salt stress at 51.33 mM, UI: ultrasonic extract applied via irrigation, UP: ultrasonic extract applied via a foliar spray, MI: maceration extract applied via irrigation, MP: maceration extract applied via a foliar spray. Each value represents the mean ± SD of ten independent repetitions. Different letters indicate significant differences at p < 0.05 according to the two-way ANOVA (factor 1, salt stress level; factor 2, SWE treatment), followed by the Student–Newman–Keuls post hoc test.
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Figure 2. Stomatal conductance (SC) of bean plants grown under salt stress conditions, measured at 07 WAS, in response to two different methods of seaweed extract (ultrasonic (U) and maceration (M)) with two concentrations (25% and 50% crude extract). C: control, SS: salt stress at 51.33 mM, UI: ultrasonic extract applied via irrigation, UP: ultrasonic extract applied via a foliar spray, MI: maceration extract applied via irrigation, MP: maceration extract applied via a foliar spray. Each value represents the mean ± SD of five independent repetitions. Different letters indicate significant differences at p < 0.05 according to a two-way ANOVA (factor 1, salt stress level; factor 2, SWE treatment), followed by the Student–Newman–Keuls post hoc test.
Figure 2. Stomatal conductance (SC) of bean plants grown under salt stress conditions, measured at 07 WAS, in response to two different methods of seaweed extract (ultrasonic (U) and maceration (M)) with two concentrations (25% and 50% crude extract). C: control, SS: salt stress at 51.33 mM, UI: ultrasonic extract applied via irrigation, UP: ultrasonic extract applied via a foliar spray, MI: maceration extract applied via irrigation, MP: maceration extract applied via a foliar spray. Each value represents the mean ± SD of five independent repetitions. Different letters indicate significant differences at p < 0.05 according to a two-way ANOVA (factor 1, salt stress level; factor 2, SWE treatment), followed by the Student–Newman–Keuls post hoc test.
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Figure 3. The effects of the seaweed concentration (25% and 50%) and extract method (ultrasonic (U) and maceration (M)) on the chlorophyll a fluorescence transient curve of bean plants grown under salt-stress conditions at seven weeks after sowing (07 WAS). The chlorophyll a fluorescence transient in O sampled at 50 μs, J sampled at 2 ms, I sampled at 30 ms and P sampled at 200 ms, C: control, SS: salt stress at 51.33 mM, UI: ultrasonic extract applied via irrigation, UP: ultrasonic extract applied via a foliar spray, MI: maceration extract applied via irrigation, MP: maceration extract applied via a foliar spray.
Figure 3. The effects of the seaweed concentration (25% and 50%) and extract method (ultrasonic (U) and maceration (M)) on the chlorophyll a fluorescence transient curve of bean plants grown under salt-stress conditions at seven weeks after sowing (07 WAS). The chlorophyll a fluorescence transient in O sampled at 50 μs, J sampled at 2 ms, I sampled at 30 ms and P sampled at 200 ms, C: control, SS: salt stress at 51.33 mM, UI: ultrasonic extract applied via irrigation, UP: ultrasonic extract applied via a foliar spray, MI: maceration extract applied via irrigation, MP: maceration extract applied via a foliar spray.
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Figure 4. The effects of seaweed concentration (25% and 50%) and extract methods (ultrasonic (U) and maceration (M)) on the root length of bean plants grown under salt stress. C: control, SS: salt stress at 51.33 mM, UI: ultrasonic extract applied via irrigation, UP: ultrasonic extract applied via a foliar spray, MI: maceration extract applied via irrigation, MP: maceration extract applied via a foliar spray. Each value represents the mean ± SD of three independent repetitions. Different letters indicate significant differences at p < 0.05 according to a two-way ANOVA (factor 1, salt stress level; factor 2, SWE treatment), followed by the Student–Newman–Keuls post hoc test.
Figure 4. The effects of seaweed concentration (25% and 50%) and extract methods (ultrasonic (U) and maceration (M)) on the root length of bean plants grown under salt stress. C: control, SS: salt stress at 51.33 mM, UI: ultrasonic extract applied via irrigation, UP: ultrasonic extract applied via a foliar spray, MI: maceration extract applied via irrigation, MP: maceration extract applied via a foliar spray. Each value represents the mean ± SD of three independent repetitions. Different letters indicate significant differences at p < 0.05 according to a two-way ANOVA (factor 1, salt stress level; factor 2, SWE treatment), followed by the Student–Newman–Keuls post hoc test.
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Figure 5. The effects of seaweed treatments on the indole acetic acid (IAA) content in the dry leaves of bean plants under salt stress. C: control, SS: salt stress at 51.33 mM, UI: ultrasonic extract applied via irrigation, UP: ultrasonic extract applied via a foliar spray, MI: maceration extract applied via irrigation, MP: maceration extract applied via a foliar spray. Each value represents the mean ± SD of three independent repetitions. Different letters indicate significant differences at p < 0.05 according to a two-way ANOVA (factor 1, salt stress level; factor 2, SWE treatment), followed by the Student–Newman–Keuls post hoc test.
Figure 5. The effects of seaweed treatments on the indole acetic acid (IAA) content in the dry leaves of bean plants under salt stress. C: control, SS: salt stress at 51.33 mM, UI: ultrasonic extract applied via irrigation, UP: ultrasonic extract applied via a foliar spray, MI: maceration extract applied via irrigation, MP: maceration extract applied via a foliar spray. Each value represents the mean ± SD of three independent repetitions. Different letters indicate significant differences at p < 0.05 according to a two-way ANOVA (factor 1, salt stress level; factor 2, SWE treatment), followed by the Student–Newman–Keuls post hoc test.
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Table 1. Selected chemical characteristics of the used soil.
Table 1. Selected chemical characteristics of the used soil.
Chemical CompoundP2O5 (ppm)K2O (ppm)N-NO3 mg/Kg
Concentration24.33 ± 0.0056220.3 ± 0.0037.017 ± 0.004
Soil characteristicsModerately poorModerately poorModerately poor
Table 2. The combined effect of seaweed concentration and extract methods on JIP parameters of bean plants grown under salt stress conditions at 07 WAS.
Table 2. The combined effect of seaweed concentration and extract methods on JIP parameters of bean plants grown under salt stress conditions at 07 WAS.
phi(Po)psi(Eo)phi(Eo)phi(Ro)PItot
C0.7110.3460.2460.1300.3708
SS0.6250.2870.1800.1180.3013
UI-250.6650.4040.2690.1320.3141
MI-250.7460.3960.2960.1570.6096
UP-250.6390.3360.2150.1080.2200
MP-250.7450.3170.2360.1400.5672
UI-500.7220.3380.2440.1480.6103
MI-500.7670.3820.2930.1590.7029
UP-500.7470.3620.2710.1730.8802
MP-500.7640.3720.2840.1760.9459
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Latique, S. Moroccan Ulva rigida Extracts: A Promising Biostimulant for Improving Growth and Photosynthetic Performance in Salt-Stressed Bean Plants. Crops 2025, 5, 61. https://doi.org/10.3390/crops5050061

AMA Style

Latique S. Moroccan Ulva rigida Extracts: A Promising Biostimulant for Improving Growth and Photosynthetic Performance in Salt-Stressed Bean Plants. Crops. 2025; 5(5):61. https://doi.org/10.3390/crops5050061

Chicago/Turabian Style

Latique, Salma. 2025. "Moroccan Ulva rigida Extracts: A Promising Biostimulant for Improving Growth and Photosynthetic Performance in Salt-Stressed Bean Plants" Crops 5, no. 5: 61. https://doi.org/10.3390/crops5050061

APA Style

Latique, S. (2025). Moroccan Ulva rigida Extracts: A Promising Biostimulant for Improving Growth and Photosynthetic Performance in Salt-Stressed Bean Plants. Crops, 5(5), 61. https://doi.org/10.3390/crops5050061

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