Open AccessFeature PaperArticle

Evaluation of Ascophyllum nodosum and Sargassum spp. Seaweed Extracts’ Effect on Germination of Tomato Under Salinity Stress

Eleni Papoui

and

Athanasios Koukounaras

Department of Agriculture, Aristotle University of Thessaloniki, 541 24 Thessaloniki, Greece

Author to whom correspondence should be addressed.

Horticulturae 2025, 11(3), 290; https://doi.org/10.3390/horticulturae11030290

Submission received: 3 February 2025 / Revised: 25 February 2025 / Accepted: 3 March 2025 / Published: 6 March 2025

(This article belongs to the Section Propagation and Seeds)

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Figure 1
Speed of germination of tomato seeds soaked for 15 min in 1, 2, 3% of Ascophyllum nodosum extracts (Algit Super) and 1, 2, 3% of Sargassum spp. extracts (Alga 300) under salinity stress. Columns (average values) with nonmatching letters indicate significant differences (p < 0.05). The red horizontal line indicates the Control H2O value. "> Figure 2
Percentage of germination (%) of tomato seeds soaked for 15 min in 1, 2, 3% of Ascophyllum nodosum extracts (Algit Super) and 1, 2, 3% of Sargassum spp. extracts (Alga 300) under salinity stress. Columns (average values) with nonmatching letters indicate significant differences (p < 0.05). The red horizontal line indicates the Control H2O value. "> Figure 3
Vigor index I (%) of tomato roots and shoots soaked for 15 min in 1, 2, 3% of Ascophyllum nodosum extracts (Algit Super) and 1, 2, 3% of Sargassum spp. extracts (Alga 300) under salinity stress. Columns (average values) with nonmatching letters indicate significant differences (p < 0.05). The red horizontal line indicates the Control H2O value. "> Figure 4
Vigor index II (%) of tomato roots and shoots soaked for 15 min in 1, 2, 3% of Ascophyllum nodosum extracts (Algit Super) and 1, 2, 3% of Sargassum spp. extracts (Alga 300) under salinity stress. Columns (average values) with nonmatching letters indicate significant differences (p < 0.05). The red horizontal line indicates the Control H2O value. "> Figure 5
Dry weight (g) of tomato roots and shoots soaked for 15 min in 1, 2, 3% of Ascophyllum nodosum extracts (Algit Super) and 1, 2, 3% of Sargassum spp. extracts (Alga 300) under salinity stress. Columns (average values) with nonmatching letters indicate significant differences (p < 0.05). The red horizontal line indicates the Control H2O value. "> Figure 6
Average length (cm) of tomato roots and shoots soaked for 15 min in 1, 2, 3% of Ascophyllum nodosum extracts (Algit Super) and 1, 2, 3% of Sargassum spp. extracts (Alga 300) under salinity stress. Columns (average values) with nonmatching letters indicate significant differences (p < 0.05). The red horizontal line indicates the Control H2O value. "> Scheme 1
Germinated tomato seeds after 8 days: no soaking—irrigation with distilled water (1st row); no soaking—irrigation with distilled water and 75 mM NaCl (2nd row); and 15′ soaking in distilled water—irrigation with distilled water and 75 mM NaCl (3rd row). "> Scheme 2
Germinated tomato seeds after 8 days, treated with 1% (1st row), 2% (2nd row) and 3% (3rd row) Ascophyllum nodosum under salinity stress. "> Scheme 3
Germinated tomato seeds after 8 days, treated with 1% (1st row), 2% (2nd row) and 3% (3rd row) Sargassum spp. under salinity stress. ">

Versions Notes

Abstract

Abiotic stresses like salinity are proven to be crucial limiting factors in the seed germination of many plant species and the later establishment of cultivation regarding plant growth, yield and fruit quality. Therefore, there is a pressing need to find practices and materials to enhance abiotic stress tolerance from early stages such as germination so that plants can overcome these stresses as soon as possible. A total of six treatments of seaweed extracts [1, 2 and 3% of Algit Super (Ascophyllum nodosum) and Alga 300 (Sargassum spp.)] and three controls were tested, with 20 seeds per replication soaked in each extract concentration for 15′; four replications were carried out per treatment and seeds were placed on Petri dishes in the dark. Speed and percentage of germination, vigor index I and II, dry weight and average lengths of roots and shoots were evaluated under 75 mM NaCl stress. All treatments positively affected all parameters evaluated, whether significant or not. Results indicate that soaking tomato seeds in seaweed extracts of various concentrations led to a significantly increased speed and percentage of germination, vigor index I and II, dry weight and average lengths of roots and shoots. The best combination of concentration and seaweed species is concluded to be 2% Sargassum spp. for all parameters evaluated.

Keywords:

biostimulants; seeds; vigor index; abiotic stress

1. Introduction

Due to the climate crisis, agricultural research is now focusing on components that are more friendly to the environment but effective enough against biotic and abiotic stresses for crops such as insects, fungi or weeds that are resistant to pesticides, drought and salinity. Biostimulants deriving from natural sources meet those needs and are being increasingly tested and applied [1,2]. Biostimulants can be applied by foliar sprays or through an irrigation system, enhancing the stamina or improving the water and nutrient use efficiency of the crop so it is able to perform even in stress conditions [3]. There are a variety of biostimulant compounds available, and seaweed extracts are among them. Using seaweed extracts as biostimulants has been found to promote activities of plant growth. Even low concentrations of seaweed extracts can promote the growth of plants, improve flowering, increase yields, enhance quality and contribute to richer nutritional content and post-harvest life. Seaweeds have also been found to increase the tolerance of crops against biotic and abiotic stresses [4,5,6] and, furthermore, promote early seed germination [7,8].

The most studied and accepted seaweed by farmers is the brown algae Ascophyllum nodosum, which has been found to be superior in performance in comparison to other seaweeds [9,10]. Ascophyllum nodosum has been found to enhance drought tolerance in soybeans [10,11] and increase anthocyanin and phenolic content in grapes and berries; however, these results may be considered crop-dependent [1]. Moreover, studies have demonstrated the contribution of Ascophyllum nodosum in protecting against abiotic stresses such as soil and water salinity, along with its ability to promote germination and plant growth [1,12,13].

Salinity is one of the major abiotic stresses because of its ability to increase osmotic pressure in the soil or substrate of cultivation, inhibit the absorption of nutrients by the crop and, furthermore, promote crop growth [13,14,15]. Every crop has a different point of tolerance against saline conditions, but in general, crops are most vulnerable at the stage of germination and tolerance increases while growth occurs. The USDA reports that tomato (Solanum lycopersicum L.) is the most sensitive crop to saline conditions, especially at the stage of germination [14]. This stage is considered to be of the greatest importance due to its capacity to determine the subsequent growth of the crop [16]. Studies have concluded that salt-tolerant seedlings have a more successful later establishment of cultivation. Germination conditions have been found to affect the percentage of germination but also the seedling growth and plant establishment later on [2]. Saline conditions are proven to reduce root and shoot length, the percentage of germination and the speed of germination, as well as plant performance in saline soils. Thus, studying salinity tolerance and ways of overcoming this stress is crucial in order to ensure plants’ optimum performance [13,17]. Seaweed extracts have been used as biostimulants to promote the tolerance of crops against saline conditions for a while now [18]. Studies on Ascophyllum nodosum and Sargassum spp. have shown that they can be beneficial regarding seed germination, growth and resistance to pests in rice plants [19]. Foliar sprays of the two seaweed extracts seemed to increase stem diameter and fresh biomass under salinity stress [18].

Brown algae of the genus Sargassum is considered a problem regarding pollution on the coast of the Caribbean. In order to mitigate environmental pollution by the seaweed and reduce its abundance on the coast, it has been used as a construction material, an element for food supplements, in the cosmetics industry and as a biostimulant in agriculture [8,20,21]. Sargassum seaweed has been proven to improve tolerance in chickpea plants and increase phenolic content and antioxidant activity in barley under salinity stress [20]. Sargassum meriocystum has been tested and proven to improve seed germination, seedling growth and the biochemical composition of Vigna mungo, commonly known as black gram [22].

Tomato (Solanum lycopresicum) is a crop with high economic value worldwide and in the Mediterranean region. The occurring climate crisis, characterized by long periods of drought along with extreme temperatures, combined with the saline conditions in the region anyway, means that tomato cultivation is experiencing plenty of inhibiting factors compared to previous years [23]. Foliar applications of seaweed extracts have been found to positively affect growth, yield and quality of tomato cultivation under salinity stress [23,24].

The benefits of seaweed extract application during cultivation under salinity have already been studied. Studies about Ascophyllum nodosum’s effectiveness are in great abundance, but Sargassum spp. could be an equal, or even better, alternative. The concentrations examined so far are around 5–10% and the duration of seed treatment is usually 24 h. The aim of the present study is to examine and evaluate the effect—positive, negative or even nonexistent—of Ascophyllum nodosum and Sargassum spp. extracts on the germination of tomato seeds under saline (75 mM) conditions. Furthermore, several smaller concentrations and shorter periods of seed soaking than usual were tested in order to determine the best combination of extract, concentration and time of soaking.

Our research hypothesis was that it is possible to achieve a positive effect on seed germination under salinity stress by using less product (seaweed extract) with less processing time. Therefore, our aim was to use lower concentrations of seaweed extracts and soak the seeds for a shorter duration than in previous studies.

2. Materials and Methods

2.1. Experimental Site

The experiment took place in the Laboratory of Vegetable Crops of the Aristotle University of Thessaloniki in northern Greece. In detail, temperature was fixed and monitored in a growth chamber (20 ± 1 °C) and the seeds in the Petri dishes were in absolute darkness throughout the entirety of the experiment.

2.2. Materials

For the purpose of this study, two commercial formulations were used: Alga 300 (LEILI AGROCHEMISTRY Co., Ltd., Beijing, China), a concentrated extract from a mild enzymolysis of brown algae of the genus Sargassum at a concentration of 35% w/v, and Algit Super (BIOERGEX SALATAS BROS SA, Kifisia, Greece), a natural product resulting from alkaline hydrolysis of the Norwegian seaweed Ascophyllum nodosum at a concentration of 7.5%. The two seaweeds were selected from a range of other commercial formulations following previous tests using various concentrations and times of seed soaking under the same conditions and considering the effect they had on tomato germination parameters. AGRIS (Alexandria, Greece), a seed and seedling production company in Central Macedonia in Greece, provided the tomato seeds for the study (CLX 38233 F1), which were a commercial open-field, self-pruning hybrid, with no salinity resistance acknowledged and no pre-treatment before this research.

A total of 20 seeds per replication, with 4 replications carried out per treatment, were placed in 9 cm diameter transparent polystyrene (PS) Petri dishes containing filter paper. The selection of a 75 mM NaCl salinity treatment was inspired by Koukounaras et al. (unpublished data).

There were 3 control treatments:

No soaking—irrigation with distilled water.
No soaking—irrigation with distilled water and 75 mM NaCl.
A 15′ soaking period in distilled water—irrigation with distilled water and 75 mM NaCl.

There were six treatments with Ascophyllum nodosum and Sargassum spp. in several extract concentrations:

A 15′ soaking period in 1% Ascophyllum nodosum—irrigation with distilled water and 75 mM NaCl.
A 15′ soaking period in 2% Ascophyllum nodosum—irrigation with distilled water and 75 mM NaCl.
A 15′ soaking period in 3% Ascophyllum nodosum—irrigation with distilled water and 75 mM NaCl.
A 15′ soaking period in 1% Sargassum spp.—irrigation with distilled water and 75 mM NaCl.
A 15′ soaking period in 2% Sargassum spp.—irrigation with distilled water and 75 mM NaCl.
A 15′ soaking period in 3% Sargassum spp.—irrigation with distilled water and 75 mM NaCl.

The seeds were soaked in a solution of each concentration of formulation diluted in distilled water. Distilled water was used to prepare the 75 mM NaCl solution as well. The latter solution was used to water the Petri dishes by adding 2 mL of the solution to the filter paper. Control No. 1 was watered with 2 mL of distilled water. The procedure of watering was repeated after 4 days. All treatments were developed under controlled environmental conditions. The experiment lasted for 8 days in total.

2.3. Measurements

The number of sprouting seeds in every Petri dish was counted every day during the experiment. At the end of the experiment cycle (8th day), the number of sprouting seeds was counted along with the length of every sprouted seed and the fresh and dry weight of the sprout. Speed and percentage of germination [(1) and (2) respectively], the average length of the sprouts and vigor index I (3) and II (4) were calculated and evaluated. The determination of total and average length of the seedling was conducted with the use of the software WinRhizo Pro, with four decamines accuracy. Speed of germination and % germination were determined with visual observation and using Equations (1) and (2).

The experiment was repeated using the same procedure and conditions once more to validate the consistency of the seaweeds’ effects, and similar results were obtained to those of Papoui et al. (unpublished data).

Speed of germination = (g₁/day₁) + (g₂/day₂) + … + (g_n/day_n)

(1)

where g = germinated seeds.

% Germination = (number of germinated seeds/number of replication seeds) × 100

(2)

Vigor Index I = % germination × seedling length (root + shoot)

(3)

Vigor Index II = % germination × seedling dry weight (root + shoot)

(4)

2.4. Statistical Analysis

The experimental design of this research was completely randomized. Statistical analysis of the data was carried out using IBM SPSS Statistics, 29.0.0.0 (241) software, applying Tukey’s range test. One-way ANOVA was also used to perform statistical analysis.

3. Results

Seed priming by soaking the seeds in water or other extracts is not recommended for all species and the duration of soaking must be carefully chosen [25]. This is due to the possibility of nutrient loss, crucial to seed emergence, resulting in non-germinating seeds [16]. In most of the research published, 12, 24, 32, 48 or even 72 h of seed soaking is used according to the size of the seed. For example, tomato seeds have been tested following 12, 24 and 32 h of soaking in water, as 32 h of soaking had a negative effect on the parameters evaluated [26]. For the reasons mentioned, for practical research purposes, and considering the small size and thickness of tomato seeds, a 15 min soaking period was selected.

Salinity treatment had a significantly negative effect on all parameters compared to watering with distilled water. Speed of germination, % of germination, vigor index I and II, dry weight and average lengths of roots and shoots were reduced by 81%, 88%, 79%, 40%, 88% and 95%, respectively (Scheme 1). Because of these enormous differences, the treatment “No soaking—irrigation with distilled water” was not included in the statistical analysis (Table 1).

The results of the comparison between control treatments with saline water for irrigation of soaked and unsoaked seeds indicate that soaking the seeds in distilled water made no difference to all of the parameters evaluated, except the percentage of germination. Control 15′ + NaCl significantly increased the percentage of germination of tomato seeds compared to Control NaCl (Scheme 1). Due to these results, we decided to use the Control 15′ + NaCl treatment as the control in order to eliminate any positive effect of the water while soaking the seeds in seaweed extracts diluted in water (Table 2).

Tomato speed germination was positively affected by the application of both seaweed extracts in all of their concentrations. The treatment with 2% concentration of Sargassum spp. extract noted the highest value, which was 92.4%—significantly higher than Control 15′ + NaCl. Soaking the seeds in 2% and 3% Ascophyllum nodosum extract significantly increased the speed of germination by 72.4% and 58.7%, respectively, compared to Control 15′ + NaCl. The 2% Sargassum spp. extract noted higher values of speed of germination of tomato seeds than 2% Ascophyllum nodosum, but this was not significant (Figure 1), (Scheme 1, Scheme 2 and Scheme 3).

Figure 1. Speed of germination of tomato seeds soaked for 15 min in 1, 2, 3% of Ascophyllum nodosum extracts (Algit Super) and 1, 2, 3% of Sargassum spp. extracts (Alga 300) under salinity stress. Columns (average values) with nonmatching letters indicate significant differences (p < 0.05). The red horizontal line indicates the Control H₂O value.

Scheme 1. Germinated tomato seeds after 8 days: no soaking—irrigation with distilled water (1st row); no soaking—irrigation with distilled water and 75 mM NaCl (2nd row); and 15′ soaking in distilled water—irrigation with distilled water and 75 mM NaCl (3rd row).

Scheme 2. Germinated tomato seeds after 8 days, treated with 1% (1st row), 2% (2nd row) and 3% (3rd row) Ascophyllum nodosum under salinity stress.

Scheme 3. Germinated tomato seeds after 8 days, treated with 1% (1st row), 2% (2nd row) and 3% (3rd row) Sargassum spp. under salinity stress.

All treatments had a positive effect on the percentage of germination compared to Control 15′ + NaCl, but this was not significant. Among them, Sargassum spp. extract at the 2% concentration increased the percentage of germination of tomato seeds compared to Control 15′ + NaCl by 33.9%; however, this increase was not significant (Figure 2), (Scheme 1, Scheme 2 and Scheme 3).

Vigor index was improved by all treatments compared to Control 15′ + NaCl (81.98), with 2% Aschophyllum nodosum (167.71) and 2% Sargassum spp. (216.25) having a significant positive impact on this parameter, increasing it by 104.6% and 163.8%, respectively. The 2% Sargassum spp. extract noted higher values of speed of germination of tomato seeds than 2% Ascophyllum nodosum, but this was not significant (Figure 3).

All treatments had a positive effect on vigor index II, whether significant or not, compared to Control 15′ + NaCl, except 1% Ascophyllum nodosum, which did not affect the parameter. The 2% Sargassum spp. extract with 15′ soaking had a significant positive effect on Control 15′ + NaCl treatment, increasing vigor index II by 235.4%. Vigor index II increased significantly upon soaking the seeds in 2% Ascophyllum nodosum for 15′ by 142.6% compared to Control 15′ + NaCl; however, this increase was not significant. The 2% Sargassum spp. extract noted higher values of speed of germination of tomato seeds than 2% Ascophyllum nodosum, but this was not significant (Figure 4).

All treatments with seaweed extracts had a positive effect on dry weight, significant or not, compared to Control 15′ + NaCl. A significantly higher value was noted when soaking the seeds in 2% Sargassum spp. for 15′ (0.0096 g) compared to the Control 15′ + NaCl treatment (0.0036 g). The 2% Ascophyllum nodosum extract tended to also increase dry weight by 103.42% compared to Control 15′ + NaCl. The 2% Sargassum spp. extract noted higher values of speed of germination of tomato seeds than 2% Ascophyllum nodosum, but this was not significant (Figure 5).

All treatments with seaweed extracts had a positive effect, whether significant or not, on average length (root and shoot), compared to Control 15′ + NaCl. The 2% Sargassum spp. 15′ treatment was the only treatment that significantly increased the average length of roots and shoots in tomato seeds, compared to Control 15′ + NaCl, by 93.46%. The 2% Sargassum spp. extract noted higher values of speed of germination of tomato seeds than 2% Ascophyllum nodosum, but this was not significant (Figure 6), (Scheme 1, Scheme 2 and Scheme 3).

4. Discussion

Abiotic stresses like salinity are proven as crucial limiting factors to seed germination in many plant species and to the later establishment of cultivation regarding plant growth, yield and fruit quality. Therefore, there is a pressing need to find practices and materials that enhance abiotic stress tolerance from early stages such as germination so that plants can overcome these stresses as soon as possible, and at the same time, these practices should be as friendly as possible to the environment and soil, presenting a safer choice than conventional fertilizers [27]. Seaweed extracts have been tested before for their ability to enhance plants’ stamina against abiotic factors, such as drought, high temperatures and salinity, by foliar sprays during cultivation. It is now crucial to investigate in depth the efficacy of seaweed extracts on seed germination and whether they can induce germination parameters under abiotic stresses.

Seed priming with water, also known as hydropriming, promotes seed germination and emergence under normal but also stressful conditions, such as salinity, by inhibiting enzymic activities in the seed. Hydropriming can promote the supply of sugars during the germination stage by stimulating amylase production, an enzyme responsible for seed germination and emergence. Research in wheat and barley shows greater activity of amylase in primed seeds comparing to non-primed seeds [16]. Hydropriming of pigeon pea has been found to mobilize proteins, sugars and other compounds responsible for germination under salinity stress. However, the effect of hydropriming seeds cannot be applied universally; in Glycine max, it showed reverse results to those mentioned above [16,26]. The species, the cultivar, the duration of seed soaking and the dehydration after soaking are major factors affecting the results of priming [16,25].

A great technique to achieve higher and faster germination under unfavorable conditions, in some cases, is combining hydropriming with the addition of seaweeds. Ascophyllum nodosum has been tested for promoting germination under salinity stress, with the results being promising. Positive results have been shown on tomato, pepper, maize and other plants, with Ascophyllum nodosum mitigating salinity stress by increasing catalase activity [13,28]. Seaweed contains a great variety of bioactive compounds such as pigments, phenolics, proteins, peptides, nutrients, polysaccharides, phytohormones, sterols, sugars, lipids, vitamins and many others. These compounds can explain the positive effects on plants under stressful conditions, acting as elicitors of the plant’s defense against stress and stimulating plant growth. Carrageenan, present in seaweed extracts, can enhance plant growth by interfering with biochemical or physiological processes. For example, Ascophyllum nodosum is proven to increase crop yield by 65% and improve quality under drought stress, but at the same time, it constitutes a sustainable and organic tool for farmers and ecosystems [28].

Seed soaking in 0.5% Ascophyllum nodosum extract for 8 h has been found to improve the percentage of germination, root and shoot length and, furthermore, dry weight of tomato and sweet pepper seedlings under various salinity concentrations; however, the mechanism of action of seaweed was not determined [13]. These results are similar to those in this work, despite a differentiation in the time of seed soaking (15 min) and probably the extraction method of seaweed, since it was not mentioned in the research or the product itself, and the concentration of the extract (1, 2, 3%). Another study shows the positive effect of priming carrot seeds in seaweed extracts in combination with other substances. The results are similar to those in our study, demonstrating a higher germination percentage, increasing from 37% to 74%, and a significantly higher vigor index I under salinity stress. These results may be due to enzymes or phytohormones present in seaweeds activating metabolic procedures [29]. The results of the current study indicate that the duration of soaking can be reduced when seaweed extract concentration increases. Specifically, the vigor index I increased from 61.4% to 167.7% and 216.3% when priming the seeds in 2% Ascophyllum nodosum and Sargassum spp. extracts, respectively, for 15 min. These results could indicate that enzymes or phytohormones present in seaweeds take effect faster in higher dosages but not excessive ones.

Sargassum spp. combined with microbes have been found to increase germination in tomato seeds, as well as when combined with Eklonia maxima seaweed, increasing the germination of Zea mays seeds by 16–19%. Sargassum spp. have also been proven to improve seed germination and growth of tomato seeds at a concentration of 0.25 g/L. The result is attributed to the potential production of a compound called dichloromethane [30]. Our results indicate that Sargassum spp. alone can significantly increase germination from 60% (in non-treated seeds) to 87.5%, 93.8% and 91.3% when soaking the seeds in 1%, 2% and 3% extract, respectively. Another study indicating positive effects of Sargassum spp. extract tested on tomato seedlings under various concentrations of salinity shows an increase in growth and the modulation of metabolic and molecular pathways that increase salinity tolerance [18]. In comparison, our research indicates that priming the seeds with 2% Sargassum spp. for 15 min before cultivation establishment can lead to a seedling length increase from 1.1 cm to 2.31 cm. These results require further investigation in order to determine whether the effect of the seaweed remains during cultivation or if more applications of the extract are needed.

The concentration of seaweed extracts is also something that needs to be addressed. Research shows that in different species, different concentrations have various results. The use of Sargassum myriocystum in lower concentrations has led to optimal results on Vigna mungo (L.), in contrast to higher concentrations of the same extract. More specifically, soaking in a 10% extract for 24 h led to 98% seed germination and increases in shoot and root length and fresh and dry weight, while higher concentrations led to declines in those parameters [22]. Likewise, in our study, the medium concentration (2%) of both Ascophyllum nodosum and Sargassum spp. had a more positive effect than low and high concentrations in terms of speed (6.04 and 6.73), percentage of germination (87.5% and 93.8%) and vigor index I (167.7% and 216.3%) and II (648 and 896). The results of our study indicate that using Sargassum spp. extract in proper concentrations (2%) with a minimum time of soaking of 15′ can be more effective than using the most studied extract, Ascophyllum nodosum, against salinity stress (75 mM NaCl).

5. Conclusions

In the present study, the results indicate that soaking tomato seeds in seaweed extracts of various concentrations led to a significantly increased speed of germination, vigor index I and II, dry weight and average length of roots and shoots and a tendency to increase the percentage of germination. Medium concentrations led to optimum results for both Aschophyllum nodosum and Sargassum spp. in all parameters evaluated. In most studies, the seeds were treated for 24 h. Still, according to our results, a few minutes can be enough for the seaweed extract to positively affect the speed and percentage of germination, along with vigor index I and II, dry weight and the average length of roots and shoots. The best combination of concentration and seaweed species is concluded to be 2% Sargassum spp. for all parameters evaluated.

The results of our study indicate that Sargassum spp. extract in proper concentrations (2%) with a minimum time of soaking of 15′ can be more effective than the most studied extract, Ascophyllum nodosum, across various concentrations and long soaking periods against salinity stress (75 mM NaCl) during tomato germination.

In further studies, extract concentration, time of soaking (short compared to long) and various salinity levels will be examined and evaluated in order to determine the most suitable combination for different stress intensities. Treated seeds ought to be established in the field or greenhouse to determine actual results in terms of larger-scale cultivation in natural growing conditions and with longer growth stages. Furthermore, mechanisms of action, enzymic activity and biochemical responses will be studied in order to determine how and why seaweed extracts positively affect salinity tolerance. This research was the initiative for future work that is in more depth and detail.

Author Contributions

Conceptualization, methodology and data analysis, E.P. and A.K.; experimental measurements, E.P.; writing—original draft preparation, E.P.; editing, E.P. and A.K.; supervision and project administration, A.K. The final manuscript has been approved by both authors. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data Availability Statement

All data are contained within the article.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 2. Percentage of germination (%) of tomato seeds soaked for 15 min in 1, 2, 3% of Ascophyllum nodosum extracts (Algit Super) and 1, 2, 3% of Sargassum spp. extracts (Alga 300) under salinity stress. Columns (average values) with nonmatching letters indicate significant differences (p < 0.05). The red horizontal line indicates the Control H₂O value.

Figure 3. Vigor index I (%) of tomato roots and shoots soaked for 15 min in 1, 2, 3% of Ascophyllum nodosum extracts (Algit Super) and 1, 2, 3% of Sargassum spp. extracts (Alga 300) under salinity stress. Columns (average values) with nonmatching letters indicate significant differences (p < 0.05). The red horizontal line indicates the Control H₂O value.

Figure 4. Vigor index II (%) of tomato roots and shoots soaked for 15 min in 1, 2, 3% of Ascophyllum nodosum extracts (Algit Super) and 1, 2, 3% of Sargassum spp. extracts (Alga 300) under salinity stress. Columns (average values) with nonmatching letters indicate significant differences (p < 0.05). The red horizontal line indicates the Control H₂O value.

Figure 5. Dry weight (g) of tomato roots and shoots soaked for 15 min in 1, 2, 3% of Ascophyllum nodosum extracts (Algit Super) and 1, 2, 3% of Sargassum spp. extracts (Alga 300) under salinity stress. Columns (average values) with nonmatching letters indicate significant differences (p < 0.05). The red horizontal line indicates the Control H₂O value.

Figure 6. Average length (cm) of tomato roots and shoots soaked for 15 min in 1, 2, 3% of Ascophyllum nodosum extracts (Algit Super) and 1, 2, 3% of Sargassum spp. extracts (Alga 300) under salinity stress. Columns (average values) with nonmatching letters indicate significant differences (p < 0.05). The red horizontal line indicates the Control H₂O value.

Table 1. Effect of seed soaking for 15 min in distilled water compared to no soaking treatment on dry weight, speed of germination, total and average seedling length, % germination and vigor index I and II under salinity stress or not. Columns (average values ± SE) with nonmatching letters indicate significant differences (p < 0.05).

Treatment	DW	Speed of Germination	Total Length	Average Length	% Germination	Vigor Index I	Vigor Index II
Control H₂O	0.0251 ± 0.0014 a	16.65 ± 0.78 a	102.41 ± 4.91 a	5.12 ± 0.25 a	100.00 ± 0.00 a	512.07 ± 24.55 a	2.51 ± 0.135 a
Control NaCl	0.0019 ± 0.0003 b	3.18 ± 0.36 b	12.28 ± 0.53 b	1.10 ± 0.18 b	60.00 ± 8.9 b	61.39 ± 2.67 b	0.12 ± 0.029 b
Control 15′ + NaCl	0.0036 ± 0.0007 b	3.50 ± 0.45 b	16.40 ± 1.62 b	1.19 ± 0.13 b	70.00 ± 8.42 b	81.98 ± 8.10 b	0.27 ± 0.078 b

Table 2. Effect of seed soaking for 15 min in distilled water compared to no soaking treatment on dry weight, speed of germination, total and average seedling length, % germination and vigor index I and II under salinity stress. Columns (average values ± SE) with nonmatching letters indicate significant differences (p < 0.05).

Treatment	DW	Speed of Germination	Total Length	Average Length	% Germination	Vigor Index I	Vigor Index II
Control NaCl	0.0019 ± 0.0003 a	3.18 ± 0.36 a	12.28 ± 0.53 a	1.10 ± 0.18 a	60.00 ± 8.9 b	61.39 ± 2.67 a	0.12 ± 0.029 a
Control 15′ + NaCl	0.0036 ± 0.0007 a	3.50 ± 0.45 a	16.40 ± 1.62 a	1.19 ± 0.13 a	70.00 ± 8.42 a	81.98 ± 8.10 a	0.27 ± 0.078 a

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MDPI and ACS Style

Papoui, E.; Koukounaras, A. Evaluation of Ascophyllum nodosum and Sargassum spp. Seaweed Extracts’ Effect on Germination of Tomato Under Salinity Stress. Horticulturae 2025, 11, 290. https://doi.org/10.3390/horticulturae11030290

AMA Style

Papoui E, Koukounaras A. Evaluation of Ascophyllum nodosum and Sargassum spp. Seaweed Extracts’ Effect on Germination of Tomato Under Salinity Stress. Horticulturae. 2025; 11(3):290. https://doi.org/10.3390/horticulturae11030290

Chicago/Turabian Style

Papoui, Eleni, and Athanasios Koukounaras. 2025. "Evaluation of Ascophyllum nodosum and Sargassum spp. Seaweed Extracts’ Effect on Germination of Tomato Under Salinity Stress" Horticulturae 11, no. 3: 290. https://doi.org/10.3390/horticulturae11030290

APA Style

Papoui, E., & Koukounaras, A. (2025). Evaluation of Ascophyllum nodosum and Sargassum spp. Seaweed Extracts’ Effect on Germination of Tomato Under Salinity Stress. Horticulturae, 11(3), 290. https://doi.org/10.3390/horticulturae11030290

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