Influence of post-maturation on the color of the seed coat of Ziziphus lotus (L.) Lam. and on their germination capacity

ABSTRACT:

Ziziphus lotus (L.) Lam. is one of the species targeted by restoration programs aimed at combating desertification. It is characterized by pronounced seed dormancy which limits its natural regeneration. This study aims to evaluate the effectiveness of various treatments to break this dormancy in freshly harvested seeds and those that have matured naturally. Seeds were divided into two lots: one was stored in a freezer (-18 °C) and the other was stored at room temperature for 12 months. The seeds underwent several pretreatments. The results showed that natural post-ripening caused a gradual change in seed color from yellow beige to dark brownish black. This color change was strongly related to the germination rate which increased from 28% (freshly harvested seeds) to 80% (post-ripened seeds, p < 0.001). The most effective treatments for dormant seeds were a combination of cold stratification and soaking in GA₃ 74%, followed by cold stratification 70%, soaking in water for 72 hours 67% and soaking in GA₃ 64%. However, post-ripened seeds had a significantly higher germination rate particularly when soaked in water for 48 hours 94%. The remarkable dormancy of these seeds is physiological in nature and their natural post-ripening is the key factor in breaking it.

Index terms:
germination; pretreatments; scarification; seed dormancy; stratification

RESUMO:

Ziziphus lotus(L.) Lam. . é uma das espécies visadas pelos programas de restauração destinados a combater a desertificação. Caracteriza-se por uma dormência pronunciada das sementes, o que limita a sua regeneração natural. Este estudo tem como objetivo avaliar a eficácia de vários tratamentos para quebrar essa dormência em sementes recém-colhidas e naquelas que amadureceram naturalmente. As sementes foram divididas em dois lotes: um foi armazenado em um freezer (-18 °C) e o outro foi armazenado à temperatura ambiente durante 12 meses. As sementes foram submetidas a vários pré-tratamentos. Os resultados mostraram que o pós-amadurecimento natural causou uma mudança gradual na cor das sementes, de bege amarelado para preto acastanhado escuro. Essa mudança de cor estava fortemente relacionada à taxa de germinação, que aumentou de 28% (sementes recém-colhidas) para 80% (sementes pós-amadurecidas, p < 0,001). Os tratamentos mais eficazes para sementes dormentes foram uma combinação de estratificação a frio e imersão em GA₃ 74%, seguida de estratificação a frio 70%, imersão em água por 72 horas 67% e imersão em GA₃ 64%. No entanto, as sementes pós-amadurecidas tiveram uma taxa de germinação significativamente maior, particularmente quando imersas em água por 48 horas 94%. A notável dormência dessas sementes é de natureza fisiológica e seu pós-amadurecimento natural é o fator-chave para quebrá-la.

Termos para indexação:
germinação; pré-tratamentos; escarificação; dormência de sementes; estratificação

INTRODUCTION

Desertification is a major environmental issue in Algeria, affecting nearly 32 million hectares of arid and semi-arid steppe (Ministry of the Environment and Renewable Energies and United Nations Development Programme, 2023). These ecosystems, traditionally used for extensive grazing, are increasingly degraded due to recurrent droughts, unsustainable land-use practices and growing pastoral pressure (Boukerker et al., 2021; Oubadi et al., 2024). The resulting impacts include biodiversity loss, reduced rangeland productivity and heightened socio-economic vulnerability (Othering and Belonging Institute, 2024). In response, ecological restoration based on native woody species adapted to water scarcity has become a priority strategy, consistent with sustainable development objectives (Réquier-Desjardins and Bied-Charreton, 2006; International Union for Conservation of Nature, 2020).

Such challenges are not unique to Algeria. Tropical dry forests are among the most threatened biomes globally, characterized by marked rainfall seasonality and xerophytic vegetation (Mesa-Sierra et al., 2025). The Caatinga of northeastern Brazil, covering approximately 850,000 km², is a representative example of seasonally dry tropical forest (Queiroz et al., 2017). It shares ecological similarities with North African semi-arid regions, including severe water deficits and nutrient-poor soils (Pennington et al., 2009; Santos et al., 2011). In both contexts, understanding the regeneration processes of native woody species, particularly seed dormancy mechanisms, is essential for effective restoration.

Among the species suitable for such programs, the genus Ziziphus (Rhamnaceae) is of particular interest. Widely distributed in tropical and subtropical regions, it includes species valued for their edible fruits and ecological functions in agro-sylvo-pastoral systems (Muhammad et al., 2022). Ziziphus lotus (L.) Lam., a thorny shrub 2-5 m tall, is widely distributed across the Mediterranean basin. In Algeria, it dominates steppe and pre-Saharan woody formations due to its strong drought tolerance, deep root system and capacity for vegetative regeneration (Nedjraoui, 2003; Aidoud et al., 2006).

The exceptional ecophysiological qualities of Z. lotus, combined with its multiple traditional uses (food, medicinal, forage), considerably enhance its interest in ecological restoration programs (Kheloufi, 2020; Bencheikh et al., 2023). Despite this considerable potential, the exploitation of this native species comes up against a major obstacle: the pronounced dormancy of its seeds, which drastically limits natural regeneration and nursery propagation (Maraghni et al., 2010). This dormancy results from a combination of physical (highly lignified endocarp and impermeable) and physiological (presence of endogenous germination inhibitors) factors. Under natural conditions, dormancy is frequently overcome by endozoochory - a process in which the passage of seeds through the digestive tract of herbivores simultaneously ensures mechanochemical scarification and spatial dispersal (Rubalcava-Castillo et al., 2020). Nevertheless, this natural strategy remains difficult to reproduce on the scale of ecological restoration programs.

Germination is one of the critical phases in a plant’s life cycle, as it marks the transition from dormancy to active growth, shaping reproduction, population dynamics, and species dispersal into new habitats (Baskin and Baskin, 2014). Many plants in arid and semi-arid regions exhibit dormancy - physical, physiological, or combined - which can delay germination even under favorable conditions (Bewley et al., 2013). This delay represents an adaptive strategy allowing seeds to wait for optimal survival conditions (Donohue et al., 2010). Seed storage is a determining factor in the evolution of physiological and morphological seed characteristics; among the most relevant visual indicators, seed coat color reflects the internal biochemical state, degree of maturation, viability, and dormancy intensity of seeds (Zemouri et al., 2020; Moulay et al., 2023).

Post-maturation - the period of post-harvest physiological transformation - appears to be a key factor in the gradual breaking of dormancy (Bewley et al., 2013; Baskin and Baskin, 2014). This temporal process induces changes in integumentary permeability, internal hormonal balances and sensitivity to germinative stimuli. However, the ways in which post-maturation duration interacts with the efficacy of different pre-germination treatments (mechanical or chemical scarification, imbibition, stratification, hormonal stimulation) remain insufficiently documented in Z. lotus. In this context, the present study aims to characterize the comparative efficacy of different pre-treatments on dormancy breaking and improvement of germination quality parameters of Z. lotus seeds, considering their physiological state (freshly harvested versus post-matured seeds). The applied objective is to develop and optimize simple, reproducible and economically viable pre-germination protocols, suitable for mass production of robust seedlings for reforestation and ecological restoration programs in semi-arid Algerian zones.

MATERIAL AND METHODS

Plant material

Sampling: Mature Z. lotus fruits were harvested in November 2019 from 10 randomly selected mature shrubs distributed over an area of approximately 5 hectares (Figure 1). The fruits were mixed to ensure the genetic representativeness of the sample and then divided into two lots. The first lot was stored in a freezer (-18 to -20 °C) in kraft paper bags as whole fruits; the seeds from this lot were considered freshly harvested (FH) (Lenoir et al., 1983; Gutterman and Nevo, 1994; Djabeur et al., 2010). The second lot was stored at room temperature (20 to 25 °C) for 12 months, also as whole fruits, to study the effect of post-maturation on germination; the seeds from this lot were considered post-matured (PM). Seed extraction was carried out simultaneously with the germination tests for both lots. Kernels were obtained by manually opening the fruits and rinsing out the pulp. After drying (24-48 h), the lignified endocarps were mechanically fractured using controlled pressure to release the seeds without damaging them.

Figure 1
Wild jujube shrub Ziziphus lotus (L.) Lam. in its natural habitat, Oran region, Algeria (August 2019). Photo: Authors.

Climate of the study area: The sampling site is located in the Oran region, of northwest Algeria, at geographical coordinates 35°34’09.7”N / 0°33’21.2”W, at an altitude of 357 meters, approximately 25 kilometers southeast of Oran city. It is part of the semi-arid bioclimatic stage with cool winters, having a rainfall-thermal index (Emberger’s Q₂) of 28 to 32, consistent with Stewart’s (1975) classification. The climate in Oran is Mediterranean, with an annual average temperature near 18 °C, a maximum in summer of around 40 °C, and often a winter minimum near 3 °C (National Meteorological Office [NMO], 2020). The average annual rainfall is approximately 400 mm, which is concentrated over a period from October to April, followed by a sustained dry phase of 5 to 6 months. This summer drought is exacerbated by hot, dry Chergui winds that increase local water-stress conditions (ONM, Es Senia station, Oran). This area, representative of the vegetative semi-arid Mediterranean variation of Z. lotus, is a suitable natural environment to examine germination strategies of seeds of this species in realistic conditions of water and heat stress (Le Houérou, 1995).

Morphometric study: Biometric analyses of 100 specimens from the standardized sample (freshly harvested whole fruits, kernels, and seeds) were performed using a caliper. Length was measured along the primary longitudinal axis (base to apex) while diameter was measured in the median equatorial region. Weight measurements of seeds were made using an analytical balance (precision of ± 0.001 g) on fresh seeds after harvest (Figure 2).

Figure 2
Morphometric measurements of Ziziphus lotus fruit components. (A) fruits; (B) kernels; (C) seeds.

Germination tests

Prior to germination testing, non-viable, damaged, or empty seeds were carefully sorted by flotation in water. This method is based on the difference in density between full (sinking) and empty (floating) seeds (Downie and Bergsten, 1991; Audinet, 1993). To prevent microbial contamination, the seeds (from which the endocarp had been removed) were disinfected by immersion in a 1% sodium hypochlorite solution for 5 minutes, followed by three rinses in sterile distilled water. They were then placed in sterile Petri dishes (90 mm in diameter) on cotton moistened in sterile distilled water, and incubated at 30 ± 2 °C, the optimum temperature for Z. lotus germination, consistent with the findings of Zouaoui et al. (2013) who showed significant germination rates at this temperature under controlled experimental conditions.

Applied pre-treatments: In addition to the controls (untreated seeds), sixteen different pre-treatments were applied to the two seed lots: those kept in the freezer were considered freshly harvested (FH) (Lenoir et al., 1983; Gutterman and Nevo, 1994; Djabeur et al., 2010), and those kept at room temperature were considered post-matured (PM) (Lenoir et al., 1983; Gutterman and Nevo, 1994; Djabeur et al., 2010).

Imbibition in cold water: immersion of seeds in distilled water at room temperature (20-25 °C) for three increasing durations: 24h, 48h and 72h.

Immersion in hot water: immersion of seeds in hot water (80 °C) for 10 minutes, followed by immediate cooling to room temperature.

Mechanical scarification: controlled abrasion of the integument with P150) sandpaper for 1 minute, avoiding the micropylar region to preserve embryonic integrity.

Chemical scarification: soaking the seeds in pure sulfuric acid (H₂SO₄ 96%) for four progressive durations (2, 5, 10, 15 minutes), followed by immediate and abundant rinsing with distilled water until neutralization is complete to remove all traces of sulfuric acid.

Germination in the presence of GA₃: seeds were germinated on cotton moistened with a 10^-3 M solution of gibberellic acid (GA₃).

Stratification: Seeds were kept at a temperature of 5 ± 1 °C in complete darkness, on moist cotton, for four different durations (15, 30, 45 and 70 days).

Combination treatments: Sequential application of two synergistic approaches: 1/Stratification for 30 days in humid cold conditions (5 °C), followed by germination at 30 °C in the presence of GA₃ at 10^-3M. 2/ Chemical scarification (soaking in H₂SO₄ for 10 minutes), followed by germination of these scarified seeds in the presence of GA₃ at 10^-3M.

Germination control

Germination was monitored daily for 15 days. Seeds were considered germinated once the radicle had pierced the integument and reached a minimum length of 2 mm (Côme, 1970; International Seed Testing Association, 2003). Each germination test was carried out on 100 seeds distributed over 4 Petri dishes (25 seeds per dish), enabling calculation of the final germination percentage (FGP) and mean germination time (MGT), as well as statistical analyses.

The percentage of germination was calculated according to the following equation, as described by Czabator (1962) and Scott et al. (1984): $Germination\%=seedsgerminated/totalseeds*100$.

Final germination percentage was calculated as the mean ± SE of four replicates, each consisting of 25 seeds. Additionally, the mean germination time (MGT) was determined using the formula described by Brenchley and Probert (1998): $MGT=\sum DN/\sum N$, where N is the number of seeds germinated on day D, and D is the number of days since sowing.

Statistical analysis

All statistical analyses were carried out using IBM SPSS Statistics for Windows, version 25.0. Prior to conducting the analyses, data were evaluated to determine if they met the assumptions for the use of parametric tests. Unifactorial analysis of variance (ANOVA) was used to analyse seed germination due to scarification treatments and application time. Levels of significance used follow standard statistical conventions: Not significant (NS): p > 0.05; Significant *: 0.01 < p ≤ 0.05; Very significant **: 0.001 < p ≤ 0.01; Extremely significant ***: p ≤ 0.001

Results are shown as means ± standard error. A confidence level of 95% (α = 0.05) was used for all analyses.

RESULTS

Morphometric results presented in Table 1 reveal that Z. lotus from the study area (Oran region, north-west Algeria) produces small, globose fruits (1.25 × 1.20 cm) with an average weight of 0.85 g. Kernels account for a substantial 42% of total fruit weight. Seeds, very small in size (0.5 × 0.46 cm), represented only 4.4% of total fruit weight.

Table 1
Morphometric characteristics (length, width, and weight) of fruits, kernels, and seeds of Ziziphus lotus. Values are expressed as mean ± standard deviation (SD), with minimum and maximum values.

		Mean ± SD	Minimum	Maximum
Fruits	Length (cm)	1.25 ± 0.14	1.00	1.50
	Width (cm)	1.20 ± 0.32	0.80	1.10
	Weight (g)	0.85 ± 0.16	0.54	1.81
Kernels	Length (cm)	0.89 ± 0.07	0.70	1.10
	Width (cm)	0.82 ± 0.06	0.40	1.00
	Weight (g)	0.36 ± 0.06	0.21	0.51
Seeds	Length (cm)	0.50 ± 0.07	0.40	0.70
	Width (cm)	0.46 ± 0.07	0.20	0.60
	weight (g)	0.037 ± 0.005	0.024	0.045

• *Note. N = 100 for each component.

The seeds were initially light brown to yellowish beige (Figure 3A), which is characteristic of recently harvested Z. lotus from this area. As shown in Figure 3, the lot gradually and uniformly darkened after being stored for a year at room temperature (20-25 °C), with the seeds turning brownish and eventually dark brown (Figure 3B).

Figure 3
Variation in the color of Ziziphus lotus seeds. (A) Freshly harvested seeds; (B) Post-matured seeds (stored for 1 year at ambient temperature).

Post-matured seeds (stored at room temperature) show a highly significant germination rate (P < 0.001) compared with freshly harvested seeds (Figure 4A). The final germination percentage (FGP) of post-matured seeds reached 80%, compared with freshly harvested seeds (28%, Figure 4A). This increase in germination percentage was accompanied by an increase in mean germination time (MGT) from 1.35 days to 4.14 days, indicating a more extended germination period (Figure 4B). These results show that Z. lotus seeds from the study area are dormant at the time of harvest, as evidenced by the low germination rate. This dormancy disappears after 12 months of post-maturation at room temperature.

Figure 4
Comparison of germination traits between freshly harvested and post-matured seeds of Ziziphus lotus. (A) Final Germination Percentage; (B) Mean Germination Time. Data represent mean ± SE. Means followed by different letters are significantly different (P < 0.001).

Soaking seeds in water progressively improved germination capacity, particularly in freshly harvested seeds. Final germination percentage (FGP) increased with soaking duration, (P < 0.01 for all times) (Table 2). For post-matured seeds, the improvement in FGP compared with the control was less pronounced but significant, with an optimum at 48h (94% vs. 80% for the control, P < 0.05) (Table 2). Mean germination time (MGT) decreased with increasing imbibition time, indicating an acceleration of the germination process (Table 2). Based on these results, the optimal duration of soaking in water was 72 h for freshly harvested seeds, with an FGP of 67% and an MGT of 1.75 days. For post-matured seeds, the optimum duration of soaking was 48 h, yielding an FGP of 94% and an MGT of 2.77 days.

Table 2
Effect of water soaking seeds on final germination percentage (FGP) and mean germination time (MGT) of Ziziphus lotus seeds at harvest and post-maturity. Values represent means ± standard error (SE). Statistical significance (S) between control (untreated seeds) and treated seeds was assessed using P-values: not-significant (P > 0.05, ns), significant (P < 0.05, *), highly significant (P < 0.01, **), and very highly significant (P < 0.001, ***).

	Duration of soaking in water	Final Germination Percentage (FGP) (% ± SE)	S	Mean Germination Time (MGT) (days ± SE)	S
Freshly harvested seeds	Control	28.00 ± 1.41	/	1.35 ± 0.07	/
	24 h	58.00 ± 2.83	**	3.73 ± 0.18	***
	48 h	61.00 ± 4.24	**	2.83 ± 0.34	**
	72 h	67.00 ± 1.41	**	1.75 ± 0.05	*
Post-matured seeds (stored for 1 year at ambient temperature)	Control	80 ± 0.00	/	4.14 ± 0.27	/
	24 h	90 ± 2.82	*	3.39 ± 0.24	ns
	48 h	94 ± 2.82	*	2.77 ± 0.35	*
	72 h	89 ± 4.24	ns	3.19 ± 0.22	ns

Soaking in hot water at 80 °C for 10 minutes had a negative impact on seed viability, as shown in Table 3. In freshly harvested seeds, the final germination percentage (FGP) dropped significantly from 28% to 16% (P < 0.05), while the mean germination time (MGT) increased from 1.35 to 2.69 days (P < 0.05). This effect was more noticeable in post-matured seeds, where FGP fell sharply from 80% to 10% (P < 0.001) and MGT decreased slightly from 4.14 to 3.41 days. (Table 3). According to these results, hot water had no beneficial effect on seed germination.

Table 3
Effect of soaking seeds in hot water at 80 °C for 10 minutes on final germination percentage (FGP) and mean germination time (MGT) of Ziziphus lotus at harvest and post-maturity. Values are presented as means ± standard error (SE). Statistical significance (S) between control (untreated seeds) and treated seeds was assessed using P-values: not-significant (P > 0.05, ns), significant (P < 0.05, *), and very highly significant (P < 0.001, ***).

		Final Germination Percentage (FGP) (% ± SE)	S	Mean Germination Time (MGT) (days ± SE)	S
Freshly harvested seeds	Control	28,00 ± 1,41	/	1,35 ± 0,07	/
	Hot water	16,00 ± 2,82	*	2,69 ± 0,66	*
Post-matured seeds (stored for 1 year at ambient temperature)	Control	80,00 ± 0,00	/	4,14 ± 0,27	/
	Hot water	10,00 ± 2,82	***	3,41 ± 0,47	ns

Mechanical scarification did not improve germination and was even detrimental to post-matured seeds (Table 4). In freshly harvested seeds, FGP remained low (22% vs. 28% in the control, NS), while MGT increased slightly (1.96 vs. 1.35 days in the control). In contrast, post-matured seeds showed a marked reduction in germination capacity (30% vs. 80% in the control), despite a faster MGT (2.94 vs. 4.14 days). (Table 4).

Table 4
Effect of mechanical scarification on final germination percentage (FGP) and mean germination time (MGT) of Ziziphus lotus seeds at harvest and post-maturity. Values represent means ± standard error (SE). Statistical significance (S) between control (untreated seeds) and treated seeds was assessed using P-values: not-significant (P > 0.05, ns), significant (P < 0.05, *), and very highly significant (P < 0.001, ***).

		Final Germination Percentage (FGP) (% ± SE)	S	Mean Germination Time (MGT) (days ± SE)	S
Freshly harvested seeds	Control	28.00 ± 1.41	/	1.35 ± 0.07	/
	mechanical scarification	22.00 ± 2.82	ns	1.96 ± 0.19	ns
Post-matured seeds (stored for 1 year at ambient temperature)	Control	80.00 ± 0.00	/	4.14 ± 0.27	/
	mechanical scarification	30.00 ± 1.41	***	2.69 ± 0.30	*

Chemical scarification with H₂SO₄ was ineffective and became harmful as exposure duration increased. Short treatments (2-5 min) had no discernible effect on FGP (~28%) in freshly harvested seeds, while longer exposures (10-15 min) decreased it to 15% (Table 5), with MGT values varying between 2.00 and 2.21 days. More sensitive seeds were post-matured ones; after 15 minutes of exposure, FGP gradually dropped from 80% in the control to 38% (Table 5), while MGT stayed mostly constant (Table 5). These results indicate that Z. lotus seeds do not exhibit physical dormancy; rather, their seed coats are fragile and vulnerable to both mechanical and chemical scarification.

Table 5
Effect of soaking in pure sulfuric acid on final germination percentage (FGP) and mean germination time (MGT) of Ziziphus lotus seeds at harvest and post-maturity. Values represent means ± standard error (SE). Statistical significance (S) between control (untreated seeds) and treated seeds was assessed using P-values: not-significant (P > 0.05, ns), significant (P < 0.05, *), and highly significant (P < 0.01, **).

Seeds	Duration of soaking in H2SO4	Final Germination Percentage (FGP) (% ± SE)	S	Mean Germination Time (MGT) (days ± SE)	S
Freshly harvested seeds	Control	28.00 ± 1.41	/	1.35±0.07	/
	2 minutes	28.00 ± 2.82	ns	1.31 ± 0.02	ns
	5 minutes	26.00 ± 1.41	ns	2.00 ± 0.00	*
	10 minutes	20.00 ± 1.41	*	2.10 ± 0.14	*
	15 minutes	15.00 ± 0.00	*	2.21 ± 0.30	*
Post-matured seeds (stored for 1 year at ambient temperature)	Control	80 ± 0.00	/	4.14 ± 0.27	/
	2 minutes	76.00 ± 1.41	ns	3.31 ± 0.30	ns
	5 minutes	66 ± 2.83	*	3.08 ± 0.55	ns
	10 minutes	56 ± 2.12	**	3.58 ± 0.71	ns
	15 minutes	38 ± 2.83	**	3.38 ± 1.02	ns

GA₃ treatment at 10^-³ M greatly improved the germination of freshly harvested seeds, doubling FGP from 28% to 64% (Table 6). MGT slightly increased in response to this stimulation. On the other hand, post-matured seeds did not respond to hormonal treatment (FGP: 80% vs. 82%), and their MGT increased marginally to 5.5 days (Table 6).

Table 6
Effect of gibberellicacidon final germination percentage (FGP) and mean germination time (MGT) of Ziziphus lotus seeds at harvest and post-maturity. Values represent means ± standard error (SE). Statistical significance (S) between control (untreated seeds) and treated seeds was assessed using P-values: not-significant (P > 0.05, ns), significant (P < 0.05, *), and highly significant (P < 0.01, **).

	Germination on GA3	Final Germination Percentage (FGP) (% ± SE)	S	Mean Germination Time (MGT) (days ± SE)	S
Freshly harvested seeds	Control	28.00 ± 1.41	/	1.35 ± 0.07	/
	Germination with GA3	64.00 ± 0.00	**	2.68 ± 0.18	*
Post-matured seeds (stored for 1 year at ambient temperature)	Control	80 ± 0.00	/	4.14 ± 0.27	/
	Germination with GA3	82 ± 2.82	ns	5.03 ± 0.66	ns

Depending on seed maturity, stratification at 5 °C had different effects. After 30 days, the fresh-harvested seeds reached their maximum efficiency, with 70% germination as opposed to 28% in the control (Table 7). The germination process has synchronized, as evidenced by the increase in MGT from 1.35 to 3.76 days. Extended periods (45-70 days) resulted in an extension of MGT and a progressive decrease in the germination percentage (30% and 25%, respectively). Post-matured seeds, on the other hand, reacted poorly to stratification; their FGP dropped dramatically from 30% at 15 days to 8% at 70 days (Table 7). A slowdown in germination speed coincided with this decline, as MGT rose from 4.14 to 6.91 days.

Table 7
Effect of stratification on final germination percentage (FGP) and mean germination time (MGT) of Ziziphus lotus seeds at harvest and post-maturity. Values represent means ± standard error (SE). Statistical significance (S) between control (untreated seeds) and treated seeds was assessed using P-values: not-significant (P > 0.05, ns), significant (P < 0.05, *), highly significant (P < 0.01, **), and very highly significant (P < 0.001, ***).

	Duration of cold stratification	Final Germination Percentage (FGP) (% ± SE)	S	Mean Germination Time (MGT) (days ± SE)	S
Freshly harvested seeds	Control	28.00 ± 1.41	/	1.35±0.07	/
	15 days	54.00 ± 1.41	**	2.00 ± 0.00	*
	30 days	70.00 ± 2.82	**	3.76 ± 0.01	***
	45 days	30.00 ± 2.82	*	3.07 ± 0.10	**
	70 days	25.00 ± 0.70	ns	3.41 ± 0.04	***
Post-matured seeds (stored for 1 year at ambient temperature)	Control	80 ± 0.00	/	4.14 ± 0.27	/
	15 days	30.00 ± 2.82	**	6.91 ± 0.41	**
	30 days	18.00 ± 2.83	***	6.45 ± 0.07	**
	45 days	15.00 ± 1.41	***	6.00 ± 0.19	**
	70 days	08.00 ± 0.00	***	5.06 ± 0.08	**

Complex synergies were found between the treatments, and these differed according to the seeds’ physiological condition (Table 8). The combination of stratification and GA₃ at 10^-³ M was the most effective in boosting germination in freshly harvested seeds, increasing it to 74% (P < 0.01) from 28% in the control, with a moderately extended MGT (2.56 ± 0.17 days, P < 0.05). However, GA₃ in combination with chemical scarification at 10^-³ M was less successful, resulting in a longer MGT (3.17 ± 0.14 days, P < 0.01) and 48% germination (P < 0.01). Both combinations significantly decreased the germination capacity of post-matured seeds, which went from 80% in the control to approximately 49% to 50% (P < 0.01) for both treatments. Chemical scarification + GA₃ did not change MGT (4.34 ± 0.81 days, ns), while stratification + GA₃ sped up germination a little (3.07 ± 0.68 days, P < 0.05).

Table 8
Effect of combined treatment on final germination percentage (FGP) and mean germination time (MGT) of Ziziphus lotus seeds at harvest and post-maturity. Values represent means ± standard error (SE). Statistical significance (S) between control (untreated seeds) and treated seeds was assessed using P-values not-significant (P > 0.05, ns), significant (P < 0.05, *), and highly significant (P < 0.01, **).

	Combined treatment	Final Germination Percentage (FGP) (%±SE)	S	Mean Germination Time (MGT) (days±SE)	S
Freshly harvested seeds	Control	28.00 ± 1.41	/	1.35 ± 0.07	/
	Stratification + GA3	74.00 ± 2.82	**	2.56 ± 0.17	*
	Scarification chimic + GA3	48.00 ± 1.41	**	3.17 ± 0.14	**
Post-matured seeds (stored for 1 year at ambient temperature)	Control	80 ± 0.00	/	4.14 ± 0.27	/
	Stratification + GA3	49 ± 4.24	**	3.07 ± 0.68	*
	Chemical scarification + GA3	50 ± 2.82	**	4.34 ± 0.81	ns

DISCUSSION

The analyzed fruits showed high variability in weight (0.54-1.81 g), attributable to inter-individual variability and local pedoclimatic conditions, which are the primary drivers of fruit development in Z. lotus (Boussaid et al., 2018). This range is typical of the genus, where the pulp-to-stone ratio constitutes an essential parameter for varietal characterization and assessment of consumption potential (Khadivi et al., 2023). Finally, the low seed proportion observed is consistent with the reproductive strategies of the genus, which balances sexual reproduction with vegetative propagation via suckering to ensure population persistence in arid environments (Gálvez-Morros et al., 2021).

Throughout our study, we noticed that post-harvest storage leads to a darkening of seeds, shifting from beige to brown, probably through oxidation of phenolic compounds (Bhattarai et al., 2024). This evolution comes with a clear increase in germination rate (from 28% to 80%) and an extension of average germination time, indicating a gradual release from physiological dormancy likely due to internal biochemical changes (Finch-Savage and Bassel, 2016; Sanches et al., 2025). This natural post-maturation process optimizes germinative potential through degradation of physiological inhibitors (Hilhorst, 2007), modification of coat permeability that facilitates water imbibition and entry of chemical signals necessary for germination (Nonogaki, 2014), and progressive enzymatic activation that promotes mobilization of energy reserves in the embryo (Nonogaki et al., 2010), a phenomenon also observed in other species of the genus Ziziphus (Kheloufi et al., 2018).

Soaking freshly harvested Z. lotus seeds in water at room temperature proved very effective in breaking dormancy (Table 2). This result is explained particularly by rehydration of embryonic tissues, activation of initial cellular metabolism necessary for germinative startup (Nonogaki et al., 2010), as well as by seed coat softening linked to degradation of pectic compounds (Nonogaki, 2014). In post-matured seeds, the effect remains positive, these having already partly overcome limitations related to imbibition. Comparable observations have been reported for Ziziphus spina-christi, where prolonged soaking improves germination, although requiring longer durations (72-96 hours), which reflects interspecific differences in coat permeability determined by morphological and genetic characteristics of the seed coat (Baskin and Baskin, 2014).

Soaking in hot water at 80 °C for 10 min has a drastically negative effect, reducing the final germination percentage down to 10%, suggesting protein denaturation, cellular membrane alteration, and enzymatic inactivation (Batra et al., 2023). This thermal vulnerability, also observed in other species of the genus Ziziphus (Kheloufi et al., 2018), reflects an evolutionary adaptation to arid environments where seeds must survive under extreme thermal conditions (Lewandrowski et al., 2021). The marked susceptibility observed in post-matured seeds may indicate increased vulnerability of embryonic tissues following after-ripening, potentially associated with hormonal shifts in the ABA/GA balance (Barakat et al., 2023) and a progressive reduction in heat-protection mechanisms (Batra et al., 2023).

Mechanical scarification also failed to improve germination and even significantly reduced FGP, especially in post-matured seeds (from 80% to 30%), presumably caused by embryonic damage (Bewley et al., 2013) as well as seed contamination due to opportunistic secondary infections occurring at sites damaged by treatment (Baskin and Baskin, 2014). This differential sensitivity suggests that dormancy is not of seed coat origin and that post-maturation further decreases resistance to mechanical damage. Such a result, making the method unsuitable for Z. lotus contrasts with the variable results observed in other hard-coated species, where the effectiveness of coat scarification strongly depends on the intensity of applied treatment (Kheloufi et al., 2018; Duarte and Cardoso, 2024), reflecting interspecific variations in coat structure and sensitivity to mechanical damage.

The effectiveness of chemical scarification by sulfuric acid (H₂SO₄) strongly depends on exposure duration: short immersions hardly improve germination, while prolonged exposures reduce viability attributable to acid hydrolysis of cellular components and osmotic disruption (Baskin and Baskin, 2014). This progressive deterioration confirms the greater susceptibility of post-matured seeds to chemical scarification. While studies on related species show that optimal concentrations and exposure durations effectively favor germination (Kheloufi et al., 2018), suggesting that Z. lotus presents coats particularly fragile to chemical treatments.

Germination in gibberellic acid (GA₃) significantly stimulated germination of freshly harvested seeds (FGP of 64%) due to activation of hormonal pathways, stimulation of hydrolytic enzymes (α-amylase, proteases) mobilizing nutritive reserves (Bewley, 1997), and antagonism of inhibitory abscisic acid (Barakat et al., 2023). The absence of notable effect in post-matured seeds is explained by the fact that post-maturation has naturally reduced this physiological dormancy, indicating that their physiological dormancy had already been largely alleviated and making exogenous GA₃ supply less necessary (Finch-Savage and Bassel, 2016; Sinhorini et al., 2025). This phenomenon of variable effectiveness according to physiological state is also reported in other species where gibberellins show differential effectiveness according to the degree of initial dormancy (Park et al., 2024).

Our results show that 30-day cold stratification significantly improves germination in freshly harvested seeds (70%), likely due to hormonal and enzymatic shifts during dormancy release (Barakat et al., 2023). Conversely, it proved detrimental to after-ripened seeds (<30%), possibly inducing secondary dormancy via thermal stress (Finch-Savage and Footitt, 2017), consistent with the thermophilic character of Z. lotus, which exhibits optimal germination at 35 °C (Maraghni et al., 2010). These findings align with Kheloufi et al. (2020), who reported 83% germination after 120-day stratification at 5 °C.

Such variability in stratification requirements - driven by physiological state, ecological origin, and phylogeny (Baskin and Baskin, 2014; Rosbakh et al., 2020; Carta et al., 2022) - reflects an adaptive strategy against frost risk (Fernández-Pascual et al., 2021). Ultimately, this differential response indicates that post-matured seeds do not benefit from additional treatments and underscores the importance of adapting protocols to the seeds’ initial physiological state. Furthermore, the differentiated stratification requirements observed between Saharan and Mediterranean populations of Z. lotus suggest precise evolutionary adjustments to contrasting local thermal regimes.

Combined treatments (30-day stratification + GA₃ or chemical scarification + GA₃) produce contrasting results: significant improvement in freshly harvested seeds (up to 74% FGP) through complementary synergistic effect (Kheloufi et al., 2018), whereby the combination of treatments enhances overall germination efficiency beyond what either treatment achieves alone - a finding consistent with Schmidt (2000), who similarly reported that synergistic interactions between pre-treatments yield superior germination outcomes compared to single treatments (Kheloufi et al., 2018). In post-matured seeds, we observe a reduction in viability (FGP ≈ 50%) attributable to signal overload or cumulative stress, a phenomenon of “over-treatment” described in literature on seed vigor (Finch-Savage and Bassel, 2016). This degradation points to a change in the stress tolerance mechanisms linked to seed aging and shows how post-matured seeds are more susceptible to the cumulative stresses of multiple treatments.

Ziziphus species differ in their ecological adaptations, with Z. lotus presenting relatively moderate dormancy reflecting its adaptations to Mediterranean and semi-arid environments (Kheloufi et al., 2018). The role of natural dispersers influences these mechanisms: animal digestion often facilitates germination through gentle enzymatic scarification, explaining the variability of responses to artificial scarifications (Rubalcava-Castillo et al., 2020). This co-evolution fits within the framework of “bet-hedging” strategies (Pausas et al., 2022), where species diversify their reproductive strategies to maximize survival in variable environments (Willis et al., 2014).

CONCLUSIONS

In conclusion, this study successfully characterized the combined dormancy of Z. lotus and identified effective strategies to alleviate it. Moderate treatments - dry post-harvest storage, water soaking, cold stratification, and gibberellic acid - effectively broke dormancy, while extreme treatments such as scarification and thermal shock impaired germination and reduced viability. In both cases, effectiveness was strictly conditioned by seed physiological state, confirming that treatment protocols must be tailored accordingly.

For practical propagation and ex situ conservation, we recommend cold stratification for fresh seeds and dry ambient storage for post-matured ones. Future research should investigate intraspecific variation between Mediterranean and Saharan populations to further refine dormancy management guidelines for this species.

ACKNOWLEDGMENTS

The authors thank all those who contributed to this work, the University of Science and Technology of Oran Mohamed Boudiaf (USTO-MB), and the Ministry of Higher Education and Scientific Research. We also extend our heartfelt thanks to our families for their constant support and encouragement.

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• DATA AVAILABILITY
  Additional data will be made available by the authors upon reasonable request.

Edited by

• Editor:
  Lausanne Soraya de Almeida

Data availability

Additional data will be made available by the authors upon reasonable request.

Publication Dates

• Publication in this collection
  20 Apr 2026
• Date of issue
  2026

History

• Received
  08 Oct 2025
• Accepted
  06 Mar 2026