The germination of seeds from many indigenous plant species presents significant challenges because of complex dormancy mechanisms and specific ecological requirements (Mkhwanazi, Maseko & Dube 2024; Nonogaki 2014). A comprehensive understanding of a species’ life history, native habitat and physiological behaviour is essential to inform effective seed management, propagation techniques and the enhancement of seed vigour and genetic integrity during cultivation (Nonogaki 2014). Each plant species possesses distinct germination cues such as temperature, photoperiod, moisture levels and even microbial interactions that have evolved as ecological adaptations to ensure survival under optimal conditions (Mkhwanazi et al. 2024; Nonogaki 2014; Talluri, Narayani & Babu 2024). Recent findings also emphasise the role of eco-physiological approaches, including water treatments and microbial inoculation, which mimic natural germination triggers and enhance seedling establishment in stress-prone environments (Mkhwanazi et al. 2024).

African indigenous leafy vegetables (AILVs), including Amaranthus thunbergii and Cleome gynandra, have long served local communities as accessible sources of nutrition and traditional medicine (Dlamini et al. 2010; Mkhwanazi et al. 2024; Moatshe-Mashiqa et al. 2024). Despite their cultural and nutritional significance, these species remain largely underutilised and are often harvested from the wild, leading to concerns over sustainability (Moatshe-Mashiqa et al. 2024). According to Raselebe (2017), there are over 53 000 underexploited indigenous plant species globally, many of which face threats from habitat degradation, climate change, overharvesting and illegal trade. Furthermore, the cultivation of such species is limited by low germination rates, largely attributable to physiological seed dormancy and the lack of standardised propagation protocols (Moatshe-Mashiqa et al. 2024).

Studies in Botswana and Nigeria confirm that pre-sowing treatments such as hot water soaking, acid scarification and mechanical abrasion significantly improve germination in indigenous species like Acacia and Tamarindus indica, underscoring the potential for similar interventions in leafy vegetables (Abdulrahman et al. 2023; Mojeremane, Rasebeka & Mathowa 2014).

Seed dormancy, while evolutionarily advantageous in natural ecosystems, poses a major barrier to domestication and commercial cultivation (Debbarma & Priyadarshinee 2017). Overcoming these dormancy traits through appropriate pre-treatment methods is therefore critical to improving germination success and enabling broader adoption of indigenous crops. Empirical research has shown that pre-sowing treatments such as scarification, hydropriming, temperature manipulation and chemical stimulants can significantly influence seed behaviour, emergence rates and early seedling vigour (Baatuuwie et al. 2019; Makuvara, Marumure & Chidoko 2022; Mkhwanazi et al. 2024; Moatshe-Mashiqa et al. 2024; Olatunji, Maku & Odumefun 2013).

In parallel, increased scientific attention on the health-promoting properties of indigenous vegetables has revealed their potential as functional foods. Species like Amaranthus are rich in provitamin A carotenoids (β-carotene), antioxidants (lutein) and other nutraceuticals that combat micronutrient deficiencies and age-related diseases (Dlamini et al. 2010). Similarly, C. gynandra, which is widely consumed in Southern Africa, is a vital source of vitamins A and C, calcium and iron. These leafy vegetables are traditionally prepared with complementary species such as Vigna spp. and Solanum nigrum to enhance flavour and nutritional content (Van den Heever & Venter 2007). Beyond nutrition, recent studies highlight their phytochemical diversity, including flavonoids and glucosinolates, which contribute to anti-inflammatory and antimicrobial properties, positioning them as candidates for functional food development (Moatshe-Mashiqa et al. 2024).

Given the urgent need for resilient, nutrient-dense crops in the face of food insecurity, promoting the domestication of indigenous vegetables such as A. thunbergii and C. gynandra through improved seed germination practices represents a viable pathway towards sustainable agriculture in Botswana and beyond. This study investigates the comparative effectiveness of different pre-treatment methods on seed germination and early growth performance in these two species, with the aim of identifying optimal strategies for their successful cultivation and wider integration into agroecological systems. By integrating traditional knowledge with modern seed biology, this research contributes to the broader agenda of conserving biodiversity while enhancing food and nutritional security in sub-Saharan Africa.

The degree of dormancy and the effectiveness of treatment techniques vary across species, influenced by factors such as pre-treatment method, duration and concentration. These differences are critical in determining germination matrix responses. A significant comparative effect (p < 0.05) was observed between A. thurnbegii and C. gynandra in terms of germination performance (Table 1). Notably, A. thurnbegii outperformed C. gynandra in GP%, imbibition period, germination period, GS and plant height, indicating more rapid and efficient seed activation. However, no significant difference (p > 0.05) was found in seed vigour metrics such as number of leaves and germination value (Table 1). Despite this, A. thurnbegii produced significantly (p < 0.05) taller plants, suggesting enhanced post-germination growth (Table 1). Similar findings were reported in other indigenous leafy vegetables (Rhaman, 2025; Hossain et al. 2005; Moatshe-Mashiqa et al. 2024), where species-specific dormancy mechanisms dictate pre-treatment success (Mangena 2022).

The comparative germination responses of A. thurnbegii and C. gynandra under different seed pre-treatment methods indicated that GP% of both species was significantly (p < 0.05) affected by pre-treatment methods (Figure 1). Overall, Amaranthus consistently outperformed Cleome across all pre-treatment methods, with exception of the control group, where no significant difference was observed (p < 0.05) (Figure 1). This highlights the species-specific nature of dormancy-breaking mechanisms.

Among the treatments, pre-heating proved most effective for Amaranthus, enhancing GP% by 16.66% compared to the control (Figure 2). In contrast, Cleome did not benefit significantly from either pre-heating or pre-chilling, both of which resulted in a 6.67% decline in GP%. This suggests that these pre-treatment methods may not be suitable for enhancing Cleome’s germination. This is supported by Mangena (2022), who emphasised that C. gynandra requires chemical priming (e.g. gibberellic acid or potassium nitrate) rather than thermal or chilling treatments to overcome dormancy.

Seed pre-treatment methods significantly (p < 0.05) influenced germination value for both A. thurnbegii and C. gynandra (Figure 3), reflecting differences in germination rate and percentage. Overall, pre-heating improved germination quality in both species, confirming thermal treatment as effective for breaking dormancy in indigenous seeds. Amaranthus showed a notably higher germination value than Cleome, which corresponded with more vigorous early root development. This aligns with findings by Moatshe-Mashiqa et al. (2024), who reported enhanced seedling growth and vigour following a 90-s pre-heat. Thermal treatments also improved drought resilience and nutrient uptake, boosting biomass and yield (Rhaman, 2025; Taylorson & Hendricks 1969). Temperatures above 20 °C deactivate phytochrome, accelerating dormancy break, whereas pre-chilling delays the process (Taylorson & Hendricks 1969). Pre-chilled seeds reduced germination effectiveness, particularly in Amaranthus, suggesting cold-induced stress, as supported by Chen et al. (2021) who advised against extended pre-chill treatment for this species because of stress-induced suppression of germination.

Seed pre-treatment methods significantly (p < 0.05) influenced imbibition (Figure 4) and germination period (Figure 5) in both A. thurnbegii and C. gynandra. Pre-chilling notably extended imbibition time doubling it compared to the control while pre-heating reduced the imbibition time (Figure 4). However, the pre-heated seeds did not significantly differ from the control, indicating accelerated seed hydration. Across all treatments, Amaranthus imbibed water faster than Cleome, with the shortest duration occurring under pre-heating (3 days) and the longest under pre-chilling (6 days). This pattern suggests that cold-induced dormancy may hinder water uptake, especially in Cleome. Seed hydration, a vital trigger for physiological and biochemical changes leading to germination, was further delayed by pre-chilling, particularly in Cleome, which required up to 10 days to complete imbibition. According to Zembele and Ngulumbe (2022) and Taylorson and Hendricks (1969), cold stress suppresses germination by stabilising the far-red absorbing form of phytochrome, which prolongs dormancy despite water availability.

Following imbibition, Amaranthus consistently demonstrated faster germination across treatments although differences were not statistically significant (Figure 5). This may indicate lower innate dormancy in Amaranthus, reducing dependence on pre-treatment. Notably, pre-heated Cleome seeds showed a 30% improvement in germination period over the control, implying that thermal pre-treatment may help overcome physiological dormancy and activate early metabolic processes.

Overall, thermal treatments, particularly pre-heating, enhanced seed responsiveness and GS more effectively than pre-chilling, with Amaranthus showing greater receptiveness to heat-based stimulation. Dos Rois (2023) and Moatshe-Mashiqa et al. (2024), who observed similar benefits in pre-heated Amaranthus accessions, support these findings while highlighting the limited effectiveness of chilling for species with physiological dormancy such as Cleome.

In terms of the impact of seed pre-treatment methods on seedling height of Amaranthus and Cleome, pre-heating resulted in a 46% – 49% increase in plant height compared to the control (p < 0.05), while pre-chilling reduced height by 39% – 67% across both species (Figure 6). The enhanced growth was attributed to the improved germination index, speed and value, reduced imbibition time when seeds were exposed to pre-heating compared to pre-chilling (Figure 1 to Figure 5). This suggests that thermal pre-treatment stimulates early growth through enhanced enzyme activity and hormonal signalling, particularly gibberellins, while cold exposure inhibits metabolic functions, inducing stress (Zembele & Ngulumbe 2022).

These findings reflect the ecological adaptation of Amaranthus and Cleome as warm-season plants native to tropical and subtropical Southern Africa. Seeds from such climates are naturally responsive to heat cues, which signal favourable growing conditions. Pre-heating emulates soil warming at the onset of the season, triggering enzymatic and metabolic pathways that facilitate germination (Reed, Bradford & Khanday 2022). Specifically, it activates amylase for mobilising stored nutrients and promotes gibberellin synthesis for cell elongation (Chen et al. 2021; Reed et al. 2022). Additionally, warmer temperatures soften the seed coat, improving water uptake and radicle emergence. At 90 s of pre-heating, Amaranthus reached a germination peak of 90% and showed marked increases in seedling height indicating optimal thermal responsiveness. However, prolonged exposure beyond this threshold diminished germination, pointing to potential heat-induced stress.

Germination percentage was significantly (p < 0.05) affected by the interaction among pre-treatment methods and duration (Figure 7). Pre-heating seeds for 90 s resulted in the highest germination rate, Amaranthus reached 85%; while Cleome achieved 75%, highlighting the efficacy of thermal stimulation in seed activation. This is attributed to heat-induced modifications to the seed coat, such as wax removal and surface cracking, which improve gaseous exchange and water uptake (Olatunji et al. 2013). However, the results demonstrate that the effectiveness of heat treatment is duration dependent. Extended exposure can damage the embryo, leading to reduced germination (Amusa 2011; Fredrick et al. 2017; Makuvara et al. 2022). The current study corroborates these findings, showing a slight decline in germination under prolonged heat, likely because of thermal stress. Similarly, prolonged chilling led to a 10% – 13% decrease in germination from control levels for both species, indicating low tolerance to cold-induced dormancy. As also shown in Figure 4 and Figure 5, chilling slowed imbibition and germination, further supporting this conclusion.

There was a significant interaction (p < 0.05) between pre-treatment methods and their duration on key germination metrics (Table 2). Cleome recorded the lowest germination value following a 72-h pre-chill, whereas Amaranthus achieved the highest value with a 90-s pre-heat. A similar trend was observed in plant height, where the shortest and tallest seedlings emerged from Amaranthus pre-chilled for 24 h and pre-heated for 90 s, respectively.

These results highlight that short-duration pre-heating substantially boosts germination and seedling vigour, while prolonged pre-chilling suppresses development, suggesting low cold tolerance in both species, particularly Cleome. Amaranthus showed greater responsiveness and resilience to thermal treatments, tolerating longer exposure with improved outcomes. This is likely because of its reduced imbibition period, which shortened germination time and enhanced germination index, value and vigour (Figure 2 to Figure 5). Baatuuwie et al. (2019) proved the findings by reporting a positive correlation between germination rate and seedling growth explaining that the pre-treatment contributes not only to germination but also to the survival and establishment of seedlings.

Overall, pre-chilling consistently reduced germination performance, particularly in C. gynandra, suggesting that warm-season species native to tropical regions are more responsive to thermal cues than to cold stress.

According to Schmidt (2000), seed coat–imposed dormancy develops during seed maturation and drying, often delaying germination. The presence of an impermeable seed coat poses a key challenge to germination in indigenous plants, which can be mitigated through thermal pre-treatment. Pre-heating seeds has proven to be an effective pre-sowing strategy, enhancing germination and establishment by removing the cuticle and part of the palisade layer, thereby breaking dormancy (Zembele & Ngulumbe 2022).

The study highlights the importance of evaluating seed quality prior to sowing, with particular attention to species-specific dormancy levels, optimal temperature ranges and effective pre-treatment methods. Thermal stimulation, notably pre-heating for short durations, proved to be the most effective approach for enhancing germination rates, seedling vigour and early growth, especially in Amaranthus. Conversely, prolonged chilling consistently hindered performance, highlighting the sensitivity of these warm-season species to cold-induced dormancy. The findings reinforce that selecting appropriate pre-treatment strategies tailored to the ecological background of each species can significantly improve propagation success. Furthermore, seed storage conditions and shelf life play a critical role in conservation programmes, ensuring seed viability and quality from harvest through to sowing. Integrating thermal pre-treatment into seed handling protocols can contribute to improved seedling establishment and resource efficiency, laying the foundation for robust production and sustainable plant development.

The results of this study carry broader implications for strengthening seed systems and advancing the propagation of indigenous crops. By establishing species-specific protocols, research can generate practical knowledge that elevates underutilised crops into mainstream agricultural practice. Policy frameworks that recognise and support indigenous species within national seed standards will ensure their inclusion in formal seed systems, while development initiatives can leverage these findings to promote community seed banks, farmer training and local seed enterprises. Such integration enhances food system resilience, diversifies dietary options and safeguards biodiversity. Ultimately, the adoption of scientifically validated pre-treatment methods, particularly thermal stimulation, can serve as a catalyst for more efficient seed systems, bridging conservation and production goals. Aligning these practices with research agendas, supportive policies and farmer-centred development programmes will not only improve propagation success but also empower communities, strengthen local economies and contribute to sustainable agricultural transformation.