Microorganisms are essential for maintaining soil health and plant growth. Therefore, microbial fertilizers composed of bacteria and fungi have been explored as environment-friendly alternatives that promote natural plant growth and replace synthetic fertilizers, which are overused and detrimental to crops [1] . When examining the role of microbial fertilizers in crops, it is important to focus on their effect on germination, which is defined as the process by which a dormant seed resumes metabolic activity and begins to develop into a seedling. This process begins when the dry seed absorbs water and ends with the elongation of the embryonic axis. This is a critical stage in the plant life cycle as it determines the success of establishing a new plant. Many factors influence germination, including availability of water and oxygen, temperature, and light [2] . Numerous studies have been conducted on the use of cyanobacteria and microalgae as biofertilizers and growth promoters, with positive results. For example, cyanobacteria have been shown to secrete growth promoters such as auxins, cytokinins, and gibberellins into their extracellular polymeric substances (EPS) [3] . These chemicals play key roles in regulating plant growth, metabolism, and development.

Research has also suggested that soaking seeds in cyanobacterial suspensions enhances water uptake, helping to create ideal conditions for seed inoculation and colonization. This stimulates seed germination and increases the seedling growth.

Spirulina, a tiny blue-green unicellular alga classified as a cyanobacterium, is an example of a cyanobacterium. This alga is typically found in freshwater and saltwater environments, and is known for its agricultural benefits. Spirulina secretes extracellular polymers that improve soil water retention. This enhances water-use efficiency.

Spirulina properties also help improve soil quality and promote beneficial microbial activity in the root zone. The EPS produced also facilitates seed colonization, thereby enhancing germination under harsh environmental conditions. In addition to improving germination, Spirulina also enhances early root growth by stimulating auxin production and water absorption. Extracellular polysaccharides promote soil aggregation and microbial colonization, creating a protective environment around the seeds [3] . These properties make Spirulina particularly useful in less-than-ideal conditions, enhancing seedling vigor and stress tolerance.

Through these mechanisms, Spirulina can partially improve plant growth, thereby contributing to the synthesis and inhibition of moisture in water-constrained areas.

In addition to Spirulina, fungi are another example of microorganisms that can influence germination and promote plant growth, particularly yeast, a single-celled microorganism classified in the kingdom of fungi. It reproduces by budding or binary fission and is widely distributed in various environments including soil, plants, and water.

Yeast plays important roles in many biological processes, including promoting plant growth, improving soil health, and enhancing plant growth and stress resistance.

Some strains produce growth regulators such as indole-3-acetic acid (IAA) and gibberellins, which stimulate root elongation and seedling establishment. Additionally, yeast helps solubilize phosphate, improve nutrient bioavailability, and release ammonia, which improves soil fertility. Yeast also improves microbial balance in the root zone by producing siderophores, which contribute to iron sequestration and inhibit plant pathogens [4] . Additionally, its enzymatic activity enhances the decomposition of organic matter, thereby improving the availability of nutrients for seed germination. These functions contribute to better seedling establishment and resilience during the early stages of growth [1] .

Agricultural efficiency is affected by carbon source availability, temperature, and microbial competition.

In summary, yeast is beneficial for agriculture as an alternative to chemicals [4] .

In addition to the benefits of agriculture, yeast and Spirulina contain many highly beneficial nutritional elements. A study confirmed that Spirulina contributes significantly to public health by reducing harmful cholesterol, supporting liver function, and weight loss [5] .

‏It is an iron-rich food source that is beneficial to humans. This supports the development of foods rich in probiotics and prebiotics in the digestive system [6] .

Yeast is a living organism known for its ability to support digestive and immune systems. It provides essential vitamins and minerals to the human body. Yeast is also involved in the manufacture of antibiotics and cancer treatment. [7] .

It also contributes significantly as a protein source and nutritional supplement to humans and animals. They are also widely used in the food industry. Yeast proteins recycle materials, such as waste, and preserve the environment. Recognizing the benefits of yeast among consumers improves their quality of life and prevents disease [8] .

In this study, we investigated the effects of soaking tomato seeds in S. platensis and S. cerevisiae suspensions on germination.

This study aimed to evaluate the effect of soaking in yeast and Spirulina suspensions on germination compared with no treatment. ‏Despite their proven potential, direct comparisons between Spirulina and yeast on seed germination, especially in uncontrolled environments, are limited.

This study hypothesizes that soaking tomato seeds in Spirulina or yeast suspensions enhances germination compared with untreated seeds.

To test this hypothesis, the experimental groups were divided as follows:

This experiment was conducted at home under simple and consistent conditions to evaluate the preliminary effects of Spirulina and yeast suspensions on tomato seed germination. The temperature during the experiment was set to approximately 25˚C, and all Petri dishes were placed in a dark, quiet area to simulate standard germination conditions. Given the home-based setting, it was not possible to precisely control environmental variables, such as humidity and airflow, which is a limitation of this study. However, efforts were made to maintain similar conditions for all treatments to ensure consistency and minimize bias.

This study evaluated the effects of yeast and Spirulina suspensions on germination, particularly the germination of tomato seeds under controlled conditions at home. Seeds were soaked in suspensions or distilled water as a control. After soaking for 24 h, the seeds were transferred to sterile 9 cm Petri dishes covered with filter paper. Each group contained five dishes each containing 10 seeds and 5 ml of distilled water, to preserve the humidity level of the dish. Seed germination was observed for 9 d at 25˚C in the dark. Seeds were considered to have germinated when the radicle reached a minimum diameter of 2 mm.

Tomato seed germination was monitored for nine days across three treatments: Spirulina, yeast, and control. The daily germination count is presented in ( Table 1 ), which shows faster and more consistent germination in the Spirulina group starting on day 3.

Visual differences between treatments can be observed in ( Figure 1(a) ), which shows the initial state of the tomato seeds in all three treatments. The control group (C5), yeast group (Y5), and spirulina group (S5) ( Figure 1(b) ) showed clear differences in seed development after nine days of incubation.

The results of this experiment indicated that the suspension had a positive effect on the germination of tomato seeds, especially Spirulina Arthrospira platensis. Seeds soaked in Spirulina had the highest germination rate (96%) and highest germination rate (13.87). The shortest germination time was 3.59 days. These findings align with previous studies, given that Spirulina contains auxins, cytokinins, and extracellular polymeric substances (EPS), which enhance germination [3] .

‏Spirulina enhances germination by improving soil water availability, nutrient uptake, and organic compound interactions, thereby creating a favorable environment for seed development [20] . The EPS produced helps retain water around the seed, supporting the rapid hydration and activation of metabolic pathways. Furthermore, these compounds enhance microbial colonization and improve soil structure, which can lead to improved oxygen availability and enzymatic activity during early seed development [3] [21] .

‏Seeds treated with Saccharomyces cerevisiae also showed better results than the control group, with germination rates of 86% and a germination speed of 11.81%, respectively. This is attributed to the ability of yeast to produce growth regulators such as indole-3-acetic acid (IAA) and gibberellins [1] [4] , which stimulate root elongation and cell division. Yeast also contributes by releasing ammonia, solubilizing phosphate, and producing siderophores and hydrolytic enzymes that enhance microbial interactions and protect seedlings from pathogens [22] .

‏The biological mechanisms underlying the observed effects can be explained by the physiological properties of both Spirulina and yeast. Spirulina enhances germination by stimulating hormone-regulated pathways, particularly via auxins and cytokinins, which are essential for initiating cell division and elongation of the radicle [3] [21] . It also secretes extracellular polysaccharides that aid in water retention and serve as a carbon source for beneficial microbes, improving seed–soil interactions. In contrast, yeast enhances germination by producing IAA, improving nutrient solubilization, and indirectly suppressing harmful fungi, thus creating a microbially favorable environment for germination [4] [22] .

‏Recent findings by Parmar et al. [21] support the outcomes of the current study. Their review emphasized that microalgae, such as Spirulina, serve as multifunctional plant growth additives by producing phytohormones, such as auxins and gibberellins, enhancing nutrient availability, and promoting root colonization. These mechanisms are particularly valuable under abiotic stress, reinforcing the biostimulant potential of Spirulina in sustainable agriculture. These results are also consistent with those of previous studies, such as those by Chua et al. [3] and Xu et al. [20] , highlighting the role of Spirulina as a biostimulant under salinity and environmental stress. The difference in performance between the Spirulina and yeast groups in this study suggests that Spirulina may be more effective under the tested conditions, although both treatments outperformed the control.

‏These comparisons confirm that even under non-laboratory conditions, bio-agents such as Spirulina and yeast can significantly affect early plant development. Post-hoc analyses (e.g., Tukey’s HSD) are recommended in future studies to validate observed differences between treatments.

Further studies under control and field conditions are required to confirm these trends.

The experiment showed that the group treated with Spirulina was more effective than the other groups, resulting in a higher germination rate and faster growth because of Spirulina’s growth-enhancing characteristics. Yeast can also be used as a biofertilizer and has a positive effect on germination. However, there is still a need for further studies at different concentrations and conditions, as this study focused only on a single concentration for each treatment.