Global food security is based on the wheat crop worldwide (Yitayew et al., 2023) as it provides one-fifth of the total intake of calories and protein. Wheat is a staple food because it is rich in essential nutrients such as carbohydrates, which constitute the largest proportion, as well as proteins, vitamins and other minerals (Shewry and Hey, 2015). Wheat grains also contain chemical compounds similar to those found in some vegetables and fruits, which contributes to a balanced diet (Tiwari et al., 2023). However, in order to sustain agricultural systems and preserve the global environment and agriculture from pollution Recently; intense researches focused on natural aqueous extracts due to their safety and diversity of use in agriculture, such as using them as a safe alternative to pesticides (Agbo et al., 2015, Diabaté et al., 2014 and Jaoko et al., 2020; Kamson et al., 2021) or as plant growth and fitness stimulators (Al-Khafaji and Al-jubouri, 2022, Ruiz and Sanjuan, 2022) Spirulina algae considered a plant biostimulant which contains (60-70%) proteins (dry weight) (Arahou et al., 2021 and Ramírez-Rodrigues et al., 2021) and has a high content of amino acids and essential acids (Marrez et al., 2014). A little amount of fat (5-8%) makes up its dry weight, but it contains unsaturated fatty acids most notably linolenic, linoleic, stearidonic, eicosapentaenoic, docosahexaenoic and arachidonic acids in quantities of up to 30% (Grosshagauer et al., 2020; Habib et al., 2008; Marrez et al., 2014). Spirulina is a good source of several vitamins and minerals, including riboflavin, nicotinamide, pyridoxine, B6, folic acid, B12, cyanocobalamin, vitamin E and ascorbic acid (Jung et al., 2019). It contains many plant hormones including 3 indole acetic acid and cytokinin, in addition to gibberellins, abscisic acid and jasmonic acid, which are important for plant growth (Amin et al., 2009). Algal-based bio-stimulants are a rich source of bioactive molecules including phytohormones, minerals and vitamins that directly stimulate plant metabolism (Parmar et al., 2023). These substances encourage the synthesis of chlorophyll and carotenoids, which are critical for capturing light energy (Michalak and Chojnacka, 2017 and Matinha-Cardoso et al., 2023). Therefore, we notice over the past three decades, research has increasingly shifted toward the utilization of sustainable and eco-friendly compounds, such as vitamins, amino acids, seaweeds and organic substances, as viable alternatives in agricultural practices (Raju et al., 2024 and Baqir et al., 2024). As for varieties, the success of cultivating any crop depends primarily on sound management practices, superior field techniques and availability of suitable growth requirements, particularly ideal environmental factors and their adaptability to local conditions. The observed variations among cultivars regarding yield and its components can be attributed to their distinct genetic architecture and their differential response to environmental conditions (Yusuf et al., 2019). Thus, varieties differ in growth, productivity and response to environmental conditions according to their genetic sensitivity. Also, that varieties differ in their response to growth factors and productivity based on their genetic origin (Al-Hassan and Mahmood, 2019 and Al-Hasany et al., 2019). This study seeks to address the following research questions:
1. To identify the superior cultivar that exhibits the maximum physiological growth performance among the tested wheat varieties.
2. To determine the optimal concentration of Spirulina algae extract required to achieve the highest physiological growth parameters.
3. To evaluate the synergistic effects (interaction) between Spirulina extract concentrations and wheat cultivars to identify the combination that yields the most favorable growth outcomes.
4. To quantify the percentage contribution of both algal concentrations and wheat cultivars to the overall variation in physiological growth characteristics.

In the winter of 2023-2024, the experiment was conducted in the field of Field Crops Department at the College of Agricultural Engineering Sciences, University of Baghdad (Al-Jadriya), located at latitude 33 degrees north and longitude 44 degrees east. There were 3 replications of the RCBD (randomized complete block design). 4 different concentrations of Spirulina extract were the primary component (0, 2500, 5000, 7500) milligrams per liter, which were sprayed in 2 stages, first in the double node stage on the main stem and the second at flowering stage (Zadoks et al., 1974). The secondary factor comprised three wheat cultivars (Adina, Buhouth-22 and Al-Hussein). Following the completion of primary and secondary tillage operations including plowing, leveling and smoothing the experimental area was partitioned into plots and irrigation channels were established. Each experimental unit measured 2 × 2 m, containing ten 2-meter-long rows with an inter-row spacing of 20 cm and a sowing depth of 5 cm. The seeding rate was maintained at 120 kg ha^-1. Fertilization was managed according to standard recommendations (Ali et al., 2014); nitrogen was applied as urea in four split doses, while P₂O₅ was incorporated before planting at a rate of 100 kg ha^-1.  To evaluate physiological growth parameters, random samples were collected from a protected one-meter-long interior area within each plot. Measured parameters included plant height (cm), number of branches per m², plant dry weight (g), crop growth rate (g), chlorophyll content (SPAD), spike length (cm) and flag leaf area (cm²). The flag leaf area was determined based on the formula proposed by Thomas (1975):
 

Flag leaf area = Length of theflag leaf × Width at the center × 0.95

 
Statistical analysis
 
Using the statistical program GenStat, we compared the mathematical means using the L.S.D. approach at 5% probability level to see if there was a statistically significant difference. A split-plot analysis of variance was performed using a randomized block design, as per (Gomez and Gomez, 1984).

Physiological growth criteria
 
Plant height (cm)
 
Statistical analysis (Table 1) revealed significant effects for both spirulina extract concentrations and wheat cultivars, as well as their interaction. The 5000 mg L^-1 concentration achieved the highest mean plant height of 92.57 cm, significantly outperforming the other treatments with percentage increases of 14.5%, 7.9% and 5.1%, respectively. Among the cultivars, Al-Hussein exhibited a distinct superiority, recording the maximum average height of 96.60 cm, which surpassed the other varieties by 17.8 % and 14.32%. Regarding the interaction, the combination of the Al-Hussein cultivar with the 5000 mg L^-1 concentration yielded the highest interaction mean at 102.07 cm. The pronounced effect of the 5000 mg L^-1 concentration on plant height can be attributed to the rich biochemical profile of Spirulina extract. It serves as a potent source of phytohormones, specifically auxins (IAA), cytokinins and gibberellins, which are essential for stimulating cell division and internodal elongation, thereby enhancing overall plant height and vegetative density (Amin et al., 2009).  This enhancement is further supported by the strong positive correlation coefficients (Table 2) between plant height and other physiological growth parameters, including the number of branches per m² (0.667), plant dry weight (0.773), crop growth rate (0.860), chlorophyll content (0.870), spike length (0.710) and flag leaf area (0.824).




 
Total number of tillers m^-2
 
The statistical analysis of variance (Table 1) revealed significant effects of both spirulina extract concentrations and wheat cultivars on the number of tillers per square meter; however, their interaction was not statistically significant. The high concentration (7500 mg L^-1) recorded the maximum mean of 501.7 tillers m^-2, representing significant increases of 32.57 % and 15.81 % compared to the control and the 2500 mg L^-1 treatment, respectively. Notably, no significant difference was observed between the 7500 and 5000 mg L^-1 concentrations. Regarding the cultivars, Al-Hussein exhibited genetic superiority, producing the highest average of 470.6 tillers m^-2 and outperforming the other varieties by 13.73 % and 7.84%, respectively. Although the interaction effect was non-significant, the combination of the Al-Hussein cultivar with the 5000 mg L^-1 concentration yielded the highest nominal value of 537.3 tillers m^-2. The variation in tiller production can be attributed to the differential response of cultivars to growth stimulants and environmental factors based on their distinct genetic backgrounds, a finding that aligns with Al-Hasany et al. (2019) and Baqir and Zeboon (2026).
 
Dry weight at flowering (100%) g
 
As illustrated in Table 1, significant differences were observed across all studied factors and their interactions. The 5000 mg L^-1 concentration demonstrated a marked superiority, yielding the highest mean dry weight of 1628.1 g m^-2. This treatment resulted in significant percentage increases of 17.02%, 5.94% and 3.50% compared to the 0, 2500 and 7500 mg L^-1 concentrations, respectively. Among the cultivars, Al-Hussein recorded the maximum average dry weight of 1578.0 g m^-2, significantly outperforming the other varieties. The interaction analysis revealed that the combination of the Al-Hussein cultivar with the 5000 mg L^-1 concentration produced the highest dry weight at 1690.3 g m^-2, representing a 19.0 % increase over the lowest interaction mean. The observed superiority in dry matter accumulation can be attributed to enhanced energy production and metabolic efficiency, which leads to higher Crop Growth Rates (CGR) and increased fresh matter accumulation, ultimately manifesting as higher dry weight. These findings are consistent with those reported by Mollo et al. (2025). The enhancement in dry matter accumulation can be collectively attributed to the increase in leaf area, tiller density and plant height. as increased plant area resulted in improved radiant energy interception and utilization, resulting in more photosynthesis and eventually more dry matter accumulation. These findings are consistent with those reported by Singh et al. (2024). Furthermore, this trend is corroborated by the strong positive correlation coefficients (Table 2) between dry weight and other physiological parameters, including plant height (0.773), tiller number m^-2 (0.898), CGR (1.000), chlorophyll content (0.965), spike length (0.897) and flag leaf area (0.945).
 
Crop growth rate (g m^-2 day^-1)
 
Statistical analysis (Table 1) indicated significant differences across all studied factors and their interactions. The 5000 mg L^-1 concentration achieved the maximum mean crop growth rate (CGR) of 12.06 g m^-2 day^-1, representing a 9.1% increase compared to the lowest concentration. Regarding the cultivars, Al-Hussein exhibited the highest average CGR at 11.69 g m^-2 day^-1, significantly outperforming the Adina and Buhouth-22 varieties, which recorded 11.00 and 11.36 g m^-2 day^-1 a decrease of 5.9 % and 2.8% respectively, relative to Al-Hussein. The interaction analysis revealed that the combination of the Al-Hussein cultivar with the 5000 mg L^-1 concentration yielded the highest mean value of 12.52 g m^-2 day^-1. This superiority can be attributed to the fact that algal-based bio-stimulants are a rich source of bioactive molecules, including phytohormones, minerals and vitamins, which directly stimulate plant metabolism. These substances promote the synthesis of chlorophyll and carotenoids, which are essential for maximizing light energy capture. These findings align with the results reported by Michalak and Chojnacka (2017) and Parmar et al. (2023).
       
Furthermore, the variation among cultivars in terms of growth, productivity and environmental responsiveness is largely governed by their distinct genetic backgrounds, as supported by Al-Hasany et al. (2019). These results are further corroborated by the strong positive correlation coefficients (Table 2) between CGR and other growth parameters, including plant height (0.773), tiller number m^-2 (0.898), dry weight (1.000), chlorophyll content (0.965), spike length (0.897) and flag leaf area (0.945).
 
Chlorophyll content: SPAD
 
Statistical analysis (Table 1) revealed significant variations among the studied factors and their interactions. The 5000 mg L^-1 concentration recorded the maximum chlorophyll content with a mean SPAD value of 48.81. This treatment significantly outperformed the other concentrations, with percentage increases of 19.55%, 11.6% and 5.2%, respectively. Among the cultivars, Al-Hussein demonstrated superior performance, achieving the highest average SPAD value of 47.73, which surpassed the other varieties by 16.3% and 8.82%. Regarding the interaction effects, the combination of the Al-Hussein cultivar with the 5000 mg L^-1 concentration yielded the highest interaction mean of 54.11 SPAD units. The significant enhancement in chlorophyll content is likely attributed to the high concentration of amino acids and essential minerals within the extract, particularly Nitrogen (N) and Magnesium (Mg), which serve as fundamental precursors for chlorophyll biosynthesis. These results are further validated by the strong positive correlation coefficients (Table 2) between SPAD values and other physiological growth parameters, including plant height (0.870), tiller number m^-2 (0.862), dry weight at full flowering (0.965), crop growth rate (0.965), spike length (0.960) and flag leaf area (0.890).
 
The spike length cm
 
Statistical results (Table 1) indicated significant differences among the experimental variables and their interaction. The 5000 mg L^-1 concentration produced the maximum mean spike length of 12.25 cm, representing a 19.5% increase over the lowest concentration. Among the cultivars, Al-Hussein demonstrated superior performance, recording the longest average spike length at 12.46 cm, with significant increases of 17.09% and 10.5% compared to the other varieties. Regarding the interaction, the combination of the Al-Hussein cultivar with the 5000 mg L^-1 concentration yielded the highest mean interaction length of 13.96 cm. This enhancement can be attributed to the role of algae extract as a potent stimulant for plant growth and cell elongation, which aligns with the findings of Al-Khafaji and Al-Jubouri (2022) and Ruiz and Sanjuan (2022). Furthermore, the high content of amino acids in the extract provides essential building blocks for protein synthesis, thereby improving nutrient uptake and enhancing vital plant growth indicators, as noted by Marrez et al. (2014). This superiority is further supported by the strong positive correlation coefficients (Table 2) between spike length and other physiological parameters, including plant height (0.870), tiller number m^-2 (0.796), dry weight at full flowering (0.897), crop growth rate (0.897), chlorophyll content (0.835) and flag leaf area (0.835).
 
Flag leaf area cm²
 
Statistical analysis (Table 1) revealed significant variations among the studied factors and their interactions. The 5000 mg L^-1 concentration demonstrated marked superiority, yielding the maximum mean flag leaf area of 40.05 cm², which significantly outperformed all other tested concentrations. Among the cultivars, Al-Hussein recorded the highest average area at 36.73 cm², representing significant increases of 11.92% and 3.70% compared to the other varieties. Regarding the interaction effects, the combination of the Al-Hussein cultivar with the 5000 mg L^-1 concentration produced the highest interaction mean of 42.19 cm². This superiority is further corroborated by the strong positive correlation coefficients (Table 2) observed between flag leaf area and other physiological growth parameters, including plant height (0.710), tiller number m^-2 (0.848), dry weight at full flowering (0.946), crop growth rate (0.890), chlorophyll content (0.890) and spike length (0.835).
       
In light of the aforementioned results, the research questions posed in the introduction can be addressed as follows:
 
Identification of the superior cultivar
 
The results confirm that the Al-Hussein cultivar exhibited the highest mean values across all physiological growth parameters (Table 1), significantly outperforming the other varieties. This superiority is attributed to the cultivar’s inherent genetic potential and its favorable responsiveness to growth stimulants, aligning with findings by Al-Hassan and Mahmoud (2023) and Mahmood and Al-Hassan (2023). This is further validated by the strong positive correlations observed between this cultivar and all studied physiological traits (Table 2).
 
Optimal bio-stimulant concentration
 
Regarding the second research question, the 5000 mg L^-1 concentration of seaweed extract yielded the most favorable results across all physiological criteria (Table 1). Notably, increasing the concentration beyond this level (7500 mg L^-1) appeared to be economically and productively unviable, as it did not yield proportional benefits. These findings are consistent with Baqir et al., (2024) and Al-Hassan et al. (2024). The 5000 mg L^-1 treatment accounted for the highest relative contribution to growth at 29%, compared to 20%, 25% and 26% for the 0, 2500 and 7500 mg L^-1 concentrations, respectively.

 
The optimal interaction treatment
 
In response to the third question, the interaction between the Al-Hussein cultivar and the 5000 mg L^-1 seaweed extract concentration proved to be the optimal combination, achieving the maximum averages for all physiological characteristics. Proportionally, the Al-Hussein variety contributed 36% to the total performance, surpassing Buhouth-22 (33%) and Adina (31%). The effectiveness of this specific combination is reinforced by the robust positive correlation coefficients presented in Table 2.

The application of Spirulina platensis extract as a foliar bio-stimulant significantly enhanced the vegetative performance of wheat across multiple physiological parameters, most notably chlorophyll content. Among the evaluated genotypes, the Al-Hussein cultivar exhibited a superior responsive capacity to the treatment. The results identify 5000 mg L^-1 as the optimal concentration for maximizing physiological growth indicators. These findings underscore the potential of Spirulina-based bio-stimulants as a sustainable agricultural strategy to improve crop vigor. Further investigation is recommended to evaluate the efficacy of this bio-stimulant under diverse environmental stress conditions to support long-term agricultural sustainability.

The present study was supported by NO ONE.
 
Disclaimers
 
The views and conclusions expressed in this article are solely those of the author and do not necessarily represent the views of their affiliated institutions. The author is responsible for the accuracy and completeness of the information provided, but do not accept any liability for any direct or indirect losses resulting from the use of this content.
 
Informed consent
 
No animals were used in this study.

The author declares that there are no conflicts of interest regarding the publication of this article. No funding or sponsorship influenced the design of the study, data collection, analysis, decision to publish, or preparation of the manuscript.