Document Type : Research Article
Authors
Department of Mechanical Engineering of Biosystems, Faculty of Agriculture, University of Jiroft, Jiroft, Iran
10.22067/jam.2026.100498.1519
Abstract
Introduction
Fennel (Foeniculum vulgare Mill.) is a widely cultivated medicinal and aromatic plant valued in the food, pharmaceutical, and traditional medicine industries for its phosphorus, potassium, calcium, and fatty acid content, as well as its antimicrobial, antifungal, hypolipidaemic, and hepatoprotective properties. Because germination directly determines field stand density and crop establishment, rapid and uniform germination is essential for efficient production. Seed-coat impermeability and endogenous growth-inhibiting compounds, however, frequently delay water uptake and reduce germination vigour, particularly in the arid and semi-arid regions typical of fennel cultivation.
Non-chemical physical pretreatments, including cold plasma, ultrasound, and magnetic fields, have emerged as environmentally friendly alternatives capable of enhancing germination without damaging the seed. Cold plasma generates reactive oxygen and nitrogen species that modify seed-surface roughness and hydrophilicity, facilitating water absorption. Ultrasound induces cavitation and pressure oscillations that create micro-channels in the seed coat, improving mass transfer. Magnetic fields interact with polar molecules and cellular ions, potentially stimulating metabolic and enzymatic activity. Although the independent effects of each technology have been studied in several crops, information on their combined and interactive effects on fennel seed germination remains limited. This study therefore aimed to evaluate, model, and optimise the germination and early seedling-growth indices of fennel seed exposed to cold plasma pretreatment followed by simultaneous magnetic field ultrasound treatment, using Response Surface Methodology.
Materials and Methods
A combined magnetic field-ultrasound generation system was designed and constructed at the University of Jiroft, Iran. The ultrasound unit operated at 20 kHz, and the magnetic-field unit generated magnetic intensities up to 450 mT. A separate low-pressure cold-plasma reactor, operating at 15,000 V between two high-voltage electrodes, was used for seed pretreatment.
Experiments followed a “3 × 3 × 3” factorial design based on a completely randomised design with three replications (27 treatments, 81 experimental units). The independent variables were cold plasma pretreatment time (CPt: 0, 1, 2 min), ultrasound power (USp: 0, 60, 120 W), and magnetic field intensity (MFi: 150, 300, 450 mT). Pretreated seeds were incubated on moistened filter paper at 25 ± 1 °C for 14 days. Daily counts allowed for the calculation of seven responses: germination percentage (GP), germination rate (GR), mean germination time (MGT), shoot length (SL), root length (RL), shoot weight (SW), and root weight (RW). ANOVA and Duncan's test (P < 0.05) were performed in SPSS 26; second-order polynomial models relating the independent variables to each response were developed and optimised via a desirability-function approach in Design-Expert 13, and response surfaces and heatmaps were generated in MATLAB R2017a.
Results and Discussion
Cold plasma pretreatment time was the most influential factor (p < 0.01) for all seven responses, followed by ultrasound power, which was also highly significant for every trait. Magnetic field intensity was significant only for shoot weight and had a negligible effect on the remaining indices. The CPt × USp interaction was significant for most traits, confirming a synergistic relationship between plasma and ultrasound, whereas interactions involving the magnetic field were largely non-significant.
All responses followed a non-linear (hormetic) pattern with respect to plasma exposure: 1 min of pretreatment produced the best performance, while extending exposure to 2 min reduced germination and growth, likely due to oxidative stress and membrane damage at higher doses. Germination percentage reached 85–87% following 1 min of cold plasma pretreatment combined with 60 W ultrasound, compared with 65–68% after 0- and 2-min plasma pretreatments.The same combination produced the highest germination rate (~6 seeds day⁻¹), the shortest mean germination time (5-6 days versus 8-9 days without plasma), and the greatest shoot length (42-48 mm), root length (25-26 mm), shoot weight (~37-38 mg), and root weight, indicating a clear synergy between plasma-induced surface modification and ultrasound-induced cavitation. Ultrasound at 120 W did not outperform 60 W in most cases, and magnetic field intensity produced no consistent significant trend for most traits.
Second-order polynomial models with significant linear and quadratic terms for plasma (and, for several traits, ultrasound) adequately described all responses, confirming an optimum plasma dose beyond which benefits diminish. Multi-response optimisation via the desirability function identified an overall optimum at approximately 1.04 min cold plasma, 63.7 W ultrasound, and 231 mT magnetic field, yielding a predicted GP of 84.13%, GR of 5.71 seeds day⁻¹, and MGT of 5.60 days, with an overall desirability of 0.859.
Conclusion
Cold plasma pretreatment was the dominant factor governing fennel seed germination and early growth, exhibiting a hormetic response with an optimum near 1 minute. Ultrasound, particularly at 60 W, acted as an effective complementary treatment, and its interaction with plasma produced synergistic improvements across all indices. Magnetic field intensity played only a minor, largely non-significant role. The developed models and the desirability-based optimum (≈1.04 min plasma, 63.7 W ultrasound, 231 mT magnetic field) provide a validated, chemical-free strategy for enhancing fennel seed germination and early growth, offering practical guidance for improving stand establishment in commercial fennel production.
Acknowledgement
The authors would like to express their sincere gratitude to the University of Jiroft for providing financial and technical support for this research.
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