Evaluation of seed germination of Nepeta haussknechtii, N. pogonosperma and N. glomerulosa subsp. staffina in response to water potential using the hydrotime model

Salehi, Parvin; Javadi, Hamideh; R, L; Fallah, Leila; M, A

doi:10.22092/ijrfpbgr.2025.366957.1466

Evaluation of seed germination of Nepeta haussknechtii, N. pogonosperma and N. glomerulosa subsp. staffina in response to water potential using the hydrotime model

Document Type : Research Paper

Authors

¹ rifr

² m

³ Research Institute of Forests and Rangelands, Tehran, I.R.Iran

⁴ u

10.22092/ijrfpbgr.2025.366957.1466

Abstract

Abstract
Background and Objectives:
Iran's arid and semi-arid regions span over 1.5 million km², accounting for nearly 92% of the country's total area. Drought is one of the most critical abiotic stresses affecting these areas. Due to challenges faced in breeding improved drought-tolerant genotypes, the domestication and cultivation of drought-resistant plants have emerged as the best solution to prevent the extinction of wild species and restore pastures. Selecting drought-tolerant plants during the germination stage is crucial for successful plant establishment. Seed germination is the first and most important developmental stage, that is influenced by genetic and environmental factors. The hydrotime model describes the relationship between water potential (ψ) and seed germination rate and percentage. This model quantifies the rate of germination progression (hydrotime constant: θ_H), the uniformity of germination (standard deviation of the base water potential: σ_ψb), and the stress tolerance of germination [base osmotic potential for 50% germination: ψ_b(50₎]. These indicators can be used to determine seed vigor and seed dormancy and the effects of treatments on seed viability. This study aimed to use hydrotime model to predict of germination response of three medicinal species of Nepeta haussknechtii, N. pogonosperma, and N. glomerulosa subsp. staffina to water potential.

Methodology:
For each species, six water potential levels (0, -0.3, -0.6, -0.9, -1.2, and -1.5 MPa) were applied using a completely randomized design with three replications in 1402 at the Seed Technological Research Laboratory of the Natural Resources Gene Bank, Iran. Seed germination of species was recorded daily at a temperature of 25°C. Since no germination was observed at a potential level of -1.5 MPa, this treatment was excluded from the analysis. The hydrotime model was then fitted to the germination data, and the hydrotime constant (θ_H), base osmotic potential for 50% germination ψ_b(50), and standard deviation of the base water potential (σ_ψb) were quantified.

Results:
The analysis of variance revealed significant effects of drought (at five levels of 0, -0.3, -0.6, -0.9, and -1.2 MPa) on all seed germination characteristics of all three Nepeta species (P<0.05). The hydrotime model results showed that the germination rate under drought stress was higher in N. haussknechtii (θ_H=48.32) than in N. glomerulosa (θ_H=52.13) and N. pogonosperma (θ_H=56.57). Furthermore, the germination uniformity of N. haussknechtii (σ_ψb=0.18) was higher than that of N. glomerulosa (σ_ψb=0.39) and N. pogonosperma (σ_ψb=0.24). In terms of drought resistance, N. pogonosperma (ψ_b(50)=-1.006) exhibited greater resistance compared to N. haussknechtii (ψ_b(50)=-0.69) and N. glomerulosa (ψ_b(50)=-0.77).
Conclusion:
Osmotic stress significantly impacted the germination pattern, timing, and rate of Nepeta seeds. Since seed quality concerning drought resistance determines the speed and uniformity of germination, the output of the hydrotime model, including parameters θ_H, σ_ψb, and ψ_b(50), was effective in predicting germination percentages under drought stress conditions. Drought-tolerant genotypes were identified using the hydrotime model, with N. pogonosperma being the most resistant species, followed by N. haussknechtii and N. glomerulosa. The hydrotime model is a tool in breeding programs for identifying high-efficiency genotypes' resistance to stress conditions.

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