Iranian Journal of Seed Research

Extended Abstract
Introduction: White Astragalus (Astragalus gossypinus Fisherr.) is one of the valuable plants for producing gum, which is of critical importance in soil conservation and the economy of the country. This plant is propagated by seed; its seeds are in the natural state of dormancy. Therefore, recognizing the factors affecting dormancy and creating optimal conditions for seed germination of this plant is necessary for the cultivation and reclamation of rangelands. This study was conducted with the aim of finding the best treatment for breaking the dormancy and improving seed germination under various chemical and physical treatments.
Materials and Methods: The experiment was carried out as a factorial based on a completely randomized design with four replications at the gene bank of cereal and legume Lab of Ilam University, 2017. The factors included two levels of scarification chemical (with and without sulfuric acid (H₂SO₄) for 10 minutes), three levels of stratification (control, moist chilling at +4 °C and dry chilling -20 °C), potassium nitrate in two levels (zero and 1% KNO₃) and gibberellic acid in two levels (zero and 5 ppm GA₃). Germination indices including germination percentage, germination rate, seedling and radicle length, seedling fresh weight and vigor index were measured.
Results: Initial assessment of vital indices in seed such as germination and primary growth showed that the simultaneous application of scarification by sulfuric acid and moist chilling at +4 °C has the most impact on removing dormancy and increasing germination percentage. The highest germination rate was observed in moist chilling at +4 °C, which was 32.19 percent more than that of the control treatment. Scarification by sulfuric acid reduced the mean germination time in moist chilling at +4 °C. Scarification by sulfuric acid increased the fresh weight of the seedling by 55.25 percent, compared with the control. Pre-treatments with potassium nitrate undre control conditions, moist chilling at +4 °C and dry chilling at -20 °C increased the fresh weight of seedlings, at 52.66, 30.94 and 17.18 percent, respectively. Application of potassium nitrate increased root length by about 60.7 percent, compared with control. The highest radicle length (78.71 mm) was obtained when the seed was treated with sulphuric acid with wet chilling at 4 ° C for two weeks, which was 30 percent higher than control. The highest seedling length (84.88 mm) was obtained in scarification with sulfuric acid, wet chilling, and potassium nitrate and gibberellic acid. The highest seed vigor index (61.85 %) was observed in the treatment of scarification with sulfuric acid under moist chilling, and pre-treatments of gibberellic acid and potassium nitrate.
Conclusions: In general, it can be concluded that seed dormancy of Astraglus gossypinus involves both physical and physiological dormancy. The best treatment for removing the dormancy of this species seems to be scarification with sulfuric acid for 10 minutes puls concentrated stratification in moist chilling at +4 °C for two weeks.
 
 
Highlights:

1. Determination of the optimal seed dormancy techniques of white Astragalus for the purpose of increasing seed germination percentage.
2. Comparison of the efficiency of different dormancy breaking techniques.
3. The combined effect of sulfuric acid, chilling and priming with gibberellic acid and potassium nitrate on germination indices.

Extended abstract
Introduction: Seed germination and seedling establishment are the most sensitive stages in the life cycle of a plant. Among the environmental factors, the water potential is an important factor affecting the seed germination of various plants. This research aims to evaluate the effects of water potential on germination components and quantify the effect of water potential on the germination responses of Thymus medicinal plant seeds.
Materials and Methods: A factorial experiment was carried out in the form of a completely randomized design with four replications in the laboratories of the Department of Agronomy and Plant Breeding, Ilam University in the winter of 2023. The factors of the experiment include two types of Thymus (Thymus daenensis and Thymus vulgaris) and water potential stress induced by polyethylene glycol (PEG-6000) at six levels (0, -0.1, -0.3, -0.5, -0.7, and -0.9 MPa).
Results: The results showed that by decreasing the water potential to -0.1, -0.3, -0.5, and -0.7 MPa, the seed germination percentage in T. daenensis decreased by 8.43, 43.26, 61.80, and 88.76, respectively and in T. vulgaris it decreased by 19.74, 44.08, 61.18 and 92.76% compared to without water potential stress, respectively. Also, T. vulgaris did not germinate at a water potential of -0.9 MPa, whereas some seeds of the T. daenensis plant did germinate under this condition. Four statistical distributions, Normal, Logistic, Log-logistic, and Gumbel, were compared to quantify the germination response of the Thymus to water potential. In order to evaluate the models, the coefficient of determination (R²_adj) root mean square error (RMSE) and Corrected Akaike Information Criterion (AICc) were used. The lowest AICc index values for T. daenensis were associated with the Log-logistic and Logistic distributions (-2012 and -2006), while for T. vulgaris, it was the Gumbel distribution (-1665), suggesting the superior distributions for quantifying Thymus's response to water potential. The fit of the hydrotime models showed that the species of T. daenensis (23.91 MPa hour^-1) compared with the T. vulgaris (28.06 MPa hour^-1) had a lower hydrotime constant value (θ_H), which indicated a higher germination rate in T. daenensis. The value of ψ_b(50)  in T. daenensis (-0.455) was lower than its value in T. vulgaris (-0.388). Therefore, based on the results, T. daenensis showed a greater ability to tolerate drought in the germination stage.
Conclusions: In general, the results showed that the effects of water potential stress on the germination components of T. vulgaris were greater than those of T. daenensis, and according to the parameters of the hydrotime model, T. daenensis was more tolerant than T. vulgaris.

Highlights: