Iranian Journal of Seed Research

Extended abstract
Introduction: Without a doubt, plant hetrotoxicity is one of the important factors in determining the distribution and abundance of some species in plant communities. Thus, the purpose of this experiment was to evaluate the effect of phenolic composition obtained from the methanol extract of Echinochola crus-galli on germination traits and cytogenetic behavior of rice.
Materials and methods: This experiment was done to assess hetrotoxic potential of various concentrations (0, 0.024, 0.048, 0.076 and 0.1 mM) of the phenolic composition obtained from the methanol extract of whole-organ of E. crus-galli on germination traits of rice as well as mitosis division of meristematic cells of radicle in a completely randomized design. To extract thephenolic composition, warm extraction method using a methanol solvent was used. For studying mitosis division, first rice seeds were germinated. Then, each of the steps such as fixation, hydrolysis, staining, squashing and microscopic studies were done on the end of the radicle. Mitosis indices and percentage of mitosis inhibition were calculated and also percentage of each of chromosomal abnormalities at four stages of prophase, metaphase, anaphase and telophase as compared to total cells was calculated.
Results: The lowest percentage and rate of germination and relative germination were found in two concentrations of the 0.076 and 0.1 mM of phenolic composition of E. crus-galli, so that no germination was observed in these treatments. In this study, mitosis division was normal in control samples, so that the rice plant included 12 chromosomes in the metaphase stage. Also the chromosomes were normal in the telophase stage and chromosomal abnormalities were not observed in meristem cells of radicle tip of the control. The lowest value of mitosis indices and the number of dividing cells were related to the concentration of 0.048 mM wuth 30.19 and 385 cells, respectively. In the present study, chromosomal abnormalities in the stages of metaphase, anaphase and telophase were increased with increasing concentration of phenolic composition, and were 28.85 and 16.95% in 0.048 mM concentration of phenolic composition, respectively. The most chromosomal abnormalities were of sticky and laggard type, which were related to the concentration of 0.048 mM of phenolic composition with 39.83 and 32.25%, respectively. The highest number of chromosomal bridges and clumping were obtained in 0.024 mM of phenolic composition with about 19.27 and 29.83%, respectively.
Conclusion: In this study, phenolic composition obtained from the methanol extract of E. crus-galli had asignificant inhibitory effect on germination traits and mitosis division in root tip cells of rice. Thus, the amount of E. crus-galli residues in the field should be considered in direct and indirect cultivation of rice.

Highlights:
1-Difference in impact of the phenolic composition obtained from the methanol extract of Echinochola crus-galli on germination and reduced cytogenetic behavior of rice is related to their threshold concentration.
2- It is advised to cultivate varieties of rice resistant to the remnants of harmful compounds of E. crus-galli as direct cultivation or under nursery condition.

Extended abstract
Introduction: Seed germination and seedling establishment are the most sensitive stages in the life cycle of a plant. Among the environmental factors, 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 indices and quantify the effect of water potential 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 at the laboratories of the Department of Agronomy and Plant Breeding, Ilam University in the winter of 2023. The factors of the experiment included two types of Thymus (Thymus daenensis and T. 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 as the water potential decreased to -0.1, -0.3, -0.5, and -0.7 MPa, seed germination percentage respectively went down by 8.43, 43.26, 61.80, and 88.76% in T. daenensis and 19.74, 44.08, 61.18 and 92.76% in T. vulgaris compared with water potential stress-free conditions. Also, T. vulgaris did not germinate at a water potential of -0.9 MPa, whereas some seeds of the T. daenensis plant germinated under this condition. The highest germination rate in both T. daenensis and T. vulgaris species was observed under stress-free conditions, and there was significant difference between the species. Four statistical distributions including normal, logistic, log-logistic, and Gumbel, were compared to quantify the germination response of Thymus to water potential. In order to evaluate the models, corrected Akaike information criterion (AICc), the coefficient of determination (R²_adj), and root mean square error (RMSE) were used. The lowest AICc index values for T. daenensis were associated with the log-logistic and logistic distributions (-2012 and -2006), and the Gumbel distribution (-1665) in T. vulgaris, suggesting the superior distributions for quantifying Thymus's response to water potential. Estimation of parameters related to the hydrotime model showed that T. daenensis species had a lower hydrotime constant value (θ_H)(23.91 MPa hour^-1) compared with T. vulgaris (28.06 MPa hour^-1), which indicated a higher germination rate in T. daenensis. The value of ψ_b(50)  in T. daenensis (-0.455 MPa) was lower than that of T. vulgaris (-0.388 MPa). Therefore, based on the results, T. daenensis showed a greater ability to tolerate drought during 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:

1. The best distribution in the hydrotime model was determined for predicting Thymus daenensis and Thymus vulgaris seed germination under water potential stress conditions.
2. The threshold level of water potential stress causing a significant decrease in the germination components of Thymus daenensis and Thymus vulgaris was determined.
3. Based on the hydrotime model, Thymus species was determined to be more tolerant to water potential stress during germination.