Iranian Journal of Seed Research

Extended abstract
Introduction: Conditional dormancy (CD) is a dynamic state between dormancy (D) and nondormancy (ND). Seeds at the conditional dormancy stage germinate over a narrower range of temporal conditions. Conditional dormancy is usually observed in seeds with physiological dormancy. However, primary conditional dormancy has also been seen in some freshly harvested seeds. The purpose of the present study was to investigate whether freshly harvested oilseeds have non-dormancy or conditional dormancy.
Materials and Methods: A factorial experiment was conducted based on a completely randomized design with four replications at Seed Technology Laboratory of Aburaihan Campus, University of Tehran, Iran, in 2018. In this experiment, seeds of rapeseed were collected from 20 different locations in Golestan and Mazandaran provinces. Following that, a germination test was carried out at different temperatures (5, 15, 20, 30, 35°C), and the germination percentage and seed germination rate were recorded. In order to break seed dormancy, two treatments were used: gibberellic acid and after-ripening. For after-ripening treatment, seeds were stored in a paper bag in a dry and dark environment for 6 months. For gibberellic acid treatment, a solution of 100 parts per million (PPM) of gibberellic acid was prepared and added to the Petri dishes. Subsequently, the percentage and rate of germination were recorded.
Results: The results showed that freshly harvested seeds had primary conditional dormancy and germinated in a narrow range of temporal conditions. In addition, cardinal temperatures for freshly harvested seeds were 4.45 and 27.8 for bases and ceilings, respectively. Following gibberellic acid and after-ripening treatments, seeds germinated in a wider range of temperatures and base and ceiling temperatures reached 1.74 and about 40°C, respectively. Thus, germination percentage of seeds treated with gibberellic acid and after-ripening increased at both high and low temperatures. However, the increase in germination percentage was higher at high temperatures than low temperatures. In addition, the effect of gibberellic acid treatment was more than that of after-ripening treatment on the release of dormancy, and after-ripening treatment had an intermediate effect between the gibberellic acid and freshly harvested seeds.
Conclusion: Based on the results of this experiment, the application of gibberellic acid and after-ripening treatments resulted in breaking the dormancy of freshly harvested seeds and increased germination temperature range at high and low temperatures.  Of the two treatments, gibberellic acid had the greatest effect on breaking dormancy and increasing temperature range. Among the cultivars, these changes were maximum in the germination capacity of Hyola 50 and Trapar cultivars and Trapar cultivar had minimum changes.
 
 
Highlights:
1-Conditional dormancy of oilseed cultivars was investigated under different environmental conditions.
2-Application of gibberellic acid and after-ripening treatments resulted in breaking primary conditional dormancy in oilseed cultivars.

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: Drought stress, as abiotic and multidimensional stress, has severe effects on plant growth. One of the new approaches in the management of drought stress is the use of nanoparticles. Nanoparticles infilterate the seeds and increase nutrient and water uptake and ultimately, improve germination. The present research was conducted to evaluate the effects of titanium dioxide nanoparticles on chickpea plant germination factors to modify the negative effects of drought stress.
Materials and Methods: A factorial experiment was conducted in a completely randomized design with four replications on chickpea seeds of Arman cultivar in the Plant Sciences Research Institute of the Ferdowsi University of Mashhad in 2019. Seeds were primed with concentrations of 0, 5, 10, 15, and 20 mg L^-1 titanium dioxide for 24 hours. The seeds were cultured in sterilized Petri dishes. Drought stress was applied using polyethylene glycol 6000 with 0, -2, -4 and -8 bar osmotic potentials.
Results: The analysis of variance results showed that the interaction effect of drought stress and titanium dioxide nanoparticles was significant on germination rate, the number of normal seedlings, seed vigor index, germination index, length of seedling, radicle length, and radicle dry weight. All germination traits were inhibited as a result of drought stress. On the other hand, the presence of titanium dioxide nanoparticles partially decreased this inhibition in some traits. Germination percentage, germination rate, normal seedling percentage, seed vigor index, germination index, epicotyl length, radicle length and radicle dry weight decreased as a result of stress.
Conclusion: At all drought stress levels, the concentration of titanium dioxide nanoparticles up to 20 mg L^-1 significantly improved traits such as germination percentage, seed vigor index, epicotyl length, and epicotyl dry weight. It seems that nanoparticles can stimulate cell activity and increase the transformation of reserves to translocatable material and consequently, improve germination characteristics. Thus, the application of titanium dioxide nanoparticles up to a concentration of 20 mg L^-1 can partially reduce the negative effects of drought stress on the germination characteristics of chickpeas.

Highlights:
1- Germination percentage and seed vigor index of chickpea increased with the application of titanium dioxide nanoparticles up to 20 mg l^-1 at all drought stress levels.
2- The radicle length and dry weight of chickpea increased by titanium dioxide nanoparticles.
3- The negative effects of drought stress on chickpea seed germination decreased by titanium dioxide nanoparticles.