Iranian Journal of Seed Research

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Extended Abstract
Introduction: Cow tail (Smirnovia iranica) is considered a valuable shrub species indigenous and adapted to the sandy lands of the Iranian central regions which besides playing an essential role in the desert cover for soil protection and of forage production, is considered important due to its great medicinal values. Considering the fact that seed germination of this plant does not easily occur due to its hard and solid seed coat, in this study, the in vitro tissue culture and seedling establishment is utilized for the first time in order to surmount the obstacles laid ahead of cow tail seed germination.
Materials and Methods: Scratched seed, unscratched seed and seed embryo of cow tail as different explants were placed in two culture media (MS, MS with free amino acids complex) following surface sterilization, and were exposed to two photoperiod treatments (16 hours of light and 8 hours of darkness as well as absolute darkness) and were investigated in a factorial experiment based on completely randomized design with six replications. Finally, germination percentage (10 days after seed culturing) and shoot length (30 days after seed germination) were evaluated.
Results: The results indicated that significance of the effect of investigated treatment conducted over some in vitro on germination characteristics. It was revealed that the cultivation of seed embryo in MS culture media along with free amino acids complex for 16 hours of light and 8 hours of darkness photo period can be considered as the best in vitro germination method, in terms of seed germination percentage (78.83%) and germinated shoot length (44.83 mm).
Conclusion: In vitro culture can be used to improve germination and seeding production of this species.

Highlights:

1. The method for seed dormancy elimination of cow tail plant was introduced.
2. The seed disinfection procedure for in vitro culture of cow tail plant was introduced.
3. The components of in vitro culture medium for rapid and efficient seed germination of cow tail plant were introduced.

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Extended abstract
  Introduction: Numerous studies are being carried out to reveal the effects of different treatments on the germination of seeds from various plants. The most commonly used method of analysis is the nonlinear regression which estimates germination parameters. Although the nonlinear regression has been performed based on different models, some serious problems in its structure and results motivated researchers to investigate alternative approaches with higher accuracy and precision. The main purpose of the present research is to introduce the alternative parametric time to event model and comparing its reliability to the nonlinear regression in experiments carried out under different conditions.
  Materials and Methods:  The results of four different experiments were used here including the effect of Potassium cyanide on walnut seed germination, the effect of salinity on wheat seed germination, the effect of water potential on corn seed germination and the effect of temperature on cotton seed germination. The nonlinear regression and time to event methods were applied based on the Gompertz model. The obtained standard errors from the two models were further assessed using the Monte-Carlo method.
  Results: Both methods provided well-fitting models according to the MSE and R²   criteria. Although the germination parameters were approximately identical in both models, the standard error of parameters in nonlinear regression was significantly less than those of time to event method except for the experiments in which all tested seeds germinated within the time frame of study so that in the latter case the estimated standard errors in both models were identical. The Monte-Carlo method confirmed the results of the time to event model and reveals the underestimation of the nonlinear regression method in estimating the standard error of parameters.
  Conclusions: Generally, the results of this research showed that the time to event model can be trustfully utilized in seed germination studies under different conditions and treatments. This model, not only provides precise estimates of the germination parameters but also provides the precise standard error of parameters that have important roles in making inferences for parameters. The drc package in R software enables researchers to fit the different time to event models.

 
Highlights:

1. Using the time to the event model in estimation of seed germination parameters.
2. Comparing the time to event and nonlinear regression methods in different seed germination experiments.
3. Using the Monte-Carlo method for investigating the accuracy of results of the used methods.