Quantification of seed germination response of Echinops aged seeds under osmotic stress using various nonlinear models and hydrotime function

The effects of accelerated aging treatment on seed germination of Echinops was quantified using nonlinear models using Sigmoid, Segmented, Gompertz and Richards models and hydrotime model in Weibull, Normal and Gombel distribution functions. Experimental factors were seed aging for (0, 24, 48, 72 and 96 hour) at relative humidity (RH)=100%, temperature (T) =40 oC and seven osmotic potential (0, -0.2, -0.4, -0.6, -0.8, -1, -1.2 MPa). Results of experiment revealed that interaction effect of aging and osmotic stress on seed germination and germination rate of Echinopsis was significant. Seed germination parameters of Echinops were increase by aging treatment up to 72 h but it was declined at aging treatment of 96 h. Seed germination and germination rate were increased by aging treatment till 72 h but at 96 h, both were declined. Gompertz exhibited the best fit for no aged, 24 h and 48 h while sigmoid function was provided the best fit for aging at 72 and 96 h. Among all studied distribution function, it was revealed that normal distribution was the most effective one thus base potential (ψb) and hydrotime constant (θH) were -0.68 MPa and 6 MPa hour, respectively. However, after 96 h of aging treatment ψb and θH were estimated 0.731 MPa and 19.3 MPa hour, respectively. It can be concluded that freshly harvested Echinops exhibited some levels of seed dormancy which was alleviated at mild to moderate aging conditions, but after 72 h, deteriorative mechanism led to damaging effects and declined seed germination quality.