A Model for Germination Rate during Dormancy Loss in Hordeum vulgare

A quantitative model for change in germination rate of barley (Hordeum vulgare L.) during and after loss of primary dormancy is presented. Change in mean germination time on a logarithmic scale is normally distributed within the period of after-ripening and the standard deviation of this distribution is shown to be a quantitative function of after-ripening temperature. The rate of change of mean germination time is in inverse proportion to the product of the standard deviation and a parameter which is characteristic of the seed population. The latter parameter is the rate constant for change in probit cumulative germination as a negative linear function of the logarithm of mean germination time. A model based solely on dormancy loss is combined with an existing model of change in probit viability as a function of mean germination time to produce a model which predicts the time to and optimum value of mean germination rate of a population as it after-ripens. The model provides a quantitative link between the effect of pre-germination and germination environments on total and rate of germination of an initially dormant population. Experimental data from dormant barley (cv. Triumph) stored at 27, 38, 45, 50 and 60 °C, and germinated at 18 °C were used to validate the model. The data show that germination rate continues to increase after primary dormancy is lost until it reaches an upper limit determined by the intrinsic germinative vigour of the seed lot. Rate of loss of primary dormancy and increase in germination rate thus appear to be quantitatively linked as a function of after-ripening temperature and factors which may be specific to the mode of induction of dormancy within a seed lot prior to harvest.