Hydrotime model: Introduction and application of this model in seed researches

Germination is the first and most important developmental stage of plants which is influenced by genetic and environmental factors. Hydrotime model describes the relationship between water potential (ψ) and seed germination rate and percentage. This model quantifies the rate of germination progression (θH)، the stress tolerance of germination (ψb(50)) and the uniformity of germination (σψb). This indicators can be used to show seed lots or varieties vigor and evaluation of dormancy in seed and some treatments effects (e. g. priming، ABA or GA) on seeds vigor. Hydrotime model is not well known amongst Iranian researchers. This study aims at introducing the application of hydrotime model in germination data analysis. To achieve this، germination data of three plants (sweet clover: Melilotus officinalis، rye: Secale cereael and wheat: Triticum aestivum) in response to drought stress were used. The θH value quantifies the inherent rate of germination، which can vary among species and different physiological stages. The ψb (50) value is an indication of the average stress tolerance of the population. A population with a high ψb (50) value (less negative) will be inhibited germination at higher ψ (less stress) than will a population with a lower ψb (50) value. The value of ψb (50) for a seed population can be shifted to higher or lower values by the induction and release of dormancy. The σψb value is a quantitative estimate of the uniformity in germination in the population as greater σψb means a wider variation between the first and last seeds to germinate.