Main content area

Quantification of Retama raetam seed germination response to temperature and water potential using hydrothermal time concept

Abdellaoui, Raoudha, Boughalleb, Fayçal, Zayoud, Dhikra, Neffati, Mohamed, Bakhshandeh, Esmaeil
Environmental and experimental botany 2019 v.157 pp. 211-216
Retama raetam, environmental factors, land restoration, physiological state, prediction, seed germination, shrubs, simulation models, temperature, water potential, Tunisia
Retama raetam (Forssk Webb; Fabaceae) is a xerophytic shrub that is distributed from northern to southern Tunisia and which is of interest for medical use and for revegetation. To quantify seed germination responses of R. raetam to temperature (T) and water potential (ψ), and to determine cardinal Ts, a hydrothermal time model (HTT) was used. The experiment was conducted at six constant Ts (5, 10, 15, 20, 25, and 30 °C) at each of the following ψs (0, –0.3, –0.7 and −1 MPa; provided by PEG 6000). Results showed that germination rate (GR) and germination percentage (GP) were significantly influenced by ψ, T and their interactions (P < 0.01). Cardinal Ts for R. raetam was 4.2 °C for Tb (the base T), 17 °C for To (the optimum T) and 30 °C for Tc (the ceiling T) in the control condition (0 MPa). The Td (the T at which ψb(50) starts to change) was estimated to be 10 °C. By increasing T to To, hydrotime constant (θH) decreased nonlinearly and then stabilized to 30 MPa °C h at Ts ranging from 15 to 30 °C. The study showed that when the HTT model is applied, it can accurately describe the time course of germination across all Ts and ψs for this plant (R2 = 0.90). Moreover, estimated parameters using HTT model were 388.6 MPa °C h for the hydrothermal time constant (θHTT), –0.913 MPa for the base water potential (ψb(50)) and 0.047 MPa °C h for the kT (the slope of the relationship between ψb(50) and T ≥ Td). The parameters presented in this study can easily be used in R. raetam SG simulation models for characterizing the physiological status of R. raetam seed populations and also for predicting germination time courses of this plant under different environmental conditions.