Quantifying water stress and temperature effects on camelina (Camelina sativa L.) seed germination

Camelina (Camelina sativa (L.) Crantz; Brassicaceae) is known as an important and low-input oilseed crop, which is widely used in the production of biopolymers, biofuels, cosmetics, food, and feed. One of the main problems of camelina cultivation is related to seed size which can directly influence its germination, seedling growth, and development. Therefore, this study was performed to evaluate the effect of temperature (T) and water potential (psi) on camelina germination behavior using population-based threshold models as the first study in this case. For this purpose, camelina seeds were incubated at eight Ts (5, 10, 15, 20, 25, 30, 35, and 40 degrees C) and at each of the following five levels of psi s (0, -0.25, -0.50, -0.75 and -1 MPa). The results illustrated that T, psi and T x psi significantly affected germination characteristics of camelina. The psi(b)(50) value remained constant at Ts <= 20 degrees C ( 1.29 MPa), afterward increased linearly to 0.81 and 0.41 MPa at 25 and 30 degrees C, respectively. The thermal time model also showed that the psi levels did not affect the value of T-b at sub-optimal Ts (T-b = 1.5 degrees C), while T-c(50) decreased linearly with decreasing psi, with the rate of 11.3 degrees C per MPa at supra-optimal Ts, conforming with the results obtained by the hydrothermal time model. This decrease in germination capacity at Ts above T-o was due to the shifts in the psi(b)(50) (become more positive), reflecting a decrease in GR(50) as a result of thermoinhibition which could be considered as an adaptive strategy under stress conditions. The cardinal Ts for camelina germination at 0 MPa were estimated 1.5 degrees C for T-b, 20.0 degrees C for T-o, and 34.4 degrees C for T-c. Consequently, camelina could be marked as a cold-tolerant plant and suitable for cultivation in arid regions due to the high resistance to low water potential (psi(b)(50) = 1.29 MPa).