Abstract
Barley (Hordeum vulgare L.) is a salt-tolerant crop with considerable economic value in salinity-affected arid and semiarid areas. In the laboratory experiment, the halothermal time (HaloTT) model was used to examine barley seed germination (SG) at six constant cardinal temperatures (Ts) of 15, 20, 25, 30, 35, and 40 degrees C under five different water potentials (psi s) of 0, -0.5, -1.5, -1.0, and -2.0 MPa. Results showed that at optimum moisture (0 MPa), the highest germination percentage (GP) was recorded at 20 degrees C and the lowest at 40 degrees C. Moreover, GP increased with the accelerated aging period (AAP) and significantly (p <= 0.05) decreased with high T. In addition, with a decrease of psi from 0 to -0.5, -1, 1.5, and -2.0 MPa, GP decreased by 93.33, 76.67, 46.67, and 33.33%, respectively, in comparison with 0 MPa. The maximum halftime constant (theta Halo) and coefficient of determination (R2) values were recorded at 20 degrees C and 30 degrees C, respectively. The optimum temperature (T-o) for barley is 20 degrees C, base psi of 50th percentile (psi b (50)) is -0.23 Mpa, and standard deviation of psi b (sigma psi b) is 0.21 MPa. The cardinal Ts for germination is 15 degrees C (T-b), 20 degrees C (T-o), and 40 degrees C (T-c). The GP, germination rate index (GRI), germination index (GI), coefficient of the velocity of germination (CVG), germination energy (GE), seed vigor index I and II (SVI-I & II), Timson germination index (GI), and root shoot ratio (RSR) were recorded maximum at 0 MPa at 20 degrees C and minimum at -2.0 MPa at 40 degrees C. Mean germination time (MGT) and time to 50% germination (T 50%) were maximum at -2 MPa at 40 degrees C, and minimum at 20 degrees C, respectively. In conclusion, the HaloTT model accurately predicted the germination time course of barley in response to T, psi, or NaCl. Therefore, barley can be regarded as a salt-tolerant plant and suitable for cultivation in arid and semi-arid regions due to its high resistance to salinity.