Evaluation of seed germination of Salicornia persica under iso osmotic conditions using hydrotime and halotime models

Seedling germination and establishment are one of the most sensitive stages of plant life that play a role in plant production, proper plant establishment, plant density, and uniformity and management goals. Osmotic stress has a significant effect on germination percentage and rate. Salicornia persica is an annual halophyte plant that can grow in saline environments. According to the studies and the importance of determining the tolerances of salinity and drought tolerance in germination and plant establishment, this study aimed to investigate the effect of osmotic potentials of polyethylene glycol and sodium chloride on germination and fit of time-moisture and time-salinity models of Salicornia seeds.

In order to investigate the effect of osmotic potentials caused by polyethylene glycol and sodium chloride on germination and fit of Hydrotime and Halotime models of Salicornia seeds, two experiments were conducted based on a completely randomized design at Yasouj University in 2020. The first experimental in drought stress treatments included 13 levels of osmotic potential (zero, -0.3, -0.6, -0.9, -1.2, -1.5, -1.8, -21, -2.4, -2.7, -3, 3.3 and -3.6 MPa) which were made of polyethylene glycol 6000 and second in salinity stress included 13 levels of sodium chloride concentration that was iso-osmotic with first experiment (Zero, 62, 122, 187, 249, 311, 368, 435, 498, 560, 622, 684 and 745 mM). After the end of the germination period, the characteristics of germination rate and percentage were calculated and the hydrotime model was used to describe the relationship between germination and water potential, and the halotime model was used to describe the relationship between germination and salinity. To select the best model among the osmotic potentials, root mean square parameters and R2 were used.

The results of mean comparison of effect of osmotic potentials on the percentage of germination showed that in PEG and NaCl treatment, it was almost 100% up to the level of -1.2 and -1.5 MPa, respectively, and after that, a decreasing trend was observed, so that at the level of -3.3 MP showed a decrease of about 90 and 85%, respectively. The output results of the models showed that the coefficient of the hydrotime and halotime models were 96.8 MPa.h and 16181.87 mM.h, respectively, and the drought and salinity tolerance thresholds were -3.28 MPa and 714.62 mM, respectively. The halotime model quantified the germination of Salicornia seeds better than the hydrotime model. Drought stress limits the absorption of water by seeds and affects germination by reducing the movement and transfer of seed reserves or by directly affecting the structure and synthesis of protein in the embryo. Salinity increases the osmotic pressure of the solution and reduces water absorption through the seeds. On the other hand, high salinity causes toxicity and disturbs the ionic balance and reduces seed germination by affecting the vital interactions of the seed.

The rate of decrease in germination rate and percentage in drought stress was higher than salinity stress. Based on the results of this study, using the halotime model in biological studies of halophyte plants under osmotic stress, the tolerance threshold and the time required for germination at different salt concentrations can be well determined.