Seed germination is a biological process that is affected by a variety of genetic and environmental factors. The cardinal temperature and thermal time are required for germination. The principal objective of this study was to identify and characterize variations in the base, optimum, and maximum germination temperatures of Haloxylon aphyllum L. from two seed sources, in order to establish models for use in predicting seeding dates. Mature H. aphyllum seeds were germinated at temperatures between 5 and 35ºC. The germination behavior of H. aphyllum seeds to different temperature regimens in light was evaluated over a temperature range of 5-35ºC at intervals of 5ºC. The rate of germination increased between base and optimum thermal conditions, and decreased between optimum and maximum thermal conditions; the germination rate varied in a linear fashion at both sub-optimal and supra-optimal temperatures. The linear regression fit the range of germination rates at 5ºC to 25ºC and 25ºC to 30ºC, and thus the base temperature, optimum temperature, and maximum temperature for the germination of H. aphyllum were measured to be 0.6ºC, 25.69ºC, 37.90ºC, and 1.76ºC, 21.56ºC, 37.90ºC for Qom and the Fars dune desert respectively.
Calotropis procera L. is a perennial shrub distributed in saline areas of deserts of South Asia. Salt stress is a very challenging subject in arid and semi-arid areas. Germination stage is very sensitive and many plants do not germinate in saline soil. The objective of this study was identifying the salinity effect on seed germination of Calotropis procera L. The experimental design was a complete randomized block design with NaCl and CaCl 2 at five levels of isobar concentrations: 0.0,-0.01,-0.05,-0.1, and-0.15 MPa. Osmotic potential had significant effects (P < 0.01) on germination percentage, germination rate, shoot length, root length, and seedling dry weight. All seedling characteristics decreased with decrease in osmotic potential. Shoot length and root length decreased more than the seedling characteristics. Germination was completely inhibited in-0.1 Mpa. Priming with NaCl and CaCl 2 (-0.1 MPa) for four days had significant effects (P < 0.01) on the germination percentages. Priming improved the seedling characteristics in all samples, especially in-0.05 Mpa, but a decrease with decrease in osmotic potential.
Plant growth regulators play an important role in control of seed germination. This experiment was conducted to investigate the effect of lant growth regulators (indole-3-acetic acid, gibberellin and kinetin) on seed germination of Hordeum spontaneum. Seeds of wild barley were soaked in distilled water (control) or different concentrations of gibberellin (25, 50, 75, 100, 125 and 150 mg L -1 ), indole-3-acetic acid and kinetin (5, 10, 15, 20, 25 and 30 mg L -1 ). The following germination parameters were determined: germination percentage, germination index, mean germination time, germination energy, germination value, seedling length and seed vigour index. The results showed that plant growth regulators, depending on the used concentration, effectively improved all germination parameters except the mean rate of germination, which was increased only by indole-3-acetic acid at concentrations of 20 and 25 mg L -1 . Gibberellin was generally shown to be more effective on all evaluated traits except the mean rate of germination. The highest values in germination percentage, germination index, germination energy, germination value, seed vigor index were obtained by using gibberellin at 75 mg L -1 and followed by 100 mg L -1 . Gibberellin also at concentration of 50 and 125 mg L -1 led to the greatest mean germination time and seedling length, respectively.
-Calotropis procera, Apocynaceae, is a wild perennial shrub that originated in the Persian deserts. It is known to provide key resources in degraded ecosystems to about 80 animal species. C. procera is regenerated by seed and produces lots of small seeds that are dispersed by wind; nonetheless, its density is very low. The purpose of this study is to estimate the cardinal temperatures including the base, optimum, and maximum temperatures of Calotropis procera looking at two different ecotypes in the Iranian desert. The germination behavior of C. procera seeds was tested at temperature regimens of 0, 5, 10, 15, 20, 25, 30, 35 and 40 o C and was analyzed using linear regression models. The rate of germination increased between base and optimum thermal conditions, and decreased between optimum and maximum thermal conditions. The base, optimum and maximum temperatures for germination of C. procera seeds were estimated at 19.10, 30.75 and 47.80 o C for the Fars and 20.00, 31.82 and 49.69 o C for the Zahedan desert, respectively. Temperature and germination were rated to determine the seeding dates of the C. procera. Overall, cardinal temperatures for germination were dependent on local climate characteristics for the range of adaptations in plant growth of the given species.
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