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Heterogeneity in seeds mostly occurs due to physiological, environmental and genetic factors, and these could affect seed dormancy and germination. Therefore, the aim of our study was to assess the effect of seed colour on germination behavior. For this, both light and temperature requirements were assessed in Lotus glinoides and Lotus halophilus (Fabaceae) from the hyper-arid deserts of the United Arab Emirates. Germination was assessed in terms of both final germination level (percentage) and germination rate, as expressed by Timson’s germination velocity index. Lotus glinoides produces black and yellow-colored seeds, and L. halophilus produces green and yellow seeds. Different seed lots were germinated in both light and darkness at different temperatures. Yellow seeds of the two species attained significantly lower germination, compared to black and green seeds. There was no specific light or temperature requirements for the germination of the two coloured seeds of L. glinoides; the effect of interactions between seed colour and both light and incubation temperature, were not significant on the final germination percentage. In L. halophilus, green seeds germinated significantly more in both light and darkness at lower temperatures (15/25 °C) and in light at higher temperatures (25/35 °C), compared to yellow seeds. Yellow seeds germinated faster, compared to black at 15/25 °C in L. glinoides and compared to green seeds at 15/25 °C and 25/35 °C in L. halophilus. Seed colour variation, at least in L. halophilus, could be a survival strategy that would determine the time of germination throughout the year in the unpredictable desert environment.

In this study, we assessed the effects of mucilage presence, thermoperiod, and photoperiod on seed germination percentage and germination velocity (mean germination time) of four Arabian desert species. We hypothesized that mucilage presence, thermoperiod, and photoperiod and their interaction would influence seed germination. Seeds with and without mucilage were germinated under different alternating temperature regimes of 15/25, 20/30, and 25/35 °C night/day temperatures with a 12/0 h light/dark photoperiod. Results showed that the incubation temperature affected the germination of all the studied species. The photoperiod significantly affected the germination of Boerhavia elegans Choisy, Salvia aegyptiaca L., and Sporobolus ioclados (Trin.) Nees, while the mucilage presence influenced the germination of S. ioclados only. The interaction between mucilage presence, temperature, and photoperiod significantly influenced the germination percentage of B. elegans and S. aegyptiaca. Neither removal of the mucilage nor light conditions affected the germination percentages of Sporobolus spicatus (Vahl) Kunth. However, the temperature affected the germination of S. spicatus. The germination of all the studied species was faster for demucilaged seeds. Ecologically, the mucilaginous seed coat is considered an important adaptation for dispersal as it anchors seeds on the ground and holds water around the seed during the germination stage in the stressful arid desert habitats. [ABSTRACT FROM AUTHOR]

Information about seed source effects on germination and stress tolerance of the multipurpose exotic Prosopis juliflora (Sw.) DC. is scarce. Here, we investigate the influence of seed provenance on salinity tolerance and germination requirements of P. juliflora. Seeds collected from saline (SH) and nonsaline (SNH) habitats were treated with different NaCl concentrations (0–600 mM) and incubated in two photoperiods and three thermoperiod regimes. The results showed that tolerance of seeds from SH and NSH to salinity depended on thermoperiod, but not on photoperiod or interactions between photoperiod with both NaCl and thermoperiod. Germination of seeds from the two habitats did not differ significantly across thermoperiods in control and 200 mM NaCl. However, in 400 and 600 NaCl, germination was significantly greater for seeds from NSH than those from SH at lower thermoperiod in both light and darkness; whereas the reverse was true at higher temperatures in light. Seed germination of both habitat types was significantly lower at higher than at both lower and intermediate thermoperiods in all salt solutions, but the difference was more pronounced at higher salinities. Germination recovery failed in darkness at all photoperiod and thermoperiod regimes. Partial germination recovery happened only for seeds that failed to germinate in 400 mM NaCl in light and intermediate thermoperiod. Germination was significantly faster for seeds from SH than from NSH at higher salinities. The results emphasize the importance of considering the seed source for the restoration of salt-affected lands. [ABSTRACT FROM AUTHOR]

In many species, seeds with different sizes show diverse responses in their requirements for temperature and light for optimal germination. In this study, the effect of seed size (i.e., small and large) on germination was tested in seeds of Brassica tournefortii Gouan, Lotus garcinii DC., and Salvadora persica L. from arid Arabian Desert habitats. The mean seed size of all three study species differs significantly between small and large-sized seeds. Differences were observed in seed germination between large and small seeds of B. tournefortii and L. garcinii. We found that the large seeds of B. tournefortii and L. garcinii showed a higher germination percentage at all tested temperatures than that displayed by the small seeds. However, both small and large seeds of S. persica germinated equally (100%) well under all tested incubation conditions. Our results show significant differences in germination percentage between the small and large seeds of B. tournefortii at 25/35 °C under a 12 h light regime. However, seeds of L. garcinii showed a significant difference in germination percentage at low temperatures (15/25 °C) under a 12 h light regime. [ABSTRACT FROM AUTHOR]

Light and growth-promoting compounds, such as gibberellic acids (GA3), are among the most important factors that can break physiological seed dormancy. Here, we investigate the effects of GA3 and light on germination of five species of Resedaceae that are known to have different levels of physiological dormancy. Seeds were incubated at 20/30 °C in both 12-hr photoperiod and complete darkness. To study the effect of growth hormone on germination, seeds were soaked for 24 h in different concentrations of GA3 before sowing. The annuals (Reseda aucheri and Oligomeris linifolia) and the perennial Ochradenus arabicus had deep physiological dormancy, and exogenous application of GA3 enhanced their germination in the light, but not in darkness; few or no seeds germinated in the dark in these species. Ochradenus aucheri and O. baccatus had intermediate and non-deep dormancy, respectively, and application of GA3 enhanced their germination in both light and darkness. Germination of the annual species was much slower than that of the shrubby perennials. Overall, these results indicate that conditions under which seed developed, matured and stored on maternal plants as well as incubation conditions should be taken into consideration when assessing germination behavior of the perennial species of Resedaceae. [ABSTRACT FROM AUTHOR]

There is limited information about the importance of seed origin, thermoperiod, and photoperiod on low water potential tolerance during seed germination of habitat-indifferent plants, which grow well in saline and non-saline habitats. This study examined the effects of seed provenance, water potential, thermoperiod, photoperiod, and their interactions on seed germination of the multipurpose exotic tree Prosopis juliflora. Seeds from saline and non-saline habitats were germinated under various water potential levels at different thermoperiods and photoperiods. Seeds could endure up to −1.5 MPa water potential irrespective of origin. Germination of seeds from saline habitats was higher than those from non-saline habitats in −1.5 MPa. At 0 and -0.3 MPa, seeds germinated in a thermoperiod-insensitive manner in light. At < -0.6 MPa, however, a higher thermoperiod was more inhibitory for germination. Seeds germinated better under dark than light conditions under low water potential and high thermoperiod. Most ungerminated seeds from different lower water potential treatments recovered their germination when transferred to distilled water. This study demonstrated that the low water potential tolerance of P. juliflora seeds depends on seed origin, thermoperiod, and photoperiod. These factors should be considered when selecting a seed lot for afforestation of P. juliflora in different soil types. • Prosopis juliflora seeds could endure high drought levels irrespective of origin. • Saline habitat seeds germinated better in high drought than non-saline origin seeds. • Seed germination was thermoperiod-insensitive in light and low simulated drought. • High thermoperiod was inhibitory for germination under high simulated drought. • Ungerminated seeds from simulated drought treatments showed high recovery in water. [ABSTRACT FROM AUTHOR]