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• Alternating temperature enhanced seed germination in four cultivars of aubergine. • The most effective treatment tested was a temperature regime of 35/20°C at 16/8 h. • Endogenous hormone analysis showed decreased ABA in seeds with higher germination. • Increased germination and emergence correlated well with increase lipase levels. • There was a corresponding increase observed in SOD with increased germination. High seed quality is important for obtaining high quality seedlings for commercial vegetable production. The rate of seed germination affects seedling quality since seeds which tend to germinate more slowly generally result in low-quality seedlings, especially in aubergine seeds. Alternating temperatures play a crucial role in determining the rate of seed germination in many plant species. This study investigated the effect of alternating temperatures on aubergine seed germination, emergence rates, and physiological changes regulating dormancy. Seeds from four open-pollinated aubergine cultivars were incubated for 14 days under the following temperature regimes: 35/20°C-24/24h, 35/20°C-16/8h, 35/20°C-8/16h, 30/20°C-24/24h, 30/20°C-16/8h, 30/20°C-8/16h, or at constant 25°C. The highest mean germination was 92%, with a corresponding highest mean emergence of 88%, which was found with the 35/20°C-16/8h treatment. All alternating temperature treatments displayed faster germination and emergence compared to the control (25°C), as well as high catalase, superoxide dismutase and ascorbate peroxidase antioxidant enzyme activities, and high auxin and salicylic acid levels. In contrast, lipase enzyme activity, abscisic acid and jasmonic acid content decreased. In conclusion, these findings showed that alternating temperatures improved aubergine seed germination rate, and seedling emergence, and also demonstrated positive correlations with enzymatic and hormonal fluctuations within the seeds. [ABSTRACT FROM AUTHOR]

Seed germination of the kiwifruit (Actinidia deliciosa A. Chev. C.F. Liang and A.R. Ferguson), a deciduous, perennial vine, is low because of seed dormancy. The main purpose of this study was to characterize kiwifruit seed dormancy and germination in response to environmental factors such as temperature and light. Dormancy of hydrated seeds is alleviated by the perception of a period at low temperatures (stratification) of at least 3 weeks at 2 or 5°C. Alleviation of dormancy is accomplished by incubation at fluctuating temperatures (20/30°C). A red light pulse did not affect germination, whereas a far-red light pulse strongly inhibited germination. This inhibition was readily reverted by a second pulse of red light, indicating that phytochromes are also involved in dormancy alleviation. Although seed germination was inhibited by the fruit pulp, the latter prevented neither perception of low temperature nor changes in the light sensitivity of the seeds. Therefore, it can be advanced that kiwifruit seeds will only germinate after dispersal if the time–temperature requirement for dormancy alleviation and fluctuating temperatures for dormancy termination are fulfilled. Perception of a closed canopy might interfere with dormancy termination. [ABSTRACT FROM PUBLISHER]

Temperature is a key factor affecting both dormancy and germination. In non-dormant seeds, when temperature is within the thermal range permissive for germination, it just regulates germination velocity, while in seeds presenting dormancy it can also be affecting dormancy level, dormancy termination and the expression of dormancy itself. This dual effect of temperature on dormancy and germination often leads to misinterpretation of obtained germination results and confounds the analysis of temperature effects in seed populations presenting some degree of dormancy. In the present paper we discuss the effect of temperature in the regulation of dormancy level and its implications in dormancy expression, as an attempt to construct a conceptual framework that allows distinguishing between the effects of temperature on dormancy and germination. Finally, we present examples of how a better understanding of these effects could help us to interpret the mixed effects of temperature on both processes during incubation of seeds presenting dormancy. [ABSTRACT FROM AUTHOR]

Cynara cardunculus (L.) seeds require incubation at fluctuating temperatures to terminate dormancy. In this study, we analysed the physiological mechanisms underlying such a requirement, focusing on the role of abscisic acid (ABA) and gibberellin (GA). As a conceptual framework, we considered the possibility that fluctuating temperatures and light trigger a similar set of hormonal processes after stimulus perception. To test this possibility, we (1) carried out hydrotime analysis of germination in seeds exposed to fluctuating temperatures (25/15°C) and constant temperature (20°C) with or without gibberellin (GA3) or red light; (2) determined the responses of seeds incubated at fluctuating or constant temperature to ABA, GA3, fluridone, an inhibitor of ABA biosynthesis, and paclobutrazol, an inhibitor of GA biosynthesis; and (3) determined the ABA content of seeds incubated at fluctuating or constant temperature. Incubation at 25/15°C or 20°C in the presence of GA3 reduced the mean base water potential [Ψ(50)] of the population to a similar extent, compared to that observed with seeds incubated at 20°C without GA3. Irradiation with red light also reduced cb(50) to a lesser extent than incubation in the presence of GA3. At all concentrations tested, exogenously applied GA3 did not promote germination of seeds incubated at 25/15°C. However, paclobutrazol inhibited germination, suggesting that fluctuating temperatures terminate dormancy through de novo GA biosynthesis. Fluctuating temperatures enhanced seed germination in the presence of ABA, but ABA content did not differ between seeds incubated at fluctuating and constant temperatures. This study provides clear evidence for the involvement of hormonal regulation in dormancy termination by fluctuating temperatures. [ABSTRACT FROM AUTHOR]

Seed germination and seedling emergence are key processes for population recruitment. Flooding and grazing are disturbances forming gaps that may strongly influence recruitment patterns in space and time, but their combined effects and action mechanisms have rarely been addressed. In this study we analysed the effects of microhabitat conditions associated with winter flooding and spring-summer defoliation on seed germination and seedling establishment of Paspalum dilatatum, a dominant perennial C4 grass in native grasslands of the Flooding Pampa, Argentina. The dynamics of seedling emergence from natural seed banks and buried seeds was studied in a factorial experiment with flooding and defoliation treatments applied to soil monoliths (mesocosms) collected from natural grassland. Additional laboratory experiments were applied to investigate seed germination under different combinations of temperature, light quality and simulated flooding. Seed germination and seedling emergence of P. dilatatum were promoted by flooding and high intensity defoliation. Gaps generated by flooding were maintained by high intensity defoliation exercising a synergistic effect on survival seedlings. Flooding resulted in the breaking of seed dormancy and higher germination rates associated with alternating temperature and the activation of the phytochrome system. Our results indicate that microhabitat conditions associated with the disturbances forming gaps, such as flooding and heavy grazing, synergistically promote the recruitment process of this dominant grass species. [ABSTRACT FROM AUTHOR]

• Kiwi seeds present dormancy which impairs seedling production in nursery. • Seeds stratified at low temperatures gradually gained the ability to germinate. • After stratification dormancy must be terminated by fluctuating temperatures. • We propose a mathematical model to optimize in time dormancy overcoming. • This constitutes a tool to optimize kiwi seedling production in nursery. Kiwifruit (Actinidia deliciosa A. Chev. C.F. Liang and A.R. Ferguson) seedling production in the nursery is usually impaired because of low seed germination resulting from primary dormancy. Dormancy of hydrated seeds is alleviated by the perception of a period at low temperatures (stratification), but further incubation under fluctuating temperatures (20/30 °C) is a requirement for dormancy termination. The aim of this study was to establish functional relationships between changes in the sensitivity of the seed population to different cycle-doses of fluctuating temperature and dormancy alleviation under different times and stratification temperatures. We propose a model based on the concept of stratification thermal time to predict changes in the fraction of the seed population that would germinate as a function of the number of fluctuating temperature cycle-doses. Results showed that stratification at cool temperatures produced higher rates of change than stratification at warmer temperatures. Construction of response curves with a thermal time scale was possible because seeds that had accumulated similar stratification thermal time achieved similar germination percentages in response to cycle-doses of fluctuating temperatures. The model was tested against independent experimental data yielding good agreement between predicted and observed data. Overall, this constitutes an important tool to overcome dormancy in a way that should result in a more efficient and faster production of kiwifruit seedlings or rootstocks. [ABSTRACT FROM AUTHOR]