Period Of Cold Stratification Research Articles

Germination Kinetics of Ferula communis L. Seeds, a Potentially Multipurpose-Use Wild Species

Despite exhibiting intriguing features associated with its multipurpose applications and drought tolerance, Ferula communis remains a wild and uncultivated species, with limited experimental research on its biology, starting from seed germination and extending to its ecology. The purpose of this study was to investigate potential germination and kinetics in F. communis seeds in response to four cold stratification periods (0, 15, 45, and 90 days at a constant temperature of 5 °C) and four temperatures (5, 10, 15, and 20 °C) under continuous darkness. F. communis exhibited a pronounced germination potential exceeding 90%, with the optimal temperature for germination falling within the range of 5 °C to 15 °C, without necessitating cold stratification. A dramatic drop of the germination percentage was observed at 20 °C (<10%), suggesting a form of conditional dormancy attributed to the higher temperature tested.

Effects of H2SO4, GA3, and cold stratification on the water content, coat composition, and dormancy release of Tilia miqueliana seeds

IntroductionTilia miqueliana is an endemic species whose population is declining. The permeability barrier and mechanical constraint of the pericarp (seed coat) are important causes of its seed dormancy. Although there has been considerable research on this subject, questions remain regarding how the permeability barrier and mechanical constraint of the seed coat are eliminated during dormancy release and how water enters the seed. Therefore, protecting the species by improving its germination/dormancy breaking in the laboratory is urgentMethodsIn this study, the changes in the cellular structure, mechanical properties, and components of the Tilia miqueliana seed coat after an H2SO4-gibberellic acid (GA3) treatment were analyzed during dormancy release. Various analyses (e.g., magnetic resonance imaging, scanning electron microscopy, and paraffin section detection) revealed the water gap and water channel.ResultsThe H2SO4 treatment eliminated the blockage at the micropyle and hilum of the seeds. Water entered the seeds through the water gap (micropyle) rather than through the hilum or seed coat, after which it dispersed along the radicle, hypocotyl, and cotyledon to the endosperm. During the cold stratification period, the cellular structure was damaged and an increasing number of holes appeared on the inner and outer surfaces of the seed coat. Vickers hardness tests showed that GA3 decreased the seed coat hardness. Additionally, the seed coat lignin and total phenol contents continuously decreased during the cold stratification period. Notably, the Liquid chromatography–mass spectrometry (LC–MS) analysis of the seed coat detected polyethylene glycol (osmoregulator), which may have destabilized the water potential balance inside and outside the seed and increased the water content to levels required for germination, ultimately accelerating seed dormancy release.DiscussionThis sophisticated and multi-level study reveals how H2SO4 and GA3 eliminate the permeability barrier and mechanical constraints of the seed coat during dormancy release of Tilia miqueliana seeds. This will be beneficial to artificially assist the natural regeneration and population expansion of Tilia miqueliana.

Dormancy-release and germination improvement of Korean bellflower (Campanula takesimana Nakai), a rare and endemic plant native to the Korean peninsula.

Korean bellflower (Campanula takesimana Nakai) is a rare and perennial herb with medicinal and ornamental values, is endemic to the Ulleung Island of Korea. In this study, we investigated the dormancy-release and germination characteristics of C. takesimana (Campanulaceae) seeds by subjecting them to varying temperatures (5, 10, 15, 20, and 25°C and diurnal/nocturnal temperatures of 15/6, 20/10, and 25/15°C), cold stratification periods (0, 4, 8, or 12 weeks at 5°C), and gibberellic acid (GA3) concentrations (0, 10, 100, or 1,000 mg·L-1 at 15/6°C and 25/15°C) to identify the ideal seed propagation conditions. The seeds were stimulated to germinate (at 25°C, 12-h photoperiod with fluorescent lamps at 40 ± 10 μmol∙m-2∙s-1) after cold stratification. To examine the germination characteristics, the seeds were tested for water imbibition and found to readily absorb water. The seeds exhibited underdeveloped embryos during dispersal, showed final germination of 37.00% ± 4.43 at 25°C and were not influenced by temperature. The seeds subjected to 0, 4, 8, or 12 weeks of cold stratification germinated at a success rate of 22.00% ± 4.76, 87.00% ± 6.80, 79.00% ± 2.52, and 77.00% ± 1.91, respectively. Additionally, the germination characteristics, which were based on final germination, mean germination time, and germination velocity (Timson index), were significantly greater in the seeds pretreated with 1,000 mg·L-1 GA3 at 25/15°C than in seeds pretreated with 0 mg·L-1 GA3. Overall, the seeds broke dormancy with GA3 and short-term cold stratification. Therefore, we concluded that C. takesimana seeds have non-deep, simple, morphophysiological dormancy, and pretreatment with cold stratification and GA3 is required for effective seed propagation.

Seed Germination Behavior, Molecular Analysis of Four Populations of Arbutus andrachne Species from Greece, and Cultivation Practice for Producing High-Quality Plants

Arbutus andrachne, the Greek strawberry tree, is an evergreen shrub or small tree in the family Ericaceae native to the Mediterranean basin, and is a valuable phytogenetic resource. In the context of sustainable exploitation of A. andrachne, four Greek natural populations of species were selected and a detailed germination protocol, molecular analysis, and cultivation practices were reported herein for the first time. The 1 month period of cold stratification or the treatment with gibberellic acid resulted in similar patterns of seed germination over a wide temperature range for all four populations. Differences among the four populations were observed in five of six morphological traits measured in 1-year-old seedlings. The 2-year-old plants grown in plastic bags (2.26 L in volume) showed superior growth rates. Foliage, but not roots, of 2-year-old seedlings supplemented with mineral fertilizers had higher fresh masses than untreated seedlings. The four A. andrachne accessions exhibited more genetic variability within than among populations.

A REVIEW OF BREAKING SEED DORMANCY IN HAWTHORNS (CRATAEGUSSPP.)

Propagation of hawthorns (Crataegusspp.) is difficult, and vegetative methods are not responsive in a sufficient manner. So, seed propagation is prevalently used to propagate hawthorns. However, hard endocarp and embryo dormancy restrict the germination of hawthorns. To overcome these restrictions, many treatments have been tested in the researches. Some of them were magnificent and others ineffective. It has been resolved that warm and cold stratification are the best for breaking dormancy in seeds of hawthorns. Thus far, no substitution has been found for warm and cold stratification treatment to release the seeds of hawthorns from dormancy, from the conventional point of view. Besides, combination with other factors may reduce the period and temperature degrees of warm and cold stratification, for instance, species, eliminating endocarp, treatment with growth regulators, and chemical scarification. In this review, the results of methods will be referred to that used in the studies to break seed dormancy in hawthorns.

Elevation impact on seed germination requirements for two Asteraceae species

Elevation and latitude correlate with environmental factors that drive natural selection. Climate-change projections in the Great Basin suggest higher temperatures and increasingly lower annual winter snowfall, especially at low elevations. The transition from dormancy to germination represents a vulnerable stage of plant phenology, given the high susceptibility to death in newly germinated seedlings. Consequently, mechanisms involved with this phenomenon and its timing play an essential role in plant population fitness. This study investigates seed dormancy and germination for 2 co-occurring Asteraceae/Compositae species: arrowleaf balsamroot (<i>Balsamorhiza sagittata</i> (Pursh) Nutt.) and shiny mule’s ear (<i>Wyethia amplexicaulis</i> (Nutt.) Nutt.) from the same geographic area (near Provo Canyon, Utah) across an elevation gradient of 1584 m to 2438 m (5200–8000 ft). In laboratory experiments, seeds received increasing periods of cold stratification at 2 °C (35.6 °F) (from 4–20 wk) followed by incubation at 10 to 20 °C (50–68 °F). Shiny mule’s ear seeds from low (1584 m [5200 ft]) and mid (2011 m [6600 ft]) elevations required 8 wk of cold stratification while seeds from the highest elevation required 12 wk to reach 50% germination. Seeds of arrowleaf balsamroot from all elevations reached 50% germination after 16 wk of cold stratification although germination rate varied by elevation. These results suggest that selection pressure in contrasting environments results in variable dormancy-breaking durations, with implications for propagation, projected climate change, and seed sourcing in restoration efforts. Brown A, Allen PS. 2023. Elevation impact on seed germination requirements for two Asteraceae species. Native Plants Journal 24(1):45–53.

Mimicking the natural thermal environments experienced by seeds to break physiological dormancy to enhance seed testing and seedling production

Physiological dormancy (PD) is the most common class of seed dormancy on earth. It is highly variable and is an important part of the adaptation of many species to their habitat. Often, two questions are asked about seeds that failed to germinate in a germination test: (1) are they non-viable or dormant, and (2) if dormant do they have PD and how is it broken? We provide an overview on how to approach studies of species with PD for which few or no data are available. Information about habitat environmental conditions during the seed stage can be used to formulate hypotheses on dormancy-breaking and germination requirements. These hypotheses can be tested by a move-along experiment. There are three levels of PD, and they are distinguished by the conditions required to break PD and promote germination. Seeds with non-deep PD (the most common level of PD) require different conditions for dormancy-break and germination, i.e.a change in the season, while those with intermediate and deep PD germinate at the dormancy-breaking conditions, e.g.during a long period of cold stratification. Knowing how to break PD enhances testing for seed viability and helps ensure high germination percentages of viable seeds.

Contrasting aspects of the physical and physiological dormancy shown by seeds from different peach rootstocks

Considering that cultivars of peach rootstocks selected to be propagated by seeds show variation in the degree of physiological dormancy and peculiarities regarding the limitation imposed by the endocarp, it is essential to define the cold stratification period and the ideal temperature to be used during the pre-germination treatment. Isolated for each cultivar, knowledge of these variables which will provide viability in the production of peach rootstocks via seeds, in the presence of the endocarp, at a larger scale. Two germination tests were carried out, in a completely randomized experimental design and 4 x 3 factorial scheme, with four replications, each one consisting of 25 endocarps. The first experiment was performed with four cultivars (Aldrighi, Capdebosq, Okinawa Roxo and Tsukuba 1) and three stratification temperatures (1°C, 4°C and 7°C) for a period of 90 days. For the second experiment, the same cultivars were used, two temperatures (7°C for ‘Aldrighi’ and ‘Capdebosq’ and 4°C for ‘Okinawa Roxo’ and ‘Tsukuba’) and three stratification periods (40, 80 and 120 days), followed by sowing in substrate under greenhouse conditions for a period of 45 days, with subsequent endocarp breaking and re-sowing. The pre-germination treatment at 7°C for 90 days is sufficient to obtain high germination percentage of ‘Aldrighi’ and ‘Capdeboscq’ seeds in the presence of the endocarp. Under the stratification conditions tested, the seeds of ‘Okinawa Roxo’ and ‘Tsukuba 1’ require rupture of the endocarp to reactivate the germinative embryonic process.

Projected winter warming unlikely to affect germination success of balsam fir regeneration in Atlantic Canada

Abstract Climate warming has the potential to influence forest composition and species recruitment over the course of the 21st century. Although many of these impacts are expected to occur during the growing season, important life history events, like seed dormancy release, may be affected during the winter. For seeds of balsam fir (Abies balsamea (L.) Mill.) to germinate, they require a lengthy cold stratification period to break seed dormancy, which may not be experienced under warmer winters. Moreover, within Atlantic Canada, balsam fir populations experience very different climates. Dissimilarities among the genetics of these balsam fir populations and adaptations to their local environments may engender variations in population response to winter warming. In this study, we selected three balsam fir seedlots each from four different seed origin zones within Atlantic Canada and subjected them to simulated winter warming in outdoor seed plots that were heated to ≈ 6°C above the ambient temperature from December to April. Contrary to our hypotheses, germination success of the heated balsam fir seeds did not significantly decrease relative to the controls, and there was no interaction between warming and seed origin zone. Seedlots of some seed origin zones exhibited variable responses to warming, suggesting that dormancy levels substantially differ among populations from similar climates. This diversity in phenotype expression within balsam fir populations may improve this species resilience under future climate change.

Cold stratification in winter is more than enough for seed dormancy-break of summer annuals in eastern North America: implications for climate change

AbstractGermination of seeds of some summer annuals in Kentucky (eastern USA) in late-winter lead to the hypothesis that under present climate conditions the whole length of the winter cold stratification (CS) period is not required for dormancy-break of seeds of summer annuals with physiological dormancy (PD). We evaluated our data from germination phenology studies of 45 species (69 datasets) and buried-seed studies of 33 species (44 datasets). We determined time and temperature of germination after CS and percentage of the total number of hours of CS during winter (% of winter CS) seeds received prior to start of germination. In the phenology studies, mean temperature during the week of first germination for C3 and C4 species was 11.1 and 14.4°C, respectively, and % of winter CS was 80.8 and 87.4, respectively. In the buried-seed studies, % of CS for C3 and C4 species was 40.8 and 48.1, respectively, when they germinated to 25% at 20/10°C. For 32 of 33 species in the buried-seed studies, the minimum temperature at which seeds germinated decreased with increased CS; thus, seeds had Type 2 non-deep PD. The time of germination is controlled by a number of hours of CS, a decrease in minimum temperature at which seeds can germinate and a temperature increase in early spring. Seeds can germinate at relatively high temperatures as early as December and January, but they continue to be CS until spring. Temperature increases in eastern North America due to global warming are not likely to inhibit the germination of summer annuals with PD in spring.

Non-Deep Simple Morphophysiological Dormancy and Germination Characteristics of Gentiana triflora var. japonica (Kusn.) H. Hara (Gentianaceae), a Rare Perennial Herb in Korea

This study investigated the kind of seed dormancy and seed germination of Gentiana triflora var. japonica (Kusn.) H. Hara for developing a seed propagation method. The seeds were collected in October 2020 from plants at Mt. Sobaeksan, Korea. In a water imbibition experiment, seed weights increased by >101.9% of their initial masses over 12 h. Effects of incubation temperature (5, 15, 20, 25, 15/6, or 25/15 °C), cold stratification period (5 °C; 0, 4, 8, or 12 weeks), and gibberellic acid (GA3; 0, 10, 100, or 1000 mg∙L−1) and potassium nitrate treatment (KNO3; 0, 1000, 2000, or 4000 mg∙L−1) on seed germination were investigated to characterize seed dormancy. These seeds exhibited underdeveloped embryos during seed dispersal. The seeds failed to reach the final germination of 15.0% after treatment at 5, 15, 20, 25, 15/6, or 25/15 °C. After cold stratification for 8 weeks, the germination increased dramatically by >90.0% compared to that at 0 weeks. After the GA3 treatment, the germination reached >80.0% within 5 days. The final germination was 90.0% in the 100 mg∙L−1 GA3 treatment group. However, the KNO3 treatment had no effect on seed germination. Therefore, the G. triflora var. japonica seeds exhibited non-deep simple morphophysiological dormancy.

Simulated winter warming has negligible effects on germination success of Acadian Forest tree species

Dormant seeds that require long periods of cold stratification to become germinable may be most sensitive to increases in winter temperatures caused by anthropogenic climate change. In this study, we used outdoor plots with infrared heaters to simulate the effects of projected winter warming (+6 °C) for Canada’s Acadian Forest Region and compared seed germination success of tree species with varying stratification requirements. We evaluated four seedlots each of balsam fir (Abies balsamea (L.) Mill.), red spruce (Picea rubens Sarg.), white pine (Pinus strobus L.), red maple (Acer rubrum L.), sugar maple (Acer saccharum Marshall), and yellow birch (Betula alleghaniensis Britton). Three central findings emerged from this study: (i) none of the tested species were significantly affected by warming; (ii) the random effect of seedlot explained more variation in germination success of deciduous species than it did for conifers; and (iii) balsam fir seedlots exhibited considerable differences in their response to warming, implying intraspecific variation in depth of dormancy. These results suggest seed germination success of the tested tree species may not be impeded by their individual seed characteristics under the magnitude of winter warming projected over the coming century in our study area.

Evidence of interpopulation variation in the germination of Eryngium maritimum L. (Apiaceae)

Germination is considered as one of the most crucial steps in a plant’s lifetime. The germination of Eryngium maritimum, a dune species located across all European coasts, has been extensively analysed in Northern populations, where it is considered a locally endangered species. However, less attention has been given to southern populations, where the knowledge about the germination of the species is very limited. The main objective of the present study was to analyse the effect of cold stratification in one Mediterranean and one Atlantic population of the species, as well as to compare the potential variation of seed dormancy among a latitudinal gradient in European populations based on current literature. Seeds collected from Mallorca (Mediterranean, Spain) and Asturias (Atlantic, Spain) were germinated at different temperatures and cold stratification periods ranging from 4 to 20 weeks. These results were merged with the results of previous studies to test the potential effect of latitude and climatic variables in germination. Although the optimal incubation temperature was 10 ºC, the highest final germination percentages (up to 96%) was obtained in both populations combining specific cold stratification periods (5 ºC) and constant incubation temperatures (15–20 ºC). Atlantic seeds needed longer cold stratification times to reach high germination percentages compared with Mediterranean seeds. Apart from the stratification response, significant differences in viability and in germination were observed between the Atlantic and the Mediterranean populations. Considering data from previous studies in the analysis, the results suggest that there is a potential effect of latitude in the ecological germination requirements, by which the higher the latitude, the longer the cold stratification period required to germinate, with a correlation with the mean annual temperature. These results suggests that two factors, modulation of dormancy relating to adaptative or maternal effects and viability, govern the germination of the species.

Seed Dormancy and Soil Seed Bank of the Two Alpine Primula Species in the Hengduan Mountains of Southwest China.

The timing of germination has long been recognized as a key seedling survival strategy for plants in highly variable alpine environments. Seed dormancy and germination mechanisms are important factors that determining the timing of germination. To gain an understanding of how these mechanisms help to synchronize the germination event to the beginning of the growing season in two of the most popular Primula species (P. secundiflora and P. sikkimensis) in the Hengduan Mountains, Southwest China, we explored their seed dormancy and germination characteristics in the laboratory and their soil seed bank type in the field. Germination was first tested using fresh seeds at two alternating temperatures (15/5 and 25/15°C) and five constant temperatures (5, 10, 15, 20, and 25°C) in light and dark, and again after dry after-ripening at room temperature for 6 months. Germination tests were also conducted at a range of temperatures (5–30, 25/15, and 15/5°C) in light and dark for seeds dry cold stored at 4°C for 4 years, after which they were incubated under the above-mentioned incubation conditions after different periods (4 and 8 weeks) of cold stratification. Base temperatures (T b) and thermal times for 50% germination (θ 50) were calculated. Seeds were buried at the collection site to test persistence in the soil for 5 years. Dry storage improved germination significantly, as compared with fresh seeds, suggesting after-ripening released physiological dormancy (PD); however, it was not sufficient to break dormancy. Cold stratification released PD completely after dry storage, increasing final germination, and widening the temperature range from medium to both high and low; moreover, the T b and θ 50 for germination decreased. Fresh seeds had a light requirement for germination, facilitating formation of a persistent soil seed bank. Although the requirement reduced during treatments for dormancy release or at lower alternating temperatures (15/5°C), a high proportion of viable seeds did not germinate even after 5 years of burial, showing that the seeds of these two species could cycle back to dormancy if the conditions were unfavorable during spring. In this study, fresh seeds of the two Primula species exhibited type 3 non-deep physiological dormancy and required light for germination. After dormancy release, they had a low thermal requirement for germination control, as well as rapid seed germination in spring and at/near the soil surface from the soil seed bank. Such dormancy and germination mechanisms reflect a germination strategy of these two Primula species, adapted to the same alpine environments.

Seed dormancy and germination of Asarum sieboldii, a disjunct relict species in East Asia.

Disjunct species in the same genus are a common feature of the flora in the temperate forests of East Asia and eastern North America. This study aimed to evaluate whether the kind of seed dormancy was maintained after species in the genus Asarum (Aristolochiaceae) were separated from their common ancestor. We classified the seed dormancy of Asarum sieboldii, an East Asian species, based on a phenology study and experiments in controlled temperature conditions, and then compared it to that of the previously studied A. canadense, an eastern North American species. The underdeveloped embryo of A. sieboldii grew and germinated (radicle emergence) in autumn but shoot emergence did not occur until the following spring. The seeds of A. sieboldii had deep simple epicotyl morphophysiological dormancy because the seeds with emerged radicle required a relatively long period of cold stratification to break epicotyl dormancy and produce a shoot. Although the seed of A. sieboldii had weaker radicle dormancy and stronger epicotyl dormancy compared to A. canadense, the kind of seed dormancy was the same for the two species. The trait of seed dormancy was inherited from a shared common ancestor and maintained in populations well after the two species (or their ancestors) separated. However, quantitative differences in temperature requirements for radicle and shoot emergence suggest the possibility of adaptation to the environment.

Seed Dormancy of &lt;i&gt;Viola mandshurica&lt;/i&gt; and &lt;i&gt;V. albida&lt;/i&gt; and Their Germination Characteristics by Seed Storage

The purpose of this study was to determine the seed dormancy types of Viola mandshurica and V. albida, and to investigate their germination characteristics during seed storage. V. mandshurica seeds were incubated at 25/15, 20/10, and 15/6°C with final germination rates of 86%, 66%, and 66%, respectively, indicating that these seeds have no physiological dormancy (PD). However, V. albida seeds were found to have PD, since germination hardly occurred during the 4-week experiment, and the final germination rate was 50% or less. When the seeds of V. albida were treated with GA3 1000 mg･L-1, the final germination rate was 100%. Moreover, the germination rate increased as the period of cold stratification for V. albida seeds increased. The germination characteristics of Viola seeds were also examined from seeds harvested in 2019. V. mandshurica seeds germinated at 25/15°C in one week, but the mean germination time decreased compared to seeds that were stored for 4 years. This shows that V. mandshurica has reduced seed viability during storage. V. albida seeds that were harvested in 2019 hardly germinated within the 4-week experiment, and the germination rate increased through cold stratification. Therefore, the seeds of V. mandshurica and V. albida do not change the seed dormancy type, but the seed viability might be affected by the type of long-term storage used.

Effects of cold stratification on the endogenous hormone, dormancy and germination of Cornus walteri Wanger seeds

The most critical phase in plant life is the germination period, which is influenced by both intrinsic and environmental factors. Assessment of cold stratification on several endogenous hormone, IAA, abscisic acid (ABA), gibberellin GA1/3 (GA1/3), zeatin-riboside (ZRs) and isopen-tenyl adenine (iPAs), and germination of Cornus walteri Wanger. seeds was done. Relationship between endogenous hormone and seed germination and mechanism of seed dormancy of C. walteri were also analysed. The results showed that the significant fluctuatation of both IAA and iPAs content was fond during cold stratification period, while the variation of ZRs was little, that of both ABA and GAs content increased with old stratification days. Effects of cold stratification on both GR and GP were significant (p &lt; 0.05), which play an important role in releaving of seed germination and improving seed germination. The GR and GP were significantly negatively correlated with the contents of ABA and GA1/3, and positively correlated with the following iPAs, ZRs/ABA, iPAs/ABA.

Predicting the consequences of global warming on Gentiana lutea germination at the edge of its distributional and ecological range.

BackgroundTemperature is the main environmental factor controlling seed germination; it determines both the percentage and the rate of germination. According to the Intergovernmental Panel on Climate Change, the global mean surface temperature could increase of approximately 2–4 °C by 2090–2099. As a consequence of global warming, the period of snow cover is decreasing on several mountain areas. Thermal time approach can be used to characterise the seed germination of plants and to evaluate the germination behaviour under the climate change scenarios. In this study, the effect of different cold stratification periods on seed dormancy release and germination of Gentiana lutea subsp. lutea, a taxon listed in Annex V of the Habitats Directive (92/43/EEC), was evaluated. Furthermore, the thermal requirements and the consequences of the temperature rise for seed germination of this species were estimated. In addition, a conceptual representation of the thermal time approach is presented.MethodsSeeds of G. lutea subsp. lutea were harvested from at least 50 randomly selected plants in two representative localities of the Gennargentu massif (Sardinia). Germination tests were carried out under laboratory conditions and the responses at 5, 10, 15, 20, 25 and 30 °C were recorded. Different cold stratification pre-treatments at 1 ± 1 °C (i.e. 0, 15, 30, 60 and 90 days) were applied. Successively, the base temperature (Tb) and the number of thermal units (θ, °Cd) for germination were estimated. Additionally, this study examined the consequences of an increase in temperatures based on the Representative Concentration Pathways (RPC) scenarios.ResultsThe results indicated that from 0 to 30 days of cold stratification, the germination was null or very low. After 60 and 90 days of cold stratification the seed dormancy was removed; however, 25 and 30 °C negatively affected the germination capacity of non-dormant seeds. Seeds cold-stratified for 90 days showed a lower Tb than those stratified for 60 days. However, 60 and 90 days of cold stratification did not cause great variations in the thermal time units. Analysing the RPC scenarios, we detected that the number of days useful for dormancy release of seeds of G. lutea may be less than 30 days, a condition that does not permit an effective dormancy release.ConclusionsWe conclude that seeds of G. lutea need at least 60 days of cold stratification to remove dormancy and promote the germination. The thermal time model developed in this work allowed us to identify the thermal threshold requirements of seed germination of this species, increasing the knowledge of a plant threatened by global warming. Our results emphasise the need for further studies aiming at a better characterisation of germination efficiency, especially for species that require cold stratification. This would improve the knowledge on the germination mechanisms of adaptation to different future global warming conditions.

Cold Stratification and Pericarp Removal Improve Seed Germination of Ptelea trifoliata and Ptelea crenulata

Two species of North American shrubs in the genus Ptelea (Rutaceae), commonly known as eastern and western hoptree or wafer ash, have unfulfilled potential to increase the diversity of managed landscapes and support populations of pollinators and swallowtail butterflies. The white flowers of Ptelea are highly fragrant, and pistillate flowers give rise to clusters of distinctive samaras. The insufficiency of information about improving germination of seeds of Ptelea trifoliata and lack of recommendations for Ptelea crenulata prompted us to investigate effects of pericarp removal and cold (4 °C) stratification periods of 0, 4, 8, and 16 weeks on the germination of seeds of these two species. Samaras were collected from multiple plants of both species in the midwestern United States (P. trifoliata) and California (P. crenulata). The germination percentage of viable seeds, calculated after tests of viability with tetrazolium chloride of seeds that did not germinate, increased with longer stratification periods, with 100% germination for P. crenulata and 91% germination for P. trifoliata after 16 weeks of stratification. The germination value, a measure of the speed and uniformity of germination, and peak value also increased with longer stratification in both species. Pericarp removal increased the germination percentage of both species and increased the peak and germination value of P. crenulata. Propagators seeking to grow these species of Ptelea from seed should remove the pericarp and cold-stratify seeds for 16 weeks to improve germination success.

Seed germination characteristics of invasive Spartina alterniflora Loisel in Japan: implications for its effective management

Spartina alterniflora, intentionally or unintentionally introduced worldwide, has adversely impacted local Japanese ecosystems. Thus, prediction of future distributions of S. alterniflora and its management are required. Local population expansion after establishment depends heavily on asexual (clonal) reproduction, whereas sexual (seed) reproduction is one of the critical factors for estimating invasion success and the likelihood of colonization to new habitats. However, knowledge about the germination characteristics of S. alterniflora is lacking. Here, we report the environmental conditions suitable for germination of S. alterniflora, under variable conditions of cold stratification periods (0, 4, 8 weeks), temperature (constant, alternating temperature), light (light/dark, dark), and oxygen (aerobic, anaerobic). Cumulative germination rate of S. alterniflora increased with an increasing period of cold stratification. Its seeds clearly preferred aerobic conditions to germinate. Also, the germination rate was higher under alternating temperature than under constant temperature regardless of light and oxygen conditions in any cold stratification period. However, long-term cold stratification, alternating temperature, and aerobic conditions were more important for germination of S. alterniflora than light. Removal of soil seed banks within 8 weeks of cold stratification after seed dispersals with matured seeds may be effective approaches for disrupting the germination of S. alterniflora.