Physiological dormancy in seeds of tropical montane woody species in Hawai`i

Worldwide, there is relatively little information on seed dormancy and germination of tropical montane species. Our aim was to help fill this knowledge gap by conducting seed dormancy/germination studies on woody species from this vegetation zone in Hawai`i. All species had water-permeable seeds with a fully developed embryo. Seeds of 29 species (23 genera) were incubated in light/dark at 15/6, 20/10 and 25/15°C and germination monitored at 2-week intervals for 16–128 weeks. Seeds of Chenopodium oahuense, Dubautia menziesii and Silene lanceolata were non-dormant (ND) and those of 26 other species had physiological dormancy (PD); 10 of the 26 species had conditional PD. The optimum germination temperature regime(s) was (were) 25/15°C, 17 species; 25/10 and 20/10°C, 2; 20/10°C, 6; 20/10 and 15/6°C, 2; and 15/6°C, 2. Worldwide, PD in the woody genera included in our study is more common than ND. In addition to its contribution to the world biogeography of seed dormancy/germination, this study will be useful to conservation biologists who need to germinate seeds of tropical montane species.     

Adaptation to habitat in Aquilegia species endemic to Sardinia (Italy): Seed dispersal,germination and persistence in the soil

Abstract

The autecology of the Sardinian endemics Aquilegia barbaricina Arrigoni et Nardi and A. nugorensis Arrigoni et Nardi were investigated. Peaks of anthesis and seed dispersal were recorded for five populations occurring in two distinct habitats, one riparian and one rupicolous. Germination tests were carried out on seed lots belonging to each population by sowing seeds at 10, 15, 20, 25 and 25/15°C. In addition, seeds were incubated for 2 months at either 25°C (summer), 5°C (winter) or 25°C for 2 months plus 2 months at 5°C (summer followed by winter–SW), and then moved to the germination temperatures. Embryo measurements were taken during pre-treatments and germination. Experimental seed burials were carried out for two populations of each species. Both species dispersed in summer. The population of A. nugorensis occurring on rocky outcrops differed in phenology from both the other A. nugorensis population from riparian vegetation and from A. barbaricina. Both species showed morphophysiological seed dormancy, with <50% germination under laboratory conditions. All riparian populations germinated only after the SW pre-treatment, while the rupicolous population germinated at 25°C, without any pre-treatment. Low germination percentages were observed in the experimental seed burials, suggesting the ability for both species to form a persistent soil seed bank.     

Effect of temperature and cold stratification on seed germination of the Mediterranean wild aromatic Clinopodium sandalioticum (Lamiaceae)

A germination study was carried out on seeds of Clinopodium sandalioticum (Bacch. & Brullo) Bacch. & Brullo ex Peruzzi & Conti (Lamiaceae), a wild aromatic plant endemic to Sardinia. Seeds were incubated at a range of constant (5–25°C) and an alternating temperatures regime (25/10°C), with 12 hours of irradiance per day. The results achieved at 10°C were also compared with those obtained after a period of cold stratification at 5°C for three months. Final seed germination ranged from ca. 28% (5°C) to ca. 72% (25/10°C). A base temperature for germination (T_b) of ca. 5°C and a thermal constant for 50% germination (S) of 89.3°Cd were identified and an optimal temperature for germination (T_o) was estimated to be comprised between 20 and 25°C. Cold stratification negatively affected seed viability and germination at 10°C. Although a typical “Mediterranean germination syndrome”, could not be detected for C. sandalioticum seeds, these results were coherent with those previously reported for other Mediterranean Lamiaceae species.     

Seed dormancy,germination and soil seed bank of Lamiophlomis rotata and Marmoritis complanatum (Labiatae), two endemic species from Himalaya–Hengduan Mountains

Seed dormancy and germination characteristics are important factors determining plant reproductive success. In this study, we aimed to explore the characteristics of seed dormancy and germination of two endemic Labiatae species (Lamiophlomis rotata and Marmoritis complanatum) in the Himalaya–Hengduan Mountains. Germination was first tested in the light using freshly matured seeds at 25/15 and 15/5°C, and then again after dry after-ripening. Dried seeds were incubated in the light at a range of constant temperatures (1–35°C). The effects of dark and GA₃ on germination were tested at several different temperatures. Base temperature (T_b) and thermal times for 50% final germination (θ₅₀) were calculated. Seeds were also buried at the collection site to test seed persistence in the soil. Increased final germination after dry after-ripening indicated that the seeds of the two species exhibited non-deep physiological dormancy; however, they exhibited different germination characteristics and soil seed bank types. In L. rotata, GA₃ only promoted germination at 5°C, producing no significant effect at other temperatures. Dark conditions decreased germination significantly at all temperatures. T_b and θ₅₀ values were 0.6 and 82.7°C d. The soil seed bank of this species was classified as persistent. In M. complanatum, GA₃ significantly promoted germination at all temperatures except 15°C. Dark conditions depressed germination significantly at warmer temperatures (20 and 25°C) but had no effect at lower temperatures. T_b and θ₅₀ values were 0.1 and 92.3°C d. The soil seed bank was classified as transient. Our results suggest that the seed dormancy and germination of the two co-existing species share some commonalities but there are also species-specific adaptations to the harsh alpine environment.     

Determination of seed viability of eight wild Saudi Arabian species by germination and X-ray tests

Our purpose was to evaluate the usefulness of the germination vs. the X-ray test in determining the initial viability of seeds of eight wild species (Salvia spinosa, Salvia aegyptiaca, Ochradenus baccatus, Ochradenus arabicus, Suaeda aegyptiaca, Suaeda vermiculata, Prosopisfarcta and Panicumturgidum) from Saudi Arabia. Several days were required to determine viability of all eight species via germination tests, while immediate results on filled/viable seeds were obtained with the X-ray test. Seeds of all the species, except Sa.aegyptiaca, showed high viability in both the germination (98–70% at 25/15 °C, 93–66% at 35/25 °C) and X-ray (100–75%) test. Furthermore, there was general agreement between the germination (10% at 25/15 °C and 8% at 35/25 °C) and X-ray (5%) tests that seed viability of Sa.aegyptiaca was very low, and X-ray analysis revealed that this was due to poor embryo development. Seeds of P.farcta have physical dormancy, which was broken by scarification in concentrated sulfuric acid (10 min), and they exhibited high viability in both the germination (98% at 25/15 °C and 93% at 35/25 °C) and X-ray (98%) test. Most of the nongerminated seeds of the eight species except those of Sa.aegyptiaca were alive as judged by the tetrazolium test (TZ). Thus, for the eight species examined, the X-ray test was a good and rapid predictor of seed viability.     

Predicting patterns of post-fire germination in 35 eastern Australian Fabaceae

Germination in 35 species from 15 legume genera of southeastern Australia was promoted by a heat treatment which broke the seed coatcaused dormancy. Once the critical temperature was reached, most seeds had their dormancy broken, independent of the duration of heating. Species fell into three classes according to whether their dormancy was broken by a temperature of 40, 60 or 80°C. Highest germination in all species was achieved by heating in the temperature range 80–100°C, although long durations (120 min) at 100°C caused seed death in several species. At 120°C, seeds of most species were killed at all but one minute's duration. A proportion of seeds from 7 species (Acacia myrtifolia, Pultenaea daphnoides, P. incurvata, P. linophylla, P. polifolia, Dillwynia floribunda and Sphaerolobium vimineurn) was not killed at 120°C and had their dormancy broken. This proportion varied markedly and resultant germination levels were significantly less than those at 80 and 100°C, except in S. vimineum. Between-site variations in the 4 species tested (A. myrtifolia, A. suaveolens, A. terminalis and A. ulicifolia) were small. These variations concerned: (i) the minimum temperature required to break seed dormancy in 2 species: 60°C in one population of A. myrtifolia and A. suaveolens, and 80°C in the other; and (ii) the intensity of the germination response. Duration of heating was less important than temperature as a determinant of germination. Ordination techniques revealed that results from one duration across temperatures were comparable with data from multiple durations. This has significant applications in studying rare species, where seed may be in short supply. Predicted germination levels after a moderate intensity fire should far exceed those after a low intensity fire. Little germination was predicted for many species after a low intensity fire and for one species, A. elongata, no germination was predicted. The potential role of indicator species in relation to the maintenance of species in a community is suggested.     

Physiological characteristics underpinning successful cryopreservation of endemic and endangered species of Bromeliaceae from the Brazilian Atlantic Forest

The germination requirements and the basis of the optimal water content before and after cryopreservation were studied for ten endangered Brazilian species of Bromeliaceae. Constant and alternating temperature regimes were used to determine the best conditions for seed germination. The relationship between seed water content and relative humidity was evaluated using water sorption isotherms at 15 °C. Seeds were cryostored at four water contents (3, 5, 7 and 9%) and three storage periods (0, 180 and 365 days), and loss in viability and vigour were estimated. Fresh seeds of all species showed maximum germination in < 30 days at temperatures between 20 and 30 °C, indicating the absence of a physical/morphological dormancy. A sigmoidal relationship between seed water content and relative humidity was observed with no apparent differences in sorption characteristics among the species. The optimum water content for cryopreservation of most of these species was c. 7%. Ultra‐drying (3% seed water content) had a detrimental effect on seed viability and vigour. Our experiments suggested orthodox storage behaviour for all species of Bromeliaceae examined as they are able to survive desiccation and freezing. This study has shown the feasibility of ex situ conservation in seed cryobanks of endangered bromeliads from the Brazilian Atlantic Forest to support future reintroduction of these species in nature. © 2014 The Linnean Society of London, Botanical Journal of the Linnean Society, 2014, 176 , 567–576.     

Combinational dormancy in seeds of Sicyos angulatus (Cucurbitaceae,tribe Sicyeae)

Seeds with a water‐impermeable seed coat and a physiologically dormant embryo are classified as having combinational dormancy. Seeds of Sicyos angulatus (burcucumber) have been clearly shown to have a water‐impermeable seed coat (physical dormancy [PY]). The primary aim of the present study was to confirm (or not) that physiological dormancy (PD) is also present in seeds of S. angulatus. The highest germination of scarified fresh (38%) and 3‐month dry‐stored (36%) seeds occurred at 35/20°C. The rate (speed) of germination was faster in scarified dry‐stored seeds than in scarified fresh seeds. Removal of the seed coat, but leaving the membrane surrounding the embryo intact, increased germination of both fresh and dry‐stored seeds to > 85% at 35/20°C. Germination (80–100%) of excised embryos (both seed coat and membrane removed) occurred at 15/6, 25/15 and 35/20°C and reached 95–100% after 4 days of incubation at 25/15 and 35/20°C. Dry storage (after‐ripening) caused an increase in the germination percentage of scarified and of decoated seeds at 25/15°C and in both germination percentage and rate of excised embryos at 15/6°C. Eight weeks of cold stratification resulted in a significant increase in the germination of scarified seeds at 25/15 and 35/20°C and of decoated seeds at 15/6 and 25/15°C. Based on the results of our study and on information reported in the literature, we conclude that seeds of S. angulatus not only have PY, but also non‐deep PD, that is, combinational dormancy (PY + PD).     

Fire‐related cues break seed dormancy of six legumes of tropical eucalypt savannas in north‐eastern Australia

Abstract This paper describes an assessment of the effect of exposure to fire‐related cues (heat shock, smoke and nitrate) and the interactions between the cues on seed dormancy release of tropical savanna legumes in north‐eastern Australia. Ten legume species were tested, comprising both native and exotic species. The ten species responded variously to the treatments. Brief exposure to temperatures between 80 and 100°C was found to break the seed dormancy of the native ephemeral herbs Chamaecrista mimosoides, Crotalaria calycina, Crotalaria montana, Indigofera hirsuta and Tephrosia juncea, as well as the exotic ephemeral herb Crotalaria lanceolata. Exposure to 80°C combined with treatment with a nitrate solution produced an additive effect on the germination of Chamaecrista mimosoides and Crotalaria lanceolata. However, the four species with the heaviest seeds, two exotic ephemeral herbs (Chamaecrista absus and Crotalaria pallida) and two native perennials (Galactia tenuiflora and Glycine tomentella) displayed no significant increase in germination with exposure to fire‐related cues. Exposure to 120°C for 5 min produced seed mortality in all species tested. Two of the largest seeded species, Crotalaria pallida and Galactia tenuiflora, displayed the lowest tolerance to heat shock, with seed mortality after exposure to 100°C for 5 min. These data indicate that fire can promote the germination of some tropical savanna legumes. As a proportion of seeds of each species displayed no innate dormancy, some germination may occur in the absence of fire, especially of exotic species.     

Seed viability of five wild Saudi Arabian species by germination and X-ray tests

Our objective was to evaluate the usefulness of the germination vs. the X-ray test in determining the initial viability of seeds of five wild species (Moringa peregrina, Abrus precatorius, Arthrocnemum macrostachyum, Acacia ehrenbergiana and Acacia tortilis) from Saudi Arabia. Usually several days were required to determine the viability of all five species via germination tests. However, X-ray test will give immediate results on filled/viable seeds. Seeds of all species, except Acacia ehrenbergiana and Acacia tortilis showed high viability in both germination (96–72% at 25/15 °C, 94–70% at 35/25 °C) and X-ray (100–80%) test. Furthermore, there was a general agreement between the germination (19%, 14% at 25/15 °C and 17% and 12% at 35/25 °C) and X-ray (8%, 4%) tests in which seed viability of Acacia ehrenbergiana and Acacia tortilis was very low due to insect damaged embryo as shown in X-ray analysis. Seeds of Abruspreca torius have physical dormancy, which was broken by scarification in concentrated sulfuric acid (10 min), and they exhibited high viability in both the germination (83% at 25/15 °C and 81% at 35/25 °C) and X-ray (96%) tests. Most of the nongerminated seeds of the five species except those of Acacia ehrenbergiana and Acacia tortilis, were alive as judged by the tetrazolium test (TZ). Thus, for the five species examined, the X-ray test was proved to be a good and rapid predictor of seed viability.     

Effect of Temperatures on Dormancy and Germination in Three Species in the Lamiaceae Occurring in Northern Wetlands

In the temperate region temperature is the main factor influencing the germination period of plant species. The purpose of this study was to examine effects of constant and fluctuating temperatures on dormancy and germination under laboratory and field conditions in the three wetland species Lycopus europaeus, Mentha aquatica and Stachys palustris. The results should give indications if the temperature-dependent regulation of dormancy and germination is phylogenetically constrained. Tests for germination requirements showed a minimum temperature for germination of 9 °C in Mentha and 12 °C in Lycopus and Stachys, and a maximum temperature of 33 °C for Lycopus and 36 °C for Mentha and Stachys. Fluctuating temperatures promoted germination in all three species but the amplitude required for high germination (>50%) differed: it was 8 °C in Mentha, 10 °C in Stachys and 14 °C in Lycopus (mean temperature 22 °C). The effect of temperatures on the level of dormancy was examined in the laboratory by imbibing seeds at temperatures between 3 °C and 18 °C for periods between 2 and 28 weeks, as well as by a 30-month burial period, followed by germination tests at various temperatures, in light and darkness. In the laboratory only low temperatures (≤12 °C) relieved primary dormancy in seeds of Lycopus, while in Mentha and Stachys also higher temperatures lead to an increase of germination. Dormancy was only induced in Lycopus seeds after prolonged imbibition at 12 °C in the laboratory. Buried seeds of all species exhibited annual dormancy cycles with lower germination in summer and higher germination from autumn to spring. Exhumed seeds, however, showed considerable differences in periods of germination success. Dormancy was relieved when ambient temperatures were below 12 °C. Ambient temperatures that caused an induction of dormancy varied depending on species and test condition, but even low temperatures (8 °C) were effective. At high test temperatures (25 °C) in light, exhumed seeds of all three species showed high germination throughout the year. The three species showed various differences in the effects of temperatures on dormancy and germination. Similarities in dormancy and germination found among the species are in common with other spring-germinating species occurring in wetlands, so it seems that the temperature dependent regulation of dormancy and germination are related to habitat and not to phylogenetic relatedness.     

Seed Treatment Optimizes Benefits of Seed Bank Storage for Restoration‐Ready Seeds: The Feasibility of Prestorage Dormancy Alleviation for Mine‐Site Revegetation

Dormant seeds of 18 species from 9 families covering a diverse range of seed dormancy syndromes and life histories from the southwest Australian biodiversity hotspot were assessed for germinability following storage at 15–25°C for 36 months. A total of 10 species with physical dormancy (PY) and 8 with either physiological dormancy (PD) or morphophysiological dormancy (MPD) were assessed as part of the study. Prior to storage, germination from dormant seeds was 1–27%, rising to 41–100% following specific dormancy‐breaking treatments. When seed dormancy was removed prior to storage for 36 months seeds from all species were found to maintain a nondormant state and germinate to a similar level to that observed at the beginning of the experiment (44–100%). Likewise, seeds that did not receive a prestorage dormancy‐breaking treatment maintained a dormant state (0–50% germination) and subsequently responded well to a dormancy‐breaking treatment immediately prior to germination assessment (49–99%). There were minimal differences in response to dormancy‐breaking treatments before and after 36 months storage (average 4–6% difference) and in the germination responses observed between both storage environments assessed (15°C/15% eRH or 15–25°C air dried). Based on these findings, storing seeds in a nondormant state does not alter germinability and this approach provides significant benefits to current seed‐based restoration programs through reduction of double handling and improved seed use efficiency.     

Seed germination ecology of the threatened endemic Iberian <Emphasis Type="Italic">Delphinium fissum</Emphasis> subsp. <Emphasis Type="Italic">sordidum</Emphasis> (Ranunculaceae)

Seeds of Delphinium fissum subsp. sordidum are physiologically dormant at maturity, with underdeveloped embryos; thus they have morphophysiological dormancy (MPD). The aims of this study were to determine the requirements for embryo growth, dormancy break and germination, to characterise the type of seed dormancy and to evaluate the effects of light, seed age, pollination mechanism, and inter-annual and inter-population variability on germinative ability. After 3 months of incubation at 5°C (cold stratification) in darkness conditions, the mean embryo length increased from 5.6 to 2.07 mm, with 76% of seeds germinating. Conversely, embryos of seeds incubated during 3 months at 20/7 or 28/14°C hardly grew and no germination was recorded. Since cold stratification was the only requirement for the loss of MPD, and both dry storage in laboratory conditions and warm stratification prior to cold stratification shortened the cold stratification period required for germination, it could be concluded that D. fissum subsp. sordidum seeds have intermediate complex MPD. Cold stratification and incubation in darkness conditions promoted higher germination percentages than those in light. In addition, germinative ability increased with seed age up to 8 months (reaching 96% at 5°C in darkness), showed a pronounced inter-annual and inter-population variability, as well as a significant decrease in seeds coming from pollination by geitonogamy. High temperatures (25/10 or 28/14°C) induced seeds to secondary dormancy, so seedling emergence in the greenhouse was restricted to February–March. The requirements for dormancy break and germination reflect an adaptation to trigger germination in late winter. This study is the first one to document a gradual increase in germination percentage with seed age for plant species with intermediate complex MPD.     

Tools for <Emphasis Type="Italic">Carex</Emphasis> revegetation in freshwater wetlands: understanding dormancy loss and germination temperature requirements

Carex is a globally distributed genus with more than 2000 species worldwide and Carex species are the characteristic vegetation of sedge meadow wetlands. In the mid-continental United States, Carex species are dominant in natural freshwater wetlands yet are slow to recolonize hydrologically restored wetlands. To aid in Carex revegetation efforts, we determined the dormancy breaking and temperature germination requirements of 12 Carex species. Seeds were cold stratified at 5/1°C for 0–6 months and then incubated in light at 5/1°C, 14/1°C, 22/8°C, 27/15°C, or 35/30°C. We found that all Carex species produced conditionally dormant seeds. The optimal temperature for germination for all but three species was 27/15°C. As is the case in other species with physiological dormancy, cold stratification increased germination percentages, broadened the temperature range suitable for germination, and increased germination rates for most species, but the magnitude of the effects varied among species. Many species germinated to 80% at 27/15°C without cold stratification and at 22/8°C with ≤1 month of stratification but required much longer stratification (up to 6 months depending on the species) to germinate to 80% at 14/1°C and 35/30°C. Our findings illustrate how a stratification pretreatment can greatly benefit Carex seed sowing efforts by triggering rapid germination to higher percentages. We recommend that cold stratification be targeted towards species with strong dormancy or used across a wider range of species when seed supplies for restoration are limiting. For Carex revegetation, establishing Carex canopies rapidly may help to prevent the invasion of undesirable species such as Phalaris arundinacea.     

Ecophysiology of seed dormancy and the control of germination in early spring‐flowering Galanthus nivalis and Narcissus pseudonarcissus (Amaryllidaceae)

Seed dormancy induction and alleviation in the winter‐flowering, moist temperate woodland species Galanthus nivalis and Narcissus pseudonarcissus are complex and poorly understood. Temperature, light and desiccation were investigated to elucidate their role in the germination ecophysiology of these species. The effect of different seasonal temperatures, seasonal durations, temperature fluctuations, the presence of light during different seasons and intermittent drying (during the summer period) over several ‘years’ on seed germination was investigated with outdoor and laboratory experiments. Warm summer‐like temperatures (20 °C) were necessary for germination at subsequent cooler autumn‐like temperatures (greatest at 15 °C in G. nivalis and 10 °C in N. pseudonarcissus). As the warm temperature duration increased, so did germination at subsequent cooler temperatures; further germination occurred in subsequent ‘years’ at cooler temperatures following a second, and also third, warm period. Germination was significantly greater in darkness, particularly in G. nivalis. Dormancy increased with seed maturation period in G. nivalis, because seeds extracted from green capsules germinated more readily than those from yellow capsules. Desiccation increased dormancy in an increasing proportion of N. pseudonarcissus seeds the later they were dried in ‘summer’. Seed viability was only slightly reduced by desiccation in N. pseudonarcissus, but was poor and variable in G. nivalis. Shoot formation occurred both at the temperature at which germination was greatest and also if 5 °C cooler. In summary, continuous hydration of seeds of both species during warm summer‐like temperatures results in the gradual release of seed dormancy; thereafter, darkness and cooler temperatures promote germination. Cold temperatures, increased seed maturity (G. nivalis) and desiccation (N. pseudonarcissus) increase dormancy, and light inhibits germination. © 2014 The Linnean Society of London, Botanical Journal of the Linnean Society, 2015, 177 , 246–262.     

Enhancement of ABA responsiveness in wheat embryos by high temperature*†

Abstract. Mature wheat (Triticum aestivum L.) grain often possesses high-temperature dormancy which restricts the grain from germinating at warm temperatures (25–30°C). Isolated embryos from such grain exhibited little high-temperature dormancy when germinated in water. Dormancy was restored by the application of abscisic acid (ABA) to the embryos. The ability of ABA to block germination in isolated embryos was enhanced significantly by elevating the germination temperature. ABA was 100 times more effective in reducing embryonic germination at 30°C than at 15°C. These temperature effects on embryonic response to ABA are a useful system for studying the mechanism of ABA action in seed dormancy.     

Variation in seed germination between populations of five sub-alpine woody species from eastern Qinghai-Tibet Plateau following dry storage at low temperatures

Effects of cold-dry storage on dormancy break and viability were determined for seeds of the five sub-alpine woody species Philadelphus incanus, Berberis vernae, Berberis dubia, Betula utilis, and Picea purpurea collected along an altitudinal gradient on the eastern part of the Qinghai-Tibet Plateau in China. Germination tests were conducted at 20/5°C for seeds stored dry at ambient room temperature for 4 weeks and then at 3–4°C for 0, 6, 12, and 24 weeks. Dormancy break during dry storage, i.e., afterripening, was indicated by an increase in germination percentages and rates. Duration of cold-dry storage and altitude of seed collection had significant effects on germination. With an increase in duration of storage, germination percentages and rates of P. incanus and B. vernae increased with a decrease in altitude of seed collection, while they increased with an increase in altitude for seeds of B. utilis and P. purpurea. Seeds of B. dubia did not exhibit changes in germination percentages and rates with altitude because a high number of seeds remained dormant during storage. Seed viability after 24 weeks of storage ranged from high (88, 93.3, 92.7%) for B. utilis to low (15% for high altitude) for P. incanus. The potential for dormancy break to occur during cold-dry storage should be considered when studies on basic seed dormancy are conducted or when seeds from various locations are stored prior to propagating plants from them.     

Effect of gibberellic acid- and water-based pre-soaking treatments under different temperatures and photoperiods on the seed germination of Allium stracheyi Baker: An endangered alpine species of Central Himalaya,India

Allium stracheyi Baker (Alliaceae, 2600–3000 m asl), an endangered species of Central Himalaya, India, has low seed germination in its natural habitat. This study is an attempt to improve seed germination by determining the seed viability with a low mean germination time (MGT) and germination index (GI) under optimum temperature, light, and pre-soaking treatments. The seeds were pre-soaked in hot water (80°C), cold water (10°C), and gibberellic acid (GA₃ at 50 and 100 mg/l) for 24 h and subjected to light (12 h light and 12 h dark) and continuous dark (24 h) conditions with different temperature regimes (10, 15, 20, 25, and 30°C). The viability varied between 66.0% and 69.67% and declined rapidly after 12 months of storage. Our studies suggest that the 100 mg/l GA₃ treatment was beneficial for seed germination and seedling growth. Pre-soaking in a 100 mg/l GA₃ solution and incubation at 20°C under light conditions enhanced the germination significantly (p < 0.05) and resulted in the highest (97.3%) germination with the lowest MGT = 5.7 days, with GI = 8.11. The recommendations of this study support the conservation of alpine A. stracheyi via simple and cost-effective techniques for optimal seed germination.     

The Role of Chilling in the Germination of some Scottish Montane Species

Summary

Seeds of 32 montane species were collected throughout northern Scotland. Germination responses, particularly the effects of chilling on breaking dormancy, were examined using a serial test incorporating single- and double-chilling treatments, alternating 20°C/10°C incubation temperatures, gibberellic acid and, for some species, nicking of the seed coat. Where practicable, any ungerminated seeds were ultimately dissected to assess their viability. Only three species had an absolute requirement for pre-chilling before seeds germinated. A further eight species required chilling to break the dormancy of 15% or more seeds; otherwise chilling generally increased the extent and rate of germination. Unusually, chilling induced dormancy in the seeds of four species whereas warm conditions induced dormancy which was not broken by subsequent chilling amongst seeds of Draba incana. Germinability and germination rates for nine species were regressed on the altitude, latitude and oceanicity of the plants' origin to assess the relative effects of chilling. These three environmental factors accounted for up to 98% of the variability in the germination parameters but few regressions attained statistical significance. Broad patterns suggest that chilling had a decreasing effect on both the extent and, rate of germination as the altitude of the seed source increased. A similar pattern, but only for germinability, was seen with respect to latitude.     

Seed dormancy and germination in Jeffersonia dubia (Berberidaceae) as affected by temperature and gibberellic acid

The genus Jeffersonia, which contains only two species, has a trans‐Atlantic disjunct distribution. The aims of this study were to determine the requirements for breaking dormancy and germination of J. dubia seeds and to compare its dormancy characteristics with those of the congener in eastern North America. Ripe seeds of J. dubia contain an underdeveloped embryo and were permeable to water. In nature, seeds were dispersed in May, while embryos began to grow in September, and were fully elongated by late November. Germination started in March of the next year, and seeds emerged as seedlings soon after germination. In laboratory experiments, incubation at high temperatures (25 °C, 25/15 °C) for at least 8 weeks was required to initiate embryo growth, while a transfer to moderate temperatures (20/10 °C, 15/6 °C) was needed for the completion of embryo growth. At least 8 weeks at 5 °C was effective in overcoming physiological dormancy and for germination in seeds after the embryos had fully elongated. Thus, both high and low temperatures were essential to break dormancy. Gibberellic acid (GA₃) treatment could substitute for the high temperature requirement, but not for the low temperature requirement. Based on the dormancy‐breaking requirements, it is confirmed that the seeds have deep simple morphophysiological dormancy. This dormancy type is similar to that of seeds of the eastern North American species J. diphylla. Although seeds require 10–11 months from seed dispersal to germination in nature, under controlled conditions they required only 3 months after treatment with 1000 mg·l^?1 GA₃, followed by incubation at 15/6 °C. This represents practical knowledge for propagation of these plants from seed.