Non-deep Physiological Dormancy Research Articles

Germination niche of co-occurring threatened native and alien species: a case study in Lindernia procumbens and L. dubia

AbstractPlant invasions have a negative impact on biodiversity and lead to species loss. Although studies on traits promoting invasiveness have been largely developed, comparative studies on germination traits of closely related native versus alien invasive species, which also take into account threatened species, are lacking. We analysed the germination requirements of two congeneric Lindernia species inhabiting paddy field in Northern Italy. Germination tests were conducted exposing seeds of both species across a broad range of temperature and conditions (i.e., cold-wet stratification, dark condition, alternate temperature, gibberellic acid). The invasive L. dubia showed higher and faster germination, occurring over a broader range of temperatures compared to the native threatened L. procumbens, along with a lighter non-deep physiological dormancy. These results show a competitive advantage of the alien species already in the early stages of plant regeneration and provide a comprehensive overview of the germination requirements, necessary for the development of future conservation and management plans.

Effects of various pre-treatments on dormancy-break and seed germination of Saussurea veitchiana (Asteraceae), an endemic medicinal herb of southwest China

Subalpine Saussurea veitchiana (Asteraceae) is useful for the treatment of various diseases and is vulnerable to extinction. Methods to break seed dormancy and enhance germination of this species, as well as the response of seeds to different temperatures, were investigated. Freshly harvested seeds germinated to very low percentages at ten temperature regimes in light conditions. Gibberellic acid (10 - 200 μM) partially broke the dormancy of fresh seeds, and the highest germination was 54% when seeds were treated with 200 μM GA3 and incubated at 20°C or 25/15°C. Cold stratification significantly increased germination over that of the control (i. e., seeds dry stored at room temperature, approximately 18°C). Seeds cold stratified at 4°C for 60 or 90 days germinated to 83 and 87%, respectively, at 25/15°C and had a MGT of 7.11 and 6.37 days, respectively. Taken together, the seeds of S. veitchiana have non-deep physiological dormancy, and cold stratification for 60 days or longer is recommended as a practical dormancy-breaking treatment for propagation of this species from seeds.

Breaking deep epicotyl physiological dormancy in C hionanthus retusus (Oleaceae) seeds

Given that the cause and the method of dormancy release in Chionanthus retusus seeds are unclear, in this study, C. retusus seeds with a hard endocarp (seed dispersal unit) were used for endocarp permeability determination, germination test after endocarp removal and isolated embryo culture to detect the cause of radicle dormancy. Endosperm removal, cold moist stratification, warm moist stratification and GA3 treatment of rooted seeds were used to detect the cause of epicotyl dormancy. The results indicated that C. retusus seeds have non-deep physiological dormancy and deep epicotyl physiological dormancy, the release of which was closely related to the length of the emerged radicle. Rooted seeds with a radicle length < 3 cm could not be effectively released from epicotyl physiological dormancy by endosperm removal, GA3 soaking or cold/warm stratification treatments, whereas those > 3 cm could be significantly promoted for release from epicotyl physiological dormancy by endosperm removal and cold moist stratification treatments. The highest shoot emergence rate of rooted seeds (radicle length > 3 cm) was achieved after 120 days of cold moisture stratification treatment. These results could improve our understanding of seed dormancy and promote the conservation and use of C. retusus.

Study on Dormant and Germination Characteristics of Chinese Olive (Canarium album) Seeds

This study aimed to determine the dormancy type of Chinese olive seeds and improve their germination rate. The water permeability and germination-inhibiting substances of Chinese olive seeds were assessed. Low-temperature stratification and soaking in a GA3 solution were implemented to measure the time lag, initial time, germination rate, and germination potential of the seeds. The findings revealed that the seed coat exhibited poor water permeability, which negatively influenced the germination rate. Additionally, Chinese olive seeds contained substances that inhibited germination. The duration of low-temperature stratification (at 4 ± 1 °C) gradually diminished the dormancy of Chinese olive seeds, resulting in early and rapid germination. The germination rate significantly increased, with the percentage of seed germination rising from 0% to 42.33% within 60 days of stratification. Furthermore, combining low-temperature stratification with different concentrations of GA3 notably enhanced the germination rate. The optimal concentrations of gibberellins for 40 and 60 days of stratification were determined to be 300 and 100 mg/L, respectively. These results indicate that Chinese olive seeds possess non-deep physiological dormancy.

A Study on the Genetic Variations and Germination Characteristics of Rhododendron sobayakiense to Prepare for Climate Change Threat

Rhododendron sobayakiense is an endemic and near-threatened species (Korean Red List, NT) found in the alpine regions of South Korea that requires conservation. This study investigated the species’ genetic variations and seed germination characteristics and predicted its potential habitat change according to climate change scenarios. The genetic diversity of R. sobayakiense at the species level (P = 88.6%; S.I. = 0.435; h = 0.282) was somewhat similar to that observed for the same genus. The inter-population genetic differentiation was 19% and revealed a relatively stable level of gene exchange at 1.22 in each population. The main cause of gene flow and genetic differentiation was presumed to be the Apis mellifera pollinator. Seed germination characteristics indicated non-deep physiological dormancy, with germination at ≥10 °C and the highest percent germination (PG) of ≥60% at 15–25 °C, while the PG was ≥50% at 30 °C. The PG increased at constant temperature than at variable temperatures; the mean germination time decreased as temperature increased. The climate scenarios SSP3 and SSP5 were analyzed to predict future R. sobayakiense habitat changes. The variables of the main effects were Identified as follows: elevation > temperature seasonality > mean diurnal range.

Seed dormancy and germination ecology of several clover species

This research was carried out to evaluate the effect of (1) different methods of breaking seed dormancy (physical and chemical scarification, high temperature, hot water and after-ripening), and (2) environmental factors (temperature, salinity and water stress) on seed germination of Trifolium angustifolium, T. arvense, T. fragiferum, T. fucatum, T. repens, T. subterraneum and Trifolium sp. All experiments were conducted in the Seed Research Laboratory of Gorgan University of Agricultural Sciences and Natural Resources, Iran, in 2021. All the examined clover species were dormant after harvest, with little germination. Mechanical scarification with sandpaper or sulphuric acid resulted in more than 88 and 52% germination, respectively. Seeds were able to germinate between 5 and 35°C, but the highest germination (≥ 98% on average) occurred at 20°C. Fluctuating temperature regimes were more efficient in improving the germination than constant temperatures. Seeds of clover species, in addition to having a hard seed coat, have a non-deep physiological dormancy. Fresh seeds showed a high sensitivity to water stress compared with after-ripened seeds. However, relative resistance to salinity stress was observed. The results obtained in this research can be used to develop effective sowing strategies and support the successful establishment of these clover species.

Non-deep physiological dormancy in seeds of two endangered medicinal alpine species of Rhodiola from the Hengduan Mountains of southwest China

We investigated seed dormancy and germination characteristics of two endangered medicinal species, Rhodiola crenulata and R. fastigiata, from the high altitude (alpine) Hengduan Mountains in China. Germination of fresh seeds was tested in light and dark at six constant (1, 5, 10, 15, 20 and 25°C) and three alternating (5/1, 15/5 and 25/15°C) temperatures and again, after six months of dry after-ripening (DAR) and cold-wet stratification (CS). Fresh seeds of R. crenulata germinated to ≥ 80% at 10, 15, 25/15 and 15/5°C in light, but germination was significantly lower at 1, 5, 20 and 25°C. Germination of fresh seeds in dark was 0 to 25% across the range of temperatures. DAR and CS for six months increased germination and/or decreased mean germination time in both light and dark. Fresh seeds of R. fastigiata germinated to > 95% in both light and dark, except at 1°C in light and 1, 5, and 5/1°C in dark, where germination was < 50%. DAR and CS for six months increased germination and/or decreased mean germination time. Seeds of the two Rhodiola species have (conditional) non- deep physiological dormancy. Germination responses to temperature and light prevent seeds from germinating in the autumn of dispersal, but allow them to germinate quickly after snow melt the next spring. This study provides a method for obtaining plants from seeds of the two Rhodiola species for medicinal uses, which could reduce the harvesting pressure placed on natural populations.

Germination biology of Hedysarum grandiflorum (Fabaceae) seeds under laboratory conditions

Germination biology of Hedysarum grandiflorum seeds research was conducted using seed material collected in one wild and one cultivated population growing in Rostov region and included an identification of seed laboratory germination degree, seed hardness, endogenic infection degree, and seed pathogens composition. A combinational dormancy type combining physical and non-deep physiological dormancy was identified in Hedysarum seeds. Stably high germination rates under laboratory conditions was demonstrated if mechanical scarification is used whereas efficiency of sulfuric acid treatment varies it relation to seeds harvest year and retention period. A proportion of hard seeds of H. grandiflorum is confirmed to increase during first three month of dry storage and then slowly decrease. A degree of Hedysarum seeds endogenic infection revealed is higher in wild population compared with seed material from cultivated plants. Micromycetes - facultative parasites and saprotrophs prevail among seed pathogens regarding their species diversity, and bacterial pathogens quantitatively.

Evaluation of Seed Germination of Six Rare Stipa Species following Low Temperature Stress (Cryopreservation).

Cryopreservation is one way to preserve rare, endangered species. However, during the cryopreservation process, plant cells undergo considerable stress, which may lead to cell death. In our work, orthodox Stipa seeds of six rare species were cryopreserved: S. sareptana, S. ucrainica, S. tirsa, S. dasyphylla, S. adoxa, and S. pulcherríma. Short-term cryopreservation (14 days) stimulated germination of all Stipa species studied. Prolonged cryopreservation (70 days and more) decreased the germination of all Stipa seeds except S. sareptana. The decrease in germination progressed over time as a result of the cumulative stress of cryopreservation rather than the initial stress. To stimulate germination, seeds were stratified and treated with GA3, KNO3, NaOH, and H2O2. After four years of seed cryopreservation, it was possible to obtain seedlings of all the Stipa species studied with 30 days of stratification and 180 days of germination. After five years of cryopreservation and seed treatment with 30% NaOH for one hour, the best germination was obtained in S. adoxa and S. pulcherrima. After treatment with 5% H2O2 for 20 min, the best germination was obtained in S. sareptana, S. ucrainica, and S. dasyphylla. S. sareptana seeds germinated in all the aforementioned experiments. S. sareptana has a non-deep physiological dormancy and is the most widespread and drought-tolerant Stipa species studied. The best habitat adaptation and stress tolerance correlated with this species'cryotolerance. S. sareptana was recommended for further cryopreservation, while storage protocols for the other Stipa species studied need further improvements.

Plant Production Protocols from Seeds of Threatened Atropa baetica and Widespread A. belladonna, Both Rich in Alkaloids.

Members of the genus Atropa contain various tropane alkaloids, including atropine ((±)-hyoscyamine) and scopolamine, which possess medicinal properties. Preserving the diverse genetic background of wild populations via optimal plant production from seeds could be essential for avoiding the loss of potential uses. We analyzed the germination ecology of two Atropa species comprising the threatened A. baetica and widespread A. belladonna to determine the: (1) influence of temperature, light, and seed age on germination patterns; (2) effects of cold stratification and gibberellic acid (GA3); (3) phenology of seedling emergence in outdoor conditions; (4) phenology of dormancy break and loss of viability in buried seeds; and (5) ability to form persistent soil seed banks. Freshly matured seeds exhibited conditional physiological dormancy, with germination at high temperatures (32/18 °C) but not at low and cold ones (5, 15/4, 20/7 °C). The germination ability increased with time of dry storage and with GA3, thereby suggesting nondeep physiological dormancy. Under outdoor conditions, no seedlings emerged during the first post-sown autumn, but emergence peaks occurred in late winter-early spring. Both species could form small persistent soil seed banks with short durations (3-5 years). A plant production protocol from seeds was established for both taxa.

Non-deep physiological dormancy and germination characteristics of Primula florindae (Primulaceae), a rare alpine plant in the Hengduan Mountains of southwest China.

Timing of seed germination is directly related to the survival probability of seedlings. For alpine plants, autumn-dispersal seeds should not germinate immediately because the cold temperature is not conducive to the survival of seedlings. Seed dormancy is a characteristic of the seed that prevents it from germinating after dispersal. Primula florindae is an alpine perennial forb endemic to eastern Tibet, SW China. We hypothesized that primary dormancy and environmental factors prevent seeds of P. florindae to germinate in autumn and allow them to germinate at the first opportunity in spring. We determined how GA3, light, temperature, dry after-ripening (DAR) and cold-wet stratification (CS) treatments affect seed germination by conducting a series of laboratory experiments. Firstly, the effects of gibberellic acid (GA3; 0, 20, and 200 mg L-1) on germination of freshly shed seeds at alternating temperatures (15/5 and 25/15 °C) were immediately investigated to characterize seed with a physiological dormancy component. Then, the fresh seeds treated with 0, 3, and 6 months of after-ripening (DAR) and cold-wet stratification (CS) were incubated at seven constant (1, 5, 10, 15, 20, 25, and 30 °C) and two alternating temperatures (5/1, 15/5, and 25/15 °C) at light and dark conditions. Fresh seeds were dormant, which only germinated well (>60%) at 20, 25, and 25/15 °C in light but not at ≤15 °C and to higher percentages in light than in dark. GA3 increased germination percentage of fresh seeds, and DAR or CS treatments increased final germination percentage, germination rate (speed), and widened the temperature range for germination from high to low. Moreover, CS treatments reduced the light requirement for germination. Thus, after dormancy release, seeds germinated over a wide range of constant and alternating temperatures, regardless of light conditions. Our results demonstrated that P. florindae seeds have type 2 non-deep physiological dormancy. Timing of germination should be restricted to early spring, ensuring a sufficient length of the growing season for seedling recruitment. These dormancy/germination characteristics prevent seeds from germinating in autumn when temperatures are low but allow them to germinate after snowmelt in spring.

Seed dormancy in Asteraceae: a global vegetation zone and taxonomic/phylogenetic assessment

AbstractThe Asteraceae with up to 30,000 species occurs on all continents except Antarctica and in all major vegetation zones on earth. Our primary aim was to consider cypselae dormancy-break and germination of Asteraceae in relation to ecology, vegetation zones and evolution. Cypselae are desiccation-tolerant and in various tribes, genera, species and life forms of Asteraceae are either non-dormant (ND) or have non-deep physiological dormancy (PD) at maturity. All six types of non-deep PD are found among the Asteraceae, and dormancy is broken by cold or warm stratification or by afterripening. Soil cypselae banks may be formed but mostly are short-lived. Much within-species variation in dormancy-break and germination has been found. Using data compiled for 1192 species in 373 genera and 35 tribes of Asteraceae, we considered ND and PD in relation to life form, vegetation zone and tribe. Senecioneae and Astereae had the best representation across the vegetation zones on earth. In evergreen and semi-evergreen rainforests, more species have ND than PD, but in all other vegetation zones, except alpine/high-latitude tundra (where ND and PD are equal), more species have PD than ND. Tribes in the basal and central grades and those in the Heliantheae Alliance have both ND and PD. The high diversity and lability of non-deep PD may have enhanced the rate of species diversification by promoting the survival of new species and/or species in new habitats that became available following globally disruptive events since the origin of the Asteraceae in the Late Cretaceous.

Distinct hormonal and morphological control of dormancy and germination in Chenopodium album dimorphic seeds.

Dormancy and heteromorphism are innate seed properties that control germination timing through adaptation to the prevailing environment. The degree of variation in dormancy depth within a seed population differs considerably depending on the genotype and maternal environment. Dormancy is therefore a key trait of annual weeds to time seedling emergence across seasons. Seed heteromorphism, the production of distinct seed morphs (in color, mass or other morphological characteristics) on the same individual plant, is considered to be a bet-hedging strategy in unpredictable environments. Heteromorphic species evolved independently in several plant families and the distinct seed morphs provide an additional degree of variation. Here we conducted a comparative morphological and molecular analysis of the dimorphic seeds (black and brown) of the Amaranthaceae weed Chenopodium album. Freshly harvested black and brown seeds differed in their dormancy and germination responses to ambient temperature. The black seed morph of seedlot #1 was dormant and 2/3rd of the seed population had non-deep physiological dormancy which was released by after-ripening (AR) or gibberellin (GA) treatment. The deeper dormancy of the remaining 1/3rd non-germinating seeds required in addition ethylene and nitrate for its release. The black seeds of seedlot #2 and the brown seed morphs of both seedlots were non-dormant with 2/3rd of the seeds germinating in the fresh mature state. The dimorphic seeds and seedlots differed in testa (outer seed coat) thickness in that thick testas of black seeds of seedlot #1 conferred coat-imposed dormancy. The dimorphic seeds and seedlots differed in their abscisic acid (ABA) and GA contents in the dry state and during imbibition in that GA biosynthesis was highest in brown seeds and ABA degradation was faster in seedlot #2. Chenopodium genes for GA and ABA metabolism were identified and their distinct transcript expression patterns were quantified in dry and imbibed C. album seeds. Phylogenetic analyses of the Amaranthaceae sequences revealed a high proportion of expanded gene families within the Chenopodium genus. The identified hormonal, molecular and morphological mechanisms and dormancy variation of the dimorphic seeds of C. album and other Amaranthaceae are compared and discussed as adaptations to variable and stressful environments.

Influence of Seed-Covering Layers on Caper Seed Germination.

Caper is a perennial shrub that is widespread in the Mediterranean Basin. Although the fruits contain many seeds, they germinate slowly and with very low percentages, due to their nondeep physiological dormancy. The influence of the testa and endosperm, as well as the effect of applying gibberellic acid (GA3) solutions on seed germination to release its dormancy, are reported in this study. The mechanical resistance exerted by the testa and endosperm against radicle protrusion in mature caper seeds was measured. The best germination results were obtained with seeds devoid of testa wetted with water and with intact seeds wetted with a 500 mg L-1 GA3 solution, without statistical differences between them. The GA3 addition triggers an increase in both the content of endogenous gibberellins (GA) and the GA/abscisic acid ratio, increasing germination. Its germination consists of two temporally separated events: testa cracking and endosperm piercing. Testa cracking begins in the hilum-micropillar area; it involves a signal from the embryo, which GA can replace, possibly by increasing the growth potential of the embryo. After testa cracking, the radicle emerges through a hole in the micropylar endosperm. The puncture force necessary to pierce the micropylar endosperm decreased drastically during the first day of imbibition, remaining practically constant until testa cracking, decreasing afterwards, regardless of the addition or not of gibberellins.

A Model for Changes in Germination Synchrony and Its Implements to Study Weed Population Dynamics: A Case Study of Brassicaceae

In every agricultural system, weed seeds can be found in every cubic centimeter of soil. Weed seeds, as a valuable trait underlying the fate of weed populations, exhibit differing levels of seed dormancy, ensuring their survival under uncertain conditions. Seed dormancy is considered as an innate mechanism that constrains germination under suitable conditions that would otherwise stimulate germination of nondormant seeds. This work provides new insight into changes in germination patterns along the dormant to nondormancy continuum in seeds with physiological dormancy. Notable findings are: (1) germination synchrony can act as a new parameter that quantitatively describes dormancy patterns and, subsequently, weed population dynamics, (2) germination synchrony is dynamic, suggesting that the more dormancy decreases, the more synchrony is obtainable, (3) after-ripening and stratification can function as a synchronizing agent that regulates germination behavior. Freshly harvested seeds of Brassica napus with type 3 of non-deep physiological dormancy showed the most synchronous germination, with a value of 3.14, while a lower level of germination asynchrony was found for newly harvested seeds of Sinapis arvensis with type 1 of non-deep physiological dormancy, with an asynchrony value of 2.25. After-ripening and stratification can act as a synchronizing factor through decreasing the asynchrony level and increasing synchrony. There is a firm relationship between seed dormancy cycling and germination synchrony patterns, ensuring their survival and reproductive strategies. By germinating in synchrony, which is accompanied by cycling mechanisms, weeds have more opportunities to persist. The synchrony model used in the present study predicts germination behavior and synchrony along the dormant to nondormancy continuum in weed seeds with physiological dormancy, suggesting a useful method for the quantification of germination strategies and weed population dynamics.

Seed dormancy alleviation by warm stratification progressively widens the germination window in Mediterranean climate Rutaceae

Context In ecosystems where rainfall is episodic or highly seasonal, plant recruitment from a soil-stored seed bank occurs during periods of elevated soil moisture conducive to germination and seedling establishment. The release of seed dormancy in response to environmental conditions has significant consequences for the temperature window over which germination occurs, and as such the timing of germination can vary between years. Aims We aimed to understand in seeds of two species of Rutaceae, Diplolaena dampieri and Rhadinothamnus anceps, how dormancy loss and germination timing is influenced by warm stratification. Methods We tested the germination response to temperatures between 5 and 30°C following increasing durations (1–12 and 4–12 weeks) of warm stratification at 20, 25, or 30°C. Key results Warm stratification for 1–8 weeks at 30°C progressively alleviated seed dormancy in D. dampieri and R. anceps, increasing germination proportion from ~0.1 to ~0.5 in both species. Stratification duration was optimal at 30°C for between 4 and 8 weeks depending on species. Warm stratification was not affected by water stress down to −0.8 Mpa. Application of aerosol smoke did not significantly improve germination, and heat treatments had a negative effect on final germination proportion. Conclusions As dormancy was progressively alleviated, the range of temperatures that support germination increased for D. dampieri and decreased for R. anceps, allowing for confirmation of type 1 and type 2 non-deep physiological dormancy (PD), respectively. Implications Arising from this conclusion, we suggest that in Mediterranean climates, type 1 and 2 PD dictate risk-taking and risk-avoiding ecological strategies by shifting the thermal requirements for germination towards that characteristic of the early- or mid-germination season. Classification of non-deep PD may offer a structured approach to predict how temperature requirements shift during dormancy loss, which will provide insight into seed germination response to year-to-year variation in seasonal environmental conditions.

Dormancy and germination characteristics of Tarenaya hassleriana (Cleomaceae) seeds

Abstract: Elucidating the physiological and ecological mechanisms of seed dormancy and germination is of great significance for species conservation and the application of plant resources. Based on Baskin and Baskin’s classification system for seed dormancy, the cause of dormancy in Tarenaya hassleriana (Cleomaceae) seeds was studied using alternating temperature, cold moist stratification, dry storage, and GA3 soaking treatment. The results indicated that fresh mature T. hassleriana seeds had a combinational dormancy, including a physical dormancy and a type 2 non-deep physiological dormancy, and were photoblastic, with an optimal germination temperature of 35°C. In addition, fresh mature T. hassleriana seeds may be efficiently released from dormancy and promoted to germinate by an alternating temperature of 20 °C/30 °C, cold moist stratification, and cold moist stratification following dry storage. Furthermore, GA3 soaking treatment could also promote dormancy release and subsequent germination at 35 °C, and dry storage treatment could promote dormancy release and subsequent germination at 5-15 °C. These results also suggested that there were complex cross-talks among phytohormone, osmotic potential, and the temperature signaling regulatory pathways during dormancy release and germination of T. hassleriana seeds, which deserve further study.

Seed dormancy and storage behaviour of the Hawaiian endemic Coprosma kauensis (Rubiaceae)

Context Seed banking is the most efficient and cost-effective method of preserving plant germplasm, but not all species can be conserved by conventional practices. Further, restoration of plant populations from seeds often is hindered by a lack of a priori knowledge of seed dormancy and germination requirements. Aims Our objective was to determine seed desiccation, initial freezing tolerance and the dormancy-breaking and germination requirements of Coprosma kauensis, a dioecious shrub endemic to Kauaʻi Island in Hawaiʻi. Methods The effects of temperature and gibberellic acid (GA3) on germination of fresh seeds were tested in light/dark at 15/5, 25/15 and 20/10°C with and without treatment with GA3. To test effects of desiccation and initial freezing on germination, seeds were dried to 15% relative humidity at 15°C and then stored at −20°C. Key results Regardless of incubation temperature and treatment (or not) with GA3, final germination ranged from 78 to 88%; however, time to 50% germination decreased at 20/10°C for seeds treated with 500 ppm GA3. There was no significant difference in final germination percentage between freshly harvested seeds and those desiccated, nor of those desiccated and then subsequently frozen at −20°C. Conclusions Fresh seeds of C. kauensis exhibit a low degree of nondeep physiological dormancy. They can germinate over a range of temperatures, but germination speed is increased by GA3. Fresh seeds are desiccation and freeze tolerant (after 6 months storage). Implications This vulnerable Kauaʻi endemic species easily can be propagated from seeds. Future studies should investigate long-term longevity at various storage temperatures.

Seed dormancy and germination characteristics of Osteomeles schwerinae, a riparian plant endemic to the Hengduan Mountains and adjacent regions

Osteomeles schwerinae, an endemic plant with ecological restoration functions from the hot/warm-dry river valleys of the Hengduan Mountains and adjacent regions, has low seed germination in cultivation. This study attempted to improve seed germination by testing the effect of several treatments including dry after-ripening (DAR), GA3, light and temperature treatments for seeds from three populations. DAR increased germination at 25/15°C but not at 15/5°C, as compared with fresh seeds. DAR was sufficient to break dormancy; GA3 could not significantly increase germination percentage, indicating that seeds of O. schwerinae appear to have non-deep physiological dormancy. After the dormancy is broken, temperature significantly affects germination. Seeds germinated significantly better at higher temperatures (20-25°C) than at lower (< 15°C) and extreme high temperatures (> 30°C). A base temperature for germination (Tb) of 4.9-9.3°C and a thermal time requirement for 50% germination (50) ranging from 158.7 to 217.4°Cd were identified for non-dormant DAR seeds, depending on the population. This study provides a theoretical basis for dormancy-break and germination of O. schwerinae seeds.

Type 2 Nondeep Physiological Dormancy in Seeds of Fraxinus chinensis subsp. rhynchophylla (Hance) A.E.Murray

Fraxinus chinensis subsp. rhynchophylla (Oleaceae), hereafter F. rhynchophylla, is an important timber species in northeast China; however, little is known about its seed dormancy and germination, which hinders regeneration of the species from seeds for reforestation and conservation. Our aim was to determine the class of seed dormancy and how to break it. Studies were conducted to determine the permeability of the seed coat to water, changes in embryo development during cold stratification and effects of cold stratification on germination over a range of temperatures. The seeds were water-permeable, and the embryo was fully developed and filled the embryonic cavity. Cold stratification at 5 °C for 8 weeks was effective in breaking dormancy; thus, we conclude that the seeds have nondeep physiological dormancy (PD). As cold stratification time was increased, the ability of seeds to germinate at low temperatures (e.g., 10 °C and 15 °C) increased, indicating the presence of Type 2 nondeep PD, in which the minimum temperature for germination decreases during dormancy-break. Nondormant seeds germinated to high percentages and rates at constant temperatures of 25 °C (germination percentage was 63%) and at alternating temperature regimes of 35 °C/25 °C, 30 °C/15 °C, 25 °C/20 °C and 20 °C/10 °C (germination percentage was 66%, 67%, 65% and 66%, respectively). To produce seedlings, we recommend 8 weeks of cold stratification at 5 °C before sowing the seeds at temperatures ranging from 15 °C to 30 °C.