Warm Stratification Research Articles

Gibberellins treatment or stratification can break dormancy of the seeds of three Ranunculus species native to Korea

In this study, the seed germination and dormancy characteristics of three Ranunculus species native to Korea (R. cantoniensis, R. chinensis, and R. sceleratus) were determined to establish an effective dormancy-breaking protocol. The results revealed that the R. cantoniensis, R. chinensis, and R. sceleratus seeds responded differently to treatment with gibberellins (GAs) and stratification. Warm stratification at 20℃ increased the germination percentage and partially broke the dormancy of the R. cantoniensis seeds; moreover, the germination temperature range of the seeds expanded upon treatment with high-concentration GA4 + 7. Meanwhile, neither cold nor warm stratification was effective at breaking the dormancy of R. chinensis seeds; however, high-concentration GA4 + 7 treatment broke the dormancy of the seeds by expanding the germination temperature range. Lastly, the R. sceleratus seeds did not respond to the treatment with GAs; however, their germination percentage increased after undergoing warm stratification at 25℃. The seeds of these three species were characterized as exhibiting nondeep morphophysiological dormancy. The findings of this study enhance our understanding of the temperature-related germination responses of the three Ranunculus species, offering valuable insights into their conservation and utilization.

Macroclimatic Convergence and Habitat Specialisation Shape the Mediterranean Seed Germination Syndrome.

Ecological theory predicts that plant reproductive phenology in the Mediterranean regions is shaped by evolutionary processes driven by strong seasonality in precipitation-evaporation patterns. Thus, it can be expected that seed germination phenology has adapted to maximise recruitment during the season of highest water availability. Cold-cued and slow germination (i.e., the 'Mediterranean seed germination syndrome') has been hypothesised to be an adaptation to ensure that seedling emergence occurs in autumn/early winter, extending the growing season before the subsequent unfavourable summer drought. However, this hypothesis has been tested on individual species or local studies, without a proper synthesis for the whole Mediterranean region. Here we tested, for the first time, the Mediterranean seed germination syndrome using experimental data for 459 species (11,363 records, 59 families) occurring in the Mediterranean Basin. We performed a phylogenetically informed Bayesian meta-analysis to model the effect on germination proportions of seven key experimental cues: mean incubation temperature, alternating temperature regime, light and dormancy-breaking treatments (scarification, warm stratification and cold stratification) and the modulating role of seed mass on seed germination. We show that species from lowland zonal habitats of the Mediterranean align with the Mediterranean germination syndrome hypothesis, with their seeds responding positively to cool, constant temperatures and negatively to light. Yet, habitat specialists (i.e., species restricted to mountains, coasts and wetlands) deviate from the syndrome, showing nearly opposite germination requirements. Seed mass further influences the germination niche and phylogenetically related species exhibit similar germination responses. Cumulatively, these results suggest that evolutionary pressures from local habitat-related conditions override the macroclimatically imposed Mediterranean seed germination syndrome.

Non-deep simple epicotyl morphophysiological dormancy in seeds of Helleborus thibetanus (Ranunculaceae)

Helleborus thibetanus is a perennial herbaceous plant with high potential for medicinal and landscaping purposes. However, the dormancy characteristics of seeds and the conditions that help this species break dormancy have not been investigated. This study investigated embryo growth and the emergence of radicles and epicotyls in seeds over a range of GA3 pretreatment and temperature sequences. Upon reaching maturity, the seeds had underdeveloped embryos that developed fully at 15 °C warm stratification within 6 weeks. Immediately after embryo growth, radicles emerged during warm stratification. However, the epicotyls failed to emerge soon after the radicle emergence. Epicotyl emergence was observed in over > 13 % of seeds with an emerged radicle following 4 weeks of cold stratification at 4 °C. The effects of GA3 on radicle and epicotyl emergence were used to determine the specific types of seed dormancy. GA3 pretreatment partially substituted 15 °C warm stratification to promote radicle emergence and effectively served as a substitute for the 4 °C cold stratification to break the epicotyl dormancy. The overall temperature and GA3 requirements for breaking dormancy and seed germination indicate non-deep simple epicotyl morphophysiological dormancy in H. thibetanus.

Seed dormancy, germination requirements, and implications of herbicides for Penstemon albidus and P. nitidus

Seed‐based restoration is dependent on seed germination, and poor germination can cause restoration failure. Many restoration failures can be attributed to a lack of knowledge of germination characteristics, species‐specific seed dormancy, or the effects of widely used herbicides on germination. White penstemon (Penstemon albidus) and Waxleaf penstemon (P. nitidus) are native to the Northern Great Plains region of North America, and increased germination of these species would contribute to improved restoration in the region. We performed two concurrent experiments to determine: (1) the germination requirements and dormancy class of these species; and (2) the effects of herbicides on germination. To determine germination requirements, we applied pretreatments (scarification, smoke, and KNO3) and three durations (2, 4, and 8 weeks) of cold and warm stratification. To test the effects of herbicides on germination, three commonly used herbicides (atrazine, trifluralin, and 2,4‐D) were applied at six concentrations (100, 50, 10, 1, 0.1, and 0% of the recommended field application rate). Germination characteristics indicate both species express physiological dormancy. Physiological dormancy denotes an embryo with low growth potential that is unable to overcome mechanical constraints but can be alleviated with proper temperature cues. Both species required cold stratification, with P. nitidus needing a longer period (8 weeks) than P. albidus (4 weeks). Final germination percentage of P. albidus decreased with higher doses of 2,4‐D but was not affected by atrazine or trifluralin. These experiments help to create protocol for the use of our study species, as well as other species, in restoration plantings.

Deep Simple Epicotyl Morphophysiological Dormancy in Seeds of Endemic Chinese Helleborus thibetanus

Helleborus thibetanus is an endemic species in China with important ornamental and medicinal value. However, the seeds have dormancy, and their germination percentage is low under natural conditions. This research was carried out to determine the seed germination requirements of H. thibetanus and to characterize the type of seed dormancy. The morphological post-ripening process of the seed embryo was studied according to the morphological anatomy, and the effects of temperature and gibberellic acid (GA3) on seed germination were investigated in H. thibetanus. The H. thibetanus seeds had a heart-shaped embryo at maturity. The embryo fully grew within the seed through warm stratification, and the embryo/seed ratio increased from 8.58% to 42.6%. The shortest time for a radicle to emerge (58.33 d) and the highest radicle emergence percentage (84.44%) were obtained at a temperature of 15 °C. The results showed that the H. thibetanus seeds had a morphophysiological dormancy. In addition, 300 mg/L GA3 treatments shortened the time of warm stratification and increased the radicle emergence percentage. Seeds with emerged radicles could not emerge epicotyl–plumule without cold stratification, which showed that the H. thibetanus seeds had epicotyl physiological dormancy. The length of the roots, cold stratification time, and GA3 markedly affected the release of the epicotyl physiological dormancy in H. thibetanus. The seeds with 2.5 cm roots required the shortest time to break their dormancy (50 d), and the epicotyl–plumule emergence percentage was the highest. Additionally, GA3 treatment also shortened the incubation time in cold stratification (5 °C) and successfully broke the epicotyl physiological dormancy. Our study showed that H. thibetanus seeds exhibited deep simple epicotyl morphophysiological dormancy. Temperature, GA3, and duration of stratification played vital roles in the seed germination of H. thibetanus. This research will provide valuable data for seed germination and practical dormancy-breaking techniques and will promote the cultivation and conventional crossbreeding of H. thibetanus.

Seed Dormancy Class and Germination Characteristics of Berberis amurensis var. latifolia Nakai, Native to Korea

Berberis amurensis var. latifolia Nakai is a plant native to the Ulleung Island in Korea. In this study, we aimed to identify seed dormancy-breaking and germination requirements of this species using water imbibition experiments, gibberellic acid (GA3) treatment (0, 10, 100, or 1000 mg/L), cold stratification (0, 2, 4, 8, or 12 weeks at 5 °C), move-along experiments, and phenological studies. In the water imbibition experiment, the seed weight increased by more than 120% after 24 h. Analysis of the internal morphological characteristics of the seeds revealed that the embryo in freshly matured seeds was fully grown and did not grow thereafter. The final germination percentages after 12 weeks of cold stratification at 5 °C were 49 ± 6.4% and 63 ± 3.4% under light and dark conditions, respectively. In move-along and phenological studies, a longer cold stratification treatment period resulted in a higher germination percentage; however, the warm stratification treatment did not affect germination significantly. The GA3 treatment had little effect on seed germination. Therefore, we concluded that B. amurensis var. latifolia seeds have intermediate physiological dormancy, and pre-treatment with cold stratification for 12 weeks and incubation in the dark are required for effective seed propagation.

Warm stratification combined with organic manure application enhances seed germination and improves Cycas revoluta growth and development

Cycas revoluta (Sago palm) is one of the widespread ornamental plant, used as an indoor and outdoor plant. Seed propagation is extremely hard and time consuming, given the physical dormancy imposed by hard coat. The use of warm stratification improves seed germination by prompting embryos development. As mean to gain more insight on the beneficial effect of warm treatment on seed germination, histological analysis of warm stratified and untreated embryos was conducted. Our results revealed that warm treatment accelerated embryos development, resulting in a rapid differentiation of embryos’ tissues. α-amylase, GA3 and ABA quantification showed that warm stratified embryos accumulated higher and lower amounts of α-amylase and ABA respectively compared to untreated embryos. Regarding plant development, our results showed that organic manures significantly improved Cycas revoluta growth and development. The best response was recorded with the application of sheep manure. Indeed, sheep manure addition increased plant height, the number of leaves per plant, stip length and width by nearby 188% and 61%, 36% and 17% respectively. In roots, the presence of nodules had been recorded in the three applied treatments and more importantly in the presence of sheep manure. At the physiological level, sheep manure supplementation improved photosynthetic apparatus and nitrogen content in leaves (by 75%), thereby explaining the growth promotion. Taken together, these results underlined the beneficial effect of organic manure on Cycas revoluta growth and development and proposed a new strategy to improve plant growth and development with the use of sheep manure as organic amendment.

Breaking of seed dormancy in ash gourd (<i>Benincasa pruriens</i>) through fruit storage and seed treatments

The dormancy in seeds collected from freshly harvested ash gourd [Benincasa pruriens f. hispida (Thunb.) de Wilde & Duyfjes] fruits reduces the seed quality and field performance viz. early germination, faster seedling establishment and vigorous seedling growth. Post harvest storage of fruits and different physical and chemical methods are useful in breaking seed dormancy in cucurbits. The present study was carried out during winter (rabi) 2020–21 and rainy (kharif) seasons of 2021–22 at the Agricultural Research Station (Tamil Nadu Agricultural University, Coimbatore, Tamil Nadu), Vaigai Dam, Tamil Nadu to identify the optimal duration of post-harvest fruit storage and dormancy-breaking method for reducing seed dormancy in ash gourd cv. CO 1. Experiment was conducted in a randomized block design (RBD) with 3 replications. Firstly, the results revealed that the seeds extracted from the fruits, which were stored for 60 days after harvest, exhibited the best field performance, viz. early emergence, higher field emergence, faster rate of emergence and more seedling length, seedling dry weight, seedling vigour index, and viability indicating that prolonged storage can effectively reduce seed dormancy. Secondly, among different dormancy-breaking treatments, warm stratification of seeds at 40–50°C for 5 days and soaking of seeds in 500 ppm ethrel for 16 h remarkably improved the field performance, indicating the usefulness of these methods in improving seed quality characteristics in ash gourd. Farmers can use ethrel to break dormancy in ash gourd.

THE EFFECT OF COLD TREATMENT ON THE GERMINATION OF <i>CARDIOCRINUM CORDATUM</i> VAR. <i>GLEHNII</i> (LILIACEAE) SEEDS

The seeds of Cardiocrinum cordatum var. glehnii are characterized by a complex morphophysiological type of dormancy. There are three mechanisms of germination inhibition: two of them are localized in the embryo and one in the surrounding structures of the seed. To overcome these mechanisms, different temperature regimes for seed stratification are required.It was revealed that the mechanism of inhibition of embryo postdevelopment is removed at higher temperatures of 18–20°C for 1.5 months for stored seeds or 2 months for fresh ones. Optimal rates of embryo development were observed at 9–10°C. At the end of postdevelopment, the embryos in different experimental variants could significantly differ in length. However, the degree of heterogeneity of the sample by embryo length did not affect the germination rate and the final percentage of germinated seeds.@The temperature regime during embryo postdevelopment did not affect the subsequent growth of the embryonic root and seed germination, as well as cold stratification at the beginning of the experiment did not stimulate embryo growth.The development of embryo root was possible only after exposure to cold (0–2°C). It was demonstrated that the energy of seed germination and the germination rate significantly depend on the duration of cold stratification, regardless of the moment of exposure to cold. The longer the cold treatment was, the faster the seed germination. At the same time, not only cold stratification on water, but also dry storage of seeds at 0–2°C accelerated their germination.Under natural conditions, seed germination of C. cordatum var. glehnii occurs in 18–19 months after dissemination. In laboratory experiment, freshly harvested seeds of this species could be germinated in 7–8 months, taking into account that approximately 4 months of warm stratification are required for the further development of the embryo, and 3.5–4 months of cold stratification are required to remove the mechanism of germination inhibition.Differences in the duration and period of exposure to cold, however, did not affect the final percentage of germinated seeds. In almost all variants, the final percentage of germination was high (from 86 to 100%).The results of the experiment indicate that the process of seed germination of C. cordatum var. glehnii is realized in nature under the effect of different durations of temperature influences, which ensures the plasticity in the reproduction of this species in natural conditions.

The Co-Occurrence of Physiological and Epicotyl Physiological Dormancy in Three Desiccation-Sensitive Castanopsis (Fagaceae) Acorns from China with Specific Reference to the Embryonic Axis Position

Ecological significance of dormancy in desiccation-sensitive seeds is poorly understood. Quercus exhibits mutually exclusive occurrence of physiological (PD) and epicotyl dormancy (ePD), with no reported co-occurrence or dormancy class in other genera. We aimed to understand the dormancy in three Castanopsis species and document desiccation sensitivity and germination patterns concerning the embryonic axis position. We hypothesized that Castanopsis acorns are recalcitrant and potentially dormant. Fresh and cold-stratified acorns of Castanopsis chinensis, Castanopsis purpurella, and Castanopsis sclerophylla were subjected to desiccation and germination. Seedling emergence and internal morphology was monitored following cold (CS) and warm (WS) stratification. Fresh acorns had radicles emerge only after CS but require WS for shoot emergence. Drying to 20% moisture content led to complete death. In C. purpurella and C. sclerophylla, the embryonic axis was near the scar, and germination occurred by cracking the pericarp near the scar, which contrasts with C. chinensis. Moderate drying relieved dormancy due to the mechanical resistance of the pericarp. All three acorns were desiccation-sensitive and dormant. This is the first explicit report on PD and ePD co-occurrence in desiccation-sensitive seeds, but literature surveys allow for inference of such coexistence. CS alleviated PD and WS relieved ePD. Winter temperatures break PD, and acorns germinate during spring, but shoot emergence is delayed until summer. Our results are instructive for research on the dormancy of desiccation-sensitive species and the reproduction of Fagaceae species in subtropical forests.

Seed germination and storage conditions of Ilex embelioides Hook.f. (Magnoliopsida: Aquifoliales: Aquifoliaceae), a threatened northeastern Indian species

Ilex embelioides Hook.f. is a threatened tree species endemic to northeastern India. The species propagates naturally through seeds but shows a brief dormancy period. The present study was carried out to assess the germination behaviour, and identify the suitable storage conditions of I. embelioides seeds. Results revealed that warm stratification for 30 days could effectively break dormancy. Seeds pre-treated with gibberellic acid (GA3, 2,000 mg L-1) showed highest germination (63.89 ± 0.91%) as compared to other concentrations of GA3 as well as potassium nitrate (KNO3). Highest in vitro seed germination percentage (65.56 ± 2.92%) was recorded on (Murashige and Skoog) MS medium containing 10 mg L-1 GA3. The viability of the seeds declined with storage period irrespective of its storage condition. After 30 days, highest viability (54.72 %) was observed in seeds stored in moist sand at 25°C. Therefore, application of GA3 and warm stratification (25 ± 1°C) along with a substrate (moist sand) for 30 days may be considered as ideal conditions for effective germination and storage of I. embelioides seeds. This study can also be used for mass propagation of the species for reintroduction in the wild.

Propagation of keystone-woody species as a first step in restoration of an overgrazed seasonal dry forest

In degraded forest ecosystems, reintroduction of keystone-woody species is an important step for restoration because it provides regeneration niches. However, lack of information on how to propagate species restricts the use of native species; specially in tropical dry forests where seed germination is seasonal and is synchronized with the onset of the wet season. We evaluated the dormancy-breaking and germination requirements of nine keystone-woody species from Dry Chaco Forest. Most fresh viable seeds of the keystone species are nondormant, but viability decreases during dry-cold storage restricting the use of some species. Seeds of three keystone species germinated to higher percentages in light than darkness and those of five species germinated equally well in light and darkness; seeds of Castela coccinea germinated to higher percentages in darkness than in light. Alternating vs. constant temperatures had no effect on germination in seven species. Seeds of Anisocapparis speciosa and Cynophalla retusa were nondormant and remained viable for only 1 month during cold-dry storage; and 62–95% of the seeds of the other seven species were nondormant. Dormancy-break was studied in five of the seven species; seeds of four species had physiological dormancy and one had physical dormancy. Dormancy-breaking was promoted by environmental conditions in the habitat, i.e. warm stratification, after seed dispersal. Castela coccinea, Achatocarpus praecox, Mimosa detinens, and Capparicordis tweedieana are the most suitable keystone species for the restoration of overgrazed areas in the Dry Chaco Forest because their seeds germinate to a high percentage and retain viability during dry storage at low temperatures. Seeds of Mimosa detinens and Capparicordis tweedieana required mechanical scarification and 6-weeks of warm stratification, respectively, for dormancy-break.

Is the protection of habitat directive Eleocharis carniolica in its northern limits really needed? – A life strategy based investigation

Eleocharis carniolica is included in the EU Habitat Directive and legally protected in many European countries. It is also considered as one of the most threatened plants in Poland. It typically occurs in muddy habitats, wet meadows, lake or pond shores or temporary puddles, but in Poland this species usually occurs at disturbed anthropogenic sites such as road verges or drainage ditches. Despite being the focus of a number of ecological and conservation studies, E. carniolica still does not have a fully recognized ecology and life-strategy, particularly with regard to breaking seed dormancy and germination. To find out the population performance and species propagation potential in Poland, we have conducted experiments aimed at assessing the seed germination conditions and efficiency. The main goal was to discover the crucial factors that stimulate germination. The results of the experiments suggest that light is a pivotal factor for triggering germination of E. carniolica seeds. Moreover, E. carniolica’s seed bank consisted of about 80 % dormant seeds. The only effective method for dormancy breaking was warm stratification (placing the seeds at high temperature on a moist substrate) with application of gibberellic acid (GA3), and even a few days of warm stratification resulted in effectively overcoming dormancy. Eleocharis carniolica's germination features are typical for plants adapted to frequent disturbances with a short life expectancy and large reproductive effort. Our results strongly suggest that E. carniolica has a ruderal life strategy at its northern distribution limits and probably can be considered as an alien species in Poland.

Alternating temperature stratification breaks seed dormancy of Paeonia ostii

Paeonia ostii T. Hong & J. X. Zhang (Paeoniaceae), a traditional ornamental and medicinal plant, is used as a new oil tree crop in China, but its cultivation is greatly hindered by seed dormancy. By using an alternating temperature stratification assay, the present study investigated seed germination of P. ostii. Seeds of P. ostii did not germinate under low temperature, and produced the root but not the shoot under continuous warm conditions. Seedling emergence of P. ostii was dependent on a warm (I) - cold - warm (II) sequence of temperature regimes. During warm (I) stratification, the embryo developed fully and the radicle emerged and grew; the activity of peroxidase increased in the embryo, the contents of soluble protein, IAA and ABA in the embryo decreased before radicle emerged and increased after radicle emerged, the contents of GA3 and the GA3: ABA ratio in the embryo increased before radicle emerged and decreased after radicle emerged,and the content of starch decreased in the endosperm.Under cold stratification, the embryo and the root developed slowly, but the GA3: ABA ratio in embryo gradually increased. Subsequent warm (II) condition allowed the epicotyl to elongate and produce a shoot. These results indicate that seeds of P. ostii have morphophysiological dormancy. The radicle and shoot of the underdeveloped embryo have physiological dormancy (PD). Warm stratification breaks PD, allowing the embryo to grow and the radicle to emerge. Cold stratification is required to break dormancy of the epicotyl, but this treatment is not effective until after the radicle has emerged.

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.

Transcriptome and proteome analyses reveal the potential mechanism of seed dormancy release in Amomum tsaoko during warm stratification

BackgroundIn Amomum tsaoko breeding, the low germination rate is the major limitation for their large-scale reproduction. We found that warm stratification was an effective treatment to break the seed dormancy of A. tsaoko prior to sowing and could be an important component of improving breeding programs. The mechanism of seed dormancy release during warm stratification remains unclear. Therefore, we studied the differences between transcripts and proteomes at 0, 30, 60, and 90 days of warm stratification, to identify some regulatory genes and functional proteins that may cause seed dormancy release in A. tsaoko and reveal their regulatory mechanism.ResultsRNA-seq was performed for the seed dormancy release process, and the number of differentially expressed genes (DEGs) was 3196 in three dormancy release periods. Using TMT-labelling quantitative proteome analysis, a total of 1414 proteins were defined as differentially expressed proteins (DEPs). Functional enrichment analyses revealed that the DEGs and DEPs were mainly involved in signal transduction pathways (MAPK signaling, hormone) and metabolism processes (cell wall, storage and energy reserves), suggesting that these differentially expressed genes and proteins are somehow involved in response to seed dormancy release process, including MAPK, PYR/PYL, PP2C, GID1, GH3, ARF, AUX/IAA, TPS, SPS, and SS. In addition, transcription factors ARF, bHLH, bZIP, MYB, SBP, and WRKY showed differential expression during the warm stratification stage, which may relate to dormancy release. Noteworthy, XTH, EXP, HSP and ASPG proteins may be involved in a complex network to regulate cell division and differentiation, chilling response and the seed germination status in A. tsaoko seed during warm stratification.ConclusionOur transcriptomic and proteomic analysis highlighted specific genes and proteins that warrant further study in fully grasping the precise molecular mechanisms that control the seed dormancy and germination of A. tsaoko. A hypothetical model of the genetic regulatory network provides a theoretical basis for overcoming the physiological dormancy in A. tsaoko in the future.

Non-deep simple and deep simple morphophysiological dormancy in seeds of three species of Ilex from subtropical and tropical regions of Taiwan

AbstractDormancy-breaking requirements and level of morphophysiological dormancy (MPD) were determined for seeds of Ilex formosana and I. uraiensis from the subtropical region, and seeds of I. rotunda from both the subtropical and tropical regions of Taiwan. We hypothesized that some Ilex species would have deep simple MPD broken by warm stratification. Germination of seeds and embryo growth was monitored at 30/20, 25/15, 20/10, 15/5°C and at 25°C. Seeds were cold-stratified and then incubated at 25/15°C, and seeds treated with GA3 and GA4 were incubated at 25/15°C. Fresh seeds reached 50% germination after 11–45 weeks of warm stratification. Pre-treatment with GA increased germination percentages of I. formosana and I. rotunda (tropical) but not I. uraiensis and I. rotunda (subtropical), while cold stratification did not promote germination of either species but increased the germination rate of I. rotunda (tropical). Embryo length in seeds of all species increased ≥710% prior to root emergence, and growth occurred during warm stratification. The positive response to GA and relatively short time for beginning of germination and to reach 50% germination indicate non-deep simple MPD in seeds of I. formosana and I. rotunda (tropical). The negative response to GA and long time for beginning of germination and to reach 50% germination indicate deep simple MPD in seeds of I. uraiensis and I. rotunda (subtropical). Thus, in both the subtropical and tropical regions of Taiwan, the seeds of Ilex species have non-deep simple and deep simple MPD that are broken by warm stratification. Furthermore, GA treatment increases the germination rate and percentage of Ilex seeds with non-deep simple MPD, and cold stratification promotes the seed germination rate of Ilex species with non-deep simple MPD in tropical region.

Seed dormancy revisited: Dormancy‐release pathways and environmental interactions

Abstract Many internal (inherent) and environmental (imposed) factors control seed dormancy and germination that we divide into three basic dormancy‐release pathways: Maternal structures and embryo physiology control inherent dormancy that is broken by various types of scarification and physiological changes, followed by imposed‐dormancy release when the prevailing environment is replaced by certain ‘standard’ conditions that stimulate germination (Pathway 1); imposed dormancy prevails even if inherent dormancy is broken or not applicable that is released when replaced by certain ‘standard’ environmental conditions which stimulate germination (Pathway 2); and release from inherent dormancy by light/dark or cold stratification is contingent on the pre‐existence of certain environmental conditions that stimulate germination (Pathway 3). On‐plant seed storage (serotiny) and frugivorous seeds are recognized here as representing special types of physical dormancy, as their properties are consistent with those of hard diaspores. Warm stratification does not require seeds to be moist as it is just a physical response. Heat may promote germination of non‐hard, as well as hard, seeds as it may increase their permeability further. Levels of germination gauge the net effect of inherent‐ and imposed‐dormancy release so that it is only possible to identify the extent of inherent‐dormancy release when conditions for germination are optimal (imposed dormancy has been annulled). While imposed dormancy may be protracted after inherent dormancy is broken by heat or chilling during the dry or cold seasons, release from both states may effectively coincide if smoke chemicals or light are received during the (wet) growing season. We suggest reserving the term secondary dormancy for seeds that return to (inherent or imposed) dormancy due to changed environmental conditions. Under seasonal climates, fluctuations in environmental conditions can lead to secondary dormancy and even dormancy cycling. We recognize four types of functional interactions between any two environmental factors that induce inherent‐dormancy release: binary interactions are ineffective, only one stimulus is effective, both are effective but non‐additive, or both are additive/synergistic. Two environmental stimuli that individually break dormancy but have no additive effect must be affecting the same process; this was demonstrated here for some interactions between heat and smoke. The three dormancy‐release pathways, together with internal, seasonal and stochastic interactions, are coordinated by the non‐dormant seed to ensure maximum germination under optimal conditions. To ignore any aspect outlined here leads to an impoverished understanding of the disparate seed ecology of species adapted to different stressful and disturbance‐prone habitats. Read the free Plain Language Summary for this article on the Journal blog.

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.

IEffect of Scarification and Stratification treatments on Germination and Seedling Vigour of Teak (Tectona grandis Linn.f) Drupes

The effect of scarification and stratification treatments on germination and seedling vigour of fresh teak drupes was investigated. The drupes were subjected to the following scarification and stratification treatments viz., control, acid scarification (500 mL/kg of drupe) for 5, 10, 15, 20, 25, 30, 40, 50 and 60 min. Cold stratification for 30, 40 and 50 days at 5o C. Warm stratification for 30, 40 and 50 days at 40o C. The treated and control drupes were sown in sand filled earthen pots and placed in direct sunlight for assessing the germination. The experiment was conducted in a Completely Randomized Block Design with ten replications. Germination percentage, number of seedlings/100 drupes, time taken for initial emergence, root length, shoot length, dry matter production and vigour index were recorded 28 days after sowing. Acid scarification for 40 minutes, cold stratification at 50°C for 40 days, and warm stratification at 40°C for 40 days resulted in 23.7, 29.8, and 22.7 percent germination, respectively. From this study it could be concluded that warm stratification of fresh teak drupes at 40 0C for 40 days gave maximum germination (29.8 per cent) and seedling vigour (468).