Conditional Dormancy Research Articles

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

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

Dormancy Characteristics of Euphorbia maculata L. Seeds and Strategies for Their Effective Germination

Euphorbia maculata L. has been confirmed to have functional properties, including anticytotoxic, anti-inflammatory, and antioxidative effects. However, studies on the dormancy and germination of its seeds for cultivation purposes are lacking. The potential of E. maculata as a valuable plant species has not been fully realized due to the lack of understanding of its seed dormancy and germination characteristics. E. maculata seeds were collected and germination tests were performed at various temperatures to determine their dormant state. Next, seeds were stratified with various temperatures, and treated temperature conditions similar to those of its natural habitat to induce dormancy release. The seeds exhibited very low germination below 30 °C, which indicates the possibility of innate dormancy. Subsequently, dormancy was released by cold stratification, and an expansion in the temperature range suitable for germination was observed, confirming that E. maculata seeds exhibit conditional dormancy. Conversely, high-temperature moist stratification did not effectively break dormancy as it led to seed decay. Therefore, we treated the seeds at various high temperatures in a dry environment. This facilitated dormancy release without the need for moist stratification, allowing for seed storage while ensuring the uniform and rapid production of E. maculata seedlings and minimizing seed wastage. Additionally, seeds with broken dormancy did not require a high temperature for germination, making them more cost-effective. Therefore, comprehensively examining germination and dormancy characteristics may optimize the cultivation process of this valuable plant species, E. maculata.

Germination and Secondary Dormancy Of Hydrocharis Dubia (Blume) Seed

The germination of freshly harvested, dry-stored and wet-stored Hydrocharis dubia seeds were treated with exogenous GA3, cold stratification, puncture, different temperatures and combined treatments under controlled laboratory conditions. The results showed that: The optimal temperature for H. dubia seed germination is 23℃ and fresh seed has conditional dormancy, which can be released by puncture. Seed germination percentage decreased significantly after dry seed storage and the main reason for the reduction of "seed germination ability" by dry storage was that dry storage. caused secondary dormancy but a reduction of seed vigor. The secondary dormancy is non- deep physiological dormancy, which can be released by cold stratification, seed puncture and combination treatments. The findings provided further insight into how germination strategy contributes to the seed bank formation and species reproduction. Bangladesh J. Bot. 52(2): 429-435, 2023 (June)

Seed germination of five species from the subalpine shrubland of a mountainous oceanic island with high conservation value (Reunion Island)

Little is known about the seed ecology of native plants from subalpine and alpine vegetation zones on oceanic islands, although their biodiversity is unique and vulnerable (e.g. facing fires and biological invasions). This study of seed germination focuses on five species, which are representative of the subalpine shrubland of Reunion Island. The main objectives are to identify the presence of dormancy and light requirements, and to evaluate whether GA3 or a smoke-infused water could substitute for the light requirement for seed germination. Over one month, germination tests were performed under different conditions at three temperatures (15, 20 and 25 °C), in light (12-hours light/12-hours dark) and in dark. Seeds were also treated using a single spraying of gibberellic acid (GA3 at 1000 ppm) and a smoke-infused water (named Smoke Water in the study). No dormancy was detected for Stoebe passerinoides. For Erica reunionensis, Agarista buxifolia, Hubertia tomentosa and Hypericum lanceolatum subsp. angustifolium, a potential non-deep physiological dormancy (with a conditional dormancy state) was detected. Moreover, for Agarista buxifolia and Erica reunionensis (Ericaceae), light is required for seed germination. Gibberellic acid (GA3 at 1000 ppm) substitutes for light, except at 25 °C for E. reunionensis. Smoke Water does not improve seed germination, except at 15 °C in dark for E. reunionensis. A better understanding of seed germination for species from subalpine and alpine vegetation zones will mean better threat management and restoration actions.

Conditional Seed Dormancy Helps Silene hicesiae Brullo & Signor. Overcome Stressful Mediterranean Summer Conditions.

Investigations on seed biology and ecology are of major importance for the conservation of threatened plants, both providing baseline information and suggesting practical approaches. In our study, we focused on the germination behavior of Silene hicesiae Brullo & Signor., a narrow endemic species to Panarea and Alicudi (Aeolian Archipelago, Italy), as well as one of the 50 most threatened Mediterranean island plants. Specifically, the effects of temperature, light, seed age, seed source, and collection year were evaluated; in addition, threshold temperatures and thermal–time parameters were estimated. The thermal range for fresh seed germination resulted between 5 and 15 °C, reaching up to 20 and 25 °C at increasing seed age, with 30 °C being clearly beyond the ceiling temperature. This behavior indicates that fresh seeds exhibit the Type 1 non-deep physiological dormancy, and that germination is regulated by conditional dormancy. This dormancy syndrome emerged as a highly efficient adaptation strategy for this species and, together with thermo-inhibition, would allow seeds to counteract or take advantage of Mediterranean environmental conditions. The comparison between the wild Panarea population and the corresponding ex situ cultivated progeny has enabled the identification of the latter as a suitable seed source for sustainable in situ reinforcement actions, at least in the short-term; indeed, plant cultivation for a single generation did not produce significant modifications in the germination behavior of the offspring.

A quantitative analysis of primary dormancy and dormancy changes during burial in seeds of Brassica napus

For plants inhabiting unpredictable environments, scheduling germination can be challenging. Various responses to environmental conditions have been evolved by plants; these responses combine with variation in local climate to construct germination niche. Germination process may be regulated by a number of factors, among them, the type of seed dormancy and dormancy cycling play an important role in promoting survival after dispersal. In the present study, seeds of Brassica napus were tested for primary conditional dormancy (CD). Dormancy changes were quantified through seed population thermal germination parameters to test whether different genotypes of B. napus seeds (944, 966, Alestrom, Danube, Okanto and Rohan) are non‐dormant (ND) at the maturity or if they present primary dormancy (D or CD). In a burial experiment, B. napus seeds dormancy cycling in the natural soil seedbank was investigated. Germination of all genotypes decreased at 5 and > 20°C, showing narrower breadth of thermal niche for germination. Dormancy‐breaking treatments lead to the widening of thermal range permissive for germination. The lower limit (Tl(50)) and higher limit (Th(50)) temperatures for germination decreased and increased, respectively, for non‐dormant (after‐ripened seeds treated with GA3) seeds compared with fresh seeds in all genotypes. In fresh seeds, the Tl(50) and Th(50) for various genotypes ranged from 3.61 to 6.5°C and 25.0 to 29.0°C, respectively and ranged from 0.2 to 1.8°C and 35 to 41.0°C in non‐dormant seeds. Thus, fresh seeds of B. napus are dormant at dispersal and adopt delayed germination strategies to avoid summer drought. In the burial experiment, the results indicated that B. napus must have D/ND cycle in which fresh seeds first become dormant and then the cycle begins (CD→D↔CD↔ND), thus adopting both risk‐prone and risk‐adverse strategies to spread the likelihood of survival over time.

To bulk or not to bulk? Intense genetic differentiation of seed dormancy among Stipa lagascae (Poaceae) genotypes accessed and multiplied in arid Tunisia

Many ecological restoration projects involving wild dryland grasses work with bulk‐harvested seed, yet bulking may lead one to overlook and lose genetic variation that turns out to be crucial for restoration success, including specific dormancy breakdown requirements (conditional dormancy) and genetic variation in these. This article reports on the genetic variation of conditional seed dormancy of Stipa lagascae Roem. & Schult. (Poaceae), a winter‐growing bunch grass with high‐grazing value, native to the circum‐Mediterranean areas but threatened with extinction. This grass is a cleistogamous inbreeder whose population remnants exhibit a fine‐grained genetic structure in many ecological traits. Seed from different lineages was obtained at the end of a seed increase program that chose not to bulk seed during seed sourcing, seed increase, nor seed harvesting for final use. Over a period of 3 years, three germination trials were run with seed coming from 15 to 20 different seed lineages and harvested over different years in two related seed increase plots. Seed lineage was the single most important factor explaining differences in conditional dormancy. Seed weight did not add much to explain these differences. The singularity of behavior of each lineage was conserved over the different harvests. Young seed exhibits the strongest differentiation in conditional dormancy. To restore genetically diversified populations of this inbreeding grass, restoration practitioners should avoid to bulk seed during sourcing and seed increase, because unique seed lineages get easily lost unseen. However, seed for final use could be bulk harvested if seed is used when still conditionally dormant.

Effect of temperature and moist conditions on seed dormancy cycling of two sympatric limestone species, Begonia guishanensis and Paraisometrum mileense, in southern China

AbstractInformation about seed dormancy cycling and germination in relation to temperature and moisture conditions in the natural environment is important for the conservation and restoration of rare species, including Begonia guishanensis and Paraisometrum mileense, two sympatric perennial limestone (karst) species. Dry afterripening (DAR) and wet and dry (WD) cycles at 15/5 and 25/15°C as well as moist chilling (MC) at 15/5°C were used to mimic the natural environment at different times of the year. A field experiment was conducted to monitor seasonal changes in germination responses of the seeds. About 40–65% of B. guishanensis and 5% of P. mileense seeds were dormant at maturity. DAR at 25/15 and 15/5°C as well as MC and WD cycles at 15/5°C alleviated dormancy for B. guishanensis but not P. mileense, and WD cycles at 25/15°C induced a deeper conditional dormancy for both species. Seeds of B. guishanensis exhibited dormancy cycling in the field, with increased dormancy under natural WD cycles at relatively high temperatures during the transition from the dry to the wet season in April to May and decreased dormancy during the wet season from June to October. KNO3 mitigated the dormancy-inducing effect of both artificial and natural WD cycles at relatively high temperatures for B. guishanensis. The field experiment indicated that seeds of B. guishanensis may be able to form a persistent soil seed bank, while almost all seeds of P. mileense germinate at the beginning of the wet season in the field.

Evaluation of Primary Conditional Dormancy in Seeds of Oilseed Rape (Brassica napus) Produced in Golestan and Mazandaran Provinces

Evaluation of Primary Conditional Dormancy in Seeds of Oilseed Rape (Brassica napus) Produced in Golestan and Mazandaran Provinces

Conditional dormancy of Stipa lagascae (Poaceae) bulk-harvested on seed increase plots in South Tunisia: a reassessment and a surprise

Background and aims – With the perspective to reseed degraded drylands, grass seeds are often stocked for several years. This common practice overlooks conditional dormancy and the necessity to preserve it. This paper reports on the germination ecology of Stipa lagascae Roem. & Schult., which is a circum-Mediterranean winter-growing bunch grass of high grazing value. However, the published record on its germination ecology is scarce and inconsistent.Methods – This record was reassessed through a series of germination trials in combination with dormancy breaking treatments on seeds that were mainly harvested on a seed increase plot in South-Tunisia.Key results –The surprise finding was that Stipa lagascae exhibits a particular kind of conditional dormancy for many months after harvest. Whereas dormant seeds barely germinate at 10°C in classical Petri dishes or on germination tables, they germinate massively (but not fully) when allowed full contact with a water-saturated substrate at 7–10°C in boxes. Dehulling provokes fast germination of near 100% of the seeds, thus showing that the substrate effect at low temperatures breaks most but not all dormancy in a particular seed lot. This remaining or residual dormancy is not conditional, as it can only be broken through dehulling. There are thus two distinct germination windows: a very broad one for non-dormant seed and a narrow one for conditionally dormant seed.Conclusions – A pattern is suggested whereby each seed lot evolves through a continuum from full over conditional to non-dormancy and finally mortality. However, only the state of conditional dormancy times germination optimally with regard to the start of the winter growing season in South-Tunisia. Its ecological significance should be interpreted in combination with its trypanocarpy. Reseeding for restoration purposes and to render grazing value to depleted drylands should thus use conditionally dormant seed.

A graphical method for identifying the six types of non-deep physiological dormancy in seeds.

We present a new seed dormancy classification scheme for the non-deep level of the class physiological dormancy (PD), which contains six types. Non-deep PD is divided into two sublevels: one for seeds that exhibit a dormancy continuum (types 1, 2 and 3) and the other for those that do not exhibit a dormancy continuum (types 4, 5 and 6). Analysis of previous studies showed that different types of non-deep PD also can be identified using a graphical method. Seeds with a dormancy (D) ↔ conditional dormancy (CD) ↔ non-dormancy (ND) cycle have a low germination percentage in the early stages of CD, and during dormancy loss the germination capacity increases. However, seeds with a CD/ND (i.e. D→CD↔ND) cycle germinate to a high percentage at a narrow range of temperatures in the early stages of CD. Cardinal temperatures for seeds with either a D/ND or a CD/ND cycle change during dormancy loss: the ceiling temperature increases in seeds with Type 1, the base temperature decreases in seeds with Type 2 and the base and ceiling temperatures decrease and increase, respectively, in seeds with Type 3. Criteria for distinguishing the six types of non-deep PD and models of the temperature functions of seeds with types 1, 2 and 3 with both types of dormancy cycles are presented. The relevancy of our results to modelling the timing of weed seedling emergence is briefly discussed.

Role of chemicals in alleviating salinity and light related seed dormancy in sub-tropical grasses

This study is based on the assumptions that annual grasses express more complex seed dormancy than perennials, while dormancy regulating chemicals (DRCs) help in recovering seeds from dormancy. The role of six such chemicals, viz. plant hormones − Kinetin, Fusicoccin; organic osmotica − Proline, Betaine; nitrogenous compounds − Nitrate, Thiourea, in alleviating effects of salinity and light on seed germination of three subtropical grasses (perennials: Phragmites karka, Dichanthium annulatum; and annual: Eragrostis ciliaris) was hence investigated. All seeds of P. karka and D. annulatum germinated in non-saline condition while in E. ciliaris, 60% seeds germinated in absence of salts, 10% were dead and 30% were dormant. Salinity reduced germination of the test species to following levels (% of non-saline control) under highest NaCl concentration used: P. karka (30% at 500mM), D. annulatum (25% at 400mM) and E. ciliaris (10% at 125mM). The application of all DRCs alleviated conditional dormancy associated with salinity more in P. karka than D. annulatum but negligibly in the case of E. ciliaris. Absence of light inhibited seed germination of P. karka (partially) and E. ciliaris (completely) but under these conditions the application of DRCs increased germination of P. karka only. Nitrate was generally more effective than other DRCs in increasing seed germination both in salinity as well as in complete darkness. Seed germination was synergistically inhibited by salinity under dark conditions compared to their individual effects and was completely alleviated in P. karka and D. annulatum seeds by DRCs. In conclusion, the annual grass (E. ciliaris) used both innate and induced type of seed dormancy along with absolute light demand for successful seedling establishment while perennials (P. karka and D. annulatum) depended on enforced dormancy. Moreover, seed dormancy could be alleviated by DRCs in perennial grasses but not in the annual species.

Germination of four riparian species in a disturbed semi-arid ecosystem

The Cuatrociénegas Valley (Coahuila, Mexico) is a highly diverse semiarid ecosystem. Its gypsum substrate has been altered because of the extensive extraction of water, resulting in the destabilization of underground water systems and an increasing formation of sinkholes that are colonized by riparian species. Sinkholes represent a set of microenvironments that could improve germination and seedling establishment of riparian species. We studied the effect of light (in controlled conditions: 18/32°C, 12/12h photoperiod), collection season (rainy and dry seasons), and time of storage on the germination, in field and controlled conditions, of four riparian species (Samolus ebracteatus var. coahuilensis, Flaveria chlorifolia, Eustoma exaltatum, and Sabatia tuberculata) that colonize the sinkholes. Seeds of each species were enclosed in permeable nylon bags and fixed to the substrate of randomly selected sinkholes. From September 2009 to July 2010, three bags per species per collection season were recovered every two months, and germinated seeds were counted. Recovered ungerminated and lab stored (control) seeds were germinated in controlled conditions. The low germination probabilities in the field (<0.47) contrast with the high probabilities (0.8) maintained by control and recovered seeds, regardless of the collection season or the light treatment. All the species showed two germination peaks in the field, coinciding with moisture availability. These results suggest the presence of conditional dormancy and the distribution of germination in time, evading the unsafe synchronic germination in the disturbed Cuatrociénegas environment.

Annual dormancy cycles in buried seeds of shrub species: germination ecology of Sideritis serrata (Labiatae).

The germination ecology of Sideritis serrata was investigated in order to improve ex-situ propagation techniques and management of their habitat. Specifically, we analysed: (i) influence of temperature, light conditions and seed age on germination patterns; (ii) phenology of germination; (iii) germinative response of buried seeds to seasonal temperature changes; (iv) temperature requirements for induction and breaking of secondary dormancy; (v) ability to form persistent soil seed banks; and (vi) seed bank dynamics. Freshly matured seeds showed conditional physiological dormancy, germinating at low and cool temperatures but not at high ones (28/14 and 32/18 °C). Germination ability increased with time of dry storage, suggesting the existence of non-deep physiological dormancy. Under unheated shade-house conditions, germination was concentrated in the first autumn. S. serrata seeds buried and exposed to natural seasonal temperature variations in the shade-house, exhibited an annual conditional dormancy/non-dormancy cycle, coming out of conditional dormancy in summer and re-entering it in winter. Non-dormant seeds were clearly induced into dormancy when stratified at 5 or 15/4 °C for 8 weeks. Dormant seeds, stratified at 28/14 or 32/18 °C for 16 weeks, became non-dormant if they were subsequently incubated over a temperature range from 15/4 to 32/18 °C. S. serrata is able to form small persistent soil seed banks. The maximum seed life span in the soil was 4 years, decreasing with burial depth. This is the second report of an annual conditional dormancy/non-dormancy cycle in seeds of shrub species.

Variation of Seed Dormancy and Germination Ecology of Cowcockle (Vaccaria hispanica)

Cowcockle, an introduced summer annual weed of the Northern Great Plains, is being considered for domestication because of its high quality starch, cyclopeptides, and saponins. Loss of seed dormancy is one of the key desirable traits for domestication. To determine the potential for domestication of this species, an understanding of the seed dormancy and germination patterns is required. The objectives of this study were to evaluate seed dormancy in cowcockle ecotypes and determine how temperature and light affect seed dormancy. We evaluated 15 populations of cowcockle for primary dormancy by exposing them to five temperatures (5, 7.5, 10, 15, and 20 C) under two temperature regimes (constant and alternating) in both dark and light conditions. Freshly matured seeds of all the populations showed high levels of primary dormancy except ‘Mongolia’. Lower levels of dormancy at medium temperatures (10 and 15 C) and greater dormancy at low and high temperatures suggest conditional dormancy, a state at which seeds germinate over a narrower range of conditions compared to nondormant seeds. The effects of temperature regime, light, and their interaction was significant only at suboptimal (5 and 7.5 C) and supraoptimal (20 C) temperatures. Under these conditions, alternating temperatures were more effective in breaking the conditional dormancy, followed by light. The variation in optimum temperature, light, and their interactions among the cowcockle populations may be due to the plants evolving to adapt to their local environments. From a domestication perspective, the conditional dormancy in cowcockle can be observed as an evolutionary mechanism that prevents untimely germination following maturity and may not be a major obstacle for its domestication.

Influence of stratification, light, and planting depth on rabbitbrush seed germination and emergence

Rubber rabbitbrush ( Ericameria nauseosa (Pall. ex Pursh) G.L. Nesom & Baird) [Asteraceae]) has potential for use as an effective element of water-conserving landscapes. To enhance availability of this species, it is important to optimize nursery seedling production. Our objectives were to determine the influence of 1) stratification (cold-moist); 2) light exposure; and 3) planting depth on germination and emergence of seeds collected from diverse populations of rubber rabbitbrush. Seeds representing a range of environments were collected from Idaho and Utah and were cleaned, sorted, and exposed to germination-enhancing treatments. Following stratification, seeds of 3 of 4 rabbitbrush populations responded with a statistically significant increase in germination percentage. More significant, stratification increased the germination rate, reducing time to culmination from 4 or more wk to 1 wk or less. Compared with seeds germinated in the dark, exposure to sunlight increased germination percentage 1.5- to 3-fold, depending on population. Any amount of seed burial markedly decreased seedling emergence for all 4 populations. Six wk after planting, removal of all but a few mm of soilless substrate resulted in emergence of a portion of the buried seeds, indicating induction and release of conditional dormancy (possibly quiescence) due to a lack of light or other factors. Responses to stratification, light, and seed burial varied by population, thus confirming previously described variability that exists among rubber rabbitbrush populations. Results of this study will help nursery growers provide optimal conditions for producing nursery stock of rubber rabbitbrush.

Dormancy in solid tumors: implications for prostate cancer

In cancer dormancy, residual tumor cells persist in a patient with no apparent clinical symptoms, only to potentially become clinically relevant at a later date. In prostate cancer (PCa), the primary tumor is often removed and many patients experience a prolonged period (>5 years) with no evidence of disease before recurrence. These characteristics make PCa an excellent candidate for the study of tumor cell dormancy. However, the mechanisms that constitute PCa dormancy have not been clearly defined. Additionally, the definition of tumor cell dormancy varies in the literature. Therefore, we have separated tumor cell dormancy in this review into three categories: (a) micrometastatic dormancy--a group of tumor cells that cannot increase in number due to a restrictive proliferation/apoptosis equilibrium. (b) Angiogenic dormancy--a group of tumor cells that cannot expand beyond the formation of a micrometastasis due to a lack of angiogenic potential. (c) Conditional dormancy--an individual cell or a very small number of cells that cannot proliferate without the appropriate cues from the microenvironment, but do not require angiogenesis to do so. This review aims to identify currently known markers, mechanisms, and models of tumor dormancy, in particular as they relate to PCa, and highlight current opportunities for advancement in our understanding of clinical cancer dormancy.

THE JOINT EVOLUTION OF DISPERSAL AND DORMANCY IN A METAPOPULATION WITH LOCAL EXTINCTIONS AND KIN COMPETITION

Dispersal and dormancy are two strategies that allow recolonization of empty patches and escape from kin competition. Because they presumably respond to similar evolutionary forces, it is tempting to consider that these strategies may substitute for each other. Yet in order to predict the outcome of the evolution of dispersal and dormancy, and to characterize the emerging covariation between both traits, it is necessary to consider models where dispersal and dormancy evolve jointly. Here, we analyze the evolution of dispersal and dormancy as a function of direct fitness costs, environmental variation, and competition among relatives. We consider two scenarios depending on whether the rates of dormancy for philopatric and dispersed individuals are constrained to be the same (unconditional dormancy) or allowed to be different (conditional dormancy). We show that only philopatric individuals should enter dormancy, at a rate increasing with increasing rates of local extinction and decreasing population sizes. When dormancy and dispersal evolve jointly, we observe a wide range of evolutionary outcomes. In particular, we find that the pattern of covariation between the evolutionarily stable rates of dispersal and dormancy is molded by the rate of extinction and the local population size.

Seed germination ecology of the endemic Iberian winter annualsIberis pectinataandZiziphora aragonensis

AbstractThe germination ecology of the winter annual Iberian endemicsIberis pectinataandZiziphora aragonensiswas investigated in order to better understand adaptations of rare species to their natural habitat and to improveex-situpropagation techniques and management of their habitat. Specifically, we analysed the following aspects: (1) influence of temperature, light conditions and seed age on germination patterns; (2) phenology of germination; (3) germinative response of buried seeds to seasonal temperature changes; and (4) temperature requirements for induction and breaking of secondary dormancy. Germination was substantially lower in darkness than with a photoperiod in both taxa, with this difference being more pronounced inZ. aragonensis. Freshly matured seeds showed conditional physiological dormancy, germinating at low and medium temperatures but not at high temperatures (28/14 and 32/18°C). Germination capability increased with time of dry storage in both species, suggesting the existence of non-deep physiological dormancy. Under greenhouse conditions, germination of both taxa was mostly concentrated in autumn (October–November), while spring percentages were less than 1% of total accumulated germination recorded during the study.I. pectinataandZ. aragonensisseeds buried and exposed to natural seasonal temperature variations in an unheated greenhouse came out of conditional dormancy in summer and re-entered it in winter, thus exhibiting an annual conditional dormancy/non-dormancy cycle. Dormant seeds of both species which were stratified at 28/14 or 32/18°C during an 8-week period, were non-dormant when they were subsequently incubated over a range of temperatures from 5 to 25/10°C. Non-dormant seeds were induced into dormancy when stratified at 5 or 15/4°C for 8 weeks, showing a particularly low germination response at high temperatures. Recommendations for wild-population reinforcement programmes and for the management of the natural habitat of both endemics are discussed.

Using thermal time models to predict seedling emergence of orchardgrass (&lt;I&gt;Dactylis glomerata&lt;/I&gt; L.) under alternating temperature regimes

The effects of alternating temperatures on seed dormancy changes, germination and seedling emergence were investigated in ‘Arctic’ and ‘Lineta’ orchardgrass (Dactylis glomerata L.). Thermal time models were successfully developed for 0, 5, 10 and 15°C temperature amplitudes, using 28 constant and alternating temperature regimes. These models were then modified by linking seed germination in Petri dishes and seedling emergence in soil. A field experiment was conducted with four seeding dates over 2 years to validate the modified thermal time models. Temperature regimes with a 5–15°C amplitude enhanced seed germination percentages of orchardgrass, indicating that the conditional dormancy was released by these temperature regimes. Base temperatures decreased with increasing temperature amplitude. Seeds germinated more rapidly under alternating temperatures than under constant temperatures. The dual effects of temperature for dormancy breaking and germination were accounted for by thermal time models based on alternating temperature regimes, which accurately predicted the timing and percentage of ‘Arctic’ and ‘Lineta’ orchardgrass seedlings emerging in the field (R2≥0.88).