ABSTRACT
Dormancy in seeds is a key persistence mechanism for many flowering plants. Physically dormant (PY) seeds have water impermeable seed coats, and in fire-prone systems a common mechanism for dormancy release is fire-induced soil heating. However, the thermal thresholds innate to seeds with PY may be influenced by vegetation, climate, and fire regimes, varying substantially between populations of the same species. To investigate intraspecific variation of thermal thresholds in PY seeds, we sampled obligate seeding Acacia pulchella (Fabaceae) which produces PY seeds. Sampling was undertaken from 13 populations across a climate gradient of rainfall and temperature, and between two vegetation communities in fire-prone Mediterranean-type ecosystems of south-west Western Australia. To test a range of weather and fire-induced soil heating dormancy-break scenarios, we conducted dry heat shock experiments between 40 and 140 °C for 10 min and scored germination for 16 weeks. We created population-specific thermal performance curves and extracted the dormancy release temperature at which 50 % of the seeds had germinated (DRT50), the optimum dormancy-breaking temperature to stimulate maximum germination (T0), and the lethal temperature at which 50 % of the seeds were killed (LT50). Generalised linear models were used to examine relationships between thermal thresholds and possible vegetation, climate, and fire regime drivers of intraspecific variation in seed traits. We found that thermal thresholds differed between vegetation communities, with thresholds consistently higher in forest-type ecosystems compared to open woodland, and the influence of climate varied significantly between the two communities. Seeds from Jarrah Forest populations had a DRT50 16.0 °C higher, a T0 9.7 °C higher, and LT50 7.8 °C higher than seeds from Banksia woodlands. A high rate of non-dormancy was identified in one population that had lost fire in its system and displayed significant germination after both summer and fire-related temperatures. The PY thermal thresholds modelled here provide insight into the strong influence of variable soil heating as a function of vegetation and fuel dynamics in fire-prone environments. Our findings highlight the significant intraspecific variation for this species and suggest that fire-induced soil heating generated by vegetation characteristics may be an overlooked element of fire regimes shaping seed traits.
Subject(s)
Acacia , Seeds , Acacia/physiology , Germination/physiology , Plant Dormancy , Hot Temperature , Climate , Western Australia , EcosystemABSTRACT
Argyreia is the most recently evolved genus in the Convolvulaceae, and available information suggests that most species in this family produce seeds with physical dormancy (PY). Our aim was to understand the evolution of seed dormancy in this family via an investigation of dormancy, storage behaviour, morphology and anatomy of seeds of five Argyreia species from Sri Lanka. Imbibition, germination and dye tracking of fresh intact and manually scarified seeds were studied. Scanning electron micrographs and hand sections of the hilar area and the seed coat away from the hilar area were compared. Scarified and intact seeds of A. kleiniana, A. hirsuta and A. zeylanica imbibed water and germinated to a high percentage, but only scarified seeds of A. nervosa and A. osyrensis did so. Thus, seeds of the three former species are non-dormant (ND), while those of the latter two have physical dormancy (PY); this result was confirmed by dye-tracking experiments. Since >90% of A. kleiniana, A. hirsuta and A. zeylanica seeds survived desiccation to 10% moisture content (MC) and >90% of A. nervosa and A. osyrensis seeds with a dispersal MC of ~12% were viable, seeds of the five species were desiccation-tolerant. A. nervosa and A. osyrensis have a wide geographical distribution and PY, while A. kleiniana, A. hirsuta and A. zeylanica have a restricted distribution and ND. Although seeds of A. kleiniana are ND, their seed coat anatomy is similar to that of A. osyrensis with PY. These observations suggest that the ND of A. kleiniana, A. hirsuta and A. zeylanica seeds is the result of an evolutionary reversal from PY and that ND may be an adaptation of these species to the environmental conditions of their wet aseasonal habitats.
ABSTRACT
Understanding the relationships between seed traits and germination responses is crucial for assessing natural regeneration, particularly in threatened ecosystems like the seasonally dry tropical forest (SDTF). This study explored links between seed traits (mass, volume, moisture content, and dispersal type), germination responses (germinability, germination speed (v¯), time to 50% of germination (T50), synchrony, and photoblastism), and physical dormancy (PY) in 65 SDTF species under experimental laboratory conditions. We found that species with smaller seeds (low mass and volume) had higher v¯ and reached T50 faster than species with larger seeds. For moisture content, species with lower moisture content had higher germinability and reached the T50 faster than seeds with high moisture content. Abiotic dispersed species germinated faster and reached the T50 in fewer days. Most of the SDTF species (60%) did not present PY, and the presence of PY was associated with seeds with lower moisture content. As for photoblastism (germination sensitivity to light), we classified the species into three ecological categories: generalists (42 species, non-photoblastic), heliophytes (18 species, positive photoblastic, germination inhibited by darkness), and sciadophytes (5 species, negative photoblastic, light inhibited germination). This study intends to be a baseline for the study of seed ecophysiology in the SDTF.
ABSTRACT
Understanding how seed functional traits interact with environmental factors to determine seedling recruitment is critical to assess the impact of climate change on ecosystem restoration. This study focused on the effects of environmental factors on the mother plant during early plant life history stages and during seed development. Desmodium brachypodum A. Gray (large tick trefoil, Fabaceae) was used as a model species. Firstly, this study analyzed seed germination traits in response to temperature and moisture stress. Secondly, it investigated how seed burial depth interacts with temperature and soil moisture to influence seedling emergence traits. Finally, it determined if contrasting levels of post-anthesis soil moisture could result in changes in D. brachypodum reproductive biology and seed and seedling functional traits. The results showed that elevated temperature and moisture stress interacted to significantly reduce the seed germination and seedling emergence (each by >50%), while the seed burial improved the seedling emergence. Post-anthesis soil moisture stress negatively impacted the plant traits, reducing the duration of the reproductive phenology stage (by 9 days) and seed production (by almost 50%). Unexpectedly, soil moisture stress did not affect most seed or seedling traits. In conclusion, elevated temperatures combined with low soil moisture caused significant declines in seed germination and seedling emergence. On the other hand, the reproductive output of D. brachypodum had low seed variability under soil moisture stress, which might be useful when sourcing seeds from climates with high variability. Even so, a reduction in seed quantity under maternal moisture stress can impact the long-term survival of restored plant populations.
ABSTRACT
Many Astragalus species exhibit seeds with physical dormancy (PY), but little is known about the ecological context of this dormancy. We focused on A. maritimus and A. verrucosus, two threatened Sardinian endemic species inside the subgenus Trimeniaeus Bunge. Fresh seeds collected from the only two respective known populations were used to investigate the effect of mechanical scarification, heat shock, and water imbibition processes on PY release and germination. PY can be overcome through mechanical scarification of the water-impermeable seed coats, while no dormancy break was detected, nor a subsequent increase in seed germination due to fire-induced heat. This suggests that fire does not trigger dormancy release and seed germination in these species. The seeds tolerate relatively high heat shock temperatures (up to 120 and 100 °C for A. verrucosus and A. maritimus, respectively), but after 120 °C for 10 min, the number of dead seeds increases in both species. These facts suggest the capacity to develop a soil seed bank that can persist after fires and delay germination until the occurrence of optimal conditions. As regards water imbibition, both Astragalus species did not show the typical triphasic pattern, as germination started without further water uptake. This study emphasizes the significance of understanding germination processes and dormancy in threatened species. In fire-prone ecosystems, PY dormancy plays a crucial role in soil seed bank persistence, and it may be selectively influenced by post-fire conditions. Understanding such adaptations provides useful insights into conservation strategies.
ABSTRACT
Fabaceae produce seeds with water-impermeable seed coats, i.e., physical dormancy (PY). We hypothesized that the proportion of PY seeds will increase with the dryness of the habitat, and some key seed ecological traits will be strongly associated with different levels of PY. Fresh seed of 25 Fabaceae species collected in northern India were used for imbibition and germination experiments to determine the proportion of seeds with PY and of nondormant (ND) seeds compared to their Sri Lankan congeners. Seed coat:seed mass ratio (SCR), 1000 seed weight, seed shape index (SSI), embryo type and median germination time of ND seeds were determined. Four imbibition and germination patterns were identified among seeds of the studied species. Seeds collected from Indian populations had a higher proportion of PY seeds than those of Sri Lankan populations. We identified a type of embryo called 'spatulate axile' that had not been identified before among the studied species. Species with ND seeds had a lower SCR and a higher SSI than those with PY. Our hypothesis was confirmed since populations from drier habitats in India produce a higher proportion of PY seeds than those from Sri Lanka. A low SCR ensures minimal resistance to germinating seeds, while seeds with a high SSI have a lower tendency to incorporate into the soil seed bank. Thus, these seed traits aid the fast germination of ND seeds, often dispersed just before the rainy season.
Subject(s)
Fabaceae , Germination , Plant Dormancy , Seeds , EcosystemABSTRACT
The persistence of subtropical seasonally dry forests urgently requires the implementation of ex situ conservation and restoration programs. We studied variation in seed traits and dormancy of six native species growing in seasonally dry Chaco forests of Argentina. We documented high intra- and interspecific variability in seed traits and dormancy. Fresh seeds of Geoffroea decorticans and Parasenegalia visco (Fabaceae) were water-permeable and nondormant (ND), while those of Parkinsonia praecox and Vachellia aroma (Fabaceae) were water-impermeable and had physical dormancy (PY). Seeds of Schnopsis lorentzii (Anacardiaceae) and Sarcomphalus mistol (Rhamnaceae) were water-permeable and had physiological dormancy (PD). Mechanical and chemical scarification were the most effective methods to break PY, and dry storage for 3 months was effective in breaking PD. Seeds of large-seeded species were ND or had PD, and those of small-seeded species had PY. Species inhabiting moist habitats had ND seeds, whereas those from seasonally dry habitats had seeds with PY or PD. These results suggest that seed traits and dormancy are species-specific and that intraspecific variation in seed traits is likely associated with high phenotypic plasticity of species in response to local environmental heterogeneity. These findings should be considered at the time of implementation of conservation techniques and for seed sourcing decisions for restoration.
ABSTRACT
Enterolobium cyclocarpum and Piscidia piscipula are two important tree Fabaceae species distributed from the Yucatan Peninsula, Mexico. Our aims were focused on the E. cyclocarpum and P. piscipula seeds for: (1) to examine the seed permeability and imbibition rate, (2) to evaluate the effect of seed pre-germinative treatments, and (3) to characterize the structures involved on the presence of physical dormancy (PY). We used fresh seeds to determine seed permeability and imbibition rate, seed viability by means of tetrazolium test, furthermore, we applied mechanical scarification and boiler shocks for 5 s, 10 s and 15 s treatments. Morphological characterization of the seed coat was by Scanning Electron Microscope (SEM). Seed viability in E. cyclocarpum and P. piscipula were 100% and 96%, respectively. Seed permeability and imbibition rate in E. cyclocarpum were low. The highest germination in E. cyclocarpum was in the mechanical scarification (92%), while in P. piscipula, this parameter was in the 10 s boiling water treatment (76.0%). The presence of PY was confirmed in both species because they showed low seed permeability, and imbibition rate; furthermore, exhibited macrosclereids cells. The present research seeks to promote the sustainable use of E. cyclocarpum and P. piscipula.
ABSTRACT
The use of wildflower species as biogas feedstock carries the risk that their seeds survive anaerobic digestion (AD) and cause weed problems if spread with the digestate. Risk factors for seed survival in AD include low temperature, short exposure and hardseededness (HS). However, it is not possible to predict how AD will affect seed viability of previously unstudied species. In laboratory-scale reactors, we exposed seeds of eight species from a mixture of flowering wild plants intended as biogas feedstock and three reference species to AD at two mesophilic temperatures. Half of the species were HS, the other was non-HS (NHS). Viability was determined using a combination of tetrazolium and germination tests. Viability and germinability were modeled as functions of exposure time using a dose-response approach. Responses to AD varied considerably among species, and none of the considered influencing factors (time, temperature, HS) had a consistent effect. Seed lots of a species differed in inactivation times and seed-killing efficacy. The HS species Melilotus officinalis, Melilotus albus, and Malva sylvestris were particularly AD-resistant. They were the only ones that exhibited biphasic viability curves and tended to survive and germinate more at 42°C than at 35°C. Viability of the remaining species declined in a sigmoidal curve. Most NHS species were inactivated within a few days (Cichorium intybus, Daucus carota, Echium vulgare, and Verbascum thapsus), while HS species survived longer (Malva alcea). AD stimulated germination in the HS species A. theophrasti and its AD-resistance overlapped with that of the most resistant NHS species, C. album and tomato. In all seed lots, germinability was lost faster than viability, implying that mainly dormant seeds survived. After the maximum exposure time of 36 days, seeds of HS species and Chenopodium album were still viable. We concluded that viability responses to mesophilic AD were determined by the interplay of AD-conditions and species- and seed-lot-specific traits, of which HS was an important but only one factor. For the use of wildflowers as biogas feedstock, we recommended long retention times and special care with regard to HS species.
ABSTRACT
The herbaceous perennial legume Mimosa pudica is an invasive weed in many tropical and subtropical regions and a serious problem for farmers since it is difficult to eliminate from crop field by hand. Moreover, it has water impermeable seeds, i.e., physical dormancy (PY), which could persist in the soil seed bank for a long period of time, thus making it a big challenge to control. The aims of this study were to test the effect of various laboratory methods on breaking PY in seeds of M. pudica, to identify the site(s) of water entry into seeds of M. pudica and compare results of dormancy-breaking methods for seeds of M. pudica with those of 36 other species of Mimosa reported in the literature. Mechanical scarification, wet heat and cycles of wet heat and ice water effectively broke PY in seeds of M. pudica. Following wet heat at 80 °C for 10 min, water uptake was via the hilar region but not the pleurogram; small cracks made in the pleurogram by this treatment were not deep enough for water to enter the seed. Neither tolerance to summer temperatures nor PY is likely to be the cause of invasiveness of this species, since seeds of rare and endemic species of Mimosa also tolerate summer temperatures and have PY.
Subject(s)
Fabaceae , Mimosa , Germination , Plant Weeds , Seeds , WaterABSTRACT
Most tree species native to arid and semiarid ecosystems produce seeds with physical dormancy, which have impermeable coats that protect them from desiccation and prevent germination when the environmental conditions are unfavorable for seedling establishment. This dormancy mechanism may confer some degree of tolerance to seeds facing warmer and drier conditions, as those expected in several regions of the world because of climate change. Scarification of these seeds (removal of protective coats) is required for stimulating germination and seedling development. However, as scarification exposes seeds to the external environmental conditions, it can promote desiccation and viability loss in the future. To test these hypotheses, we performed field experiments and sowed scarified and unscarified seeds of a pioneer tree native to semiarid ecosystems of Mesoamerica (Vachellia pennatula) under the current climate and simulated climate change conditions. The experiments were conducted at abandoned fields using open-top chambers to increase temperature and rainout shelters to reduce rainfall. We measured microenvironmental conditions within the experimental plots and monitored seedling emergence and survival during a year. Air temperature and rainfall in climate change simulations approached the values expected for the period 2041-2080. Seedling emergence rates under these climatic conditions were lower than under the current climate. Nevertheless, emergence rates in climate change simulations were even lower for scarified than for unscarified seeds, while the converse occurred under the current climate. On the other hand, although survival rates in climate change simulations were lower than under the current climate, no effects of the scarification treatment were found. In this way, our study suggests that climate change will impair the recruitment of pioneer trees in semiarid environments, even if they produce seeds with physical dormancy, but also indicates that these negative effects will be stronger if seeds are scarified.
Subject(s)
Climate Change , Fabaceae , Ecosystem , Germination , Mexico , Seedlings , Seeds , TreesABSTRACT
The encapsulation of seeds in hard coats and fruit walls (pericarp layers) fulfils protective and dispersal functions in many plant families. In angiosperms, packaging structures possess a remarkable range of different morphologies and functionalities, as illustrated by thermo and hygro-responsive seed pods and appendages, as well as mechanically strong and water-impermeable shells. Key to these different functionalities are characteristic structural arrangements and chemical modifications of the underlying sclerenchymatous tissues. Although many ecological aspects of hard seed encapsulation have been well documented, a detailed understanding of the relationship between tissue structure and function only recently started to emerge, especially in the context of environmentally driven fruit opening and seed dispersal (responsive encapsulations) and the outstanding durability of some seed coats and indehiscent fruits (static encapsulations). In this review, we focus on the tissue properties of these two systems, with particular consideration of water interactions, mechanical resistance, and force generation. Common principles, as well as unique adaptations, are discussed in different plant species. Understanding how plants integrate a broad range of functions and properties for seed protection during storage and dispersal plays a central role for seed conservation, population dynamics, and plant-based material developments.
Subject(s)
Magnoliopsida , Seed Dispersal , Adaptation, Physiological , Fruit , Germination , Seeds , WaterABSTRACT
Abstract Microorganisms have been efficiently used for the biological control of phytopathogens through the production of antimicrobial substances. However, the objectives of this work were: to study the germination of Butia purpurascens Glassman and Butia archeri Glassman seeds in different substrates, to select and identify the endophytic and rhizospheric bacterial isolates of B. purpurascens and B. archeri, and to perform antibiosis tests based on the isolated microorganisms of these tree species. No difference was found between the cultivation substrates for the percentages of germination, hard seeds, and fungal contamination in the B. purpurascens seeds. The Bacillus subtilis isolated showed the best capacity for suppressing the growth of the two deteriorative fungi tested in B. purpurascens seeds. No difference was found for inhibition of the growth of Aspergillus niger fungus (deteriorative fungus of B. archeri seeds) between the microorganisms with Bacillus sp. and Brevibacillus brevis compared to the control. In the microbiolization of B. purpurascens and B. archeri seeds performed with microbiological solutions produced from the endophytic and rhizospheric strains of Bacillus sp., no differences were observed in the percentages of germination and contamination by fungi. For B. archeri seeds, there was contamination by fungi and bacteria after one day of cultivation, primarily in the regions with lesions caused by the extraction and scarification process.
Resumo Microorganismos específicos tem sido usados eficientemente para o controle biológico de fitopatógenos através da produção de substâncias antimicrobianas. Portanto, os objetivos deste estudo foram: estudar a germinação de sementes de Butia purpurascens Glassman e Butia archeri Glassman em diferentes substratos; selecionar e identificar isolados bacterianos rizosféricos e endofíticos de B. purpurascens e B. archeri, e realizar testes de antibiose a partir de microorganismos isolados dessas espécies arbóreas. Não houve diferença entre os substratos de cultivo para as porcentagens de germinação, de sementes duras e de contaminação por fungos nas sementes de B. purpurascens. O isolado bacteriano Bacillus subtilis apresentou melhor capacidade de supressão do crescimento dos dois fungos deterioradores testados nas sementes de B. purpurascens. Não foi encontrada diferença para a inibição do crescimento do fungo Aspergillus niger (fungo deteriorador de sementes de B. archeri) entre os microorganismos com Bacillus sp. e Brevibacillus brevis em comparação ao controle. Na microbiolização das sementes de B. purpurascens e B. archeri realizada com soluções microbiológicas produzidas a partir de cepas endofíticas e rizosféricas de Bacillus sp. não foram observadas diferenças na porcentagem de germinação e contaminação por fungos. Para B. archeri houve contaminação por fungos e bactérias após um dia de cultivo, principalmente nas regiões de lesão proporcionadas pelo processo de extração e escarificação.
Subject(s)
Seeds , Arecaceae , Bacteria , Germination , Brevibacillus , FungiABSTRACT
BACKGROUND: A structure called the pleurogram makes up a large part of the seed coat of some species in subfamilies Caesalpinioideae and Mimosoideae of Fabaceae, but little is known about its function. It has been hypothesized that this structure acts as a hygroscopic valve during the maturation drying of seeds. However, a new hypothesis has recently emerged that proposes a distinct function for the pleurogram. SCOPE: Here, we provide an overview of the structure and function of the pleurogram, which is diverse and complex. This large structure can be dislodged, thereby creating a pathway for water entry into water-impermeable seeds. However, the pleurogram is non-functional as a pathway of water into the seed of some species. Thus, the evolutionary history of species with a pleurogram may be related to a loss/gain in its function. A complete model for the function of the pleurogram is proposed. CONCLUSIONS: The pleurogram may act on several stages of the seed, from maturation to germination. As a hygroscopic valve, it regulates dehydration of the seed during maturation. As a pathway for water entry into the seed, the pleurogram acts as a water gap in seeds with physical dormancy, thereby regulating dormancy break/germination. The occurrence of a pleurogram in several genera of legumes and Cucurbitaceae is confirmed. Single or multiple pleurograms can serve as (the) point(s) of water entry into seeds that do not otherwise have a hilar water gap.
Subject(s)
Fabaceae , Germination , Biological Evolution , Plant Dormancy , Seeds , WaterABSTRACT
This study investigated seed germination of Cardiospermum halicacabum, a medicinally important invasive species. We compared mass, moisture content (MC), dormancy and dormancy-breaking treatments and imbibition and germination of scarified and non-scarified seeds of C. halicacabum from a low-elevation dry zone (DZ), low-elevation wet zone (WZ1) and mid-elevation wet zone (WZ2) in Sri Lanka to test the hypothesis that the percentage of seeds with water-impermeable seed coats (physical dormancy, PY) decreases with increased precipitation. Seed mass was higher in WZ2 than in DZ and WZ1, while seed MC did not vary among the zones. All scarified DZ, WZ1 and WZ2 and non-scarified DZ and WZ1 seeds imbibed water, but only a few non-scarified WZ2 seeds did so. When DZ and WZ1 seeds were desiccated, MC and percentage imbibition decreased, showing that these seeds have the ability to develop PY. GA3 promoted germination of embryos excised from fresh DZ and WZ1 seeds and of scarified WZ2 seeds. At maturity, seeds from DZ and WZ1 had only physiological dormancy (PD), while those from WZ2 had combinational dormancy (PY+PD). Thus, our hypothesis was not supported. Since a high percentage of excised embryos developed into normal seedlings; this is a low-cost method to produce C. halicacabum plants for medicinal and ornamental purposes.
Subject(s)
Climate , Plant Dormancy , Sapindaceae/physiology , Seeds/physiology , Germination , Rain , Sri LankaABSTRACT
A set of seed dormancy traits is included in this Special Issue. Thus, DELAY OF GERMINATION1 (DOG1) is reviewed in depth. Binding of DOG1 to Protein Phosphatase 2C ABSCISIC ACID (PP2C ABA) Hypersensitive Germination (AHG1) and heme are independent processes, but both are essential for DOG1's function in vivo. AHG1 and DOG1 constitute a regulatory system for dormancy and germination. DOG1 affects the ABA INSENSITIVE5 (ABI5) expression level. Moreover, reactive oxygen species (ROS) homeostasis is linked with seed after-ripening (AR) process and the oxidation of a portion of seed long-lived (SLL) mRNAs seems to be related to dormancy release. The association of SLL mRNAs to monosomes is required for their transcriptional upregulation at the beginning of germination. Global DNA methylation levels remain stable during dormancy, decreasing when germination occurs. The remarkable intervention of auxin in the life of the seed is increasingly evident year after year. Here, its synergistic cooperation with ABA to promote the dormancy process is extensively reviewed. ABI3 participation in this process is critical. New data on the effect of alternating temperatures (ATs) on dormancy release are contained in this Special Issue. On the one hand, the transcriptome patterns stimulated at ATs comprised ethylene and ROS signaling and metabolism together with ABA degradation. On the other hand, a higher physical dormancy release was observed in Medicago truncatula under 35/15 °C than under 25/15 °C, and genome-wide association analysis identified 136 candidate genes related to secondary metabolite synthesis, hormone regulation, and modification of the cell wall. Finally, it is suggested that changes in endogenous γ-aminobutyric acid (GABA) may prevent chestnut germination, and a possible relation with H2O2 production is considered.
ABSTRACT
Most legumes are well-known for the physical dormancy of their seeds; hence, the implementation of appropriate scarification techniques is essential for introducing new legume crops within agricultural systems. This study investigated morpho-anatomical traits and dormancy-breaking requirements in two taxa of the genus Bituminaria: the widespread B. bituminosa and the point endemic B. basaltica. As the species under investigation show monospermic indehiscent legumes, pods were used in this research. We performed pod trait measurements, light microscopy observations on the seed coat anatomical structure, and germination tests after mechanical, thermal, and chemical scarification treatments for seed dormancy breaking. Moreover, germination performance at different pod maturity stages and storage times was tested. Differences in morpho-anatomical traits were found, with B. basaltica having a thicker palisade cell layer and B. bituminosa showing larger pods. All of the scarification treatments proved to be able to break physical dormancy, with mechanical and chemical scarification being the most effective methods in both species. Nevertheless, dormancy-breaking treatments performed better in B. bituminosa. Seeds at early pod maturity stages showed higher germination capacity in both species. Overall, this research provided background knowledge on seed collection time, storage strategy, and effective pre-sowing treatment, which might contribute to enhance propagation and use of Bituminaria species for multiple purposes. Under this perspective, the future characterization of additional Bituminaria genetic resources from other Mediterranean populations will have remarkable importance.
ABSTRACT
Dodonaea viscosa (Sapindaceae) is widespread in the mountainous highlands of the southwestern part of Kingdom of Saudi Arabia, where it is a medicinally important species for the people in Saudi Arabia. Seeds of this species were collected from Mount Atharb in Al-Baha region, at an altitude of 2100 m. The aims of this study were to determine if the seeds of D. viscosa have physical dormancy (i.e. a water-impermeable seed coat) and, if so, what treatments would break dormancy, and what conditions promote germination after dormancy has been broken. The dormancy-breaking treatments included: soaking of seeds in concentrated sulfuric acid (H2SO4) for 10 min, immersion in boiling water for 10 min and exposure to 50 °C for 1 min. After seeds had been pre-treated with H2SO4, to break dormancy, they were incubated at constant temperatures from 5 to 35 °C, under 12-h photoperiods or in continuous darkness, and germination recorded. Salinity tolerance was investigated by incubating acid-scarified seeds in different concentrations of mM NaCl in the light at 25 °C. Untreated seeds had low final germination 30%. Seeds that had been acid-scarified, immersed in boiling water or exposed to 50 °C all achieved 91% subsequently when incubated at 25 °C. Thus, seeds of this species in Saudi Arabia have physical dormancy, which can be broken by all three treatments designed to increase the permeability of the testa. After pre-treatment, there was a broad optimum constant temperature for germination that ranged between 5 and 25 °C but germination was inhibited by higher temperatures (30 and 35 °C). Light had little effect on this germination response. Scarified seeds were also sensitive to salinity, with the highest germination in distilled water and complete inhibition in 400 mM NaCl. Seeds that failed to germinate in saline treatments were mostly able to germinate on transfer to distilled water, suggesting osmotic inhibition.
ABSTRACT
Seed dormancy and timing of its release is an important developmental transition determining the survival of individuals, populations, and species in variable environments. Medicago truncatula was used as a model to study physical seed dormancy at the ecological and genetics level. The effect of alternating temperatures, as one of the causes releasing physical seed dormancy, was tested in 178 M. truncatula accessions over three years. Several coefficients of dormancy release were related to environmental variables. Dormancy varied greatly (4-100%) across accessions as well as year of experiment. We observed overall higher physical dormancy release under more alternating temperatures (35/15 °C) in comparison with less alternating ones (25/15 °C). Accessions from more arid climates released dormancy under higher experimental temperature alternations more than accessions originating from less arid environments. The plasticity of physical dormancy can probably distribute the germination through the year and act as a bet-hedging strategy in arid environments. On the other hand, a slight increase in physical dormancy was observed in accessions from environments with higher among-season temperature variation. Genome-wide association analysis identified 136 candidate genes related to secondary metabolite synthesis, hormone regulation, and modification of the cell wall. The activity of these genes might mediate seed coat permeability and, ultimately, imbibition and germination.
ABSTRACT
The preservation of plant species under ex situ conditions in seed banks strongly depends on seed longevity. However, detailed knowledge on this seed ecological aspect is limited and comparative studies from central European habitats are scarce. Therefore, we investigated the seed longevity of 39 calcareous grassland species in order to assess the prospects of ex situ storage of seeds originating from a single, strongly threatened habitat. Seed longevity (p 50 ) was determined by artificially ageing the seeds under rapid ageing conditions (45 °C and 60 % eRH (equilibrium relative humidity)), testing for germination and calculating survival curves. We consulted seed and germination traits that are expected to be related to seed longevity. P 50 values strongly varied within calcareous grassland species. The p 50 values ranged between 3.4 and 282.2 days. We discovered significantly positive effects of physical dormancy and endosperm absence on p 50 . Physiological dormancy was associated to comparatively short longevity. These relationships remained significant when accounting for phylogenetic effects. Seed mass, seed shape, and seed coat thickness were not associated with longevity. We therefore recommend more frequent viability assessments of stored endospermic, non-physically and physiologically dormant seeds.