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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 (DRT 50 ), the optimum dormancy-breaking temperature to stimulate maximum germination (T 0 ), and the lethal temperature at which 50 % of the seeds were killed (LT 50 ). 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 DRT 50 16.0 °C higher, a T 0 9.7 °C higher, and LT 50 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., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

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. GA 3 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., (© 2020 German Society for Plant Sciences and The Royal Botanical Society of the Netherlands.)

Background and Aims: Different structures have been shown to act as a water gap in seeds with physical dormancy (PY), and in Fabaceae they are commonly located in the hilar region. However, the function of the pleurogram, a structure in the extra-hilar region that is common in legume seeds, remains unknown. Our aims were to review the literature for occurrence of the pleurogram in Fabaceae, determine if the pleurogram can open, and compare the functional morpho-anatomy of water gaps in seeds of 11 Senna species., Methods: Imbibition tests showed that all 11 species had PY. Structural features of the hilar and extra-hilar regions of the seeds were investigated using light and scanning electron microscopy, and dye-tracking was performed to trace the pathways of water through the seed coat., Key Results: A pleurogram has been reported for 37 legume genera. Water gaps differed among Senna species, with lens, hilum, micropyle and pleurogram taking up water after PY was broken. In Senna alata seeds, only the pleurogram acted as a water gap, whereas in S. reniformis and S. silvestris water entered the seed through both the pleurogram and the hilar region. In the pleurogram of S. alata and S. reniformis, the palisade layer moved outward, exposing the hourglass cells, whereas in S. silvestris the palisade layer was broken., Conclusions: The pleurogram acts as a water gap in some of the 11 Senna species examined, but it is non-functional in others. Opening the pleurogram occurs due to the formation of a linear slit in the palisade layer. The pleurogram is of functional significance by creating a wide opening, whereby water can reach the embryo and start germination. This is the first report of the pleurogram functioning as a water gap. Because this structure is shared by at least 37 genera, it also may be a water gap in many other legume species., (© The Author(s) 2018. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Atmospheric solids analysis probe mass spectrometry (ASAP-MS) was used for the first time for direct surface analysis of plant material. It can be readily used for surface analysis of whole and intact pea seeds and their seed coats, and for the study of the profile of fatty acids on the outer surface. Furthermore, ASAP-MS in combination with multivariate statistics allowed classification of pea genotypes with respect to physical dormancy and investigation of related biological markers. Hexacosanoic and octacosanoic acids were suggested to be important markers likely influencing water transport through the seed coat into the embryo (with the highest significance for dormant L100 genotype). ASAP-MS provided higher selectivity and better signal of fatty acids compared to (MA)LDI-MS (laser desorption ionization mass spectrometry either matrix free or matrix assisted) providing on the other hand spatial distribution information and results obtained by both methods are mutually supportive. The developed ASAP-MS method and obtained results can be widely utilized in biological, food, and agricultural research. Graphical abstract ᅟ.

Cycling of sensitivity to physical dormancy (PY) break has been documented in herbaceous species. However, it has not been reported in tree seeds, nor has the effect of seed size on sensitivity to PY-breaking been evaluated in any species. Thus, the aims of this study were to investigate how PY is broken in seeds of the tropical legume tree Senna multijuga, if seeds exhibit sensitivity cycling and if seed size affects induction into sensitivity. Dormancy and germination were evaluated in intact and scarified seeds from two collections of S. multijuga. The effects of temperature, moisture and seed size on induction of sensitivity to dormancy-breaking were assessed, and seasonal changes in germination and persistence of buried seeds were determined. Reversal of sensitivity was also investigated. Fresh seeds were insensitive to dormancy break at wet-high temperatures, and an increase in sensitivity occurred in buried seeds after they experienced low temperatures during winter (dry season). Temperatures ≤20 °C increased sensitivity, whereas temperatures ≥30 °C decreased it regardless of moisture conditions. Dormancy was broken in sensitive seeds by incubating them at 35 °C. Sensitivity could be reversed, and large seeds were more sensitive than small seeds to sensitivity induction. Seeds of S. multijuga exhibit sensitivity cycling to PY-breaking. Seeds become sensitive during winter and can germinate with the onset of the spring-summer rainy season in Brazil. Small seeds are slower to become sensitive than large ones, and this may be a mechanism by which germination is spread over time. Sensitive seeds that fail to germinate become insensitive during exposure to drought during summer. This is the first report of sensitivity cycling in a tree species., (© 2018 German Society for Plant Sciences and The Royal Botanical Society of the Netherlands.)

Seed dormancy is expected to provide ecological advantages by adjusting germination to the favorable growth period. However, many species produce nondormant seeds, particularly in wet tropical forests, a biogeographic pattern that is not well accounted for in current models. We hypothesized that the global distribution of dormant seeds derives from their adaptive value in predictably fluctuating (i.e. seasonal) environments. However, the advantage conferred by dormancy might ultimately depend on other seed attributes, particularly size. This general model was tested within a phylogenetically informed framework using a data set comprising > 216 000 world-wide observations of Fabaceae, spanning three orders of magnitude in seed size and including both dormant and nondormant seeds. Our results confirmed our hypothesis: nondormant seeds can only evolve in climates with long growing seasons and/or in lineages that produce larger seeds. Conversely, dormancy should be evolutionarily stable in temperate lineages with small seeds. When the favorable season is fleeting, seed dormancy is the only adaptive strategy. Based on these results, we predict that, within a given lineage, taxa producing larger, nondormant seeds will necessarily predominate in aseasonal environments, while plants bearing small, dormant seeds will be dominant under short growing seasons., (© 2017 The Authors. New Phytologist © 2017 New Phytologist Trust.)

Premise of the Study: Species differ in their temperature germination niche. Populations of a species may similarly differ across the distribution range of the species. Anticipating the impacts of climate variability and change requires understanding the differential sensitivity to germination temperature among and within species. Here we studied the germination responses of four hard-seeded Cistaceae seeders to a range of current and future temperatures., Methods: Seeds were collected at sites across the Iberian Peninsula and exposed or not exposed to a heat shock to break dormancy, then set to germinate under four temperature regimes. Temperatures were varied daily and seasonally, simulating the temperature range across the gradient, plus an increased temperature simulating future climate. Time to germination onset and cumulative germination at the end of each season were analyzed for the effects of temperature treatments, seasons, and local climate (temperature of the germination period, T gp ) at each site., Key Results: T gp was a significant covariate of germination in all species but Cistus populifolius. Temperature treatments significantly affected Cistus ladanifer, C. salviifolius, and Halimium ocymoides. Germination occurred in simulated autumn conditions, with little germination occurring at later seasons, except in unheated seeds of H. ocymoides. Exposure to a heat shock changed the sensitivity to temperature treatments and the relationships with T gp ., Conclusions: Germination responses to temperature differ not only among species but also within species across their latitudinal range. The responses were idiosyncratic and related to the local climate of the population. This germination variability complicates generalizing the impacts of climate variability and climate change., (© 2017 Botanical Society of America.)

Premise of the Study: Temperature and water potential for germination based on the thermal and hydrotime models have been successfully applied in predicting germination requirements of physiologically dormant seeds as well as nondormant seeds. However, comparative studies of the germination requirements of physically dormant seeds from different ecosystems have not been done., Methods: Germination of scarified seeds of four legume species collected from the Qing-Tibetan Plateau and of four collected in the Alax Desert in China was compared over a range of temperatures and water potentials based on thermal time and hydrotime models., Key Results: Seeds of species from the Qing-Tibetan Plateau had a lower base temperature (T b) and optimal temperature (T o) for germination than those from the Alax Desert. Seeds of the four species from the Qing-Tibetan Plateau germinated to high percentages at 5°C, whereas none of the four desert species did so. Seeds of species from the Alax Desert germinated to a high percentage at 35°C or 40°C, while no seeds of species from the Qing-Tibetan Plateau germinated at 35°C or 40°C. The base median water potential [Ψ b(50)] differed among species but not between the two habitats., Conclusions: The thermal time and hydrotime models accurately predicted the germination time course of scarified seeds of most of the eight species in response to temperature and water potential; thus, they can be useful tools in comparative studies on germination of seeds with physical dormancy. Habitat temperatures but not rainfall is closely related to germination requirements of these species., (© 2015 Botanical Society of America, Inc.)

Ecological restoration of disturbed areas requires substantial knowledge of the germination of native plants and the creation of novel methods to increase seedling establishment in the field. We studied the effects of soil matrix priming on the germination of Dodonaea viscosa seeds, which exhibit physical dormancy. To this end, we buried both pre-scarified (in H2SO4, 3 min) and non-pre-scarified seeds in the Parque Ecológico de la Ciudad de México. After seeds were unearthed, they were post-scarified for 0, 2, 6 and 10 min and their germination percentages compared to the germination of a control batch of laboratory-stored seeds. For both control and unearthed seeds, the protein pattern was determined in the enriched storage protein fraction in SDS-PAGE gels stained with Coomassie blue. Percentage germination increased as the scarification time increased. Pre-scarification significantly increased percentage germination of post-scarified seeds in relation to the control and non-pre-scarified seeds. In seeds unearthed from the forest site, the buried pre-scarified seeds had relatively high percentage germination, even in the absence of post-scarification treatment. A 48-kDa protein was not found in unearthed, pre-scarified seeds nor in the control germinated seeds, indicating that mobilisation of this protein occurred during soil priming. Burying seeds for a short period, including the beginning of the rainy season, promoted natural priming, which increased protein mobilisation. Functionally, priming effects were reflected in high percentage seedling survival in both the shade house and the field. Seed burial also reduced the requirement for acidic post-scarification., (© 2013 German Botanical Society and The Royal Botanical Society of the Netherlands.)

Background and Aims: Physical dormancy (PY) occurs in seeds or fruits of 18 angiosperm families and is caused by a water-impermeable palisade cell layer(s) in seed or fruit coats. Prior to germination, the seed or fruit coat of species with PY must become permeable in order to imbibe water. Breaking of PY involves formation of a small opening(s) (water gap) in a morpho-anatomically specialized area in seeds or fruits known as the water-gap complex. Twelve different water-gap regions in seven families have previously been characterized. However, the water-gap regions had not been characterized in Cucurbitaceae; clade Cladrastis of Fabaceae; subfamilies Bombacoideae, Brownlowioideae and Bythnerioideae of Malvaceae; Nelumbonaceae; subfamily Sapindoideae of Sapindaceae; Rhamnaceae; or Surianaceae. The primary aims of this study were to identify and describe the water gaps of these taxa and to classify all the known water-gap regions based on their morpho-anatomical features., Methods: Physical dormancy in 15 species was broken by exposing seeds or fruits to wet or dry heat under laboratory conditions. Water-gap regions of fruits and seeds were identified and characterized by use of microtome sectioning, light microscopy, scanning electron microscopy, dye tracking and blocking experiments., Key Results: Ten new water-gap regions were identified in seven different families, and two previously hypothesized regions were confirmed. Water-gap complexes consist of (1) an opening that forms after PY is broken; (2) a specialized structure that occludes the gap; and (3) associated specialized tissues. In some species, more than one opening is involved in the initial imbibition of water., Conclusions: Based on morpho-anatomical features, three basic water-gap complexes (Types-I, -II and -III) were identified in species with PY in 16 families. Depending on the number of openings involved in initial imbibition, the water-gap complexes were sub-divided into simple and compound. The proposed classification system enables understanding of the relationships between the water-gap complexes of taxonomically unrelated species with PY.

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 FROM AUTHOR]

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 FROM AUTHOR]

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 FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

We aimed to investigate the reproduction-related traits of Vicia biennis L., an endangered and poorly known wetland species in its western marginal populations (in Hungary), and discuss the conservational and ecological implications. We measured the mass, viability, and physical dormancy of half-year-old seeds in five in-situ collected seed lots, while potential seed longevity (i.e., seed bank type) was estimated from repeatedly germinating subsamples from four ex-situ collected seed lots for 3–8 years. Plant survival, flowering, and seed production were studied in different light-, irrigation-, and competition conditions in a botanical garden experiment. We found that 1) half-year-old seeds have a high germination capacity (78–100%), 2) and high level of physical dormancy (72–100%) in all examined Hungarian populations, and 3) the seeds can preserve their germination capacity for more than five years, although their viability sharply decreases, probably falling below 10% within ten years, when they are stored at room temperature. The results of the botanical garden experiment suggested that 1) the species is annual, not biennial; 2) it shows strong sensitivity to precipitation and low competitiveness for water; and 3) it can produce hundreds of seeds even in suboptimal (dry or shady) conditions. Although the species was found to be well-adapted to a temporally heterogeneous environment, its future vulnerability can increase depending on the duration of dry seasons. Further investigation of genetic diversity and soil seed bank is needed to estimate the actual vulnerability of the species while strengthening the populations through seed sowing, and additional vegetation control in the habitats is suggested. [ABSTRACT FROM AUTHOR]

Copyright of Revista de Ciencias Agricolas is the property of University of Narino, Faculty of Agricultural Sciences and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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 FROM AUTHOR]

When plant biomass is anaerobically digested, seeds may survive the energy production process and contaminate the digestate. Hard-seeded (HS), i.e., physically dormant, species were found to be difficult to inactivate. Here, we aimed to verify this finding from lab-scale experimental reactors (ERs) in a full-scale commercial reactor (CR). In addition, we tested seed survival in a pH-buffered water bath (WB). Seeds were exposed to CR, ER and WB treatments at 42 °C for a maximum of 36 days. The viability of seeds was checked by measuring germination and response to tetrazolium staining and modeled as a function of exposure time using a dose–response approach. CR killed seeds more effectively than ER and WB treatments. The non-HS reference species, Chenopodium album, was completely inactivated by all treatments. Responses of the HS species ranged from complete inactivation to complete insensitivity. The most resistant was Malva sylvestris. The least resistant species were inactivated mainly by temperature, while additional mortality factors were effective in the more resistant species. We concluded that mesophilic AD in CRs can reduce the risk of seed contamination in the digestate for non-HS but not for HS species. Moreover, WB treatments seem suitable to estimate the minimum mortality of non-HS species in CR. [ABSTRACT FROM AUTHOR]

This article deals with the breaking down of seed dormancy in black locust (Robinia pseudoacacia L.) seeds. These seeds have a hard testa that is impermeable to water and air. In this investigation, seeds of black locust were treated with non-thermal plasma (NTP) for 0, 5, 10, and 20 min. The testa of the treated seeds had an eroded surface (SEM analysis) and showed an increased oxygen content (EDS) and increased hydrophilicity (contact-angle measurement). The exposed seeds also had a higher water absorption (seed water uptake) than the untreated ones. In seeds treated for 20 min, a significant difference (p < 0.05) was recorded in seed germination (eight times greater than the control set) and in other parameters of initial seedling development, such as the fresh weight of both seedling root and shoot and all three indexes of seedling vitality. The detected changes in the seed surface and changes in germination proved that NTP can partly break dormancy in black-locust seeds. [ABSTRACT FROM AUTHOR]

Seeds have been reported to have a combination of physical and physiological dormancy. However, this study revealed that H. dulcis seeds only have physical dormancy. The water absorption of the seeds after different periods of sulfuric acid scarification was measured, and the water gap through which water was absorbed after scarification treatment was specified. Cold stratification treatment and gibberellic acid treatment were performed after sulfuric acid scarification to determine whether H. dulcis seeds had physiological dormancy. H. dulcis seeds could absorb water completely when scarified for more than 60 min, and water was absorbed only through the hilar fissure near the micropyle, indicating that H. dulcis seeds have physical dormancy. However, there was no synergistic effect on the final seed germination percentage after the cold stratification or gibberellic acid treatments, and germination was delayed under cold temperature conditions. Thus, it was concluded that H. dulcis seeds have no physiological dormancy but only physical dormancy. This study not only clarifies the kind of dormancy in H. dulcis seeds but also provides a method to expedite seed germination without a long cold stratification treatment period of 2 or 3 months. [ABSTRACT FROM AUTHOR]

Melia dubia produces indehiscent drupes which are sown for seed germination. Studies revealed that the germination is highly protracted, sporadic and the final germination is very low (< 10 %). The exocarp and mesocarp of M. dubia fruits are impermeable to water (physical dormancy), while the endocarp causes mechanical resistance to germinating embryo (mechanical dormancy). The kernels extracted from the drupes responded well to GA3 (250 mg L-1) treatment, when applied through seed soaking (24 hours) + humid priming (2 days), compared to seed soaking (24 hours) in GA3 (250 mg L-1) alone. Excavation of ungerminated seeds from nursery beds revealed that the remaining kernels were either fresh ungerminated (FUG) or decayed. This might be due to presence of a large proportion of low vigour seeds within a seed lot. Exposing the kernels to dry heat (40 oC for 4 hours) followed by seed soaking in GA3 (250 mg L-1) for 24 hours + humid priming with GA3 (250 mg L-1) for two days, and sowing in a polyhouse with high relative humidity (80 ± 5 % RH) resulted in highest improvement in synchrony of germination, with corresponding decrease in FUG and seed decay. The protocol enabled to increase the seed germination of M. dubia to 42.3% and reduced the period of seed germination to 21 days. The poor germination behavior of M. dubia is attributed to multiple factors such as physical dormancy imposed by exocarp and mesocarp, mechanical dormancy caused by endocarp and higher proportion of low vigour seeds in a seed lot. [ABSTRACT FROM AUTHOR]

Copyright of Bulletin of Botanical Research is the property of Bulletin of Botanical Research Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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. [ABSTRACT FROM AUTHOR]

Alstroemeria pelegrina (A. pelegrina), a Chilean endemic, is considered vulnerable as its natural habitat is currently threatened. The decline in the reproductive capacity of the species due to anthropogenic impacts and climate change has made it imperative to address the problem by developing large-scale propagation methods. The objective of this study was to establish protocols for breaking the dormancy and in vitro germination of A. pelegrina seeds to speed up the germination and seedling production processes. The research began with morphological observations of the reproductive process, followed by in vitro sowing. The results showed that the seeds reached full maturity in 51 days, and physiological maturity in 41 days, at which point the seeds could be harvested for in vitro germination. The mechanical scarification pretreatment improves the in vitro germination rate to 96% and the germination time to 7 days, showing that the species is characterized by physical seed dormancy. On the other hand, if the seed coat incisions are deeper than 0.5 mm, 30% of the potential plants are lost due to embryo damage. The study provides scientific evidence for the feasibility of large-scale in vitro propagation of the species and establishes an efficient method of seedling production. [ABSTRACT FROM AUTHOR]

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The International Seed Testing Association (ISTA) recommends two methods for seed moisture content determination: high constant temperature drying, carried out at 130 °C for 1, 2, 3 or 4 hours, and low constant temperature drying, carried out at 103 °C for 17 hours. However, in species with impermeable seed coats, i.e. physical dormancy (PY), a range of temperatures and duration was used to determine the moisture content. This work found that seeds of Delonix regia (Bojer ex Hook.) Raf., Sesbania grandiflora (L.) Poir. and Adenanthera pavinona L, which all have PY, can reach constant weight between two and five hours when dried at 103 °C for 17 hours. Such high temperatures could either open the water gaps, e.g. the lens in Fabaceae which are present in the seed coat, or crack open the seed coat, as observed during episodes of fire and dry-heat treatments. Therefore, it is suggested that the low constant temperature drying method can be used for species with impermeable seed coats. [ABSTRACT FROM AUTHOR]

Summary: 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. [ABSTRACT FROM AUTHOR]

Knowledge of the hard seed content of annual legumes, and its pattern of breakdown, is critical to the understanding of their ecology and management within farming and natural ecosystems. For logistical reasons, seed that has been stored for varying lengths of time is often used for pasture establishment and agronomy experiments. However, the implications of storage on hard seed physiology are unknown. The aim of this study was to explore the impact of seed storage on its subsequent pattern of hard seed breakdown when exposed to field conditions. Experiments examined seed from six different annual legume cultivars that had been either produced the prior year or stored under ambient conditions for 11–22 years. Comparisons were then made between the two seed sources on hard seed breakdown patterns in situ. Although initial hard seed levels were mostly unaffected by storage (seed of five cultivars remained over 93% hard after more than 11 years of storage), the patterns of release from dormancy during exposure to hard seed breakdown conditions of stored seed differed greatly (p <.05) from freshly produced seed. Hard seed in the stored seed of most cultivars was reduced from >90% to <10% within 68 days over autumn, with shallow burial, whereas fresh seed remained >90% hard during the same period. Given this large and consistent impact, it is recommended that studies of the patterns of hard seed breakdown in legumes compare seed stored under consistent and well‐defined conditions. [ABSTRACT FROM AUTHOR]

Propagating snowberry (Symphoricarpos albus (L.) S.F. Blake [Caprifoliaceae]) from seed is difficult because of long stratification requirements and low germination rates. We investigated whether snowberry seeds have physical dormancy and whether imbibing seeds prior to stratification decreased the length of time required to break dormancy or increased germination rates. We found no evidence that snowberry seeds have physical dormancy. Seeds reached full imbibition after 12 h of soaking, at which time there was no significant difference in moisture content between intact and scarified seeds. No snowberry seeds germinated in the stratification experiment although viability remained high (> 90%), suggesting that dormancy-breaking requirements were not met in this study. Future germination studies for this species should examine seed collected from multiple populations and should assess the effects of fluctuating temperature and media type during stratification as well as germination temperatures. [ABSTRACT FROM AUTHOR]

???Ceanothus velutinus Douglas ex Hook. (snowbrush ceanothus [Rhamnaceae]) and Cercocarpus montanus Raf. (alderleaf mountain mahogany [Rosaceae]) are native species with urban landscape value and potential to create unique aesthetics as well as to conserve water. Propagation protocols for these native species are not well established. Because of dormancy, seed propagation requires scarification and (or) stratification. We designed a study to further define protocols necessary to consistently produce high rates of germination for these 2 species. Ceanothus velutinus seeds were scarified in hot water at 50, 70, or 90 °C (122, 158, or 194 °F) and soaked with gibberellic acid (GA3) at 0, 50, 250, or 500 mg/l (0, 50, 250, or 500 ppm) for 24 h before stratification for 1, 2, or 3 mo. Seeds of C. velutinus stratified for 2 mo after being scarified at 90 °C and treated with 500 mg/l (500 ppm) GA3 had the greatest germination percentage (74.2 ± 2.0%). Percent germination was the lowest when seeds were scarified at 50 °C (122 °F) and treated without GA3 but with 2 mo stratification. Cercocarpus montanus seeds were treated with GA3 at 0, 50, 250, or 500 mg/l (0, 50, 250, or 500 ppm) and stratified for 1, 2, or 3 mo. Seed germination of C. montanus increased as stratification time increased. Seeds dipped in 50 mg/l (50 ppm) GA3 and stratified for 2 mo had the greatest germination percentage (64.2 ± 3.6%). [ABSTRACT FROM AUTHOR]

The effects of cold atmospheric plasma (CAP) of dielectric barrier discharges on the wettability, imbibition and germination of Leucaena leucocephala were investigated. It was established that CAP treatment markedly hydrophilized the seed coat, especially at longer treatment times. From the profile of the imbibition curve and visual observation, it was possible to verify that there are two resistance barriers to water penetration: integument surface and region of the macrosclereid cell wall (light line). Although the plasma interacts only in the integument, increasing the density of hydrophilic sites increases the capacity of water absorption, producing enough driving force to overcome the second resistance barrier. The existence of these two barriers changes the three-phase pattern generally observed during seed germination. Despite an increase in imbibition, the plasma treatment conditions used in this work, were not enough to overcome completely the dormancy barrier. [ABSTRACT FROM AUTHOR]

Garcinia gardneriana (Planch. & Triana) Zappi is a native species widely distributed in Brazil. It has ornamental features, edible fruits, and its leaves have medicinal properties; however, its potential has not been explored. The aim of this study was to evaluate seed physiological performance due to dormancy, desiccation and storage tolerance. Only decoated seeds germinated. Seeds had an initial water content of 1.07 g H2O.g-1 dw and final germination of 95%. Both desiccation to 0.67 g H2O.g-1 dw and storage at 25 ºC for ninety days resulted in decreased germination, 43 and 41%, respectively. Desiccation below 0.25 g H2O.g-1 dw and storage for ninety days at 5 ºC were lethal. A rapid decrease in enzymic protection by superoxide dismutase and ascorbate peroxidase was correlated to desiccation sensitivity. Total polyamines content was higher in fresh seeds and markedly decreased with desiccation. The decrease in enzyme activity and polyamines content seems to be associated with seed viability loss. In sum, G. gardneriana seeds have a low tolerance to desiccation and are sensitive to chilling. Therefore, the seeds can be categorized as recalcitrant and dormant, a rare combination in terms of seed biology. [ABSTRACT FROM AUTHOR]

Background and aims: The occurrence of seeds with physical dormancy is an obstacle for the use and management of many plant species. Here, we studied the presence of physical dormancy in mericarps (seed-dispersal units) and seeds, the morphoanatomical structures responsible for physical dormancy, and the effects of possible methods for breaking dormancy in seeds of Malvastrum coromandelianum (Malvaceae). M&M: Imbibition essays were used to confirm the presence of physical dormancy in mericarps and seeds, and the morpho-anatomical seed structure was described by using a scanning electron microscopy. The effects of mechanical, chemical and thermal scarifications on seed germination and seed structure were also evaluated. Results: Mericarps and scarified seeds increased > 160% of their initial weight, whereas intact seeds increased < 40% of their initial weight. The presence of a palisade cell layer in seed coat and a water-gaps complex in the chalazal region were observed. Higher germination percentages and lower t50 were registered after mechanical scarification, followed by chemical and thermal scarifications (dry heat). Chemical and thermal scarifications caused the chalazal cap elimination and the contiguous cracks to form around the chalazal region; whereas the formation of a chalazal blister and its elimination were only observed after chemical scarification. Conclusions: Seeds of M. coromandelianum have physical dormancy. Water enters the seeds through a water-gap complex (Type III compound) located in the chalazal region. Mechanical, chemical and thermal scarifications are effective methods for breaking physical dormancy and increase germination. [ABSTRACT FROM AUTHOR]

The seeds of most Australian acacias have pronounced physical dormancy (PY). While fire and hot water (HW) treatments cause the lens to 'pop' almost instantaneously, for many Acacia species the increase in germination percentage can be gradual. If PY is broken instantly by HW treatment, why is germination often an extended process? Control and HW treatments were performed on seeds of 48 species of Acacia. Seeds were placed on a moist substrate and imbibition was assessed by frequently weighing individual seeds. In the two soft-seeded species all control seeds were fully imbibed within 6–24 h, while in hard-seeded species very few control seeds imbibed over several weeks. In 10 species over 50% of the HW-treated seeds imbibed within 30 h, but mostly the percentage of imbibed seeds gradually increased over several weeks. Some seeds in a replicate would imbibe early, while others would remain unimbibed for many days or weeks then, remarkably, become fully imbibed in less than 24 h. While HW treatment broke PY almost instantaneously, it appeared that in many Acacia species some other part of the testa slowed water from reaching the embryo. This process of having staggered imbibition may be a way of ensuring not all seeds in a population germinate after small rain events. Thus it appears the lens acts as a 'fire gauge' while some other part of the seed coat acts as a 'rain gauge'. [ABSTRACT FROM AUTHOR]

Bixa orellana L. (annatto) is economically and ecologically important specie. However, the seeds of this species have some mechanisms of dormancy that prevent their germination even on favorable conditions. The aim of this work was to evaluate methodologies to promote the dormancy overcoming of annatto seeds, including the use of gibberellic acid. It was used seeds of two annatto accesses, which were submitted to the germination test and germination speed index after submission to mechanical scarification, incision, sulfuric acid for 3, 5, 10, 15 and 20 minutes and hot water for 30, 60, 90 and 120 seconds. In addition, whole or incised seeds were soaked in gibberellic acid at concentrations of 0, 400, 800 and 1200 mg L-1. The experimental design was completely randomized, with 11 treatments for each access in the evaluation of dormancy overcoming methods and 4 treatments for each access in GA3 application, with and without spike. In annatto seeds, it is not evident the dormancy seed overcoming by the use of incision, mechanical scarification, sulfuric acid, hot water and gibberellic acid; however, mechanical scarification, sulfuric acid and gibberellic acid can increase the speed of germination. The results of each method to overcoming seed dormancy depend of many factors, including the origin of access. [ABSTRACT FROM AUTHOR]

Mediterranean shrublands are water-limited and fire-prone ecosystems. Post-fire seed regeneration occurs under a rainfall regime that is highly variable, with frequent drought periods. It has been shown that smoke can alter germination performance in numerous species, but little is known about its role during germination under water stress. Here, we studied the germination response to water stress and smoke of nine abundant Mediterranean shrubs. Seeds of six species with hard coats (three Cistaceae and three Fabaceae) and three with soft coats (Lamiaceae), exposed or not to smoke, were set to germinate under four levels of water availability (0; − 0.15; − 0.30; − 0.45 MPa). Seeds of hard-coat species were previously mechanically scarified. Onset of germination, final germination and viability were recorded. Water stress reduced final germination in five of the six hard-coat species and in one soft-coat species, delayed the onset of germination in all species and decreased viability in several hard-coat species. Smoke increased final germination (10%) in one soft-coat species, not affecting the rest. Additionally, smoke reduced the onset of germination in one hard- and one soft-coat species. However, there was no interaction between smoke and water stress. Hydrotime modeling of the germination responses confirmed the above findings. In conclusion, the species studied differed in germination sensitivity to water stress, with hard-coat species being more sensitive than soft-coat species. Exposing the seeds to smoke generally did not change this sensitivity. [ABSTRACT FROM AUTHOR]

Lupinus diffusus Nutt. (Fabaceae) is a floriferous, nitrogen-fixing forb native to dry, infertile sites of the southeastern US with uses in restoration, as a low-input ornamental landscape plant, and as a cut flower. Seed propagation of this species requires pretreatments because of physical dormancy. Practical information regarding the alleviation of physical dormancy for this plant is lacking. A maximum of 41% seedling emergence of viable seed after exposure to 18M sulfuric acid for 60 min has been demonstrated for L. diffusus. We conducted preliminary laboratory germination experiments testing scarification techniques and found that both abrasion in an electric seed scarifier and hand-nicking seed testas were effective in alleviating physical dormancy. We then conducted a 33-d greenhouse seedling emergence experiment comparing scarification in an electric seed scarifier (0, 15, 30, 45, and 60 s) to hand-nicking for 2 Florida L. diffusus seedlots. We found that certain treatments in the electric scarifier (30, 45, and 60 s) were as effective as hand-nicking. In this study, we improved L. diffusus seedling emergence to 85% as compared to existing scarification techniques. Mechanical scarification for 45 s in an electric seed scarifier was as effective (76% emergence) as the prohibitively labor-intensive pretreatment practice of hand-nicking individual seeds (82% emergence). [ABSTRACT FROM AUTHOR]

Desmanthus virgatus (L.) Willd. has significant fodder potential, but its seeds have high and persistent levels of physical dormancy which interfere with its field establishment. The purpose of this study was to analyse the variability of physical dormancy in three populations of seeds from humid and arid regions of Argentina, grown and collected in different years and locations. The hardseededness and the percentage of seeds with intact lenses after a softening treatment and the seed coat thicknesses were compared. The variability observed in the obtained percentages of hardseededness, intact lenses and seed coat thicknesses was related to the origin and the environment in which these seeds had developed. Although further work is needed, arid environments seem to favour the development of thicker seminal layers, being an important factor that determines the impermeable nature of the seeds in this species. This information is required for future genetic improvement programs and for understanding the evolutionary process of the populations of this species in different environments. [ABSTRACT FROM AUTHOR]

The physical dormancy of seeds has been poorly studied in species from tropical forests, such as the Atlantic Forest. This study aimed to examine the effect of moderate alternating temperatures on breaking the physical dormancy of seeds, the morphoanatomy and histochemistry of seed coats, and to locate the structure/ region responsible for water entrance into the seed, after breaking the physical dormancy of seeds of two woody Fabaceae (subfamily Faboideae) species that occur in the Brazilian Atlantic Forest: Sophora tomentosa and Erythrina speciosa. To assess temperature effect, seeds were incubated in several temperature values that occur in the Atlantic Forest. For morphological and histochemical studies, sections of fixed seeds were subjected to different reagents, and were observed using light or epifluorescence microscopy, to analyze the anatomy and histochemistry of the seed coat. Treated and non-treated seeds were also analyzed using a scanning electron microscope (SEM) to observe the morphology of the seed coat. To localize the specific site of water entrance, the seeds were blocked with glue in different regions and also immersed in ink. In the present work a maximum temperature fluctuation of 15℃ was applied during a period of 20 days and these conditions did not increase the germination of S. tomentosa or E. speciosa. These results may indicate that these seeds require larger fluctuation of temperature than the applied or/and longer period of exposition to the temperature fluctuation. Blocking experiments water inlet combined with SEM analysis of the structures of seed coat for both species showed that besides the lens, the hilum and micropyle are involved in water absorption in seeds scarified with hot water. In seeds of E. speciosa the immersion of scarified seeds into an aniline aqueous solution showed that the solution first entered the seed through the hilum. Both species showed seed morphological and anatomical features for seed coats of the subfamily Faboideae. Lignin and callose were found around all palisade layers and the water impermeability and ecological role of these substances are discussed in the work. [ABSTRACT FROM AUTHOR]

Although seed dormancy of temperate legumes is well understood, less is known about it in species that grow in subalpine/alpine areas. This study investigated dormancy and germination of four Vicia species from the Tibetan Plateau. Fresh seeds of V. sativa were permeable to water, whereas those of V. angustifolia, V. amoena and V. unijuga had physical dormancy (PY). One year of dry storage increased the proportion of impermeable seeds in V. angustifolia, but showed no effect on seed coat permeability in V. amoena or V. unijuga. Seeds of all four species also had non-deep physiological dormancy (PD), which was especially apparent in the two annuals at a high germination temperature (20°C). After 1 year of storage, PD had been lost. The hydrotime model showed that fresh seeds obtained a significantly higher median water potential [Ψb(50)] than stored seeds, implying that PD prevents germination in winter for seeds dispersed without PY when water availability is limited. After 6 months on the soil surface in the field, a high proportion of permeable seeds remained ungerminated, further suggesting that PD plays a key role in preventing germination after dispersal. Addition of fluridone, an inhibitor of abscisic acid (ABA) biosynthesis, evened-out the differences in germination between fresh and stored seeds, which points to the key role of ABA biosynthesis in maintaining dormancy. Further, fresh seeds were more sensitive to exogenous ABA than stored seeds, indicating that storage decreased embryo sensitivity to ABA. On the other hand, the gibberellic acid GA3 increased germination rate, which implies that embryo sensitivity to GA is also involved in seed dormancy regulation. This study showed that PY, PD or their combination (PY+PD) plays a key role in timing germination after dispersal, and that different intensities of dormancy occur among these four Vicia species from the Tibetan Plateau. [ABSTRACT FROM AUTHOR]

Abstract: Although Astragalus is the largest genus of seed plants, it contains only a relatively few annual species, about which little is known with regard to seed dormancy and germination. Thus, seed dormancy-break and germination were investigated in the cold-desert annual Astragalus arpilobus Kar. et Kir. Most of the seeds had a water-impermeable seed coat that became permeable after mechanical or acid scarification, i.e. physical dormancy. Both wet heat and alternate wet heat and cold (ice water) made only a small portion of the seeds permeable, and neither exposure to high nor to low temperatures was effective in breaking dormancy. Scarified seeds germinated at temperatures ranging from 5/2 to 30/15°C, with 20/10°C and 25/15°C being optimal. Non-dormant seeds germinated to high percentages in light and in darkness across the range of temperatures. Germination percentages did not increase with duration of dry storage at room temperature. Scarified seeds germinated to nearly 100% at water potentials between 0 and −0.30MPa but to 0% at −0.77MPa. Seedling emergence was higher for seeds buried at soil depths of 1 and 2cm than at 0 or >2cm. Forty-three percent of the scarified seeds sown in July in an experimental garden under natural conditions germinated in autumn, and an additional 5% germinated in spring. In contrast, no non-scarified seeds germinated in autumn, and only 5.3% of them germinated in spring. Most of the non-scarified seeds that did not germinate became part of the persistent seed bank. Our results indicate that the high intensity of hard-seed dormancy in the annual A. arpilobus is similar to that reported for the perennial species of Astragalus. [Copyright &y& Elsevier]

Physical dormancy refers to seeds that are water impermeable. Within the Fabaceae, the structure associated with the breaking of dormancy is usually the lens. This study verified the role of the lens in physical dormancy of seeds of Schizolobium parahyba, a gap species of Fabaceae from the Atlantic Forest of Brazil. The lens in S. parahyba seeds appeared as a subtle depression near the hilum and opposite the micropyle. After treatment of the seeds with hot water, the lens detached from the coat. Blocking water from contacting the lens inhibited water absorption in hot-water-treated seeds. High constant (30°C) and alternating (20/30°C) temperatures promoted the breaking of physical dormancy and germination in non-scarified seeds. Maximum percentage of germination occurred earlier for seeds incubated at 20/30°C than for those incubated at 30°C. Seeds with a blocked lens did not germinate at alternating or high temperatures. This study suggests that alternating temperatures are probably the cause of physical dormancy break of seeds of S. parahyba in gaps in the forest. [ABSTRACT FROM AUTHOR]

Westerman PR, Hildebrandt F & Gerowitt B (2012). Weed seed survival following ensiling and mesophilic anaerobic digestion in batch reactors. Weed Research 52, 286-295. Summary Digestate, the semi-solid leftover after anaerobic digestion in biogas reactors, is frequently used as a crop fertiliser. The ability of seeds from various weed species to survive anaerobic digestion was tested, because surviving seeds could be spread via the digestate. Experiments were conducted in experimental mesophilic batch reactors, either with or without ensiling as a pre-treatment to simulate biomass storage in silage prior to use in reactors. The emphasis was on weed species whose seeds have a water-impermeable layer, because these may be more thermoresistant. Species with hard seeds were more likely to survive ensiling (up to 98%) and mesophilic anaerobic digestion (up to 58%) compared with species whose seeds lack a water-impermeable layer (≤1%). There was considerable variation in survival probability between and within species, and between silages and reactors. For hard-seeded species, survival depended on the proportion of hard seeds and on the ability to remain hard-seeded during treatment. Freshly harvested seeds lost their water impermeability and survived poorly. The survival of tomato seeds, an indicator species used in the sanitation of composts, was comparable with that of the best surviving species without physical dormancy, but was not comparable with that of hard-seeded species. Tomato could therefore only represent species that are not hard-seeded. [ABSTRACT FROM AUTHOR]

Background and Aims The ‘hinged valve gap’ has been previously identified as the initial site of water entry (i.e. water gap) in physically dormant (PY) seeds of Geranium carolinianum (Geraniaceae). However, neither the ontogeny of the hinged valve gap nor acquisition of PY by seeds of Geraniaceae has been studied previously. The aims of the present study were to investigate the physiological events related to acquisition of PY and the ontogeny of the hinged valve gap and seed coat of G. carolinianum. Methods Seeds of G. carolinianum were studied from the ovule stage until dispersal. The developmental stages of acquisition of germinability, physiological maturity and PY were determined by seed measurement, germination and imbibition experiments using intact seeds and isolated embryos of both fresh and slow-dried seeds. Ontogeny of the seed coat and water gap was studied using light microscopy. Key Results Developing seeds achieved germinability, physiological maturity and PY on days 9, 14 and 20 after pollination (DAP), respectively. The critical moisture content of seeds on acquisition of PY was 11 %. Slow-drying caused the stage of acquisition of PY to shift from 20 to 13 DAP. Greater extent of cell division and differentiation at the micropyle, water gap and chalaza than at the rest of the seed coat resulted in particular anatomical features. Palisade and subpalisade cells of varying forms developed in these sites. A clear demarcation between the water gap and micropyle is not evident due to their close proximity. Conclusions Acquisition of PY in seeds of G. carolinianum occurs after physiological maturity and is triggered by maturation drying. The micropyle and water gap cannot be considered as two separate entities, and thus it is more appropriate to consider them together as a ‘micropyle–water-gap complex’. [ABSTRACT FROM AUTHOR]

The morphometric features, germination requirements (under controlled conditions of light and temperature, and after different pre-sowing treatments) and cryopreservation tolerance of Tuberaria macrosepala (Cistaceae) seeds were studied. Constant (5, 10, 15, 20, 25, 30°C) and alternating temperature regimes (25/15°C, 30/20°C) with 16 h/8 h light/dark photoperiod and constant darkness conditions were used. Mechanical scarification, dry heat, boiling water, soaking in distilled water and soaking in gibberellic acid solution were used as pre-sowing treatments to enhance germination. Tuberaria macrosepala seeds were separated into three groups (light brown, medium brown and dark brown) according to the color of their seed coat. These three types of seeds also differed in size, weight and germinability. Dark brown seeds were found to be inferior to both medium and light brown seeds in size, final germination percentage and germination rate. No significant differences were found in seed weight between the three seed color types. Most seeds of the studied population were light brown. The final germination percentages of this type of seed ranged from 12 to 69%, depending on the temperature and light conditions used. Mechanical scarification significantly improved the final germination percentages of the three seed color types (86–96%). Therefore, seed coat impermeability to water (physical dormancy) appears to be the main cause of seed dormancy present in this species and seed color may be an indicator of hardseededness. Cryopreservation did not significantly decrease the final germination percentages. Therefore, cryopreservation could provide a method for long-term storage of germplasm of this species. [ABSTRACT FROM AUTHOR]

Although many studies have been conducted on seeds with a water-impermeable seed or fruit coat (physical dormancy), the primary site of water entry into these seeds after dormancy-breaking treatments is still controversial. Thus, the role of lens, hilum, micropyle and extrahilar regions in water uptake of seeds treated to break physical dormancy was examined in Vigna oblongifolia and Sesbania sesban (Fabaceae) following pretreatment with sulphuric acid and hot water. Morphology of seed surfaces in treated versus non-treated seeds of both species was examined with scanning electron microscopy. Most seeds of V. oblongifolia first cracked in the hilum when pretreated with sulphuric acid, but they cracked in both the hilum and extrahilar regions when pretreated with hot water. However, in S. sesban seeds, a crack formed only in the lens following either acid scarification or hot-water treatments, and the seeds imbibed water only through the lens. These results indicate that the primary site of water entry into seeds following physical dormancy break can vary with species and treatments. Slow, early imbibition via the hilum, and subsequent rapid imbibition via the lens, may not be detected unless seeds are monitored for several days. Time allowed for imbibition studies may, at least in part, explain various interpretations about the role of the lens in physical dormancy reported in the literature. [ABSTRACT FROM AUTHOR]