Solute leakage is used as an indicator of membrane damage during desiccation of recalcitrant seeds. We re-examined this phenomenon and its utility by comparing recalcitrant Spartina alterniflora and orthodox Spartina pectinata seeds, as well as drying isolated embryos or embryos isolated after whole-seed drying. During drying, intact seed leakage (electrical conductivity and absorbance at 280 nm) was independent of seed moisture content, dormant/non-dormant state or desiccation tolerance. Embryos from both Spartina species, isolated after drying within the intact seed, exhibited increased leakage, especially below 40% (dry weight basis, DWB) seed moisture, the critical water content for viability loss in Spartina alterniflora. When isolated embryos were dried, the pattern and extent of increased solute leakage were similar in both Spartina species, even though S. pectinata embryos were >95% viable and S. alterniflora embryos were < 20% viable. We conclude that increased solute leakage is an artefact of embryo excision and not an accurate indicator of desiccation damage to recalcitrant Spartina alterniflora seeds.

A hypothesis by David L. Mulcahy published in Science in 1979 on pollen competition as an important force in the evolution of flowering plant diversity, via selection of favourable genes in the microgametophyte that are passed on to, and inherited in, the sporophyte, stimulated quite a bit of research on the topic. The primary aim of this opinion paper is to assess the evidence for the effect of microgametophyte competition on the sporophyte, with particular reference to seed germination. Pollen competition was associated with an increase in seed germination in 14 of 30 case studies (30 published papers). Seed mass was related to better germination in only two of the 14 cases in which there was a positive effect of pollen competition on germination. An evaluation of the four criteria that must be met to validate Mulcahy's hypothesis cast some doubt on the significance of pollen competition as an important selective force in the diversification of angiosperms. Insect pollination, via which many pollen grains are deposited on a stigma, may not be the answer to Darwin's ‘abominable mystery’ concerning the reason for the abrupt origin and rapid diversification of flowering plants during the Cretaceous.

We review the literature on effects of inbreeding depression (ID) on seed germination for 743 case studies of 233 species in 64 families. For 216 case studies, we also review the relationship between mass and germination in inbred vs. outbred seeds. Inbred seeds germinated equally well as outbred seeds in 51.1% of 743 case studies, but better than outbred seeds in only 8.1%. In c. 50.5% of 216 cases, mass of inbred seeds was equal to (38.0%) or larger than (12.5%) that of outbred seeds. The magnitude of ID spans most of the − 1 to +1 range for relative performance for germination of inbred vs. outbred seeds; in contrast to what might be expected, seed germinability often is not negatively correlated with the coefficient of inbreeding (F) or positively corrected with population genetic diversity; neither heterosis nor outbreeding depression for germination is common in crosses between populations; and ID in most endemics is low and does not differ from that of widespread congeners. Our results on the effects of ID on seed mass and germination do not agree with the limited number of comparisons Darwin (1876) made on the effects of selfing vs. outcrossing on these two life-history traits. Recommendations are made on how to improve dormancy breaking and germination procedures in order to make the results of studies on ID more relevant to the natural world.

Miconia chartacea is a widely distributed tree in Brazil, occurring at altitudes ranging from 300 m to 1900 m in the Caatinga, Cerrado and Atlantic Forest biomes. In this work we attempted to classify M. chartacea seeds regarding their behaviour during storage and their germination syndrome and to determine, from a storage test in Cerrado soil and laboratory conditions in situ and ex situ, the longevity of seeds, as well as the capacity of the species to form a soil seed bank. The results suggested that M. chartacea seeds form a transient soil seed bank in the Cerrado and can be classified as orthodox in terms of storage behaviour, although the seeds are dispersed with a relatively high water content. The life span of seeds was favoured in soil-stored seeds in comparison with dry storage at 25°C, whereas storage at low temperatures prevented a decrease of the seed's germinability with storage time (330 d). M. chartacea seeds are dispersed during the dry season and germinate during the next rainy season, which can be classified as an intermediate–dry germination syndrome. Seeds of this species are dispersed in the Cerrado when temperatures and soil moisture are relatively low, which favours the formation of a soil seed bank, considering that the seeds tolerate desiccation and their longevity is favoured by low temperatures. A transient seed bank type is favoured by the loss of viability in storage at warm temperatures linked to the rainy season, and the predictable seasonal variations in climate in the region, with germination being restricted to the beginning of the rainy season.

Glebionis coronaria (L.) Cass. ex Spach is a common Mediterranean weed producing distinctive central and peripheral dormant cypselae with a hard fruit coat, which was previously hypothesized to impose physical dormancy. Analysis of water uptake in cypselae and in naked seeds showed that it preferentially takes place at the basal end of the fruit; however, seeds within an intact pericarp do not fully imbibe when compared with naked seeds. Germination was not significantly different between the two heteromorphs, and afterripening or cold stratification did not increase germination, while warm stratification at 35/20°C, as revealed by logistic regression, resulted in a significant improvement. However, loss of viability was also rapid at these high temperatures. Central and peripheral cypselae generally showed very low germination. In both heteromorphs, faster and higher germination (60–70%) was reached only after extensive scarification of pericarp tissue, and full germination was observed only after complete removal of pericarp tissue. Although the pericarp significantly reduced water uptake, no palisade layer(s) of macrosclereids could be observed. Xylem-vessel elements were found running through the basal end of the pericarp and forming the main point of water entry. We reject the hypothesis that G. coronaria cypselae have physical dormancy. Instead, water uptake and germination are impeded by: (1) directed water uptake, mainly through a pericarp-spanning channel-like structure; and (2) mechanical constraint on embryo growth exerted by the hard pericarp. The channel-like structure forms the principal system for controlling seed germination.

Optimal sample sizes under a budget constraint for estimating a proportion in a two-stage sampling process have been derived using individual testing. However, when group testing is used, these optimal sample sizes are not appropriate. In this study, optimal sample sizes at the cluster and individual levels are derived for group testing. First, optimal allocations of clusters and individuals are obtained under the assumption of equal cluster sizes. Second, we obtain the relative efficiency (RE) of unequal versus equal cluster sizes when estimating the average population proportion, $$\tilde {>\pi } $$ $$ . By multiplying the sample of clusters obtained assuming equal cluster size by the inverse of the RE, we adjust the sample size required in the context of unequal cluster sizes. We also show the adjustments that need to be made to allocate clusters and individuals correctly in order to estimate the required budget and achieve a certain power or precision.

Species with physically dormant (PY) seeds make up over 25% of plant species in a number of ecologically important ecosystems around the globe, such as savannah and Mediterranean shrublands. Many of these ecosystems are subject to temporally stochastic events, such as fire and drought; but are in areas projected to experience some of the most extreme climatic changes in the future. Given the importance of PY in controlling germination timing for successful recruitment, we ask how plastic the PY trait is, and if changes to the maternal environment from climate change could alter recruitment. This review focuses on: (1) the evidence for inter- and intraspecific variation in PY; (2) the genetic, maternal and environmental controls involved; and (3) the ecological consequences of (1) and (2) above. Evidence for (within-community) interspecific variation in conditions required to break PY is strong, but for intraspecific variation evidence is contradictory and limited by a paucity of studies. Identifying controllers of variation in PY is complex, there is some suggestion that conditions of the maternal environment may be important, but no consensus on the nature of effects. The implications of PY plasticity for the persistence of seed banks, species and communities under climate change are discussed. We highlight a number of key knowledge gaps, such as a lack of research estimating the components of variation in non-agricultural species, and identify a suite of seed attributes relevant to understanding the potential impacts of climate change on the population dynamics of PY species in the future.

Ecological (climatic and geographic) variation in early life-history transitions is a vital determinant of the adaptive evolution of timing of seed germination. This study aimed to investigate the correlation between timing of seed germination and environmental conditions during seed development. We examined seed germination timing of 15 coniferous seed lots of lodgepole pine, ‘interior’ spruce and western hemlock collected from natural stands in British Columbia (BC), Canada, under manipulated [stratification, thermo-priming (15 or 20°C) and their combinations] and non-manipulated (control) conditions. Timing of seed germination showed strong and positive correlation with the temperature-based environmental condition during seed development. This pattern persisted across species and seed lots within species, substantiating the historic importance of environmental conditions during seed development and maturation to life-history traits. Moreover, the strategy of phenotypic plasticity affecting timing of seed germination was observed across the applied germination treatments. These results provide insight into the germination niche as affected by global warming, indicating that conifers' seed dormancy in BC (north of 54°N) tends to increase and the changes associated with early spring warm-up are expected to accelerate seedling emergence, as shortened winters would have a minimal effect on dormancy decay.

The micromorphology of a seed is linked to its dispersal and germination, but evolutionary and ecological aspects in Orchidaceae remain unclear. We investigated the seed characters of Paphiopedilum and Cypripedium that might be associated with life form and involved in possible ecological adaptations. A phylogenetic comparative analysis of nine seed micromorphological characters was performed in 24 species from two genera with close phylogenetic relationships but significant differences in their ecological characteristics. Species within Paphiopedilum had larger embryos and a smaller percentage of air space (AS) than those of Cypripedium species. Compared with 16 terrestrial species, two epiphytic Paphiopedilum species had larger embryos and smaller AS. Those larger embryos might ensure more successful seedling establishment while the higher amount of air space in both terrestrial Paphiopedilum and Cypripedium may increase seed buoyancy and enable them to disperse over longer distances. Whereas AS and seed length (SL) are phylogenetically conservative, most other characters examined here had weak signals, indicating clear convergent evolution. Across species, SL was positively correlated with AS, indicating a high degree of seed size–dispersal coordination. These findings may imply a trade-off of seed characters in relation to the possible ecological adaptations required for seedling establishment versus dispersal.

Physiological dormancy has been described as a physiological inhibiting mechanism that prevents radicle emergence. It can be caused by the embryo (embryo dormancy) as well as by the structures that cover the embryo. One of its functions is to time plant growth and reproduction to the most optimal season and therefore, in nature, dormancy is an important adaptive trait that is under selective pressure. Dormancy is a complex trait that is affected by many loci, as well as by an intricate web of plant hormone interactions. Moreover, it is strongly affected by a multitude of environmental factors. Its induction, maintenance, cycling and loss come down to the central paradigm, which is the balance between two key hormonal regulators, i.e. the plant hormone abscisic acid (ABA), which is required for dormancy induction, and gibberellins (GA), which are required for germination. In this review we will summarize recent developments in dormancy research (mainly) in the model plant Arabidopsis thaliana, focusing on two key players for dormancy induction, i.e. the plant hormone ABA and the DELAY OF GERMINATION 1 (DOG1) gene. We will address the role of ABA and DOG1 in relation to various aspects of seed dormancy, i.e. induction during seed maturation, loss during dry seed afterripening, the rehydrated state (including dormancy cycling) and the switch to germination.

Two possible sources of resistance to pre-harvest sprouting were evaluated in quinoa. They showed dormancy at harvest and significant variations in dormancy level in response to environmental conditions experienced during seed development. The aims of this work were to evaluate the importance of seed coats in the regulation of dormancy in this species, to investigate possible mechanisms of action and to assess association of seed coat properties with changes in dormancy level caused by the environment. Accessions Chadmo and 2-Want were grown under field conditions on different sowing dates during 2 years. Seed coats were manipulated and seed germination was evaluated at different temperatures. Seed coat perforation before incubation led to faster dormancy loss in both accessions. This effect decreased with delayed sowing date, and seeds expressed a level of dormancy not imposed by coats. This suggests the presence of embryo dormancy in the genus Chenopodium. Seeds of the accession 2-Want had a significantly thinner seed coat at later sowing dates, associated with a decreasing coat-imposed dormancy, but this pattern was not detected in Chadmo. The seed coat acts as a barrier to the release of endogenous abscisic acid (ABA) in quinoa, suggested by the increase in germination and a higher amount of ABA leached from perforated seeds. ABA is able to leach from seeds with an intact seed coat, suggesting that differences in seed coat thickness may allow the leakage of different amounts of ABA. This mechanism may contribute to the observed differences in dormancy level, either between sowing dates or between accessions.

Seed germination requirements of Viburnum lantana were investigated by experiments both in the laboratory and outdoors. Embryo length, radicle emergence and shoot emergence were analysed to determine the level of morphophysiological dormancy (MPD) of seeds. Mean embryo length in fresh seeds was 1.30 mm, and required growth to at least 2.51 mm to germinate. The critical embryo length was 4.1 mm. In the laboratory, the embryo reached 3 mm length after 20 weeks of warm-temperature incubation (20/7 or 25/10°C), which in fact represents a combination of warm + cold stratification. In seeds subjected to cold stratification (1.5 or 5°C) for 24 weeks, embryos hardly grew. Gibberellic acid stimulated embryo growth and germination. In the outdoor phenology test, the embryos grew from 1.30 mm, i.e. fresh seeds sown in September, to 2.98 mm at the end of the following March. In the ‘move-along’ test (laboratory), starting with temperatures of warm stratification [i.e. 25/10°C (4 weeks) →  20/7°C (4 weeks) →  15/4°C (4 weeks) →  5°C (12 weeks) →  15/4°C (4 weeks)], and in the outdoor phenology study on seeds exposed to a similar temperature sequence, radicle emergence percentages reached 73% after 28 and 35 weeks, respectively. V. lantana does not exhibit a delay between root and shoot emergence, dismissing any kind of epicotyl dormancy. Seeds of V. lantana have non-deep simple MPD, a level not detected previously in the genus Viburnum, with the physiological dormancy component overcome by a combination of warm and cold stratification, preferably in that order.

The dispersal unit of many species of Brassicaceae is an indehiscent fruit, but relatively few studies have tested the effect of the pericarp on seed germination in this family. Our aim was to determine the effect of the pericarp on seed dormancy in six species of Brassicaceae native to the cold desert of north-west China. Intact dispersal units and isolated seeds of Chorispora sibirica, Euclidium syriacum, Goldbachia laevigata, Spirorrhynchus sabulosus, Sterigmostemum fuhaiense and Tauscheria lasiocarpa were stored dry at ambient laboratory conditions for 0–12 months and tested for germination in light and in dark at 5/2, 15/2 and 30/15°C. The amount of water absorbed by fruits and by seeds within the fruits was determined. For four species, intact fruits, isolated seeds and isolated seeds plus the removed pericarps were used to test for the mechanical versus possible chemical role of the pericarp in seed dormancy. Fresh isolated seeds, which have a fully developed embryo, germinated to lower percentages and rates than afterripened seeds. Thus, seeds have non-deep physiological dormancy. The pericarp significantly reduced germination, but inhibition was not due to lack of water uptake by seeds or to chemical inhibitors. Afterripened seeds of the six species germinated to 0–50% inside the fruits. We conclude that the pericarp plays a dominant role in seed dormancy of the six study species, and it does so by mechanically restricting embryo growth. Thus, the pericarp has the potential to spread germination over an extended period of time.

In imbibing seeds, resumption of metabolism leads to the unavoidable release of volatile by-products that are perceived as cues by rodent seed predators. The crypsis hypothesis proposes that the primary function of a water-impermeable, hard seed coat is to reduce rodent seed predation by rendering seeds olfactorily cryptic. In an opinion paper, Jayasuriya et al. (2015) find the crypsis hypothesis unscientific and ‘not consistent with Darwin's theory of evolution by natural selection’. It is unfortunate that Jayasuriya et al. (2015) did not appreciate that the crypsis hypothesis offers an alternative explanation for the evolution of water-impermeable seeds: released seed volatiles are cues used by rodents to locate seeds, and variation in seed-coat permeability leading to differences in seed volatile release represents the variable under selection. Furthermore, the sealing of water-impermeable seed coats imposes a cost of increased generation time and, therefore, dormancy-release mechanisms are expected to subsequently evolve in response to local environmental conditions. We also disagree with most other claims by Jayasuriya et al. (2015), who failed to appreciate how species with dimorphic seeds – one morph with permeable and the other with impermeable seed coats – benefit from rodent caching behaviour and population dynamics. We welcome this opportunity to clarify and elaborate on key features and the evolution of water-impermeable seed coats according to the crypsis hypothesis.

As in other cultivated species, dormancy can be seen as a problem in cereal production, either due to its short duration or to its long persistence. Indeed, cereal crops lacking enough dormancy at harvest can be exposed to pre-harvest sprouting damage, while a long-lasting dormancy can interfere with processes that rely on rapid germination, such as malting or the emergence of a uniform crop. Because the ancestors of cereal species evolved under very diverse environments worldwide, different mechanisms have arisen as a way of sensing an appropriate germination environment (a crucial factor for winter or summer annuals such as cereals). In addition, different species (and even different varieties within the same species) display diverse grain morphology, allowing some structures to impose dormancy in some cereals but not in others. As in seeds from many other species, the antagonism between the plant hormones abscisic acid and gibberellins is instrumental in cereal grains for the inception, expression, release and re-induction of dormancy. However, the way in which this antagonism operates is different for the various species and involves different molecular steps as regulatory sites. Environmental signals (i.e. temperature, light quality and quantity, oxygen levels) can modulate this hormonal control of dormancy differently, depending on the species. The practical implications of knowledge accumulated in this field are discussed.

Many studies have claimed that fire acts as the chief ecological factor cueing dormancy break in seeds with a water-impermeable seed coat, i.e. physical dormancy (PY), in Mediterranean ecosystems. However, a proposal is made that seasonal temperature changes must be viewed as more meaningful dormancy-breaking cues because: (1) fire is erratic and may break PY in seasons during which seedlings cannot complete their life cycle; (2) fire may not occur for long periods, thereby only providing an opportunity for dormancy break and germination once in every several years; and (3) if fire opens the specialized anatomical structures called ‘water gaps’, in seconds, their evolutionary role of detecting environmental conditions becomes irrational. Although fire breaks dormancy in a proportion of seeds, given the risk of seed mortality and the post-fire environment providing cues for dormancy break, it is suggested that fire might possibly be an exaptation.

The seed coat of soybean (Glycine max (L.) Merrill) must protect the seed but allow water intake. Overprotection, causing impermeability, is assumed to be due to the presence of an impermeable layer in the seed coat, although validation of this assumption has relied on imbibition testing, which tends to be influenced by microfractures in the seed coat. Recent micromorphological analyses using laser-assisted topography microscopy revealed links to the surface roughness (SR) of the seed coat. To verify genetic links between hardseededness and SR, we analysed quantitative trait loci (QTLs) governing SR formation using 148 recombinant inbred lines (RILs) with a genetic linkage map covering 2663.6 cM of all 20 linkage groups of soybean, with 355 DNA markers and 5 phenotype markers. Five QTLs were detected, including previously identified hardseededness QTLs for ratio of seeds absorbing water, namely RAS1 and RAS2, which accounted for 20% of the phenotypic variance, and one near a locus inhibiting seed coat colour (I). These results indicate that the impermeability of soybean seed is genetically related to the reduction of SR.

The three tropical species Gomphandra luzoniensis, Nothapodytes nimmoniana and Goniothalamus amuyon contain important cancer-fighting drugs; however, little is known about how to propagate these species from seeds. Thus, the aim of this study was to determine the germination requirements of seeds of each of these three species in order to provide an effective protocol to produce plants. Fresh seeds of G. luzoniensis germinated up to 73% at high temperatures in light in 4 weeks, and embryos were underdeveloped. Most seeds had morphological dormancy (MD), but a proportion of them had morphophysiological dormancy (MPD). Fresh seeds of N. nimmoniana germinated up to 50% in light in 4 weeks, embryo length increased by 17% before radicle emergence and ≥ 89% of the seeds had germinated after incubation for 6 weeks in light at high temperatures. Thus, about 50% of the seeds have MD and about 50% MPD. Fresh seeds of G. amuyon incubated at 30°C in light for 4 weeks germinated to 69%, whereas at the other incubation temperatures germination took longer than 4 weeks. Embryo length increased 213% before radicle emergence, and after 8 weeks of incubation at high temperatures ≥ 80% of the seeds had germinated. As in the other two species, the seed population consisted of a mixture of MD and MPD. Incubation of seeds of these three species at high temperatures (e.g. 25, 30 and 30/20°C) for up to 2 months is recommended for germination and thus seedling production.

The genus Conostylis (Haemodoraceae) is endemic to fire-prone south-western Australia. To gain an understanding of the effect of some fire-related germination cues, eight Conostylis taxa were tested in response to water, nitrate, smoke water and karrikinolide (KAR1) under light and dark conditions, when seeds were freshly collected and after a year of burial. The germination of all taxa tested was higher in response to smoke water and KAR1 than in water alone, whereas nitrate did not stimulate germination. Germination was higher in all taxa following 1 year of burial than in fresh seeds. Recently, glyceronitrile has been identified as another chemical in smoke water, apart from KAR1, that can stimulate the germination of certain species. The relative response of eight Conostylis taxa to KAR1, glyceronitrile and smoke water was examined in laboratory-stored seeds. Germination of these taxa was promoted by both smoke water and KAR1, except for C. neocymosa, which had high germination regardless of treatment. Four of the other seven taxa germinated to higher levels in at least one of the glyceronitrile concentrations tested (10, 50 or 100 μM) than in water alone. However, in only two of these taxa, C. aculeata subsp. septentrionora and C. juncea, was germination in glyceronitrile as high as that in smoke water. Thus, the response to glyceronitrile is not uniform across Conostylis taxa. Generally, germination was higher with KAR1 than glyceronitrile, suggesting that although some Conostylis taxa have the capacity to respond to glyceronitrile, KAR1 is the more important germination stimulant for this genus.