Showing papers in "Seed Science Research in 2018"

Multispectral imaging – a new tool in seed quality assessment?

Abstract: Multispectral imaging is a new technology that is being deployed to assess seed quality parameters. Examples of applications in the detection and identification of fungi on seeds are presented, together with an example of the technology used for maturity determination in sugar beet seed. Results from multispectral imaging are compared with reference methods, and a high correlation is found. Applications of the technique for varietal discrimination and insect damage are also presented. There is a need for non-destructive, reliable and fast techniques, and it is concluded that multispectral imaging has potential for seed quality assessment, in particular for those components associated with surface structure and chemical composition, seed colour, morphology and size.

Regulation of seed dormancy and germination by nitrate

Abstract: Nitrate promotes seed germination at low concentrations in many plant species, and functions as both a nutrient and a signal. As a nutrient, it is assimilated via nitrite to ammonium, which is then incorporated into amino acids. Nitrate reductase (NR) catalyses the reduction of nitrate to nitrite, the committed step in the assimilation. Seed sensitivity to nitrate is affected by other environmental factors, such as light and after-ripening, and by genotypes. Mode of nitrate action in seed germination has been well documented in Arabidopsis thaliana and the hedge mustard Sisymbrium officinale. In these species nitrate promotes seed germination independent of its assimilation by NR, suggesting that it acts as a signal to stimulate germination. In Arabidopsis, maternally applied nitrate affects the degree of primary dormancy in both wild-type and mutants defective in NR. This indicates that nitrate acts not only during germination, but also during seed development to negatively regulate primary dormancy. Functional genomics studies in Arabidopsis have revealed that nitrate elicits downstream events similar to other germination stimulators, such as after-ripening, light and stratification, suggesting that these distinct environmental signals share the same target(s). In Arabidopsis, the NIN-like protein 8 (NLP8) transcription factor, which acts downstream of nitrate signalling, induces nitrate-dependent gene expression. In particular, a gene encoding the abscisic acid (ABA) catabolic enzyme CYP707A2 is directly regulated by NLP8. This regulation triggers a nitrate-induced ABA decrease that permits seed germination. This review article summarizes an update of our current understanding of the regulation of seed dormancy and germination by nitrate.

Functional morpho-anatomy of water-gap complexes in physically dormant seed

Abstract: Physical dormancy (PY) occurs in at least 18 angiosperm plant families and is caused by water-impermeable palisade cells in seed (or fruit) coats. Breaking of PY involves disruption or dislodgement of water-gap structures causing the seeds/fruits to become water permeable (non-dormant). The water-gap region is a morphologically distinct area of the seed or fruit coat that forms a water-gap complex. The location, anatomy, morphology and origin of water-gaps can differ between and even within families and genera. Water-gap structures sense environmental conditions that allow seeds with PY to become permeable just prior to the commencement of conditions favourable for germination and plant establishment. There are three basic water-gap morpho-anatomies characterized by the way the water-gap opens: Type-I, Type-II and Type-III. In Type-I water-gaps, specific kinds of cells pull apart to form a surface opening, while in Type-II a portion of the surface structure is pulled away from adjacent cells, opening the water-gap. Type-III is the least common type and has a circular, plug-like structure that is dislodged, whereby water entry occurs. In addition, water-gap complexes are either simple or compound, depending on whether only a single primary water-gap structure is involved in dormancy release or an additional secondary water-gap structure opens, permitting water entry.

Development of C-lignin with G/S-lignin and lipids in orchid seed coats – an unexpected diversity exposed by ATR-FT-IR spectroscopy

Abstract: Members of the orchid family occupy many germination niches, in terrestrial, epiphytic and epilithic environments. How orchid seeds attach to their substrate and survive after dispersal is largely unknown. C-lignin is a recently discovered specialized lignin, found in seed coats of some plants, including orchid species, but its functional and biological significance is obscure. We studied seed coat ontogenesis in three species (Neuwiedia veratrifolia, Cypripedium formosanum and Phalaenopsis aphrodite) that represent basal and advanced branches in orchid phylogeny and divergent life forms. From each species, controlled pollination yielded several stages of seed development, from which seed coats (testa) were isolated and analysed by ATR-FT-IR spectroscopy. The use of the ATR set-up ensured that the chemical information originated only from the integral outer seed surface layers. The FT-IR bands of C-lignin are presented here for the first time, and distinguished from bands of G/S-lignin. In the seed coats, C-lignin developed after G/S-lignin in N. veratrifolia and C. formosanum, while only G/S-lignin developed in P. aphrodite. We discuss C-lignin properties and possible function in relation to seed coat properties. The species differed with respect to sequence and amounts of deposition, not only of lignins but also lipids, resulting in differences in mature seed coat compositions. Thus we revealed an unexpected and marked diversity among orchids with respect to seed surface chemistry, with possible implications for seed and germination ecology.

Effect of maternal habitat, temperature and light on germination and salt tolerance of Suaeda vermiculata, a habitat-indifferent halophyte of arid Arabian deserts – CORRIGENDUM

Abstract: Habitat-indifferent species that can grow well in both saline and non-saline soils offer a good opportunity for studying seed dormancy and salt tolerance during germination. Here, we assess interactive effects of maternal habitat and incubation conditions on salt tolerance during germination of the habitat-indifferent halophyte Suaeda vermiculata, a common perennial shrub of the arid Arabian deserts. Seeds collected from saline and non-saline habitats were germinated at six salinity levels (0–500 mM NaCl) and incubated at three temperatures and under two light regimes. Studied germination attributes were final germination, germination rate index (GRI) and germination recovery of non-germinated seeds when transferred to distilled water. The results showed insignificant difference in salt tolerance between seeds of the two habitat types at the lower salinities. At higher salinities (400 and 500 mM NaCl), germination of the saline habitat seeds was almost inhibited, but that of non-saline habitat seeds reached various levels depending on light and temperature. Both higher temperatures and darkness resulted in significant reductions of the final germination at the higher salinities. Seeds of the two habitats that did not germinate in the different treatments recovered their germination when transferred to distilled water, indicating that these seeds maintained their viability in saline solution and were able germinate upon the arrival of suitable conditions. Seeds of the two habitats germinated within 2 days at the lower salinities and GRI decreased with the increase in salinity level. Such reduction was obvious for seeds of the saline habitat. Recovery was faster for seeds of the saline habitats, especially for those incubated at higher salinities and in the dark. The difference in dormancy and germination attributes of seeds of the two habitat types reflects ecological adaptations for survival in salt marshes of arid deserts.

Interpreting biological variation: Seeds, populations and sensitivity thresholds

Abstract: Seeds offer a unique perspective from which to view biology. An individual seed is an autonomous biological entity that must rely on its own resources (and resourcefulness) to persist after dispersal and to time its transition to germination and seedling growth to coincide with environmental opportunities for survival. At the same time, seed biology in agriculture and ecology is determined largely by the behaviours of populations of individual seeds. The percentage of seeds in a population that is in a particular state (e.g. dormant, germinated, dead) at a given time is a fundamental metric of seed biology. This duality of individual diversity underlying consistent population-wide behaviour patterns can be described quantitatively using population-based threshold (PBT) models. While conceptually simple, these models are highly flexible and can describe the wide diversity of responses of seed populations to temperature, water potential, hormones, oxygen, light, ageing and combinations of these factors. This seed behaviour is linked to respiratory rates of individual seeds, indicating that basic metabolic processes within seeds vary among individuals in accordance with PBT principles. Looking more broadly across microbial, plant and animal biology, examples of cellular diversity in hormonal sensitivity, gene expression, developmental responses and signalling abound. This variation often is termed ‘noise’, and analysis efforts are focused on extracting mean signals from this variation to understand regulatory pathways. However, extension of the PBT approach to the cellular and molecular levels suggests that population sensitivity distributions and recruitment phenomena may underlie many fundamental biological processes. Thus, concepts and quantitative approaches developed for the analysis of seed populations can be applied across biological scales from molecules to ecosystems to interpret inherent biological variation and provide mechanistic insights into the nature of biological regulatory systems.

Improvement in rice seed storage longevity from high-temperature drying is a consistent positive function of harvest moisture content above a critical value

Abstract: Drying reduces seed moisture content, which improves subsequent seed survival periods. Diverse maximum temperatures have been recommended to limit or avoid damage to seeds, but some high-temperature drying regimes may improve subsequent seed quality. Seeds from 20 different accessions of five rice (Oryza sativa L.) variety groups (aromatic, Aus, Indica, temperate Japonica, tropical Japonica) were harvested over several seasons at different stages of maturation and either dried throughout at 15°C/15% relative humidity (RH) or for different initial periods (continuous or intermittent) in different drying regimes at 45°C before final equilibrium drying at 15°C/15% RH. Subsequent seed longevity in hermetic storage at 45°C with 10.9% moisture content was determined. In no case did initial drying at 45°C provide poorer longevity than drying at 15°C/15% RH throughout. There was a split-line relation, which did not differ amongst investigations, between longevity after initial drying at 45°C relative to that at 15°C/15% RH throughout and harvest moisture content, with a break point at 16.5% (a seed moisture status of about –14 MPa). Below 16.5%, relative longevity did not differ with harvest moisture content with little or no advantage to longevity from drying at 45°C. Above 16.5%, relative longevity showed a positive relation with harvest moisture content, with substantial benefit from drying at 45°C to subsequent longevity of seeds harvested whilst still moist. Hence, there are temporal (immediately ex planta cf. subsequent air-dried storage) and water status discontinuities (above cf. below 16.5%) in the effect of temperature on subsequent air-dried seed longevity.

Potential impact of global warming on seed bank, dormancy and germination of three succulent species from the Chihuahuan Desert

Abstract: We assessed inter-seasonal dynamics of seed banks, dormancy and seed germination in three endemic Chihuahuan Desert succulent species, under simulated soil warming conditions. Hexagonal open top-chambers (OTCs) were used to increase soil temperature. Seeds of Echinocactus platyacanthus (Cactaceae), Yucca filifera and Agave striata (Asparagaceae) were collected and buried within and outside OTCs. During the course of one year, at the end of each season, seed batches were exhumed to test viability and germination. Soil temperature in OTCs was higher than in control plots. Yucca filifera seeds always had high germination independently of warming treatment and season. Agave striata seeds from OTCs had higher germination than those from control plots. Agave striata exhibited low germination in fresh seeds, but high germination in spring. Seeds from this species lost viability throughout the experimental timeframe, and had no viable seeds remaining in the soil. Echinocactus platyacanthus showed high germination in fresh seeds and displayed dormancy cycling, leading to high germination in spring, low germination in summer and autumn, and high germination in winter. Germination of this species was also higher in seeds from OTCs than those from control plots. Echinocactus platyacanthus formed soil seed banks and its cycle of inter-seasonal dormancy/germination could be an efficient physiological mechanism in a climate change scenario. Under global warming projections, our results suggest that future temperatures may still fall within the three studied species’ thermal germination range. However, higher germination for A. striata and E. platyacanthus at warmer temperatures may reduce the number of seeds retained in the seed bank, and this could be interpreted as limiting their ability to spread risk over time. This is the first experimental study projecting an increase in soil temperature to assess population traits of succulent plants under a climate change scenario for American deserts.

Near-Infrared Spectroscopy Used to Predict Soybean Seed Germination and Vigour

Abstract: Rapid, non-destructive methods for measuring seed germination and vigour are valuable. Standard germination and seed vigour were determined using 81 soybean seed lots. From these data, seed lots were separated into high and low germinating seed lots as well as high, medium and low vigour seed lots. Near-infrared spectra (950–1650 nm) were collected for training and validation samples for each seed category and used to create partial least squares (PLS) prediction models. For both germination and vigour, qualitative models provided better discrimination of high and low performing seed lots compared with quantitative models. The qualitative germination prediction models correctly identified low and high germination seed lots with an accuracy between 85.7 and 89.7%. For seed vigour, qualitative predictions for the 3-category (low, medium and high vigour) models could not adequately separate high and medium vigour seeds. However, the 2-category (low, medium plus high vigour) prediction models could correctly identify low vigour seed lots between 80 and 100% and the medium plus high vigour seed lots between 96.3 and 96.6%. To our knowledge, the current study is the first to provide near-infrared spectroscopy (NIRS)-based predictive models using agronomically meaningful cut-offs for standard germination and vigour on a commercial scale using over 80 seed lots.

Relationships between compound lipophilicity on seed coat permeability and embryo uptake by soybean and corn

Abstract: Systemic uptake of organic compounds from roots to leaves follows a Gaussian distribution in relation to the lipophilicity, as measured by the log Kow. Quantification of compound uptake with different lipophilicities, and applied as a seed treatment that diffuses through the seed coat into the embryo during imbibition, has not been reported. The aim of this investigation was to quantify the uptake of non-ionic compounds into seeds of soybean and corn. A series of fluorescent piperonyl amides were synthesized and a novel combinatorial pharmacodynamic technique was developed that provided a range of compounds from log Kow 0.02 to 5.7. Seeds were treated with a mixture of amides, imbibed and compounds chemically extracted and quantified by high-performance liquid chromatography using a fluorescence detector. The maximum uptake efficiency of the applied amide mixture from whole soybean and corn seeds was 67% at log Kow 2.9, and 43% at log Kow 3.4, respectively. The critical partition coefficient for uptake for both species was 75% of the amides were found in the soybean embryo or corn internal tissues compared with the covering layers at log Kow <4.2. The distribution of amides showed that the corn seed covering layer had similar hydrophilic/lipophilic properties as internal tissues, while soybean tissues had different hydrophilic/lipophilic properties. Collectively, the Gaussian uptake pattern for systemic uptake into plants was not found for either seed species.

Seed heteromorphy influences seed longevity in Aegilops

Abstract: The genus Aegilops belongs to the secondary gene pool of wheat and has great importance for wheat cultivar improvement. As a genus with only annual species, regeneration from seeds in Aegilops is crucial. In several species in Aegilops, spikes produce different seed morphs, both in size and germination patterns. However, little is known about the ecology of seed germination, nor about the seed longevity in this genus. Here we investigated the germination phenology of Ae. neglecta under laboratory and field conditions and assessed longevity of different seed morphs of five additional Aegilops species using controlled ageing tests. Large seeds were short-lived and germinated faster than small seeds in most of the species. Field experiments with Ae. neglecta showed that large seeds of the dimorphic pair germinated 3 months after dispersal in contrast to 14 months for smaller seeds. Differences in longevity were detected not only in dimorphic seed pairs, but also among seeds from different positions on the spike. Our results indicate that different longevities in seed morphs of Aegilops may reflect a different soil seed bank persistence, with smaller seeds able to maintain a higher viability after dispersal than larger ones, thereby spreading seedling emergence over two years. Differences of seed germination and longevities between seed morphs in Aegilops may have important implications for ex situ seed conservation and reinforce the hypothesis of a bet-hedging strategy in the germination ecology of this genus.

An examination of Job's rule: protection and repair of the proteins of the translational apparatus in seeds

Abstract: The proteins produced just prior to maturation desiccation in the developing, orthodox seed, are stored in the desiccated state and recruited as the functional proteome upon imbibition. For the resumption of protein function, these stored proteins must be protected from permanent denaturation while dehydrating, throughout desiccation, and during rehydration. For some forms of damage there is the possibility of repair following imbibition potentially coordinated with de-aggregation into monodispersed polypeptides capable of refolding into a functional configuration. While studying aspects of the natural protection and repair mechanism in seeds, evidence has accrued that those proteins directly involved in translation are particular targets of both protection and protein repair. Such a phenomenon was first described by Rajjou et al. (2008) examining the frequency with which proteins involved in translation were identified as differentially abundant between aged and un-aged Arabidopsis seeds and the translational competence of aged versus un-aged seeds. The inference drawn from these observations was that, of all the stored proteins, it is imperative that those involved in translation endure desiccation, quiescence and rehydration in a functional state if the seed is to survive. Proteins involved in any other process other than translation can be replaced from the stored transcriptome or by de novo transcription but no mRNA is of value without the translational machinery. This has become known as ‘Job's rule’ in honour of the laboratory from which this hypothesis was first put forward (Rajjou et al., 2008). We review in this manuscript the evidence accrued to date on which Job's rule is based.

Seeds vs fungi: an enzymatic battle in the soil seedbank

Abstract: Depleting the soil weed seedbank is an important integrated weed management strategy that has the potential to foster lasting weed control. Long-term dormancy and decay resistance of weed seeds pose a challenge to weed eradication efforts. Select soil fungi have been shown to cause significant decay of weed seeds. The physical and chemical mechanisms by which seeds in the seedbank defend themselves against pathogens have been well researched. However, very few studies have purposefully investigated the biochemical defence response of seeds. Enzyme-based biochemical seed defences have been detected in dormant and non-dormant seeds, and research supports their function in pathogen defence. This review summarizes current knowledge of the seed defence enzymes polyphenol oxidase, peroxidase, chitinase and oxalate oxidase. The fungal enzymes chitinase, protease and xylanase that function in pathogenesis of seeds in the soil seedbank are also reviewed. Progress in the development and standardization of in situ enzyme analyses fosters our understanding of actual enzyme activity present in soils, while high-throughput microplate techniques promote efficiency and enable greater scope. Application of genomic, proteomic and transcriptomic techniques to glean a deeper and more holistic understanding of the enzymatic interactions of weed seeds and soil fungi in the soil seedbank will support the development of improved integrated weed management strategies.

Pollen limitation and its effect on seed germination

Abstract: In nature, fruit and seed production in many plants have been shown to be pollen limited. Pollen limitation is demonstrated when open-pollinated plants that are hand-supplemented (Ps) with outcross pollen produce more fruits and/or seeds than open-pollinated controls that are not hand-pollinated (Po). There are three categories of results in such studies: Ps > Po, Ps = Po and Ps < Po, in which case pollen limitation indices are positive, zero and negative, respectively. In an index widely used to calculate pollen limitation, 1 – (Po/Ps), the bounds for Ps ≥ Po are 0 to + 1, whereas the bounds for Ps < Po are 0 to –∞. The first aim of this review was to show how the pollen limitation index can be modified so that the bounds of Ps < Po are 0 and –1, whereupon the index gives equal weight to the best performer (Ps or Po) and worst performer (Ps or Po). In addition to seed quantity, pollen supplementation can affect seed quality, including germinability. Thus, our second aim was to summarize the results of studies that have also tested the effect of pollen limitation on seed germination. In short, the 30 case studies in 15 families, 16 genera and 18 species that we identified show that seed germination percentage increased, was not affected or decreased by pollen supplementation in 12, 11 and seven cases, respectively. The effect of pollen limitation on seed germination, which can be quite large, has not been considered in developing population growth models to determine the effect of pollen limitation on λ.

Local climate controls among-population variation in germination patterns in two Erica species across western Iberia

Abstract: In seasonal climates, germination timing is mainly controlled by temperature, especially in species with physiological seed dormancy. The germination response to temperature may, however, vary among populations across the distribution range of species. Understanding how populations along climate gradients vary in their sensitivity to temperature is important for determining their vulnerability to climate variability and change. Here, we investigated the germination response of two Erica species with physiological seed dormancy (E. australis and E. umbellata) to changes in temperature throughout the seasons (simulated autumn through to spring) and to the local climate in six localities across a latitudinal gradient in western Iberia. Effects were studied with and without exposing the seeds to a heat shock. The local climate of seed provenance emerged as a key factor in modifying the germination sensitivity to germination temperature and their variation through the seasons. Although each species showed idiosyncratic germination responses to temperature treatments and across the gradient, germination of both species was sensitive to warmer temperatures and to a heat shock. Both showed similar seasonal germination patterns: as we moved from south to north, populations tended to have a larger germination peak in spring, which was greater at colder temperatures. We conclude that rising temperatures associated with climate change will affect these species, particularly at their northern ranges, where many seeds will remain dormant during warmer winters. Arguably, models aiming at assessing climate change impacts in these species need to include such variability across latitude.

Seed mass and elevation explain variation in seed longevity of Australian alpine species

Abstract: Conserving alpine ecosystems and the plant communities they contain using ex situ conservation requires an understanding of seed longevity. Knowledge of seed longevity may determine the effectiveness of ex situ seed banking for alpine plant conservation, and may provide insight into plant recruitment in situ. We sought to determine the influence of elevation and climatic variables, as well as plant and seed traits, on the seed longevity of 57 species inhabiting a unique biome, (sub-)alpine regions of mainland Australia. Seed longevity was estimated using controlled accelerated ageing tests to determine the time taken for seed viability to fall by 50%. We found that, across the study species, like alpine seeds elsewhere in the world, Australian alpine seeds are relatively short-lived and overall shorter-lived than Australian plants in general. Seed mass and elevation explained most of the variation in seed longevity among the Australian alpine species considered. Species with larger seed mass, and collections made at higher elevations, were found to have relatively short-lived seeds. Phylogeny, however, explained very little of the variation in longevity. Our results suggest that viability testing for Australian alpine seeds in ex situ seed banks should be conducted with shorter intervals than for the non-alpine flora. This study highlights how seed longevity in the Australian Alps is not dictated primarily by evolutionary lineage but rather by a complex combination of environmental variables and intrinsic seed characteristics. Potential implications for conservation ex situ and in situ in the context of climate change are discussed.

Complementary endozoochorous seed dispersal by large mammals in the Golestan National Park, Iran

Abstract: Large animals tend to disperse seeds over long distances via ingestion and defecation due to their large home range and capacity to move among different habitats for feeding. The aim of this study was to investigate the potential of endozoochorous seed dispersal by five herbivores: Ovis vignei, Capra aegagrus, Gazella subgutturosa, Cervus elaphus, Capreolus capreolus and two omnivores: Sus Scrofa and Ursus arctos in the Golestan National Park, northeast of Iran, by a greenhouse germination experiment. A total of 3107 seedlings belonging to 154 different plant taxa were germinated from 655 dung samples collected in three different habitats. Plant families that most frequently germinated were Poaceae and Brassicaceae. Urtica dioica was the most abundant germinating seed, accounting for 20% of all the seedlings recorded in our dung samples, whereas the most frequently observed species was Portulaca oleracea, which occurred in 24% of our samples. We showed that 54% of the seeds germinating were dispersed by only one of the mammals studied. Herbs and graminoids were the most frequently dispersed growth forms by the herbivores and the wild boar, whereas brown bears mostly dispersed shrubs. The seedling composition in the dung samples was strongly correlated with the local flora especially for non-selective feeders, like red deer. The differences observed in the number of plants and frequency of different growth forms dispersed among the studied mammals reflect their body size, digestive physiology, and dietary and habitat preferences. Our findings highlight the different and complementary roles of large herbivores and omnivores as long-distance seed dispersal vectors.

Three levels of simple morphophysiological dormancy in seeds of Ilex (Aquifoliaceae) species from Argentina

Abstract: As a contribution to understanding the world biogeography of seed dormancy in the cosmopolitan genus Ilex, we studied seeds of I. argentina, I. brasiliensis, I. brevicuspis, I. dumosa, I. paraguariensis and I. theezans from the subtropical region of Argentina. We hypothesized that seeds of these species have non-deep simple morphophysiological dormancy (MPD). Effects of temperature, cold stratification and gibberellic acid (GA3) on seed germination and embryo growth were tested. Regardless of incubation temperature, little or no germination occurred for any species until ≥6 weeks. There was an up to 3-fold increase in embryo length to seed length (E:S) ratio before seeds germinated, and embryos grew only during warm-stratifying conditions. Seeds of I. brasiliensis, I. brevicuspis and I. theezans had non-deep simple MPD and germinated to ≥80% after 12, 24 and 16 weeks, respectively. Cold stratification increased germination of I. brasiliensis and I. brevicuspis, and GA3 increased the rate but not final germination percentage of I. brasiliensis and I. theezans. Fresh seeds of I. dumosa required 40 weeks of warm stratification to germinate to 53%, while those after-ripened for 2 months germinated to 81% after 30 weeks; this species has intermediate simple MPD. Seeds of I. argentina and I. paraguariensis germinated to 15 and 21%, respectively, after 40 weeks of warm stratification and did not after-ripen or respond to GA3; these seeds have deep simple MPD. This is the first report of intermediate and deep simple MPD that is broken by warm stratification, thereby increasing our knowledge of seed dormancy in Ilex and in subtropical regions.

Soil seedbed engineering and its impact on germination and establishment in sugar beet (Beta vulgaris L.) as affected by seed-soil contact

Abstract: Seed-soil contact plays an essential role in the process of germination as seeds absorb water through direct contact with the moist soil aggregates that surround them. Factors influencing seed-soil contact can be considered as those pertaining to soil physical properties (e.g. texture, bulk density, porosity, etc.) and those related to environmental conditions (e.g. temperature, rainfall, frost). Seed-soil contact is furthermore influenced by the specific field management processes that farmers apply, which have developed significantly over the last 30 years. However, the precise effect of cultivation on the actual contact area of the seed with the surrounding soil is based on a series of assumptions and still largely unknown. This review considers the influence of soil management and its direct impact on seed-soil contact and establishment. We review the state of the art in methodology for measuring seed-soil contact and assess the potential for soil amendments such as plant residues and waste materials to improve seed-soil contact. Engineering the ‘optimal’ seed-soil contact remains a challenge due to the localized variation between the interaction with field management techniques and soil texture, climatic conditions and crop type. The latest imaging approaches show great promise to assess the impact of management on germination. Combining the techniques with the latest network models offer great potential to improve our ability to accurately predict germination, emergence and establishment.

Effect of simulated flooding during rice seed development and maturation on subsequent seed quality

Abstract: The resilience of seed quality in rice (Oryza sativa L.) to flooding was investigated. Pot-grown plants of the japonica cv. Gleva, the indica cv. IR64, and the introgressed line IR64-Sub1 were submerged in water, to simulate flooding, for 3‒5 days at different stages of seed development and maturation. Mean seed weight, pre-harvest sprouting, ability to germinate, and subsequent longevity in air-dry storage were assessed. Whereas seed quality in both IR64 and IR64-Sub1 was resilient to submergence, in Gleva the longer the duration of submergence and the later in development when plants were submerged the greater the pre-harvest sprouting. Thousand seed dry weight was reduced more by submergence in Gleva than IR64 or IR64-Sub1. At harvest maturity, few pre-harvest sprouted seeds were able to germinate upon rehydration after desiccation to 11‒12% moisture content. Seed longevity of the non-sprouted seed fraction in air-dry hermetic storage (40°C, 15% moisture content) was not affected greatly by submergence, but longevity of the japonica rice was less than that of the indica rices due to the former's steeper seed survival curves. Longevity of the two indica rices was predicted well by the seed viability equation and previously published estimates of viability constants for rice. The greater dormancy of IR64 and IR64-Sub1, compared with Gleva, enhanced resilience to pre-harvest sprouting and reduced thousand seed dry weight from plant submergence. There was little or no effect of plant submergence on subsequent air-dry storage longevity of non-sprouted seeds in any genotype.

Seed traits favouring dispersal and establishment of six epiphytic Tillandsia (Bromeliaceae) species.

Abstract: There are a number of studies describing the gross range of morpho-anatomical variability in epiphytic Tillandsia species, but the interspecific variation in seed traits remain largely unexplored, although these play an important role in determining dispersal and establishment success In order to evaluate interspecific variation in seed morphology, anatomy and germination, we sampled six Tillandsia species from the Yucatan peninsula, Mexico, distributed along a precipitation gradient We studied morpho-anatomical traits (seed length, seed mass, ratio of coma to seed, ratio of embryo to endosperm), seed terminal velocity in still air, and performed histochemical analyses and germination trials under controlled conditions Tillandsia recurvata differs from the other five species in the structure of the plumose coma; it was the only species lacking an endosperm and showed distinct seedling development Among the species, bigger seeds were related to longer comas, and had higher germinability Overall, seed terminal velocity was invariably slow, compared with reports of other anemochorous species, suggesting a high dispersal potential Taxonomical and ecological implications of our results are discussed

The morphophysiological dormancy of Ferula ovina seeds is alleviated by low temperature and hydrogen peroxide

Abstract: Ferula ovina is a perennial Apiaceae with great medicinal and economic value. This study was conducted to better understand the dormancy and germination behaviour of its seeds. Experiments included temperature requirements for both embryo growth and germination under field and laboratory conditions, the effects of warm stratification, gibberellic acid (GA3), dry after-ripening, exogenous hydrogen peroxide (H2O2) and diphenyleneiodonium (DPI) on dormancy, localizing the accumulation of superoxide (O2 − ) and measuring endogenous contents of H2O2 in embryos during cold and warm stratification. Embryos were under-developed and did not germinate within one month at temperatures higher than 10°C. Among all treatments, cold stratification and exogenous H2O2 could break dormancy. However, the application of DPI reduced growth and the germination of the embryo at 3°C. During cold stratification, the embryonic axes elongated more than the cotyledons, which coincided with earlier production of O2 − in the axes. Only these embryos could eventually complete growth and germinate. Moreover, such asymmetric growth between the axes and cotyledons was also observed when seeds were treated with exogenous H2O2. On the other hand, both axes and cotyledons displayed the same growth over treatments with warm stratification and DPI. Overall, seeds of F. ovina exhibit the characteristics of deep complex morphophysiological dormancy. Moreover, the embryos solely require cold to complete growth and to germinate, and this process seems to be mediated by reactive oxygen species. Under natural conditions, seeds germinate during winter in cold soil, and shoots emerge in spring.

An improved method for the rapid isolation of RNA from Arabidopsis and seeds of other species high in polyphenols and polysaccharides

Abstract: Seeds are notoriously high in polyphenols and polysaccharides, which reduce RNA quality and yield, and interfere with downstream applications. We present simple modifications to a rapid RNA extraction protocol for use with seeds. The inclusion of polyethylene glycol in place of polyvinylpyrrolidone reduced polyphenol and polysaccharide contamination. In addition, replacing NaCl with KCl improved the RNA yield from Arabidopsis seeds still bound by mucilage. On extraction of Arabidopsis seed recovered from field soils clean RNA pellets with no accompanying gelatinous matrix (polysaccharide) were seen, with A260/230 ratios greater than 1.8 confirming the lack of polysaccharide carry-over. When Brassica oleracea and Sinapis arvensis seeds were extracted, 260/230 ratios greater than 1.8 were seen. RNA yields in excess of 10 µg per 100 mg seed suitable for RT-QPCR were obtained.

Effect of storage temperature on dormancy release of sunflower (Helianthus annuus) achenes

Abstract: Published information regarding the effect of storage temperature on dormancy alleviation of sunflower achenes is contradictory and ambiguous. In the present study we explored the effect of temperature during dry storage on dormancy release in two sunflower genotypes, including a commercial hybrid and an inbred line. Dry storage at 25°C consistently accelerated dormancy release of achenes compared with 5°C. This response fits the general pattern reported for dry after-ripening in seeds of many other species. Depending on the genotype and the dormancy factor prevailing, higher temperature alleviated embryo dormancy and coat-imposed dormancy. Hormonal pathways involved in these changes were investigated at the physiological level. In both genotypes, sensitivity to abscisic acid (ABA) was reduced by storage at 25°C. Also, but only in one genotype, storage at 25°C reduced ABA levels upon imbibition and increased the response to a gibberellin (GA) synthesis inhibitor and to applied GA3, compared with storage at 5°C; these results support the idea that temperature affects both ABA and GA metabolism and signalling pathways during after-ripening. This information will be useful to define storage conditions for commercial sunflower achenes, and will also help focus future research on the underlying mechanisms of dormancy release during dry after-ripening in sunflower.

Seedling emergence of 144 subalpine meadow plants: effects of phylogeny, life cycle type and seed mass

Abstract: Timing of seedling emergence is a critical aspect of a plant's life cycle, and it may influence the expression of other plant life history traits. However, most studies have been conducted at the population level, and thus little is known about timing of seedling emergence at the community level. In the field, we determined the peak emergence season for seedlings of 144 species collected from a subalpine meadow on the eastern Tibet Plateau in China. The proportion of species with seedlings emerging in autumn, spring and summer, seedling field emergence percentage (FE) and mean emergence time (MET) were analysed in relation to seed mass, life cycle type (annual/biennial and perennial) and phylogeny. The results showed that (1) the proportion of species with seedlings emerging in autumn (33%), spring (44%) and summer (23%) differed significantly; (2) overall, species with seedlings emerging in autumn had higher FE than those emerging during spring/summer; (3) there was a positive relationship between log-seed mass and log-MET, but log-seed mass had no significant effect on log-FE; (4) life cycle type did not affect seedling emergence; and (5) phylogeny significantly explained peak emergence season. These results suggest that seed mass and phylogenetic position are the main determinants of seedling emergence season. However, seedling peak emergence season affected FE, growing season length and resource utilization, and thus may be related to the importance of a species in the community.

Different strategies for breaking physical seed dormancy in field conditions in two fruit morphs of Vachellia caven (Fabaceae)

Abstract: Differences in fruit morphology among or within species might indicate differences in other regenerative traits, such as seed dormancy and germination. In species with physical dormancy (PY), environmental conditions are suggested to be responsible for dormancy break in field. Seeds of Vachellia caven have PY. This species exhibits two fruit morphs highly represented in Cordoba forests, Argentina: one is dehiscent and the other is indehiscent. In this study we performed a burial experiment with the aim to determine if the differences in V. caven fruit morphology were related to different patterns of PY break of their seeds in field conditions. We related these patterns to (1) environmental conditions that could influence the loss of PY, and (2) histological features of the lens zone. Seeds of both morphs exhibited dormancy break within 14 months of the start of the experiment, but with different patterns. The dehiscent morph showed an abrupt percentage of seeds that broke dormancy 14 months after the beginning of the experiment, probably after undergoing environmental changes similar to those suggested by the two-stage softening model. The indehiscent morph showed a gradual increase in seeds that broke dormancy, not clearly related to any of the environmental variables studied. No differences in seed coat structure of the lens zone were observed between morphs. The existence of both morphs could confer the species with higher possibilities of establishing and coping with environmental heterogeneity. Those characteristics contribute to the understanding of the success of this species in open and disturbed environments.

Reduced plant fitness by pre-dispersal seed predation in the threatened plant species Cirsium decussatum

Abstract: Seed predation has been suggested to play a crucial role in plant population dynamics and could act as a strong selective force in the evolution of plant traits such as plant phenology, size and number of flowers. The loss of seeds could be particularly threatening for population maintenance of rare plant species. We investigated the influence of seed predators on plant fitness of the rare monocarpic thistle Cirsium decussatum. We tested the following hypotheses: (1) pre-dispersal seed predators reduce the number of dispersed propagules; (2) seed predators select larger inflorescences as oviposition sites; (3) the size of the capitulum is correlated with seed productivity; and (4) seed predators compete for the oviposition sites. We identified ten insect taxa from different taxonomic groups in the capitula of C. decussatum. Terellia longicauda larvae (Diptera: Tephritidae) were the most common. The presence of the flies’ larvae was positively correlated with the predation level in the capitula. Females of T. longicauda selected larger inflorescences for laying eggs that may increase offspring fitness as larger inflorescences promise more food resources. We could not prove the presence of competition between insect species inhabiting the capitula. Our data suggest, however, that T. longicauda, a specialized seminophagous dipteran, is one of the factors that negatively influence the fitness of threatened C. decussatum, lowering significantly the seed pool. Terellia longicauda potentially acts as a strong selective force in the evolution of C. decussatum inflorescence size.

Machine learning links seed composition, glucosinolates and viability of oilseed rape after 31 years of long-term storage

Abstract: Seed longevity is influenced by many factors, a widely discussed one of which is the seed lipid content and fatty acid composition Here, linear and non-linear regressions based on machine learning were applied to analyse germinability and seed composition of a set of 42 oilseed rape (Brassica napus L) accessions grown under the same single environment and at the same time following a period of up to 31 years storage at 7°C Mean viability was halved after 270 years of storage, but this figure concealed a major influence of genotype There was also wide variation with respect to fatty acid composition, particularly with respect to oleic, α-linolenic, eicosenoic and erucic acid Linear regression (rL) revealed significant correlation coefficients between normal seedling appearance and the content of α-linolenic acid (+052) and total oil (+059) Multivariate regression using artificial neural networks including a radial basis function (RBF), a multilayer perceptron (MLP) and a partial least square (PLS) recognized underlying structures and revealed high significant correlation coefficients (rM) for oil content (+087), eicosenoic acid (+075), stearic acid (+073) and lignoceric acid (+097) Oil content or a combination of oleic, α-linolenic, arachidic, eicosenoic and eicosadienoic acids and glucosinolates resulted in highest model fitting parameters R2 of 090 and 088, respectively In addition, the glucosinolate content, predominantly in the Brassicaceae family and ranging from 46 to 795 µM, was negatively correlated with viability (rL = ‒043) Summarizing, oil content, some fatty acids and glucosinolates contribute to variations in average half-life (152 to 507 years) of oilseed rape seeds In contrast to linear regression, multivariate regression using artificial neural networks revealed high associations for combinations of parameters including underestimated minor fatty acids such as arachidic, stearic and eicosadienoic acids This indicates that genetic and seed composition factors contribute to seed longevity In addition, multivariate regressions might be a successful approach to predict seed viability based on fatty acids and seed oil content

Seed traits and germination of native grasses and invasive forbs are largely insensitive to parental temperature and CO2 concentration

Abstract: The structure and function of grassland ecosystems can be altered by a changing climate, including higher temperature and elevated atmospheric CO2 concentration. Previous studies suggest that there is no consistent trend in seed germination and seedling recruitment as affected by these conditions. We collected seeds of two native and two invasive species over 6 years from a field study with elevated CO2 (600 p.p.m.) and temperature (1.5/3.0°C day/night) on the mixed-grass prairie of Wyoming, USA. Seed fill, viability and mass were evaluated and germination tests were conducted under alternating temperatures in growth chambers. Thermal time requirements to reach 50% germination (θ50) and base temperatures (Tb) for germination were determined using thermal time models. Climate change conditions had limited effects on seed fill, viability and mass. The combination of CO2 enrichment and warming increased germination of Bouteloua gracilis. Centaurea diffusa and Linaria dalmatica, two invasive species in this study, had the lowest θ50 and Tb required for germination among all the species studied. Although final germination percentages of these invasive species were not affected by treatments, previous studies reported increased seed production under future climate conditions, indicating that they could be more invasive at the regeneration stage in the future. We conclude that projected future temperature increases will have little effect on seed reproductive traits of native species. In addition, the distribution and abundance of B. gracilis and invasive species may be favoured by global climate change due to enhanced germination or seed production traits caused by elevated parental CO2 and temperature conditions.

Effects of day length on pollen tube elongation, embryo formation and seed development after flowering in quinoa (Chenopodium quinoa Willd.).

Abstract: The objective of this study was to evaluate the effect of day length after flowering on pollen tube elongation, embryo formation and seed development. The quinoa varieties used in this study were Amarilla de Marangani (valley type) and NL-6 (sea-level type). After sowing, the quinoa plants were cultivated in growth cabinets. From sowing to flowering, plants were exposed to a 15 h day length regime. After flowering, the plants were grown under either a 15 h or 11 h day length regime. The elongation of the pollen tube and the formation of the early embryo were not inhibited in either Amarilla de Marangani or NL-6 under the 11 or 15 h day length regimes. Although growth of the embryo in NL-6 was not inhibited by the 15 h day length regime after flowering, the same was not observed in the case for Amarilla de Marangani. In Amarilla de Marangani, seed diameter at 8 and 14 days after flowering under the 11 h day length regime was larger than that of seeds grown under the 15 h day length regime. Thus, the decrease in the number of seeds in Amarilla de Marangani grown under the 15 h day length regime may be caused by the suspension of embryo growth after fertilization.