Germination of seeds of some summer annuals in Kentucky (eastern USA) in late-winter lead to the hypothesis that under present climate conditions the whole length of the winter cold stratification (CS) period is not required for dormancy-break of seeds of summer annuals with physiological dormancy (PD). We evaluated our data from germination phenology studies of 45 species (69 datasets) and buried-seed studies of 33 species (44 datasets). We determined time and temperature of germination after CS and percentage of the total number of hours of CS during winter (% of winter CS) seeds received prior to start of germination. In the phenology studies, mean temperature during the week of first germination for C3 and C4 species was 11.1 and 14.4°C, respectively, and % of winter CS was 80.8 and 87.4, respectively. In the buried-seed studies, % of CS for C3 and C4 species was 40.8 and 48.1, respectively, when they germinated to 25% at 20/10°C. For 32 of 33 species in the buried-seed studies, the minimum temperature at which seeds germinated decreased with increased CS; thus, seeds had Type 2 non-deep PD. The time of germination is controlled by a number of hours of CS, a decrease in minimum temperature at which seeds can germinate and a temperature increase in early spring. Seeds can germinate at relatively high temperatures as early as December and January, but they continue to be CS until spring. Temperature increases in eastern North America due to global warming are not likely to inhibit the germination of summer annuals with PD in spring.

To maximize seed longevity, seeds should be harvested at optimal maturity, that is, when seeds have acquired maximum physiological quality before deterioration begins. The aim of this study was to map the variation in temporal patterns of lentil (Lens culinaris Medik.) seed quality development when grown across four regeneration environments, which differ in the level of temperature and humidity control throughout the growing season, at the Australian Grains Genebank. Seeds of two lentil accessions (76080 and 76072) were harvested at different stages throughout development, commencing at 21 d after 50% anthesis until a maximum of 130 d. At each harvest, physiological quality traits, including germinability (fresh and dried seeds) and seed longevity, were determined, as well as seed dry weight and moisture content. Seeds of both accessions, and in all environments, started to accumulate physiological quality early on in development but did not reach their maximum until 3–54 d after mass maturity. The temporal patterns of desiccation tolerance and storage longevity were highly influenced by the environmental conditions during the maturation drying phase, affecting both ‘when’ maximum quality was attained and for how long it was maintained, thereafter. Seeds did not show a typical developmental response, rather variation was observed in seed quality development both between and within accessions grown in the different environments. The poorest storage longevity was seen when seeds of both accessions were grown in the cooler, temperature-controlled glasshouse, and the maximum longevity was observed in the warmer, semi-protected environments of the green and the big igloo for accessions 76080 and 76072, respectively.

Information in the literature and unpublished results of the authors on Dobinea were used to determine the kind [class(es)] of seed (true seed + endocarp) dormancy and of non-dormancy of genera in all five tribes of Anacardiaceae, and the results were examined in relation to the taxonomic position and endocarp anatomy within the family. Reports of both seed germination and endocarp anatomy were found for 15 genera in tribe Spondiadeae, 6 in tribe Anacardieae, 30 in tribe Rhoeae, 3 in tribe Semecarpeae and 1 in tribe Dobineeae. In Spondiadeae (Spondias-type endocarp), Anacardieae, Semecarpeae and Dobineeae (Anacardium-type endocarp), seeds are either non-dormant (ND) or have physiological dormancy (PD). In Rhoeae (Anacardium-type Rhoeae Groups A, B, C and D endocarps), on the other hand, seeds are ND or have physical dormancy (PY), PD or PY + PD. PY/PY + PD in this tribe seems to be restricted (or nearly so) to Rhus s.s. and closely related genera (e.g. Cotinus, Malosma and Toxicodendron) with an Anacardium-type Rhoeae Group A endocarp. However, seeds of other genera (e.g. Astronium and Schinus) with this type of endocarp and those with Rhoeae Group B (e.g. Pistacia), Group C (e.g. Pentaspadon) and Group D (e.g. Heeria) endocarps are either ND or have PD. The fossil fruit record strongly suggests that present-day relationships between diaspore dormancy (or non-dormancy), endocarp structure and taxonomic position within Anacardiaceae extend back to at least the Palaeogene.

To persist (without immigration) in habitats with unpredictable environmental conditions, annuals must produce seeds each year or have a seed bank. Thus, we predicted that compared to perennials, annuals have a wider germination temperature range (GTR, the difference in temperature between the week with the highest and the week with the lowest germination during the natural germination season). We determined the GTR via germination phenology data for 350 herbaceous species in 59 families from the eastern USA: summer annuals (SA), 63; winter annuals (WA), 83; monocarpic perennials (MP), 28; and polycarpic perennials (PP), 176. There was no significant phylogenetic signal for the GTR. The width of the GTR during the first spring germination season was 9.6, 8.7 and 8.8°C for MP, PP and SA, respectively, and during the first autumn germination season 12.8, 11.8 and 12.4°C for MP, PP and WA, respectively. Annuals did not have a wider GTR than perennials in either the spring or the autumn germination season. Our data suggest that selection for early germination in either spring or autumn has resulted in only small differences in the GTR. We predict that global warming will have little or no effect on reshaping the germination phenology of herbaceous species of temperate eastern North America.

Despite the importance of secondary dormancy for plant life cycle timing and survival, there is insufficient knowledge about the (epigenetic) regulation of this trait at the molecular level. Our aim was to determine the role of (epi)genetic processes in the regulation of secondary seed dormancy using natural genotypes of the widely distributed Capsella bursa-pastoris. Seeds of nine ecotypes were exposed to control conditions or histone deacetylase inhibitors [trichostatin A (TSA), valproic acid] during imbibition to study the effects of hyper-acetylation on secondary seed dormancy induction and germination. Valproic acid increased secondary dormancy and both compounds caused a delay of t50 for germination (radicle emergence) but not of t50 for testa rupture, demonstrating that they reduced speed of germination. Transcriptome analysis of one accession exposed to valproic acid versus water showed mixed regulation of ABA, negative regulation of GAs, BRs and auxins, as well as up-regulation of SNL genes, which might explain the observed delay in germination and increase in secondary dormancy. In addition, two accessions differing in secondary dormancy depth (deep vs non-deep) were studied using RNA-seq to reveal the potential regulatory processes underlying this trait. Phytohormone synthesis or signalling was generally up-regulated for ABA (e.g. NCED6, NCED2, ABCG40, ABI3) and down-regulated for GAs (GA20ox1, GA20ox2, bHLH93), ethylene (ACO1, ERF4-LIKE, ERF105, ERF109-LIKE), BRs (BIA1, CYP708A2-LIKE, probable WRKY46, BAK1, BEN1, BES1, BRI1) and auxin (GH3.3, GH3.6, ABCB19, TGG4, AUX1, PIN6, WAT1). Epigenetic candidates for variation in secondary dormancy depth include SNL genes, histone deacetylases and associated genes (HDA14, HDA6-LIKE, HDA-LIKE, ING2, JMJ30), as well as sequences linked to histone acetyltransferases (bZIP11, ARID1A-LIKE), or to gene silencing through histone methylation (SUVH7, SUVH9, CLF). Together, these results show that phytohormones and epigenetic regulation play an important role in controlling differences in secondary dormancy depth between accessions.

The J. Derek Bewley Career Lectures presented at the triennial meetings of the International Society of Seed Science support early-career seed scientists by providing retrospective views, from those late in their careers, of lessons learned and future implications. Ambition, ability, inspiration, foresight, hard work and opportunity are obvious career requirements. The importance of mentoring and teamwork combined with the clear communication of results, understanding and ideas are emphasized. The role of illustration in research, and its dissemination, is outlined: illustration can support hypothesis development, testing and communication. Climate change may perturb the production of high-quality seed affecting conservation as well as agriculture, horticulture and forestry. An illustrative synthesis of the current understanding of temporal aspects of the effects of seed production environment on seed quality (assessed by subsequent seed storage longevity) is provided for wheat (Triticum aestivum L.) and rice (Oryza sativa L.). Seed science research can contribute to complex global challenges such as future food supplies from seed-propagated crops in our changing climate whilst conserving biological diversity (through seed ecology and technologies such as ex situ plant genetic resources conservation by long-term seed storage in genebanks), but only if that research can be – and then is – applied.

Fire stimulates the germination of most seeds in fire-prone vegetation. Fruits of Leucadendron (Proteaceae) are winged achenes or nutlets that correlate with their requirements for smoke and/or heat in promoting germination. We describe five possible smoke–heat dormancy-release/germination syndromes among plants, of which Leucadendron displays three (no response, smoke only, smoke and heat). As seed-coat thickness varies with seed-storage location (plant or soil) and morphology (winged or wingless), we tested its possible role in water uptake and germination. Species with winged seeds achieved 100% germination in the absence of smoke/heat, seed coats were an order of magnitude thinner, and their permeability greatly exceeded that of nutlets. As seed-coat thickness increased (1) imbibitional water uptake declined at a decreasing rate, and (2) the response to smoke, and to a lesser extent heat, increased linearly to reach levels of germination approaching those of winged seeds. For species responsive to smoke and heat, there was no additive effect when applied together, suggesting that they may have promoted the same physiological process. We conclude that seed-coat thickness holds the key to germination requirements in this genus, independent of seed-storage location or morphology. By what mechanisms (1) the smoke response is greater the thicker the seed coat and (2) smoke chemicals might increase water permeability to explain the non-additive effect of smoke and heat, warrant further investigation.

The Brazilian Cerrado, a Neotropical savanna, is a fire-prone ecosystem where the ground layer biomass consists mainly of graminoids. However, as for other savannas, the effects of fire cues (such as smoke) on Cerrado grasses do not present a clear pattern, either for germination or seedling development. Smoke can stimulate different stages of the plant life cycle, which can alter the community and invasion processes. So far, most research on the subject focuses on germination, not addressing post-germinative phases, a sensitive stage of plant development. Here, we investigated the effect of smoke on a native (Echinolaena inflexa) and an invasive (Urochloa decumbens) grass species common in the Cerrado. We analysed germinative parameters and seedling mass and length after exposing the seeds to dry smoke for 5, 10, 15 or 20 min. Seedling development was assessed by measuring shoot and root systems after cultivating germinated seeds for 3, 7 or 15 d. Smoke did not affect germination percentages. However, fumigation reduced the mean germination time of both species and the germination onset of E. inflexa. U. decumbens had higher length values in all periods of cultivation, whereas mass values only surpassed that of E. inflexa at 15 d. Smoke exposure reduced the aboveground length of 7-d seedlings of U. decumbens, and mass of 15-d plants of both species. Also, smoke enhanced the root investment of the native and invasive species in different cultivation periods. Therefore, studying post-germinative parameters on seedling development may bring further insights into the smoke effects.

Seed germination implies an expansion process restarting the growth of the embryonic axis (Ax) and which is completed by radicle emergence through the seed covering layers. In developing soybean seeds, abscisic acid in Ax (ABAa) mainly inhibits Ax growth. Additionally, the expression of the EXP1 gene at the elongation zone (EZ) was found to be involved in the promotion of mature soybean Ax growth, which increased during water incubation and which was repressed by exogenous ABA. This work aimed to evaluate (1) the ABAa and EXP1 levels at the EZ and (2) the role of the seed coat (SC) in developing soybean seed germination. Whole seeds (Se), embryos (Em) and Ax at 25–45 d after anthesis (DAA) germinated in vitro, and germination performance increased with DAA. ABAa decreased in planta from 25 DAA until its critical non-inhibitory threshold (ABAc) at around physiological maturity (45 DAA). At earlier ages, the ABAc was reached during the in vitro incubation. Concomitantly, EXP1 transcripts accumulated with age into the pool of long-lived mRNAs and were up-regulated during incubation. Additionally, isolated Ax germinated faster, took up more water and increased its water potential more rapidly during incubation than Ax in Se. Also, a lower osmotic gradient was required to germinate at 45 DAA, when ABAa was no longer inhibitory. Simultaneously, the pressure to protrude SC through the micropylar area increased from 25 to 45 DAA. These results support the role of ABAa and EXP1 in controlling Ax growth and the SC in delaying radicle protrusion.

Oxygen is a major factor of seed germination since it allows resumption of respiration and subsequent metabolism reactivation during seed imbibition, thus leading to the production of reducing power and ATP. Most studies carried out in the 60s to 85s indicate that oxygen requirement depends on the species and is modulated by environmental factors. They have also demonstrated that the covering structures mainly inhibit germination by limiting oxygen supply to the embryo during imbibition through enzymatic oxidation of phenolic compounds by polyphenol oxidases (catechol oxidase and laccase) and peroxidases. Recent use of oxygen-sensitive microsensors has allowed to better characterize the oxygen diffusion in the seed and determine the oxygen content at the level of embryo below the covering structures. Here, I will also highlight the major data obtained over the last 30 years indicating the key role of oxygen in the molecular networks regulating seed germination and dormancy through (1) the hormonal balance (ethylene, ABA and GA), the hormone-signalling pathway and, in particular, the ABA sensitivity, (2) the emerging role of mitochondria in ROS production in hypoxia and (3) the involvement of the N-degron pathway in the turnover of proteins involved in seed tolerance to hypoxia.

Post-fire flowering (PFF) species resprout, flower and disperse seeds within weeks after fire. This may be an important strategy to recruit new individuals and colonize the gaps opened by fire. The seeds released in the post-fire environment may interact with byproducts derived from plant burning, and the resulting ash may have compounds that can promote the germination of various seeds, particularly those with permeable coats. In the Cerrado ecoregion, PFF is a strategy commonly observed in the species of the ground layer, but their seeds are rarely investigated. So, we examined the quality and the germination of the seeds of 13 species that disperse seeds within 3 months after fire. We estimated the amount of empty, filled and predated seeds for each species, and tested the germination with or without ash. There was a clear separation in seed quality as dicots produced 35–75% filled seeds but grasses <15%. Pre-dispersal predation was only observed for dicots (<10%). Ash stimulated the germination of two out of the three dormant species but inhibited the germination of three non-dormant species. Overall, the seeds produced in response to fire are an important source of genetic variability in an ecosystem that has resprouting as the main persistence strategy. As most species have non-dormant seeds, ash may only be important to stimulate the germination of few PFF species. Even so, ash can be completely washed away by rains before seeds are dispersed and may not have an effect under field conditions.

Cistus species have seeds with hard coats which impose physical seed dormancy that can be released after seed scarification. In fire-prone habitats, the break of physical seed dormancy is usually related to the heat produced during fires. It is commonly accepted that most hard-seeded species, including those of the genus Cistus, are able to germinate under a wide range of temperatures in light as well as in darkness, once the seed becomes permeable. However, although many studies have focused on the release of physical dormancy only, a few have done so on the effect of environmental factors once dormancy is released. In this research, through a factorial experiment, we analysed the effects of light (light and darkness) and a range of temperatures (10, 15, 20, 25 and 30°C) on the seed germination of eight Cistus species after a heat shock. On average, almost 60% of the seeds did not germinate despite being viable, and this lack of germination increased with higher temperatures during the treatment. Although an idiosyncratic germination response emerged, temperature had a significant effect in all the species, reaching the highest levels of germination between 10 and 20°C. Light interacted with temperature in four cases by increasing the germination, especially under the least favourable temperatures. Environmental factors, such as temperature and light, appear to modulate the germination of the studied Cistus species after the release of physical seed dormancy.

Genetic and biochemical studies have greatly advanced our understanding of the biology of seeds in recent years. Another area of study, which could accelerate contemporary seed biology research, is phylogenomics that integrates the wealth of genome sequence data with evolutionary biology. The recent phylogenomic study of the DELAY OF GERMINATION1 family genes exemplifies how the molecular evolution of seed genes can be traced back through early diverging plants and what implications can be obtained from the analysis of seed gene diversification at ancient times. The identification of possible ancestors of seed genes in non-seed plants could illuminate the ancient roots of the molecular mechanisms driving seed maturation programmes. It is possible that the origins of molecular mechanisms associated with the induction of seed storage proteins and desiccation tolerance proteins date back to the time of, or even prior to, early diverging land plants. Abscisic acid-dependent growth arrest or dormancy mechanisms might date back to red algae, one of the oldest algal groups. Thus, understanding algal cell biology will also be an integral part of future seed biology research. Unravelling key events associated with the evolution of seed- and non-seed plants will not only advance basic research but could also contribute to applied aspects of seed science, potentially leading to technology development for agriculture.

Developmental signals and environmental stresses regulate carbon distribution in the vegetative and reproductive organs of plants and affect seed yield. Cleistogenes songorica is a xerophytic grass with great potential application value in ecological restoration. However, how carbohydrate transport and distribution during grain filling affect the seed yield of C. songorica under water stress is not clear. The present study showed that the soluble sugar and starch contents of cleistogamous (CL) spikes and chasmogamous (CH) spikes were significantly higher at the milk stage, which was attributed to a significantly higher seed number and seed yield per spike under water stress conditions than under well-watered conditions (P < 0.01). RNA-seq data revealed a total of 54,525 differentially expressed genes (DEGs) under water stress conditions, but only 3744 DEGs were shared among all comparison groups. Weighted gene co-expression network analysis showed that the transport and distribution of carbohydrates were regulated by ABA-responsive genes (CsABA8OX1_1, CsABA8OX1_2, CsABA8OX2_1, CsABA8OX2_2, CsNCED3, CsNCED1_1, CsNCED1_2 and CsNCED4_1) and sugar transport and starch synthesis genes (CsSUS1, CsSUS2, CsSUS3, CsAGP1, CsAGP4, CsAGP5, CsSSS1 and CsSBE5) under water stress conditions. These genes jointly regulated carbohydrate remobilization in sources (stems, leaves and sheaths) to promote grain filling and improve seed yield. The present study helped to clarify the phenotypic, metabolic and transcriptional response mechanisms of vegetative organs, such as stems and leaves, and reproductive organs, such as CL spikes and CH spikes, to promote carbohydrate redistribution under water stress, and it provides theoretical guidance for improving seed yields.

Zephyranthes tubispatha is an ornamental species distributed along several countries of South America. Although it can be multiplied through bulbs or scales, seed germination is a simpler and more cost-effective process. Temperature plays a major role in the control of germination; however, its effect has been scarcely investigated in this species. In the present work, we characterized the germination responses of Z. tubispatha seeds to different temperatures and analyzed the role of key components of the antioxidant metabolism and phytohormones in their control. Seeds showed an optimal temperature range for germination between 14 and 20°C, with higher temperatures (HTs) being progressively inhibitory. While germination was almost nil above 28°C, it could be recovered after transferring the seeds to 20°C, suggesting that thermoinhibition was the underlying phenomenon. The duration of the HT incubation period affected both the time to germination onset and the germination rate at 20°C. Similarly, the activity of antioxidant enzymes, the production of reactive oxygen species in the embryo and the sensitivity to some germination promoters varied depending on the duration of the HT treatment. The addition of 20 μM fluridone was sufficient to recover germination dynamics as in the control treatment when given after a long-term incubation period (25 d) at HT. Ethephon supply was more effective than gibberellins to suppress thermoinhibition, suggesting that changes in the balance and/or sensitivity to ethylene and abscisic acid over time play an important role in the regulation of germination responses to thermal cues in this species.

Understanding the relative longevity of different seed lots, perhaps of different species or genotypes, but also following production under different environments or using different cultivation methods, or following different post-harvest treatments, is relevant to anyone concerned with the retention of seed lot viability and vigour during storage. However, different scientists over the years have used different conditions to assess seed lot longevity, as well as different variables as the measure of ‘longevity.’ Here, we give some of the backgrounds to how two standard protocols, with an open and closed system respectively, were derived, and explain why we consider p50, defined as the time during storage when seed lot viability, as measured through a germination test, has declined to 50%, is a suitable longevity trait parameter.

Plant community-level studies on seed dormancy traits are important to understand and determine the significance of seed dormancy in different ecosystems. Hence, we studied seed dormancy and other related seed biological traits of 42 selected tropical lowland rainforest tree species from Sri Lanka, aiming to address seed dormancy class(es) for a biodiverse tropical lowland wet zone forest community and the relationship between dormancy classes, forest strata and seed dispersal mechanisms. Seed germination, imbibition, embryo length:seed length ratio, embryo morphology and the effect of gibberrelic acid on seed germination were determined. Sixty-two percent of the species with T50 < 30 days were identified as having fast-germinating seeds and the remaining 38% with T50 > 30 possessed slow-germinating seeds. Seeds of 33 species had fully developed embryos, while nine species had underdeveloped embryos; three had morphological dormancy (MD) and six morphophysiological dormancy (MPD). Treatment with gibberellic acid revealed physiological dormancy (PD) in seeds of six species, and the response to manual scarification confirmed physical dormancy (PY) in seeds of Pericopsis moonina. The majority of tropical lowland rainforests had non-dormant (ND) species (62%), and 14.3, 14.3, 7 and 2.3% of the species had MPD, PD, MD, and PY, respectively. Non-dormancy decreased for taxa from the upper strata to the lower strata of the forest. ND seeds were dispersed during the rainy season. Thus, non-dormancy seems to be the most dominant germination behaviour among the tree species in the lowland rainforest of Sri Lanka with the class of dormancy related to forest strata and dispersal time.

Reproductive strategies for specific populations are closely related to environmental factors. Consequently, they are fundamental for conservation plans and the management of threatened habitats like salt marshes. From this viewpoint, germination strategy under different temperatures and salt conditions, voltammetric parameters and molecular analysis were performed and compared in six Halocnemum populations (four of H. cruciatum and two of H. strobilaceum) growing on Mediterranean (Balearic, Tyrrenic and Adriatic) and Red Sea coasts to establish the relation to environmental variables. Significant interpopulation differences were found in all the evaluated parameters. The Mediterranean populations showed a variable opportunistic germination strategy that was directly related to the drought period length at the studied sites. Consequently, potential environmental predictors of seed response were identified. The most noteworthy were bioclimate, soil texture, continentality index, winter temperatures and summer precipitations. Additionally, voltammetric parameters were evidenced as indicators of maternal plant stress levels and, thus, as potential determinants of future seed responses. The phylogenetic analyses showed a split into two species that did not correspond to germination response. The phylogeographic analyses showed interpopulation differences in haplotype composition for H. cruciatum, but not for H. strobilaceum. In conclusion, the tight connection between seed responses and the ecological parameters of natural populations as an adaptation for successful seedling emergence was proved regardless of its phylogenetic relations.

Seeds show important variation as plant regenerative units among species, but their evolutionary co-variations with other plant characteristics are still poorly understood. Whilst a positive association of seed mass with genome size (GS) and life forms has already been documented, a broad-scale quantification of their evolutionary correlation and adaptive selection has never been conducted. Here, we tested for correlated evolution of seed mass and GS towards distinct selective regimes related to life form in angiosperms. In particular, we tested the hypothesis that the selection toward lighter seeds and smaller genomes is stronger for annual plants, ensuring high regenerative potential. Using multivariate evolutionary models over a dataset containing 3242 species, we showed an overall positive correlated evolution of seed mass and GS deviating from a pure drift process. Instead, evolutionary changes in seed and genome sizes were driven by adaptive selection towards optimal values differing among life forms. Specifically, the evolutionary optima towards which the seed and genome sizes evolve show a covariation toward small values in annuals, intermediate values in perennial herbs and a trade-off between seed mass and GS in woody plants. Moreover, the evolutionary correlation between seed mass and GS is strongest in annuals as an adaption to complete their life cycle in a short time window, when environmental conditions are favourable for regeneration and development to maturity. The asymmetry in the correlated evolution acting on seed and genome sizes due to life form could explain how life-history traits interplay with functional traits and how plants have evolved diverse successful life-history strategies.